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Ionic Transition Metal Complex Polymers as Photonic and Redox Active Materials

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Title:
Ionic Transition Metal Complex Polymers as Photonic and Redox Active Materials
Creator:
Puodziukynaite, Egle
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[Gainesville, Fla.]
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University of Florida
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english
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Doctorate ( Ph.D.)
Degree Grantor:
University of Florida
Degree Disciplines:
Chemistry
Committee Chair:
Reynolds, John R
Committee Members:
Mcelwee-White, Lisa A
Castellano, Ronald K
Schanze, Kirk S
So, Franky
Graduation Date:
12/15/2012

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Subjects / Keywords:
Absorption spectra ( jstor )
Argon ( jstor )
Chromophores ( jstor )
Colors ( jstor )
Electrodes ( jstor )
Electronics ( jstor )
Energy transfer ( jstor )
Ligands ( jstor )
Oxidation ( jstor )
Polymers ( jstor )
Chemistry -- Dissertations, Academic -- UF
cell -- chemiluminescence -- complex -- conjugated
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Electronic Thesis or Dissertation
bibliography ( marcgt )
theses ( marcgt )
government publication (state, provincial, terriorial, dependent) ( marcgt )
Chemistry thesis, Ph.D.

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Abstract:
An emerging field of organic electronics has led to various lightweight, flexible, and easily processable devices, including organic light-emitting displays, electrochromic display and window-type devices, photovoltaic cells, and field effect transistors. In these architectures, ionic transition metal complexes (iTMCs) represent an important class of active layer materials, as they posses intrinsic multifunctionality. Via structural modifications, a combination of redox activity, electrochromism, light emission, and ionic conductivity can be fine-tuned in these materials. Additionally, unique properties arise as iTMCs are combined with organic electroactive polymers, leading to controlled energy and charge transport mechanisms. This dissertation describes the design, synthesis, characterization, and structure property-relationships of iTMC polymers with the multifunctionality required to develop new architectures of optoelectronic devices. A first part of this dissertation focuses on cross-linkable Ru(II) tris(bipyridine) complexes with dual electrochromic (EC) and electrochemiluminescent (EL) characteristics. For these complexes, the structure property relationships are established between the detailed ligand design and the combination of the required properties for simultaneous emissive and reflective mode applications. Additionally, for the first time, a dual EC/EL device prototype is presented where light-emission and multi-color electrochromism occur from the same pixel comprised of a single active layer, allowing for optimal visibility in all ambient lighting situations. A second portion of this dissertation focuses on iTMC-organic conjugated polymer assemblies as light-harvesting arrays and charge transport materials for ultimate use in solar photovoltaic and fuel devices. With controlled charge and exciton transport being the key requirement in such systems, polymer building blocks having variable HOMO/LUMO levels (i.e. polyfluorene, poly(3-hexylthiophene), poly(fluorene-co-thiophene), etc.) are explored as the backbones of the macromolecular antennae. Facile energy transfer and charge separation processes between the polymer backbones and pendant iTMC units are found to occur in such systems by employing ultrafast spectroscopic techniques. Additionally, these hybrid arrays are demonstrated to exhibit fast exciton transport along the pendant Ru(II) units resulting in an antenna effect. Finally, interactions between these macromolecular assemblies and semiconductor interfaces are studied as the iTMC hybrids are utilized in solar photoelectrochemical cells. ( en )
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In the series University of Florida Digital Collections.
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Includes vita.
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Description based on online resource; title from PDF title page.
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This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
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Thesis (Ph.D.)--University of Florida, 2012.
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Adviser: Reynolds, John R.
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RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2016-12-31
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by Egle Puodziukynaite.

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Copyright Egle Puodziukynaite. Permission granted to the University of Florida to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
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12/31/2016
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1 IONIC TRANSITION METAL COMPLEX POLYMERS AS PHOTONIC AND REDOX ACTIVE MATERIALS By EGLE PUODZIUKYNAITE A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENT S FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2012

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2 2012 Egle Puodziukynaite

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3 To my F amily

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4 ACKNOWLEDGEMENTS I would like to start with thanking my advisor Prof. John Reynolds for provi ding me with an opportunit y to work in his research group. His guidance, support, patience and understanding were unprecedented, allowing me to grown not only as a scientist and independent thinker, but also as a person. I would also like to thank Dr. Kirk S. Schanze for his mentoring, scientific discussions, and making me a part of his research group as Dr. Reynolds moved to Georgia Institute of Technology. Over these past five years, I have had an opportunity to work and collaborate with a number of great people, whose efforts and insights I would like to acknowledge. I am definitely indebted to Dr. Dan Patel and Dr. Aubrey Dyer for being my synthesis and electrochemistry mentors, respectively. I would like to thank my undergraduate student Justin Oberst w ho has worked with me on light emitting electrochemical cell project, Dr. Gyu Leem and Dr. Yali Sun (Schanze group) for their input in the projects related to conjugated polymer research group (University of North Carolina at Chapel Hill), including Dr. Li Wang, Dr. Erik Grumstrup, Ryan Vary, and Dr. Ralph House for advanced photophysical studies great wor king environment, advice and friendships that I have developed. I would like to express my appreciation to Sara Klossner, Cheryl Googins and Aeryal Herrod for their assistance. Dr. Ben Smith and Lori Clark are gratefully acknowledged for their help with th e graduate school process. I would also like to thank my family particularly my mom who has always supported and understood my decisions. I am very grateful to all my friends that I have acquired while in the United States of America They will remain special to me forever

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5 as they have helped me tremendously over the years and made me part of their families. Last but not lea st, I would like to express my gratefulness to the funding agencies who have supported the research I have been involved in Fina ncial support from Nanoholdings for the initial stage of this research delineated in this dissertation is gratefully acknowledged. Hybrid assembly work was supported as part of the UNC EFRC: Solar Fuels an Energy Frontier Research Center funded by the U.S Department of E n ergy, Office of Science, Office of Basic Energy Sciences under Award Number DE SC0001011.

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6 TABLE OF CONTENTS Page ACKNOWLEDGEMENTS ................................ ................................ ............................... 4 LIST OF TABLES ................................ ................................ ................................ .......... 10 LIST OF FIGURES ................................ ................................ ................................ ........ 11 LIST OF SCHEMES ................................ ................................ ................................ ...... 15 LIST OF ABBREVIATIONS ................................ ................................ ........................... 16 A BSTRACT ................................ ................................ ................................ ................... 18 CHAPTER 1 INTRODUCTION ................................ ................................ ................................ .... 20 1.1 Organic Electronics ................................ ................................ ........................... 20 1.2 Conjugated Polymers in Organic Electronics ................................ .................... 21 1.2.1 Exciton Migration in Organic Conjugated Polymers ............................... 23 1.2.2 Electrochromis m in Organic Conjugated Polymers ................................ 24 1.2.3 Light Emission in Organic Conjugated Polymers ................................ ... 26 1.3 Ionic Transition Metal Complexes in Organic Electronics ................................ 28 1.3.1 Principles Behind Light Emission ................................ ........................... 29 1.3.2 Principles Behind Light Absorption and Electrochromism ..................... 33 1.4 Excited State Interactions in Multichromophoric Transition Metal Complex Assemblies and Transition Metal Complex Organic Chromophore Hybrids ..... 37 1.4.1 Energy Transfer ................................ ................................ ..................... 38 1.4.1.1 Energy Transfer via Forster Mechanism ................................ ... 38 1.4.1.2 Energy Transfer via De xter Mechanism ................................ .... 40 1.4.2 Photoinduced Electron Transfer ................................ ............................ 43 1.4.3 Devices Based on Ionic Transition Metal Active Layers ........................ 46 1.4.3.1 Light Emitting Electrochemical Cells ................................ ......... 46 1.4.3.2 Electrochromic Devices ................................ ............................ 48 1.4.3.3 Dye Sensitized Solar Cells ................................ ....................... 49 1.4.3.4 Solar Fuel Devices ................................ ................................ .... 51 1.5 Overview of this Dissertation ................................ ................................ ............ 52 2 EXPERIMENTAL TECHNIQUES ................................ ................................ ............ 55 2.1 Structural Characterization ................................ ................................ ............... 55 2.2 Material s and Reagents ................................ ................................ .................... 55 2.3 Electrochemical Methods ................................ ................................ .................. 56 2.3.1 Cyclic Voltammetry and Differential Pulse Voltammetry ........................ 56 2.3.2 Spectroelectrochemistry ................................ ................................ ........ 57

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7 2.3.3 In Situ Spectroelectrochemistry ................................ ............................. 57 2.4 Fi lm Colorimetry ................................ ................................ ................................ 58 2.5 Photophysical Methods ................................ ................................ ..................... 58 2.5.1 Steady State UV Vis Absorption ................................ ............................ 58 2.5.2 Transient Absorption ................................ ................................ .............. 59 2.5.3 Steady State Photoluminescence ................................ .......................... 59 2.5.4 Photoluminescence Quantum Yie ld Measurements .............................. 60 2.5.5 Time Resolved Photoluminescence ................................ ...................... 60 2.6 Device Fabrication and Characterization ................................ .......................... 61 2.6.1 Light Emitting Electrochemical Cells ................................ ...................... 61 2.6.2 Dual Electrochromic/Electroluminescent Display Devices ..................... 63 2.6.3 Solar Photoelectrochemical Cells ................................ .......................... 64 3 CROSS LINKABLE RU(II) TRIS(BIPYRIDINE) BASED IONIC TRANSITION METAL COMPLEXES FOR DUAL ELECTROCHROMIC AND ELECTROLUMINESCEN T APPLICATIONS ................................ .......................... 66 3.1 Introductory Remarks ................................ ................................ ........................ 66 3.2 Synthesis and Characterization of Acrylate Containing Ru(II) Tris(bipyridine) Complexes for Dual Electrochromic and Electroluminescent Applications ....... 71 3.2.1 Design and Synthesis ................................ ................................ ............ 71 3.2.2 Electrochemical Pro perties ................................ ................................ .... 74 3.2.3 Spectroelectrochemistry ................................ ................................ ........ 76 3.2.4 Colorimetry ................................ ................................ ............................ 79 3.2.5 Photoluminescence ................................ ................................ ............... 83 3.2.6 Light Emitting Electrochemical Cells ................................ ...................... 85 3.2.7 Dual Electrochromic/Electroluminescent Device Pr ototype ................... 91 3.3 Conclusions ................................ ................................ ................................ ...... 95 3.4 Experimental Details ................................ ................................ ......................... 96 3.4.1 Synthesis ................................ ................................ ............................... 96 3.4.2 Film Preparation and Cross Linking for Electrochromic Measurements ................................ ................................ ..................... 103 4 POLYFLUORENE RUTHENIUM(II) TRIS(BI PYRIDINE) ASSEMBLIES VIA IONIC TRANSITION METAL COMPLEX CHROMOPHORE INTERACTIONS IN MACROMOLECULAR LIGHT HARVESTING ANTENNAE ................................ .. 104 4.1 In troductory Remarks ................................ ................................ ...................... 104 4.2 Synthesis and Characterization of Polyfluorene with High Loading of Ru(II) Chromophores ................................ ................................ ................................ 106 4.2.1 Des ign, Synthesis and Structural Characterization .............................. 106 4.2.2 Electrochemistry ................................ ................................ .................. 110 4.2.3 Spectroelectrochemistry ................................ ................................ ...... 112 4.2.4 Steady State Absorption, Emission and Time Resolved Photoluminescence ................................ ................................ ............. 113 4.2.5 Femtosecond Transient Absorption ................................ ..................... 118

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8 4.3 Synthesis and Characterization of Polyfluorene Assemblies Having Low Ruthenium(II) Polypyridyl Loadings: Further Insights into Excited State Migration in Hybrid Arrays ................................ ................................ .............. 124 4.3.1 Design and Synthesis ................................ ................................ .......... 124 4.3.2 Steady State Absorption and Emission Spectra ................................ .. 127 4.3.3 Sub Nanos econd Transient Absorption ................................ ............... 128 4.3.4 Femtosecond Transient Absorption ................................ ..................... 129 4.3.5 Solvent Effects ................................ ................................ ..................... 131 4.4 Conclusions ................................ ................................ ................................ .... 133 4.5 Synthetic Details ................................ ................................ ............................. 133 4.6 Film Preparation ................................ ................................ .............................. 144 5 ENERGY MIGRATION ALONG IONIC TRANSITION METAL COMPLEX UNITS IN POLYFLUORENE RUTHENIUM(II) POLYPYRIDYL LIGHT HARVESTING ANTENNAE ................................ ................................ ................................ .......... 146 5.1 Introductor y Remarks ................................ ................................ ...................... 146 5.2 Amplified Stern Volmer Quenching of Polyfluorene Ruthenium(II) Polypyridyl Assembly ................................ ................................ ..................... 147 5.3 Synthesis and Char acterization of Ru(II) Loaded Polyfluorene Assemblies Containing Small Fractions of Low Energy Chromophores ............................ 149 5.3.1 Design and Synthesis ................................ ................................ .......... 149 5.3.2 Electrochemistry ................................ ................................ .................. 152 5.3.3 Photophysical Characterization of Osmium(II) Polypyridyl Functionalized Polyfluorene Series ................................ ...................... 155 5.3.4 Photophysical Characterization of Polyfluorene Ionic Transition Metal Assembly Series Containing Various Fractions of Ester Functionalized Ru(II) Chromophores ................................ ................... 157 5.3.5 C arboxylate Functionalized Polyfluorene Ionic Transition Metal Assemblies in Solar Photoelectrochemical Cells ................................ 160 5.4 Conclusions ................................ ................................ ................................ .... 163 5.5 Experimental Section ................................ ................................ ...................... 163 6 CONTROLLING EXCITON AND CHARGE TRANSFER IN THIOPHENE CONTAINING CONJUGATED POLYMER RUTHENIUM(II) POLYPYRIDYL ASSEMBLIES ................................ ................................ ................................ ....... 172 6.1 Introductory Remarks ................................ ................................ ...................... 172 6.2 Synthesis and Characterization of Thiophene Containing Conjugated Polymer Ruthenium(II) Polypyridyl Assemblies ................................ .............. 173 6.2.1 Design, Synthesis and Structural Characterization .............................. 173 6.2.2 Electrochemistry ................................ ................................ .................. 175 6.2.3 In Situ Spectroelectrochemistry ................................ ........................... 178 6.2.4 Steady State Photophysical Properties ................................ ................ 180 6.2.5 Transient Absorption ................................ ................................ ............ 183 6.3 Conclusions ................................ ................................ ................................ .... 192 6.4 Experimental Section ................................ ................................ ...................... 192

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9 7 CONCLUSIO NS AND FUTURE DIRECTIONS ................................ .................... 200 LIST OF REFERENCES ................................ ................................ ............................. 205 BIOGRAPHICAL SKETCH ................................ ................................ .......................... 216

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10 LIST OF TABLES Tab le Page 1 1 Colors of the Ru(II) polypyridyl complexes of the ligands L1 L5 (Figure 1 10) in all the accessible reduced states ................................ ................................ .... 37 3 1 CIE 1976 L*a*b* values a for the thermally cross linked films of compounds 5a 5b 9a and 9b at various redox states ................................ ......................... 80 3 2 CIE 1976 L*a*b* values a for the copolymeric film of 5a and 5b in 1:1 molar ratio at various redox states of 5a and 5b ................................ .......................... 80 3 3 Percent transmission contrast ( %T) and color difference ( E) data ................. 83 3 4 LEC data ................................ ................................ ................................ ............ 89 3 5 LEC data a fter active layer cross linking ................................ ............................ 91 3 6 CIE 1976 L*a*b* values for the dual electrochromic/electroluminesce nt device prototype ................................ ................................ ................................ 94 5 1 Electrochemical data for Ru Model (Chapter 4), PF Ru O s PF Os Os Model PF Ru 30%E and Ru Model E ................................ ............................ 153 6 1 Electrochemical data for PFT Hex PF2T Hex PT Br PFT Ru PF2T Ru and PT Ru DPV values are given in parentheses ................................ ........... 178 6 2 Optical data for compounds PFT Ru PF2T Ru PT Ru PFT Hex PF2T Hex and PT Br ................................ ................................ ................................ ......... 182

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11 LIST OF FIGURES Figure Page 1 1 Organic electronics ................................ ................................ ............................. 20 1 2 Simplified molecular orbital (MO) diagrams of conjugated polymers. ................. 22 1 3 Wannier and Frenkel excitons ................................ ................................ ............ 23 1 4 Electronic transitions in a thiophene trimer ................................ ......................... 25 1 5 Organic electrochromic polymers ................................ ................................ ....... 26 1 6 A simplified Jablonski diagram showing typical electronic transitions in organic chromophores ................................ ................................ ........................ 27 1 7 Energy levels in d 6 transition metal com plexes ................................ ................... 30 1 8 Relative positions of excited states in d 6 transition metal complexes ................. 31 1 9 Light absorption by Ru(II) polypyridy l complexes ................................ ............... 35 1 10 Ru(II) polypyridyl complexes exhibit ing multi color electrochromism .................. 36 1 11 Forster resonance energy transfe r conditions ................................ .................... 39 1 12 Schematic energy diagram illustrating singlet singlet and triplet triplet Dexter energy transfer ................................ ................................ ........................ 41 1 13 S tructure of a polystyrene based assembly containing Ru(II) and Os(II) polypyridyl chromophores ................................ ................................ ................... 42 1 14 Low power upconversion ................................ ................................ .................... 43 1 15 Schematic illustration of potential surface parabolas for photoinduced electron transfer reactions ................................ ................................ .................. 44 1 16 Schematic representation and operating principles of a light emitting electroch emical cell ................................ ................................ ............................ 47 1 17 Schematic representation of an absorptive/transmissive electrochromic display device ................................ ................................ ................................ ..... 49 1 18 Dye sensitized solar cells ................................ ................................ ................... 50 1 19 Schematic representation and operating principles of a solar fuel cell along with a prototypical catalyst chromophore assembly for water oxidation ............. 52

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12 3 1 Dual electrochromic/electrolumine scent (EC/EL) devices ................................ .. 67 3 2 Electrochemical data ................................ ................................ .......................... 75 3 3 Electrochemical data indicating polymerization of 9a and 9b ............................. 76 3 4 Spectroelectrochemical data ................................ ................................ .............. 78 3 5 Schematic illustra tion of CIE 1976 L*a*b* color space ................................ ....... 80 3 6 CIE 1976 a*b* values for cross linked films of 5a and 9a calculated from their absorption spectra at all the unambi guously reversible redox states .................. 84 3 7 Emission spectra of compounds 5a 5b 9a 9b and Ru(bpy) 3 .......................... 84 3 8 Electroluminescence spectra of LEC devices based on 5a 5 b 9a and 9b ....... 87 3 9 Voltage dependent radiant exitance ................................ ................................ ... 90 3 10 Schematic representation of a redesigned dual electrochromic/ele ctroluminescent device prototyp e ................................ .......... 92 3 11 Dual electrochromic/electroluminescent device characteris tics .......................... 93 4 1 Conjugated polymer ionic transition metal complex hybrids with controlled electronic properties ................................ ................................ ......................... 105 4 2 Electrochemical data ................................ ................................ ........................ 111 4 3 Spectroelectr ochemical data ................................ ................................ ............ 113 4 4 Steady state photophysical data ................................ ................................ ....... 114 4 5 Time resolved photoluminescence data ................................ ........................... 116 4 6 Femtosecond transient absorption data ................................ ........................... 119 4 7 Transient absorption and spectroelectrochemical data ................................ ..... 120 4 8 Steady state optical data ................................ ................................ .................. 127 4 9 Sub nanosecond transient absorption data ................................ ...................... 129 4 10 Femtosecond transient absorption data ................................ ........................... 130 4 11 Solvent dependant photophysical properties of PF 5%Ru ............................... 132 4 12 Solvent dependent photophysical propert ies of PF 20%Ru ............................. 133

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13 5 1 Illustration of an iTMC containing functional conjugated polymer adsorbed on nanocrystalline TiO 2 ................................ ................................ ......................... 147 5 2 Simplified schematic illustration of amplified quenching effect in light emitting polyelectrolytes ................................ ................................ ................................ 148 5 3 Amplified quenching effect in PF Ru ................................ ................................ 148 5 4 Electrochemical data for Os Model PF Os and PF Ru Os ............................. 154 5 5 Electrochemical data for Ru Model E and PF Ru 30%E ................................ 155 5 6 Optical properties of PF Ru Os PF Os and Os Model ................................ ... 156 5 7 Optical data for compounds Ru Model E and PF Ru 30%E ............................ 159 5 8 Femtosecond transient absorption data for PF Ru 10%E ................................ 159 5 9 Emission data for ester functionalized Ru(II) loaded polyfluorene assemblies 160 5 10 IR spectra of PF Ru 30%E and PF Ru 30%A and photographs of TiO 2 P25 nanoparticles before and after PF Ru 30%A absorption for 4 h ....................... 161 5 11 Solar photoelectrochemica l cell characteristics ................................ ................ 162 5 12 Illustration of functional metallopolymer assemblies adsorbed on photonic electrode with controlled patterns ................................ ................................ ..... 163 6 1 Electrochemical data ................................ ................................ ........................ 177 6 2 Spectroelectrochemical data ................................ ................................ ............ 179 6 3 Absorption and emission spectra ................................ ................................ ...... 181 6 4 Femtosecond transient absorption spectra of PFT Ru and PFT Hex ............... 184 6 5 Femtosecond transient absorption spectra of PF2T Ru and PF2 T Hex ........... 185 6 6 Femtosecond transient absorption spectra of PT Ru and PT Br ...................... 187 6 7 Temperature dependent femtosecond transient ab sorption spectra of PT Ru 189 6 8 Nanosecond transient absorption spectra of PT Ru and PT B ........................ 191 6 9 Nanosecond transient absorpt ion spectra of A) PFT Ru and B) PF2T Ru in acetonitrile with exc = 388 nm ................................ ................................ .......... 192 7 1 Dual electrochromic/electrochemilu minescent materials and devices .............. 200

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14 7 2 Conjugated metallopolymers with controlled electronic properties ................... 202 7 3 Structure of a proposed polymer chromophore catalyst assembly along with a schematic repre sentation of the respective solar fuel device electrode ......... 204

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15 L IST OF SCHEMES Scheme Page 3 1 Synthetic route to compound 5a ................................ ................................ ......... 72 3 2 Synthetic route to compound 5b ................................ ................................ ......... 73 3 3 Synthetic route to compound 9a ................................ ................................ ......... 73 3 4 Synthetic route to compound 9b ................................ ................................ ......... 74 4 1 Synthetic routes to compounds 4 and 7 ................................ ........................... 108 4 2 Synthetic route to PF Ru (polymer 8 ) ................................ ............................... 109 4 3 Synthetic routes to Ru Model (compound 9 ) and PF Hex (polymer 10 ) .......... 109 4 4 Synthetic route to PF 20%Ru ................................ ................................ ........... 125 4 5 Synthetic route to PF 5%Ru ................................ ................................ ............. 126 5 1 Synthetic route to compound 2 ................................ ................................ ......... 150 5 2 Syntheti c route to PF Ru Os (polymer 3 ) ................................ ......................... 150 5 3 Synthetic route to PF Os (polymer 4 ) ................................ ............................... 150 5 4 Synthetic route to Os Model (compound 5 ) ................................ ..................... 150 5 5 Synthetic route to compound 7 ................................ ................................ ......... 151 5 6 Synthetic routes to PF Ru 10%E ( 8 ) and PF Ru 30%E ( 9 ) .............................. 152 5 7 Synthetic route to Ru Model E (compound 10 ) ................................ ................ 152 5 8 Synthetic route to the PF Ru 30%A assembly ................................ ................. 160 6 1 Synthetic routes to PFT Ru (Polymer 5 ) and PFT Hex (Polymer 6 ) ................. 174 6 2 Synthetic routes to PF2T Ru (Polymer 10 ) and PF2T Hex (Polymer 11 ) ......... 174 6 3 Synthetic routes to PT Ru (Polymer 16 ) and PT Br (Polymer 14 ) .................... 175

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16 LIST OF ABBREVIATIONS ACN Acetonitrile APCE Absorbed photon to current conversion efficiency B PY Bipyridine CV Cycl ic voltammetry DBU 1,8 Diazabicyclo[5.4.0]undecene DCM Dichloromethane DMF Dimethylformamide DPV Differential pulse voltametry EC Electrochromic ECD Electrochromic display device ECL Electrochemiluminescent EL Electroluminescent EQE External q uantum e ffici en cy FF Fill factor F C Ferrocene FRET Fluorescence resonance energy transfer GPC Gel permeation chromatography HOMO Highest occupied molecular orbital HPLC High pressure liquid chromatography IPCE Incident photon to current conversion efficiency IR Infrare d I SC Short circuit current LEC Light emitting electrochemical cell LC Ligand centered

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17 LUMO Lowest unoccupied molecular orbital MC Metal centered MLCT Metal to ligand charge transfer M O M olecular orbital NMR Nuclear magnetic resonance OLED Organic light em itting display diode PF Polyfluorene P H CN Benzonitrile PL Photoluminescence PMMA Poly(methylmethacrylate) PT Polythiophene R PM Revolutions per minute TBAI Tetrabutylammonium iodide THF Tetrahydrofuran UV Ultraviolet UV V IS Ultraviolet visible V OC Open circ uit voltage

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18 Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy IONIC TRANSITION METAL COMPLEX POLYMERS AS PHOTONIC AND REDOX ACTIVE MATERIALS By Egle Puodziukynaite December 2012 Chair: John R. Reynolds Major: C hemistry An emerging field of organic electronics has led to various lightweight, flexible, and easily processable d evices, including organic light emitting dis plays electrochromic display and window type devices photovoltaic cells, and field effect transistor s. In these architectures, i onic transition metal complexes (iTMCs) represent an important class of active layer materials as they posses intrinsic multi functionality. Via structural modifications, a combination of redox activity, electrochromism, light emission, and ionic conductivity can be fine tuned in these materials Additionally, unique properties arise as i TMCs are combined with or ganic electroacti ve polymers, leading to controlled energy and charge transport mechanisms T his dissertation describes the design, synthesis, characterization, and structure property relationships of iTMC polymers with the multifunctionality required to develop new archit ectures of optoele c tronic devices. A first part of this dissertation focuses on cross linkable Ru(II) tris(bipyridine) complexes with dual electrochromic (EC) and electrochemiluminescent (EL) characteristics. For these complexes, the structure property rel ationships are established between the detailed ligand design and the co mbination of the required properties for simultaneous emissive and reflective mode applications. Additionally, for

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19 the first time, a dual EC/EL device prototype is presented where ligh t emission and mu lti color electrochromism occur from the same pixel comprised of a single active layer, allowing for optima l visibility in all ambient lighting situations A second portion of this dissertation focuses on iTMC organic conjugated polymer a ssemblies as light harvesting arrays and charge transport materials for ultimate use in solar photovoltaic and fuel devices With controlled charge and exciton trans port being the key requirement in such systems, polymer building blocks having variable HOM O/LUMO levels (i.e. polyfluorene, poly(3 hexylthiophene), poly(fluorene co thiophene), etc ) are explored as the backbones of the macromolecular antennae. Facile energy transfer and charge separation processes between the polymer backbones and pendant iTMC units are found to occur in such systems by employing ultrafast spectroscopic techniques Additionally, these hybrid arrays are demonstrated to exhibit fast e xciton transport along the pendant Ru(II) units resulting in an antenna effect. Finally, interact ions between these macromolecular assemblies and semiconductor interfaces are studied as the iTMC hybrids are utilized in solar photoelectrochemical cells.

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20 CHAPTER 1 INTRODUCTION 1.1 Organic Electronics Over the past few decades, the field of organic electron ics has attracted a considerable amount of attention as t his field is associated with devices having low power consumption, low weight, mechanical flexibility, inherent processability, and optoelectronic property fine tuning via r a tional structure modific ations of active layer materials As a result, various architectures of organic light emitting diodes 1,2 light emitting electrochemical cells, 3 6 electrochromic display and window devices, 7 9 along with photovoltaic cells and field effect t ransistors 10 12 have been developed and even successfully commercialized (Figure 1 1 ) Figure 1 1 Organic electronics. Photographs of a flexible Sony OLED television ( http://www.techshout.com/general/2008/07/sony debuts foldable oled screens/ ) and a leaf like organic solar cell module fabricated by Mitsubishi ( http://zedomax.com/blog/2008/06/04/organic thin film solar cell leaves ) Although o rganic electronics has b een generally associated with purely organic small molecules and conjugated polymers, transition metal complex es are an important class of active layer materials exhibiting efficient phosphorescence and excellent redox stability. 5,13 18 A particularly interesting platform is represented by t ransition metal

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21 complex organic chromophore hybrids as these materials could combine the chemical, electronic, magnetic, optical and redox properties of metal complexes with those of the organic materials allowing for true multifunctionality and novel architectures of organic optoelectronic devices. 19 1.2 Conjugated Polymers in Organic Electronics The discovery of con jugated polymers is most often attributed to the finding of Heeger, MacDiarmid and Shirakawa in 197 7 that polyacetylenes can be doped to induce conductivity over the full range from insulator to metal. 20 22 Since then, various chemical and physical aspects of conjugated polymers have been studied explaining the principles behind e xciton migration light emission and redox behavior in such systems 23,24 Additionally, via synthetic chemistry modifications the structural spectrum of conjugated polymers has been expanded from basic all carbon materials to heterocyclic systems, allowing for a wide range of property tuning. 24,25 In a general sense, the conductivity an d delocalization characteristics orbitals supported bond backbone. This phenomenon is generally explained by a simplified representation using a linear combination of ato mic orbit als to model the molecular orbi tal s (MO) (Figure 1 2). A s the number of monomeric units in a conjugated polymer orbitals become so closely spaced that they may be considered as a continuum 26 The HOMO and LUMO orbitals of a conjugated polymer then strongly resemble the top of valence and b ottom of conduction bands, allowing for electrons to delocalize, as delineat ed by semiconductor band theory 24

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22 Figure 1 2 Simplified molecular orbital (MO) diagrams of conjugated polymers. Simplified MO diagram of a sp 2 hybridized ethylene type single unit as wel l as that of several conjugated units demonstrating closely space d molecular orbital cluster s resembling semiconductor valence and conduction bands. Adapted from Stalder, R. Organic Semiconducting molecules and Polymers for Solution Processed Organic Elect ronics, Ph.D. Thesis, Univers i ty of Florida, 2012 27 While the energy gap in polyacetylene is caused by Peier l s distortion of otherwi se degenerate molecular orbitals, other conjugated polymers have intrinsic non dege ne racy arising from the energy difference s between their aromatic and quinoidal forms. Depending on the relative positions of the HOMO and LUMO MOs, semiconducting polymers can be rendered conductive by either addition of electrons (reduction, n doping) or removal of electrons (oxidation, p doping). Depending on the dominant carrier upon application of an electric field conjugated chromophores are classified into hole transp orting, electron transporting or ambipolar (capable of transporting both charge carriers) systems. T o date, t he highest carrier mobilities (> 1 cm 2 V 1 s 1 ) have been achieved p type polymers, similar to or exceeding those of amorphous silicon 28,29 While extensive literature exist s covering multiple fundamental chemical and physical characteristics of conjugated polymers, this dissertation will only ove rview scientific aspects most relevant to the research described including exciton and charge migration, electrochromism and light emission

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23 1.2.1 Exciton Migration in Organic Conjugated Polymers Due to the low dielectric constant, c harge carriers found in conju gated polymers differ in nature with respect to those of inorganic semiconductors. Photoexcitation of semiconducting crystals results in the formation of a very weakly bound electron hole pair, referred to as Wannier Mott exciton. For this type of an excit on, an electron radius is much larger the lattice spacing (Figure 1 3 A ) In simple terms, due the ease of dissociation of Wannier Mott excitons, electrons and holes are considered to be free carriers in inorganic semiconductors. 30 Figure 1 3 Wannier and Frenkel exciton s. Illustration of A) Wannier and B) Frenkel excitons as they relate to the lattice of the material Adapted from http://www.pa.msu.edu/cmp/CORE CM/ExcitonPV.pdf In contrast, Frenkel type exc itons are characteristic of non doped semiconducting polymers. Such excitons are described as e lectrically neutral electron hole pair s with a binding energ y of ca. 0. 1 1 eV. 31 In this case, the electron is essentially confined within a single lattice constant (Figure 1 3 B ) As a result, s uch Frenkel type excitons generally exhibit short diffusion lengths of around 5 to 10 nm due to high a probability of recombination 32 Such an electron hole pair is though t to migrate via hopping mechanisms taking place between adjacent parts of the same polymer chain or different polymer chains depen ding of the morphology and purity of the films. 33 For Frenkel exciton harvesting to occur, it has to be separated into carri ers with opposite

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24 charges, 31 and this is generally accomplished by employing donor and acceptor type material blends or int erface engineering. 1.2.2 Electrochromism in Organic Conjugated Polymers Electrochromism is a phenomenon directly related to conjugated polymer doping and is defined as a reversible change in an a bsorption spectrum upon electrochemical reduction or oxidation. 8 Organic polymers represent a n attractive class of electrochromic materials, as they allow for a wide range of color engineering, sub second switching, low cost processability and mechanically advanced devices 7 9,34 All these characteristics offer significant advantages over inorganic oxide based materials that have been generally associated with this appli cation. E lectrochromism in conjug ated polymers occurs due to the change of the allowed electronic transitions upon redox processes The color of a polymer in its neutral state is generally attributed to the grou transitions directly related to the optical gap of the chromophore. Upon doping, however, new intermediate bandgap states are c reated, resulting in new selection rules for electronic transitions. In conjugated polymers this is generally asso ciated with polaronic and bipolaronic states, as illustrated using a thiophene trimer in Figure 1 4 35 Once a cathodically coloring polymer is oxidized to a polaronic state, lower energy absorpt ions begin to emerge in the electronic spectra due to half filled midgap levels. Upon further oxidation, bipolaronic carriers (coupled dications) are generated, limiting the electronic transitions to those occurring from the top of the valence band to the BP1 that are often associated with absorption in the near infrared region.

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25 Figure 1 4 Electronic transitions in a thiophene trimer. S tructure s of a thiophene trimer and energy level diagrams showing the all owed electronic tr ansitions in A) n eutral, B) polaron and C) bipolaron states Adapted from Dyer, A. Conjugated Polymer Electrochromic and Light Emitting Devices, Ph.D. Thesis, University of Florida, 2007 35 The charged segments, whether polarons or bipolarons, are counter b alanced and stabilized by the oppositely charged ions of an external electrolyte. These doping processes a re also associated with an increase in polymer conductivity and geometry changes from the aromatic to quinoid form s T he reversibility of electrochrom ic transitions is strongly related to the electronic structure of a polymer and it s capability to delocalize charge in the doped state. Electrochromic conjugated polymers designed for commercial applications are desired to be capable of switching between v ividly colored and highly transmissive near colorless states. A series of such spray processable polymeric electrochromes covering the entire subtractive color palette have been demonstrated by the Reynolds group 7 and their structures are given in Figure 1 5

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26 Figure 1 5 Organic electrochromic polymers. Repeat unit structures and photographs of spray cast polymer films in the neutral colored, and oxidized transmissive states. Normalized absorption spectra of neutral sp ray cast polymer films of Adapted with per mission from Dyer, A. L.; Thompson, E. J.; Reynolds, J. R. ACS Appl. Mater. Interfaces 2011 3 1787 1795 7 1.2.3 Light Emission in Organic Conjugated Polymers Photoe xcitation of organic conjugated polymers generally leads to several decay mechanisms as shown in the Jablonski diagram in Figure 1 6 36 38 Upon absorption of a photon by a chromophore, promotion of an electr on occurs from the singlet ground electronic state (S 0 ) to a high er energy singlet excited state (S n ) on a timescale of ca. 10 16 10 14 s Each electronic state consists of multiple closely spaced vibrational and rotational levels and therefore, is often referred to as a manifold. Although excitation to S 1 is the most common for organic molecules, higher lying singlet states, such as S 2 or S 3 are also accessible, d epending on th e energy of the incident photon. In compliance

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27 de cay processes are generally initiated only from the lowest lying excited states ( S 1 or T 1 ) due to rapid vibrational relaxatio n termed internal conversion. 39 In accordance with that, i n conjugated polymers, visible light absorption is generally attributed to S 0 S 1 electronic Figure 1 6 A simplified Jablonski diagram showing typical electronic transitions in organic chromophores. Adapted from http://www.uni leipzig.de/~pwm/web/?section=introduction&page=fluorescence Immediately after excitation, r elaxation to the lowest vibrational level of S 1 generally occurs followed by either fluorescence o r non radiative d ecay processes (Figure 1 6 ) Depending on the e lectronic structure of the macromolecule and the geometry of the ground and excited states, b oth emission color and quantum yield can be controlled, and a variety of emissive polymer s have been developed with those based on polyfluorene or p oly( p ara phenylene) s being the most abundant. 40,41 I n some cases, intersystem crossing to produce the triplet excited states occurs. As this process is spin forbidden, it is usually a minor pathway that can be facilitated by the presence of a heavier atom, such as transition metals or sulfur due to an increase

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28 in spin orbit coupling I n conjugated polymers emission from triplet excited states is generally observed only at low temperat ures in oxygen free environment. 42 As a result, the relative energy levels of these triplet states are mainly studied using transient absorption techniques or heavy atom assisted sensitization. 43 It has been established in the literature that the energy difference between the S 1 and T 1 levels is typically on the or der of 1 eV or 8000 cm 1 42 The triplet excited states are thought to be lower in ene rgy electronic exchange interactions. While phosphorescence in organic conjugated polymers is negligible, it is important to understand triplet exciton energy and dynamics, as it could be exploited in design ing materials for solar energy harvesting, as well as macromolecular hosts for phosphorescent OLEDs Due to thus limited s conjugated macromolecules are thought to poss es several chromophore or luminophore segments per chain. 44 For absorption, chromophoric sequences generally contain up to 10 repeat units and this is related to the effective conjugated length, i.e. the length of exciton delocalization Effective conjugation length for emission, however, has been found to differ from that for absorption. This effect may be partly attributed to ultrafast energy transfer between adjacent luminophoric sequences confirming their strong electr onic interactions. As a result, emission of 1.3 Ionic Transition Metal Complexes in Organic Electronics Ionic transition metal complexes have emerged as attractive candidates for opt oelectronic applications due to their emissive triplet excited states, reversible redox behavi or, charge transfer transitions leading to vivid ground state color s as well as ionic

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29 conductivity readily exploitable in electrochemical devices. 8,45,46 P articular emphasis has been placed on the octahedral coordin ation complexes containing ruthenium (II) osmium (II) iron (II) and iridium(III) 15 18 Among these materials, ionic transition metal complexes based on Ru(II), especially the Ru(II) polypyridyl family, have been proven to be the most versatile finding applica tions in the fields of li ght emission, electrochromism, solar energy harvesting and storage. 4,8,15,47,48 This is due to the low er cost of ruthenium derivatives when compared to other phosphorescent transition metal coordination complexes, intrinsic multifunctionality, stability and property tunability via ligand design. As a result, this subsection describes principles behind light emission, electroch romism, and excited state interactions in transition metal complexes and their assemblies with a particular emphasis on Ru(II) derivatives. 1.3.1 Principles Behind Light Emission In Ru(II) polypyridyl complexes, the Ru(II) dication is classified as a 4d 6 metal c enter. Consequently electronic transitions leading to photoluminescence of this class of derivatives strongly resemble those of other widely studied octahedral coordination complexes including Fe(II), Os(II) and Ir(III) with characteristic metal centers o f 3d 6 5d 6 and 5d 6 respectively. 15,18 A simplified orbital and energy surface diagram depicting significant electronic transitions in such d 6 complexes is given in Figure 1 7 As can be seen in Figure 1 7 A the degenerate d orbitals of the Fe(II), Ru(II), Os(II) and Ir(III) cations are destabilized and split in an octahedral ligand field, by an amount 3d Fe center due to the lowest quantum number) and also depends on the ligand effect.

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30 Figure 1 7 Energy levels in d 6 transition metal complexes A ) D orbitals in octahedral field. B ) Orbital description of metal centered ( MC ) metal to ligand charge transfer ( MLCT ) and LC (ligand centered) transitions, where S is a substituent group capable of exerting electron withdrawing or releasing effects ( resulting in stabil ization or destabilization, respectively, of the energy C ) E lectronic transitions involving MC, MLCT, and LC excited states, where the MC levels are not emissive. Adapted from Flamigni, L.; Barbieri, A.; Sabatini, C.; Ventura, B.; Barigelletti, F. Top. Curr. Chem. 2007 281 143 203 18 Nonetheless, in suc h coordination complexes, initial electronic tran sitions potentially leading to light emission are generally singlet in nature and occur from the ground state (GS) to the ligand centered (LC), metal centered (MC) and metal to ligand charge transfer (MLCT) states (Figure 1 7 C ) It is noteworthy, however, that

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31 photoluminescence of these compounds generally occurs from the LC and MLCT electronic states that are triplet in nature with some contributions from the corresponding singlet states In iTMCs, t riplet e mission is due to the heavy atom effect and high spin orbit coupling that result in efficient intersystem crossing from the singlet to the triplet excited states Spin orbit coupling strength generally increases significantly with the atomic number of an e lement As a result, spin orbit coupling constants for Fe, Ru, Os and Ir are = 431, 1042, 33 81, 3909 cm 1 respectively. 36 Additional l y emission properties among these complexes vary greatly based on the relative energies of the emissive and non emissive states Excited state relaxation scena rios based on the relative excited state energy differences are depicted in Figure 1 8 Figure 1 8 Relative positions of excited states in d 6 transition metal complexes. Schematic representation of two limiting cases for the relative positions of triplet metal centered ( 3 MC ) and metal to ligand charge transfer ( 3 MLCT) (or ligand centered ( 3 LC )) excited states. Adapted from Campagna, S.; Puntoriero, F.; Nastasi, F.; Bergamini, G.; Balzani, V. Top. Curr. Chem. 2007 280 117 21 4 15 photoluminescence generally occurs from the lowest excited state of a compound. As a result, if MC excited state s are the lowest in energy in d 6 octahedral complexes due to t he strong displac ement of these levels with respect

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32 to the ground state geometry such compounds undergo fast radiationless deactiva tion and/or ligand dissociati on reactions. Conversely, when LC and MLCT are the lowest in energy luminescence is usually o bserved. In accordance with these rules, due to the low ligand field splitting, Fe(II) complexes are generally non emissive, as the lowest excited states are MC in nature Conversely, in Ir(III) and Os(II) complexes MC states are generally very high in energy, thus rendering the m emissive from either 3 LC and /or 3 MLCT electronic levels As a result, further differences in light emissio n properties then arise based on the relative positions of these electronic levels. Consequently, Ir(III) complexes with high energy 3 MLCT and 3 LC manifolds exhibit ligand dependent quantum yields in some cases approaching unity. 18 Meanwhile, in the case of osmium, 3 MLCT states are low in energy (~ 1.6 eV), leading to a significant fraction of radiationless de cay pathways due the energy gap law. 49,50 As a result, the quantum yield of the Os(II) polypyridyl complexes rarely exceeds 0.1. 17 Finally, Ru(II) complexes also exhibit emission (ca. 2.1 eV) from 3 MLCT electronic levels. However, in this case, 3 MC levels are also thermal ly accessible causing some deactivation. To summarize, for most Ru(II) polypyridyl complexes, absorption of a photon largely result s 1 MLCT transition s from the t 2 by intersystem crossing to a cluster of closely spaced 3 MLCT states that exhibit relatively long lifetime s crossing in such systems generally occurs wi th an effic iency approaching unity It is electron reduction process of Ru(II) tris(bipyridine) derivatives. Additionally, even in the

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33 homoleptic complexes, the emitt ing 3 ring localized orbital having a small am ount of interligand interaction s 45 Based on the MO picture it is evident that Ru(II) tris(bipyridine) complexes possess metal based HOMO and ligand based LUMO. As a result, it has been shown that the emission color and quantum yield in this class of compounds is generally controlled by ligand design, par ticularly by introducing e donating or withdrawing substituents onto the bipyridine ligands. 51 As expected, it h as been shown that e withdrawing ligands generally bathochromically shift Ru(II) complex emission by over 100 nm ( max ranges from ca. 600 to 800 nm) Additionally, the cumulative effect of e withdrawing donating substituents positions of the bipyridine ligands has been previously employed to alter the relative energies of MLCT and MC states, thus im proving the quantum yields of the respective complexes up to ca. 0.3. 51 It is interesting to note however, that once e wi t hdrawing substituents are introduced at the positions of the b i py ridine ligands, the emission efficiency of the corresponding complexes is significantly quenched. 52 This can be partially attributed to the energy gap law in such chromophores. 53 1.3.2 Principles Behind Light Absorption and Electro chromism Coordination complexes have emerged as attractive electrochromes due to their vivid color s and redox reversibility necessary for repeated switching of the resultant electrochromic films and devices. 8,9 In iTMCs, electrochromism generally arises due to low energy visible region transitions associated with M LCT inter valence charge transfer (IVCT) and in tra ligand excitation, among others Whereas Ir(III) polypyridyl coordination complexes are good light emitters, due to the high HOMO LUMO gap, such complexes rarely exhibit absorption at wavelengths longer than 400 nm and thus lack visible

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34 color. 18 Conversely, 1 MLCT states are low in energy in Fe(II), Ru(II), and Os(II) polypyridines, resulti ng in intense visible absorption bands rendering these complexes red, orange and green, respectively. 8 As mentioned previously, such complexes generally possess metal based HOMO s and ligand based LUMO s As a result, upon oxidat ion of such complexes to the M III redox state, loss of the MLCT absorption band occurs and the compound s switch to nearly colorless high l y transmissive states. 8,54 Meanwhile, iTMC electrochromic transitions u pon reduction strongly depend on the chemical structure of their ligands and are generally stabilized along with the corresponding cathodic processes upon introduction of e withdrawing substituents. While t he redox stability of Fe(II) is limited due to ligand loss upon switching, and Os(II) based iTMC s are costly, Ru(II) polypyridines have emerged as the most promising candidate s for such applications, also being the most well studied system s 48,55,56 Given in Figure 1 9 are the ground state absorption transitions in a Ru(II) tris ( bipyridine ) prototype along with a corresponding absorption spectrum, where the transition assignments are made. As can be seen, Ru(bpy) 3 exhibits ground state transitions in principle simi lar to those demonstrated by the general class of d 6 polypyridyl based coordination complexes. 15 In this case, a cluster of MLCT levels (Figure 1 9 B ) is the lowest in energy, resulting in a broad absorption band centered around ca. 450 nm (Figure 1 9 C ). As in the case of emission, moderate shifts in the ground state band position and in tensity can be introduced by rational bipyridine ligand design. Nonetheless, as mentioned previously, metal centered oxidations of such complexes generally always result in the loss of the MLCT transition and, therefore, a highly transmissive colorless sta te of these complexes in 3+ redox state.

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35 Figure 1 9 Light absorption by Ru(II) polypyridyl complexes. A ) Simplified molecular orbital diagram for Ru(II) polypyridine complexes in octahedral symmetry showing the three types o f electronic transitions occurring at low energies. B ) Detailed representation of the MLCT transition in D 3 symmetry. C ) Electronic absorption spectrum of [Ru(bpy) 3 ] 2+ in alcoholic solution showing absorption bands due to the respective electronic transiti ons along with the photograph of vividly colored Ru(bpy) 3 powder Adapted from Campagna, S.; Puntoriero, F.; Nastasi, F.; Bergamini, G.; Balzani, V. Top. Curr. Chem. 2007 280 117 214 15 and http://en.wikipedia.org/wiki/Tris(bipyridine)ruthenium(II)_chlo ride Conversely, t rue ligand substituent effects on electrochromism of Ru(II) polypyridyl complexes arise upon the reduction of the complexes. Elliot and coworkers have demonstrated that multiple vivid and distinct color changes can be invoked in the Ru( II) based iTMCs, as e withdrawing moieties are introduc positions of bipyidine ligands. 48,57 As a result, Figure 1 10 shows the structures of such hexasubs titued homoleptic Ru(II) polypyridyl derivatives along with a typi cal cyclic voltammogram for an amide based complex whereas T able 1 1 summarizes the colors observed for these materials at various redox states. It has been well established that t he number of probable electrochromic transitions is directly related to the redox processe s exhibited by a compound. While unsubstituted Ru(II) tris(bipyridine) generally shows a single metal centered oxidation

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36 and thre e stable redox based reductions; e withdrawing substituents significantly stabilize cathodic redox processes in the resultant iTMCs (Figure 1 10) leading to up to 6 total reductions or 2 per ligand. Accordingly, Table 1 1 demonstrates that a wide palette of visible colors can be achieved upon such tra nsitions, including red, blue, green, grey, brown and purple. Figure 1 10 Ru(II) polypyridyl complexes exhibiting multi color electrochromism. Structures of multi electrochromic Ru(II) polypyridyl complexes developed by Elli ott and coworker along with a cyclic voltammogram of Ru(L 2 ) 3 illustrating multiple cathodic transitions Adapted from Monk, P. M. S.; Mortimer, R. J.; Rosseinsky, D. R. Electrochromism and Electrochromic Devices ; Cambridge University Press: Cambridge, 2007 and Pichot, F.; Beck, J. H.; Elliott, C. M. J. Phys. Chem. A 1999 103 6263 6267 8,57 It is noteworthy, however, that once the same substituents are introduced at the positions of the bipyridine ligands, only slight variations of MLCT band intensity and position arise, giving rise to colors exhibiting orange, red and brown hues upon substituted complexes often exhibit absorption bands in the near IR region 47,48 Such electrochromic behavior is likely due to intraligand with near degeneracy disu bstitution, reduced state electronic transitions are more localized and strongly resemble those of the corresponding ligands.

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37 These significant differences in electrochromic behavior upon moderate structural changes have been attributed not only to electro nic effects but also sterics, where intraligand interactions are facilitated spatially upon certain functionalization patterns. 48 Table 1 1 Colors of the Ru(II) polypyridyl complexes of the ligands L1 L5 (Figure 1 10 ) in all the acce ssible reduced states (as established by bulk electrolysis in acetonitrile) Charge on RuL 3 L 1 L 2 L 3 L 4 L 5 +2 Orange Orange Orange Red orange Red orange +1 Purple Wine red Grey blue Purple Red brown 0 Blue Purple Turquoise Blue Purple brown 1 Green Blue Green Turquoise Grey blue 2 Brown Aquamarine Green 3 Red Brown Green Purple Adapted fr om Monk, P. M. S.; Mortimer, R. J.; Rosseinsky, D. R. Electrochromism and Electrochromic Devices ; Cambridge University Press: Cambridge, 2007 and Pichot, F.; Beck, J. H.; Elliott, C. M. J. Phys. Chem. A 1999 103 6263 6267. 8,57 1.4 Excited S tate I nteractions in M ultichromophoric T ransition M etal C o mplex A ssemblies and T ransition M etal C omplex O rganic C hromophore H ybrids Multichromophoric assemblies based on both multiple iTMC chromophores and iTMC organic chromophore combinations represent an important class of materials for applications based on va rious excited state migration phenomena. 15,19 Such phe nomena include Forster resonance energy transfer (FRET), Dexter electron exchange triplet sensitization and photoinduced charge separation among others. Based on these exciton/charge migration processes unique properties arise in iTMC assemblies, allowi ng for their application as light emitting host guest systems energy harvesting antenna having high optical cros s sections, charge transfer media or catalytic assemblies. As a result, t his subsection briefly overviews various types of excited state intera ction mechanism s occurring in multichromophoric architectures.

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38 1.4.1 Energy Transfer 1.4.1.1 Energy Transfer via Forster Mechanism Forster resonance energy transfer (FRET) 37,38 also referred to as coulombic energy exchange, is defined as a nonradiative transfer of an electronic excitation from a donor (D) to an acceptor (A) molecule (E quation 1 1 ) D* + A D + A* ( 1 1 ) As a result, t his process does not involve emission and re absorption of radiation but rather arises from dipole dipole interaction s between the electronic states of the donor and the acceptor. Additionally, this mech anism does not require a direct overlap of D* and A wavefunctions and the respective intermolecular collisions, thus allowing for relatively long distance interactions up to 100 The e ffective FRET distance is genera lly described as the Forster radius wh ich corresponds to the proximity of the D and A units at which energy transfer occurs with 50% efficiency Nonetheless, FRET exhibits strong distance (r) dependence, and the rate constant of the process is proportional to (1/r) 6 Additionally, the effecti veness of this process also shows direct correlation with the magnitude of the transition dipole interaction, which subsequently depends on the alignme nt and separation of the D and A dipole moments As a result, the FRET rate constant is the n proportional to both the distance and the dipole dipole coupling between the D and A chromophores i.e. k ~ E 2 ~ D A 2 D B 2 /r AB 6 where E is interaction energy, D A and D B dipoles of D and A molecules, respectively, and r AB is the distance between them. The four electron ic states to be considered when describing FRET are the electronic ground and excited states of the donor and acceptor. Generally, light absorption by the donor unit at the equilibrium energy gap is followed by rapid

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39 vibrational relaxation which dissipates the reorganization energy of the donor over ultrafast time scales leading to D* I f D* has a coherence resonant with the ground state electronic energy gap of the acceptor energy transfer occurs. This leads to the D* relaxation to the ground state in add ition to vibrational relaxation and fluorescence of A that is spectrally shifted from the donor fluorescence. In summary, as shown in Figure 1 11 A A gets excited by an amount energy equal to that lost by D* going to D, and this is referred to as the reson ance condition. Based on that, in order to occur, FRET then requires an overlap between the emission spectrum of D* and the absorption spectrum of A* (Figure 1 11 B ) Figure 1 11 Forster resonance energy transfer conditions. A ) Schematic illustration of relative donor and acceptor ground and excited state energies, as they relate to FRET resonance condition. B ) Schematic representation of integral overlap between normalized donor emission and acceptor absorption spectrum. Adap ted from www.mit.edu/~tokmakof/TDQMS/Notes/12.1.%20Forster.pdf FRET is generally associated with singlet states and does not result in triplet triplet energy transfer due to the violation of the Wigner spin conservation law. According ly Forster energy transfer in iTMC conjugated chromophore hybrids is hypothesized to produce 1 MLCT state that is then converted to 3 MLCT via intersystem crossing, as delineated in the literat ure. 58 60

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40 1.4.1.2 E nergy T ra nsfer via Dexter Mechanism Dexter energy transfer 37,38 is described a s process i n which two molecules or two parts of a molecule bilaterally exchange their electrons. Unlike in FRET, in the Dexter mechanism, physical overlap of the D and A wavefunctions is a necessity and collisions of the parti cipating unit s are required. As a result, the rate constant of Dexter energy transfer exponentially decays as the di stance between these two species increases and this process is though t to occur when the participat i ng moieties are less than ca. 5 10 apart As a result, Dexter rat e constant can be estimated from Equation 1 2 where J is the integral spectral overlap K is an experimental factor, R DA is the distance between D and A and L is the sum of van der Waals radi i. (1 2) It is noteworthy that, in thi s mechanism both singlet singlet and triplet triplet electron exc hange processes are spin allowed, as illustrated schematically in Figure 1 12 This triplet triplet energy transfer phenomenon is of particular importance in multichromophoric iTMC arrays, s uch as those based on pendant Ru(II) and Os(II) polypyridyl linked together by a polystyrene scaffold reported by Meyer et al. (Figure 1 13 ) In these arrays, exciton migration along the iTMC chromophores having long lived triplet states can occur via the Dexter mechanism allowing for an antennae effect in such assemblies. 61 It is important to note, however, that due to the singlet triplet state mixing in Ru(II) polypyridyl units, a small fraction of this exciton migration is also hypothesized to occur as FRET. A variation of this triplet triplet electron exchange process, termed triplet sensitization, can be employed to create triplet excited st ates in organic molecules,

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41 otherwise exhibiting slow intersystem crossing. 62 Although in phosphorescent host guest organic light emitting diodes this phenomenon is often associated with parasitic dec ay pathways; as delineated in this dissertation, it could potentially be used in a beneficial manner for photovoltaic applications. Figure 1 12 Schematic energy diagram illustrating singlet singlet and triplet triplet Dext er energy transfer. Adapted from http://chemwiki.ucdavis.edu/Theoretical_Chemistry/Fundamentals/Dexter_En ergy_Transfer A special case of Dexter energy transfer is triplet triplet annihilation. This process occurs when two molecules in their triplet states react photochemically to produce singlet states. If the energy gap between S 0 and T 1 of the molecules is equal or larger than that between T 1 and S 1 p roduction of one singlet excited state leading to fluorescence is of high probability. A combination of triplet sensitization and triplet triplet annihilations has been employed in low power upconversion systems. 63 Such systems

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42 could po tentially be applied in solar energy harvesting for upconversion of very low energy excitons to ones of high energy, as well as ultraviolet light emitting diodes, which are otherwise difficult to achieve due to the work functions of the metals employed as the anode and the cathode. Figure 1 13 Structure of a polystyrene based assembly containing Ru(II) and Os(II) polypyridyl chromophores Adapted from Dupray, L. M.; Devenney, M.; Striplin, D. R.; Meyer, T. J. J. Am. Chem. Soc 1997 119 10243 10244 61 A schematic representation of low power upconversion energy diagram in Ru(bpy) 3 and diphenylanthracene is given in Figure 1 14 This particular example illustrates how a Ru polypyridyl complex sensitizes the triplet state of diphenylanthracene, and upon collision of two anthracene molecules in their triplet excited states, one excited (and one ground) singlet excited s tate is produce d Accordingly, a solution of the two species can be excited by green light and produce blue emission, resulting in a negative stokes shift (anti stokes shift).

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43 Figure 1 14 Low power upconversion. Simplified J ablonski diagram illustrating low power upconversion process in solution of a Ru(II) polypyridyl complex and diphenylanthracene along with the corresponding photograph Adapted from Singh Rachford, T. N.; Castellano, F. N. Coord. Chem. Rev. 2010 254 2560 2573 63 1.4.2 Photoinduced Electron Transfer Unlike energy transfer, photoinduced charge transfer 64,65 (Equation 1 3 ) generally results in the formation of charged species rather than radiative decay processe s and leads to photoluminescence quenching. This process is shown in Equation 1 3. D* + A D + + A ( 1 3 ) Photoinduced charge separation can occur due to the excited state e lectron residing in an antibonding orbital (often LUMO) Accordingly such state is considered to be a good donor and easier to oxidize. Additionally, the excited state of a compound is also easier to reduce, a s now there is a vacancy in the HOMO orbital. As a result a molecule in the excited state can then undergo both oxidation and reduction process es depending on the electronic properties of the photoinduced charge separation partner

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44 Photoinduced charge separation is governed by Marcus theory. 64 According to this theory, a n intermolecular charge transfer process can be described using parabolic potential e nergy surfaces (Figure 1 15) These surfaces are similar to those employed to describe general chemi cal transformations. Figure 1 15 Schematic illustration of potential surface parabolas for photoinduced electron transfer reactions Adapted from http://www.public.asu.edu/~laserweb/woodbury/classes/chm341/lecture_set8/ The%20Marcus%20Theory%20of%20Electron%20Transfer.pdf In Figure 1 1 5 G 0 is the free energy change between the reactants on the left and the products on the right E is the activation energy and is the reorganization energy ( 0 ) ( 1 ) processes Accordingly, is a sum o f the energy required for the reactants to reach the same nuclear configuration as the products ( 1 ) and solvent reorganization energy ( 0 ) From mathematical equations describing parabolic fun c tions, as well as the Arrhenius equation, the activation energ y and the rate constant for photoinduced charge separation can be derived as E q uations 1 4 and 1 5 respectively In these equations, A is a pre exponential term R the universal gas constant and T temperature.

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45 (1 4) (1 5) As can be seen from Equation 1 5 the rate constant of photoinduced electron transfer increases as G 0 becomes more negative until it reaches the value that is equal to with an opposite sign At this point, the rate of the process is maximized However, once G 0 surpasses this value, the reaction rate starts to decrease again, and this regime is calle d Marcus inverted region. For intramolecula r electron transfer processes with electronic coupling constant H AB 200 cm 1 ( most assemblies described in this thesis) the rate constant is described by a function of both the thermodynamic driving force and t he electronic coupling between the initial and final states T hus E quation 1 5 can be rewritten as Equations 1 6 and 1 7 where is the sum of the hard sphere radii of the reactants and is a damping factor (1 6) (1 7) For such intermolecular processes, the driving force of the direct electron transfer ( G o ) can be determined from the simplified Rehm Weller equation (Equation 1 8) (1 8) In this equation, E 0 ( D/D + ) and E 0 ( A/A ) are redox potentials describing process es D + + e D and A + e A respectively, and E 00 is the energy of S 0 S 1 transition of

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46 a fluor o phore. The last term is columbic attraction energy experienced by the ion pair after the electron t ransfer reaction, where e is the d i electri c constant of the solvent, and d is t he distance between the charges, which is generally is assumed to be the same as same as the F o rster radius In the field of solar photoelectrochemical and fuel cells, photoindu ced electron transfer is important due to the formation of high energy redox intermediates and charge separation, slowing down back electron transfer processes at semiconductor interfa ces, as well as improving the efficiency of the catalytic assemblies. 1.4.3 De vices Based on Ionic Transition Metal Active Layers 1.4.3.1 Light Emitting Electrochemical Cells Transition metal complexes have found commercial applications as phosphors in highly efficient host guest OLEDs 66 However, these devices are typically associated with neutral complexes, as charged species generally result in exciton trapping an d deactivation pathways. 67 Meanwhile ionic transition metal complexes intrinsically satisfy the active layer requirements for light emitting electrochemical cells, as they are emiss ive, redox active and ionically conductive. 4 W hile the operating principles of OLEDs are based on electroluminescence (where mobile charg e carriers are i n jected directly into and bands and move as a result of the app lied field ) LEC performance is based on electrogenerated chemiluminescence in the presence of mobile ions 4 Upon application of a voltage higher than the energy gap of the emissive species, opposite charges begin (redox process) injecting and counter ions move to preserve the local charge neutrality. Electr ochemical p and n doping occur s in t he regions adjacent to the anode and cathode, respectively, as shown in Figure 1 1 6

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47 Figure 1 16 Schematic representation and operating pri n ciples of a light emitting electrochemical cell. Adapted from Dyer, A. Conjugated P olymer Electrochromic and Light Emitting Devices, Ph.D. Thesis, University of Florida, 2007 35 As the charges move away from the electrodes, a p i n junction is formed within the active layer, an d p and n type carriers recombine with the concomitant release of photons Uniquely, t he direction of the electrochemically induced p i n junction can be reversed simply by changing the polarity of the bias. Due to this possibility, as well as the stabili zation of the chromophore doped states by electrolyte counter ions, LEC operation is insensitive to the work function of the electrodes Based on this, air stable metals can be utilized in these devices Additionally, this also allows for simple device con stru ction with LECs being generally comprised of a single active layer material blend sandwiched between two electrodes. In LECs, p and n type doping processe s are simultaneous and balanced providing a basis for potential ly high electroluminescence quant um efficiency These devices are also associated with low operating voltages as they turn on at the bandgap voltage of the luminophore Ru(I I) tris(bipyridine) derivatives have been widely utilized as LEC active layers Whereas an external electrolyte is required in organic conjugated polymer active blends, Ru(II) polypyridyl complexes are inherently ionic and can be used in their neat

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48 form. Electrogenerated chemiluminescence mechanism 4 for Ru(II) tris(bipyridine) is given in Equations ( 1 9 ) ( 1 12 ) Ru(bpy) 3 2+ e 3 3+ (1 9) Ru(bpy) 3 2+ + e 3 + (1 10) Ru(bpy) 3 3+ + Ru(bpy) 3 + 3 *2+ + Ru(bpy) 3 2+ (1 11) Ru(bpy) 3 *2+ u(bpy) 3 2+ + h (~ 2.1 eV, 610 nm) (1 12) Orange to near infrared emission has been achieved in Ru(II) based devices with EQEs as high as 5.5%. 68 72 This application is also often associated with ionic iridium complexes due to more flexible color tu nability and efficiencies exceeding 10%. 5 1.4.3.2 Electrochromic D evices There has been littl e precedent for electrochromic display devices (ECDs) based on solid layers of iTMCs. This is due to the high solubility of monomeric complexes in liquid or gel elec trolytes often required for efficient functioning of ECDs. However, as this thesis describe s polymeric Ru(II) films that can be reversibly switched in a similar device, operating principles of ECDs are briefly discussed in this subsection. Electrochromic display devices have been generally associated with either inorganic metal oxide electroch romes or conjugated polymers. 8,9,73 Ind e pendent of the active layer materials, ECDs are classified into either absorptive/transmissive or absorptive/reflective cate gories. In both cases, however, ECD architectures are essentially similar having two substrate supported electrodes (often ITO), an electrolyte, an active electrochromic material layer and a counter electrod e material for charge balancing, as shown in Fig ure 1 1 7

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49 Figure 1 17 Schematic representation of an absorptive/transmissive electrochromic display device Adapted from Dyer, A. Conjugated Polymer Electrochromic and Light Emitting Devices, Ph.D. Thesis, University of Flor ida, 2007 35 As in the case of LECs, these devices operate based on an electrochemical mechanism necessitating reversible redox behavior of the active layer materials. In this case, however an entire active film is either oxidized or reduced allowing for a full color switch to occur. As a result, charge balancing occurs via electrolyte and counter polymer interactions. 1.4.3.3 Dye Sensitized Solar C ells Dye sensitized solar cells represent a n important class of hybrid elect rochemical photovoltaic devices as they can be constructed from relatively inexpensive materials that do not need to be highly purified. 74,75 Additionally, as such device s generally rely on a single layer of dye molecules chemically adsorbed on mesoporous semiconductor interface, the fabrication cost can be further reduced. A typical architecture as well as the operating principles of a DSSC d evice are demonstrated in Figure 1 1 8 I n a typical device architecture (Figure 1 18), electron transport, light absorption and hole transport functions are performed by diffe rent cell components. The light absorbing dye is anchored to a mesoporous semiconductor, such as TiO 2 SnO 2 or ZnO, that functions as a photoanode.

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50 Figure 1 18 Dye sensitized solar cells. A) Schematic representation of a liq uid based dye sensitized solar cell B) E nergy level diagram illustrating the operating principles of the device Reprinted with permission from Hardin, B. E.; Snaith, H. J.; McGehee, M. D. Nat. Photonics 2012 6 162 169. 75 Copyright 2012 Nature Publishing Group Once a photon is absorbed, the photoexcited electron is rapidly transferred from the chromophore to the conduction band of th e semiconductor. A redox couple, often iodide/triiodide tandem (I /I 3 ), then reduces the dye to the neutral state and transports the hole to the platinized FTO counter electrode. DSSC devices currently achieve highest power conversion efficiencies (> 12%) among alternatives to silicon based solar cells. Both o rganic donor acceptor and inorganic molecules have been employed as the sensitizers in such devices, with the

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51 the archetypical dye being cis bis(iso thiocyanato) bipyridyl di carboxylato) ruthenium(II) also referred to as N3. 1.4.3.4 Solar Fuel De vices While dye sensitized solar cells provide a basis for efficient light harvesting in real time applic ations, there are few technological developments related to solar energy storage. An attractive alternative for this application are solar fuel devices that would employ architectures similar to DSSCs yet incorporate catalytic assemblies capable of producing solar fuels, i.e. storing photonic energy in chemical bonds. 76 In solar fuel production using artificial photosynthesis, integration of visible light absorption with the sequential redox events that dri ve the coupled half reactions ( i.e. water oxidation to oxygen and either water/H + reduction to hydrogen or CO 2 reduction to CO, other oxygenates, or hydrocarbons ) is essential. While research emphasizing such solar fuel cells is still at the fundamental st age, the designed device prototype architecture (courtesy of the is given in Figure 1 1 9 This prototypical solar photoelectrochemical cell variant consists of mesoporous semiconductor interfaces functionalized with catalyst chromophore assemblies. Both CO 2 reduction and water oxidation catalysts can be employed simultaneously for charge balancing functions. As seen in Figure 1 19 once a photon is absorbed by the chromophore moiety, the electron is transferred to the semiconductor interface and the hole to the catalyst followed by water oxidation. The electron harvested by the anode is then transferred to the cathode and the respective assembly, where CO 2 reduction occurs. A water oxidation catalyst chromophore asse mbly prototype is also shown in Figure 1 19 76

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52 Figure 1 19 Schematic representation and operating principles of a solar fuel cell along with a prot otypical catalyst chromophore assem bly for water oxidation. Adapted from Ashford, D. L.; Stewart, D. J.; Glasson, C. R.; Binstead, R. A.; Harrison, D. P.; Norris, M. R.; Concepcion, J. J.; Fang, Z.; Templeton, J. L.; Meyer, T. J. Inorganic Chemistry 2012 51 6428 6430 76 1.5 Overview of this D issertation T his dissertation focuses on the design, synthesis, characterization, and structure property relationships of iTMC polymers with the m ultifunctionality required to develop new architectures of optoeletronic devices. Particular emphasis is place d on photophysics and electrochemistry fundamentals in transition metal chromophores and i TMC conjugated polymer assemblies and their relationship s to the rational synthetic design. C hapter 3 of this dissertation encompasses synthesis, as well as photophysical, electrochemical, and spectroelectrochemical characterization of acrylate containing Ru(II) polypyridyl complexes, capable of exhibiting dual electrochromism and electrochemiluminescence. The structure property relationships are established between detailed ligand design and the multifunctionality required for a successful

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53 application of these complexes in dual EC/EL devices, where multicolor e lectrochromism and electrogenerated chemiluminescence occur from a single active layer material pixel. Additionally, design principles of a dual EC/EL prototype are provided in Chapter 3 along with a general introduction to the field of display devices, ca pable of simultaneous operation in reflective and emissive modes. Chapter s 4 6 of this dissertation relate properties of individual iTMC units and chemistry approach. The resu lting chromophores combine hig h extinction coefficients of organic macromolecules with the long lived excited states of iTMC chromophores, allowing for exciton delocalization over long distances and an antenna effect. As these hybrid assemblies are intende d for solar energy harvesting and storage application s a particular emphasis is placed on controlling intramolecular ultrafast exciton and charge transfer processes. In C hapter 4 the concept of a hybrid organic conjugated polymer ionic transition metal complex light harvesting antenna is introduced with the emphasis that this area of research has previously focused on assemblies having insulating polymer backbones. As the simplest model systems, where the spectral characteristics of the assembly componen ts are aligned for singlet energy transfer, polyfluorene (PF) architectures with both high and low loadings of pendant Ru(II) polypyridyl complex are studied. Ultrafast spectroscopic, electrochemical and spectroelectrochemical techniques are employed to st udy the conjugated polymer backbone effect on the energy/charge migration fundamentals in these architectures as well as exciton migration along the polymer chain In addition to ultrafast energy transfer, ca. 10% of excited PF states are found to

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54 partici pate in high energy redox intermediate formation, i.e. Ru I (bpy) 3 Ru III (bpy) 3 and PF which may be exploitable in achieving redox separation or charge injection at semiconductor interfaces. With the PF and Ru(II) chromophore interactions described in d etail in Chapter 4, Chapter 5 of the dissertation focuses on probing exciton migration effects along the iTMC units in such assemblies. As a means to probe this effect, Stern Volmer amplified photoluminescence quenching experiments are employed. Additional ly, Ru(II) containing PF architectures with a small fraction of low energy Os(II) chromophores are described, allowing for quantification of the hopping timescale. Finally, a family of PF Ru assemblies containing various fractions of carboxylate functional ized Ru(II) units as both low energy and TiO 2 surface anchoring chromophores are studied and one of these hybrids is utilized in solar photoelectrochemical cells. Reported in Chapter 5 are Ru(II) containing poly(fluorene co thiophene) and poly(3 alkylth iophene) derivatives, where a bathochromic shift in the polymer backbone absorption is induced via introduction of various fractions of electron rich monomer units. Energy transfer and charge migration mechanism differences are studied in these systems via electrochemical, spectroelectrochemical and photophysical methods, revealing nearly quantitative and activationless charge separation in the Ru(II) polypyridyl poly(3 alkylthiophene) assembly These charge separated states in the thiophene based architect ures are found to be relatively long lived due to hole delocalization on the polymer backbones.

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55 CHAPTER 2 EXPERIMENTAL TECHNIQUES 2.1 Structural Characterization NMR spectra were measured on a Gemini 300 FT NMR, a VXR 300 FT NMR, or a Mercury 300 FT NMR. High resolu tion mass spectrometry was performed on a Bruker APEX II 4.7 T Fourier Transform Ion Cyclone Resonance mass spectrometer (Bruker Daltonics, Billerica, MA) or a a Finnigan LCQ Quadrupole Ion Trap (Thermo Finnigan, San Jose, CA). The FT IR spectra were obt ained with a Perkin Elmer Spectrum One FT IR spectrometer. Elemental analysis was performed on an Eager 200. Gel permeation chromatography (GPC) was performed using a Waters Associates GPCV2000 liquid chromatography system with its internal differential re fractive index detector (DRI) at 40 C, using two Waters Styragel HR i.d., 300 mm length) with HPLC grade THF as the mobile phase at a flow rate of 1.0 mL min 1. Injections were made at 0.05 0.07% w/v sample concentration usi injection volume. Retention times were calibrated against narrow molecular weight polystyrene standards (Polymer Laboratories; Amherst, MA). Elemental analyses were carried out an EA1108 CHNS O manufactured by Fisons Instruments 2.2 Materials an d Reagents dimethyl bipyridyl, 5,5 dimethyl bipyridyl, selenium dioxide, silver nitrate, potassium hydroxide, N,N' d icyclohexylcarbodiimide (DCC), N h ydroxysuccinimide (NHS), sodium azide, potassium carbonate, f luorene, 1,6 dibromohexane, 1,3 propanediol, triethylamine, tributylamine, acryloyl chloride, thionyl chloride, 1,8 Diazabicyclo[5.4.0]undec 7 ene 1 bromo octane A liquat 336, tetrabutylammonium bromide, 3 bromothiophene, 3

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56 octylthiophene, ammonium hexach loroosmate(IV), ruthenium(III) chloride, N bromosuccinimide, sodium ascorbate, 4 dimethyl aminopyridine (DMAP), copper(I) bromide (CuBr, 99.999 % ), copper(I) iodide (CuI, 99.999 % ), potassium acetate (KOAc), poly(methylmethacrylate) (PMMA), ethylenediaminete traacetic acid diammonium salt (ammonium EDTA) and N N N pentame thyldiethylenetriamine (PMDETA) were purchased from Sigma Aldrich. Ammonium hexafluorophosphate (NH 4 PF 6 ) and c is bis bipyridine)dichlororuthenium(II) dihydrate ( Ru(bpy) 2 Cl 2 2H 2 O) were purchased from Alfa Aesar. Tetrakis(triphenylphosphine)palladium and dichloro[1,1' bis(diphenylphosphino)ferrocene]palladium(II) dichloromethane adduct ( Pd(dppf)Cl 2 ) were purchased from STREM Chemicals, Inc. Diethylammonium diethyldithiocarbamate w as purchased from TCI America. All the chemicals were used as received unless otherwise indicated. Silica gel or alumina gel (reactivity grade I) were used for column chromatography. Dry solvents were obtained from a MBRAUN MB SPS dry solvent system or pur ified using standard methods. 77 Solvents or liquid reagents for the use in a glove box were also degassed using at least three freeze pump thaw cycles. High pressure liquid chromatography (HPLC) was performed on a Hitachi EZ chrome system, m particle size) column Preparative HPLC was carried out using a Lachrom U ltra 21.2 mm X 250 mm C18 (TMS endcapped, 10 m particle size) column. 2.3 Electrochemical Methods 2.3.1 Cyclic Voltammetry and Differential Pulse Voltammetry Cyclic voltammetry and differential pulse voltammetry measurements were performed using a single compartment three electrode cell with a platinum wire or a platinum flag as the counter electrode, a sil ver wire quasi reference or non aqueous

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57 Ag/Ag + reference electrode (calibrated versus ferrocene/ferrocenium (Fc/Fc + ) standard redox couple using a 5 mM solution of ferrocene in 0.1 M tetrabutylammonium hexafluorophosphate (TBAPF 6 )/acetonitrile), and a plat inum or gold button (0.02 cm 2 ) as the working electrode. Electrochemical studies were carried out in 0.1 M TBAPF 6 acetonitrile, dichloromethane, or tetrahydrofuran electrolyte solutions with the analyte concentration of ca. 1 4 mM. An EG&G Princeton Applie d Research model 273A potentiostat/galvanostat was operated under the control of Corrware II software from Scribner and Associates. Electrochemical measurements were performed in an argon filled glove box (Vacuum Atmospheres). 2.3.2 Spectroelectrochemistry Spec troelectrochemical studies of the analyte films, spin coated or drop cast on indium tin oxide (ITO) coated glass slide s (7 50 0.7 mm, sheet resistance, R s = 2 purchased from Delta Technologies, Ltd ) were performed on a StellarNet Inc. EPP20 00 UV Vis spectrophotometer in 1 cm quartz cuvette cells using similar conditions to those used for the electrochemical measurements. The experiments were performed in 0.1 M TBAPF 6 tetrahydrofuran or acetonitrile electrolyte solutions using an ITO/glass sl ide as the working electrode, a silver wire pseudoreference electrode (calibrated vs. Fc/Fc + standard redox couple), and a platinum wire as the counter electrode. The absorption spectra obtained were smoothed using OriginPro 7.5 software Adjacent Averaging function. 2.3.3 In Situ Spectroelectrochemistry Sub second spectroelectrochemical data acquisition was performed on an Ocean Optics USB2000+ spectrophotometer detector and associated Ocean Optics DH 2000 BAL fiber optic light source. The detector was placed, al ong with cuvette holders, in an

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58 enclosure designed to eliminate extraneous light. Spectral data was collected upon linear sweep voltammetry scans of the thin analyte films under similar conditions to those exploited in the regular spectroelectrochemistry e xperiments. All samples were prepared in an argon filled drybox and the resulting cuvettes were sealed with parafilm and teflon tape before exposure to ambient atmosphere. 2.4 Film Colorimetry Colorimetric measurements of neutral films were performed using a M inolta CS100 colorimeter in transmission mode with a GraphicLite LiteGuard II standard D50 light source. The light source and the sample to be measured were placed in a color viewing booth. The interior of the light booth was coated with a standard gray ne utral 8 (GTI Graphic Technology, Inc.) matte latex enamel (equivalent to Munsell N8) to allow for accurate assessment of color of the sample during measurement s For oxidized or reduced films, chromaticity coordinates were calculated from the respective ab sorption spectra using methods standardized by CIE. 78,79 2.5 Photophysical Methods Photophysical measurements of the compounds described in this dissertation were carried out lar gely in collaboration with John M. research group at the University of North Carolina at Chapel Hill. Contributions of Li Wang, Erik Grumstrup, Ryan Vary and Ralph House are gratefully acknowledged. 2.5.1 Steady State UV Vis Absorption UV Visible sp ectra were recorded on an HP 8543 Diode Array Spectrophotometer interfaced to a computer. UV Visible spectra were recorded on all samples before and after excited state measurements to ensure that samples did not undergo photodecomposition.

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59 For dual electr ochromic/electroluminescent chromophore solutions, UV VIS measurements were carried out on a Perkin Elmer Lambda 25 dual beam absorption spectrophotometer using 1 cm quartz cells. 2.5.2 Transient Absorption T ransient absorption measurements were conducted by u sing a pump probe technique based on a Ti : Sapphire chirped pulse amplification (CPA) laser system (Clark MXR CPA 2001). The 3 88 nm pump pulse was generated by doubling the fundamental output at 775 nm. The 470 nm pump pulse was produced by the sum frequenc y generation (SFG) from the output of Optical Parametric Amplifier (OPA) at 1200 nm and 775 nm. The femtosecond probe pulse wa s formed by continuum generation in CaF 2 This beam wa s directed through a computer controlled optical delay stage, passed through the sample, and coupled into a spectrometer to spectrally disperse the probe onto a high speed 1024 pixel CMOS detector. Spectra we re collected on a shot by shot (1 kHz) basis over the range of 300 to 900 nm resulting in a high signal to noise ratio and a n instrument sensitivity of up to 0.1 mOD. The kinetic wi ndow ranged from 250 fs approximately 1.5 ns. The probe pulse for sub nanosecond measurements was generated by continuum generation from a photonic crystal fiber and detected by a fiber optic coup led multichannel spectrometer with a CMOS sensor. The kinetic win dow range d from 500 ps he time resolution of the instrument wa s around 500 ps dictated by the width of the probe pulse and the timing electronics. 2.5.3 Steady State Photoluminescenc e Photoluminescence measurements were carried out on an ISA SPEX Triax 180 spectrograph coupled to a Spectrum 1 liquid nitrogen cooled silicon charge coupled

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60 device detector at room temperature in degassed acetonitrile solutions. 1 cm quartz cells were us ed for the measurements. Additionally e mission spectra were measured on Photon Technology International (PTI 4SE NIR ) Quantamaster spectrofluor i meter equipped with a continuous xenon arc lamp as the excitation source. The emitting light was collected at 90 to the excitation beam and detected by a Multi mode 814 photomultiplier tube (PMT) in photon counting mode (digital) 2.5.4 Photoluminescence Quantum Yield Measurements Solutions of the analyzed compounds were prepared with the optical density less than 0.1 and degassed for at least 40 minutes. Standards with known photoluminescence quantum yields were employed as actinometers. In a large number of cases, r uthenium tris( bipyridine ) hexafluorophosphate solution, having a quantum yield of 0.062 was used as a st andard. The optical densities of the standard and the samples were matched within 0.002. The following equation was used to calculate the phosphorescence quantum yield: ( 2 1) A is the absorbance at the excitation wavelength, F is the area under the emission curve and is the refractive index of the solvent used. Subscripts s and x refer to the standard and the sample, respectively. 2.5.5 Time Resolved Photoluminescence The lifetimes of excited state in the picosecond scale were measured by a streak camera setup. The excita tion pulse wa s generated from a mode locked Ti:Sapphire laser (Spectra Physics, Tsunami) pumped by a 13.5 W frequency doubled continuous wave diode laser (Spectra Physics Millenia). This system generate s an 80 fs pulse

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61 duration at an 80 MHz repetition rate tunable between 720 and 850 nm with a maximum power output of approximately 3 W. The laser output was sent through a pulse picker and frequency doubler to obtain 370 450 nm pulses at repetition rate at least 5 times the natural lifetime of the sample. F luorescence was collected 90 to the excitation beam and focused into the entrance slit of a C11119 01 spectrograph, which was coupled to a Hamamatsu C10627 streak camera. The instrument response function was ~ 1 5 ps. The lifetimes of the excited state in t i.e. Ru polypyridyl complexes) were measured by using the time correlated single photon counting (TCSPC) technique on the FLS920 system with the Edinburgh EPL 445 nm picosecond pulsed diode laser (74.4 ps pulse width) as the excitation s ource, and R2658P photomultiplier tube as the detector. The Instrument Response Function (IRF) of the photomultipliers, measured with the short pulse laser excitation is 200 ps in the visible range. 2.6 Device Fabrication and Characterization 2.6.1 Light Emitting El ectrochemical Cells Light emitting electrochemical cells described in this dissertation were fabricated and characterized by Justin Oberst. His efforts and input are gratefully acknowledged. LECs were fabricated on pre patterned ITO coated glass substrates with a sheet resistance of ~ The ITO substrates were cleaned sequentially with a sodium dodecyl sulfate solution, acetone and isopropanol followed by an oxygen plasma treatment. The active layer solutions were prepared and processed in an MBraun g lovebox with < 0.1 ppm of oxygen and water using a general procedure similar to that described in the literature. 68 Master acetonitrile solutions of a Ru(II) polypyridyl complex

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62 (40 mg/mL) complex and PMMA (25 mg/mL) were prepared and allowed to fully dissolve with magnetic stirring. The active layer solution was then prepared by mixing the two master solutions in 3:1 = Ru(II):PMMA volume ratio, filtered through a 0.45 m syring e filter, and spincoated at 1000 rpm spinrate. The obtained films were kept under vacuum at 80 C for 1 hour to remove any trace solvent. For cross linked devices, TEGDMA was used instead of PMMA in the active layer solution while retaining the same propor tions of the components, and 0.5 wt% of AIBN was also added. Each spincoated layer was thermally cross linked at 150C overnight and rinsed to remove any non cross linked components. Au cathodes were then deposited to a thickness of 100 nm for all devices in a thermal evaporator under a vacuum of 10 6 Torr. As a result, each 25 x 25 mm substrate featured 8 independently addressable pixels with an area of 0.071 cm 2 each. The devices were sealed in a holder prior to being removed from an inert atmosphere. An Ocean Optics HR4000 spectrometer and a Triax180 CCD spectrometer were used to collect electroluminescence spectra. As a source, a Keithley programmable smu was used. A UDT S471 optometer and Minolta CS 100 chroma meter were used to collect irradiance, l uminance and CIE values. Each pixel was initially preconditioned with an applied bias that was previously determined. The pixels were then sequentially stepped from 0.5 V to a bias that demonstrated decreased pixel intensity; the circuit returned to open between each step. The pixel was held at each bias until a stable power output had been achieved (1 5 mins) prior to returning to open circuit and stepping to the next bias. Power and current data were recorded as a function of time. Luminance data w er e

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63 output had been recorded. 2.6.2 Dual E lectrochromic/ E lectroluminescent D isplay D evices Pre patterned ITO coated glass substrates with a s heet resistance of ~ 3 were cleaned as described previously in the LEC fabrication section. The active layer solutions were prepared by dissolving 40.20 mg of a Ru(II) complex, 5.63 mg of tetraethylene glycol dimethacrylate ( TEGDMA ) 2.81 mg of trimethylolpropane triacryla te ( TMPTA ) and 0.80 mg of PMMA in 330 L of acetonitrile, followed by filtering through a 0.45 L syringe filter and spincoating onto ITO/glass substrates at 950 rpm using a Laurell Technologies Corporation WS 400BZ 6NPP/LITE spincoater. The active layers were then cross linked at 185 o C for 15 h in a VWR 1415M vacuum oven refilled with nitrogen. The substrates were allowed to cool to room temperature, rinsed with acetonitrile to remove any non cross linked components, and transferred to an MBraun glovebox with < 0.1 ppm of oxygen and water. Patterned gold cathodes were then deposited using the same procedure as for the LEC fabrication. At this point, each 25 x 25 mm substrate featured four individually addressable pixels where the patterned gold electrodes consisted of two 1 x 5 mm digits separated by a 1 mm spacing. Counter electrodes to trigger the electrochromic response were constructed using ITO coated glass sheets cleaned as described previously. The charge balancing polymer layer was spincoated at 11 00 rpm using a solution containing 20 mg of an N alkyl substituted poly(3,4 propylenedioxypyrrole) derivative and 0.8 mg of TBAPF 6 in 1 m L of chloroform. A well for gel electro lyte was made on each substrate using 3M double sided tape. The prepared units were then transferred to the glovebox, where gel electrolyte was added to the wells and the ITO/Ru(II)/gold electrodes were placed on

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64 top. The obtained dual EC/EL devices were then removed from an inert atmosphere and immediately sealed with silicone rubbe r. Typical procedure to prepare gel electrolyte involved dissolving 3.87 g of TBAPF 6 in 20 m L of propylene carbonate followed by the addition of PMMA (1.79 g) and stirring the resulting mixture at 100 o C overnight or until the polymer dissolved. Triax180 C CD spectrometer was used to collect electroluminescence spectra, while OL 770 LED Multi Channel Spectroradiometer System was employed for absorption and CIE L*a*b* measurements. As a source, a Keithley programmable smu was used. Photographs of the dually performing pixels were taken either in a glovebox or a light booth using a FujiFilm FinePix S7000 camera at a shutter speed of 1/160 s, f stop of f/4, aperture value of f/4.0, ISO of 200, and focal length of 18 mm. The photograph file type was JPEG, and th e files were cropped to only the polymer film pixel to exclude extraneous background using Photoshop. No additional alterations to the files were performed. 2.6.3 Solar Photoelectrochemical Cells Solar Photo electrochemical cells described in this dissertation we re fabricated and characterized by Gyu Leem His efforts and input are gratefully acknowledged Fluorin e doped tin o xide ( FTO ) coated glass substrates (10 cm 2 Hartford glass ) we re cleaned by sonication in pH = 13 sodium dodecy l sulfate deionized water solution, followed by sonications in isopropyl alcohol and in acetone (20 minutes each). FTO coated glass slides were then refluxed in 40 mM TiCl 4 isopropy l alcohol solution (prepared from 90 mM TiCl 4 in 20% HCl solution, Aldrich) for 30 min and calcined at 420

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65 o C for 30 min. Electrodes were then taped conductive side up to a solid substrate and TiO 2 paste featuring 18 nm diameter particles (DSL 18NR T, Dyes ol) was spread on the slide by a doctor blade ( a frame that moves along a stationary casting surface ) After each film was dried, a scattering titanium layer was then calcined at 420 o C for 30 min (heating rate = 1 o C/min and cooling rate = 1 o C/min ) The resulting anode was then ution for 24 96 h to allow for dye adsorption. Pt counter electrode was prepared by d rill ing two holes into opposite sides of the anticipated active area of a FTO coated glass subs trate by a dremmel with diamond bit and 0.01 M H 2 PtCl 6 isopropyl alc ohol solution was sp i n cast on FTO substrates followed by sintering at 450 C for 30 min. Afterward, a Surlyn (25 m, Solaronix) film, used as a spacer, was sandwiched between a TiO 2 photo anode and a Pt counter electrode and annealed using a commercially available iron. Finally, the gap between the electrodes was filled through the holes in Pt electrode with a n electrolyte solution (0.5 M 1 methyl 3 propyl imidazolium iodide (MPII, Aldrich) and 0.05 M iodine solution (Aldrich) in 3 methoxypropionitrile (Aldrich)) 2400 source meter under AM1.5 (100 mW/cm 2 ) solar simulator. For IPCE measurements, the cells were illuminated by monochromatic light from an Oriel Cornerstone spectrometer, and the current response under short circuit conditions was recorded at 10 nm intervals using a Keithley 2400 source meter. The light intensity at each wavelength was calibrated with an energy meter (S350, UDT Instruments).

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66 CHAPTER 3 CROSS LINKABLE RU(II) TRIS(BIPYRI DINE) BASED IONIC TRANSITION METAL COMPLEXES FOR DUAL ELECTROCHROMIC AND ELECTROLUMINESCENT APPLICATIONS 3.1 Introduct ory Remarks Display devices based on organic electroactive small mol e cules and polymers have become an emerging technology due to their high c ontrast, low power consumption, low weight, and wide viewing angle. Additionally, there exists the possibility for display devices that exhibit mechanical flexibility, inherent processability, and optoelectronic property fine tuning via r a tional structure modifications of active layer materials. 8,80,81 While organic light em itting diode (OLED) displays 14,81 83 have been su c cessfully commercialized, electrochromic display devices (ECDs) 8,84 86 are finding applications in the areas of e paper, smart windows, and large effe ctive area information panels. Although scientific efforts remain strong in both fields, such technologies possess some intrinsic limitations. Namely, ECDs rely on ex te r nal light sources and can generally be viewed only when there is sufficient ambient light available. To overcome this problem, a front or back light is provided for operation of such displays in dark conditions, however, this often results in deteriorat ed i m age quality and increased power consumption. 87 Conver sely, OLEDs generally display limited visibility in bright ambient lighting situations, i.e. as the intensity of the sunlight or an ambient light source becomes stronger than that of the light emitted by the device, the displayed image bleaches. Chapter 3 has been published as Puodziukynaite, E.; Oberst, J. L.; Dyer, A. L.; Reynolds, J. R. J Am. Chem. Soc. 2012 134 968 978 This material is reprinted/adapted with permission. Copyright 2012 American Chemical Society.

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67 As a resu lt, initial attempts are being made in deve l opment of dual electrochromic/electroluminescent (EC/EL) display d e vices capable of simultaneous operation in reflective and emi s sive modes. Such systems would be emissive in low light environments and change the ir colored states when suff i cient light is available for a reflective mode, allowing for optimal visibility in any ambient lighting situation. Some dual EC/EL prototypes reported to date have generally been comprised of stacked ECD and OLED or light emitti ng electrochemical cell (LEC) d e vices, 3,4,88 as well as several layers of different active materials. 89 92 However, as a result of their complex design, poor performance and low efficiencies have been demonstrated by such systems. Recently, dual EC/EL display devices with single active layer architectures have be en de veloped in our group (Figure 3 1) 87,93 Figure 3 1 Dual electrochromic/electroluminescent (EC/EL) devices. Sch ematic representation of A) type I and B) type II single layer dual EC/EL devices along with C) the photographs of a type I device pixel operating in the e missive and reflective modes. A dapted from Dyer, A. Conjugated Polymer Electrochromic and Light Emitting Devices, Ph.D. Thesis, University of Florida, 2007 35

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68 As shown in Figure 3 1, these device s are designed to merg e together the operating principles of ECD and LEC technologies utilizing a single dual active material Each device is comprised of three electrodes or two resulting electrode pairs, triggering either LEC like electrogenerated chemil uminescence or EC response, depending on which electrode pair is biased. The fundamental difference between the two device constructions lies in the LEC component being either sandwiched (type I, Figure 2 1 A ) or planar (type II, Figure 2 1 B ), thus offering distinctive advantages for different applications. 35 Although the innovative construction of single layer dual EC/EL displays could offer significant advantages over the existing systems, thes e EC/EL display devices require active layer materials that demonstrate both electrochromic and electrochemiluminescent (ECL) behavior, possess accessible oxidized and reduced states, and preferably contain motifs having ionic conductivity. While a well ba lanced set of requirements for the active materials is difficult to access in purely organic compounds, some ionic transition metal c o ordination complexes (iTMCs) could potentially demonstrate the required properties. Ruthenium(II) tris(bipyridine) (Ru(bpy ) 3 ) based complexes are of particular significance due to their ability to reversibly oxidize and reduce, exhibit light emission from both singlet and triplet states, display electrochromism, as well as possess inherent ionic conductivity 15,45,47,48,54 57,88,94 103 In addition, photophysical and electrochem i cal properties of such materials can be significantly altered via rational design of the bipyridine ligands. A cumul a tive effect of the withdraw ing ligand substituents has been previously employed to control the energies of various photoe x cited states of such complexes (i.e.

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69 triplet metal to ligand charge transfer excited state ( 3 MLCT), triplet metal ce n tered excited state, etc.) thus altering the ir internal conversion barriers, photolumine s cence quantum yields and emission maxima. 51,99,104 In parallel, Elliot et al. have reported that when electron withdrawing su b stit bipyridine ligands, distinct polyelectrochromic transitions can be observed for the resulting ruthenium polypyridyl co m plexes. 48,55,57 While solid state electrogenerated chemiluminescence and electrochromic behaviors have been studied separately for iTMCs, to the best of our knowledge, there have been scarce research efforts in combining these properties. Wang et al. 105 have reported on a series of polymers containing dinuclear Ru(II) complexes as pendants that exhibit electrochromism and electrogenerated che miluminescence in the near infrared r e gion; however, the spectroelectrochemical properties of the compounds were only examined in solution based optically transparent thin layer cells, and no possibility of obtaining ele c trochromic films insoluble in liqui d electrolytes was discussed. In addition, the emission was of low efficiency. There exist a few liter a ture precedents for organic polymers and oligomers having dual electrochromism and photo or electroluminescence with e x amples being of those that conta in 2 methoxy 5 (2' ethylhexyloxy) p phenylene vinylene 3,106,107 carbazolyl 108 (thienylene) [1,6 dithienylhexa 1,3,5 trienylene] 109 or fluorene carbazole 2,5 bis(2 thienyl) 1H pyrrole 110 repeat units, as well as those that possess donor acceptor type architectures 111 However, while electroluminescence (where mobile charge carriers are i n jected directly into and bands and move as a result of the applied field, and no doping occurs) was demonstrated in most of the reported cases, there was no evidence of

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70 electrogenerated electroluminescence in the presence of mobile ions (the opera t ing principle of an LEC) ; 4 a necessity for a single mat e rial that is to be employed as both a light emitter and an electrochrome in the same device. Moreover, su ch highly non polar structures are known to often exhibit strong phase separation when blended with polar, ion transporting materials such as polyet h ylene oxide, which is essential to achieve adequate ionic co n ductivity in the corresponding electrochemical devices. Such phase separation results in strong aggregation and electrolum i nescence quenching of the light emitting polymers, as well as inferior lifetimes of the respective devices. 112 Meanwhile, as MEH PPV has been extensively applied in light emitting ele c trochemical cells, it suffers from poor redox reversibility and, as a result, poor el ectrochromic properties including the lack of the ability to access a highly transmissive, near colorless state needed for practical applic a tions. As functional Ru(II) complexes previously reported in the li t erature for electrochromism and electrochemilumi nescence generally differ in structure and are optimized only for a single application, the purpose of this study is understand the rel a tionship between the detailed ligand design and combined EC/EL behavior of the resulting compounds. Thus, described in C hapter 3 is a new family of ruthenium(II) tris(bipyridine) coordination complexes, combining intrinsic electrochromism, electrochemiluminescence, ionic conductivity, and reversible redox beha v ior. Moreover, the EC and ECL properties of the iTMCs are demons trated to be truly paired, as they are applied in a dual EC/EL device pr o totype, where light emission and mu lti color electrochromism occur from a single Ru(II) based active layer within a single pixel.

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71 3.2 Synthesis and Characterization of Acrylate Containing Ru(II) Tris(bipyridine) C omplexes for Dual Electrochromic and Electroluminescent Applications 3.2.1 D esign and Synthesis In this study, chromophores based on derivatized Ru(II) tris(bipyridine) were chosen as potential dual EC/EL chromophores. T o study the stru cture property relationships, as well as to i n duce color tuning of the emissive and reflective states of the complexes, the iTMCs were functionalized with both ele c tron withdrawing and electron donating substituents at various positions of the bipyridine l igand s Two reactive acrylate moieties were introduced into the structures allowing for insol u ble film formation upon thermal cross linking and for the resultant films to be utilized in the presence of presence of liquid electrolytes or gel electrolytes wi thout risk of dissolution upon application in dual EC/EL devices. This di a crylate approach was anticipated and later shown to be synthetically robust giving mater i als with a long shelf life when compared to the previously r eported hexaacrylate derivatives. 55,99 Ru(bpy) 3 based diesters 5a and 5b were synthesized via similar multi step routes, as depicted in Schemes 3 1 and 3 2 Compounds 1a and 1b were obtained by dimethyl dimethyl b ipyridine, correspondingly, with potassium dichromate in sulfuric acid. Compounds 4a and 4b were then synthesized by employing minimal purification multistep route s modified from that previously described in the literature. 55,99 Briefly, diaci ds 1a and 1b were refluxed in thionyl chloride for 24 h to give diacid chlorides 2a and 2b which were immed i ately converted to their ester derivatives by employing addition elimination reaction with 1,3 propanediol in the presence of triethylamine. The r esulting products 3a and 3b were then reacted with acryloyl chloride

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72 to give compounds 4a and 4b in 56 % and 52 % yields, correspondingly. Compound 5a was then synthesized by employing well established complexation with Ru(bpy) 2 Cl 2 2H 2 O and ion metathesis pr ocedures (Scheme 3 1). Complex 5b (Scheme 3 2), however, could not be obtained using the same protocol as for 5a due to the positions with the alcoholic solvents, i.e. ethylene glycol, methanol a nd ethanol. A sim i lar observation has been reported by Grabulosa et al. 113 In addition, further evidence, although not very detailed, for such side reactions can be found in the li terature. 114 The observed transesterification reactions could be partially inhibited by using sterically hindered secondary alcohols as solvents; however, a large decrease in the rate of the complexation rea c tion was also observed. Thus, the desired product 5b could only be efficiently synthesized by the complexation reaction of 4b and the activated ruthenium complex Ru(bpy) 2 (acetone) 2 (OTf) 2 115,116 in N methylpyrrolidone (Scheme 3 2). It is noteworthy, that the use of butylated hydroxytoluene (BHT) as a free radical scavenger resulted in significantly increased yields of the complexation rea ctions via inhibition of acrylate polymerizations. Scheme 3 1 Synthetic route to compound 5a

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73 Scheme 3 2 Synthetic route to compound 5b Compounds 9a and 9b having alkyl ester positions, respectively, were synthesized according to Scheme s 3 3 and 3 4 Starting materials 6a and 6b were obtained by esterification reactions from the corresponding diacids and ethanol in the presence of sulfuric acid as a catalyst. The esters synthesized were later converted to dialcohols 7a and 7b using sodium borohydride, reacted with acryloyl chloride and used in the complexation reactions with Ru(bpy) 2 Cl 2 2H 2 O t o give target molecules 9a and 9b Scheme 3 3 Synthetic route to compound 9a

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74 Scheme 3 4 Synthetic route to compound 9b 3.2.2 Elect rochemical Properties The electrochemical properties of complexes 5a, 5b, 9a and 9b were studied in 0.1 M tetrabutylammonium hexafluorophosphate (TBAPF 6 ) acetonitrile solutions using platinum button, platinum flag, and silver wire (calibrated versus the fe rrocene/ferrocenium standard redox couple) as working, counter and reference electrodes, respectively. The cyclic voltammograms and the corresponding half wave redox potentials for compounds 5a, 5b and 9a are given in Figure 3 2 It has been well establis hed that the electrochemical behavior of Ru(II) polypyridyl complexes is usually observed as a metal centered oxidation and a series of ligand centered reductions. 45 As a result, reversible oxidations were characteristic of all the ruthenium(II) complexes reported with the corresponding E 1/2 values only somewhat cathodically shifted for compounds 9a and 9b with respect to those of their diester analogue s 5a and 5b due to the electron donating character of the alkylester substituents on the bipyridine ligands. Conversely, significantly pronounced substituent effects upon reduction of the studied complexes were evident. Complexes 5a and 5b having electron withdrawing ester moieties, were verified to possess four reduction waves that were anodic with respect to those of 9a and 9b Stabilization of anion radicals was particularly evident in

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75 the case 5b as seen from the well defined reduction peaks with exce llent reversibility, indicating a significant extent of LUMO present on the carboxyl functionalities of the bipyridine ligand. 48 Figure 3 2 Electrochemical data. Cyclic voltammograms of compounds A) 5a B) 5b C) 9a and D) 9b in 0.1 M TBAPF 6 acetonitrile solutions at 100 mV/s scan rate. Platinum button, platinum flag and silver w ire (cal i brated versus the ferrocene/ferrocenium standard redox couple) were used as working, counter and reference electrodes, correspondin g ly. A dapted with permission from Puodziukynaite, E.; Oberst, J. L.; Dyer, A. L.; Reynolds, J. R. J. Am. Chem. Soc. 2012 134 968 978 117 Copyright 2012 American Chemical Society Moreover, processes in ruthenium polypyridyl complexes (i.e., each additional electron is stabilized on a specific ligand) 45 for 5b even remote reduction waves occurred at potentials ca. 100 mV more positive than those for 5a demonstrating some delocalized character.

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76 Compounds 9a and 9b possessed one reversible reduction band, whereas other si milar transitions were significantly destabilized. In addition, with such dialkylester substituted bipyridine ligands being more difficult to reduce, preferential electrochemical polymerization of the acrylate moieties was observed for the complexes upon c ycling ( Figure 3 3 ). 118 In the cyclic voltammograms of 9a and 9b upon sequential reduction scans (Figure 3 3), an increase in current density was evident, indicating deposition of the resulting polymers on the wo rking electrode surface. Figure 3 3 Electrochemical data indicating polymerization of 9a and 9b Cyclic voltammograms of compounds 9a and 9b in 0.1 M TBAPF 6 acetonitrile solutions at 100 mV/s scanrate showing reductive polym erization of their acrylate moieties. Platinum button, platinum flag and silver wire (calibrated versus the Fc/Fc + standard redox couple) were used as working, counter and refere nce electrodes, correspondingly. Adapted with permission from Puodziukynaite, E.; Oberst, J. L.; Dyer, A. L.; Reynolds, J. R. J. Am. Chem. Soc. 2012 134 968 978 117 Copyright 2012 American Chemical Society 3.2.3 Spectroelectrochemistry In order to study the spectroelectrochemical properties of the compounds synthesized, ruthenium complexes 5a and 5b were mixed with trimethylolpropane triacrylate (TMPTA) and t etraethylenegl y col dimethacrylate (TEGDMA) as auxiliary cross linking agents and cast on ITO/glass transparent electrodes by spin coating

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77 followed by thermal crosslinking to yield insoluble polymer films. To demonstrate the ability to introduce additional co l ored states and the possibility for designed color tuning, the copolymer of 5a and 5b in 1:1 molar ratio ( 5a co 5b ) was also prepared. To overcome poor electrode wetting effects and a t tain uniform coatings with glassy morphology, 5 wt% of PMMA was used in the case of 9a and 9b in addition to the auxiliary crosslinking agents. All insoluble films obtained demonstrated electroactive character with polyelectrochromic transitions as determined by spectroelectrochemical and colorimetric studies. Spectroelectr ochemistry data for the polymeric films of co m plexes 5a 5b, their copolymer in 1:1 molar ratio ( 5a co 5b ), 9a and 9b at all the stable formal redox states were assessed and are given in Figure 3 4 (spectroelectrochemistry data for 9b is essentially identi cal to that for 9a ) For all the complexes, including the blend film, the as cast 2+ oxidation state exhibited an absorption centered around 450 nm with each differing in the intensity and breadth of that absorption, resulting in various hues of yellow, o range or tan for each co m plex. Once oxidized to the 3+ oxidation state, all the studied polymer films demonstrated bleaching of MLCT bands and a subsequent change from colored to transmissive states. Ho w ever, upon reduction of the 2+ state, spectral trend differences for each of the complexes became significantly pronounced. Poly 5a demonstrated only a small increase in absorption inte n sity as well as a 10 nm red shift for max at the 1+ oxidation state resulting in a dark red orange color. Poly 5b exhibited an add i tional absorption band with the maximum at abs = 675 nm in addition to substantially pronounced absorption increase at each reduced state, resulting in correspo nding dark

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78 blue green and subsequent dark orange colors for the 1+ and 0 oxidation states, respectively. Figure 3 4 Spectroelectrochemical data. Spectroelectrochemi cal data and the corresponding photographs of the polymeric films of A) 5a B) 5b C) 5a and 5b blend in 1:1 molar ratio and D) 9a at all the unambiguously stable redox states in 0.1 M TBAPF 6 acetonitrile solutions. ITO/glass, platinum flag and silver wire (calibrated versus the ferrocene/ferrocenium standard red ox couple) were used as working, counter and reference electrodes, co r respondingly. Reprinted with permission from Puodziukynaite, E.; Oberst, J. L.; Dyer, A. L.; Reynolds, J. R. J. Am. Chem. Soc. 2012 134 968 978 117 Copyright 2012 American Chemical Society

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79 The cumulative spectroelectr o chemical behavior of the complexes 5a an d 5b was characteristic of their copolymer (Figure 3 4 C ), resulting in switching b e tween intermediate colored states. It is noteworthy that while additional reduced states could be accessed for most of the studied co m pounds, as is show n in the cyclic volt ammograms in Figure 3 2 the reversibility of such redox transitions was li m ited by either stability of the solvent window, formation of mixed valence states upon cycling, or dissolution of the pol y meric films. For instance, the 1+ oxidation state for poly 9a did not prove to be spectroelectrochemically beneficial, as the cross linked film dissolved upon repeated switching between the 2+ and the 1+ redox states. 3.2.4 Colorimetry Colorimetry studies were carried out on the electrochromic polymer networks obtained allowing for effective quantific a tion of their color as it is perceived by the human eye. The 1976 CIE LAB (or L*a*b*) color space (Figure 3 5) has been chosen as a standard method of color representation, where the L* value corresponds to the lightness of the material, a* indicates red green balance, and b* designates yellow blue balance of the substance. Additionally, the terms of hue, saturation, and l u minosity are used in color specification. Hue is generally described by the dominant absorption wave length, saturation refers to the dominance of hue in the color and increases towards the edges of the a*b* color wheel, while luminosity repr e sents the amount of white in the color and is related to L*. In this study, L*a*b* chromaticity coordinates were calculated from the absorbance spectra of the polymer films at all their studied redox states using methods standardized by CIE. 78,79 In an effort to verify the accuracy of the chosen technique, color coordinates of the polymer networks at their as prepared 2+ redox states were also measured using

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80 a Minolta CS 100 colorimeter (transmission mea s urement method) 119 and were found to be in good agreement with those calculated. L*a*b* chromaticity coordinates for compounds 5a 5b 5a co 5b 9a and 9b at all their studied r e dox states are su mmarized in Tables 3 1 and 3 2. Figure 3 5 Schematic illustration of CIE 1976 L* a*b* color space ( http://www.thyon.com/blog/gamut lets get techni colour ) Table 3 1 CIE 1976 L*a*b* values a for the thermally cross linked films of compounds 5a 5b 9a and 9b at various redox states Redox state Co m pound 5a 5b 9a 9b 3+ 94, 1, 9 96, 1, 2 98, 1, 5 97, 0, 7 2+ 86, 12, 85 (89, 13, 83) 88, 14, 32; (92, 13, 35) 96, 3, 46 (95, 3, 55) 94, 1,51 (96, 3, 57) 1+ 66, 31, 66 63, 8, 2 0 63, 29, 58 a Values were calculated from the absorbance spectra of the crosslinked films. Given in brackets are CIE 1976 L*a*b* values measu red with a Minolta CS 100 co l orimeter. Table 3 2 CIE 1976 L*a*b* values a for the copolymeric film of 5a and 5b in 1:1 molar ratio at various redox states of 5a and 5b Redox state 5a 3+ 2+ 2+ 1+ 1+ 5b 3+ 2+ 1+ 1+ 0 L*a*b* 9 8, 1, 9 87, 13, 56 (91, 13, 62) 66, 3, 36 66,14, 45 73, 27, 70 a Values were calculated from the absorbance spectra of the crosslinked films. Given in brackets are CIE 1976 L*a*b* values measured with a M i nolta CS 100 colorimeter.

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81 In the as prepared 2+ ox idation state, compounds 5a 5b and 5a co 5b were ver i fied to have an orange color exemplified by the large positive a* and b* values, while compounds 9a and 9b possessed hues in the pure yellow region exemplified by the relatively small a* value and large b* value. Such a finding was in good agreement with the spectral data (Figure 3 4 ), w here all the compounds in their 2+ oxidation state absorbed wav e lengths attributed to either blue or green light. As detailed earlier, the reduced states of the polymeri c films exhibited complex spectral profiles with multiple absorption peaks and var i ances in intensity making the exact color displayed by the film difficult to determine by a b sorbance spectra alone. The use of colorimetry in this situation could provide va luable insight into the colors observed, verifying those shown in the phot o graphs in Figure 3 4 Specifically, the reduced poly 5a film ( 1+ oxidation state) had a decrease in L*, an increase in a*, and a decrease in b* values indicating a darker orange re d color rel a tive to the 2+ oxidation state. For the two reduced states of poly 5b ( 1+ and 0 oxidation states), the L* value remained the same, while signif i cant changes were observed in the a* and b* values with the film changing from a blue green to an o range red color. The colorimetric values for the copolymer of 5a and 5b also showed the subtleties in the differences between the colors exhibited by each of the mixed valence states with add i tional switching to dark green brown and grey brown states (Tabl e 3 2) due to color mixing. A slight mismatch between the green color observed in the photographs and the calculated L*a*b* values for this copolymer film in the 2+/1+ mixed oxidation state could possibly be due to subtleties in color perce p tion associated with a low a* value of 3. Co n versely, as a result of loss of their MLCT absorption bands, all the studied co m pounds were switched to nearly colorless, highly

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82 transmissive, states upon oxidative bleaching, as designated by significantly lower a* and b* val ues, as well as L* values as high as 98 (Table 3 1). While these Ru(II) complexes reported herein are attractive candidates for multi colored ECD type device applications, we have pr e viously emphasized that electrochromic window and display devices requi re solution processable active layer mater i als that are capable of switching from a vibrantly colored state to a colorless, transmissive state. 34 As such, the oran ge and yellow Ru(II) based electr o chromes 5a and 9a were chosen to be further characterized in terms of electrochromic contrast (pe r cent transmission change, %T) and color difference ( E) when switched between the colored and bleached states. 120 The orange and yellow electrochromes were ch o sen as yellow is one of the primary subtractive c olors that are used to access any color of the visible spectrum in reflective displays (R Y B and C M Y). Moreover, such transitions are generally difficult to achieve in organic polymeric electrochromes and the corresponding prot o types have only recently been reported by our group in completion of the color palette of electrochromic spray processable pol y mers (ECPs). 7,121,122 While %T is defined as the difference in percent transmittance between the clear and the dark states of the material at one parti cular absorption wavelength, color di f ference [i.e. E = v 1/2 ] takes into account diffe r ences in all three color coordinates of an electrochrome at two co l ored states and mathematically can be described as a vector connecting the two states in the three d i mensional L*a*b* color space. The optical data obtained for compound 5a and 9a as cross linked films, in addition to the r e cently reported polymer electrochromes poly(3,4 di(2 ethylhexyloxy)thiophene) ( ECP Orange) and a substituted poly(propylenedioxythiop hene alt phenylene) (ECP Yellow) are

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83 summarized in Table 3 3. Additio n ally, CIE 1976 a*b* values for poly 5a and poly 9a at their stable and reversible redox states are plotted in Figure 3 6 to illustrate their orange and yellow to transmissive transition s. Here, the b* value changes for 9a from 46 to 5 demonstrating the yellow to nearly colorless switch, while the orange hues evident for 5a in the 2+ and 1+ oxidation states convert to the transmissive state with the a*b* values of 1 and 9, respectively, upon oxidation. As is evident by examining the optical data, Ru iTMCs studied have high transmission contrast and color difference values, which are comparable to state of the art orange and yellow to transmissive ECP electr o chromes. Table 3 3 Percent transmission contrast ( %T) and color difference ( E) data %T and E data for 5a 9a ECP Orange, and ECP Yellow, as they switch from vibrantly colored to transmissive states Compound Color % T ( max ) E 5a Orange a 74% (480 nm ) 78 5a Orange b 80% (487 nm) 72 9a Yellow 68% (456 nm) 50 ECP O Orange 48% (485 nm) 75 ECP Y Yellow 73% (456 nm) 64 Optical properties of 5a are given at redox transitions a ( 2+ 3+) and b ( 1+ 3+) % T values are calculated at the wav e lengths indica ted. Values for ECP O and ECP Y are of similar optical density for max of the colored state to those indicated for the iTMC polymer films. 3.2.5 Photoluminescence P hotoluminescence spectra from dilute deaerated solutions and thin solid films (normalized) of c omplexes 5a 5b 9a and 9b are given in Figure 3 7 It has been well established that, due to spin orbit coupling and efficient inte r system crossing, light emission from Ru iTMCs mostly occurs as phosphorescence with broad unstructured emission bands chara cteristic of MLCT electronic transitions. 45,123,124 A c cordingly, the compounds studied demonstrated broad featur e less photoluminescence profiles in the

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84 orange red and red r e gions with the emission maxima at 640 nm for the complexes 9a and 9b and 680 nm for their diester analogue 5a The red shift of ca. 40 nm in the emission of compound 5a was h y pothesized to arise from a decrease in its ligand based LUMO value and the resulting lower energy MLCT transitions. Figure 3 6 CIE 1976 a*b* values for cross linked films of 5a and 9a calculated from their absorption spectra at all the unambiguously reversible redox states. Reprinted with permission from Puodziukynaite, E.; Oberst, J. L.; Dyer, A. L.; Reynolds, J. R. J. Am. Chem. Soc. 2012 134 968 978 117 Copyright 2012 American Che mical Society Figure 3 7 Emission spectra of compounds 5a 5b 9a 9b and Ru(bpy) 3 A) Photolum inescence spectra of compounds 5a 5b 9a 9b and Ru(bpy) 3 in degassed acetonitrile solutions with the absorption max ~ 0.1 at excitation wavelength exc = 450 nm. B) Photoluminescence spectra of compounds 5a, 9a, 9b and Ru(bpy) 3 2PF 6 in solid state (normalized) at excitation wavelength exc = 450 nm Adapted with permission from Puodziukynaite, E.; Oberst, J. L.; Dy er, A. L.; Reynolds, J. R. J. Am. Chem. Soc. 2012 134 968 978 117 Copyri ght 2012 American Chemical Society

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85 No significant spectral differences were observed for the photol u minescence properties when compounds 5a 9a and 9b were compared in degassed acetonitrile solutio ns and solid state. Conversely, complex 5b having ester s ubstituents at the positions showed weak phot o luminescence with max = 700 nm in solution, whereas no light emission was detected in the solid state. Such spectral behavior of this co m plex is consistent with literature examples 52 and can be partially attributed to the energy gap law for such co m plexes. 49 51,125 Photoluminescence quantum yield values for complexes 5a 9a and 9b in deaerated acetonitrile solutions were a s sessed using Ru(bpy) 3 2PF 6 as a standard and w ere found to be E = 10.3 % 13.1 % and 8.1 % respectively. 3.2.6 Light Emitting Electrochemical Cells In an effort to explore the electrochemil u minescent behavior of the compounds reported, LEC devices, 3,69,71,97,98,126 129 comprised of the newly synthesize d ruthenium complexes 5a 5b 9a and 9b as active materials, were fabricated. The LEC devices studied were comprised of an ITO/glass anode onto which the active electroluminescent layer was prepared by spin coating from a solution of the Ru(II) polypyridyl complex and 21wt% of PMMA in acetonitrile, followed by a thermally evaporated gold cathode. The PMMA was utilized as a supporting polymer m a trix as it results in an improved film quality and higher overall device efficiencies, as has been previously repor ted in the literature. 68 Immediately prior to optical and electrical measur e ments of the devices, a precharging of each pixel was performed wherein a short time (~ 2 sec) high voltage bias was applied (typically ~ 1 2 V higher than that necessary for initial light output) causing redistribution of charge balancing ions at the a n ode and cathode but not resulting in degradation of active layer materials. This method has been prev iously

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86 demonstrated in the literature to give nearly instantaneous device response even at low voltages that otherwise cause sluggish turn on times (on the order of minutes to hours) for pristine d e vices. 100 As can be seen in the emission spectra and pixel photographs in Figure 3 8 all devices exhibited emission evenly across the entire pixel with the devices comprised of the Ru based iTMCs 5a and 5b exhib iting emission with max values ranging from 688 nm to 722 nm, coinciding with the solution and solid state photoluminescence spectra, while those comprised of co m plexes 9a and 9b exhibited significant bathochromic shifts of ca. 50 nm from their solution and solid state photo luminescence spe c tra. It is h ypothesize d that this is due to destabilization of the excited states upon device operation resulting from electrochemically induced chemical side reactions that are occurring at the acr y late sites, hampering electron injectio n events resulting in the ca. 50 nm bathochromic shift in emission maxima, and lower light output as will be discussed later. 130 This hypothesis is supported by extensive cyclic voltammetry studies (Figure 3 3 ) where the reductive polym erization of the complexes occurred at approximately the same potential as their first reductions. These differences in optical properties between the co m plexes were also noted in colorimetric measurements of the emitted light, presented as the CIE x,y col or coordinates in Table 3 4. Devices comprised of 5a and 5b showed ECL response in the red region with x,y coordinate values x = 0.68, y = 0.32 and x = 0.67, y = 0.29, respectively. Dimethylesters 9a and 9b although having ca. 10 nm bathochromically shift ed ECL maxima when compared to that of 5a devices, showed emission color coord i nates (x = 0.64, y = 0.36 and x = 0.65, y = 0.34, correspondingly) that were

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87 characteristic of red orange emi s sion. This is not unexpected given that, while the peak emission oc curs at longer wavelengths, the increased emi s sion in the range from ca. 550 nm to 600 nm contributes substantially to the color observed, as these wavelengths are the region where the human eye is the most sensitive. Figure 3 8 Electroluminescence spectra of LEC devices based on 5a 5b 9a and 9b Normalized EL spectra of LECs based on 5a 9a and 9b biased at 4.5 V, as well as the blend of 5a and 5b in 1:1 molar ratio, biased at 7 V and the corresponding photographs of the LEC pixels (diameter = 3 mm). Reprinted with the permission from reference. Adapted with permission from Puodziukynaite, E.; Oberst, J. L.; Dyer, A. L.; Reynolds, J. R. J. Am. Chem. Soc. 2012 134 968 978 117 Copyright 2012 American Chemical Society Table 3 4 presents the optical properties (radiant exitance and luminance) and efficiencies (external quantum efficiency (EQE)) measured for LEC devices containing each of the complexes in addition to the 5a / 5b blend. B oth luminance and radiant ex i tance data are reported as the luminance is the most common representation of light o utput for visible displays, while it is also desired to understand the total power emitted for a more fundamental understanding of device performance. Additionally, we present both maximum external quantum efficiency (EQE max ), which may occur at lower vol tages and minimal light output due to the low current densities, and the EQE at the peak light output (peak EQE). As can be seen, LEC devices containing 5a demonstrated the brightest light output with radiant exitance values as high as 1.03

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88 mW/cm 2 and the EQE max of 2.22 % These performance results are consistent with similar systems presented in the literature with examples of pristine LEC devices co m prised of Ru(II) bis(2,2' bipyridine)(dimethyl [2,2' bipyridine] 4,4' dicarboxylate) bis(hexafluorophosphat e) and Ru(II) tris(dimethyl [2,2' bipyridine] 4,4 dicarboxylate) bis(hexafluoro phosphate) having red ECL response with max = 690 nm and EQEs of 0.1 0.4 % at 3 5 V. 100 It is notable that EQE max values as high as 5.5 % have been reported in the literature for Ru based LECs, h owever, the corresponding devices were operated under very specific pulsed voltage conditions to obtain the maximum performance. 70 It is interesting to note that, although a weak solution photoluminescence response (and no solid state photoluminescence r e sponse) was observed for compound 5b LECs based on the complex demonstrated visible light emission upon electroexcitation. While a significant decrease in radiant exitance, lum i nance and EQE values were observed for devices comprised of 5b as well as for devices based on the blend of 5a and 5b (1:1 mo lar ratio), this observation can be partly attributed to the strongly red shifted low energy light emission of the respective LECs. Additionally, it is noteworthy that devices comprised of 5b and the blend of 5a and 5b (1:1 molar ratio) as their active lay ers are among the deepest red light emitting mononuclear Ru(II) complex based LECs reported in the literature with their emission wavelength and EQEs comparable to those reported by Bolink et al. 72 The performance of 9a and 9b based devices was lower than that demonstrated by similar Ru(II) based systems 100 and, as explained above, resulted from the possible d e stabilization of the excited states caused by the electrochemica l side reactions during device operation. 130

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89 Table 3 4 LEC data. Optical and efficiency characteristics, as well as time required to reach half of the peak radiant exitance value (precharged mode), of the L EC devices based on co m pounds 5a 5b, 9a 9b, and the blend of 5a and 5b (1:1 molar r atio) at the indicated voltages Com pound max (nm) CIE (x,y) coordinates Peak Radiant Ex i tance ( W/cm 2 ) Peak Lum i nance (cd/m 2 ) Max. EQE (%) EQE at Peak Light Ou t put (%) 1/2 (s) 5a 688 (0.68, 0.32) 1031.0 (5.5 V) 153.0 (5.5 V) 2.22 (3.0 V) 0.49 (5.5 V) 2 (5.5 V) 5b 722 (0.67, 0.29) 48.9 (6 .0 V) 2.0 (6.0 V) 0.04 (4.0 V) 0.03 (6.0 V) 2 (6.0 V) 9a 699 (0.64, 0.36) 220.2 (5.5 V) 56.4 (5.5 V) 0.11 (3.5 V) 0.03 (5.5 V) 2 (5.5 V) 9b 692 (0.65, 0.34) 32.1 (6.0 V) 16.7 (6.0 V) 0.37 (3.5 V) 0.02 (6.0 V) 1 (6.0 V) 5a+5b 717 (0 .67, 0.34)* 40.0 (6.0 V) 2.0* (6.0 V) 0.05 (4.0 V) 0.02 (6.0 V) 1 (6.0 V) *Values were calculated from spectral and radiant exitance data As mentioned previously, for ultimate application as the a c tive layer in a dual EC/EL device, the electroluminescent mat e rial shoul d be that of an insoluble, electrode supported film. To demonstrate the ability of these Ru(II) based LECs to retain their emissive properties (color and intensity) when employed as insoluble films, we studied LEC devices where the active layer is cross l inked, as was performed for the electrochromism study. As the molecular LEC devices comprised of compound 5a demonstrated the best overall performance, we further studied this system as the crosslinked electrochemiluminescent layer in the polymeric LEC de vices. The active layers were cast as thin films by spin coating, onto ITO/glass anodes, from a solution containing compound 5a 21 wt% TEGDMA, and 0.5 wt% of az o bisisobutyroni trile (AIBN), in acetonitrile. The active layer was then subjected to thermal c ross linking by heating at 150 o C for 12 hours and a gold cathode was deposited as previously described. In such devices, TEGDMA served as both a cross lin k ing agent and a

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90 supporting matrix replacing PMMA. Initial devices prepared in this manner had the ultimate film thickness much lower ( ca. 50 % ) than that of the molecular LECs, resul t ing i n electrical shorts. As such, a second film deposition process was added to create two sequentially depo s ited, cross linked bilayers to increase the film thickness. As is indicated by radiant exitance measurements shown in Figure 3 9 and the spectral data provided in Table 3 5, while the light output at lower applied vol t ages was less intense for the multilayer device compared to the single layer, molecular device, the peak light output in the mu l tilayer cross linked devices demonstrated slightly elevated ECL performance and an emission color co m parable to that of their molecular prototypes. Figure 3 9 Voltage dependent radiant exitance Voltage dependent radiant exitance for LEC devices comprised of 5a as a molecular compound blended with PMMA (black squares) and those comprised of 5a as a polymer cross linked with TEGDMA (red circles) Reprinted with permission from Puodziukynaite, E.; Oberst, J. L.; Dyer, A. L.; Reynolds, J. R. J. Am. Chem. Soc. 2012 134 968 978 117 Copyright 2012 American Chemical Society 117 The decrease in the EQE values and light output at lower operating voltages after cross linking is possibly due to inhibition of functional group local motion, lea d ing to decreased counter ion mobility and charge transfer, as e x pected when comparing molecular and polymeric s ystems. The device characterization results show, however, that the cross linking process, necessary to pr o duce thin films of the complexes for use

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91 in dual EC/EL d e vices, is not detrimental to the light emitting properties nor emission color; which is the first step in demo n strating the applicability of these systems in the dual mode d e vices. Table 3 5 LEC data after active layer cross linking. Optical and efficiency characteristics, as well as time required to reach half of the peak radiant exitance value (precharged mode), of the LEC devices based on 5a as a molecular compound blended with PMMA and those comprised of 5a as a polymer c ross linked with TEGDMA at 5.5 V Supporting matrix max (nm) CIE (x,y) coordinates Peak Radiant Exitance ( W/cm 2 ) EQE at Peak Light Output (%) 1/2 (s) PMMA 688 (0.68, 0.32) 1031.0 0.49 2 TEGDMA 682 (0.70, 0.30) 1284.9 0.27 2 3.2.7 Dual Electrochromic/Electroluminescent Device Prototype In an effort to demon strate that dual electrochromic and electrogenerated chemiluminescence response can be observed from a single active material layer in a single device architecture, dual EC/EL device prototypes have been constructed. In accordance with the fabrication of t he polymeric LEC devices, complex 5a has been chosen as the basis for the dual EC/EL prototype active film. Due to fundamental differences between conjugated polymers and iTMCs, a new device architecture was designed differing from those previously describ ed by our group 35,87,93 (Figure 3 1). As delineated previously by Dyer et al 35 type I (Figure 3 1 A ) devices were found to pose general challenges due to poor contact between the active layer and the metalized porous membrane electrode. Meanwhile, the LEC component in type II dual EC/EL device s possessed planar architecture which was previously demonstrated to be unsuitable for utilizing Ru(II) chromophores 128,131,132 This is due to l ower conductivity values of iTMCs, leading to narrow recombination zones between the interdigitated planar electrodes and, th us low luminance of the corresponding LEC s Additionally,

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92 active layer delamination and degradation a re often observed in such devices as a result of uneven swelling of iTMC films upon opposite doping and an increase in the required operating voltages with increasing electrode spacings respectively The redesigned device architecture (Figure 3 10 ) there fore possessed a sandwiched pair of electrodes triggering electrogenerated chemiluminescence. Additionally, the patterned gold cathode was deposited via thermal evaporation, allowing for good contact with the active layer material. Figure 3 10 S chematic representation of a redesigned dual electrochromic/elec troluminescent device prototype Reprinted with permission from Puodziukynaite, E.; Oberst, J. L.; Dyer, A. L.; Reynolds, J. R. J. Am. Chem. Soc. 2012 134 968 978 117 Copyright 2012 American Chemical Society As shown schematically in Figure 3 10 the device was fabricated by spincoating the active layer, on a glass/ITO electrode (electrode I), from a solution containing compound 5a 14 wt% TEGDMA, 7wt% of TMPTA, and 2 wt% of PMMA, in acetonitrile. The films were then subjected to thermal cross linking at 185 o C for 15 h, and a patterned gold electrode (electrode II) was deposited via thermal evaporation. The counter electrode for electrochromism (electrode III) was prepared by spincoating, onto ITO/glass, a thin layer of a minimally color chang ing polymer (MCCP) along with 4wt%

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93 of TBAPF 6 from a chloroform solution. MCCP, an N alkyl substituted poly(3,4 propylenedioxypyrrole) derivative was employed as the charge balancing material. 73 Finally, a gel electrolyte, containing PMMA and TBAPF 6 in propylene carbonate, was sandwiched between the ITO/poly 5a /Gold and ITO/MCCP ele c trodes. In this device construction, ITO coated glass with the active polymer layer was designed to fun c tion as both the anode for light emission and the working ele c trode for electrochromism. A s a result, the dual EC/EL prototype allowed for light emission upon the applic a tion of bias between the ITO I anode and gold cathode, while the electrochromic mode could be triggered as a result of applying vol t age between the electrodes I and III. Absorp tion and emission spectra for the device ope rated in the reflective electro chromic and emissive modes along with the corresponding p hotographs are given in Figure 3 1 1 Respe c tive colorimetric data are summarized in Table 3 6 Figure 3 11 Dual electrochromic/electroluminescent device characteristics. A) Absorption spectra of a dual EC/EL device pixel as it is operated in the electrochromic mode in the as prepared (Ru 2+ ), oxidized (Ru 3+ ), and reduced (Ru 1+ ) states at the i ndicated voltages along with the corr e sponding photographs of the pixel in these states: ( C ), ( D ), and ( E ), respectively. B) Emission spectra of the device pixel ope r ated in the electrochemiluminescent mode at 7 V along with the corr e sponding photograph ( F ) Adapted with permission from Puodziukynaite, E.; Oberst, J. L.; Dyer, A. L.; Reynolds, J. R. J. Am. Chem. Soc. 2012 134 968 978 117 Copyright 2012 American Chemical Society

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94 Table 3 6 CIE 1976 L*a*b* values for the dual electrochromic/electroluminescent device prototype CIE 1976 L*a*b* values fo r the dual electrochromic/electroluminescent device prototype comprised of poly 5a operated in the electrochromic mode at the indicated voltages along with Device Redox State L*a*b* max ) As prepared (Ru 2+ 0 V/ 1.5 V) 82, 14, 53 Oxidized (Ru 3+ 2.5 V) 90, 5, 5 53 % (485 nm) 49 Reduced (Ru 1+ 8.0 V) 63, 29, 43 59 % (486 nm) 52 As can be seen (Figures 3 1 1 A,C E Table 3 6 ), the electr o chromic behavior of the dual EC/EL protot ype was, in principle, analogous to that of the poly 5a film described previously (Figure 3 4 A Table 3 1) with minimal deviations in the a b sorption spectra and L*a*b* coordinates being caused by the add i tional MCCP and gel electrolyte layers. As prepared, the device exhibited an o r ange color (L*, a*, b* = 82, 14, 53), that was switched to a dark red orange hue (L*, a*, b* = 63, 29, 43) upon reduction at 8 V, and reached a nearly colorless highly tran s missive state (L*, a*, b* = 90, 5, 5) upon oxidation at 2.5 V. Additionally, the dual EC/EL prototype maintained rel a tively high %T and E va l ues of 53 and 59 ( 2+ 3+ ), as well as 49 and 52 ( 1+ 3+ ), respectively (Table 3 6 ). It is notable that the color changes occurred across the entire pixel including th e area under the gold digits. While prolonged operation u n der reduced cond i tions led to device degradation, the prototype could be reversibly switched i dized states. Furthermore, this reversibility was preserved as the devic e was cycled between the EC (oxidation transition) and ECL modes. When operated in the emissive state, as seen in Figure 3 1 1 the dual EC/EL prototype exhibited red lumine s cence with max = 680 nm, identical to that previously observed for 5a solutions, f ilms, and LEC devices (Figures 3 7, 3 8 ). As this d e vice is unoptimized with rather large pixels, the operating vol t age is slightly higher than the

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95 individual operations of EC and ECL demonstrated previously. This is not unexpected as there is a fairly significant IR drop across the larger transparent ele c trode area utilized in this dual device demonstration. Additio n ally, this prototype performance is highly affected by the nature of the employed gel electrolyte and charge balancing materials. As a result, it is anticipated that lower operating voltage, brighter light output, and improved evenness in EC and ECL can be obtained with further efforts towards device optimiz a tion through en gineering. Regardless, this is the first reported demonstration of bright light emission and full EC switching in a single active material when employed as a single layer in a dual EC/EL device. 3.3 Conclusions In conclusion, demonstrated herein is a new seri es of ruthenium(II) tris(bipyridine) based coordination complexes that form insoluble films with dual electrochromic/electrochemiluminescent character upon crosslinking. A wide palette of colors is obtained upon electrochemical switching of the polymeric n etworks. In addition, orange red to deep red electrogenerated chemiluminescence with max ranging from 680 to 722 nm is observed as the Ru(II) polypyridyl complexes are applied in light emitting electrochemical cell devices. It is shown that the complexes synthesized retain their ECL character upon cross linking, enabling their applic a tion in electrochemical devices containing liquid electrolyte, while simultaneously leading to advanced architectures of the resulting active layers. Finally, an EC/EL device prototype is demo n strated where the dual response is achieved from a single Ru(II) complex active layer in a single architecture. This concept has been difficult to achieve in the past as the requirements for a mat e rial to exhibit both EC and ECL in the s ame device are rather stringent. However, due to their reversible redox switching, electroluminescent

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96 and polyelectr o chromic behavior, as well as the reactive nature of the pendant acrylate moieties, cross linkable ruthenium complexes presented in this st udy are attractive candidates for well defined dual EC/EL active layers. 3.4 Experimental Details 3.4.1 Synthesis Dicarboxy bipyridine (1a) 53 dicarboxy bipyridine (1b) 133 bipyridine dicarbonyl chloride (2a) 99 bipyridine 5, dicarbonyl chloride (2b) 55 diethyl 2,2 bipyridine 4,4 dicarboxylate (6a) 134 and diethyl 2,2 bipyridine 5,5 dicarboxylate (6b) 135 were synthesized as described in the corresponding literature sources. bis[(3 hydroxypropoxy)carbonyl] bipyridine (3a) 99 was synthesized using a modified literature p rocedure. Diacid chloride 2a (1 g, 3.558 mmol) was dissolved in anhydrous dichloromethane (20 mL ) and added dropwise to the solution of 1,3 propanediol (12 m L 12.72 g, 167.113 mmol) and triethylamine (1.4 m L 1.02 g, 6.461 mmol) in anhydrous dichlorometh ane (20 m L ). The reaction mixture was refluxed under nitrogen atmosphere for 12 hours, cooled down to room temperature, and washed with 0.2 M aqueous potassium carbonate solution. The dichloromethane layer, containing the desired compound, was dried over sodium sulfate and brought to dryness by rotaevaporation. The crude reaction product was used for the next step of the synthesis without further purification. bis[(3 hydroxypropoxy)carbonyl] bipyridine (3b) 55 was synthesized using diacid chloride 3a (1 g, 3.558 mmol), 1,3 propanediol (12 mL 12.72 g, 167.113 mmol), and triethylamine (1.4 mL 1.02 g, 6.461 mmol) by employing the same

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97 procedure as for compound 3a and was used for the n ext step of the synthesis without further purification. Bis(3 (acryloyloxy)propyl) [2,2' bipyridine] 4,4' DEAB) (4a) 99 The solution of compound 3a mL 2.67 g, 29.671 mmol) in acetonitrile (50 mL ) was re fluxed for 6 hours, cooled down to room temperature, and the excess acryloyl chloride and the solvent were then removed by vacuum distillation. The crude product was then refluxed under nitrogen atmosphere in 40 mL of a 10% v/v solution of triethylamine i n dichloromethane for 4 h to reverse the addition of hydrochloric acid across the acrylate double bonds. The resulting product was purified by silica gel column chromatography using the eluent mixture of acetone and dichloromethane in 1:10 volume ratio an d recrystallized from methanol to give white crystals. The overall yield for three synthetic steps was 56 % 1 H NMR (300 MHz, CDCl 3 2.22 (p, 4H); 4.37 (t, 4H, J = 6.3 Hz); 4.52 (t, 4H, J = 6.3 Hz); 5.83 (dd, 2H, J 1 = 10.5 Hz, J 2 = 1.4 Hz); 6.14 (dd, 2H, J 1 = 17.3 Hz, J 2 = 10.5 Hz); 6.43 (dd, 2H, J 1 = 17.3 Hz, J 2 = 1.4 Hz); 7.91 (dd, 2H, J 1 = 5.1 Hz, J 2 = 1.7 Hz); 8.88 (dd, 2H, J 1 = 5.1 Hz, J 2 = 0.9 Hz); 8.95 (dd, 2H, J 1 = 1.7 Hz, J 2 = 0.9 Hz). 13 C NMR (75 MHz, CDCl 3 (ppm): 27.98, 61.09, 62.5 7, 120.46, 123.18, 128.12, 131.03, 138.49, 150.08, 156.44, 165.00, 166.01. Bis(3 (acryloyloxy)propyl) [2,2' bipyridine] 5,5' DEAB) (4b) 55 was obtained using compound 3b mL 2.67 g, 29.671 mmol) by employing the same synthetic method as for compound 4a White crystals were obtained. The overall yield for three synthetic steps was 52 % 1 H NMR (300 MHz, CDCl 3 2.21 (p 4H); 4.37 (t, 4H, J = 6.2 Hz); 4.51 (t, 4H, J

PAGE 98

98 = 6.2 Hz); 5.85 (dd, 2H, J 1 = 10.5 Hz, J 2 = 1.4 Hz); 6.13 (dd, 2H, J 1 = 17.3 Hz, J 2 = 10.5 Hz); 6.43 (dd, 2H, J 1 = 17.3 Hz, J 2 = 1.4 Hz); 8.43 (dd, 2H, J 1 = 8.2 Hz, J 2 = 2.0 Hz); 8.59 (dd, 2H, J 1 = 8.2 Hz, J 2 = 0.9 Hz); 9.30 (dd, 2H, J 1 = 2.0 Hz, J 2 = 0.9 Hz); 13 C NMR (75 MHz, CDCl 3 28.04, 61.08, 62.18, 121.30, 126.20, 128.14, 131.09, 138.11, 150.57, 158.34, 165.00, 166.04. Ru(bpy) 2 DEAB)2PF 6 (5a) 0.20 g (0.427 mmol) of compound 4a 0.23 g (0.448 mmol) of Ru(bpy) 2 Cl 2 2H 2 O and a catalytic amount of BHT were added to 10 mL of ethylene glycol. The content of the flask was degassed, heated to 90 o C, and kept at this temperature for 3 hours under a nitrogen atmosphere. The reaction mixture was then cooled down to room temperature, precipitated into an aqueous soluti on of ammonium hexafluorophosphate (2 g of NH 4 PF 6 in 50 mL of H 2 0), vacuum filtered, redissolved in acetone, and reprecipitated in diethyl ether. The red precipitate was further purified by neutral alumina gel column chromatography using acetonitrile as a mobile phase. The solution of the desired product in acetonitrile was then brought to dryness by rotoevaporation, redissolved in acetone, and precipitated in diethyl ether to give a dark red precipitate. Yield: 78%. 1 H NMR (300 MHz, acetone d 6 ): 2.20 (m, 4H); 4.34 (t, 4H, J = 6.2 Hz); 4.54 (t, 4H, J = 6.2 Hz); 5.86 (dd, 2H, J 1 = 10.5 Hz, J 2 = 1.7 Hz); 6.15 (dd, 2H, J 1 = 17.3 Hz, J 2 = 10.5 Hz); 6.35 (dd, 2H, J 1 = 17.3 Hz, J 2 = 1.7 Hz); 7.54 7.64 (m, 4H); 8.00 8.09 (m, 6H); 8.21 8.29 (m, 4H); 8.3 4 (d, 2H, J = 6.0 Hz), 8.83 8.86 (m, 4H); 9.32 (d, 2H, J = 1.4 Hz); 13 C NMR (75 MHz, CDCl 3 61.72, 64.00, 124.77, 125.56, 127.82, 128.99, 129.05, 129.35, 131.44, 139.48, 139.51, 139.54, 152.64, 152.93, 153.93, 157.81, 157.94, 158.94, 164.19, 166.40. ESI TOF MS m/z calculated for C 44 H 40 N 6 O 8 Ru 2+ [M 2+ ]: 441.0976, found: 441.0989.

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99 Ru(bpy) 2 (acetone) 2 (OTf) 2 115 Silver trifluoromethanesulfonate (0.234 g, 0.911 mmol) was added to a degassed solution of Ru( bpy) 2 Cl 2 2H 2 O (0.236 g, 0.454 mmol) in acetone (110 mL). The reaction mixture was then stirred at room temperature for 2 hours under a nitrogen atmosphere. After gravity filtration of the solution, the filtrate was evaporated to dryness and the residue o btained was immediately used for the following reaction. Ru(bpy) 2 DEAB)2PF 6 (5b). Ru(bpy) 2 (acetone) 2 (OTf) 2 residue obtained in the previous reaction, was dissolved in 12 mL of dry degassed N methylpyrrolidone and transferred via a syringe to a r ound bottom flask containing 4b (0.18 g, 0.384 mmol) and a catalytic amount of BHT. The reaction mixture was stirred at 100 C for 48 h under nitrogen, allowed to cool down to room temperature, and precipitated into an ice cooled aqueous solution of ammon ium hexafluorophosphate (2 g of NH 4 PF 6 in 50 mL of H 2 0). A dark red precipitate was collected by filtration and purified using the same procedure as for compound 5a Yield: 75 % 1 H NMR (300 MHz, acetone d 6 2.03 (m, 4H); 4.15 (t, 4H, J = 6.2 H z); 4.34 (t, 4H, J = 6.2 Hz); 5.89 (dd, 2H, J 1 = 10.2 Hz, J 2 = 1.7 Hz); 6.13 (dd, 2H, J 1 = 17.3 Hz, J 2 = 10.5 Hz); 6.35 (dd, 2H, J 1 = 17.3 Hz, J 2 = 1.7 Hz); 7.52 7.70 (m, 4H); 8.12 8.40 (m, 10H); 8.65 (dd, 2H, J 1 = 8.5 Hz, J 2 = 2.0 Hz); 8.86 (dd, 4H, J 1 = 17.3 Hz, J 2 = 7.9 Hz); 9.03 (d, 2H, J = 8.5 Hz); 13 C NMR (75 MHz, CDCl 3 (ppm): 28.48, 61.67, 63.53, 125.52, 125.61, 126.55, 128.98, 129.00, 129.30, 130.99, 131.54, 139.14, 139.37, 139.48, 153.04, 153.29, 157.89, 158.27, 160.54, 163.29, 166.41. ESI TOF MS m/z calculated for C 44 H 40 N 6 O 8 Ru 2+ [M 2+ ]: 441.0976, found: 441.0987.

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100 4,4' Bis(hydroxymethyl) 2,2' bipyridine (7a) 134 2.19 g (57.891 mmol) of sodium borohydride were added to a cooled suspension of 6a (0.8 g, 2.664 mmol) in 60 mL of absolute ethanol. The reaction mixture was refluxed for 15 hours under nitrogen and allowed to cool to room temp erature. 50 mL of ammonium chloride (4 g) aqueous solution was then added to the flask and the content was stirred for 3 hours to decompose the excess borohydride. The ethanol was then removed under vacuum, the precipitated solid was dissolved in a minim um amount of water, and the resulting solution was extracted with ethyl acetate (3 x 100 mL). The organic phases were combined, dried over sodium sulfate and evaporated to dryness. The residue was then dissolved in methanol and filtered through a silica plug. A light yellow precipitate was obtained upon evaporation of the solvent. Yield: 80 % 1 H NMR (300 MHz, DMSO d 6 ), (ppm): 4.65 (s, 4H), 5.55 (s, 2H), 7.46 (d, 2H, J = 4.8 Hz), 8.41 (s, 2H), 8.63 (d, 2H, J = 5.1 Hz). 13 C NMR (75 MHz, DMSO d 6 ), (ppm): 61.62, 118.36, 121.94, 148.36, 153.55, 154.28. 5,5' Bis(hydroxymethyl) 2,2' bipyridine (7b) 136 was synthesized from 0.8 g (57.891 mmol) of 6b and 2.19 g (2.664 mmol) of sodium borohydride using the same synthetic proce dure as for 7a Yield of a white precipitate: 72 % 1 H NMR (300 MHz, DMSO d 6 ), (ppm): 4.59 (s, 4H), 5.53 (s, 2H), 7.86 (dd, 2H, J 1 = 8.2 Hz, J 2 = 1.7 Hz); 8.33 (d, 2H, J = 8.2 Hz); 8.61 (d, 2H, J = 1.7 Hz). 13 C NMR (75 MHz, DMSO d 6 ), (ppm): 60.52, 11 9.92, 135.58, 138.04, 147.75, 153.99. [2,2' bipyridine] 4,4' DMAB) (8a). Acryloyl chloride (0.62 mL, 0.69 g, 7.665 mmol) was slowly added via syringe to a stirring solution of 7a (0.4 g, 1.850 mmol), triethylamine (1.7 1 mL, 1.24 g, 7.892 mmol), and

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101 BHT (2 mg, 0.009 mmol) in dry methylene chloride (50 mL) at 0 C under a nitrogen atmosphere, and the reaction mixture was stirred at this temperature for 1 hour. After the solution was allowed to warm to room temperature, a catalytic amount of 4 (dimethylamino)pyridine (DMAP) (3.9 mg, 0.032 mmol) was added, and the flask was stirred overnight. The reaction mixture was then washed with water, the organic fractions were combined, dried over sodium sulfate and evaporated to dr yness. The crude product was purified by silica gel column chromatography, eluting with methylene chloride:acetone in 100:7 volume ratio to afford light yellow crystals in 52 % yield. MP = 87.0 89.0 o C. 1 H NMR (300 MHz, CDCl 3 ), 5.30 (s, 4H); 5.93 (dd, 2H, J 1 = 10.5 Hz, J 2 = 1.4 Hz); 6.24 (dd, 2H, J 1 = 17.3 Hz, J 2 = 10.5 Hz); 6.53 (dd, 2H, J 1 = 17.3 Hz, J 2 = 1.4 Hz); 7.32 (dd, 2H, J 1 = 5.1 Hz, J 2 = 1.7 Hz); 8.41 (d, 2H, J = 1.7 Hz); 8.95 (d, 2H, J = 5.1 Hz). 13 C NMR (75 MHz, CDCl 3 ), (ppm): 64.47, 119.43, 122.04, 127.74, 131.79, 145.89, 149.43, 156.08, 165.61. CI MS m/z calculated for C 18 H 16 N 2 O 4 [M+H + ]: 325.1183, found: 325.1190. [2,2' bipyridine] 5,5' DMAB) (8b) was synthesized acco rding to the same procedure as for 8a using 0.4 g of 7b acryloyl chloride (0.62 mL, 0.69 g, 7.665 mmol), triethylamine (1.71 mL, 1.24 g, 7.892 mmol) and BHT (2 mg, 0.009 mmol). White crystals were obtained in 55 % yield. MP = 98.5 100.0 o C. 1 H NMR (300 MHz, CDCl 3 5.29 (s, 4H); 5.90 (dd, 2H, J 1 = 10.5 Hz, J 2 = 1.4 Hz); 6.19 (dd, 2H, J 1 = 17.4 Hz, J 2 = 10.5 Hz); 6.49 (dd, 2H, J 1 = 17.4 Hz, J 2 = 1.4 Hz); 7.86 (dd, 2H, J 1 = 8.2 Hz, J 2 = 2.1 Hz); 8.43 (d, 2H, J = 8.2 Hz); 8.70 (d, 2H, J 1 = 2.0). 13 C NMR (75 MHz, CDCl 3 ), (ppm): 63.62, 120.92, 127.92, 131.60, 131.64,

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102 136.97, 149.05, 155.67, 165.79 CI MS m/z calculated for C 18 H 16 N 2 O 4 [M+H + ]: 325.1183, found: 325.1189. Ru(bpy) 2 DMAB)2PF 6 (9a). Compound 8a (0.20 g, 0.617 mmol), Ru(bpy) 2 Cl 2 2H 2 O (0.34 g, 0.647 mmol), BHT (catalytic amount) and 40 mL of ethanol were combined in a flask and degassed. The solution was stirred at 70 o C under a nitrogen atmosphere for 15 hours. The reaction mixture was brought to dryness by rotaevaporation, dissolved in 2 0 mL of water, and washed with dichloromethane. To a vigorously stirred aqueous phase 1 g of ammonium hexafluorophosphate was added and the resulting precipitate was filtered. The reaction product was purified using neutral alumina column chromatography with acetonitrile:acetone (1:3 volume ratio) as the eluent. The product solution was concentrated and precipitated into diethyl ether. Yield of an orange red precipitate: 88 % 1 H NMR (300 MHz, acetone d 6 ), (ppm): 5.46 (s, 4H); 6.01 (dd, 2H, J 1 = 10.5 H z, J 2 = 1.4 Hz); 6.27 (dd, 2H, J 1 = 17.3 Hz, J 2 = 10.5 Hz); 6.47 (dd, 2H, J 1 = 17.3 Hz, J 2 = 1.6 Hz); 7.54 7.60 (m, 4H); 8.03 8.07 (m, 6H); 8.16 8.22 (m, 6H), 8.78 8.83 (m, 6H). 13 C NMR (75 MHz, acetone d 6 ), (ppm): 64.34, 123.47, 125.39, 126.77, 128.61, 128.84, 132.75, 139.02, 139.05, 149.12, 152.74, 158.01, 158.15, 158.16, 165.95. ESI TOF MS m/z calculated for C 38 H 32 N 6 O 4 Ru 2+ [M 2+ ]: 369.0764, found: 369.0784. Ru(bpy) 2 DMAB)2PF 6 (9b) was obtained from 8b (0.20 g, mmol Ru(bpy) 2 Cl 2 2H 2 O (0.34 g, mm ol) and BHT (catalytic amount) using the same synthetic procedure as for 9a Yield of a bright orange precipitate: 91 % 1 H NMR (300 MHz, acetone d 6 ), (ppm): 5.16 (s, 4H); 5.96 (dd, 2H, J 1 = 10.2 Hz, J 2 = 1.7 Hz); 6.06 (dd, 2H, J 1 = 17.0 Hz, J 2 = 10.2 Hz); 6.30 (dd, 2H, J 1 = 17.0 Hz, J 2 = 1.7 Hz); 7.53 7.61 (m,

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103 6H); 8.03 8.09 (m, 6H); 8.17 8.26 (m, 4H), 8.75 8.86 (m, 6H). 13 C NMR (75 MHz, acetone d 6 ), (ppm): 63.15, 125.19, 125.19, 125.40, 125.45, 128.48, 128.79, 128.84, 132.73, 137.93, 137.99, 139.06, 139.13, 151.23, 152.83, 152.87, 157.41, 158.15, 158.21, 165.82 ESI TOF MS m/z calculated for C 38 H 32 N 6 O 4 Ru 2+ [M 2+ ]: 369.0764, found: 369.0784. 3.4.2 Film P reparation and Cross Linking for Electrochromic Measurements Typically, 26.8 mg of a Ru(II) complex, 3.828 mg of trimethylolpropane triacrylate and 7.656 mg of tetraethyleneglycol dimethacrylate were dissolved in 250 L of acetonitrile and stirred for 1 ho ur. The solutions were then spin coated at 1000 rpm using a Chemnat Technology KW 4A spin coater and dried in a VWR 1415M vacuum oven at 70 o C under vacuum for 30 minutes. The vacuum oven was then refilled with nitrogen and the samples were further heate d at 150 o C for 4 h to obtain the crosslinked films, which were then rinsed sequentially with dichlorometane and acetonitrile to remove any non crosslinked components.

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104 CHAPTER 4 POLYFLUORENE CHEMISTRY: PROBI NG CONJUGATED POLYMER BACKBONE IONIC TRANSITION METAL COMPLEX CHROMOPHORE INTERACTIONS IN MACROMOLECULAR LIGHT HARVESTING ANTENNAE 4.1 Introductory Remarks Ionic transition metal complexes have emerged as attractive light harvesting, charge transport, and ca t a lytic media for solar electrochemical cells and solar fuel devices. 74,76,137 § Among such systems, multichrom o phoric iTMC arrays, especially those based on Ru(II) polypyridyl complexes as pendants, have attracted a considerable amount of attention due to their large cumulative optical cross section s and long lived ph o tostable excited states enabling exciton migration over l ong dis tances. 61,138 141 Given the combination of these properties, an antenna effect can be induced in such assemblies, a necessity in designing ar tificial photosynthetic system s 142 146 To date, multichromophoric assemblies have been mostly comprised of non conjugated polymer backbones, such as polystyrene or polyproline. 61,140,147 However, while scaffolds with saturated linkages act as exce l lent templates to precisely a lign the pendant iTMC units, thu s allowing for interchromophore exciton migration control i n trinsically such polymers are non electroactive and do not perform functions related to solar energy conversion As a result, conjugated polymer iTMC hybrids with controlled electronic properties are of interest, as they provide a basis for solar energy harvesting/storage by the conjugated polymer backbone, followed by ultrafast energy § Part of Chapter 4 has been published as Wang, L.; Puodziukynaite, E.; Vary, R. P.; Grumstrup, E. M.; Walczak, R. M.; Zolota rskaya, O. Y.; Schanze, K. S.; Reynolds, J. R.; Papanikolas, J. M. J. Phys. Chem. Lett. 2012 3 2453 2457 This material is reprinted/adapted with permission. Copyright 2012 American Chemical Society.

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105 and/ or charge transfer processes (Figure 6 1) In addition to facilitating electronic communication be tween the two kinds of moieties, such hybrids are also anticipated to combine the desired properties of both material categories. For instance, whereas individual Ru(II) tris(bipyridine) chromophores possess relatively weak molar 4 M 1 cm 1 ), thus requiring longer path lengths for efficient light collection; large extinction coefficients are generally exhibited by conjugated polymers on both a per unit and per chain basis. Similarly, conjugated polymers, despite rapid intra and interc hain excited state tra nsport, 44,148 pose challenges due to short singlet state lifetime limiting exciton diffusion length. As a result, once designed to undergo energy transfer, hybr id architectures allow for these short lived singlet excited states to be translated into iTMC centered triplets with the lifetimes on the order of 1 s. Figure 4 1 Conjugated polymer ionic transition metal complex hybrids with controlled electronic properties. A) Energy levels of conjugated polymer ionic transition metal complex assembly building blocks B) Illustration of controlled energy and charge transfer processes in a hybrid polymeric array The focus of C hapter 4 is a polyfluorene assembly with dense Ru(II) loading in which the conjugated polymer chain acts as an efficient, multichromophoric antenna that absorbs light and transfers the photonic energy to the pendant Ru(II) complexes,

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106 resulting in a long lived excitation that can potentially be used to drive light harvesting and/or catalytic functions. This assembly serves as a model system to study conjugated poly mer pendant iTMC interactions in this general class of materials. Additionally, further insight in exciton migration pathways in such antennae is gained, as polyfluorene derivatives with low iTMC loadings and/or induced backbone aggregation are explored. 4.2 Synthesis and Characterization of Polyfluorene with High Loading of Ru(II) Chromophores 4.2.1 Design Synthesis and Structural Characterization A densely loaded p olyfluorene Ru(II) polypyridyl ( PF Ru ) hybrid was chosen as an initial system to study electronic in teractions between the conjugated polymer backbones and covalently linked pendant iTMC chromophores. This system was of interest due to the fact that that PF backbone emission and Ru(II) tris(bipyridine) MLCT absorption signatures exhibit a large overlap, which is one of the main requirements for efficient Forster resonance energy transfer. Additionally, absorption band maxima characteristic of PF and Ru (bpy) 3 MLCT transitions are centered ca. 60 nm apart, allowing for selective excitation of the two chromophores and, therefore, fewer complications in the photophysical studies. The densely loaded polyfluorene Ru(II) polypyridyl hybrid was synt hesized as shown in Schemes 4 1 and 4 2. Cu(I) assisted azide chemistry has been chosen as a versatile post polymerization functionalization method to obtain the PF Ru assembly. The concept has been introduced in 2001 b y Sharpless et al as a genera l term describing reactions that are wide in scope, high yielding, demonstrate atom economy, create easily removable byproducts and are simple to perform 149 T here are several reactions that fit thi s description and have been

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107 employed in post polymerization functionalization transformations previously, including amide coupling, thio l ene reaction, etc. Cu(I) assisted 1, 3 dipolar Huisgen cycloaddition, however, has been the most widely applied approac h in macromolecular chemistry and a wide scope of conditions has been developed to carry out such transformations. 150 152 In the case of PF Ru assembly, this method is anticipated to proceed in a benign manner, thus, not detrimentally affecting the polymer backbone or the Ru(II) polypyridyl complex. Additionally the 1,4 triazole ring result ing from this transformation is not expected to interfere with any excitonic or redox processes proceeding in the hybrid macromolecular assembly, unlike, for example, thioester moieties, which are capable of Ru(II) polypyridyl 3 MLCT excited states via a ch arge transfer mechanism 153 The building blocks of the PF Ru assembly were s ynthesized by employing multi step routes as shown in Schemes 4 1 and 4 2. Bromide containing polyfluorene precursor (compound 4 Scheme 4 1) was synthesized via the P d mediated Suzuki cross coupling 154 156 approach to obtain polymer 3 in 99 % yield. Subsequent treatment of compo und 3 with sodium azide then afforded azide functionalized precursor 4 in 96 % yield. This reactive polymer 4 was estimated to contain ca. 60 repeat units and, thus, ca. 60 reactive azide functionalities. Alkynyl containing Ru(II) alkynyl containing a m ide functionalized Ru(II) polypyridyl complex (compound 7 Scheme 4 2) was chosen as a building block of the PF Ru assembly as i n troduction of an e withdrawing amide functionality to the 4 bipyridine ligands of the Ru(II) chromophores, ha s been previously demo n strated to contribute to the excited MLCT state dipole alignment in the respective iTMC polystyrene arrays, allowing for orders of ma g nitude faster Ru* Ru

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108 interchromo phore exciton hopping rates 140 Compound 7 dimethyl bipyridine by employing selective oxidat ion procedures with SeO 2 and AgNO 3 to obtain monoacid 5 in 46% overall yield. Compound 5 was then reacted with propargyl amide under amide coupling conditions affording ligand 6 in 93 % yield. Com plex 7 was then synthesized from 6 by employing well establis hed complexation with Ru(bpy) 2 Cl 2 2 H 2 O and ion metathesis procedures in 88 % yield. Scheme 4 1 Synth e tic route s to compounds 4 and 7 Finally, azide contain ing polymer precursor 4 and alkynyl containing complex 7 were subjected to modified Cu(I) to obtain the PF Ru assembly in 91 % yield o dium ascorbate were used as the C u(I) sou rce, base/ligand and reducing agent, respectively. Additionally, an excess of NH 4 PF 6 salt was added to the rea c tion mixture to prevent the Ru(II) complex counterion exchange, leading to precipit a tion of the reaction intermediates and the consecutive inhib i tion of the click conversion. Upon completion of the reaction, essentially 100% functionaliza tion of the PF backbone with iTMC units was co n firmed using 1 H NMR and IR spectroscopies.

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109 Scheme 4 2 Synthetic route to PF Ru ( polymer 8 ) Complex 7 was reacted with 1 azido hexane to obtain chromophore 9 ( Ru Model Scheme 4 3) as a model complex for photophysical and electrochemical studies. Similarly, a zide containing polyfluorene precu r sor 7 was su with 1 octyne to obtain hexyl functionalized model polymer PF Hex ( polymer 10 Scheme 4 3). This polymer was obtained in 94 % having M n = 35.9 kDa, PDI = 1.8 Scheme 4 3 Synthetic route s to Ru Model (compound 9 ) and PF Hex ( polymer 10 )

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1 10 4.2.2 Electrochemistry The electrochemical properties of Ru Model (compound 9 Scheme 4 3) and hybrid PF Ru ( polymer 8 Scheme 4 3) were studied in 0.1 M TBAPF 6 ACN solutions using platinum button, platinum flag, and non aqueous Ag/Ag + electrode (cal i brated versus the ferrocene/ferrocenium standard redox couple) as working, counter, and reference electrodes, respectively. Anodic e le c trochemical experiment s on the PF Hex system were carried out under similar conditions in DCM solutions. Meanwhile, due to the low reduction potential of this polymer, cathodic scans were conducted in THF using Au button as the working electrode in order to access the required electrochemical window. The cyclic voltammograms, differential pulse voltamm o grams and the corresponding redox potentials for compounds PF Hex Ru Model and PF Ru are given in Figure 4 2 As can be seen in Figure 4 2A B model polymer PF Hex exhibited qua si reversible oxidation and reduction transitions with the onset values of 0.61 V (0.60 V from DPV) and 2.49 V ( 2.53 V from DPV), respectively. The corresponding DPV half wave potentials were determined to 0.81 V and 2.71 V In good agreement with elect rochemistry rules for Ru(II) polypyridyl complexes, Ru Model exhibited a single metal centered Ru 2+/3+ oxidation at 0.90 V and three well defined ligand centered reductions at 1.63 V, 1.89 V and 2.14 V As a result, cumulative electrochemical behavior o f the polymer backbone and the iTMC chromophores was expected while studying PF Ru As the PF reduction band was inaccessible using the experimental conditions required to study the hybrid assembly, both cyclic and differential pulse voltammograms of PF Ru strongly resembled those of Ru Model

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111 Figure 4 2 Electrochemical data. Cyclic voltammograms and differential pulse voltammograms of PF Hex ( A B ), Ru Model ( C D ) and PF Ru ( E F ) in 0.1 M TBAPF 6 acetonitrile, d i chlorometha ne (oxidation scans of PF Hex ) or tetrahydrofuran (reduction scans of PF Hex ) solutions Platinum or gold (reduction scans of PF Hex ) button platinum flag and non aqueous Ag/Ag + electrode (cal i brated versus the Fc/Fc + standard redox couple) were used as t he working, counter and reference electrodes, correspondingly Cyclic voltammograms were recorded at a 100 mV/s scan rate Reprinted with permission from Wang, L.; Puodziukynaite, E.; Vary, R. P.; Grumstrup, E. M.; Walczak, R. M.; Zolotarskaya, O. Y.; Scha nze, K. S.; Reynolds, J. R.; Papanikolas, J. M. J. Phys. Chem. Lett. 2012 3 2453 2457. 157 Copyright 2012 American Chemical Society In both sets of experiments, only one anodic band centered at ca. 0.9 V was characteristic of PF Ru indicati ng that the oxidations of main chain and Ru(II) chromophores were occurring at approximately the same potential. This is not

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112 unexpected, provided there was only ca. 0.1 V difference between th e half wave potentials of the separate model systems (Figure 4 2 A D ). Additionally, the bulky iTMC substituents were expected to somewhat distort the planarity and conjugation of the PF backbone even further increasing the polymer oxidation potential and m aking it essentially identical to that of the parent Ru(II) polypyridyl chromophore. The broadening of the cathodic ban ds in the case of PF Ru hybrid was also evident This is hypothesized to occur due to some heterogeneity in the local environments experi enced by the individual iTMC chromophores in the polymeric array 153 4.2.3 Spectroelectrochemistry To elucidate spectroelectrochemical properties of PF Ru and PF Hex thin films of the pol y mers studied were prepared on ITO coated glass transparent working electrodes by spin coating from either acetonitrile or chloroform solutions To achieve better electrode wetting by the polymer film PF Hex was premixed with ca. 2 0 wt % of PMMA. Spectroele ctrochemical data for PF Ru upon oxidation and reduction and for PF Hex upon oxidation are given in Figure 4 3 As is evident in Figure 4 3A, upon oxidation of the PF Hex absorption band ( max = 400 nm) decreased in intensity, and the PF + s ignal appeared at ca. 550 nm. Similar spectral changes were observed when the PF Ru film was oxidized (Figure 4 3B). In addition to the transitions due to the PF polymer backbone, the Ru(II) complex MLCT absorption band also bleached indicative of the oxid ation of the pendant iTMC units. As delineated in Chapter 3, this behavior is typical of most coordination complexes based on Ru(II) tris(bipyridine). It is noteworthy that the spectral transitions due to the oxidation of both chromophores appeared at appr oximately the same potentials supporting the trends previously observed in the corresponding

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113 electrochemical data (Figure 4 2). Upon reduction of the PF Ru assembly, a new band at ca. 540 nm appeared characteristic of the Ru(bpy) 3 in its 1+ formal redox st ate. This is in accordance with the literature data di substituted Ru(II) polypyridyl complexes general ly exhibit red shifted absor p tion bands resembling those of the 2+ state MLCT. 48,117,157 Figure 4 3 Spectroelectrochemical data. Spectroelectrochemistry data for A) PF Hex (compound 10 ) film ( prepared using 20 wt% of PMMA) upon oxidation in 0.1 M TBAPF 6 acetonitrile solution as well as that for PF Ru (compound 8 ) film upon B) oxidation and C) reduction in 0.1 M TBAPF 6 THF solution. ITO/glass, platinum flag and silver wire pseudoreference electrode were used as the working, counter and reference electrodes, correspondingly Grey lines are the absorption spectra of the polymers at the intermediate redox states. Adapted with permission from Wang, L.; Puodziukynaite, E.; Vary, R. P.; Grumstrup, E. M.; Walczak, R. M.; Zolotarskaya, O. Y.; Schanze, K. S.; Reynolds, J. R.; Papanikolas, J. M. J. Phys Chem. Lett. 2012 3 2453 2457. 157 Copyright 2012 American Chemical Society 4.2.4 Steady State Absorption, Emission and Time Resolved Photolumines c ence Steady state photophysical pro perties of PF Ru were studied in a dilute deaerated benzonitrile solution, and the spectra obtained are given in Figure 4 4 C For comparison purposes, steady state solution absorption and emission spectra for PF Hex and Ru Model are s hown in Figures 4 4 A,B Figure 4 4 D shows the integral overlap between PF Hex emission and Ru Model absorption spectra.

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114 Figure 4 4 Steady state photophysical data. Steady state UV Vis absorption, photoluminescence, and excitation spectra of A) PF Hex B) Ru Model and C) PF Ru in dilute deaerated benzonitrile or acetonitrile ( Ru Model ) solutions. D ) Integral overlap of PF Hex emission and Ru Model absorption spectra Adapted with permission from Wang, L.; Puodziukynaite, E.; Vary, R. P.; Grumstrup, E. M.; Walczak, R. M.; Zolotarskaya, O. Y.; Schanze, K. S.; Reynolds, J. R.; Papanikolas, J. M. J. Phys. Chem. Lett. 2012 3 2453 2457. 157 Copyright 2012 American Chemical Soci ety As is evident in Figure 4 4C, the absorption spectrum of PF Ru closely corresponded to a superimposition of the individual spectra for the PF (Figure 4 4A) and Ru(II) polypyridyl complex (Figure 4 4B) i.e. signals due to the transition of PF (3 90 nm), the MLCT transition of Ru(II) complex (456 nm) and the transition localized on bipyridyl (bpy) ligand (288 nm) were all present Moreover, the transitions from each component show ed little or no spectral shift, suggesting an absence of signi ficant electronic coupling between PF and Ru(II) polypyridyl complex in the ground state. It is notable that PF exhibited a remarkably high molar absorptivity (2.910 6 cm 1 M 1 ) on a per chain basis, which corresponded to an extinction coefficient of 10 5 per repeat unit being about 3 4 times greater than that of the attached Ru(II) complexes.

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115 This observation suggests a strong potential for polymer backbone assisted spectral coverage control and light harvesting by the hybrid assemblies. Whereas the absorp tion spectra indicated no signal shifts relative to those of the parent building blocks, variations emerged as the photoluminescence properties of the polymers were explored. As expected, p hoto excitation of an alkyl only functionalized polyfluorene PF Hex at 380 nm resulted in a bright blue singlet state PF* emission (quantum yield, = 0.91) with max at 410 nm (Figure 4 4 A ) The emission band showed a clear vibronic progression with = 1400 cm 1 The emission spectrum of the PF Ru system, however, was distinctly different ( Figure 4 4 C ) Upon excitation of the PF backbone at 380 nm, it showed a very weak emission band at 410 nm and an intense 640 nm 3 MLCT Ru(II) emission. The fluores cence excitation spectrum obtained while monitoring the 3 MLCT emission ( Figure 4 4 C red line) nearly reproduced the ground state absorption spectrum, suggestive of significant excitation energy transfer, as was expected based on the large integral overlap of the PF emission and Ru(II) absorption (Figure 4 4 D ). This energy transfer process can be described by the following equations: PF + h PF* ( 4 1) PF* + Ru(II) Ru(II)* + PF ( 4 2) To further investigate this finding, time resolved photoluminesce nce experiments were also employed. Lifetime profiles characteristic of PF Ru and PF Hex are shown in Figure 4 5

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116 Figure 4 5 Time resolved photoluminescence data A ) Time resol ved emission profile of PF Hex at 410 nm in tolu ene (red circles) and PF Ru at 410 nm in acetonitrile (blue) at 298 3 K. B ) Time resolved emission profile of PF Ru at 640 nm in acetonitrile at 298 3 K C mixture ( to obtain PF Ru ) before and after the reaction occurs visually illustrating energy transfer process as the conjugated and iTMC chromophores are placed at a close proximity As seen in Figure 4 5 A (red circle s) u pon excitation at 365 nm on the high energy side of the t he photoluminescen ce intensity of PF Hex in toluene decayed almost to zero within the time window of 1 ns Accordingly, the kinetics wa s adequately modeled as a single exponential decay with the lifetime of 380 ps. In contrast, for PF Ru with the excitation of the PF backbo ne at 365 nm the decay of PF* photoluminescence wa s signif i cantly attenuated ( Figure 4 5 A blue line) with the lifetime shorter than 15 ps and was convoluted with the instrument response function (I RF ) Futhermore, the rise of Ru(II) 3 MLCT emission at 640 nm was observed simultaneously, occurring on the same timescale (not plotted for clarity). This observation i s strongly indicative of ultrafast energy transfer occurring from the PF backbone to the Ru(II) chromophores on a timescale faster than the instru ment response. This energy transfer process is also visually illustrated in Figure 4 5 C where photographs of the reaction mixture (excluding Cu(I) catalyst) before and after the are

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117 given. As seen in the photographs, the ini tially dominant PF sky blue emission wa s replaced with the red phosphorescence from Ru(II) as the reaction progressed and the two chromophores we re placed at FRET distances. As shown in Fig ure 4 5 B t he lifetime profile of the 3 MLCT state of Ru(II) in th e PF Ru assembly was modeled as a bi exponential decay with 85% of a long lived 1. 0 s, component and 15% of a short lived 2 3 0 ns component. This slight deviation from the monoexponential decay with ca. 1 s lifetime characteristic of monomeric Ru(II) p olypyridyl complexes most likely arose due to the conform a tional disorder of PF in solution phase, which lead to i n homogeneou s surrounding s for the pendant Ru(II) complexes. As strong evidence of FRET was observed in both steady state and time resolved pho toluminescence experiment, t he fraction of PF* in the PF Ru assembly undergoing energy transfer ( EnT ) was estimated from quantum yield measurements using Equation 4 3 : ( 4 3) In this equation, for the PF Ru assembly, f Ru f PF were the fractions of Ru* and PF* created by 388 nm excitation, respectively. Meanwhile, t he quantum yield s observed for 640 nm emission following excitation at 388 nm were 0.095 and 0.11 for PF Ru ( PF Ru ) and Ru Model correspondingly B ased on these result s EnT was estimated to be 858%. It is noteworthy, h owever, that the excitation spectrum (Figure 4 4 C ) wa s not superimposable on the ground state absorption spectrum at < 400 nm, indicating that the fluorescence efficiency ( PF Ru ) wa s dependent on the

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118 excitation frequency. Additionally this observation provided the direct spectroscopic evidence for the onset of another non radiative decay pathway. 4.2.5 Fem tosecond Transient Absorption As delineated in the previous subsection, the rate of the excited state energy transfer in PF Ru assembly could not be extracted from the time resolved photoluminescence data due to the process rate being higher than the instrument response time. Additionally, the lack of the superimposition between the ab sorption and excitation spectra of PF Ru was indicative of another type of a non radiative decay process occurring in the system. As a result, t he early time dynamics of PF Ru and PF Hex after direct excitation of the PF backbone at 388 nm were probed usin g femtosecond transient absorption spectroscopy. The full spectra and representative kinetic trace s for both PF Hex and PF Ru dissolved in benzonitrile are shown in Figure 4 6 At t = 0, the tra nsient spectrum of PF Hex (Figure 4 6 A ) had a prompt bleach du e to the loss of the ground state of PF Hex at 380 400 nm, as well as three vibronic stimulated emission bands at 410 nm, 443 nm and 475 nm, and a broad excited state absorption band extending in the range of 500 700 nm. The decay of the 443 nm feature ( Fi gure 4 6F) indicated a PF* excited state lifetime of 370 ps. The red shift of the stimulated emission bands with increasing pump probe delay ( Figure 4 6C) most likely reflected either excited state migration a long the PF backbone as it seeked out lower en ergy segments, or the temporal evolution involving the dynamic planarization of the polymer backbone following photoexcitation.

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119 Figure 4 6 Femtosecond transient absorption data. A ) Femtosecond transient absorption spectra of PF Hex in PhCN ( exc = 388 nm ) at different delays (blue). The pump pulse energy was 25 nJ/pulse. Instrument response is 250 fs. B ) F emtosecond transient absorption spectrum of PF Ru in PhCN ( exc = 388 nm ) at different delays. T he pump pulse energy wa s 50 nJ/pulse. C ) Expanded view of the ground state bleach and stimulated emission region for PF Hex D ) Expanded view of the ground state bleach and stimulated emission of PF Ru E ) Ground state absorption (black) and emission (red) of PF Hex in benzonitr ile. F ) The decays of the transient signals at 443 nm for both PF He x and PF Ru Reprinted with permission from Wang, L.; Puodziukynaite, E.; Vary, R. P.; Grumstrup, E. M.; Walczak, R. M.; Zolotarskaya, O. Y.; Schanze, K. S.; Reynolds, J. R.; Papanikolas, J. M. J. Phys. Chem. Lett. 2012 3 2453 2457. 157 Copyright 2012 American Chemical Society The transient spectra from the PF Ru system at early times were essentially similar to th ose of PF Hex ( Figure 4 6 B ), consistent with the initial formation of the PF* state. However, in contrast to PF Hex the loss of the structured stimulated emission in

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120 PF Ru wa s much faster than that of PF Hex occurring with both fast (450 fs) and slow ( 1.5 ps) kinetic components (Fig ure 4 6 F ). As the structured P F* spectrum disappeared, it wa s replaced by bleach features centered at 406 nm and 450 nm, and a broad absorption centered at 5 50 nm. While the 450 nm bleach wa s consistent with Ru(II)* formed by energy transfer (Eq uation 4 2), the sharp 406 nm band wa s not, indicating the presence of another photoproduct channel. Figure 4 7 Transient absorption and spectroelectrochemical data. A ) Transient absorption spectrum of PF Ru in benzonitrile obtained at 1.0 ns after photoexcitation at 388 nm. The grey line, labeled A Red is the difference between the absorption spectra for the reduced and the neutral PF Ru The blue line, labeled A Ox is the diff erence between the absorption spectra of oxidized Ru(III) and PF and neutral PF Ru The red line is the sum of the oxidized and reduced difference spectra for PF Ru B ) Kinetic traces at 400 nm, 450 nm and 550 nm of PF Ru with 388 nm excitation Reprinte d with permission from Wang, L.; Puodziukynaite, E.; Vary, R. P.; Grumstrup, E. M.; Walczak, R. M.; Zolotarskaya, O. Y.; Schanze, K. S.; Reynolds, J. R.; Papanikolas, J. M. J. Phys. Chem. Lett. 2012 3 2453 2457. 157 Copyright 2012 American Chemical Society Evolution on time scales ranging from nanoseconds to microseconds, with 500 ps time resolution, was monitored by using a continuum probe pulse generated by a diode laser pumpe d photonic crystal fiber. Band assignments were made on the basis of several key observations in the spectra (Fig ure 4 7A) and kinetics (Fig ure 4 7B)

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121 obtained on the nanosecond time scale. In particular, the MLCT bleach at 450 nm and the 550 nm band decay e d on different time scales (Fig ure 4 7B ), suggesting that the visible absorption wa s not simply the Ru(II)* excited state absorption that is typically observed to the red of 500 nm. Inste ad, the 550 nm absorption decayed on the same time scale as the 406 nm bleach, indicating that the species giving rise to the two different features are kinetically correlated. In addition, s pectroelectrochemical data recorded previously (Figure 4 3 ) w ere employed to gain insight into the band assignments. Difference spect ra were obtained by subtracting the absorption spectrum of the assembly in the as cast state from the absorption signatures obtained following quantitative oxidation or reduction ( Ox = A Ox ( ) A( ) and Red = A Red ( ) A( ) respectively). These spectra are provided in Fig ure 4 7 represent ing contributions of oxidized (PF Ru(III)) and reduced (Ru(I)) species to the transient absorption spectrum. The Red spectrum exhibited a band centered at 520 nm that was assigned to Ru complex in 1+ formal redox state (referred to as Ru(I) ) Meanwhile, t Ox spectrum, revealed two bleach features at 390 nm and 450 nm that correspond ed to the loss of absorption intensity upon oxidation o f the polymer backbone and the iTMC chromophore s respectively, as well as a weak absorption of the oxidized polymer (PF ) at 540 nm. These spectra suggest ed that photoexcitation of the PF backbone also resulted in the formation of a charge separated (CS ) state by direct electron transfer from PF* to Ru(II) : PF* + Ru(II) Ru(I) + PF ( 4 4 ) The sum of the difference spectra, Ox Red depicted as the red line in Figure 4 7 A was employed to estimate the contribution of the CS state to the transient

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122 spectrum. This analysis suggested that the 550 nm visible absorption band in the transient spectrum ar ose primarily from Ru(I ), with perhaps a weak contribution from PF and the 406 nm bleach reflect ed the loss of the ground state polymer absorption upon oxidation. The kinetic correlation between the 406 nm bleach and 550 nm absorption indicated that the formation of the CS st ate du ring the first few picoseconds wa s followed by back electron transfer on the significantly slower nanosecond time scale. In the transient absorption data, the bleach feature at 450 nm wa s most ly due to Ru(II)* formed via energy transfer. However th e electrochemical measurements (Figure 4 2 ) indicate d similar oxidation potentials for PF and Ru(II), suggesting that subsequent hole transfer from the polymer to the metal complex is possible : PF + Ru(II) ( 4 5 ) As a result, the 450 nm bl each may have also contain ed contributions from Ru(III). As indicated by ultrafast spectroscopic methods, quenching of the PF* occurred through parallel energy and electron transfer mechanisms (Eq uations 4 2 and 4 4 ), both taking place on ultrafast time scales. Close inspection of the transient spectra, particularly the evolution of th e 410 nm bleach feature, enabled the disentanglement of these two processes. The position of the 410 nm feature was relatively constant during the first picosecond, but then shifted hypsochromically over the next 2 3 ps to its final positio n at 406 nm as the charge separation features we re established. Based on this observation, the faster 450 fs component was assigned to energy transfer (Equation 4 2) an d the slower 1.5 ps c omponent was associated with charge separation (Eq uation

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123 4 4 ). The other vibronic features in the PF Ru spectra at 443 and 478 nm did not show the time dependent red shift associated with expansion of the excited state and/or exciton migration that was ob served in PF Hex (Fig ure 4 6 D ), indicati ng that the PF* quenching occurred before these processes could be triggered As indicated by fs TA experiments, both energy transfer and electron transfer in PF Ru we re taking place on ultrafast time scales. While t he hybrid system was designed to undergo energy transfer, the charge transfer was somewhat unexpected. It is noteworthy, however, that this later process is beneficial from the final application standpoint, allowing for the formation of high energy redox i ntermediates that could potentially facilitate electron injection into the semiconductor interface in solar photoelectrochemical cells. As mentioned previously, rapid energy transfer is presumably the result of a large overlap between the PF emission and t he Ru(II) absorption, most likely producing a 1 MLCT excited state through a dipole dipole coupling mechanism. 58 60 Meanwhile ultrafast electron transfer is likely facilitated by a small barrier and/or a large electronic coupling. The similarity between the driving for ce ( G 0.72 eV) and estimates of the reorganization energy ( = 0.5 1.0 eV) based on dielectric continuum models and comparisons with other systems wa s evident, suggesting the possibility of a nearly activation less electron transfer process. 64 The magnitudes of the two rate constants indicate d an energy transfer efficiency, EnT = k EnT /( k EnT + k CS ), of 776% correspond ing to that determined from the emission spectra (858%). As mentioned previously, d ecay of the charge separated state in the PF Ru assembly occur red by back electron transfer on the nanosecond time scale, resulting in

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124 a decay of both the 550 nm and 406 nm bands. The decay traces we re multi exponential with both fast and slow kinetic components (Figu re 4 7 B ). The fast 5.5 6.5 ns component wa s assigned to the back electron transfer of the i nitially formed charge separation products (Equation 4 4 ). Meanwhile, t he slower component reflect ed either Ru(II)* decay or slower back electron transfer events tha t we re delayed due to potential electron or hole migration to other sites. As a result, t he 550 nm signal decayed to baseline within 0.85 s (Figure 4 7 B ), signifying a complete loss of the CS products and residual excited states. Back electron transfer co uld either result in the formation of either ground or excited state Ru(II) : Ru(I) + PF u(II) + PF, G = 2.54 eV ( 4 6 a) Ru(I) + PF G = 0.45 eV ( 4 6 b) Given the presence of Ru(II)* formed by direct excitation and also energy transfer, it is difficult to distinguish between these two processes. The large driving force for formation of ground state Ru(II) most likely places that process in the inverted regime, which would suggest excited state formation. However, formation of Ru(II)* would involve the transfer of an electron from the Ru metal, which would correspond to a longer electron transfer distance than formation of Ru(II) where the elec tron would transfer from the bipyridine ligand. 4.3 Synthesis and Character ization of Polyfluorene Assemblies Having Low Ruthenium (II) Polypyridyl Loadings: Further Insights into Excit ed State Migration in Hybrid Arrays 4.3.1 Design and Synthesis The PF Ru assembly described in the previous subsections was found to exhibit ultrafast energy and electron transfer phenomena Due t o the high iTMC loading (ca. 50% of the pendant chains) the rate constants obtained for these processes wer e

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125 associated with direct electronic interactions of the conjugated polymer and Ru(II) polypyridyl chromophores. However, t o fully understand energy /electron transfer processes in this class of assemblies, there exi sts a necessity to probe exciton migration rates along the po lymer chain. In addition, insight into the backbone conformation effect s on these phenomena would be desirable Accordingly PF Ru assembly variants with low Ru(II) loadings were designed. T he sy nthe tic routes to PF 20%Ru and PF 5%Ru in which ca. 20% and 5% of the alkyl side chains respectively, were functionalized with Ru(II) chromophores are shown in Schemes 4 4 and 4 5 The PF 20%Ru assembly (Scheme 4 5) was synthesized by subjecting the azid e containing polymer 4 (Scheme 4 1) with the mixture of complex 7 and 1 octyne in 40:6 0 molar ratio Premixing the two alkynyl containing building blocks was f ound to be a more reliable method for random functionaliz ation than sequential addition of each r eagent This is likely due to the ability of the triazole ri ng within close proximity thus affording block like polymers if the azide containing macromolecular precursor is reacted with each component s eparately Scheme 4 4 Synthetic route to PF 20%Ru

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126 Scheme 4 5 Synthetic route to PF 5%Ru The PF 5%R u assembly was obtained as depicted in Scheme 4 6. I n contrast to PF 20%Ru where the random reaction, PF 5%Ru was synthesized via macromolecular precursor 13 containing ca 5% azidoalkyl side chains Polymer 13 was obtained using random Suzuki polym erization followed by S N 2 reaction with sodium azide and then subjected to cycl oaddition with complex 7 (Scheme 4 1). The PF 5%Ru hybrid was specifically designed to undergo phase aggregation, providing insights into the effect of polymer confo rmation on the energy/charge transfer kinetics Polyfluorene phases are defined by the torsional angle between the monomers 158 phase is associated with the conformational d isorder of the phase indicates planarization and aggregation of the main chain. In the PF 5%Ru a rra y, b oth low iTMC functionalization and oc tyl side chain introduction strategies we re employed to achieve such aggregation Low transition metal com plex

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127 functionalization has previously been phase pattern in polyfluorene Iridium assemblies 83 M eanwhile octyl side chains have been documented to planarize the polymer backbone via balanced aliphatic interactions 159 4.3.2 Steady State Absorption and Emission Spectra The stead y state photophysical properties of the PF assemblies having low Ru(II) polypyridyl loadings were studied in dilute benzonitrile solutions. The absorption, emission and excitation spectra of PF 5%Ru and PF 20%Ru are given in Figure 4 8 Figure 4 8 Steady state optical data. Ground state absorption (black), excited state emi s sion ( blue ) and excitation (640 nm, red) spectra of A) PF 5%Ru and B) PF 20%Ru in benz o nitrile at 298 3 K As can be seen in Figure 4 8 A B t he absorption spec tra of PF 5%Ru and PF 20%Ru consisted of the typical PF ( 390 nm ) and Ru(II) 1 MLCT (450 nm) transitions In addition, a h ighly resolved absorption band at ca. 437 nm was evident in the case of PF 5%Ru indicating phase conformation of the PF b ackbone (Figure 4 8 B ) 83,159 Upon excitation at 390 nm t he emission spectra of PF 5%Ru and PF 20 %Ru possess ed pattern s characteristic of both the polyfluorene main chain ( ~ 420 nm) and Ru(II) units (~ 640 nm) (Figure 4 4 C ) T he emission signals from polymer backbone however, we re significantly attenuated when compared to that of PF Hex with em of 0.24 and 9.1 10 3 respectively. For both assemblies, t he excitation spectra ( mon itored =

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128 640 nm ) nearly reproduce d the ground state absorption pattern at > 400 nm with significant deviations at shorter wavelengths ( < 400 nm ) As in the case of PF Ru assembly, t his observation indicated direct energy tran s fer from PF* to Ru(II) along with another non radiative decay pat h way likely related to photoinduced charge separation. 4.3.3 Sub Nanosecond Transient Absorption The sub n ano s econd transient absorption spectr a of PF 5%Ru and PF 20 %Ru were recorded and are summarized in Figure 4 9 As can be seen in Figure 4 9 A the direct p hotoexcitation of the polymer backbon e in the PF 5%Ru assembly resulted in the ground state bleach of PF ( 360 400 nm ) Additionally, t he transient absorption spectrum also displayed stimulated emission with vibronic structure at 420, 440 and 470 nm, as well as broad transient absorption bands from 5 0 0 to 90 0 nm. The characteristi c spectral evidence of the Ru(II)* excited sta te formed by energy transfer was the MLCT contribution to the bleach at ca. 45 0 nm. The transient absorption band at 80 0 nm wa s a s signed as the triplet absorption of excit ed state PF, 105 and the signal at 590 nm was attributed to the absorption of the reduced Ru(I) a direct e lectron transfer product For PF 20%Ru the excitat ion at 388 nm of PF also resulted in energy and electron transfer with the spectroscopic evidence for both processes being the bleach of Ru(II) MLCT at 450 nm and the absorption of Ru(I) centered at 550 nm, respectively. It is noteworthy that the steady st ate and simulated emission characteristic of the PF backbone was more significantly quenched in the case of PF 20%Ru .This is consistent with the rate determining step for energy/electron transfer being the exciton migration along the polymer chain. As the loading density of Ru(II) is relatively higher in PF 20%Ru than that in PF 5%Ru the exciton migration along the backbone is anticipated

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129 to take less time to reach the favorable dipole dipole orientation and the di s tance required for the polymer iTMC inter actions. Figure 4 9 Sub nanosecond transient absorption data. Sub n anosecond transient absorption spectr a of A) PF 5%Ru and C) PF 20%Ru in Ar saturated benzonitrile solution s with ex c = 388 nm The kinetic traces of B) PF 5 %Ru and D) PF 20%Ru at 410 nm and 550 nm 4.3.4 Femtosecond Transient Absorption The early time dynamics of PF 5%Ru and PF 20 %Ru in PhCN after direct excitation of the polyfluorene backbone at 388 nm were monitored by femtosecond transient absorption spectroscop y and the data obtained are summarized in Figure 4 10 The tra n sient absorption spectra of PF 5%Ru and PF 20%Ru bore a great resemblance to that of PF Hex (Figure 4 10F) i.e. the instant ground state bleach from 380 to 400 nm, the stimulated emission at 405, 435, and 470 nm as well as the

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130 absorption in the range 500 700 nm were evident The kinetic trace s (Figure 4 10E) at 4 43 nm (PF emission) decayed with the fast and slow components of 4.5 ps and 80 ps as well as 3.8 ps and 25 ps for PF 5%Ru and PF 2 0%Ru respectively. This observation quantified the similar phenomena observed in the sub nanosecond transient absorption data, sugge sting the excited state migration along the polymer chain to a point sufficiently close to the acceptor prior to the energy transfer. Figure 4 10 Femtosecond transient absorption data. Femtosecond transient absorption spectr a of PF 5 % Ru ( A, B ) PF 20 %Ru ( C, D ) and F ) PF Hex in benzonitrile ( e xc = 388 nm ) at different d elays. E ) The d e cays of the transient absorption signals at 443 nm for PF 5 %Ru PF 20%Ru and PF Ru

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131 4.3.5 Solvent E ffects Photophysical properties of PF 5%Ru and PF 20%Ru were studied in various organic solvents in an effort to establish the effects of the main chain conformation on the exciton migration in these hybrid architectures. As shown in the ground state absorption spectra ( Figure 4 11 A ) PF 5%Ru was prone to phase formation in PhCN and THF solutions, as indicated by an absorption peak at 437 nm Only in the case of CHCl 3 did the PF backbone of the hybrid exhibit virtually no phas e. It has been well established that a more enhanced chain planarity is generally attribute d to the phase with the related emission signature showing a distinct red shift When these segments ( phase) coexist with less ordered phase domains in the same chai n, phase segments act as efficient energy traps quench ing the fluorescence from the disordered regions. 160 Accordingly, as established by employing time resolved photoluminescence experiments the fluorescence lifeti me of PF* of the PF 5%Ru assembly wa s much shorter in PhCN than in CHCl 3 Each decay exhibited biexponential profiles with the lifetime s of the fast component being 7. 0 ps (9 2 %) in PhCN and 1 3 ps (7 0 %) in CHCl 3 and t he lifetime s of slow component being 10 5 ps (8%) in PhCN and 130 ps ( 30 %) in CHCl 3 Phase conformation was shown to be favorable for the energy /electron transfer from PF* to Ru(II). With increased fractions of p hase conformation present, the quenching rate s of the PF* emission at early tim es ( indicative of energy/charge transfer processes ) decreased from 450 fs to 1 ps and 3.8 ps for chloroform, THF and PhCN solutions, respectively (Figure 4 1 1 B ).

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132 For medium loaded PF 20%Ru the phase conformation of the polymer backbone was dominant in a cetonitrile. As can be seen in Figure 4 12A, the intensity of the respective absorption peak at 437 nm from phase conform a tion was relatively high. In contrast with PF 5%Ru essentially no phase was observed for PF 20%Ru in PhCN and THF solutions. This was likely the outcome of the increased density of bulky Ru(II) complex substituents, as well as longer aliphatic side chains, disrupting aggregation Figure 4 11 Solvent dependant photophysical pro perties of PF 5%Ru A ) Solvent s effect on the phase formation in PF 5%Ru B ) Kinetic traces of fs TA in CHCl 3 PhCN and THF As mentioned previously, after the direct photoexcitation of the conjugated backbone in PF 20%Ru the exciton was first anticipa ted to migrate along the polym er chain, and then undergo energy transfer. As is evident in Figure 4 12B, the kinetic traces in PhCN and THF exhibited the same fast component of 3.7 3.8 ps, suggesting

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133 intrastrand energy migration along the chain with the ra te constant of 2.7 10 11 s 1 (1/ k ENT = 3.7 ps). Figure 4 12 Solvent depend e nt photophysical properties of PF 20 %Ru A ) Solvent effect on the phase formation of PF 20 %Ru B ) Kinetic traces in ACN, P hCN and THF 4.4 Conclusions The polyfluorene ruthenium(II) assemblies described in C hapter 4 combine functional elements of both conjugat ed polymer s and Ru(II) complexes. The polymer backbones provide light harvesting and exciton transport that enables energ y to be collected and funneled to specific locations. This energy can then be efficiently off loaded to, and exploited by, the pendant metal complexes on ultrafast timescale s (~ 500 fs) In addition, the se hybrids also demonstrate photoinduced electron tra nsfer processes ( 1 2 ps) 4.5 Synthetic Details 2,7 Dibromo 9,9 dioctylfluorene 161 2,7 dibromo 9,9 bromohexyl )fluorene ( 1 ) 162 methyl bipyridine 4 ca r boxylic acid ( 5 ) 147 and

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134 1 azidohexane 163 were synthesized as described in the corresponding literature sources. 2,7 Bis(4,4,5,5 tetramethyl 1,3,2 dioxaborolan 2 yl) 9,9 dioctylfluorene ( 2 ) 67 was synthesized via a modified literature procedure. 164 2,7 Dibromo 9,9 dioctylfluorene 161 (2.000 g, 3.65 mmol), dry KOAc (2.147 g, 21.87 mmol) and bis(pinacolato) diboron (2.778 g, 10.94 mmol) were suspended in anhydrous 1,4 dioxane (40 mL) and degassed for 45 min. Under argon, Pd(dppf)Cl 2 (0.179 mg, 0.22 mmol) was added and the content of the flask was stirred at 85 C for 12 h. The reaction mixture was cooled to room temperature, filtered, and the solvent from the filtrate was removed by rotary evaporation. The resulting residue was purified via sil ica gel column chromatography using dichloromethane :hexanes (1:2 volume ratio) as the mobile phase. The solution obtained was evaporated to dryness followed by recrystallization from ethanol/diethyl ether (diethyl ether was evaporated under a gentle nitro gen stream at room temperature to cause the recrystallization), to obtain 2 as white crystals in 68 % (1.595 g) yield. 1 H NMR (300 MHz, CDCl 3 0.62 (m, 4 H), 0.81 (t, 6 H, J = 7.1 Hz) 0.96 1.24 ( m, 20 H), 1.39 ( s, 24 H), 1.95 2.05 (m 4H ), 7.72 (d, 2H, J = 7.6 Hz), 7.75 (s 2H ), 7.81 (dd, 2 H J 1 = 7.6 Hz, J 1 = 1.0 Hz). 1 H NMR data matches that previously published in the literature. 67 Poly[(9,9 bis(6' bromohexyl)fluorene) co (9,9 bis(6' octyl)fluorene)] ( 3 ). Potassium carbonate (2M, 30 mL) in deionized water was purged under argon at reflux for approximately one hour, cooled to room temperature and stored under argon. To a 250 mL 3 neck round bottom flask containing a magnetic stir bar, and outfitted with a glass stopper, condenser, and rubber septum, was added 2,7 dibromo 9,9

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135 bromohexyl)fluorene (1) (2.78g, 4.28 mmol), 2,7 bis(4,4,5,5 tetramethyl 1,3,2 dioxaborolan 2 yl) 9,9 dioctylfluorene ( 2 ) (2.75g, 4.28 mmol), and toluene (45 mL). This mixture was purged with argon for approximately 30 min and the potassium carbonate solution was transferred to become a quiescent mixture via cannula. Tetrakis(triphenylphosphino)palladium (67 mg, 0.043 mmol) was added under argon. The mixture was immersed in an 85 C oil bath and stirred under a dynamic argon atmosphere for 15 h. The reaction was cooled to room temperature and precipitated into 50% m ethanol in water (300 mL). The solids were filtered over membran e, washed with copious amounts of 1N hydro chloric acid redissolved in hot chloroform (75 mL) ; and the resulting solution was allowed to cool to room temperature. Diethylammonium diethyldithiocarbamate (200 mg) as a palladium scavenger was added to the mix ture and after stirring for 30 min, the yellow color of the solution lightened significantly. After precipitation into acetone (300 mL ) the product was isolated as a light yellow powder in 99% ( 3. 72 g ) yield. GPC (versus polystyrene in THF ): M n = 20.0 k Da, PDI = 2.4. 1 H NMR (300 MHz, CDCl 3 ), (ppm): 0.62 2.34 (m, 54H); 3.32 (t, 4H, J = 6.8 Hz); 7.47 8.00 (m, 12H). 13 C NMR (75 MHz, CDCl 3 (ppm): 14.10, 22.61, 23.69, 23.91, 27.76, 29.06, 29.23, 30.04, 31.80, 32.62, 33.90, 40.34 (broad), 55.25, 55.37, 12 0.07, 121.32, 121.42, 126.17, 126.31, 140.05, 140.35, 140.58, 151.41, 151.84. Anal. calculated for C 54 H 70 Br 2 : C, 73.79; H, 8.03; N, 0.00; found: C, 73.49; H, 8.37; N, 0.00. Poly[(9,9 bis(6' azidohexyl)fluorene) co (9,9 bis(6' octyl)fluorene)] ( 4 ). To a solution of 3 (2.000 g, 2.28 mmol) in 120 mL of dry THF and 60 mL of dry N,N dimethylformamide ( DMF ), at room temperature sodium azide (0.470 g, 7.29 mmol)

PAGE 136

136 was added. ( Caution! Sodium azide is highly toxic and presents a severe explosion risk when shocked heated, or treated with acid. ) The mixture obtained was stirred overnight at 55 C under an argon atmosphere. The reaction mixture was cooled to room temperature and precipitated into 1 L of methanol. The solid was filtered, washed with methanol, water a nd dried. Yield of light yellow solid: 1.72 g, 94 % GPC (versus polystyrene in THF): M n = 24.5 kDa, PDI = 2.3. 1 H NMR (300 MHz, CDCl 3 0.62 2.32 (m, 54H); 3.17 (t, 4H, J = 6.8 Hz); 7.47 8.11 (m, 12H). 13 C NMR (75 MHz, CDCl 3 ), (ppm): 14.08, 22.60, 23.78, 23.89, 26.36, 28.72, 29.22, 29.50, 30.03, 31.79, 40.35 (broad), 51.33, 55.25, 55.37, 120.08, 121.31, 121.43, 126.15, 126.30 140.05, 140.35, 140.55, 151.41, 151.83 Anal. calculated for C 54 H 70 N 6 : C, 80.75; H, 8.78; N, 10.46; found: C, 80.54; H, 8.67; N, 10.44. 4' Methyl 2,2' bipyridine 4 carbonyl propargyl amine ( 6 ). 165,166 DCC (1300 methyl bipyridine 4 ca r boxylic acid ( 5 ) (900 mg, 4.20 mmol), DMAP (cat. amount), NHS ( 725 mg, 6.30 mmol), anhydrous dichloromethane (300 mL ) and anhydrous dimethylformamide (6 mL ) at 0 C under an argon atmosphere. The resulting suspension was stirred at 0 C for 1 h, allowed to warm up to room temperature and stirred at that temperature fo r 1 h. The reaction mixture was cooled down to 0 C again and propargyl amine (694 mg, 12.60 mmol) was added dropwise. The content of the flask was kept at that temperature for 1 h, allowed to warm up to room temperature, and stirred overnight under argon. The reaction mixture was then filtered, the filtrate was washed with water, saturated sodium carbonate solution, and evaporated to dryness. The resulting residue was then redissolved in ethyl acetate and filtered to remove the insoluble by product. The fil trate

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137 obtained was evaporated to dryness, redissolved in a mixture of ethyl acetate:dichloromethane in 1:1 volume ratio, and purified via two short silica plugs. The resulting solution was then brought to dryness by rotary evaporation followed by precipit ation from dichloromethane in to hexanes to afford white crystals in 93 % (981 mg) yield. 1 H NMR (300 MHz, CDCl 3 J = 2.6 Hz), 2.43 (s, 3H), 4.28 (dd, 2H, J 1 = 5.1 Hz, J 2 = 2.6 Hz), 7.00 (bs, 1H); 7.16 (ddd, 1H, J 1 = 5.1 Hz, J 2 = 1.7 H z, J 3 = 0.9 Hz), 7.76 (dd, 1H, J 1 = 5.1 Hz, J 2 = 1.7 Hz), 8.24 (dd, 1H, J 1 = 1.7 Hz, J 2 = 0.9 Hz), 8.51 (d, 1H, J = 5.1 Hz), 8.81 (br.s, 1H), 8.63 (dd, 1H, J 1 = 1.7 Hz, J 2 = 0.9 Hz). 13 C NMR (75 MHz, CDCl 3 21.17, 29.82, 72.22, 78.85, 117.39, 12 1.71, 122.13, 125.23, 141.78, 148.44, 148.88, 150.07, 154.85, 156.99, 165.28. ESI TOF MS m/z calculated for C 15 H 13 N 3 O+H + [M+H + ]: 252.1131, found: 252.1138. 2 ( 4' Methyl 2,2' bipyridine 4 carbonyl propargyl amine )](PF 6 ) 2 ( 7 ). 166 Compound 6 (230 mg, 0.92 mmol), Ru(bpy) 2 Cl 2 2H 2 O (500 mg, 0.96 mmol), and 50 mL of ethanol were combined in a flask and degassed for 20 min. The solution was then stirred at reflux under an argon atmosphere for 24 hours. The reaction mixture was then allowed to cool to room temperature, brought to dryness by rotary evaporation redissolved in 40 mL of water, and washed with dichloromethane. The aqueous phase was then subject ed to a gentle nitrogen stream to evaporate any leftover dichloromethane. To the resulting solution ammonium hexafluorophosphate (ca. 1 g ) was added upon vigorous stirring, and the resulting precipitate was filtered, washed with water and dried. The solid obtained was then purified via neutral alumina gel column chromatography using acetonitrile:toluene in 1:1 volume ratio as a mobile phase. The solution of the desired product was brought to dryness by rotary

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138 evaporation redissolved in acetone, and precipi tated in diethyl ether. The resulting orange precipitate was collected by vacuum filtration and dried. Yield: 773 mg, 88 % 1 H NMR (300 MHz, acetonitrile d 3 2.53 (t, 1H, J = 2.6 Hz); 2.56 (s, 3H); 4.19 (dd, 2H, J 1 = 5.4 Hz, J 2 = 2.6 Hz); 7.28 (d d, 1H, J 1 = 5.7 Hz, J 2 = 1.0 Hz); 7.36 7.43 (m, 4H); 7.56 (d, 1H, J = 5.7 Hz); 7.63 (dd, 1H, J 1 = 6.0 Hz, J 2 = 2.0 Hz); 7.68 7.76 (bm, 5H), 7.87 (d, 1H, J = 6.0 Hz); 8.03 8.09 (m, 4H); 8.50 (d, 5H, J = 7.4 Hz); 8.77 (d, 1H, J = 1.5 Hz). 13 C NMR (75 MHz, a cetonitrile d 3 21.31, 30.12, 72.54, 80.55, 122.61, 125.32, 125.45, 126.60, 128.62, 128.68, 129.82, 138.93, 138.97, 142.74, 151.78, 151.89, 152.61, 152.69, 152.73, 152.79, 153.57, 156.96, 157.84, 157.96, 158.01, 158.04, 159.14, 164.19. ESI TOF MS m/z calculat ed for C 35 H 29 N 7 ORu 2+ PF 6 [M 1+ ]: 810.1123, found: 810.1134. PF Ru ( 8 ) Polymer 4 (50.0 mg, 0.062 mmol), complex 7 (142.6 mg, 0.149 mmol), PMDETA (25.9 mg, 0.149 mmol), sodium ascorbate (14.8 mg, 0.075 mmol), NH 4 PF 6 ( ca. 2 g), THF (50 mL ), and DMF (20 mL ) w ere combined in a round bottom flask and degassed for 30 min (argon purging) After the addition of CuBr (21.4 mg, 0.149 mmol), the content of the flask was further degassed for 10 more min and stirred at room temperature for 48 h under an argon atmosphere (the photoluminescence of the solution gradually changed from blue to red when illuminated with a long wave length UV lamp). Under argon, additional compound 7 (71.3 mg, 0.075 mmol), PMDETA (13.0 mg, 0.075 mmol), sodium ascorbate (7.4 mg, 0.037 mmol) and C uBr (10.7 mg, 0.075 mmol) were added to the reaction mixture and the solution was further stirred for 24 h. After the completion of the reaction (FT IR control : azide signal at ca. 2095 cm 1 disappear ed ), the reaction mixture was subjected to a gentle nitr ogen stream

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139 to evaporate the THF and the remaining solution was precipitated into water containing ca. 0.5 g of NH 4 PF 6 The resulting precipitate was collected by vacuum filtration and washed with water, methanol and THF The solid obtained was dissolved i n a small amount of acetonitrile; the resulting solution was filtered through a 0.45 m Whatman syringe filter to remove an insoluble impurity and evaporated to dryness. The remaining residue was then redissolved in 50 mL of HPLC grade acetone containing ca. 2 mL of PMDETA and ca. 0.5 g of NH 4 PF 6 stirred for 1 h, precipitated upon additio n of deionized water (ca. 100 mL) and collected by vacuum filtration. The procedure was repeated two more times (excluding PMDETA addition and reducing the stirring time to 20 min), and the red precipitate was collected by filtration, wa shed with water, me thanol and diethyl ether and dried u nder vacuum. Yield: 153.0 mg, 91%. 1 H NMR (300 MHz, acetone d 6 ), (ppm): 0.60 2.34 (m, 54H); 2.55 (bs, 6H); 4.24 (bs, 4H); 4.62 (bs, 4H); 7.27 9.27 (m, 60H). Anal. calculated for C 124 H 128 F 24 N 20 O 2 P 4 Ru 2 : C, 54.91; H, 4.76; N, 10.33; found: C, 55.47; H, 4.97; N, 9.64. Ru Model ( 9 ). Complex 7 (60 mg, 0.063 mmol), 1 azidoh exane 163 (40 mg, 0.315 mmol), PMDETA (11 mg, 0.063 mmol), sodium ascorbate (12 mg, 0.063 mmol) and DMF (6 mL) were combined in a round bottom flask and degassed for 20 min (argon purging). CuBr (9 mg, 0.063 mmol) was then added to the reaction mixture under argon and the content of the flask was further degassed for 20 min. The resulting solution was stirred for 24 h at room temperature under argon followed by precipitation into an aqueous NH 4 PF 6 solution. The resulting solid was collected via vacuum filtration, dried, redissolved in acetone, and purified via a neutral alumina plug (prepared in a Pasteur pipet). The resulting solution was concentrated and reprecipitated into diethyl ether to

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140 obtain orange red precipitate after vacuum filtration. Yield: 61 mg, 89 % 1 H NMR (300 MHz, acetonitrile d 3 J = 7.1 Hz); 1.21 1.31 (m, 6H); 1.83 (p, 2H, J = 7.1 Hz); 2.55 (s, 3H); 4.31 (t, 2H, J = 7.1 Hz); 4.64 (d, 2H, J = 5.7 Hz); 7.27 (dd, 1H, J 1 = 5.7 Hz, J 2 = 0.9 Hz); 7.35 7.42 (m, 4H); 7.56 (d, 1H, J = 6.0 Hz); 7.64 (dd, 1H, J 1 = 6.0 Hz, J 2 = 2.0 Hz); 7.68 7.74 (m, 5H), 7.84 7.92 (m, 2H); 8.02 8.09 (m, 4H); 8.50 (d, 5H, J = 8.2 Hz); 8.78 (d, 1H, J = 1.4 Hz). 13 C NMR (75 MHz, acetonitrile d 3 14.31, 21.31, 23.21, 26.79, 30.98, 31.89, 36.35, 50.90, 122.59, 123.70, 125.32, 125. 50, 126.58, 128.60, 128.66, 129.78, 138.92, 143.18, 145.02, 151.76, 151.89, 152.63, 152.71, 152.79, 153.49, 157.00, 157.84, 157.96, 158.01, 158.04, 159.06, 164.21. ESI TOF MS m/z calculated for C 41 H 42 N 10 ORu 2+ PF 6 [M + ]: 937.2234, found: 937.2251. PF Hex ( 10 ). To a solution of 4 ( 217 mg, 0.27 mmol) in 40 mL of dry THF 88 mg of 1 octyne (0.8 mmol) and 0.22 mL (1.1 mmol) of PMDETA w ere added. The reaction mixture was degassed for 30 min followed by the addition of 103 m g (0.54 mmol) of CuI. The reaction mixt ure was stirred at 35 C for 48 h under argon atmosphere, cooled down to room temperature, and poured into 200 mL of diethyl ether The resulting precipitate was collected by vacuum filtration and dried. To remove trace copper impurities, a solution of 10 in 10 mL of DCM was stirred vigorously with 10% aqueous solution of ammonium EDTA overnight. The organic fraction was collected and evaporated to dryness by rotary evaporation. The remaining residue was re dissolved in THF, and precipitated into diethyl eth er The precipitate was collected by filtration dried. Yield of light yellow solid: 224 mg, 81 % GPC (versus polystyrene in THF): M n = 35.9 kDa, PDI = 1.8. 1 H NMR (300 MHz, CDCl 3 ), (ppm): 0.62 2.33 (m, 76H); 2.67 (t, 4H, J = 7.6 Hz); 4.18 (t, 4H, J = 6. 8 Hz); 7.13 (s, 2H), 7.47 8.02 (m, 12H). 13 C NMR (75 MHz,

PAGE 141

141 CDCl 3 14.04, 14.07, 22.53, 22.57, 23.82 (broad), 25.65, 26.24, 28.90, 29.18, 29.41, 29.98, 30.23, 31.53, 31.77, 40.36 (broad), 49.96, 55.22, 55.37, 120.18, 121.33 (broad), 126.25 (broad), 140.03, 140.23, 140.50, 148.31, 151.30, 151.81 Anal. calculated for C 70 H 98 N 6 : C, 82.14; H, 9.65; N, 8.21; found: C, 81.84; H, 10.05; N, 8.12. PF 20%Ru ( 11 ) Polymer 4 (50.0 mg, 0.062 mmol), complex 7 (28.5 mg, 0.030 mmol), 1 octyne (13.2 mg, 0.120 mmol), PMDETA (25.9 mg, 0.149 mmol), sodium ascorbate (14.8 mg, 0.075 mmol), NH 4 PF 6 (ca. 2 g), THF (50 mL), and DMF (20 mL) were combined in a round bottom flask and degassed for 30 min (argon purging). After the addition of CuBr (21.4 mg, 0.149 mmol), the conte nt of the flask was further degassed for 10 more min and stirred at room temperature for 48 h under an argon atmosphere. Under argon, additional CuBr (10.7 mg, 0.075 mmol), PMDETA (13.0 mg, 0.075 mmol), sodium ascorbate (7.4 mg, 0.037 mmol) and 1 octyne (6 .6 mg, 0.060 mmol) were added to the reaction mixture and the solution was further stirred for 24 h. After the completion of the reaction (FT IR control: azide signal at ca. 2095 cm 1 disappeared), the reaction mixture was subjected to a gentle nitrogen st ream to evaporate the THF and the remaining solution was precipitated into water containing ca. 0.5 g of NH 4 PF 6 The resulting precipitate was collected by vacuum filtration and washed with water and methanol. The solid obtained was dissolved in a small am ount of THF; the resulting solution was filtered through a 0.45 m Whatman syringe filter to remove an insoluble impurity. To the DM F solution ca. 0.5 mL of PMDETA and ca. 0.2 g of NH 4 PF 6 were added, the resulting mixture was stirred for 1 h, precipitated upon addition of deionized water (ca. 100 mL) and collected by v acuum filtration. The resulting solid was redissolved in a small amount of DM F and precipitated into ca. 1:1

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142 methanol:water mixture two more times. The light orange precipitate was collected by filtration, washed with water, methanol and diethyl ether, and dried under vacuum. Yield:76 mg, 90 % 1 H NMR (300 MHz, acetone d 6 ), (ppm): 0.60 2.3 6 (m, 67.2 H); 2.5 7 (bs, 4.8 H); 4. 36 (bs, 4H); 4.76 (bs, 1.6H); 7.24 9.32 (m, 32.4 H). Anal. c alculated: C, 71.25 ; H, 7.69; N, 8.78; found: C, 70.17; H, 6.92 ; N, 8.96 PF 5%Br ( 12 ). 2 M potassium carbonate solution was prepared as for the s ynthesis of 7 To a 100 mL 3 neck round bottom flask containing a magnetic stir bar, and outfitted with a glass stopper, condenser, and rubber septum, was added 2,7 d ibromo 9,9 dioctylfluorene (230 mg, 0.419 mmol ), 2,7 dibromo 9,9 bromohexyl)fluore ne ( 4 1 ) (30 mg, 0.047 mmol), 2,7 bis(4,4,5,5 tetramethyl 1,3,2 dioxaborolan 2 yl) 9,9 dioctylfluorene (4 2) (300 mg, 0.467 mmol), and toluene (5 mL). This mixture was purged with argon for approximately 30 min and 3 mL of the potassium carbonate solution was transferred to the reaction mixture. Tetrakis(triphenylphosphino)palladium (16 mg, 0.010 mmol) was then added under argon. The mixture was immersed in an 85 C oil bath and stirred under a dynamic argon atmosphere for 24 h. The reaction flask was the n cooled to room temperature and precipitated into methanol/acetone/1N HBr mixture (70 mL/20 mL/20 mL). The methanol The solid obtained were redissolved in a small amount of TH F and precipitated in 1:1 methanol:water solution (150 mL). The precipitate was collected by vacuum filtration, washed with water, methanol, acetone, as well as dried under vacuum. The product was isolated as a light yellow solid in 78 % (287 mg) yield. Not e: as diethylammonium diethyldithiocarbamate was observed to be somewhat reactive

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143 towards alkyl bromide functionalities of the polymer side chains, the Pd scaveng ing step was performed on the azide functionalized polymer (compound 12 ) instead. GPC (versus polystyrene in THF): M n = 12.2 kDa, PDI = 3.4. 1 H NMR (300 MHz, CDCl 3 ), (ppm): 0.62 2.3 5 (m, 33.3 H); 3.3 1 (t, 0.2 H, J = 6.8 Hz); 7.45 8.00 (m, 6 H). PF 5%N3 ( 13 ). To a solution of 12 (150 mg) in 120 mL of dry THF and 60 mL of dry DMF at room temperatur e, sodium azide (70 mg, 1.08 mmol) was added. ( Caution! Sodium azide is highly toxic and presents a severe explosion risk when shocked, heated, or treated with acid. ) The mixture obtained was stirred for 48 h at 45 C under an argon atmosphere. The reactio n mixture was cooled to room temperature and the excess THF was evaporated under vacuum. To the resulting suspension, methanol (100 mL) was added; the precipitate was collected by vacuum filtration, and washed with methanol, water and acetone. The solids o btained were then redissolved in a small amount of chloroform along with ca. 20 mg of diethylammonium diethyldithiocarbamate (Pd scavenger), stirred for 10 min, precipitated into methanol, filtered, washed with methanol, water, acetone, and dried. Finally, the solid obtained was subjected to Soxhlet extraction with methanol for 6 h to remove any remaining salts or low MW oligomers. Yield of light yellow solid: 107 g, 72 % GPC (versus polystyrene in THF): M n = 9.7 kDa, PDI = 2.2. 1 H NMR (300 MHz, CDCl 3 2.3 7 (m, 33.3 H); 3.16 (t, 0.2 H, J = 6.8 Hz); 7.45 8.11 (m, 6 H). Anal. calculated: C, 8 8.77; H, 10.22; N, 1.01 ; found: C, 8 7.90; H, 9.88; N, 0.93 PF 5%Ru (14) Polymer 4 (35.0 mg, 0.090 mmol), complex 4 7 (13 mg, 0.013 mmol), sodium ascor bate (4.9 mg, 0.025 mmol), PMDETA (8.7 mg, 0.050 mmol), NH 4 PF 6 ( ca. 0.5 g), THF (50 mL), and DMF (10 mL) were combined in a round bottom

PAGE 144

144 flask and degassed for 30 min (argon purging). After the addition of CuBr (7.2 mg, 0.050 mmol), the content of the flas k was further degassed for 10 more min and stirred at room temperature for 48 h under an argon atmosphere. Under argon, additional CuBr (3.6 mg, 0.025 mmol), compound 7 (7.0 mg, 0.007 mmol), PMDETA (4.40 mg, 0.025 mmol) and sodium ascorbate (2.5 mg, 0.012 mmol) were added to the reaction mixture and the solution was further stirred for 24 h. After the completion of the reaction (FT IR control: azide signal at ca. 2095 cm 1 disappeared), the reaction mixture was subjected to a gentle nitrogen stream to evapo rate the DM F and the remaining solution was precipitated into water containing ca. 0.5 g of NH 4 PF 6 The resulting precipitate was collected by vacuum filtration and washed with water and methanol. The solid obtained was dissolved in a small amount of DM F; the resulting solution was filtered through a 0.45 m Whatman syringe filter to remove an insoluble impurity. To the THF solution ca. 0.5 mL of PMDETA and ca. 0.2 g of NH 4 PF 6 were added, the resulting mixture was stirred stirred for 1 h, precipitated upon addition of deionized water (ca. 100 mL) and collected by vacuum filtration. The resulting solid was redissolved in a small amount of THF and precipitated into ca. 1:1 methanol:water mixture two more times. The light orange precipitate was collected by fil tration, washed with water, methanol and diethyl ether, and dried under vacuum. Yield: 31.7 mg, 72 %. 1 H NMR (300 MHz, CDCl 3 ), (ppm): 0.60 2. 28 (m, 33.3H); 2.51 (bs, 0.3H); 4.20 (bs, 0.2 H); 4. 70 (bs, 0.2 H); 7. 31 9.04 (m, 8.4 H). Anal. calculated: C, 87.60 ; H, 10.04 ; N, 0. 60; found: C, 86.12; H, 9.7 7; N, 0.85 4.6 Film Preparation The thin polymer films were spin coated on transparen t ITO/glass electrodes using a Laurell Technologies Corporation WS 400BZ 6NPP/LITE spin coater at 9500

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145 rpm for 50 sec. PF Ru films were spin coated from acetonitrile solutions (6 mg in 400 L), and PF Hex films containing 20 wt% of PMMA were spin coated fr om tetrahydrofu ra n solutions (10 mg of PF Hex and 2 mg of PMMA in 1 m L ).

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146 CHAPTER 5 ENERGY MIGRATION ALONG IONIC TRANSITION METAL COMPLEX UNITS IN POLYFLUORENE RUTHENIUM(II) POLYPYRIDYL LIGHT HARVESTING ANTENNAE 5.1 Introductory Remarks The focus of Chapter 4 was a Ru( II) loaded polyfluorene assembly exhibiting ultrafast energy and electron transfer processes. S uch PF and Ru(II) chromophore interactions could be beneficial in backbone assisted solar energy conversion However, to fully utilize large cumulative cross sec tions and induce long range charge separa tion in hybrid arrays facile energy self exchange between the pendant iTMC units is required. This exciton hopping phenomenon is enabled by the long lifetime s of Ru(II) excited st ates and has been previously observ ed in polymer ic iTMC assemblies with non conjugated polymer bac kbones. 61, 140,142,167,168 As a result, Chapter 5 of this dissertation focuses on probing exciton migration along the pendant units in conjugated polymer iTMC hybrids As a means to explore this effect, Stern Volmer amplified photoluminescence quenching experiments are employed. Additionally, Ru(II) containing PF architectures with a small fraction of low energy O s(II) chromophores are described, allowing for quantification of the hopping timescale. With application of conjugated polymer iTMC hybrids in solar photoel ectrochemical cells being the ultimate goal of this research, assemblies capable of TiO 2 surface anchoring are explored. For this purpose, th e PF Ru array is functionalized with a small fraction of ester containing Ru(II) polypyridyl pendants that act as b oth low energy chromophores and semiconductor anchors, as shown in Scheme 5 1. These macromolecular antennae are demonstrated to perform light harvesting functions when applied in conventional solar photoelectrochemical cell architecture s

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147 Figure 5 1 Illustration of an iTMC containing functional conjugated polymer adsorbed on nanocrystalline TiO 2 ( via surface chelating Ru(II) polypyridyl moieties ) 5.2 Amplified Stern Volmer Quenching of Polyfluorene Ruthenium(II) Polypyridyl As sembly Amplified quenching effect is described as a phenomenon when a photoluminescent polyelectrolyte exhibits a constant K SV than a monomeric model luminop hore 169,170 For such Stern Volmer analysis, Equation 5 1 is employed, where I 0 and I denote photoluminescence intensities before and after quencher addition and [Q] refers to the quencher concentration. I 0 /I = 1 + K sv [Q] (5 1) Oppositely charged quen cher ions with respect to polyelectrolyte are generally used to achieve ion pairing and photoluminescence attenuation in the static region Amplified quenching effect in light emitting polymeric electro ly tes is mainly attributed to exciton delocalization o ver a long distance, allowing for a single quencher molecule to interact with several adjacent re peat units participating in such delocalization ( Figure 5 2).

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148 Figure 5 2 Simplified schematic illustration of amplified quench ing effect in light emitting polyelectrolytes Adapted from Swager, T. M. Acc. Chem. Res. 1998 31 201 207 Although most studies to date have focused on backbone emission quenching in conjugated polyelectrolytes, amplified quenching effect has been demonstrated to occur in non conjugated ionic polymers with pendant chr omophores. 4,153 Based on that, PF Ru assembly and Ru Model monomer (Chapter 4) were subjected to Stern Volmer analysis using 9,10 anthraquinone 2,6 disulfon ic acid disodium salt (AQS) as an anionic quencher (Figure 5 3) For these experiments, both Ru(II) containing compounds were treated with tetrabutylammonium chloride to obtain their chloride salts with higher solubility in aqueous media Figure 5 3 Am plified quenching effect in PF Ru Stern Volmer plots for PF Ru and Ru Model along with the chemical structure of 9,10 anthraquinone 2,6 disulfon ic acid disodium salt (AQS) quencher

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149 As can be seen in Figure 5 3, linear fit s of the quenching data at low AQS concentration s gave Stern Volmer constants of 3.6 10 6 M 1 and 9.3 10 3 M 1 for PF Ru and Ru Model respectively. Based on the se results PF Ru 3 MLCT emission was quenched ca. 400 times faster indicating a strong amplified quenching effect and exciton delocalization along the pendant chromophores It is notewo rthy that the a mplification factor for PF Ru wa s comparable or higher than those observed for Ru(II) loaded polystyrene assemblies 153 5.3 Synthesis and Characterization of Ru(II) L oaded Polyfluorene Assemblies Containing Small Fractions of Low Energy Chromophores 5.3.1 Design and Synthesis Exciton hopping along pendant iTMC chromophores in the PF Ru a rra y was qualitatively demonstrated via Stern Volmer amplified quenching analysis (Figure 5 3) T o quantify this effect a variation of PF Ru assembly containing a small fraction (~ 15%) of low energy Os(II) chromophores was designed. In this array, prior to Ru(II)* Os(II) energy transfer, exciton migration along pendant Ru(II) sites was anticipa ted to occur with the hopping time scale measurable using time resolved spectroscopic techni ques. Synthesis of this architecture referred to as PF Ru OS was car ried out as shown in Schemes 5 1 and 5 2 Alkynyl containing Os(II) chromophore 2 was synthesiz ed by using sequent ial complexation of ammonium hexachloroosmate(IV) with bipyridine and ligand 4 6 in 90% and 48% yields (Scheme 5 1) Polymer PF Ru Os was then obtained under the Os(II) chrom opho res ( 85%:15% ) in 89% yield and essentially 100% conversion. As model systems, Os(II) functionalized polyfluorene ( PF Os ) and hexyl containing Os(II) t ris(bipyridine) complex ( Os Model ) were prepared as shown in Schemes 5 3 and 5 4

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150 Scheme 5 1 Synthetic route to compound 2 Scheme 5 2 Synthetic route to PF Ru Os (polymer 3 ) Scheme 5 3 Synthetic route to PF Os (polymer 4 ) Scheme 5 4 Synthetic route to Os Model (compound 5 )

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151 To exploit large cumulative optical cross sections of conjugated polymer iTMC an tennae in solar photoelectrochemical cells, PF Ru derivatives having variable fractions of ethyl ester functionalized Ru(II) chromophores were prepared. These complexes were hypothesized to fun c tion as TiO 2 surface anchor ing units following ester hydrolysi s Additionally, provided the ligand based LUMO control of Ru(II) iTMCs, these chromophores were also expected to act as lower energy sites facilitating directional energy hopping to the semiconductor interface. As a result, PF Ru analogs having ca. 10% an d 30% tetraester functionalized Ru(II) units ( PF Ru 10 %E and PF Ru 30%E respectively ) along with a model monomeric complex Ru Model E were synthesized using the based series (Schemes 5 5, 5 6 and 5 7). The yields of polymers PF Ru 10 %E and PF Ru 30%E reactive tetraester based Ru(II) tris(bipyridine) 7 was obtained using a complexation reaction between 6 and ligand 4 6 in ethylene glycol which ha d bee n previously demonstrated to catalyze this transformation. 113 Such solvent assistance was required as complex 6 possessed significantly lower reactivity caused by the electron with drawing nature of the ester substituents. Following this transformation, the crude complex 7 obtained was refluxed in eth anol to reverse any side reactions at the carboxylate sites via transesterification. Scheme 5 5 Synthetic route to compound 7

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152 Scheme 5 6 Synthetic routes to PF Ru 10%E ( 8 ) and PF Ru 30%E ( 9 ) Scheme 5 7 Synthetic route to Ru Model E (compound 10 ) 5.3.2 Electrochemistry The e lectrochemical properties of PF Ru Os PF Os Os Model PF Ru 30%E and Ru Model E were studied in 0.1 M TBAPF 6 acetonitrile solutions using platinum button, platinum flag, and non aque ous Ag/Ag + (cal i brated versus the ferrocene/ferrocenium standard redox couple) as the working, counter, and reference electrodes, respectively. The cyclic voltammograms and differential pulse voltamm o grams for all the compound s studied are given in Figures 5 4 and 5 5 and the corresponding redox potentials are summarized in Table 5 1

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153 Table 5 1 Electrochemical data for Ru Model (Chapter 4), PF Ru Os PF Os Os Model PF Ru 30%E and Ru Model E Compound Cyclic Voltammetry Diffe rential Pulse Voltammetry E 0 ox V E 0 red V E 0 ox V E 0 red V Ru Model 0.90 1.63, 1.89, 2.14 0.90 1.63, 1.89, 2.14 Os Model 0.47 1.57, 1.82, 2.12 0.47 1.57, 1.82, 2.12 PF Ru Os 0.47, 0.90 1.62, 1.81, 2.22 0.47, 0.90 1.60, 1.84, 2.19 P F Os 0.47, 0.8 9 1.57, 1.76, 2.18 0.47, 0.85 1.54, 1.77, 2.16 Ru Model E 1.10 1.34, 1.52, 1.67, 1.87, 2.16, 2.41 1.10 1.33, 1.52, 1.67, 1.86, 2.17, 2.42 PF Ru 30%E 0.90, 1.10 1.33, 1.61, 1.88, 2.23 0.90, 1.10 1.32, 1.60, 1.87, 2.21 As can be seen in cyclic and differential pulse voltammograms (Figure 5 4 Table 5 1) Os Model exhibited electrochemical behavior qualitatively similar to that of Ru Model (Chapter 4, Figure 4 2 ) with a single reversible metal centered oxidation (0 .47 V) and three ligand centered reductions ( 1.57 V, 1.82 V, 2.12 V). In accordance with the lower oxidation potential of Os metal, the oxidation transition of the monomeric complex Os Model was shifted ca. 0.4 V cathodically with respect to that of Ru Model (Table 5 1). Meanwhile, the ligand based redox band half wave potentials were essentially similar for the two complexes with deviations within 100 mV. Accordingly, oxidation signatures due to Os 2+/3+ couple at ca. 0.47 V were evident in the CVs and D PVs of PF Os and PF Ru Os Whereas in the voltammograms of PF Ru Os an oxidation band at 0.90 V contained contributions from both Ru 2+/3+ and PF/PF + redox couples, PF oxidation wave could be clearly resolved in the case of PF Os with the peak potential of 0.85 V (DPV). In analogy with Os Model lower overall electrochemical HOMO LUMO gap was observed for Ru Model E with respect to that of Ru Model (Scheme 5 5, Table 5 1). However, for the ester functionalized chromophore, this decrease in the gap energy

PAGE 154

154 mai nly resulted from the electron withdrawing substituents lowering the reduction potential of the complex. Whereas the Ru 2+ / 3+ transition of Ru Model E exhibited a ca. 0.2 V increase in the oxidation potential with respect to that of Ru Model an anodic shif t of ca. 0.3 V was observed for the ligand based Ru 2+/1+ transition. Figure 5 4 Electrochemical data for Os Model PF Os and PF Ru Os Cyclic voltammograms and differential pulse voltammograms of Os Model ( A, B ), PF Os ( C, D ) and PF Ru Os ( E, F ) in 0.1 M TBAPF 6 acetonitrile solutions. Platinum button platinum flag and non aqueous Ag/Ag + electrode (cal i brated versus the Fc/Fc + standard redox couple) were used as the working, counter and reference electrodes, correspondingly Cyclic voltammograms were recorded at a 100 mV/s scan rate

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155 Figure 5 5 Electrochemical data for Ru Model E and PF Ru 30%E Cyclic voltammograms and differential pulse voltammograms of Ru Model E ( A, B ), and PF Ru 30%E ( C, D ) in 0.1 M TBAPF 6 acetonitrile solutions. Platinum button platinum flag and non aqueous Ag/Ag + electrode (cal i brated versus the Fc/Fc + standard redox couple) were used as the working, counter and reference electrodes, correspondingly Cyclic voltammograms w ere recorded at a 100 mV/s scan rate Overall stabilization of the cathodic transitions for Ru Model E was also evident, as this complex exhibited 6 reduction waves ( 1.33 V, 1.52 V, 1.67 V, 1.86 V, 2.17 V, 2.42 V) with good reversibility. As expected, cumulative electrochemical behavior of Ru Model and Ru Model E was characteristic of the mixed PF Ru 30%E array 5.3.3 Photophysical Characterization of Osmium(II) Polypyridyl Fun c tionalized Polyfluorene Series The photophysical properties of PF Ru Os PF Os a nd Os Model were studied in deaerated acetonitrile solutions by employing steady state absorption, emission and time resolved photoluminescence measurements (Figure 5 6)

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156 Figure 5 6 Optical properties of PF Ru Os PF Os and Os Model Steady state A) absorption and C) emission spectra of PF Ru Os PF Os and Os Model in dilute Ar saturated acetonitrile solutions along with time resolved photoluminescence decays for PF Ru Os (B, D) I n addition to the well established ligand and polymer based transitions (289 nm and 395 nm) Os Model and PF Os exhibited MLCT spectral profiles strongly red shifted with respect to those of their Ru(II) analogues (Figure 5 6) T he lowest energy absorption band s of these compounds were centered at 650 nm. Mean while, Os Model and PF Os demonstrated 3 MLCT emission peaks at 762 nm with quantum efficiencies of ca. 0.3%. Such photophysical and electrochemical characteristics of Os(II) polypyridyl derivatives rendered them energy transfer acceptors when Ru(II) units were used as donors, while simultaneously allowing for separate addressab ility of the two chromophores in time resolved photophysical studies. As seen in Figures 5 6 A,C while absorption spectr um of PF Ru Os was essentially a linear superimposition of the individual building blocks, distinctio ns arose in the emission spectrum Despite ~ 40 times higher em ission quantum efficiency and

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157 significantly larger (85% :15% ) functionalization fraction of Ru(II) trisbipyridyl moieties, prominent Os(II) emission was se en in the photoluminescence spectrum of PF Ru Os hybrid Additionally, the overall quantum efficiency of the MLCT emission in this assembly was ca. 50% lower than that for PF Ru indicating energy transfer from Ru(II) to Os(II) chromophores. This initial o bservation was further confirmed by time resolved photoluminescence measurements. When the assembly was selectively excited for Ru(II) and monitored for Os(II) photoluminescence at 780 nm, a slow rise component of ca. 20 ns was observed in the kinetic trac e This slow module could be attributed to the combined process of energy migration along Ru(II) units and Ru(II)* Os(II) energy transfer. It is interesting to note that s uch hopping timescale is comparable to that of the state of the art polystyrene syste ms (ca. 10 ns) with similar Ru(II) and Os(II) functionalization densities 61,140 indicating significant exciton delocalization along the pendant iTMC chromophores in hybrid polyfluorene iTMC assemblies. 5.3.4 Photophysical Characterization of Polyfluorene Ionic Transition Metal Assembly Series Containing Various Fractions of Ester Functionalized Ru(II) Chromophores The photophysical properties of the PF Ru 30%E PF Ru 30%E and Ru Model E were studied in dilute deaerated acetonitrile solutions by employing s teady state and time resolved UV Vis absorption and photoluminescence techniques. Graphs summarizing optical properties of these assemblies are given in Figures 5 7 and 5 8 I n compliance with the electrochemical measurements, Ru Model E exhibited ca. 20 r ed shifted steady state absorption ( max = 475 nm) when compared to Ru Model (Figure 5 7) As expected, cumulative ground state absorption behavior was characteristic of PF Ru 30%E with the transient absorption measurements revealing facile energy and elec tron transfer from PF backbone to the pendant iTMC

PAGE 158

158 chromophores. It is noteworthy, however, that the rates of energy / electron transfer processes somewhat increased with higher ester containing Ru(II) chromophore functionalization. Kinetic trace analyses of PF Ru 10% (Figure 5 8) and PF Ru 30 % (Figure 5 7) afforded e nergy and electron transfer rate constants of 250 fs and 1 ps, as well as 100 fs and 0.8 ps, respectively. In addition, the Ru(I) transient absorption signatures w ere ca. 50 nm red shifted for th e ester functionalized polymer s when compared to PF Ru possibly indi cating preferential polyfluorene backbone interaction s with the tetrasubstituted pe n dant units. While the in depth photophysical studies of these assemblies are underway, some evidence fo r directional exciton hopping to Ru(II) tetraester functionalized chromophores was observed by analyzing steady state and time resolved photoluminescence data. As can be seen in Figure 5 9, upon introduction of only ca. 10% of lower energy units, the emiss ion band of PF Ru 10%E broadened, exhibiting a significant contribution from the ester functionalized chromophore excited states. Upon further functionalization (ca. 30%), the photoluminescence of PF Ru 30% became essentially identical to that of Ru Model E ( max = 663 nm) Furthermore, PF Ru 10%E emission decay was biexponential, with ca. 50% of short 476 ns component, indicating emission quenching of regular Ru(II) chromophores. Meanwhile, PF Ru 30% photoluminescence had monoexponential decay with 1003 ns li fetime identical to that of ester functionalized model monomeric chromophore Ru Model E showing dominant emission from the lower energy units in this assembly.

PAGE 159

159 Figure 5 7 Optical data for compounds Ru Model E and PF Ru 30%E Femtosecond transient absorption spectra of A) PF Ru 30%E and B) Ru Model E in dilute Ar saturated acetonitrile solutions at different time delays along with D) the respective kinetic traces. C) Steady state absorption spectra o f Ru Model Ru Model E and PF Ru 30%E band Figure 5 8 Femtosecond transient absorption data for PF Ru 10 %E Femtosecond transient absorption spectra of PF Ru 1 0 %E in dilute Ar saturated acetonitrile solution along with the res pective kinetic trace at 420 nm

PAGE 160

160 Figure 5 9 Emission data for ester functionalized Ru(II) loaded polyfluorene assemblies. A) Steady state photoluminescence sp ectra of PF Ru PF Ru 10%E PF Ru 30%E and Ru Model E B) T ime resolved emission decays of PF Ru 10%E and PF Ru 30%E in dilute deaerated acetonitrile solutions 5.3.5 Carboxylate Functionalized Polyfluorene Ionic Transition Metal Assemblies in Solar Photoelectroc hemical Cells Finally, to explore interactions of polyfluorene based iTMC macromolecular antennae with TiO 2 semiconductor interface, PF Ru 30%E assembly was transformed in to the corresponding carboxylic acid tetrabutylammonium salt ( PF Ru 30%A ) using base mediated ester hydrolysis conditions assisted by l ithium salts ( Scheme 5 8 ) For solubility purposes, PF Ru 30%E was converted to the respective iodide salt with tetrabutylammonium iodide prior to the deprotection step. S cheme 5 8 Synthetic route to the PF Ru 30%A assembly

PAGE 161

161 Essentially quantitative hy d rolysis was observed by FT IR spectroscopy where ester signal at ca. 1723 cm 1 characteristic of ester functionalities in PF Ru 30%E disappeared after the reaction (Figure 5 10 ) Additionally, PF Ru 30%A demonstrated facile adsorption to conventional P25 TiO 2 nanoparticles and films, whereas PF Ru 30%E required prolonged exposure times (> 1 week) and base pretreated TiO 2 substrates to achieve some anchoring Figure 5 10 IR spectra of PF Ru 30% E and PF Ru 30%A and photographs of TiO 2 P25 nanoparticles before and after PF Ru 30%A absorption for 4 h Finally, PF Ru 30%A was exploited as the dye in conventional DSSC archit ectures. IPCE curve for a corresponding solar photoelectrochemical cell UV Vis absorption spectrum of the surface anchored dye, as well as SEM images of TiO 2 slides before and after PF Ru 30%A adsorption are given in Figure 5 11 As seen in Figure 5 11, s olar photoelectrochemical cells comprised of PF Ru 30% A exhibited peak IPCE value of 2 0% at 480 nm Additionally, the respective DSSCs demonstrated EQE = 0.43%, J sc = 1.31 mA/cm 2 V oc = 0.56 V and FF = 59%. Such values were not unexpected w ith the intend of this research being fundamental photonic process studies rather than highly efficient devices. Nonetheless, polymer PF Ru 30% A

PAGE 162

162 demonstrated peak APCE (APCE = IPCE/[1 10 abs ]) value of ca. 30% at 480 nm. This efficiency was higher tha n that previously re ported for a monomeric Ru(II) tris(bipyridine) dye (APCE = 20%), likely resulting from the antennae effect. A ccordingly, iTMC iTMC and polymer iTMC interactions in PF Ru 30%E anchored onto nanocrystalline TiO 2 are being further explored using femtosecond t ransient absorption techniques. These experiments are also expected to explain significant attenuation of the intense PF ground state absorption band in the IPCE curve (Figure 5 11 ). Figure 5 11 Solar photoelectrochemical ce ll characteristics. IPCE curve for a dye sensitized solar cell comprised of PF Ru 30% A as an active layer material, UV Vis absorption spectrum of the surface anchored dye, as well as SEM images of as well as SEM images of TiO 2 slides before and after PF Ru 30%A adsorption It is interesting to note that limitations of polyfluorene Ru(II) polypyridyl assemblies in conventional DSSC architectures are anticipated to arise due to their high molecular weights and potentially hindered diffusion inside TiO 2 active layers. Accordingly, future applications of such arrays are associated with nanostructured semiconducting photonic electrodes as shown in Scheme 5 1 2

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163 Figure 5 12 Illustration of functional metallopolymer assemblies adsorbe d on photonic electrode with controlled patterns. Reprinted with permission from Meyer, T.; Papanikolas, J.; Heyer, C. Catal. Lett. 2011 141 1 7 Copyright 2011 Springer 5.4 Conclusions Demonstrated in C hapter 5 are facile iTMC iTMC interactions allowing for long range exciton delocalization in conjugated polymer Ru(II) polypyridyl assemblies. Polyfluorene Ru(II) polypyridyl array is found to exhibit amplified Stern Volmer photoluminescence quenching effect with the amplification factor of 400. Additionally, Ru(II) containing polyfluorene architectures with a small fraction of low energy Os(II) chromophores are described, allowing for quantification of the hopping timescale. In these arrays, exciton migration over ca. 10 pendant iTMC units is demonstrated to o ccur within 20 ns. Finally, a family of polyfluorene ruthenium(II) polypyridyl assemblies containing various fractions of carboxylate functionalized Ru(II) units as both low energy and TiO 2 surface anchoring chromophores are studied Solar photoelectrochem ical cells comprised of these materials allow for APCE = 30% at 480 n m 5.5 Experimental Section Os(bpy) 2 Cl 2 ( 1 ) 161 and R u(deeb) 2 Cl 2 ( 5 ) 171 were synthesized as described in the corresponding literature sources.

PAGE 164

164 [ Os 2 ( 4' Methyl 2,2' bipyridine 4 carbonyl propargyl amine )](PF 6 ) 2 ( 2 ). 166 Ligand 4 6 (66.4 mg, 0. 264 mmol), Os (bpy) 2 Cl 2 (150 mg, 0.2 6 2 mmol), and 10 mL of eth ylene glycol were combined in a flask and degasse d for 20 min. The solution was stirred at 90 o C under an argon atmosphere for 24 hours. The reaction mixture was allowed to cool to room temperature, diluted with 2 0 mL of water, and washed with dichloromethane. The aqueous phase was then subjected to a gentle nitrogen stream to evaporate any leftover dichloromethane. To the resulting solution ammonium hexafluorophosphate (ca. 300 m g ) was added upon vigorous stirring, and the resulting precipitate was filtered, washed with water and dried. The solid obta ined was then purified via neutral alumina gel column chromatography using acetonitrile:toluene in 1:1 volume ratio as a mobile phase. The solution of the desired product was brought to dryness by rotary evaporation redissolved in acetone, and precipitate d in die thyl ether. The resulting dark green precipitate was collected by vacuum filtration and dried. Yield: 131 mg, 4 8%. 1 H NMR (300 MHz, acetone d 6 ), (ppm): 2.70 (s, 3H); 2. 75 (t, 1H, J = 2.6 Hz); 4. 23 (dd, 2H, J 1 = 5. 7 Hz, J 2 = 2.6 Hz); 7. 37 7.51 (m 5H); 7.74 7.81 (m, 2H); 7.93 8.03 (m, 8H); 8.15 (d, 1H, J = 6.2 Hz); 8.49 8.53 (m, 1H); 8.77 8.80 (m, 5H); 9.08 (s, 1H) ESI TOF MS m/z calculated for C 35 H 29 N 7 O Os 2+ [M 2 + ]: 377.6020, found: 377.6007 PF Ru Os (3) Polymer 4 4 (12.0 mg, 0.015 mmol), compl ex 2 (5.6 mg, 0.0054 mmol), complex 4 7 (29.2 mg, 0.0306 mmol), PMDETA (6.2 mg, 0.036 mmol), sodium ascorbate (3.6 mg, 0.018 mmol), NH 4 PF 6 (ca. 0.5 g), THF (12 mL), and DMF (6 mL) were combined in a round bottom flask and degassed for 30 min (argon purging ). After the addition of CuBr ( 5.1 mg, 0. 036 mmol), the content of the flask was further

PAGE 165

165 degassed for 10 more min and stirred at room temperature for 48 h under an argon atmosphere Under argon, additional complex 2 ( 2.8 mg, 0.0 027 mmol), complex 4 7 ( 14.6 mg, 0.0153 mmol ), PMDETA ( 3.1 mg, 0.018 mmol), sodium ascorbate (2.3 mg, 0.009 mmol) and CuBr ( 2.6 mg, 0.018 mmol) were added to the reaction mixture and the solution was further stirred for 24 h at 40 o C upon slow argon purging allowing for slow gradual THF evaporation After the completion of the reaction (FT IR control : azide signal at ca. 2095 cm 1 disappear ed ), the reaction mixture was subjected to a gentle nitrogen stream to evaporate the leftover THF and the remaining solution was precipitated into water containing ca. 0.5 g of NH 4 PF 6 The resulting precipitate was collected by vacuum filtration and washed with water, methanol and THF The solid obtained was dissolved in a small amount of acetonitrile; the resulting solution was filtered through a 0. 45 m Whatman syringe filter to remove an insoluble impurity and evaporated to dryness. The remaining residue was then redissolved in 20 mL of HPLC grade acetone containing ca. 0.5 mL of PMDETA and ca. 0.2 g of NH 4 PF 6 stirred for 1 h, precipitated upon ad dition of d eionized water (ca. 5 0 mL) and collected by vacuum filtration. The procedure was repeated two more times (excluding PMDETA addition and reducing the stirring time to 20 min), and the brown precipitate was collected by filtration, wa shed with wat er, methanol and diethyl ether and dried u nder vacuum. Yield: 36 4 mg, 89 %. 1 H NMR (300 MHz, acetone d 6 ), (ppm): 0.6 0 2.3 7 (m, 54H); 2. 52 2.60 (m 6H); 4.2 0 (bs, 4H); 4. 5 8 (bs, 4H); 7.27 9. 1 3 (m, 60H). Anal. calculated: C, 54. 40 ; H, 4.7 2; N, 10.23; found: C, 55.27; H, 5.06 ; N, 9. 4 4. PF Os ( 4 ) Polymer 4 4 ( 12 .0 mg, 0.0 15 mmol), complex 2 ( 37.4 mg, 0.036 mmo l), PMDETA ( 6.2 mg, 0. 036 mmol), sodium ascorbate ( 3.6 mg, 0.0 18 mmol),

PAGE 166

166 NH 4 PF 6 (ca. 0.5 g), THF (12 mL ), and DMF (6 mL) were combined in a round bottom flask and degassed for 30 min (argon purging). After the addition of CuBr ( 5.1 mg, 0. 036 mmol), the cont ent of the flask was further degassed for 10 more min and stirred at room temperature for 48 h under an argon atmosphere Under argon, additional compound 2 ( 18.7 mg, 0.018 mmol), PMDETA ( 3.1 mg, 0.018 mmol), sodium ascorbate (2.3 mg, 0.009 mmol) and CuBr ( 2.6 mg, 0.018 mmol) were added to the reaction mixture and the solution was further stirred for 24 h at 40 o C upon slow argon purging allowing for slow gradual THF evaporation After the completion of the reaction (FT IR control : azide signal at ca. 2095 cm 1 disappear ed ), the reaction mixture was subjected to a gentle nitrogen stream to evaporate the leftover THF and the remaining solution was precipitated into water containing ca. 0.5 g of NH 4 PF 6 The resulting precipitate was collected by vacuum filtrat ion and further purified as described for PF Ru Os (polymer 3 ). Yield: 40.1 mg, 9 3 % of dark green solid 1 H NMR (300 MHz, acetone d 6 ), (ppm): 0.60 2.32 (m, 54H); 2.61 (bs, 6H); 4.21 (bs, 4H); 4.59 (bs, 4H); 7.27 9.10 (m, 60H). Anal. calculated for C 124 H 128 F 24 N 20 O 2 P 4 Os 2 : C, 5 1.52; H, 4.46; N, 9.69 ; found: C, 5 0.68 ; H, 4.9 8 ; N, 8.8 4. Os Model ( 5 ). Complex 2 ( 66 mg, 0.063 mmol), 1 azidohexane 163 (40 mg, 0.315 mmol), PMDETA (11 mg, 0.063 mmol) and DMF (6 mL) were combined in a round bottom flask and degassed for 20 min (argon purging). CuBr (9 mg, 0.063 mmol) was then added to the reaction mixture under argon and the content of the flask was further degassed for 20 min. The resulting solution was stirred for 24 h at room temperature under argon followed by precipitation into an aqueous NH 4 PF 6 s olution. The resulting solid was collected via vacuum filtration, dried, redissolved in acetone, and purified via a

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167 neutral alumina plug (prepared in a Pasteur pipet). The resulting solution was concentrated and reprecipitated into diethyl ether to obtain dark green precipitate after vacuum filtration. Yield: 6 8 mg, 92 % 1 H NMR (300 MHz, acetonitrile d 3 (t, 3H, J = 6.8 Hz); 1.23 1.35 (m, 6H); 1.83 (p, 2H, J = 6.8 Hz); 2. 64 (s, 3H); 4.31 (t, 2H, J = 7.1 Hz); 4.64 (d, 2H, J = 5.7 Hz); 7. 19 7.91 ( m 1 8H ); 8. 48 (d, 5H, J = 7.6 Hz); 8.7 6 (d, 1H, J = 1.4 Hz). 13 C NMR (75 MHz, acetonitrile d 3 (ppm): 14.30, 21.08, 23.22, 26.80, 30.99, 31.90, 36.33, 50.92 122. 87, 123.68, 125.54 126.37 126.68, 12 9.07 1 29.15, 130.03 138. 25 138.34, 138.45, 141.96, 14 5.0 8, 151.21, 151.33, 151.70, 151.77, 151.98, 152.03, 152.40, 159.04, 159.62, 159.79, 160.07, 161.09, 163.99 ESI TOF MS m/z calculated for C 41 H 42 N 10 O Os 2+ PF 6 [M + ]: 1027.2797 found: 1027.2813 [ Ru ( deeb ) 2 ( 4' Methyl 2,2' bipyridine 4 carbonyl propargyl amine ) ] (PF 6 ) 2 ( 7 ). Ligand 4 6 ( 97.6 mg, 0. 388 mmol), Ru(deeb ) 2 Cl 2 ( 8 ) (300 mg, 0. 388 mmol), and 2 0 mL of ethylene glycol were combined in a flask and degassed for 20 min. The solution was stirred at 6 0 o C under an argon atmosphere for 60 hours. The reaction mixture was allowed to cool to room temperature, diluted with 8 0 mL of water, and washed wit h dichloromethane. The aqueous phase was then subjected to a gentle nitrogen stream to evaporate any leftover dichloromethane. To the resulting solution ammonium hexafluorophosphate (ca. 6 00 mg ) was added upon vigorous stirring, and the resulting precipit ate was filtered, washed with water and dried. The solid obtained was then refluxed in ethanol for 24 h under argon, cooled down, brought to dryness by rotary evaporation redissolved in acetone, and precipitated in aqueous NH 4 PF 6 solution. The resulting p recipitate was collected by vacuum filtration, dried, redissolved in acetone and reprecipitated in die thyl ether. The resulting brownish red precipitate was collected

PAGE 168

168 by vacuum filtration and dried. Yield: 367 mg, 76 %. 1 H NMR (300 MHz, acetone d 6 ), (ppm): 1.35 1.41 (m, 12H), 2.61 (s, 3H); 2.75 (t, 1H, J = 2. 3 Hz); 4. 22 (dd, 2H, J 1 = 5.4 Hz, J 2 = 2.6 Hz); 4.42 4.50 (m, 8H), 7.44 7.47 (m, 1H), 7.88 8.01 (m, 6H), 8.25 8.41 (m, 5H), 8.93 (s, 2H), 9.23 9.36 (m, 5H) ESI TOF MS m/z calculated for C 47 H 45 N 7 O 9 Ru 2+ [M 2 + ]: 476.6162, found: 476.6157 PF Ru 10%E ( 8 ) Polymer 4 4 (12.0 mg, 0.015 mmol), complex 7 (4.5 mg, 0.0036 mmol), complex 4 7 (30.8 mg, 0.032 mmol), PMDETA (6.2 mg, 0.036 mmol), sodium ascorbate (3.6 mg, 0.018 mmol), NH 4 PF 6 (ca. 0.5 g), THF (12 mL), and DMF (6 mL) were combined in a round bottom flask and degassed for 30 min (argon purging). After the addition of CuBr ( 5.1 mg, 0. 036 mmol), the content of the flask was further degassed for 10 more min and stirred at room temperature for 48 h unde r an argon atmosphere Under argon, additional complex 7 ( 2.3 mg, 0.0018 mmol), complex 4 7 ( 15.4 mg, 0.016 mmol) PMDETA ( 3.1 mg, 0.018 mmol), sodium ascorbate (2.3 mg, 0.009 mmol) and CuBr ( 2.6 mg, 0.018 mmol) were added to the reaction mixture and the s olution was further stirred for 24 h at 40 o C upon slow argon purging allowing for slow gradual THF evaporation After the completion of the reaction (FT IR control : azide signal at ca. 2095 cm 1 disappear ed ), the reaction mixture was subjected to a gentle nitrogen stream to evaporate the leftover THF and the remaining solution was precipitated into water containing ca. 0.5 g of NH 4 PF 6 The resulting precipitate was collected by vacuum filtration and further purified as described for PF Ru Os (polymer 3 ). Y ield: 36.4 mg, 88 % of dark red solid 1 H NMR (300 MHz, acetone d 6 ), (ppm): 0.60 2.34 (m, 5 6.4 H); 2.56 (bs, 6H); 4.24 (bs, 4H); 4.44 (bs, 1.6 H); 4.63 (bs, 4H); 7.28

PAGE 169

169 9.40 (m, 5 9.2 H). Anal. calculated: C, 54. 82; H, 4.77 ; N, 10. 15 ; found: C, 55. 59; H, 4.98 ; N, 9. 46 PF Ru 30%E ( 9 ) Polymer 4 4 (12.0 mg, 0.015 mmol), complex 7 ( 13.4 mg, 0.011 mmol), complex 4 7 ( 24.0 mg, 0.0 25 mmol), PMDETA (6.2 mg, 0.036 mmol), sodium ascorbate (3.6 mg, 0.018 mmol), NH 4 PF 6 (ca. 0.5 g), THF (12 mL), and DMF (6 mL) were combined in a round bottom flask and degassed for 30 min (argon purging). After the addition of CuBr ( 5.1 mg, 0. 036 mmol), the content of the flask was further degassed for 10 more min and stirred at room temperature for 48 h under an argon atmosphere Under argon, additional complex 5 ( 6.7 mg, 0.006 mmol), complex 4 7 ( 12.0 mg, 0.013 mmol) PMDETA ( 3.1 mg, 0.018 mmol), sodium ascorbate (2.3 mg, 0.009 mmol) and CuBr ( 2.6 mg, 0.018 mmol) were added to the reaction mixture and the solution was further stirred for 24 h at 40 o C upon slow argon purging allowing for slow gradual THF e vaporation After the completion of the reaction (FT IR control : azide signal at ca. 2095 cm 1 disappear ed ), the reaction mixture was subjected to a gentle nitrogen stream to evaporate the leftover THF and the remaining solution was precipitated into water containing ca. 0.5 g of NH 4 PF 6 The resulting precipitate was collected by vacuum filtration and further purified as described for PF Ru Os (polymer 3 ). Yield: 36.7 mg, 85 % of dark red solid 1 H NMR (300 MHz, acetone d 6 ), (ppm): 0.60 2.34 (m, 61 H); 2.5 6 (bs, 6H); 4.24 (bs, 4H); 4.44 (bs, 5 H); 4.6 3 (bs, 4H); 7.2 8 9. 40 (m, 58 H) Anal. calculated: C, 54. 65; H, 4.80; N, 9.79; found: C, 54.12; H, 4. 7 6; N, 9.23 Ru Model E ( 10 ). Complex 7 ( 78.3 mg, 0.063 mmol), 1 azidohexane 163 (40 mg, 0.315 mmol), PMDETA (11 mg, 0.063 mmol) and DMF (6 mL) were combined in a round bottom flask and degassed for 20 min (argon purging). CuBr (9 mg, 0.063 mmol)

PAGE 170

170 was then added to the reaction mixture under argon and the content of the flask was further degassed for 20 min. The resulting solution was stirred for 24 h a t room temperature under argon followed by precipitation into an aqueous NH 4 PF 6 solution. The resulting solid was collected via vacuum filtration dried and redissolved in a small amount acetone. A few drops of PMDETA were added to the mixture the resulti ng solution was stirred for ca. 15 min and precipitated in diethyl ether. The solid obtained was redissolved in acetonitrile and purified via a neutral alumina plug (prepared in a Pasteur pipet 1/3 of the volume ). The resulting solution was evaporated to dryness by rotary evaporation. The solid residue was then refluxed in ethanol for 24 h under argon, cooled down, brought to dryness by rotary evaporation redissolved in acetone, and precipitated in aqueous NH 4 PF 6 solution. The resulting precipitate was co llected by vacuum filtration, dried, redissolved in acetone and reprecipitated in die thyl ether. The resulting brownish red precipitate was collected by vacuum filtration and dried. Yield: 53 mg, 62% 1 H NMR (300 MHz, acetonitrile d 3 ), (ppm): 0.8 4 (t, 3H, J = 6.4 Hz); 1.21 1.31 (m, 6H); 1. 4 0 (t, 12 H, J = 6. 6 Hz); 1.8 2 (p, 2H, J = 7.1 Hz); 2.5 4 (s, 3H); 4. 29 (t, 2H, J = 7.1 Hz); 4.45 (t, 8H, J = 6.6 Hz); 4.6 3 (d, 2H, J =5.1 Hz); 7.27 (dd, 1H, J 1 = 5.7 Hz, J 2 = 0.9 Hz); 7.35 7.42 (m, 4H) ; 7.56 (d, 1H, J = 5.1 Hz); 7.27 (d, 1H, J = 5.6 Hz); 7.48 (d, 5H, J = 8.2 Hz); 7.66 7.93 ( m 1 2H) ; 8.12 (s, 1H); 8.56 (s, 1H); 8.88 9.04 (m, 5H) ESI TOF MS m/z calculated for C 53 H 58 N 7 O 9 Ru 2+ [M 2 + ]: 540.1718, found: 540.1705 PF Ru 30%A ( 11 ) Polymer 9 ( 1 8 .0 mg, 0.0 06 mmol) was dissolved in a small amount of acetonitrile and an excess of tetrabutylammonium iodide was added to induce counter ion metathesis and precipitation. The resulting red precipitate was filtered, washed with acetonitrile dried and red issolved in ca. 20 mL of methanol and

PAGE 171

171 acetonitrile mixture in 2:1 volume ration. LiI (35 mg), Bu 3 N (4 pasteur pipet drops), DBU (1 drop) and deionized water (1 drop) were added to the reaction mixture and the resulting solution was stirred at 40 o C for 4 d ays in the dark. The solution was then filtered to remove any insoluble impurities and subjected to a gentle nitrogen stream to evaporate methanol. The resulting suspension of polymer 11 in acetonitrile was then filtered to collect the red precipitate, was hed with acetonitrile and dried. Ca. 16 mg of polymer 11 was obtained. FT IR signal at ca. 1732 cm 1 diminished indicating quantitative ester hydrolysis.

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172 CHAPTER 6 CONTROLLING EXCITON AND CHARGE TRANSFER IN THIOPHENE CONTAINING CONJUGATED POLYMER RUTHENIUM(II) P OLYPYRIDYL ASSEMBLIES 6.1 Introductory Remarks Ru(II) loaded polyfluorene asse m blies described in Chapters 4 and 5, represent a new concept in light harvesting materials merging together the photophysical properties of ionic transition metal complexes and con jugated polymers. In these macromolecular antennae ultrafast energy and electron transfer processes occur from the conjugated main chain to the pendant chromophores resulting in the formation of either high energy redox intermediates or long lived iTMC ex cited states thus allowing for extended exciton diffusion lengths. However, whereas such polyfluorene R u(II) tri s ( bipyridyl ) hybrid s essentially serve as model system s that provi d e insight into the excitonic processes in th e general class of iTMC conjugat ed polymer assemblies, the lim i tations of th ese scaffold s arise due to the high energy gap of the polymer backbone Polyfluorene exhibits an absorption band positioned at around 390 nm, where the solar emission spectrum is limited. Additio n ally, energy tra nsfer process is the dominant photophysical phenomenon in th ese a s semblies ; while electron transfer leading to high energy redox intermediates accounts for only ca. 15% of the total energy a b sorbed by the polymer backbone. To fully utilize and understand t he light harvesting potential of hybrid conjugated polymer iTMC assemblies, inducing a bathochr o mic shift in the polymer absorption becomes a necessity Additionally, to ultimately e x plore such hybrids as catalytic scaffold building blocks in solar fuel de vices, control of energy transfer and charge separation fractions is of particu l ar impo r tance. C hapter 6 describes a new family of Ru(II) based polymeric arrays containing conjugated polymer backbones based on poly(fluorene co thiophene s ) and regioregular (rr) poly(3

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173 alkylthiophene). In these assemblies, the optical and electronic properties of the polymer backbones are co n trolled by incorporation of various fractions of electron rich thiophene units leading to an increased fraction of charge separation A d ditionally, due to the high hole mobility of rr poly (3 alkylthiophene) derivatives a strong emphasis is placed on suppressing back electron transfer in the respective iTMC arrays via hole delocalization on th e conjugated polymer backbone. 6.2 Synthesis and Ch aracterization of Thiophene Containing Conjugated Polymer Ruthenium(I I) Polypyridyl Assemblies 6.2.1 Design, Synthesis and Structural Characterization Ru(II) loaded assemblies based on poly(fluorene co thiophene) ( PFT Ru ), poly(bithiophene co fluorene) ( PF 2 T Ru ) and poly(3 alkylthiophene) ( P T Ru ) backbones were obtained u sing multi step route s as shown in Schemes 6 1, 6 2, and 6 3 Among the key steps to prepare these hybrid arrays, metal mediated polymerization As in the case of polyfluorene, bromide functionalized (fluorene co thiophene) based polymer precursors 3 and 8 were synthesized via a Pd mediated Suzuki cross coupling a p proach with the yields of their chloroform soluble fractions being 58 % and 70 % respective ly. Dibrominated bithiophene monomer 7 required for the synthesis of polymer 8 was obtained by employing the Pd catalyzed C H homocoupling 172,173 of 2 bromo 3 octylthiophene as delineated in the experimental subsection of Chapter 6 Meanwhile, Ni mediated Grignard metathesis polymerization (GRIM) was employed to obtain regioregular bromide functionalized poly (3 alkyl thiophene ) 174 177 homopolymer 1 4 in 46% yield. The required monomer 2,5 dibromo 3 (6 bromohexyl)thiophene for this polymerization was obtained using the hydroquinone monomethyl ether protection /deprotection 178 and NBS

PAGE 174

174 bromination 179 procedures essentially similar to those previously reported in the literature (experimental subsection) Scheme 6 1 Synthetic routes to PFT R u (Polymer 5 ) and PFT Hex (Polymer 6 ) Scheme 6 2 Synthetic routes to PF2T Ru (Polymer 10 ) and PF2T Hex (Polymer 11 )

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175 Schem e 6 3 Synthetic routes to PT Ru (Polymer 1 6 ) and PT Br (Polymer 1 4 ) All the bromide containing polymer precursors obtained were treated with sodium azide to prepare 4 9 and 15 (Schemes 6 1, 6 2 and 6 3) The se reactive polyme rs, due to their inc reased sensitivity to azide cross linking, 180 were immed i ately subjected to the Cu(I) an alkynyl containing a m ide functionalized Ru(II) polypyridyl complex (Chapter 4 compound 7 ) using conditions similar to those previously employed to obtain PF Ru (Chapter 4 compound 8 ) In all three cases, quantitative functionaliz a tion of PFT, PF 2 T and PT backbones with iTMC units was confirmed using 1 H NMR and IR spectroscopies Azide containing precu r sors PFT N 3 ( 4 ) and PF2T N 3 ( 9 ) were also reacted with 1 octyne to obtain hexyl fu n ctionalized model polymers PFT Hex and PF2T Hex (Schemes 6 1 and 6 2 ) I n the case of the regioregular poly(3 alkylthi o phene) family, PT Br (polymer 14 ) (Scheme 6 3) was chosen as a model polymer for photophysical and electrochemical studies. 6.2.2 Electrochemistry The electrochemical properties of hybrids PFT Ru PF2T Ru and PT Ru were studied in 0.1 M tetrabutylammonium hexafluor o phosphate (TBAPF 6 ) aceton itrile solutions using platinum button, platinum flag, and non aqueous Ag/Ag + electrode (cal i brated versus the Fc / Fc + standard redox couple) as the working, counter, and reference electrodes, respectively. Ele c trochemical experiments on PFT Hex and

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176 PF2T He x systems were carried out under similar conditions in DCM and THF for the oxidation and reduction scans respective ly, while PF Br was studied in THF solutions. The cyclic voltammograms and differential pulse voltamm o grams for polymers PFT Hex PF2T Hex PT Br PFT Ru PF2T Ru and PT Ru are given in Figure 6 1 R e dox potentials of the studied systems are summarized in Table 6 1 As can be seen in Figure 2 A B in CV and DPV experiments, PFT Hex PF2T Hex and PT Br systems exhibited reversible oxidation and reduction processes with the potentials of 0.45 V and 2.37 V, 0.38 V and 2.37 V, as well as 0.12 V and 2.24 V for PFT Hex PF2T Hex and PT Br scaffolds, respectively. The observed 70 mV and 330 mV cathodically shifted oxidation potential s were characte ristic of PF2T Hex and PT Br correspondingly, consistent with the more electron rich character of the polymer backbone s As expected, hybrid systems PFT Hex PF2T Hex and PT Br exhibited cumulative electrochemical behavior of both pendant Ru(II) polypyrid yl complexes and polymer backbones. As a result, each cyclic voltammogram contained a single reversible metal centered Ru 2+/3+ oxidation wave at ca. 0.9 V along with polymer backbone oxidation transitions with irreversibility caused by overoxidation upon h igh scanning potentials utilized to study the overall behavior of the assemblies. Forward cathodic scans revealed three ligand based iTMC reduction waves for PFT Ru and PF2T Ru essentially similar to those of the parent Ru(II) complex. 157 The lack of band definition and limited reversibility of the reduction transitions upon the reverse cathodic scans for the polymer hybrids were hypothesized to arise due to high density and het erogeneity of pendant iTMC chromophores, likely resulting in

PAGE 177

177 mixed valence states, aggregation owing to partial reduction of the assembly, or different local environments felt by separate iTMC units of the macromolecule. Similar observations were previousl y made for polystyrene ruthenium(II) polypyridyl systems with high iTMC functionalization density. 153 Figure 6 1 Electrochemical data. Cyclic voltammogram s and differen tial pulse voltammograms of A) PFT Hex and C) PF2T Hex in 0.1 M TBAPF 6 d i chloromethane (oxidation scans) or THF (reduction s c ans) solutions, those of E) PT Br in 0.1 M TBAPF 6 THF solutions as well as those of B) PFT Ru D) PF2T Ru and F) PT Ru in 0.1 M TB APF 6 acet onitrile solutions Platinum button, platinum flag and non aqueous Ag/Ag + electrode (cal i brated versus the Fc/Fc + standard redox couple) were used as the working, counter and reference electrodes, respectivel y Cyclic voltammograms were recorded a t a 100 mV/s scan rate

PAGE 178

178 Table 6 1 Electrochemical data for PFT Hex PF2T Hex PT Br PFT Ru PF2T Ru and PT Ru DPV values are g iven in parentheses Compound E 0 ox V E 0 red V PFT Hex 0.45 a (0.45 a ) 2.46 a ( 2.37 a ) PF2T Hex 0.38 a (0.37 a ) 2.37 a ( 2.37 a ) PF Br 0.12 a (0.12 a ) 2.25 a ( 2.24 a ) PFT Ru 0.59 a 0.90 (0.57 a 0.90) 1.67 b 1.83 b 2.26 b ( 1.61) PF2T Ru 0.49 a 0.90 (0.46 a 0.90) 1.63 b 1.84 b 2.26 b ( 1.60) PT Ru 0.29 a 0.90 (0.27 a 0.90) 1.62, 1.79, 2.27 ( 1.59) a Onset values of redox transitions. b Peak values of forward cathodic scans. 6.2.3 In S itu Spectroelectrochemistry I n situ spectroelectrochemical studies were employed to eluc i date the properties of the polymer backbone oxidized and iTMC chromophore reduced stat es, as these states are antic i pated to be the products of photoinduced charge separa tion. For spectroelectrochemical studies, thin films of the pol y mers were prepared on transparent ITO coated glass working electrodes by either spin coating from acetonitri le solutions ( PFT Ru PFT Ru and PF Ru ) or drop casting from THF or toluene solutions. Changes in the polymer film absorption were monitored as they were subjected to linear sweep voltammetry scans. Spectroele c trochemistry plots for all the polymer s studie d are given in Fi g ure 6 2 U pon oxidation of PFT Hex PF2T Hex and PT Ru visible region absorption signa tures a p peared at ca. 560 nm, 610 nm and 840 nm, respectively (Figure 6 2A,D,G) A moderate 50 nm and significant 280 nm red shift in the oxidized stat e absorption peak s of PF2T Hex and PT Br with respect to that of PFT Hex can be attrib uted to an increase in charge carrier delocalization and, poss i bly, overall stabilization of the oxidized states. Similar trends were observed upon oxidation of PFT Ru P F2T Ru and PT Br where the polymer backbone polaron signals arose at ca. 585 nm, 630 nm and 765 nm, respectively.

PAGE 179

179 Figure 6 2 Spectroelectrochemical data. Spectroelectrochemi cal data for A) PFT Hex D) PF2T Hex and G) PT Br f ilms immersed in 0.1 M TBAPF 6 acetonitrile solution s as well as PFT Ru ( B, C ) PF2T Ru (E, F) and PT Ru (H, I) films immersed in 0.1 M TBAPF 6 tetrahydrofuran solution. I TO/glass, platinum flag and silver wire pse u doreference elect rode were used as the work ing, counter and reference electrodes, respectively. Grey lines represent spectra of intermediate redox states As in the case of PF Ru spectral changes associated with the other redox transitions studied were characteristic of the pendant Ru(II) chromopho res. Further oxidation of the hybrid assemblies was accompanied by a bleach ing of the Ru (II) complex MLCT absorption bands 8,9,117 wh ile Ru(I) signal s at ca. 550 nm appeared upon reduction 48,117,157

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180 6.2.4 Steady State Photophysical Properties Photophysica l properties of PFT Ru PF2T Ru and PT Ru as well as the corresponding model polymers PFT Hex PF2T Hex and PT Br were studied by employing stea dy state UV Vis and photoluminescence spectroscopies. Normalized solution absorption and emission spectra of PFT Ru PF2T Ru PT Ru PFT Hex PF2T Hex and PT Br are given in Figure 6 3 and the optical properties of the polymers are summarized in Table 6 2 As can be seen in Figure 6 3 A model polymers PFT Hex and PF2T Hex exhibited, in principle, similar UV Vis absorption behavior with broad a b sorption bands centered around 40 5 nm. The similar absorption behavior was hypothesized to arise from opposing ste ric and electronic effects. T he presence of an additional electron rich thiophene moiety in the polymer repeat unit would be expected to generate a bathochromic shift in the ground state absorption of PF2T Hex while backbone twisting caused by the sterica lly bulky thiophene octyl chains adjacent to the fluorene units might result in a hypsochromic shift Despite the lack of shift in the peak position a slight 8 nm bath o chromic shift of the absorption band onset, as well as somewhat lower optical gap was characteristic of PF2T Hex This observation is consistent with the increased fraction of electron rich thi o phene units in the polymer backbone. Following this trend, the ground state absorption band ( max = 445 nm) of PT Br (Figure 6 3 B ) was significant ly ( ca. 40 nm ) red shift ed with respect to those of copolymers PFT Hex and PF2T Hex While the absorption properties of the two model homopolymers PFT Hex and PF2T Hex were essentially identical, m ore pronounced vari a tions emerged in the ir photo luminescence spectra. Namely, a red shift of ca 25 nm, as well as a

PAGE 181

181 correspon d i ng increase in the Stokes shift were observed for PF2T Hex (Figure 6 3 A ) This finding is indicative of more pronounced conformational relaxation of the polymer backbone upon excitation and /or excitonic ene rgy migration differences between the PFT and PF2T sca f folds. 181 Figure 6 3 Absorption and emission spectra. Normalized absorption and photoluminescence spe c tra of A) PFT Hex and PF2T Hex in dilute tetrahy drofuran sol u tions; as well as C) PFT Ru and PF2T Ru in dilute Ar saturated acetonitrile sol u tions. B) Absorption and emission spectra of PT Br and PT Ru dilute Ar saturated solutions in tetrahydrofuran and aceonitrile, respectively. D) Comparison of PT Ru and Ru Model (Chapter 4, compound 9 ) normalized emission spectra As expected, PT Br demonstrated emission at 575 nm that was the lowest in energy (Figure 6 3 B ) Polymers PFT Hex PF2T Hex and PT Br exhi bited quantum yields and singlet excited state lifetimes of 65%, 50% and 35%, as well as 380 ps, 350 ps and 580 ps, respectively.

PAGE 182

182 Absorption spectra of PFT Ru PF2T Ru and PF Ru generally rese m bled l inear combination s of the polymer backbone and Ru (II) p olypyridyl complex absorption signatures, suggesting little or no electronic ground state interactions b e tween the two components. For PFT Ru PF2T Ru (Scheme 6 3c), i n addition to the transitions of the polymer backbones at ca. 41 6 419 nm, each absorption spectra also e x hibited shou l ders at ca. 470 nm characteristic of metal to ligand charge transfer (MLCT) in Ru(II) complexes as well as the bipyridine ligand transition peaks centered at around 289 nm. Table 6 2 Optical data for compounds PFT Ru PF2T Ru PT Ru PFT Hex PF2T Hex and PT Br Compound Abs max ( nm ) [ onset ( nm)] Pl max ( nm ) PFT Hex 40 5 [454] 460 PF2T Hex 40 5 [462] 485 PT Br 445 57 5 PFT Ru 289, 419, 470 456, 644 PF2T Ru 289, 416, 470 473, 644 PT Ru 289 644 In the case of PT Ru ( Figure 6 3 C and Ru(II) complex MLCT transitions, only two absorption peaks at 289 nm and 470 nm were obse rved. Emission spe c tra of the hybrid polymers ( excitation = 388 nm), nonetheless, were dominated by the broad featureless Ru(II) complex MLCT triplet emission bands peaking at 644 nm with the pol y mer backbone signals ( peaks at 456 nm and 473 nm for PFT Ru and PF2T Ru respectively as well as a 500 550 nm shoulder for PT Ru ) being strongly quenched. This result can be attributed to Forster resonance energy tran s fer occurring from the polymer backbones to the iTMC units via 1 MLCT excited state and is consis tent with literature examples when the donor emission and acceptor absorption spectral signatures overlap. 58,60,157 It is n oteworthy, ho w ever,

PAGE 183

183 that in this case, the 3 MLCT emission signals of the h y brid polymers were significantly weaker with the quantum eff i ciencies ca. 10 60% of that observed for the previously described PF Ru system ( Chaper 4, e = 0.095 at excitation = 388 nm (T 1 S 0 ) = 1240 ns ) and lifetimes < 100 ns This is likely due to a significant portion of excited state charge transfer from the polymer main chain to the Ru(II) units and/ or triplet energy backtransfer 62 from Ru(II) to the polymer backbones. This hypoth e sis is further supported by energetically lower triplet excited states of the polymer backbones and a decrease in the overlap of the d o nor emission and acce ptor absorption spectra as the thiophene units are introduced into the polymer backbone and the main chain emission red shifts, decreasing the efficiency of energy transfer as the dominant relaxation pathway. 6.2.5 Transient Absorption To better understand the early time regime photophysical behavior of the thiophene based hybrids af ter photoexcitation as well as distinguish the electron and energy transfer pathways femtosecond broadband pump probe spe c troscopy w as used to monitor the excited state dynamics of PFT Ru PF2T Ru and PT Ru solution s after direct excitation at 388 nm. PFT Hex PF2T Hex and PT Br model polymers were also studied using femtosecond pump probe spectros copy conditions to eliminate possible contributions from interchain interaction s The full spectra and representative k i netic trace s for each hybrid and model polymer are shown in Figure s 6 4, 6 5 and 6 6.

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184 Figure 6 4 Femtosecond transient absorption spec tra of PFT Ru and PFT Hex A ) Femtosecond t ransient absorption spectra of PFT Ru in benzonitrile with exc = 388 nm at 50 nJ/pulse. B ) Femtosecond t ransient absorption spectra of P F T Hex in benzonitrile with exc = 388 nm at 50 nJ/pulse. C ) Normalized stea dy emission and absorption spectra of PFT Hex in dilute tetrahydrofuran solutions. D ) Kinetic traces of PFT Ru (b lue circle s ) and PFT Hex (black circle s ) probed at 490 nm with exc = 388 nm In the case of PFT Ru and PF2T Ru scaffolds (Figures 6 4 and 6 5) the early time regime dynamics were somewhat similar to those observed for the parent PF Ru polymer (Chapter 4 polymer 8 ). The kinetic trace s of the backbone stimulated emission, after direct excitation at 388 nm possessed ultrafast energy and electron transfer components D ue to the more electron rich nature of the co polymer backbones, the fraction s of the electron transfer increased from 15% for PF Ru to 25% and 75% for PFT Ru and PF2T Ru respectively. A significant increase in charge separation for P F2T Ru could be attributed to the smaller integral overlap of the polymer backbone photoluminescence and Ru(II) acceptor absorption spectral signatures kinetically slowing down the energy transfer process. This was further supported by the rate

PAGE 185

185 constant a nalysis. While the electron transfer processes were found to occur within ca. 2 ps for both Ru(II) functionalized co polymers, energy transfer rates were 700 fs and 5.0 ps for PFT Ru and PF2T Ru respectively. Figure 6 5 Femtosecond transient absorption spectra of PF 2 T Ru and PF 2 T Hex A ) Femtosecond t ransient absorption spectra of PF 2 T Ru in benzonitrile with exc = 388 nm at 50 nJ/pulse. B ) Femtosecond t ransient absorption spectra of PF 2 T Hex in be nzonitrile with exc = 388 nm at 50 nJ/pulse. C ) Normalized steady emission and absorption spectra of PF 2 T Hex in dilute tetrahydrofuran solutions. D ) Kinetic traces of PF 2 T Ru (b lue circle s ) and PF 2 T Hex (black circle s ) probed at 490 nm with exc = 388 nm Even more pronounced tendency to exhibit preferential electron transfer and ultra long lived charged separated state s was characteristic of PT Ru Because such properties rendered this assembly an opposite to PF Ru (Chapter 4) in terms of excited state re laxation pathways, transient absorption data (Figure 6 6) for this polymer was analyzed in greater detail.

PAGE 186

186 At t = 0, the transient spectrum of PT Br ( Figure 6 6 ) exhibited a ground state bleach at 450 nm and stim u lated emission band centered at 550 nm. Acc ordingly, the respective decay component at 580 nm (Figure 6 6 F ) indicated a PT Br excited state lifetime of ca. 585 ps W ith time evol u tion th e stimulated emission red shifted ( ca. 2 5 nm in the first 50 ps ) and at 200 ps d e lay, a clear vibronic structur e with peaks at 575 nm and 615 nm appeared The red shift of the stimulated emi s sion w ith increasing pump probe delay and a rising comp o nent at the low energy side was hypothesized to reflect the intramolecular excitonic energy transfer or the excited stat e self trapping. If excitonic energy transfer occurs the excitation and the bleach should shift to the lower energy region of the spectrum I n this case, the ground state bleach d id not display any bathochromic shift with the increased delay time. Therefo re, the observed changes in the transient absorption data most likely arose due to the excited state self trapping via torsional relaxation rather than the excitonic energy transfer to lower energy segments. 182 The transient absorption spectra of the PT Ru assembly ( Figure 6 6A) subsequent to excitation at 388 nm were significantly different from those of PT Br ( Figure 6 6C). In this case, the spectra displayed a prompt absorption band at 370 n m and a bleach at 465 nm arising from the direct excitation of the pendant Ru(II) complexes. Due to the overlapping ground state absorption signatures of PF backbone and Ru(II) pendants, the direct excitation of PT backbone was also expected to contribute to the bleach in the region from 400 to 500 nm. The stimulated emission from PT was quenched rapidly within 1 2 ps and replaced by an absorption band around 550

PAGE 187

187 nm. Concurrent with the appea r ance of the signal at 550 nm, the bleach in the 400 500 nm regi on blue shifted by ca. 5 nm within 50 ps. Figure 6 6 Femtosecond transient absorption spectra of PT Ru and P T Br Femtosecond t ransient absorption spectra of A) PT Ru in acetonitrile C) PT Br in te trahydrofuran E) Ru Model (Chapter 4, compound 9 ) in acetonitrile with exc = 388 nm at 50 nJ/pulse. B ) Spectra of PT Ru in acetonitrile (blue), Ru Model in acetonitrile (green), and PT Br in tetrahydrofuran (red) at 2.0 ps delay s E ) Transient absorption spectrum of PT Ru in acetonitrile obtained at 50 ps ( exc v = 388 nm ) The red line, labeled A Red is the difference between the absorption spectra for the reduced PT Ru and the neutral PT Ru The grey line, labeled A Ox is the difference between the ab sorpt ion spectra of oxidized PT Ru and neutral PT Ru The blue line is the adjusted sum of the ox i dized and reduced difference spectra F ) Kinetic traces of PT Ru in acetonitrile at 550 nm (black circle s ) and Ru Model in acetonitrile at 550 nm (black lin e) and kinetic trace of PT Br in tetrahydrofuran at 580 nm (red line ) with exc = 388 nm

PAGE 188

188 In accordance with the spectroelectrochemistry data the transient absorption band at 550 nm was assigned to the electron transfer product Ru(I), while the changes i n the bleach region, as well as a we a k absorption band ranging from ca. 550 9 00 nm region were attributed to PF + Additionally, the adjusted sum of the oxidized ground ( A Ox ) and reduced ground ( A Red ) state difference spectra obtained from spectroelectro chemistry experiments ( A Sum = A Ox + 0. 3 A Red ) was in good agreement with a transient absorption spectrum at 50 ps, providing strong evidence for photoin duced charge separation process ( Equation 6 1 ) PT* +Ru(II) PT + Ru(I) ( 6 1) The kinetic traces at 550 nm and 580 nm for PT Ru and PT Br respectively, are shown in Figure 6 6 F F or PT Br a monoexponential decay with = 585 ps was obtained which wa s ascribed to the lif e time of the polymer backbone excited state. Meanwhile the 550 nm kinetics o f PT Ru with 388 nm excitation w ere fit ted as a bi exponential decay with fast (1.2 ps, 85% 5%) and slow (8.2 ps, 15% 5%) components with the 1.2 ps factor being assigned to electron tran s fer. In this array, the integral overlap between the emission from P T* and the absorption of Ru(II) (2.8 10 14 cm 1 ) was reduced even more sufficiently than in the case of PF2T Ru further supporting th is assig n ment. The F or ster energy transfer rate constant for PT Ru was estimated to be ca. 10 ps This result was in good agreement with the exper i mental data for the slow component indicating kinetic competition between the two excited state relaxation pathways The photoinduced electron transfer process in PT Ru was further explored by employing Marcus theory 65 and temperature dependant transient absorption

PAGE 189

189 measurements. Data from kinetic traces of PT Ru at 550 nm in acetonitrile at various temperatures is summarized in Figure 6 7. Figure 6 7 Temperature dependent femtosecond transient absorption spectra of PT Ru Kinetic traces of PT Ru at 550 nm in acetonitrile at different temperatures ( exc = 388 nm ) at 50 nJ/pulse and a plot of ln k ET v s 1/T with 1% error bars G o ) in this assembly wa s estimated to be 0.49 eV from the modified Re h m Weller equation. Theoretically, this value indicated a minimal or no thermodynamic activation ba r rier for the photoinduced elect ron transfer process, given the estimated reorganization energy for polymeric assemblies of ca. 0.5 eV 64 Experimentally t he direct electron tra nsfer from PT to Ru(II) displayed no temperature dependence as shown in Figure 6 7 This finding provided additional evidence for photoinduced charge separation in this assembly occurring due to a v ery small activation barrier and likely, a large electronic coupling To study the photophysical behavior of PT Ru ass embly at later time delays spectral e volution on time scales ranging from nanoseconds to microseconds was monitored by using a continuum probe pulse generated by a diode laser pumped

PAGE 190

190 photonic crystal fiber ( 500 ps time resolution ). T he transient absorp tion spectra obtained with pump pulses at 388 nm and 475 nm are given in Figure 6 8 As shown in Figure 6 8 A upon excitation at 388 nm ( generating PT* and Ru(II)* excited states in 3:1 ratio ), the transient spectra of PT Ru initially resembled the early t ime profiles (Figure 6 6 A ) with the prominent signatures of charge separated products. However, at increased pump probe delays, the band at ca. 700 nm emerged, which was simultaneously followed by a blue shift of the bleach from 455 nm to 445 nm, as well a s the decay of bpy signal at 370 nm. Based on the correlated kinetics of all these processes, band at 700 nm was attributed to the triplet excited state absorption of 3 PT* formed via sensitization of PT backbone by the Ru(II) 3 MLCT*. Kinetic data anal ysis at 550 nm showed a 70 ns rise component, assigned to the triplet energy transfer rate from Ru(II) 3 MLCT* to PT. Meanwhile, each kinetic trace associated with 3 PT at 445 nm, 550 nm and 680 nm exhibited a slow decay component of ca. 22 25 3 PT It is noteworthy, however, that the absorption band at 550 nm, characteristic of the photoinduced charge separation products of PT Ru retained a significant amplitude at t compared with the spe ctrum of PT Br Ru(I) most likely persists on a comparable time scale, generating redox intermediates (required for potential light harvesting or catalytic applications) with hundredfold Ru(I). This is most likely due to the high hole mobility of rr PT and oxidized state stabilization via hole delocalization.

PAGE 191

191 Figure 6 8 Nanosecond transient abs orption spectra of P T Ru and P T Br A ) Nanosecond t ransient absorption spectra of PT Ru in acetonitrile with exc = 388 nm along with the spectrum of PT Br in tetrahydrofuran at 1.0 s (orange) B ) Nanosecond t ransient absorption spectra of PT Ru in acetonitrile with exc = 388 nm (black) and with exc = 475 nm (red). C ) Nanosecond t ransient absorption spectra of PT Ru in acetonitrile with exc = 475 nm. D ) Kinetic traces at 380 nm (b lack) and 550 nm (green) of PT Ru in acetonitrile with exc = 475 nm Graphs summarizing nanosecond transient absorption data for PFT Ru and PF2T Ru are given in Figure 6 9 Briefly, in the spectra of the copolymers, signatures due to the main chain triplet excited state s were also evident with the b ackbone sensitization by Ru(II) 3 MLCT* occur r ing on a timescale of ca 60 70 ns T his process however, is not expected to interfere with dominant photonic processes in the thiophene containing iTMC arrays present ed in Chapter 6 as it is slower than both

PAGE 192

192 energy/electron transfer from the polymer backbones to Ru(II) chromophores (500 fs 10 ps) and hopping along pend ant iTMCs ( < 20 ns). Figure 6 9 Nanosecond t ransient absorption s pectra of A) P F T Ru and B) P F2 T Ru in acetonitrile with exc = 388 nm 6.3 Conclusions A new family of ionic transition metal complex conjugated pol y mers based thiophene repeat units have been synthesized via the Pd mediated Suzuki cross coupling and the 1,3 di cycloaddition chemistry approach. The resulting sca f folds exhibit a bathochromic shift in ground state absorption and thus enhanced overlap with the solar emission spectrum when compared to their polyfluorene counterpart. Similarly incorpora tion of electron rich thiophene units into these arch i tectures allows for stabilization of the main chain oxidized states and increased efficiency of photoinduced charge separation process es 6.4 Experimental Section 9,9 bromohexyl) 2,7 bis(4,4,5,5 tet ramethyl 1,3,2 dioxaborolan 2 yl)fluorene 183 ( 1 ), 2,5 dibromo 3 octylthiophene ( 2 ) 178,179 and 5,5' dibromo 4,4' dioctyl 2,2' bithiophene ( 7 ) (additional HPLC purification performed: C18 column,

PAGE 193

193 acetonitrile:tetrahydrofutan in 75%:25% volume ratio as an eluent mixture) 173 were prepared as described in the corresponding literature so urces. Poly[(9,9 bis(6' bromohexyl)fluorene) co (3 octylthiophene)] ( 3 ) 2 M p otassium carbonate solution was prepared as for the synthesis of 4 4 To a 100 mL 3 neck round bottom flask containing a magnetic stir bar, and outfitted with a glass stopper, co ndenser, and rubber septum, was added 9,9 bromohexyl) 2,7 bis(4,4,5,5 tetramethyl 1,3,2 dioxaborolan 2 yl)fluorene ( 1 ) ( 441 mg, 0. 593 mmol), 2,5 dibromo 3 octylthiophene ( 210 m g, 0. 593 mmol), and toluene ( 9 mL). This mixture was purged with argon f or approximately 30 min and 5 mL of the potassium carbonate solution was transferred to the reaction mixture Tetrakis(triphenylphosphino)palladium ( 32 mg, 0.02 0 mmol) was then added under argon. The mixture was immersed in an 85 C oil bath and stirred un der a dynamic argon atmosphere for 24 h. The reaction flask was then cooled to room temperature and precipitated into m ethanol /acetone/1N HBr mixture (70 mL/20 mL/20 mL). The precipitate was filtered over membrane, washed with water and methanol The solid obtained were redis solved in a small amount of THF and precipitated in 1:1 methanol:water solution (150 mL). The precipitate was collected by vacuum filtration, washed with water, methanol, acetone, as well as dried under vacuum. The sol id obtained was then subjected to Soxhlet extraction with methanol (36 h) and chloroform (24 h). The chloroform soluble fraction was then concentrated, precipitated into methanol, filtered and dried. T he product was isolated as a light yellow solid in 58 % ( 2 35 mg) yield. GPC (versus polystyrene in THF): M n = 15.6 kDa, PDI = 2.9 1 H NMR (300 MHz, CDCl 3 ), (ppm): 0.60 2. 20 (m, 35 H);

PAGE 194

194 2.76 (bs, 2H); 3.3 0 (t, 4H, J = 6. 5 Hz); 7. 30 7.85 (m, 7 H). Anal. calculated for C 37 H 48 Br 2 S: C, 64.91; H, 7.07; N, 0.00; found: C, 65.89; H, 7.21; N, 0.00. Poly[(9,9 bis(6' azidohexyl)fluorene) co (3 octylthiophene)] ( 4 ) To a solution of 1 2 (110 mg, 0.161 mmol ) in 1 0 0 mL of dry THF and 5 0 mL of dry DMF at room temperature sodium azide ( 104 m g, 1.607 mmol) was added. ( Caution! S odium azide is highly toxic and presents a severe explosion risk when shocked, heated, or treated with acid. ) The mixture obtained was stirred for 48 h at 45 C under an argon atmosphere in the dark The reaction mixture was cooled to room temperature and the excess THF was evaporated under vacuum. To the resulting suspension, methanol (100 mL) was added; the precipitate was collected by vacuum filtration, and washed with methanol, water and acetone. Due to the increased sensitivity to azide cross linking, polymer 4 was immediately used for the next synthetic steps without further purification Additionally, this reaction and the work up of polymer 4 were carried out with minimal exposure to light. Yield of light yellow solid: 91 g, 93 % 1 H NMR (300 MHz, CDC l 3 (ppm): 0.57 2. 23 (m, 35 H); 2.75 (bs, 2H); 3. 14 (bs 4H); 7. 30 7.85 (m, 7 H). PF T Ru (5 ) Polymer 4 ( 25 .0 mg, 0.0 41 mmol), complex 4 7 ( 109.8 mg, 0. 115 mmol ), PMDETA ( 19.8 mg, 0. 115 mmol), sodium ascorbate ( 11 .6 mg, 0.0 5 8 mmol), NH 4 PF 6 (ca. 1 g), THF (30 mL ), and DMF (15 mL ) were combined in a round bottom flask and degassed for 30 min (argon purging) After the addition of CuBr ( 16.3 mg, 0. 115 mmol), the content of the flask was further degassed for 10 more min and stirred at room temperature for 48 h under an argon atmosphere Under argon, additional complex 4 7 ( 2.8 mg, 0. 058 mmol), PMDETA ( 9.9 mg, 0. 058 mmol), sodium ascorbate ( 5.8 mg, 0.0 2 9 mmol) and CuBr ( 2.6 mg, 0.0 5 8 mmol) were added to the reaction

PAGE 195

19 5 mixture and the solution was further stirred f or 24 h at 40 o C upon slow argon purging allowing for slow gradual THF evaporation After the completion of the reaction (FT IR control : azide signal at ca. 2095 cm 1 disappear ed ), the reaction mixture was subjected to a gentle nitrogen stream to evaporate the leftover THF and the remaining solution was precipitated into water containing ca. 0.5 g of NH 4 PF 6 The resulting precipitate was collected by vacuum filtration and washed with water, methanol and THF The solid obtained was dissolved in a small amoun t of acetonitrile; the resulting solution was filtered through a 0.45 m Whatman syringe filter to remove an insoluble impurity and evaporated to dryness. The remaining residue was then redissolved in 20 mL of HPLC grade acetone containing ca. 0.5 mL PMDET A and ca. 0.2 g NH 4 PF 6 stirred for 0.5 h, precipitated upon addition of d eionized water (ca. 5 0 mL) and collected by vacuum filtration and this process was repeated three times The procedure was repeated two more times (excluding PMDETA addition and redu cing the stirring time to 20 min), and the brown precipitate was collected by filtration, wa shed with water, methanol and diethyl ether and dried u nder vacuum. Yield: 91 mg, 8 8 %. 1 H NMR (300 MHz, acetone d 6 ), (ppm): 0.60 2.3 0 (m, 35 H); 2. 39 2. 80 ( m, 8 H); 4.2 2 (bs, 4H); 4. 58 (bs, 4H); 7. 30 9. 14 (m, 55 H) Anal. calculated for C 1 07 H 106 F 24 N 20 O 2 P 4 S Ru 2 : C, 51.03 ; H, 4. 24 ; N, 1 1.12 ; found: C, 51.64; H, 4.75; N, 10.62 PFT Hex ( 6 ). To a solution of 4 ( 50 mg, 0. 082 mm ol) in 5 0 mL of dry THF 36 mg of 1 octyne (0. 32 8 mmol) and 26 mg (0.150 mmol) of PMDETA w ere added. The reaction mixture was degassed for 30 min followed by the addition of 22 m g (0. 150 mmol) of Cu Br The reaction mixture was stirred at 35 C for 48 h unde r argon atmosphere, cooled down to room temperature, and poured into 200 mL of diethyl

PAGE 196

196 ether The resulting precipitate was collected by vacuum filtration and dried. To remove trace copper impurities, a solution of 6 in 10 mL of DCM was stirred vigorously with 10% aqueous solution of ammonium EDTA overnight. The organic fraction was collected and evaporated to dryness by rotary evaporation. The remaining residue was re dissolved in THF, and precipitated into methanol/water (1:1) The precipitate was collecte d by filtration dried. Yield of light yellow solid: 55 mg, 81 % GPC (versus polystyrene in THF): M n = 25.8 kDa, PDI = 1.4 1 H NMR (300 MHz, CDCl 3 ), (ppm): 0.57 2.23 (m, 57 H); 3.65 (t, 4H, J = 7.5 Hz); 2.7 4 (bs, 2H); 4 .1 6 (bs, 4H); 7.14 (bs, 2H); 7.30 7.85 (m, 7H). Anal. calculated for C 53 H 7 8 N 6 S : C, 76.76; H, 9.24 ; N, 10.13 ; found: C, 75.90 ; H, 9.43 ; N, 9.19 Poly[(9,9 bis(6' bromohexyl)fluorene) co ( 5,5' dibromo 4,4' dioctyl 2,2' bithiophene )] ( 8 ) was synthesized by employing the same procedure as for the synthesis of 3 using 9,9 bromohexyl) 2,7 bis(4,4,5,5 tetramethyl 1,3,2 dioxaborolan 2 yl)fluorene ( 1 ) (418 mg, 0.5 62 mmol) and 5,5' dibromo 4,4' dioctyl 2,2' bithiophene ( 7 ) (308 mg, 0 .562 mmol) T he product was isolated as a yellow solid in 58 % ( 235 mg) yield. GPC (versus polystyrene in THF ): M n = 1 3.1 kDa, PDI = 2.3 1 H NMR (300 MHz, CDCl 3 ), (ppm): 0.62 2.18 (m, 50H); 2.72 (bs, 4H); 3.31 (t, 4H, J = 6.8 Hz); 7.13 (bs, 1H); 7.42 7.52 (m, 5H), 7.73 7.81 (m, 2H). Anal. calculated for C 49 H 66 Br 2 S 2 : C, 66.95; H, 7.57; N, 0.00; found: C, 65.90; H, 7.04 ; N, 0.00. Poly[(9,9 bis(6' azidohexyl)fluorene ) co ( 5,5' dibromo 4,4' dioctyl 2,2' bithiophene )] ( 9 ) was synthesized by employing the same procedure as for 4 using polymer 8 (1 42 mg, 0.161 mmol ) and sodium azide ( 104 m g, 1.607 mmol) Yield of the bright yellow solid: 118 g, 90 % 1 H NMR (300 MHz, aceto ne d 6 ), (ppm): 0.62 2. 18 (m,

PAGE 197

197 5 0 H); 2.72 (bs, 4H) ; 3. 16 (t, 4H, J = 6.8 Hz); 7.13 (bs, 1 H) ; 7.42 7.52 (m, 5 H) 7.73 7.81 (m, 2 H) PF 2 T Ru ( 10 ) was obtained by employing the same procedure as for the synthesis of p olymer 5 using polymer 9 ( 25 .0 mg, 0.0 31 mmol), c omplex 4 7 (81.8 mg, 0.086 mmol ), PMDETA ( 1 4 .8 mg, 0.086 mmol), sodium ascorbate ( 8 .6 mg, 0.0 43 mmol), NH 4 PF 6 ( ca. 1 g) and CuBr ( 1 2.2 mg, 0.086 mmol) The second addition of reagents contained complex 4 7 ( 40 9 mg, 0.043 mmol), PMDETA ( 7.4 mg, 0.0 43 mmol) sodium ascorbate (4.3 mg, 0.022 mmol) and CuBr ( 6.1 mg, 0.043 mmol) Yield of the orange red solid : 91 mg, 88%. 1 H NMR (300 MHz, acetone d 6 ), (ppm): 0.60 2.34 (m, 5 0 H); 2.5 2 2.80 (bm 10 H); 4.2 8 (bs, 4H); 4.6 9 (bs, 4H); 7. 13 9.11 (m, 56 H). Anal. calculated for C 119 H 124 F 24 N 20 O 2 P 4 S 2 Ru 2 : C, 5 2.69; H, 4.61; N, 10.33; found: C, 53.36; H, 4.92 ; N, 9.6 0 PF 2 T Hex ( 11 ) w as obtained by employing the sa me procedure as for the synthesis of polymer 6 using polymer 9 ( 50 mg, 0. 0 61 mmol) 1 octyne ( 27 mg, 0. 244 mmol) PMDETA (26 mg, 0.150 mmol) and Cu Br ( 22 m g 0. 150 mmol) Yield of yellow solid: 49 mg, 78 % GPC (versus polystyrene in THF): M n = 13.3 kDa, PD I = 2.0 0.62 2.18 (m, 72 H); 2. 61 2.76 (bs, 8 H); 4.17 (t, 4H, J = 7.4 Hz); 7.13 (bs, 3 H); 7.42 7.52 (m, 5H), 7.73 7.81 (m, 2H). Anal. calculated for C 65 H 94 N 6 S 2 : C, 76.27; H, 9.26 ; N, 8.21; found: C, 75.54; H, 9.22; N, 7.62 Poly[ 3 (6 bromohexyl)thiophene ] ( PT Br 14 ) To a dry 100 mL 3 neck round bottom flask ( equipped with a condenser and two rubber septa ) containing 1.198 g (2.96 mmol) of 2,5 dibromo 3 (6 bromohexyl)thiophene 24 mL of THF were added under an argon atmosphere The resulting solution was de gassed for 20 min via argon purging,

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198 and 0.986 mL (2.96 mmol) of MeMgBr (3 M solution in diethyl ether) was added via a syringe. The resulting solution was then refluxed for 2 h and cooled down to room temperature. Under argon, 9 mg (0.017 mmol) of Ni(dppp )Cl 2 were added to the flask, the reaction mixture was refluxed for additional 2 h and quenched by pouring into 200 mL of methanol containing ca. 2 m L of concentrated hydrochloric acid upon stirring. The resulting precipitate was collected by filtration an d subjected to Soxhlet extraction with methanol (48 h) and chloroform (48 h). The chloroform soluble fraction was concentrated by rotary evaporation, precipitated into methanol, filtered and dried to obtain dark purple solid in 4 8 % (348 mg) yield GPC (ver sus polystyrene in THF ): M n = 21.2 kDa, PDI = 1.7 1 H NMR (300 MHz, CDCl 3 ), (ppm): 1.39 1.96 (m, 8 H); 2.83 (t, 2 H, J = 7.6 Hz); 3. 44 (t, 2H, J = 6.8 Hz); 6.99 (s, 1 H). Anal. calculated for C 10 H 13 S Br : C, 48 .9 9 ; H, 5 34 ; N, 0.00; found: C, 48 91 ; H, 5 28 ; N, 0.00. Poly[3 (6 azido hexyl)thiophene] ( 15 ) was synthesized by employing a procedure essentially similar to that f or polymer 4 using polymer 14 (30 mg, 0.122 mmol ) sodium azide ( 104 m g, 1.607 mmol) and a catalytic amount of 18 crown 6 (phase transfer c atalyst) The reaction temperature was 45 o C. Yield of the dark purple solid: 25 m g, 9 9 % 1 H NMR (300 MHz, CDCl 3 ), (ppm): 1.39 1.96 (m, 8H); 2.83 (t, 2H, J = 7.6 Hz); 3.29 (t, 2H, J = 6.8 Hz); 6.99 (s, 1H). P T Ru (1 6 ) was obtained by employing the same procedure as for the synthesis of polymer 5 using polymer 15 ( 25 .0 mg, 0. 12 1 mmol), complex 4 7 ( 161.7 mg, 0. 169 mm ol ), PMDETA ( 29.1 mg, 0.1 6 9 mmol), sodium ascorbate ( 17.0 mg, 0.0 85 mmol), NH 4 PF 6 ( ca. 1 g) and CuBr ( 24.0 mg, 0. 169 mmol) The second addition of reagents contained complex 4 7 ( 82.0 mg, 0.0 85 mmol), PMDETA ( 14.6 mg, 0.0 85 mmol),

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199 sodium ascorbate ( 8.5 mg, 0.0 4 2 mmol) and CuBr ( 12.0 mg, 0.085 mmol) Yield of the orange red solid: 91 mg, 88%. 1 H NMR (300 MHz, acetone d 6 ), (ppm): 1.12 1.94 (m, 8 H); 2. 49 2.87 (b m 5 H); 4. 30 (bs, 2 H); 4. 59 (bs, 2 H); 7. 10 9.10 (m, 25 H). Anal. calculated for C 45 H 42 F 1 2 N 1 0 OP 2 Ru : C, 46.52; H, 3. 6 4 ; N, 1 2.05 ; found: C, 46.03; H, 3.87; N, 11 .64.

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200 CHAPTER 7 CONCLUSIONS AND FUTURE DIRECTIONS The emerging fi eld of organic electronics has offered innovative devices combining beneficial mechanical features (light weight, flexibility, etc.) with optical and redox properties that can be fine tuned on a molecular level. Accordingly, this dissertation focuses on th e design, synthesis, characterization, and structure property relationships of ionic transition metal complex polymers that could function as multifunctional active layer materials in new types of organic electronic devices. Chapter 3 of this dissertation describes acrylate containing Ru(II) polypyridyl complexes intended for use in single layer dual electrochromic/electrochemiluminescent display devices with optimal visibility in all ambient lighting situations (Figure 7 1) Figure 7 1 Dual electrochromic/electrochemiluminescent materials and devices. Structure of a cross linked Ru(II) polymer with dual EC/EL characteristics and the respective device pixel operating in electrochromic and electro chemi luminescent modes The s tructure property relationships are established between the detailed ligand design and the required multifunctional characteristics of Ru(II) polypyridyl complexes, as they are utilized in cross linked electrochromic films and active layers of light emitti ng electrochemical cell devices. Electrochromic switching of the polymeric networks between yellow, orange, green, brown and transmissive states is demonstrated, and electrochemiluminescent devices based on the complexes synthesized show red

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201 orange to deep red emission with max ranging from 680 to 722 nm with luminance up to 135 cd/m 2 Finally a dual EC/EL device prototype comprised of these materials is presented where light emission and multicolor electrochromism occur from the same pixel com prised of a single active layer. While not delineated in this dissertation, further developments of the field of dual electrochromism and electroluminescence encompass research efforts directed towards both active layer materials and the respective device constructio n engineering. Conjugated polymers and iTMC conjugated polymer hybrids represent an attractive platform for dual performing macromolecules allowing for property tuning and cost reduction. Meanwhile, in device construction, cathode for light emission requir es further enhancements. In this case, particular emphasis should be placed on electrode materials and patterning techniques. For instance, increasing the contact and decreasing the gap area for external electrolyte diffusion is of interest, as it could le ad to essentially even and uniform light emission from a pixel. Furthermore, replacing gold with transparent electrode materials, such as ITO silver nanowires or carbon nanotubes, could result in all transparent devices desired for commercial applications Chapters 4 6 of this dissertation focus on iTMC conjugated polymer hybrids intended for use as light harvesting arrays, charge transfer media or catalytic assemblies in solar photoelectrochemical cells T hese assemblie s combine high extinction coefficie nts of organic macromolecules with the long lived excited states of iTMC chromophores, allowing for exciton delocalization over long distances and an antenna effect. With cont rolled charge and exciton transport being the key requirement in such systems, po lymer building blocks having variable HOMO/LUMO levels (i.e.

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202 polyfluorene, poly(fluorene co thiophene) poly(bithiophene co fluorene and poly(3 alkylthiophene) ) are explored as the backbone s of the macromolecular assemblies (Figure 7 2) Figure 7 2 Conjugated metallopolymers with controlled electronic properties. Structures and energy levels of conjugated polymer ionic transition metal complex assemblies along with the photographs of the respective unfunctionalized polymer s olutions under UV irradiation As demonstrated by employing ultrafast spectroscopic techniques, facile electron and energy transfer occurs between the conjugated polymer backbones and the pendant iTMC units of the hybrid arrays, and the relative fractions o f these processes can be controlled via synthetic tailoring of the hybrid building blocks. While the use of polyfluorene leads to primarily energy transfer process occurring in less than 500 fs,

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203 poly(3 alkylthiophene) backbone allows for the formation long lived charge separated states within 1 ps with ca. 85 % probability. Similarly, coverage of the solar radiation spectrum can be fine tuned in these assemblies. In addition to polymer iTMC excited state interactions, conjugated polymer iTMC hybrids are demo nstrated to exhibit exciton hopping along the pendant transition metal chromophores. Directionality in this process can be facilitated by lowering the energy of the targeted transition metal complex chromophore s. As a result, conjugated polymer arrays cont aining small fractions of Os(II) or ester functionalized Ru(II) units are explored exhibiting exciton hopping rates on the order of several nanoseconds. Finally, both conjugated polymer iTMC and iTMC iTMC energy and/or electron transfer processes are prob ed as carboxylate containing assemblies are appended to semiconductor interfaces in solar photoelectrochemical cells. With this research being at fundamental stage, the main goal s herein are to establish photophysical and redox phenomena occurring in the hybrid systems, and how these processes could benefit the fields of solar energy harvesting and storage. This knowledge could then ultimately lead to the development of artificial photosynthetic systems comprised of cost effective and efficient materials. Based on that, several future directions are proposed for the development of this field. For further fundamental studies, there exists a necessity to explore novel hybrid assemblies by modifying general architectural aspects, molecular weight s and composit ion s Varying the electronic properties of the polymer backbones and iTMC units should be considered along with a potential option of pendant organic chromophores. Additionally, for light harvesting and storage applications, new fundamental photophysical p rocesses

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204 including low power upconversion, singlet fission or triplet sensitization could be induced in the assemblies. For instance, in thiophene based Ru(II) arrays described in this dissertation, iTMC assisted triplet energy backtransfer was found to occur within ca. 60 70 ns. While in the reported cases this process is slow, kinetically favoring singlet energy and electron transfer, the hybrid a ssemblies could be redesigned to primarily undergo triplet sensitization. A possibility of reverse injection where ultimate exciton transfer to the semiconductor interface occurs from ultra long lived polymer excited triplet states ( > 10 s) rather than iTMCs, could be probed This mode of exciton migration might be studied by attaching TiO 2 surface anchoring units directl y to polythiophene backbone and the resulting solar photoelectroch emical cells could be analyzed Finally, with solar e nergy storage being the ultimate goal of this research, polymeric arrays presented in this dissertation c ould be functionalized with water oxidation or CO 2 reduction catalysts. This would allow for novel catalyst chromophore assemblies leading to functioni ng solar fuel cell prototypes. Figure 7 3 Structure of a proposed polymer chromophore catalyst assembly along with a schematic representation of the respective sola r fuel device electrode

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216 BIOGRAPHICAL SKETCH Egle Puodziukynaite was born and raised in Kaunas, Lithuania. She received her B.S. in a pplied c hemistry at Kaunas University of Technology in 2007. She came to study o rganic chemistry at the University of Florida and joined Professor John R. will receive her Ph.D. in December 2012