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Synthesis and Photophysical Characterization of Organometallic Platinum Complexes with Donor-Acceptor Chromophores and Effects of Direct Metallation

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Title:
Synthesis and Photophysical Characterization of Organometallic Platinum Complexes with Donor-Acceptor Chromophores and Effects of Direct Metallation
Creator:
Gundogan, Ali S
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[Gainesville, Fla.]
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Degree:
Doctorate ( Ph.D.)
Degree Grantor:
University of Florida
Degree Disciplines:
Chemistry
Committee Chair:
SCHANZE,KIRK S
Committee Co-Chair:
CASTELLANO,RONALD K
Committee Members:
KLEIMAN,VALERIA DANA
MILLER,STEPHEN ALBERT
XUE,JIANGENG
Graduation Date:
12/19/2014

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Absorption spectra ( jstor )
Chromophores ( jstor )
Electrons ( jstor )
Fluorescence ( jstor )
Ligands ( jstor )
Oxidation ( jstor )
Photoluminescence ( jstor )
Platinum ( jstor )
Room temperature ( jstor )
Solvents ( jstor )
Chemistry -- Dissertations, Academic -- UF
donor-acceptor -- organometallics -- photophysics
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bibliography ( marcgt )
theses ( marcgt )
government publication (state, provincial, terriorial, dependent) ( marcgt )
born-digital ( sobekcm )
Electronic Thesis or Dissertation
Chemistry thesis, Ph.D.

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Abstract:
In this dissertation, photophysics of a series of platinum acetylides with strong electron acceptor units were studied. We found that all the oligomers showed strong absorption in the visible region and emission from visible to NIR region of the spectrum. In order to determine the energy of charge transfer (CT) state, electrochemical experiments were conducted and we found out that CT State is below the first triplet excited state. Second, a series of platinum complexes in which the platinum is directly attached to various oligothiophene and charge-transfer chronophers, were synthesized. Photophysical and electrochemical properties was investigated and compared to those in which metal is attached to the ring system via acetylene bridge. Complexes with oligothiophenes showed strong triplet-triplet absorption, and relatively good singlet oxygen quantum yields suggesting that complexes promotes triplet state formation upon excitation, on the other hand, relative intensity of triplet-triplet absorption and singlet oxygen quantum yield was lower than those complexes with acetylene linkage. One of the important properties of synthesized complexes is that they all showed very low oxidation potentials, less than 0.1V. These observations lead us to study electron transfer study with methyl violegen which is a known electron acceptor in the literature. Third, a new method to form platinum-carbon bond was discovered and developed. Mimicking Stille coupling reaction, it was shown that aryl group can indeed be transferred into platinum metal having strong phosphine ligand provided that Cu(I) salts used as catalyst. Different ligands were tested to investigate the scope of the reaction, a library of monosubstituted, symmetrically disubstituted and asymmetrically disubstituted platinum complexes were prepared. Basic photophysical properties i.e. ground-state absorption, steady-state emission in both air-saturated and argon purged solutions were studied. Finally, the novel carbon-platinum bond formation reaction was used to synthesize a series of platinum complexes in which 2,1,3-benzothiadiazole was ligated with various electron-rich systems was connected via platinum metal. Extensive photophysical and electrochemical investigation was conducted on these novel platinum complexes. ( en )
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Includes vita.
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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.
Thesis:
Thesis (Ph.D.)--University of Florida, 2014.
Local:
Adviser: SCHANZE,KIRK S.
Local:
Co-adviser: CASTELLANO,RONALD K.
Electronic Access:
RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2015-12-31
Statement of Responsibility:
by Ali S Gundogan.

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12/31/2015
Resource Identifier:
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SYNTHESIS AND PHOTOPHYSICAL CHARACTERIZATION OF ORGANOMETALLIC PLATINUM COMPLEXES WITH DONOR ACCEPTOR CHROMOPHORES AND EFFECTS OF DIRECT METALLATION By ALI S. GUNDOGAN A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2014

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© 2014 Ali S. Gundogan

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To my parents, my sister and my brother in law

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4 ACKNOWLEDGMENTS First of all, I would like to present my greatest appreciation to Fulbright Fellowship sponsored by United States Department of State. I could never ever make my dreams real without such a fellowshi p. It is great honor and privilege to be a part of community of people with unexceptional intelligence. I need to thank former Turkish Fulbright Officer, Gulesen Odabasioglu, former and present representatives of Institute of International Education, Joanne Forster , Alane Roberts and Emily Bosio for providing endless support and guidance throughout my studies in the United States. I also need to present my appreciation to the Board of Directors of TUPRAS Turkish Petroleum Company who agreed to provide financial support during the first two years of my education at University of Florida. I would like to thank my advisor, Dr. Kirk Schanze, for his encouragement, guidance, patient and endless support. He challenged me with developing my synthetic chemistry skills which lead me to discover and devel op new synthetic methodology. He also introduced me different aspects of physical organic chemistry and allow me to expand my knowledge and critical thinking towards any research problem. I would also like to thank my committee members, Dr. R onald Castella no, Dr. Stephen A. Miller, Dr. Valeria Kleiman and Dr. Jiangeng Xu e for their time and support. Everyone in the Schanze group is great friends and coworkers in and out of the laboratory. Special thanks should be given to Dr. Anand Parthasarathy, Dr. Galin a Dubinina, who discussed and helped me overcome the problems that I encounter during my work in the lab. I owe many thanks to Dr. Xiengli Meng for her great collaboration with me on one of my projects. I would also like to thank Russell Winkel for his con tribution on one of my project. My graduate years in the Schanze group was fun with

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5 great coll eag ue Subhadip Goswami whom I always share and discuss chemistry in the lab. I owe many thanks to the research colleagues I sh with, name ly Dr. Gyu Lee m, Dr. Randi Sue, Junlin Jiang and Yajing Yang and o ther group members Dr. Zhuo Chen , Dr. Hsien Yie, Zhenxing Pan, Seda Cekli, Jiang, Shanshan Wang.

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6 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ ............ 9 LIST OF FIGURES ................................ ................................ ................................ ........ 10 ABSTRACT ................................ ................................ ................................ ................... 16 CHAPTER 1 INTRODUCTION ................................ ................................ ................................ .... 18 Introduction to Photophysics ................................ ................................ ................... 18 Photophysical Characterization Methods ................................ ................................ 25 Absorption and Emission ................................ ................................ .................. 25 Transient Absorption ................................ ................................ ........................ 26 Platinum Acetylides ................................ ................................ ................................ 27 Synthesis ................................ ................................ ................................ .......... 28 Photophysics ................................ ................................ ................................ .... 29 aryl complexes ................................ ................................ ...................... 34 Synthesis ................................ ................................ ................................ .......... 34 aryl complexes. ................................ .................... 36 Photophysics of Donor Acceptor Syste ms ................................ .............................. 38 The overview of this study ................................ ................................ ...................... 42 2 SYNTHESIS, PHOTOPHYSICAL AND ELECTROCHEMICAL CHARACTERIZATION OF NOVEL PLATINUM ACETYLIDES W ITH DONOR ACCEPTOR CHROMOPHORES ................................ ................................ ........... 45 Background ................................ ................................ ................................ ............. 45 Results ................................ ................................ ................................ .................... 47 Synthes is ................................ ................................ ................................ .......... 47 ................................ ............................... 50 Steady State and Time Resolved Photoluminescence ................................ .... 51 Transient Absorption ................................ ................................ ........................ 54 Electrochemistry ................................ ................................ ............................... 56 Discussions ................................ ................................ ................................ ............. 59 Summary ................................ ................................ ................................ ................ 62 Experimental ................................ ................................ ................................ ........... 63 Instrumental and Methods ................................ ................................ ................ 63 Materials ................................ ................................ ................................ ........... 63 Synthesis ................................ ................................ ................................ .......... 64

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7 3 SYNTHESIS, CHARACTERIZATION, PHOTOPHYSICAL AND ELECTROCHEMICAL STUDIES ON Pt DIMERS WITH OLIG OTHIOPHENES AND CHARGE TRANSFER CHROMOPHORES ................................ ................... 73 Background ................................ ................................ ................................ ............. 73 Results ................................ ................................ ................................ .................... 75 Synthesis ................................ ................................ ................................ .......... 75 UV Vis Absorption Spectroscopy ................................ ................................ ..... 78 Steady State and Time Resolved Photoluminescence ................................ .... 79 Transient Absorption Spectroscopy ................................ ................................ .. 8 5 Electrochemistry ................................ ................................ ............................... 86 Discussion ................................ ................................ ................................ .............. 89 Oligothiophenes, Pt 2 Th n Series ................................ ................................ ........ 89 Charge Transfer Chromophores. ................................ ................................ ..... 93 Summary ................................ ................................ ................................ ................ 93 Experimental ................................ ................................ ................................ ........... 94 Instrumentation and Methods ................................ ................................ ........... 94 Materials ................................ ................................ ................................ ........... 94 Synthesis ................................ ................................ ................................ .......... 95 4 Pt CARBON BOND FORMATION VIA CuI CATALYZED STILLE TYPE TRANSMETALLATION: STRUCTURE AND SPECTROSCOPIC STUDY ........... 102 Background ................................ ................................ ................................ ........... 102 Results and Discussion ................................ ................................ ......................... 103 Structure and Synthesis ................................ ................................ ................. 103 Photophysical Properties ................................ ................................ ................ 108 Summary ................................ ................................ ................................ .............. 114 Experimental ................................ ................................ ................................ ......... 115 Instrumental and Methods ................................ ................................ .............. 115 Materials ................................ ................................ ................................ ......... 115 Synthesis ................................ ................................ ................................ ........ 116 5 SYNTHESIS, CHARACTERIZATION, PHOTOPHYSICAL AND ELECTOCHEMICAL PROPERTIES NOVEL PLATINUM COMPLEXES WITH DONOR ACCEPTOR CHROMOPHORES ................................ ........................... 126 Background ................................ ................................ ................................ ........... 126 Results ................................ ................................ ................................ .................. 128 Synthesis ................................ ................................ ................................ ........ 128 1 H NMR Characterization ................................ ................................ ............... 131 UV Vis Absorption and Photoluminescence ................................ ................... 133 Transient Absorption ................................ ................................ ...................... 136 Electrochemistry ................................ ................................ ............................. 137 Density Functional Theory Calculations ................................ ......................... 139 Discussion ................................ ................................ ................................ ............ 143 Summary ................................ ................................ ................................ .............. 144

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8 Experimental ................................ ................................ ................................ ......... 145 Instrumentation and Methods ................................ ................................ ......... 145 Materials ................................ ................................ ................................ ......... 147 Synthesis ................................ ................................ ................................ ........ 147 APPENDIX A SUPPORTING INFORMATION FOR CHAPTER 2 ................................ .............. 154 B SUPP ORTING INFORMATION FOR CHAPTER 3 ................................ .............. 162 LIST OF REFERENCES ................................ ................................ ............................. 173 BIOGRAPHICAL SKETCH ................................ ................................ .......................... 183

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9 LIST O F TABLES Table page 2 1 Summary of photophysical properties ................................ ................................ 56 2 2 Table of Energetics. ................................ ................................ ............................ 59 3 1 Photophys ical Summary of Complexes ................................ ............................. 86 3 2 Summary of electrochemical data. ................................ ................................ ..... 88 4 2 Summary of Photophysical Properties. ................................ ............................. 109 4 3 Computed Pt C bond lengths. ................................ ................................ .......... 110 5 1 Summary of Photophysical Properties. ................................ ............................. 137 5 2 Wavelength, Molecular Orbitals Involved, and Oscillator Strength for the Strongest Predicted Electronic Transition ................................ ......................... 141 5 3 Wavelength, Molecular Orbitals Involved, and Oscillator Strength for the Strongest Predicte d Electronic Transitions in the Triplet State. ........................ 142 5 4 Calculated HOMO and LUMO Energies as well as the band gap of complexes ................................ ................................ ................................ ........ 143

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10 LIST OF FIGURES Figure page 1 1 State Energy Diagram (Figure was adapted from Reference 3) ......................... 20 1 2 Fluorescence Resonance Energy Transfer ................................ ........................ 22 1 3 Dexter Interaction. ................................ ................................ .............................. 22 1 4 Energy diagram for photoinduced electron transfer. ................................ ........... 23 1 5 Changes in electron affinity between the S 0 and S 1 states. ................................ 25 1 6 Simple representation of nanosecond transient absorption system. ................... 27 1 7 Structure of platinum(II) acetylides with various ligands. ................................ .... 27 1 8 Synthetic scheme for the generation of platinum acetylides ............................... 28 1 9 Potential energy surface for the d d excited state in square planar d 8 complex, formed by population of the d x2 y2 orbital. ................................ ............. 29 1 10 Potential energy surface of square planar Pt(II) complexes with ligand excited states and metal d 8 orbitals. ................................ ................................ ... 30 1 11 Platinum acetylide polymers series stu died by Wilson and coworkers. 16 ............ 31 1 12 Platinum acetylide oligomers studied by Rogers et al. ................................ ....... 32 1 13 UV Vis a bsorption and photoluminescence spectra of PAOs series of compounds in THF. (adapted with permission from ACS) ................................ .. 32 1 14 Fulleropyrrolidine end capped platinum acetylide donor acceptor triad. ............. 33 1 15 Synthesis of platinum aryl complexes using organolithium reagents. 27 .............. 34 1 16 aryl complexes using Pt(COD)Cl 2. ................................ .......... 35 1 17 Examples of platinum carbon bond formation via oxidation addition known in the literature. 35, 38 ................................ ................................ ................................ 36 1 18 Examples of direct metallated complexes from literature. ................................ .. 37 1 19 bonded to metal. ...................... 38 1 20 Schematic diagram for the potential energy of charge transfer complexes ........ 41

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11 2 1 Schematic representation of D Pt A Pt D system and t he chemical structure of complexes that are subject of this chapter. ................................ .................... 46 2 2 Synthetic scheme for the synthesis of 2,1,3 benzothiadiazole (BTD) based complexes. ................................ ................................ ................................ ......... 48 2 3 Synthetic scheme for 1,4 diketo 3,6 diphenylpyrrolo [3,4 c] (DPP) based complexes. ................................ ................................ ................................ ......... 49 2 4 Synthetic scheme for the synthesis o f isoindigo (isoI) based complexes ........... 50 2 5 Photoluminescence spectra of (PhPt) 2 DPP and (TPAPt) 2 DPP at 77K in MeTHF solvent matrix. ................................ ................................ ....................... 52 2 6 Absorption and photoluminescence spectra of the complexes in THF solution. ................................ ................................ ................................ .............. 53 2 7 Ground state absorption and transient absorption spectra of (PhPt) 2 and (TPAPt) 2 ................................ ................................ ......................... 54 2 8 Ground State (top ) Transient Absorption (bottom) Spectra of (PhPt) 2 and (TPAPt) 2 ................................ ................................ .......................... 55 2 9 Cyclic Voltammogram of A) (PhPt) 2 BTD, B) (TPAPt) 2 BTD and differential 2 2 BTD. ................................ 57 2 10 Cyclic voltammogram of A) (PhPt) 2 DPP, B) (TPAPt) 2 DPP on left column and 2 2 DPP. .............. 58 2 11 Cyclic Voltammogram of A) (PhPt) 2 isoI, B) (TPAPt) 2 isoI and differential pulse 2 2 isoI. ................................ ............. 58 2 12 Representative J ablonski Diagram for the photophysical processes for (TPAPt) 2 BTD. ................................ ................................ ................................ ..... 59 2 13 Representative Jablonski Diagram for the photophysical processes for (TPAPt) 2 DPP ................................ ................................ ................................ ...... 61 2 14 Representative Jablonski diagram for the possible photophysical processes for (TPAPt) 2 isoI. ................................ ................................ ................................ .. 62 3 1 Structure of the complexes disc ussed in this chapter. ................................ ........ 74 3 2 Synthesis of Complexes Pt 2 Th 1 and Pt 2 Th 3 . ................................ ....................... 76 3 3 Synthesis scheme of Pt 2 Th 2 and Pt 2 Th 4 . ................................ ............................ 77 3 4. Synthesis scheme for Pt 2 TBT ................................ ................................ ............. 77

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12 3 5 Synthetic Scheme for Pt 2 TQT ................................ ................................ ............. 78 3 6 Absorption Spectra of Sn 2 Th 1 and Pt 2 Th 1 ................................ ........................... 79 3 7 Absorption Spectra of the complexes Pt dimers with oligothiophenes and their correspondin g tin derivatives. ................................ ................................ ..... 80 3 8 Normalized Absorption Spectra of Pt 2 TBT and PT 2 TQT and their corresponding tin precursors Sn 2 TBT( ---) and Sn 2 TQT. ................................ .... 81 3 9 Photoluminescence Spectra for A) Pt 2 Th 2 , B) Pt 2 Th 3 and C) Pt 2 Th 4 with emission from exciting different wavelength. ................................ ...................... 83 3 10 Photoluminescence spect ra of platinum dimers featuring oligothiophenes at 273K in THF and 80K in MeTHF solvent glass. ................................ .................. 84 3 11 Absorption and photoluminescence spectra of the complexes Pt 2 TBT and Pt 2 TQT reco rded in THF. ................................ ................................ .................... 84 3 12 Nanosecond microsecond transient absorption spectra of A) Pt 2 Th 2 (black), Pt 2 Th 3 (red) and Pt 2 Th 4 (blue) and B) Pt 2 TBT (black) and Pt 2 TQT(red) on the deoxygenated THF solutions ................................ ................................ .............. 85 3 13 Anodic sweeps in cyclic voltammogram and differential pulse voltammogram of Pt 2 Th n where n =1,2,3,4. ................................ ................................ ................. 87 3 14 Cyclic Voltammogram (on the left) and Differential Pulse Voltammogram (on the right) of Pt2TBT. ................................ ................................ ........................... 88 3 15 Transient absorption difference spectra of A) Pt 2 Th 3 B) Pt 2 Th 4 and MV 2+ in THF/MeCN (3:2) solution. ................................ ................................ ................... 92 4 1 Synthesis of Monosubstituted Aryl Platinum Complexes ................................ .. 103 4 2 Synthesis of Disubstituted Aryl Platinum Complexes ................................ ....... 103 4 3 Yield of mono and symmetrically disubstituted complexes. ................................ .................... 105 4 4 P roposed Mechanism for the Cu(I) mediated transmetallation ......................... 106 4 5 Yields and Structures of Heterodisubstituted Aryl Platinum Complexes. .......... 108 4 6 Absorption (left) and photoluminescence (right) spectra of complexes 3a (top) and 3b (bottom) ................................ ................................ ........................ 111 4 7 Absorption (left) and photoluminescence (right) spectra of complexes 3a (top) and 3b (bottom). ................................ ................................ ....................... 111

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13 4 8 Absorption (left) and photoluminescence (right) spectra of complexes 3a (top) and 3b (bottom). ................................ ................................ ....................... 112 4 9 Transient Absorption Spectra of trans DPAFPt(PBu 3 ) 2 Cl (7a) and trans DPAFPt(PBu 3 ) 2 DPAF (7b). ................................ ................................ ............... 11 3 4 10 Transient Absorption Spectra of trans BThPt(PBu 3 ) 2 Cl (9a) and t rans BThPt(PBu 3 ) 2 BTh (9b). . ................................ ................................ .................... 113 5 1 Several donor acceptor donor (D A D) systems studied by Pina et al. 98 .......... 126 5 2 The structures of the complex es discussed in this chapter. ............................. 128 5 3. Synthesis of platinum dimer with 2,1,3 benzothiadiazole. ................................ 129 5 4 Synthet ic scheme for triisopropyl(5' (tributylstannyl) [2,2' bithiophen] 5 yl)silane. ................................ ................................ ................................ ........... 129 5 5 Synthesis Scheme for triisopropyl(6 (tributylstannyl)dithieno[3,2 b:2',3' d]thiophen 2 yl)silane . ................................ ................................ ...................... 130 5 6 Synthetic scheme for the formation of Donor Platinum Acceptor Complexes. . 130 5 7 1H NMR Spectra of A ) (ClPt) 2 BTD, B) (ThPt) 2 BTD, C) (BThPt) 2 BTD D) (DTTPt) 2 BTD ................................ ................................ ................................ .... 132 5 8 Normalized absorption specta of (ClPt) 2 BTD (black line), (ThPt) 2 BTD (dash line), (BThPt) 2 BTD (dot line), (DTTPt) 2 BTD (dash dot line). ............................. 134 5 9 Absorption Spectra (on the left) and Photoluminescence Spectra .................... 135 5 10 Transient Absorption Spectra of (CIPt) 2 BTD (on the left) and (ClCCPt) 2 BTD (on the right). . ................................ ................................ ................................ ... 136 5 11 Transi ent Absorption Spectra of (DTTPt) 2 BTD (on the left) and (BThPt) 2 BTD (on the right). ................................ ................................ ................................ .... 137 5 12 Cyclic Voltammogram (on the left) and Differential Pulse Voltammogram (on the right) of the (ClCCPt) 2 BTD (top) and (ClPt) 2 BTD (bottom) ......................... 138 5 13 Cyclic Voltammogram (on the left) and Differential Pulse Voltammogram (on the right) of the (DTTPt) 2 BTD (top) and (BThPt) 2 BTD (bottom). ....................... 139 5 14 DFT//B3LYP/6 31G(d) optimized groun d state geometry together with the frontier molecular orbitals energy levels and the molecular orbital contours for (ClPt) 2 BTD, (ThPt) 2 BTD, (DTTPt) 2 BTD, (BThPt) 2 BTD and (ClCCPt) 2 BTD oligomers. ................................ ................................ ................................ ......... 140 A 1 1 H NMR (500 MHz, CDCl 3 ) of (PhPt) 2 BTD ................................ ....................... 154

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14 A 2 13 C NMR (125 MHz, CDCl 3 ) of (PhPt) 2 BTD ................................ ..................... 154 A 3 31 P NMR (121 MHz, CDCl 3 ) of (PhPt) 2 BTD ................................ ...................... 155 A 4 HRMS (MALDI DTL), [M] + isotope pattern of (PhPt) 2 BTD ................................ 155 A 5 1 H NMR (500 MHz, CDCl 3 ) of (TPAPt) 2 BTD ................................ .................... 156 A 6 13 C NMR (500 MHz, CDCl 3 ) of (TPAPt) 2 BTD ................................ ................... 156 A 7 31 P NMR (500 MHz , CDCl 3 ) of (TPAPt) 2 BTD. ................................ .................. 157 A 8 HRMS (MALDI DTL), [M] + isotope pattern of (TPAPt) 2 BTD ............................. 157 A 9 1 H NMR (500 MHz , CDCl 3 ) of (PhPt) 2 DPP. ................................ ...................... 158 A 10 13 C NMR (500 MHz, CDCl 3 ) of (PhPt) 2 DPP ................................ ..................... 158 A 11 31 P NMR (500 MHz, CDCl 3 ) of ( PhPt) 2 DPP ................................ ...................... 159 A 12 HRMS (APCI), [M] + isotope pattern of (PhPt) 2 DPP ................................ .......... 159 A 13 1 H NMR (500 MHz, CDCl 3 ) of (TPAPt) 2 DPP ................................ .................... 160 A 14 13 C NMR (500 MHz, CDCl 3 ) of (TPAPt) 2 DPP ................................ ................... 160 A 15 31 P NMR (500 MHz, CDCl 3 ) of (TPAPt) 2 DPP ................................ ................... 161 A 16 HRMS (MALDI DTL), [M] + isotope pattern of (TPAPt) 2 DPP. ............................ 161 B 1 1 H NMR (300 MHz, CDCl 3 ) of Pt 2 Th 1 . ................................ .............................. 162 B 2 31 P NMR (121 MHz, CDCl3) of Pt 2 Th 1 ................................ .............................. 162 B 3. HRMS (MALDI DTL), [M] + isotope pattern of Pt 2 Th 1 ................................ ........ 163 B 4 1 H NMR (300 MHz, CDCl 3 ) of Pt 2 Th 2 . ................................ .............................. 163 B 5 13 C NMR (75 MHz, CDCl 3 ) of Pt 2 Th 2 . ................................ ............................... 164 B 6 31 P NMR (121 MHz, CDCl 3 ) of Pt 2 Th 2 . ................................ ............................. 164 B 7 HRMS (MALDI DTL), [M] + isotope pattern of Pt 2 Th 2 . ................................ ....... 165 B 8 1 H NMR (300 MHz, CDCl 3 ) of Pt 2 Th 3 . ................................ .............................. 165 B 9. 13 C NMR (75 MHz, CDCl 3 ) of Pt 2 Th 3 ................................ ................................ 166 B 10 31 P NMR (121 MHz, CDCl 3 ) of Pt 2 Th 3 . ................................ ............................. 166

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15 B 11 HRMS (MALDI DTL), [M] + isotope pattern of Pt 2 Th 3 . ................................ ....... 167 B 12 1 H NMR (300 MHz, CDCl 3 ) of Pt 2 Th 4 ................................ ............................... 167 B 13 13 C NMR (75 MHz, CDCl 3 ) of Pt 2 Th 4 ................................ ................................ 168 B 14 31 P NMR (121 MHz, CDCl 3 ) of Pt 2 Th 4 ................................ .............................. 168 B 15 HRMS (MALDI DTL), [M] + isotope pattern of Pt 2 Th 4 ................................ ........ 169 B 16 1 H NMR (300 MHz, CDCl 3 ) of Pt2TQT ................................ ............................. 169 B 17 13 C NMR (75 MHz, CDCl 3 ) of Pt2TQT ................................ .............................. 170 B 18 31 P NMR (121 MHz, CDCl 3 ) of Pt2TQT ................................ ............................ 170 B 19 HRMS (APCI), [M]+ isotope pattern of Pt 2 TBT ................................ ................. 171 B 20 1 H NMR (300 MHz, CDCl 3 ) of Pt 2 TBT ................................ .............................. 171 B 21 13 C NMR (75 MHz, CDCl 3 ) of Pt 2 TBT ................................ ............................... 172 B 22 HRMS (APCI), [M] + isotope pattern of Pt 2 TBT ................................ ................. 172

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16 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 SYNTHESIS AND PHOTOPHYSICAL CHARACTERIZATION OF ORGANOMETALLIC PLATINUM COMPLEXES WITH DONOR ACCEPTOR CHROMOPHORES AND EFFECTS OF DIRECT METALLATION By Ali S. Gundogan December 2014 Chair: Kirk Schanze Major: Chemistry In this dissertation, photophysics of a series of platinum acetylides with strong electron acceptor units were s tudied. We found that all the oligomers showed strong absorption in the visible region and emission from visible to NIR region of the spectrum. In order to determine the energy of charge transfer (CT) state, electrochemical experiments were cond ucted and w e found out that CT s tate is below the first triplet excited state. Second, a series of platinum complexes in which the platinum is directly attached to various oligothiophene and charge transfer chronophers, were synthesized and characterized. Photophy sic al and electrochemical properties was investigated and compare d to those in which metal is att ac he d to the ring system via acetylene linker. Complexes with oligothiophenes showe d str ong triplet triplet absorption, and relatively good singlet oxygen quantum yields suggesting that complexes promotes triplet state formation upon excitation, on the other hand, relative intensity of triplet triplet absorption and singlet oxygen quantum yield was lower than those complexes with acetylene linkage. One of the impor tant properties of synthesized complexes is that they all

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17 showed very low oxi dation potentials, less than 0.1 V. These observations lead us to study electron transfer study with methyl violegen which is a known electron acceptor in the literature. Third, a new method to form platinum carbon bond was discovered and developed. Mimicking Stille coupling reaction, it was shown that aryl group can indeed be transferred into platinum metal having strong phosphine ligand provided that Cu(I) salts used as catalyst. Different ligands were tested to investigate the scope of the reaction, a library of monosubstituted, symmetrically disubstituted and asymmetrically disubstituted platinum complexes were prepared. Basic photophysical properties i.e. ground state absorptio n, steady state emission in both air saturated and argon purged solutions were studied. Finally, the novel carbon platinum bond formation reaction was used to synthesize a series of platinum complexes in which 2,1,3 benzothiadiazole was ligated with variou s electron rich systems was connected via platinum metal. Extensive photophysical and electrochemical investigation was conducted on these novel platinum complexes.

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18 CHAPTER 1 INTRODUCTION In this chapter, a short overview of two topics is provided; t he f irst part of the introduction will focus on the fundamental photophysical processes that occur when a molecules absorbs a photon of light. The second part will mainly outline up to date research overview of synthesis and photophysical properties of platinu m acetylides and aryl complexes. Introduction to Photophysics Absorption of a photon by a molecule transforms light energy into electronic excitation energy. The energy of the absorbed photon is used to energize an electron and e rive from the electronic orbital configuration produced by light absorption. In one state, the electron spins are paired (antiparallel) and in the other state the electron spins are unpaired (pa rallel). The state with paired spins has no resultant spin magnetic moment, but the state with unpaired spins possesses a net spin magnetic moment. A state with paired spins remains a singlet state in the presence of a magnetic field and is termed singlet state. A state with unpaired spins interacts with magnetic fields and splits into three quantized states, and is termed as a triplet state. The energy required to produce an excited state is obtained by inspection of the absorption or emission spectrum of the molecules in question, together with the application of Equation (1 1) . 2 E 1 (1 1) 1 ) at which absorption occurs and E 2 and E 1 are the energies of single molecule in the final and initial state. The position of an

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19 absorption band is often expressed by its wave wavenumber. An energy diagram is a display of the relative energies of the ground state, the excited singlet states, and triplet states of a molecule for a given, fixed nuclear geometry. It is generally assumed that the nuc lear geometries of all states displayed in a single state diagram are not very different from the equilibrium nuclear geometry of the ground state. Each excited state is different from the ground state even though their molecular constitutions are identica l. Photophysical processes can be defined as transitions which cause excited states to be converted with each other or with the ground state. The important photophysical processes, in turn, are designated as radiat ive and nonradiative processes. The common ly encountered photophysical radiative and nonradiative processes as shown in Figure 1 1 . 1. Allowed or singlet singlet absorption (S o + hv S 1 ), characterized S o +hv S 1 ); 2. triplet absorption ( S o + hv T 1 ), characterized S o +hv S 1 ); 3. singlet emission, called fluorescence (S 1 S o + hv), characterized by radiative rate constant k F ; 4. triplet singlet em ission called phosphorescence (T 1 S o + hv), characterized by radiative rate constant k P 5. T ransitions between states of the same spin called internal conversion (e.g., S 1 S o + heat), characterized by a rate constant k IC ; 6. T rans itions between excited states of different spin, called intersystem crossing (e.g., S 1 T 1 + heat), characterized by a rate constant k ST ;

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20 7. also called intersystem crossing (e.g., S 1 T 1 + heat) and characterized by a rate constant, k TS Figure 1 1 . State Energy Diagram ( Figure was a dapted from Reference 3 ) The transition from S 0 to S 1 is basically very rapid ; it occurs over 10 1 6 10 15 s. No chemical s cale reaction or process can compete with the time scale of absorption. Absorption happens so rapidly because the electron motion is involved. Because of the substantially greater mass of nuclei vs electrons, nuclear motions are considerably slower. They o ccur on a time scale of 10 13 10 12 s. This fact le ads to an important concept in photoph ysics, the Frank Condon principle, which states that because the electronic transitions occur faster than nuclear motion, absorption is vertical on an x ax is that rep resents the nuclear p o si tion. This means that electronic transitions are most favorable when the geometries of the initial and final states are the same . 1 3 Experimentally, efficiency of absorption is defined by th e molar extinction 2.) The quantity log[Io/I] or, A is termed the optical density (OD) or absorbance of the sample. log[I o (1 2)

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21 In equation 1 2, I o is the intensity of incident light, I = intensit y of transmitted light, b absorptivity of the solution. It is possible that an excited molecule may encounter another molecule during its excited state lifetime. The re are several processes that can occur including the enhancement of intersystem crossing, electronic energy transfer, and complex formation. A significant property of bimolecular excited state dynamics is that these processes are dependent on the concentr ation of the excited molecules and quenchers and is also a diffusion controlled process. 4 Fluorescence r esonance ener gy transfer ( FRET) is one of the mechanisms of bimolecular excited state dynamics which describe ener gy transfer between two chromopho res. A donor chromophore initially in its electronic excited state may transfer energy to an acceptor chromophore through nonradiative dipole dipole coupling. The efficiency of this energy transfer is inversely proportional to the sixth power of the distance between donor and acceptor, making F RET extremely sensitive to small changes in distance. The F RET efficiency depends o n many physical parameters such as the distance between the donor and acceptor, the spectral overlap of donor emission spectrum and the acceptor absorption spectrum and the relative orientation of the donor emission dipole moment and the accept or absorptio n dipole moment. (Figure 1 2)

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22 Figure 1 2 . Fluorescence Reso nance Energy Transfer . 5 Dexter interaction is a nother deactivation pathway for an excited state and it occurs through electron exchange energy transfer This interaction occurs between do nors D E and A E , where E indicates electron exchange. Dexter transfer may occur at short donor acceptor distances, but the donor will be completely quenched by F RET or Dexter transfer, and thus non observable. Dexter transfer can be observed if the spectral overlap is small, so that large rates of exchange become significant. Additionally, high concentrations are need ed for significant Dexter transfer, whereas F RET occurs at much lower concentrations. For an unlinked donor and acceptor , the bulk concentratio n of the acceptor needs to be about 10 2 M to have an average distance of 30 Ã… . Figure 1 3 . Dexter Interaction . 6

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23 Photoinduced electron transfer (PET) has been extensively studied to understand quenching and to develop photovoltaic devices. Most descriptions of PET derive the energy change due to electron transfer starting with the basic p rinciples of electrochemistry. T he following figure (Figure 1 4 ) shows an energy diagra m for PET with an excited molecule being the electron donor. Upon excitation the electron donor transfers an electron to the acceptor with a rate k p , forming the charg e transfer complex [D p A p ]*. This complex may emit as an exciplex or be quenched and return to the ground state. Figure 1 4 . Energy diagram for photoinduced electron tr ansfer. The excited molecules are assumed to be the electron donor, v F and v E are the emissi on from the fluorophore and exci plex, respectively. The important part of this process on the decrease in total energy of the charge transfer complex. B ecause the ability to donate or accept electrons changes when a molecule is in the excited state, total energy decreases. Excitation provides the energy to drive charge separation. D and A do not form a complex when both are in the ground state because this is energetically unfavorable. The energy released by electro n transfer

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24 can also change if the ions become solvated or separated in a solvent w ith a high dielectric constant. 7 The energy change for PET is given by the Rehm Weller equa tion: + /D) E(A/A ) 00 e 2 (1 3) In this equation the potential E(D + /D) describe s the process D + + e D (1 4) and the reduction potential E(A/A ) describe s the process A + e A (1 5) G 00 is the energy of the S o S 1 transi tion of the fluorophore, which can either D or A. The last term on the right is the columbic attraction energy experienced by the ion pair following the electron transfer reaction where is the dielectric constant of the solvent and d is the distance betw een the charges. Studies of PET are usually performed on polar solvents, frequently acetonitrile, which is a common solvent used when determining the redox potentials. For complete separation of one electron charge in acetonitrile e 2 kc a l/mol = 0.06 eV The contribution of this term to the overall energy change for PET is usually small. The reason why the energy of the charge transfer state is lower than the energy before electron transfer can be understood by considering the energy requ ired removing an electron completely from the electron donor which is the energy needed to ionize a donor fluorophore. When the fluorophore is in the e xcited state, the electron is a t a higher energy level than ground state electron. Hence it will require less energy to remove an electron from S 1 state from the S o state. This means the donor fluorophore in the S 1 state h as a higher propensity to donate an electron. Considering a quencher that is an electron

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25 acceptor, the energy released on binding the elect ron is larger of the electron returns to the S o state than the S 1 state. The electron can returns to the lowest orbital of the quencher because the donor acceptor complex is momentarily and excited state complex. When the electron acceptor is in the excite d state there is a place for the electron to bind to the lowest orbital. (Figure 1 5.) Figure 1 5 . Changes in electron affinity between the S 0 and S 1 states . Photophysical Characterization Methods Absorption and Emission Absorption spectrum is collected using spectrophotometer which can be either single beam or double beam. A single beam instrument is relies on the measurement of sample before and after sample is inserted, on the other hand, double beam instrument relies on comparison of the light intensity between two light paths: one which passes through the sample in the related solvent and one that contains only solvent. The modern spectrophotometer generally consists of a white light source, a monochromator which make s discrete wavelengths of the light to pass through the sample, and a detector such as photomultiplier tube.

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26 Emission spectra can be measured with a spect rofluoro meter which consists of an excitation light source, a grating monochromator, and a detector. The excitation light source is typically a white light source such as a xenon arc lamp which passes through a monochromator to single out the excitation wavelengths of interest before hitti ng the sample. The luminescence from the sample is collected at 90° to the excitation beam with condensing optics and passed through a second monochromator with a grating which can be scanned stepwise through the detection region of interest. Detection is usually with a photomultiplier tube which produces an amplified sig nal upon det ection of photons. Spectrofluoro meters can also be double beam to correct for fluctuations in lamp intensity during the experiment. Transient Absorption s pectroscopy or flash photolysis is a powerful tech nique which allows the study of short lived transient species. These transient species can involve photoreaction intermediates as well as higher excited states of a mole cule accessed by the absorption of photons. Spectral infor mation are acq uired which provide information about the evolution of excited states that are populated upon excitation with light. The absorption spectra acquired by TA depend on the e nergy gap of the excited state involved in the transition. Using TA spec troscopy al ongside the other spectroscopic techniques described above, it is possible to complete a photophysical profile of the most important electronic transitions of a molecule.

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27 Figure 1 6. Simple representation of nanosecond transient absorption sy stem. 4 Platinum Acetylides Platinum acetylides are a broad class of air stable organometallic compounds with potential applications in the area of non linear absorption, electroluminescent devices and solar cells. Although a large number of platinum acetylides with several different ligands are reported in the literature, some of the important class of these materials (A, B,C) are shown in the following figure, Figure 1 7 , and however, only those with trans positioned monodentate phosphine ligands (C) will be discussed in the subject of the following overview. Figure 1 7 . Structure of pla tinum(II) acetylides with various ligands.

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28 Synthesis Interest with Pt(II) acetylides containing phosphine ligands originally began in the 1970s from work on polymeric materials. I n 1977, Sonogashira and Hagihar a first demonstrated the facile synthesis of Pt acetylides by the direct reaction of a metal halide with acetylenes in the presence of a secondary amine and catalytic amount of CuI. Monoalkynyl platinum(II) complexes can be synthesized by the reaction of cis Pt(PBu 3 ) 2 Cl 2 and acetylene without cup rou s halide, route b, Figure 1 8 . 8, 9 Figure 1 8 . Synthetic s cheme for the generation of pl atinum acetylides, where route a is reacted in diethylamide in the presence of CuI, 10 and where route b is reacted i n refluxing diethylamine. The geometry of the starting material is of little importance as an isomerization to the trans form will occur f rom either the c is or trans geometry in the pres ence of tertiary amine. The two isomers can be distinguished by observing the coupling between the phosphorus and an NMR active Pt isotope; the magnitude of which is dependent on the ligands presents on the p latinum center. Upon establishing these mild synthetic reaction conditions, they went on to develop poly yne monomers, oligomers and polymers containing Pt (II) and trialkylphosphine either in the cis or trans geometry with the latter being more prevalen t. 12 15 Since the middle of the 1990s, Pt acetylides containing phosphine ligands have seen a dramatic increase in interest due to the versatility

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29 provided by the phosphine ligands and dramatic triplet state photophysics that have been demonstrated in a va riety conjugated structure. Photophysics The d 8 electronic configuration of Pt(II) within the square planar geometry leads to the d xy orbital acting as the highest occupied molecular orbital (HOMO), while the lowest unoccupied molecular orbital (LUMO) orig inates from d x2 y2 orbital which is strongly anti bonding; population of this orbital via absorption of light result s in significant distortion upon formation of the excited state, and visualized the d d excited state potential surface where energy minimum is largely d isplaced from the ground state, ( Figure 1 9 . ) 11 Figure 1 9 . Potential energy surface for the d d excite d state in square planar d 8 complex, formed by population of the d x2 y2 orbital. The thermally a ccessible isoenergetic crossing point leads to deactivation of the excited state via nonreactive internal conversion to the ground state rather than luminescent pathway. For that reason, platinum acetylides with simple inorganic ligand are no luminescent o r, at best, slightly luminescent. Nevertheless, the excited state properties of Pt complexes can be altered by the attachment of conjugated organic

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30 system via metal to ligand charge transfer (MLCT, d e fact that MLCT o r LC states are located at lower energies than d d states as illustrated in Figure1 9 makes the HOMO orbital in such complexes originating from d xy orbital, but LUMO could originate fro Figur e 1 10 . Potential energy surface of square planar Pt(II) complexes with ligand excited states and metal d 8 orbitals. conj ugated materials dates back 1990s. when abovementioned hybridiz ation is shown to occur between the metal d orbitals and p z orbital of the ligand, which strongly modifies the optical response of the conjugated chain . 12 Phosphorescen ce can be measured in these system when the T 1 emission becomes partially allowed by spin orbit coupling, which readily give access to the energy, vibrational st ructure and lifetime of triplet state. 13 Even though early work that has been done on platinum acetylides showed d/d emission states, time resolved infrared spectroscopy indicates that fundamental optical

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31 transitions in these materials originates from mainly some contributions from Pt(II) d orbitals. 14 Initial photochemical characterization of platinum acetylides was conducted by Kohler, Friend and coworkers. 8, 13, 15 26 Wilson and coworkers studied the effect of aromatic spacer on the singlet and triplet energie s of various platinum acetylide polymers. (Figure1 10) Phot ophy sical results showed that energy of the triplet state decreased as the lifetime and intensity of the triplet state decreased. 19 . The results of this series also revealed a constant singlet triplet splitting (~0.7eV) regardless of the spacer used. Figure 1 11 . Platinum acetylide polymers series studied by Wilson and coworkers. 19 In another study, Roger and coworkers studied various phenylacetylen e oligomers to understand the sensitivity of state energies to molecular size. They found that So and T 1 states were more localized than S 1 and T n states suggesting that So to S 1 and T 1 to T n transitions have charge transfer character, while T 1 to S o was f ound to be from a confined state to another confined state. 15

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32 Figure 1 12 . Platinum acetylide oligomers studied by Rogers et al. Past 15 years witnessed rapid development of the area of platinum acetylides containing phosphine ligands not only for understanding the fundamental photophysical properties of those systems bu t also for applications to many different areas. One research in early years from our group showed the synthesis of monodisperse platinum acetylide oligomers (PAOs) up to seven repeat unit and demonstrated that singlet excited state is delocalized over nearl y six repeat unit whereas triplet state was delocalized over one or at most two repeat unit s . 8 Figure 1 13 . UV Vis absorption and photoluminescence spe ctra of PAOs series of c ompounds in THF. ( adapted with permission from ACS)

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33 Marder and coworkers demonstrated electronic coupling facilitated by the Pt II center was only slightly less than observed in the all organic benzene bridged an alogue by designing mixed valence compound and investigate the intervalence charge transfer. 27 Fundamental investigations continued with the investigation of the structural changes that occurs upon intersystem crossing to the t riplet state with the time resolved infrared spectroscopy. 14 Additional work from our group explored the aggregation effect on the triplet state and interchange triplet energy transfer. As mentioned earlier, p latin um acetylides not only plays important role in understanding the fundamental photophysical properties of conjugated system s but also constitute a part of materials that can be used in useful applications. One such work was done to use the platinum acetylid e in bulk heterojuction solar cells. 28 Transient absorption studies displayed evidence for photoinduced electron transfer from Pt acetylide to PCBM by the temporal evolution of the TA spectrum, observing the formation of PCBM r adical anion at 1050nm. For similar purposes, fulleropyrrolidine end capped platinum acetylide donor acceptor triad was synthesized, photoinduced intramolecular charge transfer was shown to occur rapidly and electron transfer was believed to occur predomin ately through the triplet state as ISC crossing was efficient. 29 Figure 1 14 . Fulleropyrrolidine end capped platinum acetylide donor acceptor triad .

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34 aryl complexes Syn thesis Using organometallic reagents such as organolithium or organomagnesium is probably the earliest technique to generate a bond between sp 2 hybridized aryl carbon and group 10 transition metals.(Pt, Pd, Ni). The following figure illustrated the synthe sis of platinum complexes using those reagents. Figure 1 15 . Synthesis of platinum a ryl complexes using organolithium reagents. 30 One of the drawbacks regarding to this technique is tha t ligands that contain sensitive group s to those highly basic organometallic reagents ca nnot be employed, plus monosubstituted products are achieved via cleavage of one of the ligands of isolated di substituted product (Figure 1 15 ). The reaction between aryl tin compounds and Pt(COD)Cl 2 is another technique to build a bond between platinum an d arenes. 31 The room temperature reaction between Pt(COD)Cl 2 and corresponding aryl trimethyl or tributyltin compounds yield s 1,5 cyclooctadiene platinum complexes in cis configuration in the first step .

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35 Figure 1 16. aryl complexes using Pt(COD)Cl 2 . The cyclooctadiene complex is generally insoluble in common organic solvents and is washed with the reaction solvent to remove tributyltinchloride elimina ted in the reactions. This complex is re suspended in appropriate solvent and subjected to a reaction with desired phosphine ligand. While reaction with one equivalent of aryl tin compounds yields monosubstituted product with phosphine ligands in trans form (Figure1 16a) , the use of two equivalents of tin compound results in the formation of disubstituted product in cis configuration, isomerization of which is necessary if the desired configuration is trans. 32 35 One of the well known synthetic path ways to create bond between arylenes and abovementioned transition metals is oxidative addition. 36 43 Oxidative addition takes place between the aryl halides (chlorides, bromides or i odides) and corresponding zero valent metal complexes. The reaction condition (temperature, reaction time etc.) varies depending on the metal or aryl halides employed. Oxidative addition indeed constitutes

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36 the first step of many of the metal catalyzed reac tions such as Suzuki cross coupling, Stille cross coupling reactions. Figure 1 1 7 . Examples of platinum carbon bond formation via oxidation addition known in the literature. 38, 41 The major disadvantage associated with this techn ique is that zero valent metal complexes used as starting material are generally air and moisture sensitive which make the reaction to be run under inert atmosphere . Second, it generates cis and trans isome ric mixture when platinum is considered as a metal to bind to aromatic system. 44 Photophysics of platinum aryl complexes. Platinum (II) complexes in which platinum is attached to aromatic ring system are not as common as platinum acetylides . The part of the reason is the difficulties associated with their synthesis. Oxidation addition, which has been mentio ned previously, is typically preferred route for achieving their synthesis. Some of the complexes whose photophysical properties have been studied are shown in Figure 1 18 .

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37 Figure 1 18 . Examples of direct metallated comple xes from literature. Eve n though these type molecules were synthesized, they are generally tested as catalyst in cross coupling reactions. The photophysical investigation and consequences of attaching the platinum metal directly to organic chromophores is rare. 45 47 The main purpose of these studies is to address the fundamental questions such as effects of heavy atom on the absorption and emission properties of the organic chromophores when it is attached to the ri bond. For example, such effects have been studied on pyrene whose photophysical properties are well studie d (Figure 1 18a). This report indicated that the metal ion strongly perturb s the electronic structure and causes a red ons and intensify the otherwise forbidden 1 S o to 1 L b transition. Another important observation was the presence of in tramolecular heavy atom effect and P value accompanied by a F . Cyclometallated complexes involving a covalent metal carbon bond can also be given as an example in this class of materials. Synthesis and photophysical investigation of metal complexes where metal is connected to sp 2 hybridized aromatic carbon dates back to 1990s. The first such complex was reported in 1992, where biphenyl was used a s ligand as shown in Figure 1.19 a. 48

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38 Figure 1 bonded to metal. Since the processes involve a net deprotonation of aromatic C H, ligands , like 2 phenylpyridine i s anionic, rather than neutral like dpy. The C ligating atom is a very strong d onor, so that these ligands offer the metal ion a very strong ligand field. The most important consequence for the photophysics and excited state properties is that energy of d d states is raised dative to analogous N N complexes. These types of platinum ( II) complexes have generally 3 MLCT as lowest emitting excited state with the microsecond lifetimes. Switching the ligand from bisdentate (N C) to terdentate (N N C) increases the emission of luminescence due to diminishing of the D 2 d distortion that bisden date complex can undergo . Most of the work on this type of complexes has been done by Che and co workers where lowest excited state is assigned as MLCT or MMLCT depending on the concentration of the c omplexes that is being studied. Photoph ysics of Donor Ac ceptor System s Donor acceptor structures have significance in understanding various numerous processes in chemical and biological system s such as charge and electron transfer. 49 51 They are also ideal system s for st udying nonlinear ab sorption and solvation dynamics. 52 S everal donor acceptor systems find use in laser application and as fluorescent probes. Excited state dipole moment of donor acceptor molecules is an important parameter that suggests the nature of fluorescent state. It is important property of molecules th at not only

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39 provides information on electronic and geometrical structure of the molecule in the short lived excited state but also designing nonlinear optical materials and determination of a course of photochemical transformation. Among the methods to det ermine the dipole moment of excited state of molecule, the most com monly used one is based on the linear correlation between the difference in the wavenumber of the absorption and fluorescence maxima and a solvent polarity function, which usually involves both the dielectric constant linear correlation are known, the most commonly used expression is the one developed by Lippert and Mataga. 53 (1 5) where, (1 6) T he donor acceptor (D A) complex possesses no stabilization energy except the very small resonance ene rgy due to the ionic structure D + A when both the electron donor (D) and the acceptor (A) are in the ground state Figure 1 20a shows t he potential energy (PE) curve for the D A pair in the ground state as a function of donor acceptor di stance (R) . Stability of the complex in the ground state, as indicated by the little depth minimum, is often t oo small to be detected in solution . Figure 1 20b corresponds to zero order neutral, lo cally excited (LE) state of the exciplex, D, A*, where A* represents the lowest singlet excited state of A. , T he cur ve is similar to ( a ) except that it is shifted from the ground state curve by the energy of the photon abso rbed in this case of a large

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40 inte rmolecular distance. The minimum in the curve b, however, is much deeper due to considerable binding energy between the donor and the acceptor in the excited state, and charge transfer resonances due to closeness of the charge transfer (CT) and locally exc ited (LE) states. The PE curve corresponding to the zero order CT state (D + A ) is designated by curve c . When the separation is large, the energy difference between the ground and the CT state is I P E A, where I P is the ionization potential of the donor and E A the electron affinity of the acceptor. Typically, I P of the aromatic compounds are of the order of 7 10 eV, and E A's are of the order of 0 1 eV. Thus at infinite separation the CT state is at least 6 eV above the ground state, and the CT state is above the LE state in order of energy. This causes generation of the free radical ions D + and A from D,A* almost impossible in the vapor phase for normal UV excitation. However, a t smaller intermolec ular separation, the zero order state (D + A ) gains stability partly due to covalent interaction between the radical pairs and partly due to the attractive electrostatic potential between oppositely charged ions. Fo r a typical distance of about 3 Ã… , the gain in energy due to the latte r cause alone will be about 4.8eV if one neglects mutual polarization of the two charged ions. Thus, at smaller intermolecular separation, the energy of the CT state may be gr eater, nearly equal to, or less than that of the neutral LE state. In the first case, only luminescence from the ne utral LE state is possible and the luminescence is al m ost like the donor luminescence. In the second case, strong resonance is expected, leading to a change in the character of luminescence. In the last case, t he luminescence emerges from CT state.

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41 Figur e 1 20. Schematic diagram for the potential energy of charge transfer complexes, as a function of intermolecular separation. Curve a c, in the vapor phase or nonpolar solvent (d) in polar solvent. (adapted with permission from ACS) T he solvation energy due to solute solvent interaction needs to be added to the curves 1a c in solution. The differential solvation of the LE and the CT states due to the difference in their dipole moments brings about large change in energy ordering of the states and curve cross ing. The energy of the LE and the CT states in a solution can be obtained from the experimentally determined electrode potential as explained by Rehm and Weller 54 or using the d ifferent theo retical models of t he dielectric properties of the media In the simplest case, assuming both D + and A are spherical ions of radii R d and R a , respectively the solvation energy is given by In a medium of dielectric constant = 10, for R D =R A = 3 Ã…, this comes out to be 4.3 eV. Thus, even far large D A separation, E CT may be lower than E LE . Figure 1 20 d

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42 gives the PE curve of the CT state in a polar solvent. Evidently curve d in polar medium is much more shallow compared to that in vapor or nonpolar solvent. The difference in energies of the exciplex at large separation and at the distance, R SSIP , corresponding to the solvent shared ion pair (SSIP), is giving by e 2 / R SSIP , which decreases as the polarity increases. In polar solvents there are usually two minima corresponding to the solvent shared ion pair (SSIP) and the contact ion pair (CIP), respectively. The two minima of the curve are separated by an energy barri er, because in going from the SSIP to the CIP solvent has to be squeezed out. The barrier heights are difficult to obtain either theoretically or experimentally. These are expected to be dependent not only on the dielectric constant of the medium but also the specific interaction, such as H bonding ability og the solvent molecules. Thus, isodielectric protic and nonprotic solvents may behave differently. Further, in mixed solvent s due to dielectric enrichment the local composition in the intermediate neighb orhood of the ion pair might be different from that in the bulk. 55 The overview of this study The overview of this dissertation is to synthesize, characterize platinum acetylide and platinum aryl complexes to understand the solution excited state photophysical and electrochemical behaviors of newly synthesized system s . In the second chap ter of this dissertation, the photophysics of a series of platinum acetylide complexes with strong electron acceptor units were studied. We found that all the oligomers showed strong absorption in the visible region and emission from visible to NIR region of the spectrum. In order to determine the energy of charge transfer (CT)

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43 state, electrochemical experiments were cond ucted and we found out that energy of CT s tate is below the energy of first signle t excited state. Second, a series of platinum complexes in which the platinum is directly attached to various oligothi ophene and charge transfer chrom ophores were synthesized. Photop hys ical an d electrochemical properties were investigated and compared to those in which the metal is at t ac h ed to the ring system v ia acetylene unit. Complexes with oligothiophene s showed strong triplet triplet absorption, and relatively good singlet oxygen quantum yields suggesting that complexes promotes triplet state formation upon excitation, on th e other hand, relative intensitie s of triplet triplet absorption and singlet oxygen quantum yield s were lower than those complexes with acetylene linkage. One of the important properties of synthesized complexes is that they all showed very low oxida tion potentials, less than 0.1 V. This observation leads us to study electron tran sfer study with methyl violegen which is a well known electron acceptor in the literature. Third, a new method to form platinum carbon bond was discovered and developed. Mimicking Stille coupling reaction, it was shown that aryl group can indeed be transferred into platinum metal having strong phosphine ligand provided that Cu(I) salts used as catalyst. Different ligands were tested to investigate the scope of the reaction, a library of monosubstituted, symmetrica lly disubstituted and asymmetrically disubstituted platinum complexes were prepared. Basic photophysical properties i.e. ground state absorption, steady state emission in both air saturated and argon purged solutions were studied. Finally, t he novel carbon platinum bond formation reaction was used to synthesize a series of platinum complexes in which benzothiadiazole was and various electron rich

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44 systems was connected via platinum metal. Extensive photophysical and electrochemical investigation was conduct ed on these novel platinum complexes.

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45 C HAPTER 2 SYNTHESIS, PHOTOPHYSICAL AND ELECTROCHEMICAL CHARACTERIZATION OF NOVEL PLATINUM ACETYLIDES WITH DONOR ACCEPTOR CHROMOPHORES Background Investigation of the photophysical properties of donor acceptor system s dates b ack as early as 1980s. 56 58 The concept of intramolecular donor acceptor charge interaction and its influence on molecular photophysics has been studied for many years . 59, 60 The concept of reducing band gap by alternating electron poor and electron rich monomer within a conjugated chain has been used extensively in the past decade to develop polymers and oligomers that exhibit broad absorption and emission throughou t the visible and into the near infrared (near IR) regions of the spectrum . 61 65 Amo ng many building blocks that have been employed to form low band gap materials, 2,1,3 benzothiadiazole (BTD), diketopyrrolopyrrole (DPP) and isoindigo (isoI) emerged as extensively studied electron acceptor unit due to their extended conjugation, large local dipole, low lying frontier orbital level, and good solubility and ease of synthesis on a large scale. 66 68 The oligomers and polymers featuring these acceptor units has been synthesized to generate low band gap materials for applications ranging from sensors 69 71 , electroluminescent materials, organic photovoltaics. The research on donor acceptor systems is of significance in terms of fundamental point of view as well as materials applications. Despite the current significance of donor acceptor conjugated systems in applications, relatively little is known regarding the photophysics of their excited states especially triplet manifold. Platinum acetylides are except ional systems for investigating triplet excited state phenomena like ground stat e absorption to the triplet state, intersystem crossi ng, triplet state absorption to higher tripl et states, and

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46 phosphorescence. 15, 72 Several different electronically rich and poor chromophores were linked by plati num acetylide as spacer and their photochemical and electrochemical behaviors was examined for understanding fundamental phenomena such as photoinduced electron transfer 73 and non linear absorption. 74 As a continuation of our work on platinum acetylides materials, our present contribution focuses on designing and investigating the photophysical behaviors of a Pt acetylide oligomer family in which some electron donating and afo rementioned strong electron withdrawing groups are separated by Pt(II) center as illustrated below. The figure 2 1 shows chemical structure of the complexes that are subject of this chapter. Figure 2 1. Schematic repre sentation of D Pt A Pt D system and t he chemical structure of complexes that are subject of this chapter.

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47 The present investigation explores conjugated oligome rs in which platinum(II) acetylide center don acceptor moi eties i.e. P t A Pt D in which 2,1,3 b enzothiadiazole, 1,4 diketo 3,6 diphenylpyrrolo [3,4 c]pyrrole (DPP) and i soindigo (isoI) as elect ron acceptor units along with tri phenylamine (TPA) as electron donor unit. The objective of this study is two folds, fi rst is to explore the photophysics of two widely used dye molecules in the literature and second is understand ing the degree of donor acceptor interaction that is transmitted through Pt acetylide centers. Results Synthesis Figure 2 1 shows the syn thesis of complexes based on 2,1,3 benzothiadiazole (BTD) acceptor core unit. The first three steps were carried out according to the literature procedures in straightforward way. In the first step, commercially available o phenylenediamine was converted to 2,1,3 benzothiadiazole (BTD) core acceptor unit using thionyl chloride with high yield after direct steam distillation. Bromination was achieved with molecular bromine in the presence of HBr to yield the 4,7 dibromo derivative of BTD (3). Reaction of compound 3 in Sonogashira reaction condition afforded bisacetylated BTD (4). The deprotection reaction that yields bisacetylated BTD was carried out using K 2 CO 3 in MeOH/CHCl 3 . As this unprotected compound was not air stable at room temperature, it was reacted in th e same pot with excess of Pt(PBu 3 ) 2 Cl 2 to yield corresponding platinum dimer (7). This dimer was then reacted with slightly more than 2 equivalents of phenylacetylene (8) and 4 ethynyl diphenylaniline (9) in separate reactions to obtain complexes 10 an d 11.

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48 Figure 2 2. Synthetic s cheme for the synthesis of 2,1, 3 benzothiadiazole (BTD) based c omplexes. The complexes containing 1,4 diketo 3,6 diphenylpyrrolo [3,4 c] (DPP) as core acceptor unit were synthesized using the same strategy as the BTD based complexes The DPP core acceptor unit w as synthesized starting from 4 b romobenzonitrile and diisopropylsuccinate and the resulting deep red colored solid (13) was suspended into DMF to carry out N alkylation using literature p rocedures. Sonogashira reaction between this soluble DPP derivative (14) and trimethylsilyacetylene afforded protected bisacetylene ( 15 ), which then was deprotected to yield 16 in 75% yield. Reaction of compound 16 with excess of Pt(PBu 3 ) 2 Cl 2 gave diplatin ated dimer 17, which then reacted with phenylacetylene and 4 ethynyl presence of a catalytic amount of CuI in Et 3 N to afford complexes 18 and 19 respectively.

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49 Figure 2 3. S ynthetic s cheme for 1,4 diketo 3,6 diphenylpyrrolo [3,4 c] (DPP) based c omplexes. T he complexes containing isoindig o (i so I) were synthesized using similar strategy used for BTD and DPP based complexes. Two commercially available compounds, namely 6 bromois atin and 6 bromooxindole were reacted in the presence of acid catalyst to give 6 , d ibromoisoindigo , which was then alkylated to in crease the solubility of the isoindigo ring system. The Sonogashira reaction was then employed to yield protected a bisacety lene derivative (24). The reaction from compound 24 to 26 ince bisacetylene derivative of isoindigo ( 25 ) is difficult to purify and isolate , we decided to de protect the corresponding pr otected bisacetylene and carry out the next reaction in the same flask after removal of the solvent and filtering K 2 CO 3 . After we

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50 obtained desired Pt dimer, it was reacted with phenylacetylene and 4 ethynyl diphenylaniline in separate reactions to afford complexes 27 and 28. Figure 2 4. Synthetic s cheme for the synthesis of isoindigo (isoI) based complexes Visible Absorption Spectroscopy The absorption and emission spectroscopy of these new complexes were measured to characterize the processes that occur upo n light absorption. Ground state absorption and emission spectra of compounds are shown in Figure 2 6 . In general, all complexes showed one broad absorption band appearing in near UV region which is assigned as 1 er ener gy in the visible region which can be attributed to intramolecular charge transfer (ICT) band. Triphenylamine containing complexes exhibited low energy bands which are 20 nm red shifted with respect to

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51 corresponding phenyl capped complexes, however, no suc h change was observed for the low energy ICT band. Molar extinction coefficients are in the range of 0.5 1.5 x 10 5 cm 1 M 1 , indicating strong light absorption by these complexes. It was noted that the complexes featuring terminal diphenyl amino groups have h igher molar absorptivity than corresponding phenyl capped complexes. Steady State and Time Resolved Photoluminescence Photoluminescence spectroscopy was car ried out on these complexes to gain information regarding the active excited states. The emission e xperiments were carried out under air saturated and degassed conditions. In all cases , single broad structureless emission band ranging between 500 1100 nm region was observed. This observation is very consistent with the previous reports of structures hav ing electron donor and acceptor units in the conjugated backbone. A s these complexes strongly emit in the visible region, one can guess that triplet emission (phosphorescence) should be within the near infrared region of the spectrum. However, unfortunatel y no phosphorescence emission was observed from deoxygenated solutions of these complexes at ambient temperature. Same experiments were carried out at 77K to probe whether any phosphorescence can be detected at low temperature, only the complexes with dike topyrrolopyrrole (DPP) acceptor unit showed small emission peak around 1000nm which corresponds to triplet state energy of 1.26 eV. The figure 2 5 shows the emission spectra of both (PhPt) 2 DPP and (TPAPt) 2 DPP collected in MeTHF solvent glass at 77K. This o bserved peak is more likely ligand based triplet emission and peak value is similar to the published work that report similar emission wavelength from an iridium substituted diketopyrrolopyrrole. 75

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52 Figure 2 5. Photoluminescence spectra of (PhPt) 2 DPP and (TPAPt) 2 DPP at 77K in MeTHF solvent matrix. Samples were excited 350 nm and spectra were recorded using 850 nm long pass filter and scanning the region between 800 1600 nm. Quantum yields of fluorescence were calculated according to the relative actinometry technique. Ru(bpy) 3 2 + f = 0.0 37 in water) 76 was used as standard for the complexes featuring both BTD and DPP acceptor core structure and TPP f = 0.11 in toluene ) 77 was chosen as standard for the isoindigo based complexes. Fluore scence lifetimes obtained with picosecond and nanosecond time resolutions were seen to be fitted to a single exponential decay law. Fluores cence lifetimes varies from 1 to 5 ns giving rise to radiative rate constant, k r , to be in the range of 2x10 8 2x10 9 . The efficiency CT ) and rate constant (k CT ) of decay process from first singlet excited state to charge separated state is calculated for BTD and DPP containing donor acceptor complexes as follows

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53 Where DA is the fluorescence lifetime of donor acceptor (DA) system, and o is the lifetime of non DA system. Figure 2 6 . Absorption and photoluminescence spectra of the complexes in THF solution. The absorption spectra were normalized with respect to low energy absorption band

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54 Transient Absorption In an attempt to observe excited species present following nanosecond excitation of the Pt acetylide complexes, nanosecond microsecond transient absorption spectroscopy was carried out for s amples in degassed THF solution at room temperature. In each case, degassed solutions of the complexes were excited by using 10 ns, 355 nm pulses from a Nd:YAG laser. All the complexes, e xcept those with isoindigo as core acceptor unit, exhibit strong trip let triplet absorption in the visible region (5 50 to 800 nm) . Figure 2 7 . Ground state a bsorption and transient absorption s pectra of (PhPt ) 2 BTD and (TPAPt) 2 BTD ( ) . Experimental Condition for both (PhPt) 2 BTD and (TPAPt) 2 BT D Q Switch: 34 s, Camera Delay : 50 ns , Camera Delay Increments : 500ns

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55 Figure 2 8 . Ground State (top) Transient Absorption (bottom) Spectra of (PhPt) 2 DPP and (TPAPt) 2 DPP ( ) Experimental Condition for (PhPt) 2 DPP , Q Switch : 34 : 50 ns , Camera Delay Increments : 3 s. Experimental Conditions for (TPAPt) 2 DPP Q Switch: 34 Camera Delay : 50ns Camera Delay Increments : 1 s The spectra characterized by bleaching of the ground state absorption in the 450 550 nm re gion , combined with a broad excited state absorption featu re extendin g from 550 to 800 nm (Figure 2 7 and Figure 2 8 ). The transient gives rise to the absorpt ion decays with a lifetime of 2 8 . Virtually similar transient absorption spectra and relativel y similar decay lifetimes were observed for complexes consisting of same acceptor core units .

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56 Table 2 1. Summary of photophysical p roperties Complexes UV VIS max /nm 1 M 1 ) x 10 4 F max / nm f % < f > (ns) TA k CT x10 8 C T % (PhPt) 2 BTD 343 , 489 8.41, 4.07 590 58 5.3 2.53 (TPAPt) 2 BTD 353, 493 14.4, 5.02 600 32 2.8 2.54 1.68 5.6 (PhPt) 2 DPP 323, 512 7.14, 6.22 584 95 3.0 8.00 (TPAPt) 2 DPP 346, 512 12.6, 7.57 586 12 0.46 a 7.14 18.4 80 (PhPt) 2 isoI 320, 57 6 5.40, 3.90 754 0.084 <200ps (TPAPt) 2 isoI 347, 57 9 12.7, 6.24 760 0.054 <200ps a 1 1 ) = 0.46 ( 90.3%); 2 2 ) = 1.18 (2.77 ) Electrochemistry Electrochemical response of the complexes was determined by cyclic voltammetry and differential pulse voltammetry experiments carried out in nitrogen saturated dichloromethane solution with 0.1 M tetrabutylammonium hexafluorophosphate (TBAH). T he ferrocene/ferrocenium couple was used as internal standard. A summary of relevant pot entials is provided in Table 2 2. The complexes with phenyl end group showed two quasi reversible oxidation peaks . The first oxidation is probably metal based oxidation and is around 0.5 V which remains almost identical among similar complexes. This valu e is consistent with those of pr eviously investigated platinum acetylides hav ing [Ph Pt(PBu 3 ) 2 Pt ] unit. 78 The anodic sweeps of all the complexes carrying triphenylamino (TPA ) terminal group as electron rich unit showed oxidation potentials around 0.2 5 0.30 V, which is lower than corresponding phenyl capped complexes due to electron donating effec t of the diphenyl amino group. The cathodic scans of the complexes revealed one electron quasi reversible reduction originating from the electron poor core unit. Complexes having the sa me electron acceptor unit displayed ve ry similar reduction potentials. The cathodic sweeps showed that 2,1,3 benzothiadiazole has least electron

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57 accep ting ability with average reduction potential of 1.90 V, which is slightly higher than those reported in the literature. 79 The observed trend in reduction potentials reflects the electron accepting strength of thes e electron poor chromophores , as BTD being the least and IsoI b eing the most strongly electron acceptors within these series. Figure 2 9 . Cyclic Voltammogram of A) (PhPt) 2 BTD , B) (TPAPt) 2 BTD and differential pulse voltammogram of 2 (TPAPt) 2 BTD .

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58 Figure 2 10 . Cyc lic voltammogram of A) (PhPt) 2 DP P, B ) (TPAPt) 2 DPP on left column and 2 2 DPP. Figure 2 11 . Cyclic Voltammogram of A) (PhPt) 2 isoI, B) (TPAPt) 2 isoI and differential 2 2 isoI.

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59 Table 2 2. Table of Energetics. Complexes E ox a (V) E red a (V) CSS b /(V) E Singlet c /eV E Triplet /eV (PhPt) 2 BTD 0.52 1.88 2.30 1.50 d (TPAPt) 2 BTD 0.28 1.95 2.20 2.27 1.50 d (PhPt) 2 DPP 0.51 1.71 2.12 1.26 e (TPAPt) 2 DPP 0.26 1.71 1.97 2.11 1.26 e (PhPt) 2 isoI 0.52 1.32 1.84 (TPAPt) 2 isoI 0.29 1.28 1.57 1.83 a Potentials reported versus Fc/Fc + b CSS: Cha rge Separated State = E ox E red c Singlet transition energy from photoluminescence spectra. d Estimated from corresponding polymer e Phosphorescence 0 0 band transition energy from Discussions The ground state absorption and emission studies revealed that there is no spectral difference between the complexes which has triphenylamine and phenyl as terminal group. This observation suggests that the dono r and acceptor are weakly coupled in both ground and excited s tate across the platinum center. The model below shows the events that are more likely occurring for the complexes that features the BTD acceptor core unit. Fi gure 2 12. Representative Jablonski Diagram for the photophysical processes for ( TPA Pt) 2 BTD.

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60 The state energies indicate that the energy of the first excited state of this complex is slightly above with that of charge separated state. Deactivation via CT state is possible nonetheless, not quite strong as suggested by the slight decrease observed in the fluorescence quantum efficiency and li fetime. The triplet energy of this complex is assumed to be the same as that of the corresponding platinum acetylide p olymer with 2,1,3 benzothiadiazole as monomer. 80 since the energy of triplet state is below the energy of charge separated state, it is not influenced by the nature of charge separated state. Similar model can be drawn for the DPP based donor acceptor complex, (TPAPt) 2 DPP, shown in Figure 2 13 to map out the events th at takes place upon excitation. First, although singlet excited state and cha rge separated state is close in energy, quantum efficien c y of CT formation is high and the process is very rapid . The triplet state is produced via intersystem crossing directly from singlet excited state as suggested by nanosecond microsecond transient ab sorption experiments. The results of this experiment also revealed that the intensity of transient observed from donor acceptor complex is larger than that of corresponding model complex, which suggest that triplet state can also be formed through the reco mbination of charges from the CT state. S ingle exponential decay rate of triplet excited state remains unaffected by the attachment of the terminal diphenylamino group as the energy of the first triplet excited state, T 1 , is lower than that of charge separ ated state (CSS), just as in the case of BTD based complex.

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61 Figure 2 13 . Representative Jablonski Diagram for the photophysical processes for (TPAPt) 2 DPP Th e isoindigo containing complex, on the other hand, shows very low fluorescence quantum yield efficiency and short singlet excited state lifetimes. The main deactivation mechanism for singlet excited state i s probably nonradiative pathway. it is strongly believed that double bond isomerization upon excitation is the main cause of the quenching of fluorescence. In addition, no triplet triplet absorption signal is obtained in complexes featuring isoindigo (isoI) as acceptor unit. The energy of charge separated state for these complexes is around 1.8eV. It is suggested that such a low lying charge excitation thus not populating triplet excited state (Path a). Alternatively, even though no phosphorescence p eak could be observed from this com plex , the first triplet excited state, T 1 , presumably has very low energy and very short lifetime and once it was generated through the intersystem crossing from the first singlet excited state, it rapidly decays back to ground st ate following nonradiative path (p ath b).

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62 F igure 2 14 . Representative Jablonski diagram for the possible photophysical processes for (TPAPt) 2 isoI. Summary Six new platinum acetylides complexes featuring 2,1,3 benzothiadiazole (BTD), diketopyr rolopyrrole (DPP) and isoindigo (isoI) as electron poor and diphenylamine (TPA) as electron rich chromophores were synthesized and characterized by spectroscopic and electrochemical methods. The donor acceptor interaction transmitted through the platinum ce nter is shown to be weakly coupled in this series of complexes. The laser flash photolysis experiments revealed that acquired transients has lifetimes in the microsecond regime, which indicates that they are triplet states. Electrochemical experiments pre dicted the approximate energy level of charge separated state which is found to be slightly lower than singlet excited state but higher in energy than first triplet quantum yields and very low lifetimes, further investigation with ultrafast spectroscopy system is necessary to find out the fast processes occurring upon absorption of light.

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63 Experimental Instrumental and Methods All the reactions were conducted under a nitrogen atmosphere. 1 H, 13 C, 31 P nuclear magnetic resonance (NMR) s pec tra were recorded on Mercury FT 300 MHz and Inova FT 500 MHz Instruments . The chemical shifts in 1 H and 13 C NMR spectra were recorded to relative to protonated solvent CHCl 3 1 7.16 for 13 C NMR). The chemical shifts in 31 P NMR spectra were recorded relative to 85% H 3 PO 4 as an internal standard. High Resolution Mass spectra were obtained using Agilent 6200 ESI TOF or AB Sciex 5800 MALDI TOF/TOF Instruments. Steady state absorption spectra were recorded on a UV 1800 Simadzu spectrop hotometer. Corrected steady stat e emission measu rements were conducted in SPEX F 112 Fluorescence Spectrometer. Samples were degassed by argon purging for 30 minutes. Concentrations were adjusted such tha t the solutions were optically dilute. Photoluminescence quantum yields were dete rmined by relative actinometry. Materials Thionyl chlori de, hydrogen bromide, bromine, copper (I) i odide, phenyl acetylene, 4 bromobenzonitrile, diisopropylsuccinate, 2 ethyl hexylbromide, sodium tert butoxide was purchased from Sigma Aldrich. Bis(triphenylphosphine)palladium(II) dichloride and t rimethylsilyacetylene were purchased from Stem chemicals. 4,7 bis((trimethylsilyl)ethynyl)benzo[c][1,2,5]thiadiazole 79 , 3,6 bis(4 bromophenyl) 2,5 pyrrolo[ 3,4 c]pyrrole 1,4(2H,5H) dione 81 , 3,6 bis(4 bromophenyl) 2,5 bis(2 ethylhexyl)pyrrolo[3,4 c]pyrrole 1,4(2H,5H) dione 82 , dibromoisoindigo -

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64 dibromo (2 ethylhexyl) isoindigo 8 3 were synthesized according to literature procedures. Synthesis (2,1,3 benzothiadiazoledi 4,7 ethynyldiyl 2 )]tetrakis( tributylphosphine) diplatinum (7 ) This complex was synthesized according to the modification of the literature procedur e. Dichlorobis(tributylphosphine)platinum (II) (400 mg, 0.597 mmol) was dissolved in 20 ml Et 2 NH and degassed for 30 minutes with argon and then, 4,7 (b isethynyl) 2,1,3 benzothiadiazole (50 mg, 0.271 mmol) was added to the system at once. The resulting sol ution was stirred at 60 o C and heated at this temperature until all starting materials were used up as followed by TLC (approximately one hour). The mixture was cooled to room temperature and solvent was evaporated in vacuo . The crude material was purified by column chromatography using silica gel as adsorbent and 1:1 DCM/Hexane mixture as eluent (Yield : 48%). 1 H NMR (300 MHz, CDCl 3 ) 7.27 (s, 2H), 2.05 2.16(m, 24H), 1.67 1.52 (m, 24H), 1.45 (sextet, J= 7.2Hz, 24H), 0.90 (t, J=7.2Hz 36H). 13 C NMR (75 MHz, CDC l 3 ) 156.24, 130.20, 119.23, 98.53, 93.18 (t, J P C = 14.5Hz) 26.09, 24.26 (t, J P C = 6.7 Hz) 21.87 (t, J P C = 16.7), 13.78. 31 J Pt P = 2355 Hz) . (PhPt) 2 BTD (10 ) Phenylacetylene (20 mg, 0.076 mmol) was dissolved in 10 ml of freshly disti lled Et 3 N and degassed for 30 minutes, then 50 mg of (PtCl) 2 BTD ( 6 ) was added along with a catalytic amount of CuI (~2 mg) and resulting mixture was stirred at room temperature overnight. CH 2 Cl 2 was added to the residue followed by the evaporation of solve nt and extracted with deionized water several times. The organic layer was dried over MgSO 4 and

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65 evaporated in va cuo . The resulting crude sample was purified by column chromatography using silica gel as adsorbent and 1:1 DCM/Hexane mixture as eluent (Yield : 65 % ) . 1 H NMR (500 MHz, CDCl 3 ) 7.29 (s, 2H), 7.27 (d, 4H, J =7.5), 7.20 (t, 4H, J =7.5), 7.11 (t, J =7.5), 2.3 2.10 (m, 24H), 1.70 1.50 (m, 24H), 1.50 1.38 (sextet, J =7Hz, 24H), 0.90 (t, J =7Hz, 36H). 13 C NMR (75 MHz, CDCl 3 ) 156.56, 131.01, 130.59, 129.34 , 128.06, 125.00, 119.7, 109.44, 24.64 (t, J =7Hz), 24.61(t, J =17Hz), 24.01, 14.07 . 31 4.21 ( J Pt P = 2347 Hz). HRMS (ESI M + ) m / z calcd for C 74 H 120 Cl 2 N 2 P 4 Pt 2 S 1582.7412, found 1582 . 7451 (T PAPt) 2 BTD (11 ) 4 ethynyl diphenylaniline (20 mg, 0.076 mmol) was dissolved in 10 ml freshly distilled Et 3 N and degassed for 30 minutes , then 50 mg of (PtCl) 2 BTD (6) was added along with catalytic amount of CuI (~2 mg) and the resulting mixture was stirred at room temperature overnight. CH 2 Cl 2 was added to the residue and extracted with deionized water several times . The organic layer was dried over MgSO 4 and evaporated under vacuum . The resulting crude sample was purified by column chromatography using silica gel as adsorbent and 1:1 DCM/H exane mixture as eluent (Yield: 55 % ). 1 H NMR (300 MHz, CDCl 3 ) 7.30 (s, 2H), 7.29 7.19 (m, 8H), 7.18 7 .16 (m, 4H), 7.10 7.05 (m 8H), 2.23 2.15 (m, 24H), 1.69 1.50 (m, 24H), 1.50 1.38 (sextet, J =7Hz, 24H), 0.90 (t, J =7Hz, 36H). 13 C NMR (75 MHz, CDCl 3 ) 156.57, 148.03, 144.92, 131.88, 130.51, 129.34, 124.26, 122.62, 119.32, 109.190, 107.53, 106.50, 26.63, 24. 63 (t, J =Hz) 24.05 (t, J= 17Hz), 14.09 . 31 P ( J Pt P = 2344 Hz). HRMS (MALDI, M+H + ) m / z calcd for C 98 H 138 N 4 P 4 Pt 2 SH 1917.8903 , found 1917.89 31 .

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66 2,5 B is(2 ethylhexyl) 3,6 bis(4 ((trimethylsilyl)ethynyl)phenyl)pyrrolo[3,4 c]pyrrole 1,4(2H,5H) dione (15) 25 ml Schenk Flask was char ged with 3,6 bis(4 bromophenyl) 2,5 bis(2 ethylhexyl)pyrrolo[3,4 c]pyrrole 1,4(2H,5H) dione (14) (0.1628 g, 0.243 mmol) 10 ml of iPr 2 NH/Toluene mixture was injected and the resulting mixture was degassed for 30 minutes. Pd(PPh 3 ) 2 Cl 2 (42.6 mg ) and CuI (11.5 mg, 0.0607 mmol) were added to the system via a stream of argon and the system was degassed for 30 minutes more. Trimethylsilyacetylene (0.119 g , 1.21 mmol) was added at once. The temperature was brought to 80 o C and the system was stirred at this temperat ure overnight. The crude product was purified by column chromatography using silica gel as adsorbent and 2: 1 DCM/Hexane as eluent (Yield : 82 % ) . 1 H NMR (500 MHz, CDCl 3 ) 7.76 (d, 4H , J= 9Hz), 7.61 (d, 4H, J= 9Hz), 3.75 (m, 4H), 1.49 (m, 2H), 11.27 1.10 (m, 16H), 0.82 (t, 6H, J =7 Hz), 0.72 (t, 6H, J =7.5 Hz), 0.29 (s, 18H). 13 C NMR (125 MHz, CDCl 3 ) 162.8, 148.1, 132.5, 128.7, 128.4, 126.03, 110.50, 104.6, 97.7, 45.4, 38.7, 30.5, 28.5, 23.9, 23.1, 14.2, 10.62, 0.12. HRMS (APCI, M+H + ) m / z calcd for C 44 H 60 N 2 O 2 Si 2 705.4246 , found 705.428 1 . 2,5 B is(2 ethylhexyl) 3,6 bis(4 ethynylphenyl)pyrrolo[3,4 c]pyrrole 1,4(2H,5H) dione (16) 2,5 B is(2 ethylhexyl) 3,6 bis(4 ((trimethylsilyl)ethynyl)phenyl)pyrrolo[3,4 c]pyrrole 1,4(2H,5H) dione (15) (166 mg, 0.235 mmol) was dis solved in 15 ml of DCM in 50 m l round bottomed flask then tetrabutylammonium difluorotriphenylsilicate (254 mg, 0.471 mmol) was transferred to the reaction vessel. The reaction was complete after 4 hours . The crude product was purified by column chromatogr aphy by using silica gel as

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67 adsorbent and 3:1 DCM/ Hexane as eluent . (Yield : 75%) 1 H NMR (500 MHz, CDCl 3 ) 7.76 (d, 4H , J = 9Hz), 7.62 (d, 4H, J = 9Hz), 3.73 (m, 4H), 3.23 (s, 2H), 1.47 (m, 2H), 1.25 1.03 (m, 16H), 0.79 (t, 6H, J=7 Hz), 0.70 (t, 6H, J=7 .5 Hz). 13 C NMR (125 MHz, CDCl 3 ) 162.79, 148.20, 135.21, 132.71, 128.85, 128.76, 125.01, 83.23, 79.97, 45.31, 38.79, 30.52, 28.47, 23.94, 23.08, 14.16, 10.62. HRMS (APCI, M+H + ) m / z calcd for C 38 H 44 N 2 O 2 561.3476, found 561.3478 Complex (PtCl) 2 DPP (17) Dic hlorobis(tributylphosphine)platinum (II) was dissolved in 5 ml of HNEt 2 and argon purged for 30 minutes then 5 bis(2 ethylhexyl) 3,6 bis(4 ethynylphenyl)pyrrolo[3,4 c]pyrrole 1,4(2H,5H) dione (25 mg, 45 mmol) was added to the system and the resulting solut ion was stirred at 60 o C under static argon pressure overnight. The crude product was purified by column chromatography using silica gel as adsorbent and 4:1 Hexane/DCM mixture as eluent. (Yield : 50%) 1 H NMR (500 MHz, CDCl 3 ) 7.70 (d, 4H, J= 8.5Hz), 7.34 (d, 4H, J= 8.5Hz), 3.78 (m, 4H), 1.96 2.09 (m, 24H) 1.52 1.63 (m, 24H), 1.51 1.43 (m, 24H), 1.29 1.03 (m, 18H), 0.95 (t, 36H) 0.80 (t, 6H, J =7 Hz), 0.73 (t, 6H, J =7.5 Hz). 13 C NMR (125 MHz, CDCl 3 ) 163.22, 148.42, 132.04, 131 .19, 128.61, 125.19, 109.8, 45.39, 38.63, 30.53, 28.46, 26.38, 24.55 (t, J = 7 Hz) 23.97, 23.11, 22.27 (t, J = 17 Hz) 14.19, 14.05, 10.65. 31 J Pt P =2345 Hz). HRMS (MALDI, M+H + ) m / z calcd for C 86 H 15 0 C 2 N 2 O 2 P 4 Pt 2 1828.9323, found 1828.92 99 . (PhPt) 2 DPP (18) Phenylacetylene (7 mg, 68.5 3 N and degassed for 30 minutes, then (PtCl) 2 DPP (17) (50 mg, 27.4 of CuI (~2 mg) was added to the system under a stream of argon. The resulting solution

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68 was stirred at room temperature overnight. The crude product was purified by column chromatography using silica gel as adsorbent and 1:1 DCM/Hexane as eluent (Yield : 70 %) . 1 H NMR (500 MHz, CDCl 3 ) 7.68 (d, 4H , J= 8.5Hz), 7.345 (d, 4H, J= 8.5Hz), 7.27 (d, J =7Hz, 4H), 7.20 (m, 4H), 7.11 (d, J =7Hz, 2H), 3.78 (m, 4H), 2.16 2.11 (m, 24H) 1.65 1.54 (m, 24H), 1.51 1.43 (sextet, J = 7.5 24H) 1.26 1.05 (m, 18H), 0.93 (t, J =7.5, 36H) 0.79 (t, 6H, J =7 Hz), 0.72 (t, 6H, J =7.5 Hz). 13 C NMR (125 M Hz, CDCl 3 ) 163.28, 148.4, 132.21, 131.18, 131.03, 129.21, 128.60, 128.08, 125.11, 124.92, 114.88 (t), 109.76(t), 107.79 (t), 45.4, 38.6, 28.4, 26.3, 24.6 (t, J =6.6 Hz) 23.9, 23.1, 22.2 (t, J = 16.5 Hz) 14.2, 14.1, 10.7. 31 J Pt P = 2345 Hz). HRMS (APCI , M+H + ) m / z calcd for C 102 H 160 N 2 O 2 P 4 Pt 2 H 1961.0823, found 1961.0743 (T PAPt) 2 DPP (19) 4 ethynyl diphenylaniline (9 ) ( 16 mg , 60 3 N and degassed for 30 minutes then, (PtCl) 2 DPP ( 17) ( 50 mg, 27 as added to the system with the catalytic amount of CuI (~2 mg). The resulting mixture was stirred at room temperature overnight. The crude product was purified by column chromatography using silica gel as adsorbent and 1:1 DCM/ Hexane as eluent. (Yield : 60 % ) 1 H NMR (500 MHz, CDCl 3 ) 7.68 (d, 4H , J= 8.5Hz), 7.345 (d, 4H, J= 8.5Hz), 7.27 (d, J =7Hz, 4H), 7.20 (m, 4H), 7.11 (d, J =7Hz, 2H), 3.78 (m, 4H), 2.20 1.96 (m, 24H) 1.65 1.52 (m, 24H), 1.51 1.43 (sextet, J = 7.2 24H) 1.26 1.03 (m, 18H), 0.92 (t, J =7.2, 36H) 0.79 (t, 6H, J =7 Hz), 0 .72 (t, 6H, J =7.5 Hz). 13 C NMR (125 MHz, CDCl 3 ) 163.28, 148.03, 145.02, 131.88, 131.170, 129.35, 128.60, 124.22, 124.19, 122.66, 45.43, 38.60, 30.55, 26.60, 24.66 (t, J =7 Hz) 24.12 (t, J =17Hz), 23.98, 23.12, 14.20, 14.09, 10.65. 31

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69 ( J Pt P = 2352 Hz). HRMS ( MALDI, M + ) m / z calcd for C 126 H 178 C l2 N 4 O 2 P 4 Pt 2 2294.2217, found 2294.2222. B is(2 ethylhexyl) 6,6' bis(trimethylsilyl)ethynyl) isoindigo (24) 25 ml round diethylhexyl d ibromo isoindigo ( 23) (500 mg, 0.78 mmol) then 10 ml iPr 2 NH/toluene solvent mixture was injected and the system was degassed for 30 min utes by bubbling argon. Pd(PPh 3 ) 2 Cl 2 (136 mg, 0.19 mmol) and CuI (37 mg, 0.19 mm ol) were added to the system under a stream of argon, then the system was degassed for 30 minutes more. Trimetylsilyacetylene was added (381 mg, 3.88 mmol) via syringe at once. The temperature was brought to 80 o C and the reaction was refluxed overnight. The resulting crude mixture was passed through a short path o f alumina and celite concentrated in vacuo. The title compound was obtained after column chromatogra phy by using gradient elution ( 25 % to 50 % DCM in Hexane (Yield : 50 %) 1 H NMR (300 MHz, CDCl 3 ) 9.11 (d, 2H, J =6Hz), 7.12 (dd, 2H, J 1 = 6Hz J 2 = 1Hz), 6.8 2(d, 2H, J 2 =1Hz) 3.70 3.60 (m, 4H), 1.91 .85 (m, 2H), 1.48 1.24 (m, 16H), 0.97 0.90 (m, 12H) 0.31(s, 18H). 13 C NMR (75 MHz, CDCl 3 ) 168.4, 145.2, 133.1, 129.7, 126.9, 126.4, 122.1, 111.2, 105.51, 98.10, 44.6, 37.6, 30.8, 28.8, 24.2, 23.3, 14.3, 10.9, 0.14 . HRMS (APCI, M+H + ) m / z calcd for C 42 H 58 N 2 O 2 Si 2 679.4110, found 679.4137. B is(2 ethylhexyl)6,6' bisethynyl isoindigo (25) bis(2 ethylhexyl) 6,6' bis(trimethylsilyl)ethynyl) isoindigo (225 mg, 0.328 mmol) was dissolved in 15ml of DCM in 50ml round bottom flask then tetrabutylammonium difluorotriphenylsilicate (354 mg, 0.655 mmol) was transferred to the reaction mixture. The reaction was completed after 4h as monitored by TLC. The crude product was subjected to column chromatography with silica gel and 1/1 DCM/Hexane as eluent (Yield

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70 : 30%) 1 H NMR (300 MHz, CDCl 3 ) 9.15 (d, 2H, J = 8Hz), 7.12 (dd, 2H, J 1 = 8Hz J 2 = 1.5Hz), 6.82 (d, 2H, J 2 =1.5Hz) 3.72 3.62 (m, 4H), 3.3(s, 2H) 1.91 1.85 (m, 2H), 1.44 1.27 (m, 16H), 0.97 0.90 (m, 12H). 13 C NMR (75 MH z, CDCl 3 ) 168.29, 145.30, 133.32, 129.89, 126.50, 125.96, 122.29, 111.47, 84.13, 80.27, 44.60, 37.68, 30.86, 28.84, 24.25, 23.31, 14.29, 10.90. HRMS (ESI, M+Na + ) m / z calcd for C 36 H 42 N 2 O 2 Na 667.1331 found 667.1342 . (PtCl) 2 iso I (26) bis(2 ethylhexyl)6 ,6' bis(trimethylsilyl)ethynylisoindigo ( 113 mg, 0.153 mmol ) was dissolved in a mixture of CHCl 3 and MeOH and argon purged for 30 minutes. Then K 2 CO 3 (0.3655 mmol, 51 mg) was added to the mixture. The reaction was completed after 2h as it was followed by TLC, then all solvent was evaporated and 113 mg, 0.153 mmol of cis d ichlorobis(tributylphosphine)platinum (II) and catalytic amount of CuI (~3 mg) in Et 2 NH/CHCl 3 solvent mixture added via syringe. The temperature of the system was brought to 60 o C and heat ed at this temperature overnight. The resulting residue was subjected to column chromatography using silica gel as adsorbent and 1:1 Hexane/DCM mixture as eluent (Yield : 50%) 1 H NMR (300 MHz, CDCl3) 9.15 (d, 2H, J =8Hz), 7.12 (dd, 2H, J 1 = 8Hz J 2 =1.5Hz), 6.82 (d, 2H, J 2 =1.5Hz) 3.72 3.62 (m, 4H), 3.3(s, 2H) 1.91 1.85 (m, 2H), 1.44 1.27 (m, 16H), 0.97 0.90 (m, 12H). 13 C NMR (125 MHz, CDCl3) 169.19, 145.01, 131.45, 131.11, 129.09, 125.07, 121.80, 119.59, 110.27, 91.51, 44.61, 37.99, 31.09, 29.13, 26.51, 2 4.75 (t, J = 7Hz), 24.37, 23.54, 22.41 (t, J = 17Hz) , 14.49, 14.49, 11.11. 31 P NMR (121 MHz, CDCl 3 ) 8.27 ( HRMS (MALDI, M + ) m / z calcd for C 84 H 148 Cl 2 N 2 O 2 P 4 Pt 2 1803.9243 found 1803. 9165 .

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71 (PhPt) 2 iso I (27) Phenylacetylene (6.2 as dissolve in 10ml of Et 3 N and degassed for 30 minutes then, (PtCl) 2 iso I (50 mg, 0.03 mmol) was added with catalytic amount of CuI (~2 mg) and the resulting mixture was stirred overnight. The resulting mixture was poured into water and extracted with DCM several times. The o rganic layers were collected and dried over MgSO 4 before evaporation. The crude product was purified by using column chromatography using silica gel as adsorbent and 1:1 DCM/Hexane as eluent (Yield : 65 %). 1 H NMR (500 MHz, CDCl 3 ) 8.9 8 (d, 2H, J =10Hz), 7.30 (d, 4H) 7.23 (t, J =7.5Hz, 4H) 7.14 (t, J =7.5Hz, 2H), 6.65 (s, 2H), 3.65 (m, 4H), 2.09 2.26 (m, 24H), 1.90 (m, 2H), 1.53 1.70 (m, 24H), 1.43 1.53 (sextet, J =7.2 24H), 1.28 1.40 (m, 16H), 0.95 (t, J =7.5, 36H), 0.90 (t, J =7.5, 12H ). 13 C NMR (125 MHz, CDCl3) 169.19, 145.01, 131.45, 131.11, 129.09, 125.07, 121.80, 119.59, 110.27, 91.51, 44.61, 37.99, 31.09, 29.13, 26.51, 24.75 (t, J = 7Hz), 24.37, 23.54, 22.41 (t, J = 17Hz) , 14.49, 14.49, 11.11. 31 P NMR (121 MHz, CDCl 3 ) 4.37 ( HRMS (MALDI, M + ) m / z calcd for C 100 H 158 N 2 O 2 P 4 Pt 2 1935. 0666 found 1935.0644. (TPAPt) 2 isoI (28) 4 ethynyl diphenylaniline ( 16 mg, 0.059 mmol ) was dissolve d in 15 ml of Et 3 N and degassed for 30 minutes then, (PtCl) 2 iso I ( 48mg, 0.027 ) was added with catalytic amount of CuI (~2mg) and the mixture was stirred overnight. The resulting mixture was poured into water and ext racted with DCM several times. The o rganic layers were collected and dried over MgSO 4 before evaporation. The crude product was purified by using column chromatography using silica gel as adsorbent and 1:1 DCM/Hexane as eluent (Yield : 65 %). 1 H NMR (500 MHz, CD 2 Cl 2 ) 8.95 (d, 2H, J =8.5Hz), 7.23 (m, 4H) 7.13 (d, J

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72 =8.5Hz, 2H) 7.04 (dd, J 1 =8.5Hz, J 2 =1Hz), 6.98 (m, 2H), 6.90 (d, J =8.5Hz, 2H), 6.87 (dd, J 1 =8 .5Hz, J 2 =1.5Hz), 6.63 (s, 2H) 3.64 (d, J =8Hz, 2H), 2.07 2.20 (m, 24H), 1.56 1.66 (m, 24H), 1.41 1.50 (sextet, J =7.2 24H), 1.26 1.40 (m, 9H), 0.93 (t, J = 7Hz, 39H), 0.88 (t, J =7Hz, 6 H). 13 C NMR (125 MHz, CD 2 Cl 2 ) 168.78, 147.78, 144.930, 144.82, 131.46, 130.86, 129.11, 128.83, 124.28, 123.94, 123.89, 122.51, 119.07, 109.93, 108.99, 44.02, 37.60, 30.67, 29.68, 28.69, 26.36, 24.44 (t, J = 7Hz), 23.91 (t, J = 17Hz) , 23.14, 13.85, 13.62, 10.45. 31 P NMR (121 MHz, CDCl 3 ) 4.37 HRMS (MALDI, M + ) m / z calcd for C 84 H 148 Cl 2 N 2 O 2 P 4 Pt 2 2269.2139 found 2269.2136.

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73 CHAPTER 3 SYNTHESIS, CHARACTERIZATION, PHOTOPHYSICAL AND ELECTROCHEMICAL STUDIES ON Pt DIMERS WITH OLIGOTHIOPHENES AND CHARGE TRANSFER CHROMOPHORES Background conj ugated semiconducting materials that has potential applications in sensors 84 , photovoltaic cells 85, 86 , field effect transistors 87 , and light emitting diodes 88 . The extensive investigation of the photophysical properties of the oligothiophenes dates back to 1995. 89 In subsequent years, many othe rs worked on solution and thin film photophysics of oligothiophenes in order to gain insight on the excited state energies and dynamics. 90 96 Substitutional effects on pho to physical properties of oligothiophenes wer e also studied by various research groups. 89, 92, 97 101 Chromophores featuring donor acceptor intramolecular charge transfer (ICT) band has also been extensively employed in last two decades to generate low band g ap materials for desired applications, however , there are only few reports that investigations of the triplet excited states of these compounds. 102, 103 Even though intersystem crossing to triplet excited state is n ot efficient in purely organic molecules because of the weak spin orbit coupling, the first triplet excited state of oligothiophenes is accessible due to the heavy atom effect of sulfur atom. 89 The attachment of heavy atom, i.e. platinum, conjugated system significantly enhance s the spin orbit coupling and leads the efficient production of long lived triplet excited states. 12, 14, 104 Metal complexes of both oligothiophenes and charge transfer chromophores were prepared to explore the effects of metal on the photophysical and electrochemical properties of these systems. In many of the complexes studied so far, platinum metal are introduced to the organic framework via acetylene bridge. For

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74 example, one recent study in our group has disclosed the systematic photophysical investigation (singlet and triplet excited state) of a series of D A D type charge transfer chromophores with varying acceptor strength in which terminal donor units are linked to me tal center via acetylene bridge (unpublished results by Seda Cekli) . As a continuation of conjugated materials, we have synthesized and explored the photophysical and electrochem ical properties of Pt complexes with various oligothiophenes and charge transfer chromophores in which the platinum is directly attached to the ring system. The figure 3 1 shows the structure of the complexes which are the subject of this chapter. Figure 3 1. Structure of the complexes discussed in this chapter.

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75 The synthesis of Pt 2 Th1 and Pt 2 Th 2 was described earlier. 105 (PtCC) 2 TBT, (PtCC) 2 TQT were synthesized, photophysical and electroc hemical properties were studied by Seda Cekli . They will be discussed for comparison with Pt 2 TBT and Pt 2 TQT. Results Synthesis

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76 Figure 3 2. Synthesis of Complexes Pt 2 Th 1 and Pt 2 Th 3 .

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77 Figure 3 3. Synthesis scheme of Pt 2 Th 2 and Pt 2 Th 4 . Figure 3 4. Synthesis s cheme for Pt 2 TBT

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78 Figure 3 5. Synthetic Scheme for Pt 2 TQT UV Vis Absorption Spectroscopy UV visible absorption spectra of complexes and corresponding tin compounds were taken in THF to investigate spectral changes upo n attachment of platinum metal to conjugated system. The smallest member of the oligothiophene family, Pt 2 Th 1 , showed broad absorption with three shoulder like peaks at around 240, 260 and 290 nm respec tively. (Figure 3 6) . Platinum dimers w ith higher number of thiophene rings showed a single absorption peak around near UV region of the spectrum. max values of each complexes are found as 356, 401 and 435 nm respective ly . It was noted that intense bands are accompanied by the relatively w eak bands for Pt 2 Th 2 , Pt 2 Th 3 and Pt 2 Th 4 in the visible region of the spectrum, roughly from 400 to 550 nm region depending on the number of thiophene rings in each complexes.

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79 Figure 3 6. Absorption Spectra of Sn 2 Th 1 and Pt 2 Th 1 On the other hand, t hose dimers with charge transfer chromophores , Pt 2 TBT and Pt 2 TQT exhibited two peaks, o ne of which is in the UV region and oth er one is in the visible region which can be attributed as internal charge transfer band. Both of the bands in these spectra also showe d red shift upon binding to the platinum center (Figure 3 8 ) with respect to their tin derivatives . Steady State and Time Resolved Photoluminescence

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80 Fi gure 3 7. Absorption Spectra of the complexes Pt dimers with oligothiophenes and their corresponding tin derivatives.

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81 Figure 3 8. Normalized Absorption Spectra of Pt 2 TBT and PT 2 TQT and their corresponding tin precursors Sn 2 TBT( ---) and Sn 2 TQT.

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82 Steady state p hotoluminescence measurement was carried out with solutions deoxygenated via three freeze pump thaw cycles in order to detect phosphorescence from these complexes. However, no phosphorescence was observed at both 273 K in THF and 80 K in MeTHF solvent glass. Decreasing the temperature to 80 K resulted in f luorescence bands slightly blue shifted due to well known rigidochromic effect resolution of bands into more structured shape is noticed, each of whic h corresponds to the vibrational progressions (Figure 3 10). Photoluminescence spectra of the complexes having charge transfer chromophores were also recorded in dilute THF solution. (Figure 3 12). Broad single structureless emission bands are obtained as expected from typical chromophores with internal charge transfer band. The fluorescence lifetimes of these complexes, Pt 2 TQT and Pt 2 TBT are relatively similar to those of platinum acetylide, however, fluorescence quantum yields are found to be lower than t hat of parent platinum acetylides suggesting that stronger intersystem crossing takes place in the former.

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83 Figure 3 9 . Photoluminescence Spectra for A) Pt 2 Th 2 , B) Pt 2 Th 3 and C) Pt 2 Th 4 with emission from exciting different wavelength .

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84 Figure 3 10 . Ph otoluminescence spectra of platinum dimer s featu ri ng oligothiophenes at 273K in THF and 80K in MeTHF solvent glass. Figure 3 11 . Absorption and photoluminescence spectra of the complexes Pt 2 TBT and Pt 2 TQT recorded in THF.

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85 Transient Absorption Spectrosc opy We have also studied t he transient absorption of platinum dimers having charge transfer chromophores. These complexes showed relatively weak er triplet triplet absorption transients with respect to structurally similar platinum acetylide complexes. [( PtCC ) 2 TBT and ( PtCC ) 2 TQT) ] . These complexes are also found be to be singlet oxygen sensitizer with si nglet oxygen quantum yields of 0.05 for Pt 2 TBT and 0.21 for Pt 2 TQT in CDCl 3 relative to terthiophene used as standard. However, singlet oxygen quantum yield are somewhat smaller than those similar platinum acetylide complexes . Figure 3 12 . Nanosecond m icrosecond transient absorption s pectra of A) Pt 2 Th 2 (black) , Pt 2 Th 3 (red) and Pt 2 Th 4 (blue) and B) Pt 2 TBT (black) and Pt 2 TQT (red) on the deoxygenated THF solutions

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86 Table 3 1. Photop hysical Summary of Complexes Electrochemistry

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87 Figure 3 13 . Anodic sweeps in cyclic voltammogram and differential p ulse v oltammogram of Pt 2 Th n where n =1,2,3,4.

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88 Figure 3 14 . Cyclic Voltammogram (on the left) and Differential Pulse Voltammogram (on the right) of Pt2TBT . T able 3 2 . Summary of electrochemical data. * Data provided by Seda Cekli,

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89 Discussion Oligothiophenes , Pt 2 Th n Series UV Visible A bsorption . UV visible absorption spectra of complexes and corresponding tin compounds were recorded in THF. The observed absorption bands near UV region . It is noticed that there is a red shift up to 50 n m upon replacing the terminal tin groups with platinum metal, electronic system of organic system. Almost same degree of bathochromic shift was also noticed among the dimers as the number of thie nyl unit increases f rom 1 to 4 due to increased conjugation. It was noted that there is no correlation between the number of thiophene units and experimentally measured extinction coefficients among the complexes, however in general, extinction coefficient s of the complexes are less than those of structurally similar platinum acetylides due to the absence of acetylene linking unit in these complexes. 106 Fluorescence quantum yields are found to be very low in these c omplexes . ( f < f ranges from 5 to 18 %) indicating that intersystem crossing is efficiently working due to enhanced spin orbit coupling induc ed by the heavy metal platinum.

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90 Redox States . Bimolecular Electron Transfer . The electrochemical experiments indicated that the first oxidation potentials of platinum dimers are lower than 0.1 V. Gi ven this fact, a bimolecular electron transfer quenching experiment was carried out using Pt 2 Th 3 and Pt 2 Th 4 and dimethyl bipyridinium ( also known as methyl violegen, MV 2+ ) as an electron transfer quencher to acquire information concerning photo physic s of polaron states, i.e. the absorption spectra of radical cations.

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91 For an electron transfer to be thermodynamically feasible, difference between the excited stat e oxidation potential and the ground state reduction potential of the acceptor should b e negative. In order to show that electron transfer is thermodynamically feasible, excited state oxidation potential can be calculated as follows E (T*/T + ) = E(T/T + ) E es (T) ( 3 1) In equation 3 1, E(T*/T + ) represents excited state oxidation potential, E(T/T + ) represents ground state oxidation potential and E es represents the excited state energy of the donor molecules. E es is designated as the E es (T) since the states of the abovementioned platinum dimers could not be derived from relevant electron trans fer is believed to occur from the first triplet excited state of the donor. The energies of the first triplet excited photoluminescence spectra since these complexes failed to show phosphorescen t any at both 29 timtche 3 K and 80 K. However, the first tripl et excited state energies can be estimated following the assumption of E T = E S 0.7 eV where E T is the first lowest triplet excited state and E S is the first lowest singlet excited state. From this assumption, the first triplet excited state of Pt 2 Th 3 and Pt 2 T h 4 was calculated as 2.02 and 1.78 eV respectively. When the corresponding number s are placed in the equation above, the excited state oxidation p otentials are going to be 1.98 and 1.73 V. Then, the free energy change regarding the electron transf er can be calculated as follows. ET ,Pt2Thn = E Ox (T*/T + ) Ered (MV 2+ /M +. ) (3 2) ET ,Pt2Th3 = 1.93 ( 0.45) = 1.48 (3 3) ET ,Pt2Th 4 = 1.73 ( 0.45) = 1.28 (3 4)

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92 Figure 3 15 . Transient a bsorption difference spectra of A ) Pt 2 Th 3 B ) Pt 2 Th 4 and MV 2+ in THF/MeCN (3:2) solution. The solution of com plexes was prepared with optical density of 0.7 at 355 nm a nd the concentration of MV 2+ was 1mM. Spectra obtained at delay increments of 100ns. The spectral evolution indicates the decrease in intensity of triplet triplet absorption band and raising a ban d that corresponds to the absorption of radical cations of Pt 2 Th 3 at around 575 nm and Pt 2 Th 4 at around 650 nm with the concomitant methyl violegen radial anion peak around 390 nm. These observed absorption values are red shifted with

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93 res pect to those obse oligothiophenes which suggests that generated radical cations are in conjugated through the platinum centers. Charge Transfer Chromophor es . Extensive photophysical properties of charge transfer chromophores, TBT and TQT, which are the core or ganic ligand s used to build corresponding platinum dimer was examined recently. 102 max values of two platinum dimer of TBT and TQT fall in between of those of pure ligand and platinum acetylides. The f = 73 % for TBT and 78 % for TQT ). It was noted that attachment of platinum causes the significant reduction of fluorescence quantum yields and lifet imes indicating strong interaction between the platinum center and organic ligand. (See Table 3 1 for the values). Given the fact that the fluorescence quantum yield efficiency of both unsubstituted and bisethy nyl substituted organic chromophore are almost the same, effect of direct metal lation on intersystem crossing seems to be larger when the metal attached to the ring system directly. S ummary A series of platinum dimers in which the platinum is directly attached to various oligothi ophene and charge transfer chromophores were synthesized and characterized. Photophy sical and electrochemical properties was investigated and compare d to thos e in which metal is attach ed to the ring system via ethynyl linker. Complexes with oligothiophenes showed strong triplet triplet absorption, and relatively good singlet oxygen quantum yields suggesting that complexes promotes triplet state formation upon e xcitation, however, relative intensity of triplet triplet absorption and singlet oxygen

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94 quantum yield was lower than those complexe s with acetylene linkage. One the major important properties of synthesized complexes are that they all showed very low oxi da tion potentials, less than 0.1 V. These observations lead us to explore electron transfer study with methyl violegen which is a known electron acceptor in the literature . Experimental Instrumentation and Methods Materials

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95 Synthesis

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102 CHAPTER 4 P t CARBON BOND F ORMATION VIA CuI CATALYZED STILLE TYPE TRANSMETALLATION: STRUCTURE AND SPECTROSCOPIC STUDY Background Bond formation between aromatic ligands and late transition metals such as Ni, Pd, and Pt is typically carried out by the reaction between a metal hali de and a corresponding aryl organolithium or organomagnesium reagent. 30, 119 A major disadvantage of this technique is that the excessive basicity of the organometallic reagents do not tolerate substituents sensitiv e to this type of environment. Oxidative addition is known to be one of the best ways to create a carbon metal bond. 38 42 However, this technique requires the use of air sensitive zero valent metal complexes, and therefore the reactions need to be carried out under inert conditions. There is considerable interest in the properties and applications of aryl substituted Pt(II) complexes of the type, L 2 Pt II Ar 2 , due to their useful linear and non linear optical properties. 120 One approach that has been used to form carbon platin um bonds for these types of complexes is based on the room temperature reaction between (COD)PtCl 2 and 3 32 However, complexes of the type L 2 PtCl 2 , where L = PR 3 , have not been demonstrated to react with aryl tin compounds. It has b een shown that the Stille coupling reaction can be accelerated 100 fold using Cu(I) salts. 121 125 Following this lead, a similar strategy was considered, i.e., using a Cu(I) catalyst to facilitate the coupling react ion between ArSnR 3 and L 2 PtCl 2 complexes. Herein, the development of a facile and general route to synthesizing compounds of the type, trans (PBu 3 ) 2 Pt(Ar)Cl and trans (PBu 3 ) 2 PtAr 2 by using a Cu(I) assisted transmetallation of aromatic tin compounds onto t he phosphine bearing Pt -

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103 complexes is reported. The reported CuI assisted transmetallation process was used to generate platinum complexes that could potentially show interesting photophysical behavior. Results and Discussion Structure and Synthesis Synth esis of aryl platinum(II) complexes is achieved by mixing cis (PBu 3 ) 2 PtCl 2 and an aryl stannane in DMF in the presence of 10 mol% CuI. At elevated temperatures, as presented in Figure 4 1, only the monosubstituted complex ( trans (PBu 3 ) 2 Pt(Ar)Cl, Xa is obse rved to form. This reaction works at room temperature, but requires longer reaction times to achieve the same yield. Upon isolation of Xa, it can be reacted in a separate pot, again with catalytic CuI in DMF, but this time at room temperature, the disubsti tuted complex ( trans (PBu 3 ) 2 PtAr 2 , Xb) can be formed ( Figure 4 2. ). Isolation of Xa is necessary for generation of Xb, as adding another portion of CuI after completion of the monosubstitution did not yield any further reaction. Yields for all mono and ho modisubstituted complexes under their respective conditions are given in Figure 4 3. Figure 4 1. Synthesis of Monosubstituted Aryl Platinum Complexes Figure 4 2. Synthesis of Disubs tituted Aryl Platinum Complexes

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104 When the aryl stannane is thiophene based (8 and 9), this substitution reaction behaves very differently. Reaction time is greatly reduced (~0.5 hours at room temperature), and the control to stop at monosubstitution is most ly lost (~15% monosubstituted product vs. 72 75% disubstituted). This result holds even when an equimolar amount of aryl stannane and cis (PBu 3 ) 2 PtCl 2 were mixed in the presen c e of 10 mol% CuI. (See Table 4 3 for yields) Employing two equivalents of t he th iophene type stannane yielded exclusively trans disubstituted complexes, as expected, in 70% yield on average. This unexpected behavior could be explained by 8a and 9a having greater reactivity than the cis (PBu 3 ) 2 PtCl 2 , probably due to the minimal steric effects of the thiophene based rings. The mechanism for this transformation is believed to be of an analogous nature to that of the Cu aided Stille Coupling (Figure 4 4 ). In the first step, copper replaces tin on the aryl moiety, generating an organocopper species as well as tributyltin iodide. The organocopper reagent then transmetallates to platinum, giving Xa and CuCl. Finally, tributyltin iodide and copper chloride undergo halogen metathesis to regenerate the CuI catalyst.

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105 Figure 4 3. Yield of mono and symmetrically disubstituted complexes.

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106 Figure 4 4. Proposed Mechanism for the Cu(I) mediated transmetalla tion Upon further investigation into the products of the monosubstitution reaction, it was discovered that a second monosubstituted platinum complex was being formed. This complex had an identical 1 HNMR (with respect to both chemical shift and integration ratios) to that of the desired monosubstituted product ; however, the 31 PNMR showed an ~5.5 ppm shift upfield. This product was ambiguously assigned to trans (PBu 3 ) 2 Pt(Ar)I. Support for this formula stems from mixing only Xa with CuI, which gives rise to a peak in the 31 PNMR spectrum at the same shift as the peak observed from the monosubstitution reaction mixture. Attempts to react trans (PBu 3 ) 2 Pt(Ar)I with the corresponding aryl stannane yielded no disubstituted product. Additionally, reaction of Xa with CuCl and the corresponding aryl stannane also gave no further substitution. Thus control of the reaction to stop at the monosubstituted form seems to stem from formation of the platinum iodo complex, which deactivates the reaction mixture in multiple ways. Synthesis of the symmetrical trans disubstituted complexes was achieved when the isolated trans monosubstituted complexes (1a 7a) were subjected to a second transmetallation reaction using an equimolar amount of aryl stannane and 10 mol% CuI at room temp erature. Temperature was found to be a key component in the formation of the

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107 disubstituted complexes 1b 7b. Any elevation in temperature favors the halogen metathesis pathway, giving no observable disubstituted product. When the aforementioned experiment i s run at 60ºC, only the platinum iodide product forms. The rest of the starting material remains unreacted. This allows assignment of the aryl platinum iodide side product as the thermodynamic product, and the disubstituted platinum complexes 1b 7b as the kinetic products. This halogen metathesis is more pronounced with the electron rich compounds 6a and 7a. When either of these complexes are mixed with 1 eq. of CuI at room temperature, rapid consumption of the CuI is observed by 31 PNMR, resulting in format ion of the presumed aryl platinum iodide side product. This observation accounts for the low yields given by the electron rich disubstituted compounds 6b and 7b. Despite the aforementioned nuances, this method allows for the facile synthesis of platinum co mplexes with mixed aryl ligands, as shown by compounds 10 13. The synthesis of 13 offers further evidence to the copper tin transmetallation being the rate limiting step. The monosubstituted intermediate of 13 can theoretically be either 5a or 6a; however, reaction of 5a with 6 does not produce 13 at any reaction temperature. Conversely, reaction of 6a with 5 at room temperature gives 13 in 45% yield.

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108 Figure 4 5 . Yields and Structures of Heterodisubstituted Aryl Platinum Complexes . Photophysical Properties

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109 Table 4 2. Summary of Photophysical Properties .

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110 Table 4 3. Computed Pt C bond lengths. Complex Bond length (Ã…) PEP Pt (3a) 2.0335 DPAF Pt (7a) 2.0387 Naph Pt (4a) 2.0363 (PEP) 2 Pt (3b) 2.1151 (DPAF) 2 (7b) 2.1213 (Naph) 2 (4b) 2.1178 To look for room temperature phosphorescence, samples were de gassed by three freeze pump thaw cycles before the emission spectra were recorded. Only compounds containing the 4 (phenylethynyl)phenyl, DPAF, and naphthalene ligands ( 3a,b, 4a,b, 7a,b ) showed this phenomena. Phosphorescence quantum yields were not measur ed, but are approximately the same between a mono and disubstituted complex containing the same aryl ligand.

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111 Figure 4 6. Absorption (left) and photoluminescence (right) spectra of complexes 3a (top) and 3b (bottom) Figure 4 7. Absorption (left) and photoluminescence (right) spectra of complexes 3a (top) and 3b (bottom) .

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112 Figure 4 8. Absorption (left) and photoluminescence (right) spectra of complexes 3a (top) and 3b (bottom) .

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113 Figure 4 9. Transient Absorption Spectra of trans DPAFPt(PBu 3 ) 2 Cl (7a) and trans DPAFPt(PBu 3 ) 2 DPAF (7b). Experimental Conditions for 7a: O. D . = 0.7, Q a Delay Increment: 250ns, Experimental Conditions for 7b : O. D. = 0.7, Q 50ns, Camera Delay Increment: 100ns, Figure 4 10. Transient Absorption Spectra of trans BThPt(PBu 3 ) 2 Cl (9a) and trans BThPt(PBu 3 ) 2 BTh (9b). Experimen tal Conditions for 9a: O.D. = 0.7, Q Experimental Conditions for 9b: O.D. = 0.7, Q 50ns, Camera Delay Increment: 500ns .

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114 Summary

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115 Experimental Instrumental and Methods All reactions were conducted under a nitrogen atmosphere. 1 H, 13 C, 31 P nuclear magnetic resonance (NMR) Spectra were recorded on Varian Gemini, VXR, and Mercury spectrometers. 1 H and 13 C NMR spectra were recorded to relative to protonated solvent (CHCl 3 1 13 C NMR). The chemical shifts in 31 P NMR spectra were recorded relative to 85% H 3 PO 4 as a standard. Hi gh Resolution Mass spectr a were obtained using MALDI TOF. Steady state absorption spectra were recorded on a Simadzu spectrophotometer. Corrected steady state emission measurements were conducted on a SPEXF 112 Fluorescence Spectrometer. Samples were dega ssed by three freeze pump cycles on a high vacuum line (10 5 Torr). Concentrations were adjusted such that the solutions were optically dilute. Photoluminescence quantum yields were determined by relative actinometry and quinine sulfate were used as actino meter. 128 Materials All commercially available reagents were used as received unless otherwise noted. cis Pt(PBu 3 ) 2 Cl 2 129 biphenyl] 4 yltributylstannane 130 , tributyl(4 (phenylethynyl)phenyl)stannane 131 , tributyl(naphthalene 2 yl)stannane 132 , tributyl(4 nitrophenyl)stannane 122 , N,N diphenyl 4 (tributylstannyl) aniline 133 , 9,9 diethyl N,N diphenyl 7 (tributylstannyl) 9 fluoren 2 amine 134 (tributylstannyl) [2,2 bithiophene] 5 yl)silane 135 were synthesized following literature procedures.

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116 Synthesis General Procedure for the formation of Monosubstituted Products 1 equivalent of cis Pt(PBu 3 ) 2 Cl 2 was dissolved in 10 mL of dry DMF and degassed for 30 minutes, then 1.2 equivalents of a corresponding tin compound was added to the system along with CuI (10 mol% with respect to tin). The temperatur e of the system was brought to 6 0 o C and stirred at this temperature for 4 hours. The s olvent was then removed in vacuum . Column chromatography, using silica gel as adsorbent, was employed to purify the monosubstituted products. trans BPhPt(PBu 3 ) 2 Cl (2a) Yield: 63% , R f = 0.45 (1:1 DCM/Hexane). 1 H NMR (300 M Hz, CDCl 3 ) 7.58 (d, J = 9Hz, 2H), 7.40 (m, 4H), 7.28 (m, 2H), 7.18 (d, J = 9Hz, 2H), 1.70 1.55 (m, 12H), 1.55 1.41 (m, 12H), 1.41 1.27 (m, 12H), 0.89 (t, J = 6Hz, 18H). 13 C NMR (75 MHz, CDCl 3 ) 142.00, 137.66, 137.46(t, J = 2.3Hz), 134.35(t, J= 6.5Hz), 128.60, 126.30, 126.12, 125.97, 25.85 ( J Pt C =23Hz), 24.26 ( J Pt C =13Hz), 21.18 ( J Pt C =32Hz), 13.76. 31 P NMR (121 MHz, CDCl 3 ) 5.98 ( J Pt P = 2755 Hz). Calculated for C 36 H 63 P 2 P t 752.4051, found DART MS (m/z) : 752.4039 [M Cl] + . trans PEPPt(PBu 3 ) 2 Cl (3a) Yield: 60% , Rf = 0.51 (1:1 DCM/Hexane)

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117 1 H NMR (300 MHz, CDCl 3 ) 7.51 (d, J = 9Hz, 2H), 7.36 7.28 (m, 5H), 7.09(d, J = 9Hz 2H), 1.68 1.52 (m, 12H), 1.51 1.42 (m, 12H), 1.40 1.31 (m, 12H), 0.90 (t, J = 6Hz, 18H). 13 C NMR (75 MHz, CDCl 3 ) 141.36 (t, J = 9 Hz), 137.19(t, J=2 .3), 131.31, 130.43(t, J= 37Hz), 128.24, 127.60, 124.02, 115.79, 90.92, 87.34, 25.83( J Pt C = 23Hz), 24.23( J Pt C = 13Hz), 20.98 ( J Pt C = 33Hz), 13.78. 31 P NMR (121 MHz, CDCl 3 ) 5.80 ( J Pt P = 2733 Hz). Calculated for C 38 H 63 P 2 Pt 776.4051, foun d DART MS (m/z): 752.4020 [M Cl] + . trans NaphtoPt(PBu 3 ) 2 Cl (4a) Yield: 65%, R f = 0.56 (1:1 DCM/Hexane) 1 H NMR (300 MHz, CDCl 3 ) 7.74(s, 1H), 7.68(dd, J = 9Hz, J = 2.1,1H), 7.58(dd J =9Hz, J =2.1 2H), 7.42 (m, 1H), 7.36 7.24 (m, 2H), 1.68 1.42 (m, 24H), 1.33 (sextet, 12H), 0.87 (t, J =7.2Hz, 18H). 13 C NMR (75 MHz, CDCl 3 ) 127.34, 126.00, 125.59, 124.71, 123.03, 25.87 ( J Pt C =23Hz), 24.22 ( J Pt C =13Hz), 21.05 ( J Pt C = 33Hz), 13.72. 31 P NMR (121 MHz, CDCl 3 ) 6.00 ( J P t P = 2740 Hz ) Calculated for C 34 H 61 P 2 Pt 726.3894, found MALDI TOF MS (m/z): 726.3878 [M Cl] + . trans p NO 2 PhPt(PBu 3 ) 2 Cl (5a) Yield: 45%, R f =0.41 (1:1 DCM/Hexane) 1 H NMR (300 MHz, CDCl 3 ) J =6Hz), 7.56 (d, J =9Hz), 1.70 1.56 (m, 12Hz), 1.49 1.29 (m, 24H), 0.88 (t, J =9Hz). 13 C NMR (75 MHz, CDCl 3 ) 155.47 ( J Pt C =15Hz),

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118 143.33, 137.54( J Pt C =39Hz), 121.53( J Pt C =80Hz), 25.80( J Pt C =23Hz), 24.16( J Pt C =13Hz), 21.05( J Pt C =33Hz), 13.71. 31 P NMR (121 MHz, CDCl 3 ) 5.61 ( J Pt P =2666 Hz). DIP CI MS (m/z): 756.3363 [M] + trans TPAPt(PBu 3 ) 2 Cl (6a) Yield: 53%, R f = 0.6 (1:1 DCM/Hexane) 1 H NMR (300 MHz, CDCl 3 ) 7.28 (m, 2H), 7.17 (m, 4H), 7.04 (m, 4H), 6.91 (t, J = 7.5Hz, 2H), 6.77 (d J = 7.8Hz 2H), 1.79 1.75 (m, 12H), 1.50 1.34 (m, 24H), 0.92 (t, J = 7.2Hz, 18H). 13 C NMR (125 MHz, CDCl 3 ) 148.31, 141.39, 137.71, 133.95 ( J Pt C = 10Hz), 128.80, 126.58, 122.35, 121.17. 31 P NMR (121 MHz, CDCl 3 ) 6.31 ( J Pt P = 2756 Hz) . Calculated for C 42 H 68 NP 2 PtCl 879.4162, found MALDI TOF MS (m/z) : 879.4170 [M] + . tr ans DPAFPt(PBu 3 ) 2 Cl (7a) Yield: 30%, R f =0.45 (1:1 DCM/Hexane) 1 H NMR (300 MHz, CDCl 3 ) J =8Hz, 1H), 7.30 7.22 (m, 7H), 7.14 7.08(m, 5H), 7.03 6.96 (m, 3H), 1.89(q, J =7.2, 4H), 1.61(m, 12H), 1.53(m, 12H), 1.38(m, 12H), 0.82(t, J =7.2Hz, 18H), 0.36 (t, J =7.2Hz, 6H). 13 C NMR (75 MHz, CDCl 3 ) 150.01, 148.98, 148.21, 145.75, 138.56, 137.36 ( J Pt C =10Hz), 135.52, 135.31, 130.86, 129.05, 124.22,

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119 123.30, 121.97, 120.16, 119.18, 118.46, 32.87, 25.92 ( J Pt C =23Hz), 24.24 ( J Pt C =13Hz), 20.85 ( J Pt C =33 Hz), 13.9, 8.69. 31 P NMR (121 MHz, CDCl 3 ) 6.09 ( J Pt P = 2775Hz) . Calculated for C 53 H 80 NP 2 PtCl 1023 .5065, found MALDI TOF MS (m/z): 1023.5065 [M] + . trans TIPSBThPt(PBu 3 ) 2 Cl (9a) Yield: 16%, R f = 0.40 (1:1 DCM/Hexane) 1 H NMR (300 MHz, CDCl 3 ) 7.10 (s , 2H), 7.05 (d, J = 6Hz, 2H), 6.45(d, J =6Hz, J Pt H =23Hz), 1.81 1.55(m, 12H), 1.50 1.45(m, 12H), 1.43 1.31(m, 15H), 1.12 (d, J =7.2, 18H, 2H), 0.91 (t, J =7Hz, 18H) . 13 C NMR (75 MHz, CDCl 3 ) 144.92, 137.34, 136.25, 130.45, 129.85, 128.85, 124.80 ( J Pt C =40Hz ), 122.33, 25.93 ( J Pt C =23Hz), 24.26 ( J Pt C =13Hz), 20.64 ( J Pt C =32Hz), 18.61, 13.79, 11.79. 31 P NMR (121 MHz, CDCl 3 ) 6.22 ( J Pt P = 2554 Hz) . Calculated for C 41 H 79 P 2 S 2 SiPtCl 956 .4197, found MALDI TOF MS (m/z) : 956.4213 [M] + . Disubstituted Symmetric an d Asymmetric Products General Procedure for s ymmetric disubstituted products 1 equivalent of trans PtAr(PBu 3 ) 2 Cl was dissolved in 5 mL of dry DMF and degassed for 30 minutes, then 1.2 equivalents of a corresponding tin compound was added to the system alon g with CuI (10 mol % with respect to tin). The system was stirred at room temperature overnight and the precipitated product was filtrated and dried under vacuum. trans (PEP) 2 Pt(PBu 3 ) 2 (3b)

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120 Yield : 45 %, R f = 0.80 (1:1 DCM/Hexane) 1 H NMR (300 MHz, CD Cl 3 ) 7.51 (d. J =6Hz, 4H), 7.45(d, J =6Hz, 4H), 7.34 7.29 (m, 6H), 7.17 (d, J =6Hz, 4H), 1.46 1.37 (m, 12H), 1.34 1.25 (m, 24H), 0.89 (t, J = 6Hz) 13 C NMR (75 MHz, CDCl 3 ) 165.43 ( J =21Hz), 139.82, 131.28, 129.48 ( J =21Hz), 128.1, 127.22, 124.53, 115.13, 91. 88, 86.80, 26.00 ( J Pt C =23Hz), 24.14 ( J Pt C =13Hz), 21.82 ( J Pt C =33Hz), 13.58. 31 P NMR (121 MHz, CDCl 3 ) 0.75 ( J Pt P =2775 Hz). Calculated for C 52 H 72 P 2 PtH 954.4834, found MALDI TOF MS (m/z): 954.4898[M+H] + . trans (Naphto) 2 Pt(PBu 3 ) 2 (4b) Yield: 52 %, R f = 0.85 (1:1 DCM/Hexane) 1 H NMR (300 MHz, CDCl 3 ) 7.98(s, J Pt H =20Hz, 2H), 7.81(d, J =6Hz, 4H), 7.72(m, 2H), 7.60(dd, J =6Hz, =1.2Hz, 2H), 7.44(m, 2H), 7.35(m, 2H ). 13 C NMR (75 MHz, CDCl 3 ) 160.54, 139.85, 137.36, 134.43, 130.64, 127.46, 126.26, 124. 49, 124.13, 122.36, 26.25( J Pt C = 23Hz), 24.39( J Pt C =13Hz), 22.00( J Pt C =32Hz), 13.90. 31 P NMR (121 MHz, CDCl 3 ) 1.65, 1.59 ( J Pt P = 2775 Hz). Calculated for (C 44 H 68 P 2 Pt)H 854.4521, found DIP CI MS (m/z): 854.4507[M+H] + . trans ( p NO 2 Ph) 2 Pt(PBu 3 ) 2 (5b) Yield: 60 %, R f = 0.82 (1:1 DCM/Hexane)

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121 1 H NMR (300 MHz, CDCl 3 ) 7.95 (d, J =8Hz, 4H), 7.74 (d, J = 8Hz, J Pt H =23Hz, 4H), 1.54 1.43 (m, 12H), 1.4 1.27 (m, 24H), 0.96 (t, J =9Hz, 18H). 13 C NMR (125 MHz, CDCl 3 ) 179.03 ( J Pt C =40Hz), 143.92, 139.63, 120 .63( J Pt C =86Hz), 26.02 ( J Pt C =23Hz), 24.28 ( J Pt C =13Hz) , 21.71 ( J Pt C =33Hz), 13.85. 31 P NMR (121 MHz, CDCl 3 ) 0.12 ( J Pt P = 2687 Hz) . Calculated for (C 36 H 62 N 2 O 4 P 2 Pt)H 844.3909, found DIP CI MS (m/z): 844.3932 [M+H] + . trans ( p NPh 2 Ph) 2 Pt(PBu 3 ) 2 (6b) Yield: 10 %, R f = 0.87 (1:1 DCM/Hexane) . 1 H NMR (300 MHz, CDCl 3 ) J =7.5Hz, 2H), 7.20 7.14(m, 8H), 7.08 7 .05 (m, 8H), 6.87 (m, 8H), 1.42 1.31(m, 36H), 0.89 (t, J =6Hz, 18H). 13 C NMR (75 MHz, CDCl 3 ) 157.79 ( J Pt C =21Hz), 148.56, 140.81, 140.27, 128.66, 125.73, 122.19, 120.73, 25.94, 24.30( J Pt C =13Hz), 21.86 ( J Pt C =33Hz), 13.78. 31 P NMR (121 MHz, CDCl 3 ) 1.00 ( J Pt P =2787 Hz). Calculated for (C 60 H 82 N 2 P 2 Pt) 1088.5616, found MALDI TOF MS (m/z): 1088.5634 [M] + . trans (DPAF) 2 Pt(PBu 3 ) 2 (7b)

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122 Yi eld: 5 %, R f = 0.75 (1:1 DCM/Hexane) 1 H NMR (300 MHz, CDCl 3 ) 7.31 (m, 6H), 7.25 7.22 (m, 8H), 7.13 7.08 (m, 10H), 7.01 6.93 (m, 6H), 1.94 1.86 (m, 6H), 1.52 1.38(m, 12H), 1.32 1.27 (m, 24H), 0.88 (t, J =7.8Hz, 18H), 0.36(t, J =14Hz, 1 2H). 13 C NMR (75 MHz, CDCl 3 ) 162.21 ( J Pt C =21Hz), 150.08, 148.31, 147.85, 145.11, 139.78, 138.08, 134.81, 133.67, 128.9, 124.4, 123.07, 121.71, 120.55, 118.83, 55.49, 53.41, 33.02, 26.17, 24.25, 13.99. 31 P NMR (121 MHz, CDCl 3 ) 1.08, 0.91 ( J Pt P =2805 Hz ). Calculated for (C 82 H 106 N 2 P 2 Pt)H 1375.7478, found MALDI TOF MS (m/z): 1375.7582[M+H] + . trans (TIPSBTh) 2 Pt(PBu 3 ) 2 (9b) Yield: 16 %, R f = 0.90 (1:1 DCM/Hexane) 1 H NMR (300 MHz, CDCl 3 ) J =1.8Hz, 2H), 7.12 (d, J =1.8Hz), 7.11(d, J =1.8Hz, 2H), 6.55 (d, 1.8Hz), 1.50 1.40 (m, 24H), 1.37 1.31(m, 18H), 1.13 (d, J =6Hz, 36H), 0.90 (t, J =6Hz, 18H). 13 C NMR (75 MHz, CDCl 3 ) 153.61, 145.78, 138.35, 136.40, 131.28, 129.74, 125.43, 122.09, 26.22, 24.41 ( J Pt =13Hz), 21.21 ( J Pt =33Hz), 18.75, 13.93, 11 .93. 31 P NMR (121 MHz, CDCl 3 ) 2 . 33 ( J Pt P =2 556 Hz) . Calculated for (C 82 H 106 N 2 P 2 Pt)H 1041.3921, found MALDI TOF MS (m/z): 1041.3940 [M+H] . trans BPhPt(PBu 3 ) 2 BTh (10)

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123 50 mg, 62 mmol of trans PEPPt(PBu 3 ) 2 Cl was dissolved in 5 mL dry DMF and degassed for 30 min. then 52 mg, 74 mmol of triisopropyl(5' (tributylstannyl) [2,2' bithiophen] 5 yl)silane was added to the system along with 2 mg of CuI. The system was stirred at room temperature overnight. The resulting precipitate was filtered off and dried un der vacuum. Yield: 60 %, R f = 0.80 (1:1 DCM/Hexane). 1 H NMR (300 MHz, CDCl 3 ) 7.62 (d, J = 6.6Hz, 2H), 7.46 7.38 (m, 5H), 7.28(m, 3H), 27.13 (m, 2H), 6.60 (s, J Pt H =23Hz, 2H), 1.53 1.38(m, 24H), 1.37 1.31(m, 15H), 1.14 (d, J = 7.2Hz, 18H), 0.88 (t, J =9Hz, 18Hz). 13 C NMR (125 MHz, CDCl 3 ) J Pt C =21Hz), 157.04 ( J Pt C =23Hz ), 145.93, 142.58, 139.62, 138.17, 136.31, 133.71, 131.46, 129.27, 128.51, 126.30, 125.79, 125.33 ( J Pt C = 45Hz), 121.80, 26.07( J Pt C =23Hz), 24.28 ( J Pt C =13Hz), 21.57( J Pt C =33Hz), 18.54, 13.78, 11.82. 31 P NMR (121 MHz, CDCl 3 ) 1.00 ( J Pt P = 2770 Hz) . Calc ulated for (C 53 H 88 S 2 SiP 2 Pt) 1074.5227, found MALDI TOF MS (m/z): 1047.5267 [M] + . trans PEPPt(PBu 3 ) 2 BTh (11) trans PEPPt(PBu 3 ) 2 Cl ( 50 mg, 62 mmol ) was dissolved in 5 mL of dry DMF and degassed for 30 min. then 52 mg, 74 mmol of triisopropyl(5' (tribut ylstannyl) [2,2' bithiophen] 5 yl)silane was added to the system along with 2 mg of CuI. The system was stirred at room temperature overnight. The resulting precipitate was filtered off and dried under vacuum. Yield: 65%, R f =0.86 (1:1 DCM/Hexane) . 1 H NMR (300 MHz, CDCl 3 7.12 (m. 12H), 6.58 ( J Pt H =46Hz, 1H). 1.5 1.23(m, 39H), 1.14 (d, J =7Hz, 18H), 0.89 (t, J =7.2,

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124 18Hz) . 13 C NMR (125 MHz, CDCl 3 J Pt C = 21Hz), 156.14( J Pt C =12Hz), 145.83, 139.26, 138.28, 136.32, 131.49, 131.31, 129.76 ( J Pt C = 46Hz), 129.39, 128.21, 127.40, 125.33, 124.30, 121.87, 115.09, 91.67, 86.90, 26.06( J Pt C =23Hz), 24.27 ( J Pt C =13Hz), 21.39( J Pt C =33Hz), 18.64, 13.83, 11.82. 31 J Pt P = 2675 Hz) Calculated for (C 55 H 88 S 2 P 2 Si Pt) 1098.5227, found MALDI T OF MS (m/z): 1047.5223 [M] + . trans PhPt(PBu 3 ) 2 p NO 2 Ph (12) trans PhPt(PBu 3 ) 2 Cl ( 50 mg, 70 mmol ) was dissolved in dry DMF and degassed for 30 min. then 43 mg, 68 mmol of tributyl(4 nitrophenyl)stannane was added to the system along with 2 mg of CuI. Th e system was stirred at room temperature overnight. The resulting precipitate was filtered off and dried under vacuum. Yield : 60%, R f =0.5 (1:5 DCM/Hexane) . 1 H NMR (300 MHz, CDCl 3 ) 7.82 (d, J =9Hz, 2H), 7.68 (d, J = 9Hz, J Pt H =41Hz, 2H), 7.35 (d, J = 7.2Hz , J Pt H =42Hz, 2H), 6.98 (t, J =7.2Hz, 2H), 6.81 (t, J =7.2Hz, 1H), 1.51 1.35(m, 12H), 1.30 (m, 24H) 0.86 (t, J =7.2Hz, 18H). 13 C NMR (125 MHz, CDCl 3 ) 139.82 ( J Pt C =40Hz), 127.04, 121.43, 120.06 ( J Pt C =46Hz), 25.93 ( J Pt C =23Hz), 24.10( J Pt C =13Hz), 21.62( J Pt C =33Hz). 31 J Pt P =2749 Hz). Calculated for (C 36 H 63 NO 2 P 2 Pt)H 799.4058, found DIP CI MS (m/z): 799.4029 [M+H] + . trans TPAPt(PBu 3 ) 2 p NO 2 Ph (13)

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125 TPAPt(PBu 3 ) 2 Cl (40 mg, 45 mmol) was dissolved in DMF and degassed for 30 minutes then 30 mg, 68 mmol of tributyl(4 nitrophenyl)stannane was added to the system along with 2 mg of CuI. The system was stirred at room temperature overnight. The solvent was evaporated and the product was isolated via preparative thin layer chromatography using silica gel as an adsorbent and 1:1 DCM/Hexane mixture as eluent. Yield : 45%, Rf =0.5 (1:5 DCM/Hexane). 1 H NMR (300 MHz, CDCl3) 7.84 (d, J =9Hz, 2H), 7.69(d, J=9Hz, 2H JPt H=23Hz), 7.34(d, J=9Hz, 2H JPt H=23Hz), 7.17(m, 4H), 7.05(m, 4H), 6.89(m, 4H), 1.57 1.37(m, 12H), 1.37 1.27(m, 24H), 0.88(t, J=7.2Hz, 18H). 13 C NMR (125 MHz, CDCl 3 ) Pt C =20Hz), 154.78(J Pt C =22Hz), 148.47, 143.42, 141.39, 140.05(J Pt C =20Hz), 139.70(J Pt C =23Hz), 128.70, 125.97(J Pt C =43Hz), 122.27, 120.91, 120.16, 25.90(J Pt C =23Hz ), 24.22(J Pt C =13Hz), 21.69(J Pt C Pt P =2773Hz). Calculated for (C 48 H 72 N 2 O 2 P 2 Pt) 966.4793, found MALDI TOF MS (m/z): 966.4849 [M]+.

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126 CHAPTER 5 SYNTHES IS, CHARACTERIZATION, PHOTOPHYSI CAL AND ELECTOCHEMICAL PROPERTIES NOVEL PLATIN UM COM P LEXES WITH DONOR ACCEPTOR CHROMOPHORES Background conjugated polymers and oligomers have gained attention in the recent years. Encouraging candidates are low band gap materials with donor acceptor units (D A). Fine tuning of the band gap is possible due to the intramolecular charge transfer (ICT) from the donor to the acceptor moiety. 136 Control over the band gap allowed this materials to be used various application such organic light emitting diodes 137 139 , organic dye sensitized solar cells 140, 141 , organic field effect transistors 142 144 and nonlinear optics. 145 147 Even though the first singlet excited state, S 1 of these systems has been extensively studied, the first triplet excited state T 1 remained unexplored due to low yield of intersystem crossing to triplet manifold upon excitation. There are few reports exploring the extensive photophysical characterization, i.e. both singlet and triplet excited states of fully o rganic donor acceptor system 102, 103, 148, 149 (Figure 5 1). Figure 5 1 . Several donor acceptor donor (D A D) systems studied by Pina et al. 102

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1 27 Attachment of heavy metal such as platinum to the conjugated backbone is one of the ways to increase intersystem crossing yield, which ultimately allow one to examine triplet excited state of these systems. 150 152 In the second chapter of this dissertation, the synthesis of Pt(II) acetylide complexes with various electron poor ligands ligated with triphen ylamine as electron rich uni ts was described. In these complexes, electron poor and electron ric h ligands are 3 ) 2 An extensive photophysical and electrochemical characterization of these donor acceptor systems revealed that the first triplet excited state is not influenced by terminal diamino group whereas first singlet excited state is dramatically affected suggested by the decrease in fluorescence quantum yields and lifetimes. In this chapter, taking advantage of the synthetic methodology developed to make platinum carbon bond efficiently, we desig ned platinum complexes in which the electron donating and electron poor ligands was connected by a platinum metal, i.e. 3 ) 2 arms. For the present study, 2,1,3 benzothiadizole as electron poor unit was chosen along with the three electron rich bithiophene and dithieno[3,2 d]thiophene . 2,1,3 B en zothiadiazole is an electron acceptor unit that is extensively studied over a decade in many donor acceptor oligomers and polymers. 102, 137, 140, 144, 145, 153 while bithiophene 9 8, 152, 154 and dithieno[3,2 d]thiophene 155 159 are two well known electron rich ligands that has been employed to generate low band gap material s . The following figure shows the structure of the c omplexes that are the subject of this chapter (Figure 5 2).

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128 Figure 5 2. The structures of the complexes discussed in this chapter. Results Synthesi s All the complexes described in this chapter are synthesized following the method described in the previous chapter (Chapter 4). The synthesis towards obtaining the donor acceptor oligomers described in this chapter starts with the direct attachment of the platinum onto the 2,1,3 benzothiadiazole ring. In order to achieve th is goal, stannylated derivative of this chromophore was obtained using S tille type stannylation. Dibromo derivative of 2,1,3 benzothiadiazole was converted to bisstannylated derivative using hexabutylbistin in the presence of Pd(PPh 3 ) 4 as catalyst with 40% yield (Figure 5 2).

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129 Figure 5 3 . Synthesis of platinum dimer with 2,1,3 benzothiadiazole. In order to obtain the desired donor P t acceptor complexes, monostan nylation of the donor units was necessary, however, attemp ts to monostannylate employing one equivalent of n BuLi and quenching the resulting solution with SnBu 3 Cl leaded to the formation of an inseparable mixture of mono and distannylated products as well as some unreacted starting materials. Therefore, a stepwis e strategy in which one side is initially blocked by TIPS group was followed. The following figures (Figure 5 4 ) show how stannyl derivatives of donor units were synthesized. Figure 5 4 . Synthetic s cheme for triisopropy l(5' (tributylstannyl) [2,2' bithiophen] 5 yl)silane. The platinum dimer bridged by benzothiadiazole was capped with the each of the monostannylated donor units to yield final complexes as shown below. (Figure 5 5)

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130 Figu re 5 5 . Synthesis Scheme for triisopropyl(6 (tributylstannyl)dithieno[3,2 b:2',3' d]thiophen 2 yl)silane. Figure 5 6 . Synthetic s cheme for the formation of Donor Platinum Acceptor Complexes.

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131 1 H NMR Characterization Al l the complexes were characterized by 1 H, 13 C and 31 P NMR Spectroscopy as well as Mass Spectroscopy Techniques and detailed procedures were given in the experimental section. A B

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132 C D Figure 5 7 . 1 H NMR Spectra of A) (ClPt) 2 BTD, B ) ( ThPt) 2 BTD, C) (BThPt) 2 BTD D ) (DTTPt) 2 BTD

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133 Unfiel d positioned relative to the platinum center is ev idence of platinum carbon bond. These protons appear around 6.7 7.0ppm range and undergo coupling with platinum with a coupling constant of 23 Hz . This value is consistent with th at of previously synthesized analogous platinum complexes. Each complex exhibits 31 P NMR signal around ~2ppm except the one with chlorine terminal group showed up around 5.5ppm. Each phosphorous peak has accompanying satellite peaks originating from the co upling between the platinum and phosphorous. The coupling constant is found to be around 2700Hz , indicating a trans configuration around the platinum metal center. UV Vis Absorption and Photoluminescence The absorption spectra of all complexes were taken in dilute THF solutions (Figure 5 8 ). Generally, the absorption spectra feature two absorption bands. One intense band is in UV or near UV region and other relatively weak one is in the visible region. The first member of the series, (ClPt) 2 BTD has two ba nds centered at 320 nm and 430 nm respectively. Absorption maximum and molar extinction coefficient are smaller than those of corresponding platinum acetylide complex (ClCCPt) 2 electrons of the acetylene that causes the red shift in the spectra. Replacing terminal Cl ligand with thienyl group does no t change absorption maxima excep t the fact the molar extinction coefficient of each related band is sl ightly increased. When Cl ligand was exchanged with bithiophene or dithienothiophene, another absorption band that are originating from those ligands appeared and centered around ~350 nm . Even though these bands are predominant, position and intensity of the intramolecular charge transfer (ICT) band remained unchanged. Photoluminescence spectra were also recorded in both air saturated and deaerated THF solutions to investigate the emissive states from these

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134 new complexes (Figure 5 7) . All the complexes sh owed broad structureless emission band from 500nm to 800nm in aerated THF solution. Figure 5 8. Normalized absorption s pecta of (ClPt) 2 BTD (black line), (ThPt) 2 BTD (dash line), (BThPt) 2 BTD (dot line), (DTTPt) 2 BTD (dash dot line) . Virtually almost no spectral change was observed upon dearation of the solutions except those of (BThPt) 2 BTD, which shows second broad band around 600 to 800nm region upon deoxygenation of the solvent. As this peak disappeared upon purging the solution w ith oxygen, it was assiged as phosphorescence. The lifetime of emission was yields are measured with respect to air saturated Ru(bpy) 3 2+ as stansdard. Fluorescence quantum yi eld efficiency of (ClPt) 2 BTD is 6%. This value is ten times lower than that of

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135 strucuturally similar platinum acetylide, (ClCCPt) 2 BTD, indicating that strong spin orbit coupling between the metal and 2,1,3 benzothiadiazole unit. Figure 5 9 . Absorption Spectra (on the left) and Photoluminescence Spectra (on the right) of A) (ClPt) 2 BTD, B) (ThPt) 2 BTD, C) (BThPt) 2 BTD and D) (DTTPt) 2 BTD in aerated and deaerated THF solutions.

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136 Transient Absorption In order to understand the transients that are involved in t he excited state, we studied nanosecond picosecond laser flash photolysis for those complexes. Figure 5 8 and 5 9 show the transient absorption spectra of the complexes that are subject of this chapter. All the complexes except (ThPt) 2 BTD displayed broad a bsorptions which cover the entire visible region. Figure 5 10 . Transient Absorption Spectra of (CIPt) 2 BTD (on the left) and (ClCCPt) 2 BTD (on the right). Experimental Conditions for (CIPt) 2 BTD, Q Camera Delay :50 ns, Camera Delay Increments :750 ns. Experimental Conditions for (CICCPt) 2 BTD, Q ns, Camera Delay Increments: 300 ns. Intensities of transient absorption are found to be relatively lo wer than that of parent platinum acetlyide complexes even with increased laser power intensity. For example, (ClPt) 2 BTD exhibit relatively broad and weaker transient absorption band with respect to corresponding platinum acetylide complex, (ClCCPt) 2 BTD, wh ich has absorption peaks at both 388nm and ~700nm. However, triplet lifetime of former was found to be longer than that of platinum acetylide complex. Even though the mono exponential decay rate of the transients associated with the each complex (see Table 5 1)

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137 indicates that transients are originating from triplet excited state, the broad nature of the transient suggests that there might be some charge transfer contribution. Figure 5 11 . Transient Absorption Spectra of (DTTPt) 2 BTD (on the left) and (B ThPt) 2 BTD (on the right).Experimental Conditions for both (DTTPt) 2 BTD and (BThPt) 2 BTD, Q amera Delay:50 ns, Camera Delay Increments: 1000 ns Table 5 1. Summary of Photophysical Properties . Compounds UV Vis max (nm) a a x 10 3 (cm 1 M 1 ) max (nm) a f % f (ns) p T 1 T n T1 Tn (ClCCPt) 2 BTD 3 31, 484 6.5, 4.1 60 6 b 388, 708 1.5 (ClPt) 2 BTD 312, 434 5.6, 3.8 540 6 1.6 b 490 4.8 (ThPT) 2 BTD 310, 428 9.0, 6.7 528 3.5 1.0 b c c (DTTPt) 2 BTD 331, 428 33.5, 4.0 511 2 0.3 b 385,482 6.2 (BThPt) 2 BTD 356, 428 28.0, 4.3 530 1 0.2 14 401,484 5.9 a in THF, b no phosphorescence is observed, c no transient absorption signal is observed. Electrochemistry In order to understand the redox states associated with the each complexes, cyclic voltammetry and differential pulse voltammetry experiment s were c arried out. Initial investigation is to compare the redox states of (C lPt) 2 BT D and (ClCCPt) 2 BTD to understand if there is any effect of acetylene bridge on redox properties.

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138 The following figure shows the anodic scans taken by cyclic voltammetry and diffe rential pulse voltammetry experiments. No significant change was observed in terms of their first oxidation potential, which appeared around 0.56 V for both complexes. (ClCCPt)BTD showed a cathodic peak around 2.1 V relative to Fc/Fc+, however no cathodic peak was observed for (ClPt) 2 BTD within the potential window of the solvent. This might be probably due to high LUMO level associated with this complex. Figure 5 12 . Cyclic Voltammogram (on the left) and Differential Pulse Voltammogram (on the right) of the (ClCCPt) 2 BTD (top) and (ClPt) 2 BTD (bottom) Replacement of Cl ligand by electron rich organic ligands causes first oxidation potential reduced by nearly 0.2 V. The following figure (Figure 5 11) shows the anodic sweeps in cyclic voltammetry and diff erential pulse voltammetry experiments related to (DTTPt)2BTD and (BThPt)2BTD. In these systems, after first oxidation takes place, second closely spaced another oxidation occurs, which is nearly 70 mV apart. This is

PAGE 139

139 more likely from two back to back oxida tion of one ligand and then second one right after the first oxidation. Bithiophene containing complex exhibits approximately 0.1 V lower in oxidation potential. This finding agree with the literature observation that bithiophene is better electron donatin g ligand than dithienothiophene. Unfortunately, no cathodic peak was observed from those complexes within the potential window of the solvent employed (DCM). Figure 5 1 3 . Cyclic Voltammogram (on the left) and Differential Pulse Voltammogram (on the ri ght) of the (DTTPt) 2 BTD (top) and (BThPt) 2 BTD (bottom ). Density Functional Theory Calculations Besides the synthetic efforts and electrochemical data, we computationally analyzed and compared a series of five oligomers which are the subject of this chapter. We chose density functional theory (DFT) methods, known to have a go od balance between accuracy and the computational time requi red. Methyl substituents were chosen

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140 to simplify the comp utations with the computational details supplied in the e xper imental Section. The HOMO and LUMO lev els obtained computationally in the gas phase are summarized in Table 5 2. Figure 5 1 4 . DFT//B3LYP/6 31G(d) optimized ground state geometry together with the frontier molecular orbitals energy levels and the molec ular orbital contours for (ClPt) 2 BTD , (ThPt) 2 BTD, (DTTPt) 2 BTD, (BThPt) 2 BTD and (ClCCPt) 2 BTD oligomers.

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141 Table 5 2. Wavelength, Molecular Orbitals Involved, and Oscillator Strength for the Strongest Predicted Electronic Transition of both the Low and High Energy Region in the Singlet State. Compound Wavelength /nm Orbital transitions Oscillator strength, f (ClPt) 2 (100%) 0.0878 (ThPt) 2 284.8 HOMO HOMO HOMO ( 100%) (80.3%) (5.0%) (2.2%) (4.3%) (8.2%) 0.0982 0.0680 (BThPt) 2 338.5 HOMO HOMO (3.9%) (96.1%) (21.5%) (74.1%) (4.4%) 0.0984 1.0175 (DTThPt) 2 316.1 HOMO HOMO (2.1%) (97.9%) (21.7%) (78.3%) 0.0833 1 .2341 (ClPtCC) 2 339.7 (100%) (90.3%) (9.7%) 0.3688 0.6965 As can be seen from the tables 5 3 and 5 4, main transitions are basica lly from HOMO to LUMO. Typically, HOMO is seemed to be spread out the entire molecule, however, LUMO is mainly localized on the BTD acceptor core unit.

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142 Table 5 3. Wavelength, Molecular Orbitals Involved, and Oscillator Strength for the Strongest Predi cted Electronic Transitions in the Triplet State. Compound Wavelength/ nm Orbital transition s Oscillator strength, f (ClPt) 2 HOMO HOMO (15.5%) (80.1%) (4.4%) 0.0775 Manifold of weak excitations from 520 370 nm (ThPt) 2 414.3 188A HOMO (100%) (45.8%) (2.8%) (2.7%) (48.7%) 0.0624 0.0593 Manifold of weak excitations from 450 350 nm (BThPt) 2 564.9 HOMO HOMO HOMO (100%) (1.4%) (1.6%) (94.1%) (1.5%) (1.4%) 0.0838 0.0160 Manifold of weak exc itations from 570 370 nm (DTThPt) 2 958.1 HOMO HOMO (100%) (100%) 0.0677 0.0255 Manifold of weak excitations from 520 400 nm (ClPtCC) 2 480.6 HOMO HOMO HOMO HOMO O HOMO HOMO HOMO ( (4.7%) ( ( 2.2%) ( ( 4.8%) ( ( 47.6%) ( ( 40.7%) (48.2%) (27.3%) (21.7%) (1.1%) (1.7%) 0.3216 0.1866

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143 Table 5 4. Calculated HOMO and LUMO Energies as well as the band gap of complexes Complexes HOMO (eV) LUMO (eV) Band Gap (eV) HOMO(eV) * (ClPt) 2 BTD 5.23 1.84 3.39 5.30 (ThPt) 2 BTD 4.89 1.57 3.32 (DTTPt) 2 BTD 4.79 1.77 3.02 4.98 (BThPt) 2 BTD 4.73 1.69 3.04 4.91 (ClPtCC) 2 BTD 4.81 2.17 2.64 5.30 * Experimentally obtained from CV c alculated as E HOMO = (Eonset, ox + 4.75) eV. Discussion Ground state absorption spectrum of (ClPt)2BTD displayed two bands, one of which appears in nearly visible region. This experimentally observed band is suggesting that there is a charge transfer interaction between platinum metal and BTD acceptor unit. The interaction between platinum and BTD acceptor unit was also suggested by TD DFT calculations as shown in LUMO molecular o rbital contours. Attachment of donor l igands to the platinum center cause s neither any shift nor an increase in the molar extinction coefficient of that particular band indicating that there is a weak electronic coupling between electron rich and electron poor ligands. Short fluorescence lifetimes and low fluorescence quantum yields indicates effi cient intersystem crossing in these system s . The fact that fluorescence lifetimes and quantum yields decreases in the series as the electron rich thiophene derivative is replaced by terminal chlorine in (ClPt)2BTD suggest that another deactivation process is operating and this deactivation mechanism is probably photoinduced electron transfer from donor to acceptor. Only t he complex that features bithio hene donor unit showed phosphorescence emission around 600 800 region. This emission is probably originatin g from the triplet state of bithiophene donor unit.

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144 Laser flash photolysis experiments indicate that transients observed from these complexes have triplet character due to their long T1 Tn lifetimes ca.5 lifetimes are found to be longer than typical value obtained from platinum acetylide complexes. However, the broad n ature of observed transients might indicate charge transfer type contribution. Only oxidation potentials were obtained from the electrochemical experiments as the reduction pote ntials are too negative to be detect ed within the potential window of the solvent employed (DCM). Even though LUMO level could not be extracted from electrochemical data, TD DFT calculations shed light on both HOMO and LUMO energies of each complex . Comput ationally e stimated oxidation potentials are in close proximity with experimentall y observed oxidation potentials, although latter is slightly lower than former. HOMO LUMO band gap was found to be similar regardless of the different electron rich ligand wi th varying levels of oxidation potentials. Summary Four donor s acceptor s donor type complexes were synthesized where acceptor is 2,1,3 benzothiadiazole and s stands for spacer which is Pt(PBu 3 ) 2 unit in this case. The chemistry th at was developed and discussed previous chapter was used to make corresponding complexes in this chapter. The goal was here to understand donor acceptor interaction transmitted platinum metal and effects of direct metallation on photophysical properties of those systems. Elec tronic coupling seemed to be weak between donor and acce ptor as suggested by data from UV V isible spectroscopy measurements. The acceptor is probably not in conjugation with donor units due to the bulky phosphine ligand which are perpendicular to the plane . Transient absorption studies

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145 indicates that observed transients are triplet in nature suggested by their long life time, however, broad nature of the transient might indicate some charge transfer character observed in these transients. Experimental Instr umentation and Methods All NMR spectra were recorded on Gemini 300 FT NMR, a Mercury 300 FT NMR, or an Inov a 500 FT NMR. High Resolution mass spectrometry was performed a Bruker APEX II 4.7 Fourier Transform Ion Cyclone Resonance mass spectrometer. Stead y state absorption measurements were carried out on a Shimadzu UV 1800 dual beam spectrophotometer using 1cm quartz cells. Corrected steady state emission measurements were conducted with fluorimeter from Photon Technology International (PTI) using 1cm qua rtz cells. Samples were degassed by argon purging for 30 minutes and concentrations were adjusted such that the solutions were optically dilute. Photoluminescence quantum yields were determined according to the relative actinometry. Solution of Ru(bpy) 3 2 + wer e used as a reference 76 in air saturated water). Fluorescence lifetimes were obtained with a multichannel scales /photon counter system with a PicoQuant FluoTime 100 Compact Luminescence Lifetime Spectr ophotometer . A high performance Coherent CUBE diode laser provided the excitation at 375nm (P<10Mv). Decays were obtained using the single exponential fitting parameters (FluoroFit software). Nanosecond triplet triplet transient absorption measurements we re acquir ed with excitation at 355nm (10m j/pulse) using the third harmonic of Continuum Surelite II 10

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146 Nd:YAG laser. Perkin Elmer LS 1130 3 pulsed xenon lamp used as a probe source and the transient absorption signal was detected with a gated intensified C CD mounted on a 0.18 M spectrograph . Samples were prepared to an optical density of 0.7 at the excitation wavelength in a continuously circulating 1 cm path length flow cell. Triplet lifetimes were calculated with a single exponential global fitting of the transient absorption decay data using SpecFit analysis software. Electrochemical measurements were recorded in dry dichloromethane solutions containing 0.1M tetra n butyl hexafluorophosphate (TBAH, Aldrich) as supporting electrolyte. The setup consisted of a platinum microdisk (2 mm 2 ) as working electrode, platinum wire auxiliary electrode as a silver wire quasi reference electrode. A positive pressure was maintained during the measurements. The concentrations of the oligomers were ca. 0.15 m M. All the po tentials obtained were calibrate against the ferrocene/ ferrocenium couple (E=0.43 vs SCE in dichloromethane). All calculations were carried out using DFT as implemented in Gaussian 09 160 Rev. C.01. Geometries were optimized using the B3LYP functional along with the 6 31G(d) basis set for C, H, N, the 6 31+G(d) basis set for P, S, and the SDD basis set for Pt. To minimiz e computational cost, solubilizing PBu 3 moieties were replaced with PMe 3 . These (ClPt) 2 BTD is termed as (ClPt) 2 All singlet optimizations were started from idealize d geometries and run without symmetry constraints. Triplet optimizations were started from the optimized singlet geometry and used the unrestricted B3LYP functional. All optimized structures were characterized by vibrational frequency calculations and were shown to be minima by the absence of imaginary frequencies. Time Dependent DFT calculations were

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147 performed for all optimized structures at the same level of theory with the same basis sets. Structures and orbitals were visualized at an isovalue of 0.02 us ing Chemcraft Version 1.7. 161 Materials All the solvents and chemicals used for the synthesis of platinum complexes were reagent grade and used without further purificati on unless noted. Silica gel (Silicycle Inc. 230 400 mesh, 40 bithiophene, tributyl(thiophen 2 yl)stannane were purchased from Sigma Aldrich. D iethyl dithieno[3,2 b:2',3' d]thiophe ne 2,6 dicarboxylate 156 was synthesized according to literature procedure Synthesis 4,7 bis(tributylstannyl)benzo[c][1,2,5]thiadiazole 0.5 g of 4,7 dibromob enzo[c][1,2,5]thiadiazole and Bu 3 SnSnBu 3 as dissolved in 10ml of toluene and degassed for 30 minutes, then 27mg of Pd(PPh 3 ) 4 was added to the system and degassed for 30 min utes more. The temperature was set to 80 o C and the reaction was stirred at this temperature overnight. The product was purified using hexane as eluent and silica gel as absorbent. Yield: 40%. 1 H NMR (300 MHz, CDCl 3 ) : 7.62(s, J Sn H = 24Hz, 2H),1.67 1.52(m, 12H), 1.40 1.27(m, 12H), 1.24 1.18(m, 12H), 0.87(t, J=7.5Hz, 18). 13 C NMR (300 MHz, CDCl 3 ) : 159.50, 137.37 (J Sn C =18Hz)), 137.10, 29.13(J S n C =20Hz), 27.31(J Sn C =56Hz), 13.65, 10.14.

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148 (ClPt) 2 BTD 4,7 bis(tributylstannyl)benzo[c][1,2,5]thiadiazole (300 mg, 0.42 mmol) was dissolved in 30 ml of dry DMF then degassed for 30 minutes. Then, 619 mg Pt(PBu 3 ) 2 Cl 2 and 8 mg of CuI was added to the system. The reaction mixture was heated to 80 o C and stirred at this temperature overnight. The solvent was removed under vacuo and the desired product was obtained via crystallization from MeOH. Yield :40 % 1 H NMR (300 MHz, CDCl 3 ) : 7.10 (s, J Pt H = 23Hz, 2H), 1.66 1.40(m, 48H), 1.37 1.24 (m, 24H), 0.88 (t, J=6Hz, 36H). 31 P NMR (121 MHz, CDCl 3 ) 5.12 ( J Pt P = 2727 Hz). Calculated for C 54 H 110 N 2 P 4 S Pt 2 Cl 2 1403.6001 , found MALDI TOF MS (m/z) :1403.60333 [M ] + . [2,2' bithiophen] 5 yl triisopropylsilane 135 In a dry flask, 2.5 M butyllithium in hexanes (4.8 mL, 12 .0 mmol) was added dropwise to a bithiophene (2 g, 12 mmol) in THF (100 mL) at 0 °C under a N 2 atmospher e. After stirring fo r 1 h at this temperature, neat trii sopropylchlorosilane (2.56 mL, 12 mmol) was added dropwise. The solution was stirred for anoth er 3 h and allowed to warm to room temperature , followed by dilution with hexanes and washing with wate r a nd brine. The organic layer was collected and dried over anhydrous Na 2 SO 4 . After remo ving the solvent in vacuum , the residue was purified by column chromatography on silica gel, eluting with hexanes to yield title compound (1.5 g, 40 %) as a white solid . 1 H

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149 NMR (300 MHz, CDCl 3 J=5.1, 1.1 Hz, 1H), 7.17 (d, J=3.5Hz, 1H), 7.02 (dd, J = 5.1, 3.7 Hz, 1H), 1.36 (sep, J=7.3 Hz, 3H), 1.14 (d, J=7.4 Hz, 18H). Triisopropyl (5' (tributylstannyl) [2,2' bit hiophen] 5 yl)silane. 135 In a dry flask, 2.5 M butyllithium in hexanes ( 0.15ml, 0.37mmol, 1.2equiv. ) was added dropwise to a solution of [2,2' bithiophen] 5 yltriisopropylsilane ( 100m g, 0.31mmol) in THF a t 0 °C under a N 2 atmosphere. After stirring f or 1 h at this temperature, ne at tributylstannyl chloride (120mg, 0.1ml, 1.2 equal ) was ad ded dropwise. The solution was stirred for another 12 h and allowed to warm to room temperat ure, followed by dilution with hexanes and washing with brine. The organic layer was coll ected and dried over anhydrous Na 2 SO 4 . The crude stannyl product was obtained after removing the solvent in vacuum and used directly in the next step without further purification. Crude yield: 80%. 1 H NMR (300 MHz, CDCl 3 7.28(d, J = 3Hz, 1H), 7.16(d, J = 3Hz, 1H), 7.07(d, J = 3Hz, 1H), 1.62 1.56(m, 6H), 1.40 1.31(m, 10H), 1.14 1.11(m, 24H), 0.92(t, J=9Hz, 9Hz) . 2,6 dibromodithieno[3,2 b:2',3' d]thiophene 156 To a suspension of DTT diester 1 (1.7 g, 10 mmol) in the THF (20 mL) was added 20 mL of 1 M LiOH. After the reaction mixture had been heated under reflux for 3 h, water was added to give a clear brownish yellow solution. Excess sol id N bromosuccinimide ( 5.3 g,

PAGE 150

150 30 mmol ) was then added and the reaction mixtur e was stirred overnight at room temperature. The reaction mixture was extracted with CH 2 Cl 2 . The combined organic layers were washed wit h saturated NaHCO 3 (aq), water, and brine, then dried with MgSO 4 . After the solve nt was removed via rotary evaporator, the residue was precipitated with EtOH and then filtered to give the title compound ( 1 g, 50 % yield) as a white solid. 1 H NMR (300 MHz, CDCl 3 s). (6 bromodithieno[3,2 b:2',3' d]thiophen 2 yl)triisopropylsilane In a dry flask 2.5 M butyllithium in hexanes (0.56 mL, 1.41 mmol) was added dropwise to a solution of the 2,6 dibromodithieno[3,2 b:2',3' d]thiophene (500 mg, 1.41 mmol) in THF (1 00 mL) at 78°C under a N 2 atmosphere. After stirring fo r 1 h at this temperature, neat trii sopropylchlorosilane (0.3 mL, 1.41 mmol) was added dropwise. The solution was stirred for anoth er 3 h and allowed to warm to room temperature , followed by dilution with hexanes and washing with wate r and brine. The organic layer was collected and dried over anhydrous Na 2 SO 4 . After remo ving the solvent in vacuum , the residue was purified by column chromatography on silica gel, eluting with hexanes to yield title compo und (200mg, 32%) as a viscous liquid that solidifies over the time under vacuum. 1 H NMR (300 MHz, CDCl 3 7.28 (s, 1H), 7.37 (s, 1H), 1.14 (d, J = 7.3 Hz, 18H), 1.38 (sep, J=7.3Hz, 3H). Triisopropyl(6 (trimethylstannyl)dithieno[3,2 b:2',3' d]thiophen 2 yl)silane

PAGE 151

151 In a dry flask, 2.5 M butyllithium solution in hexanes ( 0.1 ml, 0.28 mmol, 1.2 equiv . ) was added drop wise to a solution of (6 bromodithieno[3,2 b:2',3' d]thiophen 2 yl)triisopropylsilane (100 mg , 0.23 mmol ) in THF at 78 °C under a N 2 atmosphere. After stirring f or 1 h at this temperature, ne at trimethylstannyl chlo ride (0.15 ml, 0.28 mmol, 1.2 equiv. ) was ad ded dropwise. The solution was stirred for another 12 h and allowed to warm to room temperat ure, followed by dilution with hexanes and washing with brine. The organic layer was coll ected and dried over anhydrous Na 2 SO 4 . The crude stannyl product was obtained after removing the solvent in vacuum and used directly in the next step without further purification. Crude yield : 80 %. 1 H NMR (300 MHz, CDCl 3 7.36 (s, 1H), 1.14 (d, J=6Hz, 18H), 1.36 (sep, J = 6Hz, 3H), 0.42 (s, SnMe 3 , 9H). (ThPt) 2 BTD T ributyl(thiophen 2 yl) stannane (30 mg, 0.0783 mmol) was dissolved in 10 ml of dry THF and degassed for 30 minutes then 50 mg of (ClPt) 2 BTD and 2 mg of CuI was transferred to the reaction mixture. The mixture was stirred at room temperature overnight. The precipitate was filtered and washed with DMF. The product was dried under vacuum overnight. The filtered product was pure, no further treatment was necessary. Yield: 60% 1 H NM R (300 MHz, CD 2 Cl 2 ) : 7.50 (d, J=6Hz, 2H), 7.28 (s, 2H), 7.10 (t, J=24), 6.78 (s, 2H), 1.54 1.35 (m, 12H), 1.32 1.13 (m, 24H), 0.85 (t, J=6Hz, 18H). 13 C NMR (75 MHz, CDCl 3 ) 164.27, 153.61, 143.10, 139.33, 130.14, 127.16, 125.27, 25.81, 24.40, 21.60,

PAGE 152

152 13.53 . 31 P NMR (121 MHz, CDCl 3 ) 2.01 ( J Pt P = 2730 Hz). Calculated for C 62 H 116 N 2 P 4 S 3 Pt 2 1498.6472 , found MALDI TOF MS (m/z):1498.6545[M ] + . (BThPt) 2 BTD T riisopropyl(5' (tributylstannyl) [2,2' bithiophen] 5 yl)silane (48 mg, 0. 0783 mmol) was dissolved in 10 ml of dry THF and argon degassed for 30 minutes then 50 mg of (ClPt) 2 BTD and 2 mg of CuI was transferred to the reaction mixture. The mixture was stirred at room temperature overnight. The precipitate was filtered and washed with DMF. The product was dried under vacuum overnight. The filtered product was pure, no further treatment was necessary. Yield: 45%. 1 H NMR (300 MHz, CDCl 3 ) : 7.32 (s, 2H), 7.17(s, 4H), 6.75(s, 2H), 1.50 1.45(m, 24H), 1.42 1.36(m, 24H), 1.27 1.17(m, 30H), 1.18(d, J =3Hz, 30Hz), 0.90(t, J =6Hz, 36H). 13 C NMR (75 MHz, CDCl 3 ) : 164.16, 157.51, 146.05, 142.69, 139.30, 137.75, 136.47, 131.64, 129.27, 125.22, 121.66, 25.86, 24.41, 21.65, 18.41, 13.56, 11.83 . 31 P NMR (121 MHz, CDCl 3 ) 1.65 ( J Pt P = 2700 Hz). Calculated for C 88 H 160 N 2 P 4 S 5 Pt 2 Si 2 1403.6001, fou nd MALDI TOF MS (m/z):1403.6033 [M] + . ( DTT Pt) 2 BTD T riisopropyl(6 (trimethylstan nyl)dithieno[3,2 b:2',3' d]thiophen 2 yl)silane (83mg, 0.0783 mmol) was dissolved in 10 ml of dry THF and degassed for 30 minutes then 102 mg of

PAGE 153

153 (ClPt) 2 BTD and 3 mg of CuI was transferred to the reaction mixture. The mixture was stirred at room temperature overnight. The precipitates was filtered and dried in vacuo overnight. The filtered product was pure, no further treatment was necessary. Yield: 53 %. 1 H NMR (300 MHz, CDCl 3 ) : 7.37 (s, 2H), 7.31 (s, 2H), 6.97 (bs, 2H), 1.57 1.36 (m, 48H), 1.1 9 1.07 ( m, 66H), 0.86 (t, J=9Hz, 36H). 13 C NMR (75 MHz, CDCl 3 ) : 139.0, 137.2, 131.1, 128.7, 25.9, 24.4, 21.7, 18.7, 13.8, 11.9. Carbons adjacent to platinum were not observed. 31 P NMR (121 MHz, CDCl 3 ) 1.87 ( J Pt P = 2700 Hz).

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154 APPENDIX A SUPPORTING INFORMATION FOR CHAPTER 2 Figure A 1 . 1 H NMR (500 MHz, CDCl 3 ) of (PhPt) 2 BTD Figure A 2 . 13 C NMR (125 MHz, CDCl 3 ) of (PhPt) 2 BTD

PAGE 155

155 Figure A 3 . 31 P NMR (121 MHz, CDCl 3 ) of (PhPt) 2 BTD Figure A 4 . HRMS (MALDI DTL), [M] + isotope pattern of (PhPt) 2 BTD

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156 Figure A 5 . 1 H NMR (500 MHz, CDCl 3 ) of (TPAPt) 2 BTD Figure A 6 . 13 C NMR (500 MHz, CDCl 3 ) of (TPAPt) 2 BTD

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157 Figure A 7 . 31 P NMR (500 MHz, CDCl 3 ) of (TPAPt) 2 BTD. Figure A 8 . HRMS (MALDI DTL), [M] + isotope pattern of (TPAPt) 2 BTD

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158 Figure A 9 . 1 H NMR (500 MHz, CDCl 3 ) of (PhPt) 2 DPP. Figure A 10 . 13 C NMR (500 MHz, CDCl 3 ) of (PhPt) 2 DPP

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159 Figure A 11 . 31 P NMR (500 MHz, CDCl 3 ) of (PhPt) 2 DPP Figure A 12 . HRMS (APCI), [M] + isotope pattern of (PhPt) 2 DPP

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160 Figure A 13 . 1 H NMR (500 MHz, CDCl 3 ) of ( TPA Pt) 2 DPP Figure A 14 . 13 C NMR (500 MHz, CDCl 3 ) of (TPAPt) 2 DPP

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161 Figure A 15 . 31 P NMR (500 MHz, CDCl 3 ) of (TPAPt) 2 DPP F igure A 16 . HRMS (MALDI DTL), [M] + isotope pattern of (TPAPt) 2 DPP.

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162 SUPPORTING INFORMATI O N FOR CHAPTER 3 Figure B 1. 1 H NMR (300 MHz, CDCl 3 ) of Pt 2 Th 1 . Figure B 2. 31 P NMR (121 MHz, CDCl3) of Pt 2 Th 1

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163 Figure B 3. HRMS (MALDI DTL), [M] + isotope pattern of Pt 2 Th 1 Figure B 4. 1 H NMR (300 MHz, CDCl 3 ) of Pt 2 Th 2 .

PAGE 164

164 Figure B 5. 13 C NMR (75 MHz, CDCl 3 ) of Pt 2 Th 2 . Figure B 6. 31 P NMR (121 MHz, CDCl 3 ) of Pt 2 Th 2 .

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165 Figure B 7. HRMS (MALDI DTL), [M] + isoto pe pattern of Pt 2 Th 2 . Figure B 8. 1 H NMR (300 MHz, CDCl 3 ) of Pt 2 Th 3 .

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166 Figure B 9. 13 C NMR (75 MHz, CDCl 3 ) of Pt 2 Th 3 Figure B 10. 31 P NMR (121 MHz, CDCl 3 ) of Pt 2 Th 3 .

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167 Figure B 11. HRMS (MALDI DTL), [M] + isotope pattern of Pt 2 Th 3 . Figure B 12 . 1 H NMR (300 MHz, CDCl 3 ) of Pt 2 Th 4

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168 Figure B 13 . 13 C NMR (75 MHz, CDCl 3 ) of Pt 2 Th 4 Figure B 14. 31 P NMR (121 MHz, CDCl 3 ) of Pt 2 Th 4

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169 Figure B 15. HRMS (MALDI DTL), [M] + isotope pattern of Pt 2 Th 4 Figure B 16. 1 H NMR (300 MHz, CDCl 3 ) of Pt2TQT

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170 Figure B 17 . 13 C NMR (75 MHz, CDCl 3 ) of Pt2TQT Figure B 18. 31 P NMR (121 MHz, CDCl 3 ) of Pt2TQT

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171 Figure B 19. HRMS (APCI), [M]+ isotope pattern of Pt 2 TBT Figure B 20. 1 H NMR (300 MHz, CDCl 3 ) of Pt 2 TBT

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172 Figure B 21. 13 C NMR (75 MHz, CDCl 3 ) of Pt 2 TBT Figure B 22. HRMS ( APCI ), [M] + isotope pattern of Pt 2 TBT

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183 BIOGRAPHICAL SKETCH Ali Senol Gundogan was born in Istanbul, Turkey in 1983. He is a son of Turkan Gundogan and Eren Gundogan. After finis hing Kurtulus High School, he enrolled in Chemistry Department at Abant Izzet Baysal University, Bolu. During his last year, he worked with Professor Nihat Celebi on 1 ,3 Dipolar Cycloaddition Reactions. He received his B.S c . in 2006 with two honors, as the top student of the chemistry department and second best student of Faculty of Arts and Science and joined Istanbul Technical University (ITU), in Istanbul, Turkey for his M.Sc. degree in organic chemistry. He worked under the guidance of Professor Turan O zturk on the synthesis and photophysical characterization of dithienothiophene and its various copolymers. During his studies at ITU. Ali was awarded with prestigious scholarship given by Turkish Education Foundation and received the best MSc student award given by the same institution. Ali got accepted to the University of Florida with Fulbright Award given by the United States, Department of State and joined the Schanze Group in the fall of 2009. While at Florida, his work included studying solution excit ed states properties of various platinum complexes with donor acceptor architectures, developing a new metal carbon bond formation reaction and applied this new reaction to investigate the effect of direct attachment of the metal in donor acceptor system. Ali move d back to Turkey to work as a chemist in chemical industry in Istanbul.



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ThepolarsideofpolyphenylenedendrimersBrentonA.G.Hammer,RalfMoritz,Rene ´ Stangenberg,MartinBaumgartenand KlausMu ¨ llen*Polyphenylenedendrimers(PPDs)representauniqueclassofdendrimersbasedontheirrigid,shape persistentchemicalstructure.Thesemacromoleculesaretypicallylookedatasnonpolarprecursorsfor conjugatedsystems.Yetovertheyearstherehavebeensyntheticachievementsthathaveproduced PPDswitharangeofpolaritiesthatbreakthehydrophobicstereotype,andprovidedendrimersthatcan besyntheticallytunedtobeusedinapplicationssuchasstabletransitionmetalcatalysts,nanocarriers forbiologicaldrugdelivery,andsensorsforvolatileorganiccompounds(VOCs),amongmanyothers. ThisisbasedonstrategiesthatallowforthemodificationofPPDsatthecore,scaold,andsurfaceto introducenumerousdierentgroups,suchaselectrolytes,ions,orotherpolarspecies.Thisreviewis aimedtodemonstratetheversatilityofPPDsthroughtheirsite-specificchemicalfunctionalizationto producerobustmaterialswithvariouspolarities.1.Introductiontopolyphenylene dendrimersPolyphenylenedendrimers(PPDs)arehighlybranched,rigid, monodispersemacromoleculesconsistingofsubstitutedbenzene rings.1,2Thesematerialsinherentlyhavetheappealingcharacteristicsofbeingchemicallystableandshape-persistent,yettheir abilitytobefunctionalizedwithnano-siteperfectionisoften overlooked.3Thechemicalmodificationofthesedendrimers cantakeplaceinthecore,scaold,oronthesurfacewhich oersflexibilitytowardstargetingspecificqualities.4,5Combiningtheseconceptsaordsararetypeofmaterialthatcanbe tailoredtowardsanassortmentofapplicationsthroughclever syntheticdesign. Thekeytomakingsuchmulti-functionaldendrimersarises fromthemoleculartoolkitemployedintheirsynthesis,which consistsofacore,scaold,andsurfacebuildingblocks(Fig.1). PPDscanbeformedbyeitheradivergent(palladiumcatalyzed couplingreaction)6,7orconvergent(Diels…Aldercycloaddition reaction)2,8approach,thoughcurrentlynearlyalldendrimersare synthesizedbytheconvergentgrowthmechanism.Thus,PPDs Max-Planck-Institutfu ¨ rPolymerforschung,Ackermannweg10,55128Mainz, Germany.E-mail:muellen@mpip-mainz.mpg.de BrentonA.G.Hammer BrentonHammerwasbornin Colorado(USA)in1985.He receivedhisbachelorsdegreein ChemistryfromColoradoSchoolof Minesin2007.Then,hejoinedthe groupofProfessorToddEmrick attheUniversityofMassachusetts Amherstandworkedonthesynthesisandassemblyofconjugated polymers.AfterreceivinghisPhD in2012hewenttotheMaxPlanck InstituteforPolymerResearchin Mainz(Germany)whereheis currentlyapostdoctoralfellow inthegroupofProf.DrKlausMu ¨ llen.Hisresearchfocuseson thesynthesisanddesignofpolyphenylenedendrimersfor biomedicalapplications. RalfMoritz RalfMoritzwasborninPassau (Germany)in1984.Heobtained hisMasterdegreeinchemistry (2010)fromtheUniversityof Regensburgandisnowatthe Max-Planck-InstituteforPolymer ResearchinMainzunderthesupervisionofProf.DrKlausMu ¨ llenfor hisPhD.Hiscurrentresearchis focusedonweaklycoordinating ions,organicsynthesisandhydrophobicelectrolytes.Received17thJuly2014 DOI:10.1039/c4cs00245h www.rsc.org/csr ChemSocRev REVIEWARTICLE

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aresynthesizedthroughrepetitiveDiels…Aldercycloaddition reactions,whichmeantheonlyrequirementistohaveaproper dieneanddienophile.Thisopensthedoorforavarietyofpolar moietiestobeinsertedatallthreelevelsofthedendrimer, becauseaslongastheyaretoleranttoelevatedtemperatures theycanwithstandthedendrimerformation. First,acore(depictedasthegraysphere)mustbechosen withtwothingsinmind:(1)whatisthedesiredfunctionforthe interiorofthedendrimerand(2)whatisitstargetedgeometry? Sincetheonlyrequirementistohaveaccessibleethynylgroups (dienophile),avarietyofpolarfunctionalitiescanbesynthesizedtobethedendrimercoreaswillbediscussedbelow. Specifically,itisimportanttoobservehowthebulkydendrimer armsshieldtheinternalpolarorchargedcoreandtheresulting eectontheirfunction( i.e. iondissociation,conductivity, catalyststability, etc. ).Additionally,thedesignofthecore moleculewilldeterminethege ometryofthemacromolecule throughthenumberandlocatio noftheethynylgroups,which alsohasasignificantimpactont heresultingpropertiesofthe material.Itisalsopossibletomakeasymmetricdendrimers throughastepwisecoresynthesis.Here,thecoremolecule musthavereactiveandunreactive(protected)ethynylgroupsand dendrimerformationonlyoccursforthereactivesites.Thenupon deprotectionofthepreviouslyinertbranchingpoints,theother partofthedendrimercanbeexpandedwithdierentmoleculesto formasymmetricPPDs.Thisconceptcanbeextremelyusefulfor applicationssuchasinterfacialorsurfaceboundchemistries, aswellasforthesynthesisofJanustypeparticles.These particlesaredefinedashavingatleasttwodistinctlydierent surfacefunctionalities.9…11Thismulti-functionalsurfacecan beadvantageousfordoingdifferenttypesofchemistryonthe sameparticles,whichcanbeimportantforthefieldsofselfassembly,emulsifiers,andcatalysis.12…21Thescaoldbuildingblocks,asillustratedasgreenspheres inFig.1,areinstrumentalintuningthepolaritywithinthe interiorofPPDs.Thecyclopentadienone(diene)(CP)isthe essentialaspectofthisconceptbecauseitistheunitthatreacts Fig.1 Illustrationofthemoleculartoolkitforpolyphenylenedendrimer synthesis. MartinBaumgarten MartinBaumgartenreceivedhis PhDinorganicchemistryatthe FreieUniversitatBerlinin1988. From1988…1990heheldapostdoctoralpositionandaDFG fellowshipatPrincetonUniversity withProf.G.C.Dismukes.In 1990hejoinedtheMaxPlanck InstituteforPolymerResearchin Mainzasaprojectleaderinthe groupofK.Mu ¨ llen.In1996/1997 heachievedhishabilitationand wasappointedPrivatdozentand laterProfessorattheJohannes Gutenberg-UniversityofMainz.Hisprimaryinterestsincludethe synthesisandcharacterizationofnovelconjugatedoligomers, polymers,dendrimers,organichighspinmolecules,andhybrid spinnetworks. KlausMu ¨ llen KlausMu ¨ llenreceivedhisPhDin 1972attheUniversityofBaselin Switzerland.Hewasapostdoctoral fellowatETHZu ¨ richwherehe obtainedhishabilitationin1977. AfterworkingasaProfessorof OrganicChemistryattheUniversitiesofCologneandMainz,he becametheDirectorofthe DepartmentofSyntheticChemistry attheMaxPlanckInstitutefor PolymerResearchinMainz (Germany)in1989.Hisresearch interestsinclude macromolecular andsupramolecularchemistryaswe llasthedesign,synthesis,and characterizationofnovelorganic semiconductorsandgraphenesfor electronicandoptoelectronicapplications. Rene ´ Stangenberg Rene ´ Stangenbergwasbornin 1986inBadKreuznach(Germany) andreceivedhisdiplomadegree inchemistryattheJohannes Gutenberg-UniversityMainzin 2010.HereceivedhisPhDin macromolecularchemistryatthe MaxPlanckInstituteforPolymer Researchafterworkingwith Prof.DrK.Mu ¨ llenin2014.His primaryresearchinterestsfocused onthesynthesisofpolyphenylene dendrimerswithdefinedsurface amphiphilicityandpatchedsurface textures,aswellassemi-fluorinatedalkanes.SinceMay2014heis workingforSIMONAAGfocusingonthedevelopmentofhalf-finished plasticconstructionmaterials.ReviewArticle ChemSocRev

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withtheethynylgroupsfromthecoretoemitcarbonmonoxide andformabenzenering,andhencebuildthenextdendrimer generation.Itisimportanttonotethearchitecturesatthe2-, 3-,4-,and5-positionsofthecyclopentadienone,becausethis iswhatincorporatesdesiredpolargroupswithinthescaold (2-and5-positions)anddierentiatesthesemoleculesfrom thoseusedtoformthesurface.ThescaoldCPtypicallyhave triisopropylsilyl(TIPS)acetylenemoietiesatthe3-and4-positions, whichcanbedeprotecteduponreactionwithtetrabutylammonium fluoride(TBAF)toyieldethynylgroups.Therefore,theseDielsÂ… Aldercycloadditionreactionsprovidetwobranchingpointsper reactionsiteandthemole culescanbedefinedasA2Bmonomers. Thesenewlyformedethynylspeciescanthenbeutilizedwith additionalbuildingblockstoeithercontinuetoformhigher generationdendrimersortosurfacecapthePPDs.Itisalso possibletomakeA4BmonomersbyplacingTIPS-acetylene moietiesatallfourpositionsofaCP,whichwouldthenafford theopportunitytoformfourreactiveethynylgroupsper reactionsite.PPDsmadewithA4BCParedenserthanthose formedbyA2Bunitsduetotheextrabranchingpositions.The manydifferentapproachestofunctionalizethescaffoldsof PPDswillbereviewedbelow. Whilesurfacebuildingblocks(blueandredspheres)share thenecessarycyclopentadienonemotifwiththosethatareused forthescaold,itisthecomponentsplacedatthe3-and 4-positionsthatdierentiatebetweenthem.Asmentioned above,scaoldrepeatunitshavetheTIPS-acetylenegroups there,sothattheycanbedeprotectedforsequentialdendrimer generationformation.Conversely,themoleculesusedforsurface modificationdeterminewhichpo largroupsareplacedoverthe PPDsurfaces.Inthiscase,dierentmoietiescanbeplacedatany ofthepositionsonthecyclopentadienone,givingrisetoavariety ofsurfacefunctionalizationswhichwillbediscussedtowards theendofthisarticle. Rightnowwewouldliketoreiteratethatthisarticlewill focusonPPDsfunctionalizedwithvariousheteroatoms,which changethepolarityofthedendrimerstovaryingdegrees.The capabilitytoregulateaPPDspolar ityfromunipolar(unmodified), toslightlypolar( i.e. additionofpyridyls,carboxylicesters,nitrophenols, etc. ),tohighlypolar( i.e. introduceionsorelectrolytes)is apowerfultechniqueforcontro llingthefinalmolecularproperties.Thisisnotmeanttoignorethemanysignificantachievementsofunpolardendrimers,whichcanalsobefunctionalizedin anassortmentofwayswithunpo largroups,withsomeexamples beingshowninFig.2. TheseincludethecyclodehydrogenationofPPDstoplanarize thestructuresformingnanographenes(Fig.2A),whichweresome ofthefirstreportedsynthesisofgraphenetypemolecules.2,22,23Suchwell-definednanographenestructuresholdtremendous potentialfororganicelectronica ndoptoelectronicapplications.24Â…27Inthiscase,PPDsaretypicallyreactedwithFeCl3forthe cyclodehydrogenationandplanarizationofthedendrimers, wheretheresultingdimensionsofthegraphenederivativeare determinedbythegeometryandgenerationofthePPDprecursor.23,28,29Furthermore,thesolubilityofthesematerialsis controlledbytheedgefunctionalities,whichcanbemanipulated byalteringthesurfacegroupsofthedendrimer.Theseedge moietiesalsoinfluencetheself-assemblyofthenanographene structuresintocolumnstructuresindiscoticliquidcrystals through p Â… p stacking.30,31Therehasbeenimmenseeorttowardsusingthesedendrimers inoptoelectronicapplications,basedontheabilitytoincorporate unitssuchasperylenetetracarboxydiimides,triphenylamines, andtriphenylenes,amongothers,throughoutthemultilayer moleculardesign.32Â…34TherehavebeenmanyPPDsbuiltfrom corescomprisedofpyrene,perylenetetracarboxydiimidedyes, oriridiumcomplexes,wherethedendrimerarmscanprevent aggregationofthespecies,whilealsoinfluencingtheirphotophysicalpropertieslikeincreasingtheirphotoluminescence quantumyieldsorsuppresstripletÂ…tripletannihilation.34Â…39Fig.2Bisanexampleofamultilay erdendrimerthathastriphenyl aminesonthesurfaceandapyrenecorethatactsasablue emitter.40AnotherexamplewasaPPDbuiltfromaterrylenetetracarboxdiimide(TDI)corethathadperylenedicarboximide(PDI) andnaphthalenedicarboximide(NMI)unitsatdifferentdistances onthesurface.33,41Thismacromoleculedisplayedastepwise energytransferfromthesurfaceboundNMIandPDIgroups tothecoreTDI,anditalsowasabletoabsorbradiationoverthe wholevisiblespectrum. Additionally,someapplicationsdesireunpolarsurfaces,which wasthecaseforthedodecylfunctionalizedPPDs(Fig.2C)that wereusedtoformself-assemblednanorods.42Â…44Whilethereare numerousotherexamplesofscien tificallyinterestingPPDswith unpolarfunctionaliti es,therehavebeenanumberofwellwritten reviewsthathavealreadydiscussedthesematerialsindetail whicharehighlyrecommended.4,45Â…47Thus,wewouldliketo focusthisarticleonthecuttingedgeaccomplishmentsinthefield ofpolyphenylenedendrimerswhichtendtofocusonavarietyof polarfunctionalizationsinaneff orttoeliminatethemisconceptionthatPPDsaresolelyacolle ctionoffusedbenzenerings.2.DendrimercoreAsstatedabove,adendrimercorecanbeusedtoestablishthe numberofarmsandgeometryofthemacromolecule,whileit canalsoinfluencetheoverallcharacteristicsofthesystemsuch asphotophysicalproperties,iondissociation,orconductivity. Forinstance,aspecialtypeofcorestemsfromchargedanions (boronbased)orcations(phosphorusbased),wherethepolyphenylenedendronsshieldthechargesresultinginwhatare definedasweaklycoordinatingions(WCIs).Theoverallionic characterofthesematerialsisdependentonthedendrimer generationinasensethatathighergenerationsthereismore chargeshieldingandthusCoulom bicforcesdecrease.Currently, thereareimmenseeortstowardsfindinglesscoordinatingWCIs forthefieldsofcatalysis,electrochemistry,batterytechnology, andionicliquids.48Â…59AnionicPPDshavebeensynthesizeduptothe3rdgeneration fromanethynylfunctionalizedtetraphenylboratecore,asseenin Fig.3,whichleadtotheformationofweaklycoordinatinganions (WCAs).60TheboroncorehadtobestabilizedbyfourelectronChemSocRev ReviewArticle

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withdrawingtetrafluorophenylgroupsinordertoenablethe build-upforhighergenerations.Theintroductionoffluorine atomstotheinnerphenyleneringscausedtheappearance ofseveralconformationalisomers(atropisomers),which hamperedthecrystallizationofhighergenerationboratesalts. Tetrabutylammonium(TBA)wasinitiallyusedasthecounterion givenitsstabilizingeciencyandsolubilityinarangeoforganic solvents.However,ionexchangetechniqueswithvariousresins enablestheexchangeofthecounteriontobedierentalkali andalkalineearthmetalions,organiccations,andevenother chargedpolyphenylenedendrimersofvariousgenerations. 3rdgenerationboratedendrimersstabilizedwithTBAwere foundtohaveadiameterof B 6nm,anditwasobservedthat astheionsizeincreasedsotoodidtheiondissociationin lowpolaritysolvents.Theconductivityvalues(boratesaltsof dierentgenerationsandsurfacemodifications)slightlyincreased withanionsizedespitethesubstantialdecreaseofanionmobility thataccompaniedthegrowth.Thus,reducedmobilitymustbe overcompensatedforbyanincreaseddegreeofdissociation, whichisattributedtoabetterstericshieldingofthechargeby thehydrophobicdendriticshell.Finally,afurtherenhancement ofiondissociationwasobservedwhenpentafluorophenylor3,5-bis(trifluoromethyl)phenylunitswereattachedtothe Fig.2 Chemicalstructuresof(A)PPDcyclodehydrogenation,(B)blueemittingdendrimerand(C)dodecyl-functionalizedPPDforself-assembly applications. Fig.3 TetrabutylammoniumboratebasedPPDs.ReviewArticle ChemSocRev

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dendrimersurface(seeFig.4).60Thus,thepowerfulconcept ofdendronizationisreflectedbyitsversatileabilitytotailor iondissociationandsolubilityforbothcationicandanionic species.ThesizeofthePPDscaold,thedegreeofbranching (A2BorA4Bgrowthstep)aswellassurfacefunctionalization (fluorination,CF3decoration)canbespecificallyaddressedin ordertocontrolelectrolytepropertiesinorganicsolvents. TheabilitytotunethepolarityofPPDsbasedanionswas furtherexploitedbytheincorporationofphotoswitchableazobenzeneunitsthroughouttheirscaold.Itiswelldocumented thatazobenzenegroupscanundergoreversible trans … cis isomerizationsuponexposureto365nm( trans to cis) and450nm ( cis to trans )radiation.61…65Forthisreasonahighlyfunctionalized2ndgenerationboratesalt(Fig.5)wassynthesizedinwhich theionconductivitycouldbealteredbylight.66Inthiscase,when theazo-benzeneunitswereinthe trans configurationthedendrimer armswerefullyextendedresultinginlargeryetlessdensestructures. Thenexposureto365nmradiationinduceda trans … cis isomerizationwhichshrunkthedendrimer,andincreasedtheshielding effectbetweenthePPDanditscounterionbasedonamoredense packingofthedendrons,asseeninFig.5.ThePPDscouldtransformbacktothe trans orientationuponirradiatingwith450nm light,illustratinganefficientphoto-sensitivesystem.Thesize changeforthisisomerizationwasquantifiedbyDOSY-NMRspectroscopywhichdeterminedthehydrodynamicradiusofthe cis configuration B 1.6nm,whiletheradiusincreasedto B 1.9nm forthe trans isomer. Thereversibletransformationfrom trans to cis configurationshadaminimalimpactontheiondissociationofthese materials.SwitchingthePPDsfromthe trans to cis isomers resultedinanincreaseoflessthan B 5%inthedissociationofthe dendrimerwithTBA,withvaluesbetween0.64…1.01dependingon theconcentration(1.5…5.0 10 4MinTHF).However,therewasa morenoticeabledifferenceintheconductivitymeasurements betweentheisomers.Inthiscasetheisomerizationfrom trans to cis formsgenerallyresultedina B 20…25%increaseinthe molarconductivityofthedendrimers,withmaximumvalues of35.8Scm2mol 1( trans isomer)and41.6Scm2mol 1( cis isomer)occurringataconcentrationof1.5 10 4MinTHF.66Theabilitytonotonlytailorthephysicalpropertiesofthese dendrimersbygenerationsize,butalsobyaphoto-switchable triggerrepresentsastimuli-responsivefieldofweaklycoordinating anions(WCAs)thathadpreviouslybeenunstudied. ItwasimperativetosynthesizePPDweaklycoordinating cations(WCCs)tocomplementtheWCAs,thusprovidinga multipurposeensembleofweaklycoordinatingions.Thiswas accomplishedbyencapsulatingaphosphoniumspeciesinthe coreofPPDsthroughusingatetra -4-ethynylphen ylphosphonium moleculetosynthesizedendrimersuptothe3rdgeneration,as showninFig.6.67Tothebestofourknowledgethisrepresents thelargestorganiccationicmoleculeknown,establishingitas averyimportantWCC. OncePPDswithbothborateandphosphoniumcoreswere synthesizedtovaryinggenerationsitwasnecessarytoconduct studiesonthedissociationpropertiesofdierentionpairs. Interestingly,thesystematicvariationofthecationsizein conjunctionwiththelargeborateanionsprovidedthemeansof approachingtheBjerrumlength( lB)insolventsoflowpolarity resultinginsuper-weakionpairs.67,68Thesignificanceherewas inspiredbyincreasingtheconductivityofthesesystemsinnonpolar solvents.Iondissociationinnonpolarsolventsisdescribedby theCoulomblawfortwomonovalentchargecarriersgivenas: Ec¼ e24 p rceSe0Here, e istheelementarycharge, e0thepermittivityoffree space, rcthedistanceseparatingapoint-likecationfromapointlikeanion,and eSthedielectricpermittivityofthesurrounding medium.TheescapedistancefromtheCoulombenergyisset bytheBjerrumlength, lB= e2/4 p e0eSkBT ,givingthecharacteristic Fig.4 DegreeofdissociationofdierentTBA+boratesaltsinTHF.PhF= pentafluorophenylunit; Gx=valueofdendrimergeneration;(CF3)x=total numberofCF3groupsonthedendrimersurface. Fig.5 Illustrationofsize-anddensityswitchingofarigidlydendronizedanion byazobenzenephotoisomerization,andthestructureofboratesaltX,which bears8azo-benzeneunitsthroughoutitsdendrimerscaold.(Reprinted withpermissionfromJohnWileyandSons(2013).)66ChemSocRev ReviewArticle

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separationbetweentwoionsatwhichCoulombicinteractions arebalancedbythermalenergy.69Thesestudieswerecarried outbyelucidatingtheiondissociationcharacteristicsofdierentsizedPPDswitheitherborateorphosphoniumcoresas illustratedinFig.6. Forsaltswithsmallcations(Li+BFÂ…G1,Na+BFÂ…G1andK+BFÂ…G1),increasingcationsizelowerstheionicconductivity, whereastheoppositetrendwasobservedforbulkycations (PÂ…G1+BFÂ…G1,PÂ…G2+BFÂ…G1,andPÂ…G3+BFÂ…G1).Thiscan beattributedtothelargepolyphenylenedendronsthatshield thephosphoniumcations.Asthesizeofthedendriticionis increasedtheshieldingeffectofthedendrimerarmscauses adecreaseiniondissociationenergy.TheseWCIsystems representauniquebalancebetweeniondissociation(promoted bythebulkyions)andchargetransport(inhibitedbythelarge ions),withtheabilitytotargetthed esiredelectrolytecharacteristics insolutionthroughtheuseofacombinationofdendronized ionsandnon-dendriticmaterials.67BesidesimplantingionicspeciesintoPPDcores,another areaofinterestistransitionmetalcatalyststhatbenefitfrom theshieldingeectofthedendrimerarms.Polyphenylene dendronsweresynthesizedwithapyridineunitthatactedas aligandforapalladiumcatalystasdepictedinFig.7.70,71By orientingtwodendrimerarmsaroundthecatalystitsterically shieldedtheactivesitesbetweenneighboringmolecules,and thuspreventedthemfromreactingtoformpalladiumblack whichresultsincatalystfailure.72Thesematerialswereusedas catalystsfortheaerobicoxidationofalcohols,wherethe dendronizedcatalystmaintaineditsactivityandsolubility duringtheprocess,whilepalladiumcatalystswithoutthearms precipitatedduetopalla diumblackformation.70Hence,introducing dendrimerarmsasligandsfortransitionmetalcatalyststhrough polarpyridinegroupsallowedthemtomaintaintheiractivity.This representsanewclassofstablecatalyststhroughtheutilization offunctionalPPDsactingasshieldingligands. Anotherexampleofplacingatr ansitionmetalcatalystinto thecoreofPPDscamefromfunctionalizingcyclopentadienyl(dicarbonyl)cobaltwithaccessibleethynylgroups,whichthen underwentDielsÂ…Alderreactionswithcyclopentadienonesto buildpolyphenylenedendronsaroundthecatalyst(Fig.8).73Inthiscase,fourdendrimerarmswerecoordinatedtothecobalt speciesthatresultedinthestabilizationoftheelectro-active17 electronstate.Thisprocessincreasedtheoxidationpotentialof thesystemupto0.83Vbasedonthestabilizationfromthebulky dendrons,andproducedanactivecobaltspeciesthatwasstable toairandwater. Itwasalsopossibletoincorporatecobaltasthecorefor PPDsthroughtheuseofthemorepolarmetallophthalocyanine (MPc)baseddendronsasligands,asshowninFig.9.74Thisled to1stgenerationdendrimerswith4armsthatwereableto stabilizethecobaltcore,andthisprocessprovidedanavenueto tunethesolubilityofthecomplexes.Inparticular,itbecame possibletodispersethesePPDsinpolarsolventswherethe dendrimersarmspreventedaggregationofthecobaltthatwas observedforothercomplexes.Furthermore,thestericshielding Fig.6 Structuresofthedendriticmoleculesasafunctionofthecation size.Allsaltssharethesameanion, i.e. ,borate(BFÂ…G1).Monovalentand divalentionsareshown,respectively,inblueandred.(center)Effective Coulombenergy(greensolidline)demonstratingtheeffectofincreasing dielectricpermittivityofthemediumandtheeffectofincreasingcation size(dashedlines). Fig.7 PalladiumcatalystwithPPDligands. Fig.8 Cobaltcatalystsurroundedbyfour1stgenerationPPDarms.ReviewArticle ChemSocRev

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ofthedendrimerarmslimitedtheax ialcoordinationselectivityof thecobaltcore,specificallyfordierentsizedpyridinederivatives. Thesecomplexesprovedtobeviablechemosensorsthroughthe uptakeofsmallguestmolecules.Here,whenthePPDswere exposedtovariousgaseousanalytestherewereobservedchanges intheirabsorptionandfluorescencecharacteristicsbasedon interactionsbetweentheguestsandMPccobaltcore. Aspreviouslymentioned,akeypropertyofthedendrimer coreisitsabilitytodeterminethenumberofarmsandthe geometryoftheresultingmacromolecule.Auniqueaspectof introducingfunctionaltransitionmetalsasthecoreisthe potentialtoachievecomplexgeometriesbasedonthechosen metalandligandstructures.Forexample,bipyridinebased polyphenylenedendronswereusedasligandsforasymmetric, cationicrutheniumcomplexesthathadanoctahedralgeometry (Fig.10).75The3rdgenerationdendronswereabletostabilizethe chargedrutheniumcore,whilethegeometrywasdeterminedbythe numberofarmsthatwerecoordi natedtotherutheniumthrough ligandexchangewith4,4-bis(TIPS-ethynyl)-2,20-bipyridineunits. Thisapproachachievedlarge,asymmetricPPDcationsthatwere usedtostudysaltpropertieswithcounteranionsofdierent sizes.Additionally,thereactivityofthechargedrutheniumcore couldbecontrolledbasedontheratioof4,4-bis(TIPS-ethynyl)2,20-bipyridineorPPDfunctionalizedbipyrines,whichisquite rareforrutheniumbasedcatalysts.76Â…803.PolarscaoldsWhilethecoreprimarilydeterminesthenumberofarmsand geometryofPPDs,thescaoldcanbeusedtotunethepolarityof thedendrimercavity,specificallytowardstailoringinteractions withguestspecies.TypicallyPPDsareassumedtohavenonpolar voidsowingtothemanybenzeneringsofthearchitecture,but thisignoresthecreativesyntheticapproachesthathavebeen implementedwhenaddressingstructuralobjectives. Forinstance,3rdgenerationPPDsweresynthesizedwith12 carboxylicacidsplacedthroughou ttheirscaoldsthatprovideda polarenvironmentforguestmolecules,whilethesurfacewas coveredwithunfunctionalizedphenylrings(Fig.11).81Thefunctionalcavitieswereshowntobeabletoencapsulatepolarguest species,specificallyproflavinhy drochloride,throughpossible hydrogenbondingthathadneverbeenpreviouslyseenforPPDs. Thisprocessledtotheuptakeof3Â…4guestmoleculesper dendrimer,andaffordedapathwaytotransporthighlypolar smallmoleculesintohydrophobicmedia,illustratingavaluable approachtoversatileencapsulationindifferentsolvents. ThecyclopentadienoneisthebuildingblockofPPDs,and throughthemitispossibletotailorthefunctionalitiesinthe Fig.9 Cobaltcatalystsurroundedbymetallophthalocyaninebaseddendronsasligands. Fig.10 AsymmetricrutheniumcatalystwithPPDsligands. Fig.11 PPDswithcarboxylicacidsorientedi ntheirscaoldsforencapsulating proflavinhydrochloride.ChemSocRev ReviewArticle

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dendrimerscaoldoronitssurface.ItispossibletoaccomplishthisaslongastheCPisavailablefortheDielsÂ…Alder cycloadditionreaction,meaningthatarangeofpolargroups canbeplacedatthe2,3,4,and5-positionsonthering,which aretheninsertedintoorontopofthedendrimer.Throughthis approachPPDscaffoldshavebeensynthesizedwithunitsthat rangeinpolarityfromunpolar(pyrene,benzene)tohigherlevels ofpolarity(4-nitrophenol,4-cyanobenzene,or N , N -dimethylformamide),illustratedinFig.12.82Inthiscasethedendrimers werethensurfacecappedwithphenylgroupsthatledto PPDswithpolarscaffoldsthatwerestillsolubleinnonpolar solvents.Thisyieldeduniquestructuresthatcouldbeloaded withpolarguestmolecules(benzaldehyde,4-nitrobenzene, N , N0-dimethylformamide)andthentransferredtoarangeof organicsolvents. Whentalkingaboutencapsulationofsmallmoleculesitis importanttothinkabouttheapplication,andhowecienta systemisforaspecificprocess.Anexcellentexampleofthe needforhighlyecienthostsystemsisinthefieldofdetectors, wherethedetectionimproveswiththesensitivityoftheassembly. Thisisevenmoreimportantwheninvestigatingthedetectionof delicatesubstancessuchasexplosives,forwhichthedetectormust beextremelyaccurateandableto senseeventhesmallestamount ofmaterial.Itwasfoundthatintroducingpolargroupswithinthe scaoldsofPPDsmadethemabletodetecttriacetoneperoxide (TATP),awell-knownandhighlydangerousexplosive.82Â…874th generationPPDswerefunctionalizedwith56pyridylunits throughouttheirscaffoldsandcoatedontoaquartzcrystal microbalance(QCM)detector(Fig.13).Itwasnecessaryto calibratethedevicestodifferentiatebetweenthetargetedTATP andmaterialsusedforitssynthesis(acetoneandhydrogen peroxide).ThenanitrogenflowenrichedwithTATPwaspassed overthedendrimercoatedQCM.Theinteractionbetweenthe pyridylmoietiesandTATPaffordedthissystemanextremely highaffinityformolecularuptakewithdetectionlimitsaslow as0.1ppmconcentration.TheabilitytofabricateaTATP detectorwithsuchsensitivityhighlightstheefficiencyofguestÂ… hostinteractionswithfunctionalizedPPDs. ItwasimportanttounderstandthedrivingforcesforinteractionsbetweenguestmoleculesandPPDs,andthiswas characterizedthroughisothermaltitrationcalorimetry(ITC) analysis.88Inthiscase,thereisasignificantdierencebetween thesestudiesandthePPDbasedQCMsensorsinthatmolecularuptakeforthedetectorsoccurredinthegaseousstateand theITCexperimentsinvolveencapsulationofguestspecies invarioussolvents.Therefore,thisapproachlookedatthe thermodynamicinteractionsbetweenthehost(PPD)andguest speciestodeterminetheenthalpicorentropicinfluencesof encapsulationinsolution.Fortheuptakeofunpolarguest moieties,suchasbenzeneortoluene,intounfunctionalized Fig.12 Representative2ndgenerationPPDsforfunctionalguestÂ…host interactions. Fig.13 PyridinefunctionalizedPPDsforthedetectionofTATP. Fig.14 FunctionalPPDsandsmallmoleculesusedforITCencapsulation studies.ReviewArticle ChemSocRev

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PPDsitwasfoundthatthereleaseofsolventmoleculesand theirexchangewithincomingguestswasentropicallydriven (Fig.14).WhenPPDsweremadetohavepolarscaolds ( i.e. carboxylicacids,nitriles,nitrobenzenes)andloadedwith polargroups(acetonitrile,diethylamine,nitromethane, etc. )the encapsulationprocesswasdeterminedbyenthalpicinfluences, typicallyhydrogenbondingor p … p interactions.Thesestudies wereinstrumentaltowardstheunderstandingofhowfunctional scaffoldscaninteractwithguestspecies,aswellashowtotune thedendrimersinamannertocontroltheencapsulationof variousguestsubstituents. InaneorttoenhancethestabilityofPPDbasedguest…host structuresazo-benzenefunctionalitieswereintroducedintothe dendrimerscaffold.Thesegroupshavebeenpreviouslymentioned, andtheirutilitycomesfromtheirabilitytoundergoareversible cis … trans isomerizationuponirradiationat450nm( cis … trans )or 365nm( trans … cis )(Fig.15).89Additionally,pyridylunitswereplaced throughoutthescaffoldtoincreasethepolarityofthecavitiesto promotetheencapsulationofguestmolecules.OpenPPDs( trans isomer)wereloadedwith p -nitrophenolunitsanduponisomerizationtothe cis structureanaverageoftwoguestmoleculeswere stericallysealedperdendrimer.Theseguest…hostassemblieswere stablethroughmultipleprecipitationsandwashings,andthe encapsulatedmoleculeswereonlyreleaseduponisomerizationback tothe trans structure.Thiswasaformidableexampleofthestable uptakeandreleaseofsmallmoleculesfromahostthathada controlledtriggerfortheexpulsionoftheguest,whichwasprovided throughthecleversynthesisofhighlyfunctionalPPDs. AdierentapproachtousingPPDsashostsforguest moleculescamefromtheincorporationofthiolsintotheir scaolds.Thisachievedtwopurposes,thethiolsincreasedthe polarityofthedendrimercavitiestoencouragefunctional guestspeciestoenterthem,whiletheycouldalsobeusedto formdisulfidebondswithguestmoleculestocovalentlyattach themtothestructure(Fig.16).902ndgenerationPPDswere synthesizedwith8freethiolsthroughouttheirscaold,and whenthedendrimerswereexposedtoathiol-functionalized nitrophenolderivativeitwasobservedthateachPPDcovalently boundupto4guestmoleculestoitsscaold.Thisconjugation isappealingbecauseitprovidedanextremelystablemacromolecularassembly,wheretheguestmoleculescouldbereleased underreductiveconditions,atriggeredmechanism.Theability tocovalentlybondguestmoleculestoamacromoleculartransportsystemtoyieldstablematerials,whichhappentohavea highlyecientmechanismforthereleaseofthespecies,isan attractivecontributiontothefieldofdendrimer/smallmolecule conjugations. Fig.15 Photo-switchablePPDsforstableencapsulationandreleasestudies withsmallmolecules.(Reprintedwithpermission,copyright2012,American ChemicalSociety.)89 Fig.16 ReversiblesmallmoleculeconjugationtoPPDsfunctionalized withthiolgroups.(ReproducedwithpermissionfromtheCentreNational delaRechercheScientifique.)90ChemSocRev ReviewArticle

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4.Scaoldandsurface functionalizationThesurfacesofPPDsplaycrucialrolesintheirsolubilityand polarity.Therefore,itisveryimportanttotunethechemistry ofthebuildingblockstowardsthedesiredapplication.Itis alsopossibletointroducesimilarpolargroupswithinthe scaoldandonthesurfacetoprovideacomprehensivefunctionalization.Onesuchexamplewasdonewheresugarunits wereplacedbetweenthe1stand2ndgenerationofPPDs,as wellasonthesurfacetoachieveamacromolecularstructure thatresembledtheactivecenterinnaturallyoccurringenzymes (Fig.17).91,92ThisapproachledtotwentyfourD-glucopyranosyl trichloroacetimidatebasedunitsbeingintegratedthroughout the2ndgenerationPPD,whichincreasedthepolarityofthe glycodendrimerstructure.Thesematerialsweresolublein weaklyacidicaqueoussolutionsorpolarsolvents,suchasDMSO.It wasshownthatthedendrimerswerecapableofencapsulatinga fluorescentprobe(ANS)basedoninteractions(H-bonding)between theguestmoleculeandthesugarsinthedendrimercavities.There wasanobservedhypsochromicblueshiftintheemissionfrom thedyeasaresultofsuppressednon-radiativerelaxationwhen encapsulatedwithinthedendrimerscaold.93AnotherexampleoftailoringtheoverallstructureofPPDs wasachievedbyintroducingpyridineunitsthroughoutthe dendrimers,whichweresubsequentlyalkylatedtoproduce watersolublepolycationicstructures,asseeninFig.18.942nd through4thgenerationPPDsweresynthesizedandmixedwith poly(styrenesulfonate)(PSS)orDNAcomplexestostudythe interactionsbetweenthechargedpolymerions.Bychanging therelativesizeofthedendrimersandPSS,alongwiththe relativechargeratios( i.e. pyridinium:sulfonategroups)itwas possibletocontroltheoverallsizeoftheassemblies.Forsmall molecularweightPSS(DPbetween19…78units)mixedwiththe PPDs(1stor2ndgeneration)itwasfoundthataggregates(sizes upto30nm)wereobserved,whilelargerPSS(DP=316units) mixedwiththedendrimersformedcomplexesbetween6…8 nanometersdependingonthedendrimergeneration.This processenabledtheformationofwatersoluble,polyelectrolyte nanoparticleswithvariablesizesbasedonpolymerchain lengthsandthenumberofincorporatedcharges. Asmentionedabove,PPDshavebeenusedastheactivelayer inQCMdetectorsbecausetherigidityoftheirpolyphenylene backboneprovidesvoidsintheirstructurewhichcantrap guestmolecules.Thispropertywasfirstexploitedwhen2nd generationdendrimersweresurfacefunctionalizedwithpolar groups( i.e. carboxylicacids,nitriles,ordiphenylmethyleneamines)andcoatedontoaQCM(Fig.19).95Thesesensorswere exposedtodierentvolatileorganiccompounds(VOCs)in thegasphase,andeachdendrimerwasabletoencapsulate upto B 5 1015polarmolecules(acetophenone,aniline, benzonitrile,ornitrobenzene),ascharacterizedbyPositron EmissionTomography(PET). Thereareapplicationswherehavingadierenceinpolarity betweenthescaoldandsurfacecanbeutilized.Typically, PPDshaveunipolarscaoldsowingtothecopiousnumber ofphenylrings,whilethesurfacecanbefunctionalizedwith arangeofpolargroups.Onesuchexamplecamefromthe aposterioribasichydrolysisofsurfaceboundcyano-groups on2ndgenerationPPDstoform16highlypolarcarboxylic acidsaroundthedendrimers(Fig.20).96Thesemacromolecules wereexposedtodierentconcentrationsofcyaninedyepinacyanoltostudywherethedyeoriented(onthesurfaceorwithin thedendriticvoids)withthestructuresascharacterizedby single-moleculespectroscopy(SMS).Throughthismethodit wasfoundthatatlowconcentrationsthedyeenteredthe scaoldcavitiesofthedendrimers(2perdendrimer),while athigherconcentrationsdyemoleculesformedionpairswith thesurfaceboundcarboxylicacids.Hence,itbecamepossible tocontroltheorientationofguestmoleculesaroundorinside ofdendrimersbasedonconcentrationanddierencein localpolarities. Fig.17 PPDswithsugarsorientedthroughoutthescaoldsandon thesurfaces.(Reprintedwithpermission,copyright2004,American ChemicalSociety.)91 Fig.18 CationicPPDsassociatedwithPSSasthecounterions.ReviewArticle ChemSocRev

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IntroducingpolargroupsonthesurfaceofPPDscanprovide anecientmethodtotunethesolubilityandfunctionofthe dendrimers.ItwaspossibletocreatewatersolublePPDsthat resemblesurfacefunctionalizedorganicnanoparticlesthrough aposterioriatomtransferradicalpolymerizations(ATRP) fromthedendrimersurface.Here,2ndgenerationPPDswere synthesizedwithsurfacesfunctionalizedwith2-bromo-2methylpropionicestersthatwereusedforthesurfaceinitiated ATRPof2tert -butoxycarbonylaminoethylmethacrylate.The t -bocgroupsweredeprotectedtotheresultingamines(Fig.21), whichdemonstratedtheabilitytoecientlycomplexwithDNA andplasmidDNAfragmentsevenatlowconcentrations.97Thisprocesscouldbecontrolledbychangingthenumber ofaminegroupsthroughvaryingthedegreeofpolymerization duringtheATRPreaction.Interestingly,thesecomplexescouldbe disturbedbyexposuretosodiumchlorideatconcentrationshigher than1M,achievingstimuli-respon siveassemblies .Furthermore, itwaspossibletointroduceperyl enediimidederivativesinto thedendrimercoreofthesestructures,whichcouldactasa fluorescenttagfor invivo studies.ItwasfoundthatthePPDswere abletoactasastainintheextrac ellularmatrix(ECM)inanimal tissueatphysiologicalpHs,whileintroducingcationicspecieson thedendrimersurfaceprovide danavenuetoachieveecient transportthroughcellmembranes.98,99Thismethodprovedto beextremelyvaluabletowardsthesynthesisofwatersoluble, coreshelldendrimerswherethesolubilityandinteractionsin biologicalmediacouldbecontrolledthroughtheaposteriori functionalizationofthesurfaceboundpolymers. Thesedendrimershaverecentlybeenstudiedascomplexes withdierentRNAstrainsforgeneexpression.Specifically, dendrimerswerecomplexedwithaRNAstrainthattargetsthe mid-gutchitinasegene(CHT10-dsRNA)intheAsiancornborer (oneofthemostprominentpestsofcorn).Theseassemblies wereecientatsuppressingthedevelopmentalgeneexpressionintheinsects,eventuallyleadingtotheirdeath.Oneofthe mostsignificantdevelopmentsconcerningthistopicwasthe abilitytoadministerthePPDbasedRNAtofreshlyhatched larvaeandobservethatitpreventedtheirnaturalgrowth,which representsthefirstreportedcomplextobeorallygivento insectsthatcouldprovidecontrolovercertaingeneexpression.100Anotheradvantageofthissystemisitsnon-viralgene therapyapproach,whileitprovidesanavenuetowardsinsect controlwithouttheneedforharshchemicalinsecticides. Theaposteriorifunctionalizationof2ndgenerationPPDs via surfaceinitiatedATRPwasexpandedtothesynthesisof Fig.20 CarboxylicsurfacedfunctionalizedPPDsforinteractionwith guestspecies. Fig.19 2ndgenerationPPDwithpolarsurfacefunctionalities. Fig.21 CoreshellPPDswithsurfaceinitiatedpoly(2-aminoethylmethacrylate)chains.ChemSocRev ReviewArticle

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diblockcopolymersinaneorttoformamphiphilicdendrimers. Poly(2-hydroxyethylmethacrylate)(PHEMA)b -polystyrene(PS) wassynthesizedfromthedendrimersurfacetoyieldamulticoreshellparticlethatexhibiteduniquesolubilityproperties basedonrearrangementsofthepolymerarmsdependingon theirenvironment(Fig.22).101ItwasfoundthatthehydrodynamicradiusofthePPDscouldshrinkfrom15.6nmwhen thepolymerarmswerefullysolvatedto8.5nmuponexposure toapoorsolventforthePS( i.e. 5vol.%methanolinTHF).This wasjustifiedbythePSoutershellcollapsingintothePHEMA layertoescapetheunfavorablemethanolsolvent,essentially displayingastimuli-responsivenesstothesolventconditions. SampleswerealsomadetohavetheouterlayerbethePHEMA blockwiththePSdirectlyattachedtothedendrimers,which couldthenshowresponsivenesstosolventsthatareunfavorableforthePHEMAblock.Theuseofdiblockcopolymers aordedthePPDsuniqueamphiphiliccharacteristicsthrough themulticoreshellapproach. Otherbenefitstointroducingpolarity(carboxylicacids)into multicoreshellPPDscamefromtheiruseastemplatesfor mesoporousmetaloxides.Inthiscase,PPDswereaposteriori functionalizedwith12PSblock -poly(acrylicacid)(PAA),andthe PAAblockwasloadedwithtitaniumoxide(TiO2)nanoparticles (Fig.23).102,103ItwasthenshownthatthehydrophobicPPD supportandPSblockcouldbedegradedbyhydrolysis,condensation,andcalcinationtoleaveahollowsphereorringshaped structureofthePAAloadedwiththenanoparticles.Thesize ofthedendrimerandPSblockdeterminedtheporesize,while thesizeofthePAAblockdeterminedtheshellthicknessofthe resultingassemblies.Thisrepresentsacutemethodforthe formationofmesoporousmetaloxidestructureswithacontrol mechanismovertheirdimensionality,whichhasapplications inphotocatalysis,gassensors,andlithiumionbatteries.104…108Adierentconcepttowardstheformationofmetalassemblies assistedbyPPDsinvolvedtheformationofmultilayeredstructures ofgoldnanoparticleso nsiliconsubstrates.H ere,polyphenylene Fig.22 PPDswithsurfacefunctionalizedPSb -PHEMAarms.(ReprintedwithpermissionfromJohnWileyandSons(2007).)101ReviewArticle ChemSocRev

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dendronswerefunctionalizedwithanalkylthiol,whichwasused asaligandforgoldnanoparticles(Fig.24).109Poly(ethyleneimine) (PEI)wasdepositedonasiliconsurface,followedbypoly (4-vinylbenzylazide)(P4VBA)block -PAAwhichattachedtothe surfacethroughCoulombicinteractions.Thegoldnanoparticles functionalizedwiththePPDdendronswerethencovalently attachedtothesurfaceboundazidesthroughclickchemistry. Thesideofthenanoparticleswithfreeethynylgroupswas reactedwithanewbatchoftheP4VBAb -PAApolymer,and sequentiallyalayerbylayerassemblyofgoldnanoparticles wasproduced.Thesizeandshapeofthelayerscouldbetailored throughtheshapeandsizeofthedendrons,whilethestability ofthestructureswasdeterminedthroughthenumberofactive azideunitsinthediblockcopolymer.Thisyieldedanovelmethod toformnanometerthickmultil ayersofgoldnanoparticles. Thephotophysicalpropertiesofo rganicdyescanbemanipulated throughinteractionswithnanosco picmetalthroughplasmonicgap resonances.110…115Thiscanbeadifficultconceptthoughbasedon theabilitytoorientsuchdyesbetweenmetallicobjectsonsuch smalllengthscales.116…120Oneapproachthatprovedsuccessfulwas toincorporateaPDIdyeintothecoreof2ndgenerationPPDs,and thensurfacefunctionalizetheden drimerswith16dithiolaneunits, whichshowedhighaffinityforsilver.Thesestructureswereoriented betweenasilverplateandsilversph ere(seeFig.25),whichprovided Fig.23 CoreshellPPDsfortheformationofmesoporousmetaloxidestructures.(ReprintedwithpermissionfromJohnWileyandSons(2008).)102 Fig.24 Multi-layeredgoldnanoparticlesandpolymerfilmsutilizingPPDligands.ChemSocRev ReviewArticle

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anavenuetoachievedendrimerthicklayersontheorderof3nm.121Suchasphere-on-plane(SOP)geometrywasidealforproducing dendrimerlayersinwhichthefluorescencefromthePDIwas quenchedonthesilverplane,yetamplifiedby B 1000timeson thesilversphere via plasmonicresonators. Furthermore,PPDsthatpossesssurfacebounddithiolane orthiomethylgroupsexpressahighanityforgoldnanoparticles.MixingPPDswithsurfacebasedthiomethylspecies andgoldnanoparticlesledtotheformationofstablecomposites.Uponevaporationofthesolventtherigiddendrimers promotetheaggregationofthenanoparticlestoyieldacrosslinkedassembly,andthisledtoafacilemethodtoformgold nanoparticlebasedcomposites.Suchmaterialscanbeusedas theselectivelayerinchemiresistorbasedsensorsforVOCs (Fig.26).122Â…124InthiscasethePPDscross-linkthegoldnanoparticles,stabilizetheactivelayer,andincreasethesensitivityof thesensortowardsVOCs;whilethegoldnanoparticlesprovide goodsignaltransduction.Thesede viceswereefficientatdetecting organicsolvents,suchastolueneandtrichlorobenzene,while havingnegligiblesensitivitytohumidity,anecessityformost sensingapplications. AdierentapproachtoassemblePPDsthroughtheirsurface functionalizationwastointroduceperfluorinatedphenyl rings,anexampleofinvestigatingdierenttypesofpolarity onadendrimer.Inthiscase,2ndgenerationPPDswere asymmetricallyfunctionalizedwherehalfofthesurfacewas occupiedwithunmodifiedphenylringswhiletheotherhalf wasfluorinatedphenylrings(seeFig.27).125Thiswasoneof thefirstexamplesofaJanustypedendrimerwherethequantity ofphenylandfluorinatedphenylmoietiescouldbecontrolled throughtheasymmetricsynthesis.ThroughtuningthefluorophilicityofthePPDsitwaspossibletoself-assemblethe macromoleculesintomicrometerlongnanofibersonhighly orientedpyrolyticgraphite(HOPG).126Thedrivingforce wasattributedtothe p Â… p interactionsbetweenfluorinated andnon-fluorinatedphenylrings,andtheresultingnanofibers werehighlyordered. TheasymmetricfunctionalizationofPPDswithpolarspecies alsoopensthedoorformorecomplexfieldsofchemistrysuchas interfacialinteractions,surfaceattachedthinfilms,andavariety ofothers.Again,itisthefundamentalsyntheticapproachto formPPDsfromcyclopentadienonesthatcanbefunctionalized inavarietyofmannersthatallowsforsuchasymmetricgrowth. Forinstance,1stgenerationPPDsweresurfacemadewiththree Fig.25 PPDSsurfacedfunctionalizedwithdithiolanesactingasalubricationlayerbetweenasilverplateandsphere.(Reprintedwithpermission, copyright2010,AmericanChemicalSociety.)121 Fig.26 PPDSandgoldcompositesastheactivelayerinadetector. (ReprintedwithpermissionfromJohnWileyandSons(2002).)124 Fig.27 FluorinesurfacefunctionalizedPPDs.ReviewArticle ChemSocRev

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perylenemonoimidedyesandasinglebiotinunit,whichcould actasananchorpointonforeignsurfacesorstructures,as showninFig.28.127WhenthisdendrimerwasmixedwithTween 20detergentthestructurebecamewatersoluble,providingan aqueousperylenemonoimidedye.Moreover,thisPPDwasable tospecificallybindtotheproteinstreptavidinthroughthebiotin unit,whichledtotheabilitytofluorescentlytagtheprotein. TheconceptofasymmetricPPDswasexpandedtoinclude otherpolargroupssuchasamines,carboxylicesters,oralkyl chloridesthatcanactasananchoringgroupforeitherattachmenttoanotherstructureorforpost-dendrimerformation functionalization.Theothersurfacesitescouldthenbesynthesizedtohaveeithernonpolar(typicallybenzenerings,TIPSacetylene)orpolargroups(amides,diphenylmethylamines, carboxylicacids, etc. )basedonthedesiredapplication ( i.e. surfactants,surfaceattachment,orproteinbinding).This highlightedthecapabilitytoincorporatemultiplefunctionalitiesontoPPDstotunetheirpolarity(Fig.29).128Biologicalapplications( i.e. celluptake,nanocarriersfor therapeuticdrugs,complexesforgeneexpression)areafield thatmostdonotthinkPPDsshouldberelevanttobasedon hypotheticaleectsofthebenzeneringsthatmakeupthe dendrimers.However,throughthemanywaystomodifythese materialsithasbecomepossibletointroducePPDsinarange ofbiologicalsettings.Forexample,1stand2ndgeneration PPDsweresurfacefunctionalizedwithaminegroupswhich werethencoupledtotheC-terminusactivatedcarboxylicacid groupsofpoly(L-lysine)(Fig.30).129,130Theattachmentofthe peptidestothedendrimersurfacemadethematerialssoluble inaqueousmediaandpromotedtheirbiocompatible.Moreover, thelengthofthepoly(L-lysine)determinedtheself-assemblyof thedendrimerswheresmallorlargepeptidelengthsledto undefinedmixturesof a -helicaland b -sheetstructures,while intermediatelengthsproducedprimarily a -helicalassemblies.131ThisprocesswasimportanttowardsproducingpolarPPDsthat werewatersolubleandbiocompatible,andtheabilityto regulatetheself-assemblyprocessthroughcontrollingthe peptidechainlengthwasadvantageousaswell. ArecentbreakthroughinthesurfacemodificationofPPDs camefromtheabilitytoplacealternatingpolar(sulfonate)and unpolar(propyl)groupsaroundthedendrimerwithnano-site perfection(Fig.31).1stto3rdgenerationPPDsweresynthesized whichhadbetween8(1stgeneration)to32(3rdgeneration) sulfonateandpropylgroupsonthesurfaces.131,132Thisarchitectureproducedanon-polardendrimerwithpolarpatcheson theperiphery,wheretheamount,order,location,anddistance ofthefunctionalgroupscanbedeterminedthroughthesyntheticmodificationoftheorganicbuildingblocks.Moreover,the shape-persistentnatureofPPDsprovidedastablenano-phase separationbetweenthepatternedpolarandunpolarsections, whichresultedinbothattractiveandrepulsiveforceswith solventmolecules.Hence,theperipheryledtoauniquesurface polarityforPPDswhichresultedinunprecedentedsolubilityin solventsrangingfromtoluenetowater. Anadditionalaspectofthesurfaceamphiphilicitywasits impactonhowthedendrimersinteractedinbiologicalapplications,specificallycelluptake.Achievingecientbiological macromoleculesisasignificantchallengeduetocriticalstructuralandconformationalrequirements,andtherearelimited examplesofdendrimersthattrulyresemblebiologicalspecies ( i.e. proteins).133,134Yetwiththe3D-globularnatureandnano-site definitionofthefunctionalgroups,combinedwiththelipophilic interiorcavitieshaveclosedthegapbetweensyntheticandnatural amphiphiles,andmadethesedendrimersattractiveoptions towardscellstudies.Thecavitiesformedbythedendronsofthe Fig.28 AsymmetricallyfunctionalizedPPDsforproteinbinding. Fig.29 PPDsasymmetricallymodifiedwithdierentpolargroups. Fig.30 PeptidefunctionalizedPPDs.ChemSocRev ReviewArticle

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PPDsmatchtheshapeandpolarityoffattyacidsordoxorubicin guestmolecules,andnine16-DSAligandswereaccommodated indicatinguptakecapabilitiesthatsurpassthenativeprotein transporterHSA.ThePPDfeaturesalsoencouragedmembrane uptakeandminimizedcellulartoxicity,aswellastheintegrity ofbiologicalbarriers.Thus,therefinedmacromoleculardesign emulatesimportantfeaturesofHSAproteinsandallowed trackingpayloadsintoA549cancercellsand,moreexciting, thepermeationintoendothelialcellsthatareamajorcomponentoftheextremelytightbloodbrainbarrier.135Therewasno significanttoxicityobservedafter invivo treatmentofzebrafish embryos,comparedtomanyreportedpolycationsandnanoparticles.Finally,PPDsloadedwithdoxorubicin(ananti-tumor drug)weremoreecientattransportingandreleasingthe moleculethanHSA,indicatingthatithassignificantpotential asamacromolecularvehiclefordrugdeliveryapplications.5.ConclusionsandoutlookPolyphenylenedendrimersrepresentadistinctfieldofdendrimerchemistrybasedontheirrigid,shape-persistentstructure. Theycanbemodifiedatthecore,scaold,oronthesurface withvariousfunctionalities,butofsignificantinterestisintroducingdierentgroupsofvaryingpolarity.BuildingPPDs aroundcations(phosphonium)oranionic(borate)coresleads toweaklycoordinatingionsthatcanbetunedtohavedierent iondissociationandconductivitycharacteristics.Whentransitionmetalcatalystsaresurroundedbybulkydendrimerarms, thesedendronsshieldthemetaltopromotestability,determinethePPDgeometry,andcontrolaccesstothecatalytically activesites. Thepolarityofdendrimerscaoldscanbetunedbytheuseof dierentmoieties( i.e. carboxylicacids,pyridines,nitriles,thiols, nitrobenzenes,amongothers),topromotetheuptakeorencapsulationofguestmolecules.Theseprocessescouldbetailoredby thermodynamicinteractionsbetweentheguestandhostspecies throughvaryingthefunctionalitiesofthedendriticcavities.The stabilityofthedendrimerencapsulationexperimentswas improvedbyintroducingazo-benzeneunitsthroughoutthescaffold,whichcouldstericallysealincomingmoleculesthrougha trans … cis isomerizationtoaclosedconfiguration.Releaseof thesemoleculesoccurreduponthetransformationbacktothe trans configuration,whichrepresentsastimuli-responsiveencapsulationandreleasesystem.Alternatively,PPDsweresynthesized withthiolsintheirscaffoldsthatwereusedtocovalentlyattach smallmolecules via disulfidebondformation.Theboundspecies weredischargedunderreductiveconditionsdemonstratinga reversibleconjugationandreleaseassembly. PPDsurfaceshavebeenmodifiedwitharangeofpolar functionalitiestoencourageinteractionswithothermaterials suchassmallmolecules,proteins,orDNA.Stimuli-responsive polymers(PSb -PHEMAandPSb -PAA)weresynthesizedby surfaceinitiatedATRPfromdendrimers,andshowedversatile solubilitieswhilealsoforminguniqueassemblieswithmetal oxides.Dendrimerswithsulfurbasedligandsontheirsurfaces havebeenusedtocoordinatetogoldnanoparticlesina proceduretoformultra-thinlayer-by-layerfilms,whilesuch functionalitieshavealsobeenusedtobridgesilverinterfaces formanipulatingthephotophysicalpropertiesofdyemolecules.TheasymmetricfunctionalizationofPPDswithbiotin groupswasusedtofluorescentlytagtheproteinstreptavidin, whileotherpolargroupswereimplantedtoactassitestobind todierentsurfaces. Fig.31 PPDswithpatchedsurfacesofalternatingsulfonateandpropylgroups.ReviewArticle ChemSocRev

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Introducingpeptidesorpatchedpatternsofsulfonatesand propylunitsondendrimersurfacesmadethestructureswater solubleandbiocompatible.The patchedsurfacedendrimers demonstratehighcelluptakeandlowcytotoxicity,whiletheyhave evenbeenabletocrosstheblood…brainbarrier.ThesePPDshave beenloadedwithdoxorubicinandexhibitedahighefficiencyof transportingandreleasingtheanti-tumordrugwithincells. Thesearesomeofthemanyaccomplishmentsinthefieldof PPDswithregardtointroducingvariouspolargroupsthroughoutthedendrimerarchitecture.However,bynomeansdowe wishtolimitPPDstothepast,asthereisstillavastamountof potentialfortheminthefuture.Currentresearchfocuses oncharacterizingthecrystalstructureoflargeWCIs(phosphoniumandborate)PPDionpairs,aswellasinvestigating theirinfluenceascounterionsinmetallocenechemistry.Anew seriesofPPDbaseddrugconjugatesthatpossesscleavable linkersarebeingstudiedfortheirabilitytotransportand releasetherapeuticdrugsintocells.Thefieldofpatched surfacesisevolvingtomoreintricatearchitecturesinhopesof expandingthetypesofcomplexesthatcanbeformedwith dierentproteins,RNA,andDNA.PPDsarebeingfunctionalizedwithnewpeptidesequencestoaltergeneexpression characteristics.Theoutlookforthisgenreofdendrimerslooks promising,aslongasthescientificimaginationcancontinueto envisionnewchallenges.AcknowledgementsWewouldliketogratefullythan ktheDeutscheForschungsgemeinschaft(SFB625)andVolkswage nStiftung(5645)forfinancial support.References1F.Morgenroth,C.KubelandK.Mu ¨ llen, J.Mater.Chem. , 1997, 7 ,1207…1211. 2F.Morgenroth,E.ReutherandK.Mu ¨ llen, Angew.Chem., Int.Ed.Engl. ,1997, 36 ,631…634. 3F.Morgenroth,A.J.Berresheirn,M.Wagnerand K.Mu ¨ llen, Chem.Commun. ,1998,1139…1140,DOI: 10.1039/A801395K. 4R.Bauer,A.GrimsdaleandK.Mu ¨ llen,in Functional MolecularNanostructures ,ed.A.D.Schlu ¨ ter,Springer, Berlin,Heidelberg,2005,ch.7,vol.245,pp.253…286. 5S.Campagna,P.CeroniandF.Puntoriero, Designing dendrimers ,Wiley,Hoboken,NJ,2012. 6T.M.MillerandT.X.Neenan, Chem.Mater. ,1990, 2 , 346…349. 7T.M.Miller,T.X.Neenan,R.ZayasandH.E.Bair, J.Am. Chem.Soc. ,1992, 114 ,1018…1025. 8F.Morgenroth,C.Ku ¨ bel,M.Mu ¨ ller,U.M.Wiesler, A.J.Berresheim,M.WagnerandK.Mu ¨ llen, Carbon , 1998, 36 ,833…837. 9S.Zhang,Z.Li,S.Samarajeewa,G.Sun,C.Yangand K.L.Wooley, J.Am.Chem.Soc. ,2011, 133 ,11046…11049. 10A.WaltherandA.H.E.Mu ¨ ller, Chem.Rev. ,2013, 113 , 5194…5261. 11A.J.Swiston,C.Cheng,S.H.Um,D.J.Irvine,R.E.Cohen andM.F.Rubner, NanoLett. ,2008, 8 ,4446…4453. 12K.D.Anderson,M.Luo,R.Jakubiak,R.R.Naik, T.J.BunningandV.V.Tsukruk, Chem.Mater. ,2010, 22 , 3259…3264. 13J.Zhang,J.JinandH.Zhao, Langmuir ,2009, 25 ,6431…6437. 14S.YeandR.L.Carroll, ACSAppl.Mater.Interfaces ,2010, 2 , 616…620. 15J.A.Chute,C.J.Hawker,K.Ø.Rasmussenand P.M.Welch,Macromolecules ,2011, 44 ,1046…1052. 16J.DuandR.K.OReilly, Chem.Soc.Rev. ,2011, 40 , 2402…2416. 17T.Nisisako,T.Torii,T.TakahashiandY.Takizawa, Adv. Mater. ,2006, 18 ,1152…1156. 18K.-H.Roh,D.C.MartinandJ.Lahann, Nat.Mater. ,2005, 4 , 759…763. 19B.P.BinksandP.D.I.Fletcher, Langmuir ,2001, 17 , 4708…4710. 20L.Hong,S.JiangandS.Granick, Langmuir ,2006, 22 , 9495…9499. 21A.Walther,M.HomannandA.H.E.Mu ¨ ller, Angew. Chem. ,2008, 120 ,723…726. 22Z .Tomovic ´ ,M.D.WatsonandK.Mu ¨ llen, Angew.Chem., Int.Ed. ,2004, 43 ,755…758. 23M.Mu ¨ ller,C.Ku ¨ belandK.Mu ¨ llen, Chem.…Eur.J. ,1998, 4 , 2099…2109. 24P.Avouris,Z.ChenandV.Perebeinos, Nat.Nanotechnol. , 2007, 2 ,605…615. 25L.Liao,J.Bai,Y.-C.Lin,Y.Qu,Y.HuangandX.Duan, Adv.Mater. ,2010, 22 ,1941…1945. 26S.G.Jang,D.-G.Choi,S.Kim,J.-h.Jeong,E.-s.Leeand S.-M.Yang, Langmuir ,2006, 22 ,3326…3331. 27J.Bai,X.Zhong,S.Jiang,Y.HuangandX.Duan, Nat. Nanotechnol. ,2010, 5 ,190…194. 28S.Pang,H.N.Tsao,X.FengandK.Mu ¨ llen, Adv.Mater. , 2009, 21 ,3488…3491. 29J.Wu,W.PisulaandK.Mu ¨ llen, Chem.Rev.,2007, 107 , 718…747. 30C.D.Simpson,G.Mattersteig,K.Martin,L.Gherghel, R.E.Bauer,H.J.Ra ¨ derandK.Mu ¨ llen, J.Am.Chem.Soc. , 2004, 126 ,3139…3147. 31C.D.Simpson,J.Wu,M.D.WatsonandK.Mu ¨ llen, J.Mater.Chem. ,2004, 14 ,494…504. 32T.Weil,T.Vosch,J.Hofkens,K.PenevaandK.Mu ¨ llen, Angew.Chem.,Int.Ed. ,2010, 49 ,9068…9093. 33T.Weil,E.Reuther,C.BeerandK.Mu ¨ llen, Chem.…Eur.J. , 2004, 10 ,1398…1414. 34T.Qin,J.Ding,L.Wang,M.Baumgarten,G.Zhouand K.Mu ¨ llen, J.Am.Chem.Soc. ,2009, 131 ,14329…14336. 35A.Herrmann,T.Weil,V.Sinigersky,U.-M.Wiesler, T.Vosch,J.Hofkens,F.C.DeSchryverandK.Mu ¨ llen, Chem.…Eur.J. ,2001, 7 ,4844…4853. 36J.Qu,N.G.Pschirer,D.Liu,A.Stefan,F.C.DeSchryver andK.Mu ¨ llen, Chem.…Eur.J. ,2004, 10 ,528…537.ChemSocRev ReviewArticle

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