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Structure-Property-Function Relationships of Information-Rich Pi-Conjugated Molecules for Organic Electronics

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Title:
Structure-Property-Function Relationships of Information-Rich Pi-Conjugated Molecules for Organic Electronics
Creator:
Bou Zerdan, Raghida M
Place of Publication:
[Gainesville, Fla.]
Florida
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University of Florida
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english
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Thesis/Dissertation Information

Degree:
Doctorate ( Ph.D.)
Degree Grantor:
University of Florida
Degree Disciplines:
Chemistry
Committee Chair:
CASTELLANO,RONALD K
Committee Co-Chair:
FANUCCI,GAIL E
Committee Members:
SCHANZE,KIRK S
MILLER,STEPHEN ALBERT
XUE,JIANGENG
Graduation Date:
8/8/2015

Subjects

Subjects / Keywords:
Absorption spectra ( jstor )
Chromatography ( jstor )
Electronics ( jstor )
Molecular structure ( jstor )
Molecules ( jstor )
Nuclear magnetic resonance ( jstor )
Nucleobases ( jstor )
Oligomers ( jstor )
Purines ( jstor )
Solvents ( jstor )
2-ethylhexyl -- chiral -- dna -- h-bonding -- morphology -- nucleobases -- oligomers -- purine -- pyrimidine -- stereochemistry
Chemistry -- Dissertations, Academic -- UF
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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.

Notes

Abstract:
Considerable interest in organic semiconductive materials, including pi-conjugated oligomers and polymers, has emerged as a result of their potential advantages over their inorganic counterparts. Many such systems exhibit promising optoelectronic properties at the molecular level. However, these are rarely predictably reflected within devices, as charge injection, separation, and transport are greatly affected by the supramolecular assembly of the pi-conjugated organic molecules within a thin film active layer. Designing smart building blocks, capable of mutually controlling supramolecular architecture and tuning optoelectronic properties represents a possible solution but also a significant challenge. Required is an optimized approach to pi-conjugated supramolecular structure through programmed self-assembly dictated by molecular design. Initial work focuses on the incorporation of the canonical nucleobases into pi-conjugated materials to tailor the supramolecular structure, and rationally optimize the corresponding optoelectronic characteristics. Experimental and theoretical structure-property trends have been established using a set of purine- and pyrimidine-terminated oligomers. The absorption-emission profiles, as well as the redox behavior and the estimated HOMO-LUMO energies, respond in understandable ways to nucleobase and pi-linker electronic structure. The complementary nucleobases self-assembly is then investigated in solution. These studies will permit a better understanding of how bio-inspired structure can confer tunable and useful application relevant properties to functional pi-systems. To address the low solubility of the nucleobases, rac-2-ethylhexyl groups were installed. Herein, we study the influence of its asymmetric carbon on the molecular organization, optoelectronic properties, and photovoltaic device performance of a well-studied diketopyrrolopyrrole-based pi-conjugated oligomer (SMDPPEH) through the asymmetric synthesis of its three stereoisomers (RR, SS, and RS). The different SMDPPEH stereoisomer compositions exhibit nearly identical optoelectronic properties in dilute solution, as well as in amorphous films blended with PCBM. The meso (RS) isomer was also investigated, and found to crystallize more readily than the other materials. Bulk heterojunction photovoltaic devices were fabricated and investigated; all but the meso (RS) isomer showed a substantial increase in device performance after annealing. The overall results reveal that the side chain chirality, while strongly impacting the thin film morphology and optical properties of SMDPPEH, has modest effects on the photovoltaic performance of the material as blends with PCBM. ( en )
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In the series University of Florida Digital Collections.
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Includes vita.
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Includes bibliographical references.
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Description based on online resource; title from PDF title page.
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This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Thesis:
Thesis (Ph.D.)--University of Florida, 2015.
Local:
Adviser: CASTELLANO,RONALD K.
Local:
Co-adviser: FANUCCI,GAIL E.
Electronic Access:
RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2016-08-31
Statement of Responsibility:
by Raghida M Bou Zerdan.

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UFRGP
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Applicable rights reserved.
Embargo Date:
8/31/2016
Classification:
LD1780 2015 ( lcc )

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STRUCTURE PROP ERTY FUNCTION RELATIONSHIPS OF INFORMATION RICH Pi CONJUGATED MOLECULES FOR ORGANIC ELECTRONICS By RAGHIDA BOU ZERDAN A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL F ULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2015

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© 2015 Raghida Bou Zerdan

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To the love of knowledge

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4 ACKNOWLEDGMENTS First and foremost, I would like t o thank my family who believed in and supported me on this long journey. I have been truly blessed to have them in my life. I particularly thank my mother for making me realize the importance of educat ion and for crafting in me the personality and the enth usiasm of a young scientist. I thank my father for supporting my dreams and ambition, even when they seemed far fetched or silly to everyone. Thank you for teaching me how to be positive in life and face my fears with a smile . I thank my brother for being my inspiration, he was and still the best example I can follow : kind, smart, and humble . My most sincere thanks go to my advisor, Dr. Ronald Castellano. I thank him for his excellent guidance, for introducing me to the wonders and frustrations of scientif ic research, and for his encouragement and support during the last five years. I hope that one day I would become as good an advisor to my students as he has been to me. I would like to thank my lab mates in the Castellano lab and friends at the University of Florida. My sincerest gratitude to Ania Sotuyo, Danielle Fagnani, Renan and Ricardo Ferreira for being by my side and acting as my family away from home. I owe you tons for giving me a pool of awesome nostalgia . Special thanks to Dr. Watkins for the lo ng sess ions of brain storming with her. I also would like to thank my committee members individually: Dr. Kirk Schanze, Dr. Stephen Miller , Dr. Gail Fanucci, and Dr. Jiangeng Xue for continually and persuasively convey ing a spirit of curiosity and adventu re in research .

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5 TABLE OF CONTENTS page ACKNOWLE DGMENTS ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ ............ 8 LIST OF FIGURES ................................ ................................ ................................ .......... 9 LIST OF SCHEMES ................................ ................................ ................................ ...... 14 LIST OF ABBREVIATIONS ................................ ................................ ........................... 15 ABSTRACT ................................ ................................ ................................ ................... 18 CHAPTER 1 INTRODUCTION ................................ ................................ ................................ .... 20 Molecular Self Assembly: from Nature to the Lab ................................ ................... 20 ................ 22 Tuning the Optical and Electronic Properties of Nucleobases ................................ 29 Nucleobases for Assembly and Optoelectronic Properties Control ......................... 32 Molecular Self Assembly for Organic Electronics ................................ ................... 34 Role of Alkyl Chains in Organic Semiconducting Materials ................................ ..... 40 Motivation and Organization of Dissertation ................................ ........................... 44 2 SYNTHESIS, OPTICAL P ROPERTIES, AND ELECT RONIC STRUCTURES OF NUCLEOBASE CONJUGATED OLIGOME RS ............................ 46 Introductory Remarks ................................ ................................ .............................. 46 Synthesis ................................ ................................ ................................ ................ 49 Selection of Solubili zing Group ................................ ................................ ......... 49 Adenine Terminated Oligomers ................................ ................................ ........ 50 Guanine Terminated Oligomers ................................ ................................ ....... 52 Uracil Terminated Oligomers ................................ ................................ ............ 56 Cytosine Terminated Oligomers ................................ ................................ ....... 58 Thermal Properties ................................ ................................ ................................ . 59 Optical Properties ................................ ................................ ................................ ... 60 Electrochemical Properties ................................ ................................ ..................... 68 Electronic Structure Calculations ................................ ................................ ............ 72 Conclusion ................................ ................................ ................................ .............. 77 Experimental ................................ ................................ ................................ ........... 78 General Methods ................................ ................................ .............................. 78 Synthesis of Adenine Terminated Oligomers ................................ ................... 79 Synthesis of Guanine Terminated Oligomers ................................ ................... 83 Synthesis of Uracil Terminated Oligomers ................................ ....................... 89

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6 Attempted Synthesis of Cytosine Terminated Oligomers ................................ . 92 Photophysical Measur ements and Additional Data ................................ ................. 93 Absorption Measurements ................................ ................................ ................ 93 Steady State Fluorescence and Quantum Yield Measurements ...................... 94 Fluorescence Lifetime Measurements in 1,4 dioxane ................................ ...... 94 Electrochemistry ................................ ................................ ............................... 95 Co mputational Analysis ................................ ................................ .................... 96 3 SYNTHESIS, CHARACTERIZATION, AND COMPLEMENTARY HYDROGEN CONJUGATED NUCLEOBASE OLIGOMERS ............................ 97 Introductory Remarks ................................ ................................ .............................. 97 Synthesis ................................ ................................ ................................ ................ 99 Adenine Terminated Oligomer ................................ ................................ ......... 99 Guanine Terminated Oligomer ................................ ................................ ......... 99 Uracil Terminated Oligomer ................................ ................................ ........... 100 Cytosine Terminated Oligomer ................................ ................................ ....... 102 Thermal Properties ................................ ................................ ............................... 103 Optical Properties ................................ ................................ ................................ . 104 Electronic Properties ................................ ................................ ............................. 106 Evaluation of Dimerization Constants ................................ ................................ ... 111 Determination of Stoichiometry ................................ ................................ ............. 113 Eval uation of the Association Constant ................................ ................................ . 116 Conclusion ................................ ................................ ................................ ............ 120 Experimental ................................ ................................ ................................ ......... 121 General Methods ................................ ................................ ............................ 121 Synthesis of Adenine Terminated Oligomers ................................ ................. 122 Synthesis of Guanine Terminated Oligomer ................................ ................... 122 Attempted Synthesis of Uracil Terminated Oligomer ................................ ...... 127 Synthesis of Cytosine Terminated Oligomer ................................ .................. 128 Photophysical Measurements and Additional Data ................................ ............... 130 Absorption Measurements ................................ ................................ .............. 130 Electrochemistry ................................ ................................ ............................. 130 Computational Analysis of Oligomer Conformations ................................ ...... 131 NMR experiments ................................ ................................ ................................ . 131 NMR Dilutions ................................ ................................ ................................ 131 Job Plots (Continuous Variation Method) ................................ ....................... 131 NMR Titrations ................................ ................................ ............................... 132 4 THE INFLUENCE OF SOL UBILIZING CHAIN STER EOCHEMISTRY ON SMALL MOLECULE PHOTO VOLTAICS ................................ .............................. 133 Introductory Remarks ................................ ................................ ............................ 133 Synthesis ................................ ................................ ................................ .............. 137 Isomeric Composition ................................ ................................ ........................... 140 Optical Properties ................................ ................................ ................................ . 141 Electronic Properties ................................ ................................ ............................. 143

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7 Thermal Properties ................................ ................................ ............................... 144 Characterization of the SMDPPEH Compositions in the Solid State .................... 148 Photovoltaic Device Performance ................................ ................................ ......... 155 Conclusion ................................ ................................ ................................ ............ 158 Experimental ................................ ................................ ................................ ......... 160 General Methods ................................ ................................ ............................ 160 Synthesis of RR SMDPPEH (4 1 RR ) ................................ ............................. 162 Synthe sis of syn SMDPPEH (4 1syn) ................................ ............................ 168 Solution Based Characterizations ................................ ................................ ......... 169 Absorption Measurements ................................ ................................ .............. 169 Electrochemistry ................................ ................................ ............................. 169 Solid State Characterizations ................................ ................................ ................ 170 Thermal Analysis ................................ ................................ ............................ 170 X Ray Experimental ................................ ................................ ....................... 170 Thin Film Characterization ................................ ................................ .............. 172 Device Fabrication and Charac terization ................................ ........................ 172 5 CONCLUSIONS AND FUTU RE DIRECTIONS ................................ .................... 174 APPENDIX A PROTON NUCLEAR RESON ANCE ( 1 H NMR) SPECTRA ................................ .. 180 B CARBON NUCLEAR RESON ANCE ( 13 C NMR) SPECTRA ................................ . 1 87 C SOLID STATE DATA ................................ ................................ ............................ 194 LIST OF REFERENCES ................................ ................................ ............................. 210 BIOGRAPHICAL SKETCH ................................ ................................ .......................... 225

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8 LIST OF TABLES Table page 2 1 Solubility of u racil derivatives in chloroform ................................ ........................ 49 2 2 Bromination of 2 4 ................................ ................................ .............................. 51 2 3 Optimization of the cross coupling conditions to prepare 2 16 ........................... 54 2 4 Bromination of 2 29 ................................ ................................ ............................ 57 2 5 Absorption Properties of 2 1 , 2 2 , 2 10 , 2 24 , and 2 25 in 1,4 Dioxane and DMF a ................................ ................................ ................................ .................. 62 2 6 Emission Properties of 2 1 , 2 2 , 2 10 , 2 24 , and 2 25 in 1,4 dioxane a ............... 67 2 7 Electronic Properties of 2 1 , 2 2 ................................ ................................ ......... 71 3 1 Solubility of uracil derivatives in chloroform ................................ ...................... 101 3 2 Thermal properties of compounds 3 1 4 ................................ .......................... 104 3 3 Absorption Properties of 3 in DMF a ................................ ........................... 105 3 4 Electronic Properties of 3 1 4 ................................ ................................ .......... 108 4 1 Optical properties of 4 1 in CHCl 3 (20 × 10 6 M) ................................ ............... 142 4 2 Electronic properties of 4 1syn , 4 1com , and 4 1 RR ................................ ....... 144 4 3 Thermal properties of 4 1 ................................ ................................ ................. 145 4 4 Characteristics of 4 1 photovoltaic devices ................................ ...................... 156 C 1 Crystal data and structure refinement for 4 1syn ................................ ............. 194 C 2 At omic coordinates ( x 10 4 ) and equivalent isotropic displacement parameters (Å 2 x 10 3 ) for 4 1syn . U(eq) is defined as one third of the trace of the orthogonalized U ij tensor ................................ ................................ ............ 195 C 3 Bond lengths [ Å ] and angles [ ° ] for 4 1syn ................................ ....................... 196 C 4 Anisotropic displacement parameters (Å 2 x 10 3 ) for 4 1syn . The anisotropic displacement factor exponent takes the form: 2 2 [ h 2 a* 2 U 11 + ... + 2 h k a* b* U 12 ] ................................ ................................ ................................ ............. 206 C 5 Hydrogen coordinates ( x 10 4 ) and isotropic displacement parameters (Å 2 x 10 3 ) for 4 1syn ................................ ................................ ................................ . 207

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9 LIST OF FIGURES F igure page 1 1 Schematic representation of different non covalent interactions. ....................... 21 1 2 Some of the possible non covalen t interactions with the guanine nucleotide.. ... 22 1 3 Watson Crick base pairing. ................................ ................................ ................ 23 1 4 Cation induced formation of a guanine, a G q uartet, and a G quadruplex. ........ 24 1 5 a) Chemical structure of the K + sensing oligonucleotide pyrene (PSO py); b) the expected quadruplex formation induced by K + .. ................................ ........... 25 1 6 Formation of a hexadecamer by a guanine derivative in aqueous media.. ......... 26 1 7 a) Energy transfer between zinc porphyrin and quinine through G C Watson Crick interactions; b) molecular receptor specific to the guanosine. ................... 27 1 8 a) Copolymerization ; b) representation of adhesive formation. .......................... 28 1 9 The schematic structure of supramolecular multiarm hyperbranched copolymer H40 star PCL A:U PEG.. ................................ ................................ .. 29 1 10 Fluorescent analogues of natural nucleobases. ................................ ................. 30 1 11 2 Cl 2 ; b) hydrogen stac king interactions in the X ray crystal structure of a purine .. . 31 1 12 Electroluminescence spectra of purines 1 1 (blue) and 1 2 (red) in solid state fi lms (5 wt% in mCP) when excited at ex = 292 nm.. ................................ ......... 32 1 13 a) A C 4 symmetric G quadruplex based on the GPDI conjugate b) Aliphatic substituents in the quadruplex are omitted for clarity.. ................................ ........ 33 1 14 a) Chemical structures of tetracene and its H bonded analogue epindolidione; b) Intermolecular hydrogen bonds . ................................ .............. 35 1 15 a) Molecular structures of the oligothiophenes (MeBQ and MeLQ) ; b) illustration of the self assembly. ................................ ................................ .......... 36 1 16 a) Chemical structure of B2PyMPM and B4PyMPM molecules; b) schematic illustration of the molecular orientation of the molecules in devices. . ................. 37 1 17 Chemical structure of dithienosilole based small molecules with different terminal groups ; the amide terminal groups can form hydrogen bonds. ............. 38

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10 1 18 Chemical structures of DTT ester and DTT amide with their corresponding PCEs from bulk heterojunction solar cells. ................................ ......................... 39 1 19 Solubilizing group consequences on optoelectronic properties. ......................... 42 2 1 The guanosine ribbons of Gottarelli that comprise the active semiconductive layers of various optoelectroni c devices. ................................ ............................ 47 2 2 Purine and pyrimidine containing conjugated targets. R = 2 ethylhexyl. ......... 48 2 3 1 H (bold) and 13 C (italics) chem ical shifts (in ppm) and key 1 H 13 C gHMBC correlations for 2 4 . ................................ ................................ ............................. 50 2 4 The TGA for 2 1 and 2 2 compounds obtained at a heating rate of 10 °C/min under nitrogen. ................................ ................................ ................................ ... 59 2 5 Absorption spectra (1.5 × 10 M) for 2 and 2 in a) 1,4 dioxane; and b) DMF. ................................ ................................ ................................ ........ 60 2 6 Absorption spectra and Beer Lambert plots in 1,4 dioxane for a) 2 1a ; b) 2 1b ; and c) 2 1d . ................................ ................................ ................................ .. 63 2 7 Absorption spectra and Beer Lambert plots in 1,4 dioxane for a) 2 2a ; and b) 2 2b . ................................ ................................ ................................ ................... 64 2 8 Absorption spectra and Beer Lambert plots in 1,4 dioxane for a) 2 1c ; b) 2 2c ; c) and 2 2d . ................................ ................................ ................................ .. 65 2 9 Absorption spectra for 2 10 , 2 24 , and 2 25 in a) 1,4 dioxane; and b) DMF (15×10 6 M). ................................ ................................ ................................ ......... 66 2 10 a) Em ission spectra in 1,4 dioxane for a) 2 1a d and 2 2a d ; and b) 2 10 , 2 24 , and 2 25 (1 3 × 10 6 M). ................................ ................................ ................ 66 2 11 Computational analysis of o ligomer conformations 2 10 based on B3LYP/6 31+G** calculations. . ................................ ................................ .......................... 72 2 12 Computational analysis of oligomer conformation s 2 29 based on B3LYP/6 31+G** calculations. . ................................ ................................ .......................... 73 2 13 Calculated HOMO and LUMO plots for 2 1a d based on B3LYP/6 31+G** c alculations. ................................ ................................ ................................ ........ 74 2 14 Calculated HOMO and LUMO plots for 2 2a d based on B3LYP/6 31+G** calculations. ................................ ................................ ................................ ........ 75 2 15 Calculated HOMO and LUMO plots for subunits comprising the compounds investigated based on B3LYP/6 31+G** calculations. ................................ ........ 76

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11 3 1 a) The TGA; and b) DSC for 3 1 4 compounds operated at a heating rate of 10 °C/min under nitrogen. ................................ ................................ ................. 104 3 2 Absorption spectra (20 × 10 M) for 3 in DMF. ................................ ......... 106 3 3 Conformational analysis of 2 33 based on B3LYP/6 31G** calculations. . ........ 109 3 4 Calculated HOMO and LUMO plots for 3 1 6 based on B3LYP/6 31G** calculations. ................................ ................................ ................................ ...... 110 3 5 Concentration dependent 1 HNMR spectra for a) 2 27 and c) 3 1 ; 1 HNMR binding isotherm for b) 2 27 and d) 3 1 . ................................ ........................... 113 3 6 Correlation between stoichiometry ( a , b ) and x c oordinate at the maximum of the curve in a Job plot. ................................ ................................ ..................... 115 3 7 a) 1 H NMR spectra of 3 1 (50 mM) with increasing amount of 2 27 (50 mM) in CDCl 3 ; b) Job plot of 3 1 with 2 27 in CDCl 3 . ................................ .................... 115 3 8 Titration 1 HNMR spectra monitoring a) NH 2 of 3 1 and c) N(3) H of 2 27 ; b) 1 HNMR binding isotherm and global fitting for 2 27 and 3 1 . ............................ 118 3 9 Deuterated chloroform solution of 3 4 , 2 33 and a 1:1 mixture of 3 4 and 2 33 . ................................ ................................ ................................ .................... 119 4 1 Schematic p T diagram for preparative techniques for advanced materials . ... 134 4 2 Conjugated polymers (a,b,c) and small molecules (d,e) prepared in stereocontrolled fashion with respect to their 2 ethylhexyl side chains. ............ 135 4 3 Chi ral HPLC analysis of 4 1 (8/92 i PrOH/hexane, eluting rate: 0.8 mL/min, detecting wavelength: 350 nm) ................................ ................................ ......... 140 4 4 Normalized absorbance spectra of 4 1 in CHCl 3 (20 × 10 6 M). ........................ 142 4 5 Absorption spectra and Beer Lambert plots in CHCl 3 (2.5×10 6 M 30×10 6 M) for a) 4 1syn ; b) 4 1com ; c) 4 1 SS ; d) 4 1 RR ; e) 4 1 RS . ................................ 143 4 6 a) TGA analysis of 4 1 samples; b) DSC analysis of 4 1 samples. ................... 145 4 7 a) 4 1syn single crystal ; b) unit cell of 4 1syn conjugated backbone overlapping in the unit cell. ................................ ............ 147 4 8 Conjugated backbone conformation of 4 1syn determined from the si ngle crystal structure. ................................ ................................ ............................... 147 4 9 XRD spectra for spin coated films of (a,b) neat 4 1 or (c,d) 4 1 :PC 61 BM. Films (a,c) were not annealed, whereas films (b,d) were annealed . ................. 149

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12 4 10 AFM images of neat unannealed (top) and annealed (bottom) spin coated films . All images are 5 x ................................ ................................ .......... 151 4 11 AFM images of unannealed (top) and annealed (bottom) spin coated blended films ................................ ......... 152 4 12 Absorption spectra for spin coated films of 4 1 on glass/PEDOT:PSS not annealed (a,c) and annealed (b,d) neat (a,b) and blended with PCBM (c,d). ... 154 4 13 Characterization of 4 1 BHJ photovoltaic devices. ................................ ........... 157 A 1 Proton nuclear magnetic resonance ( 1 H NMR) spectrum (CDCl 3 , 500 MHz) of 3 1a . ................................ ................................ ................................ ................. 180 A 2 1 H NMR spectrum (CDCl 3 , 500 MHz) of 3 8 . ................................ .................... 180 A 3 1 H NMR spectrum (CDCl 3 , 500 MHz) of 3 9 . ................................ .................... 181 A 4 1 H NMR spectrum (CDCl 3 , 500 MHz) of 3 10 . ................................ .................. 181 A 5 1 H NMR spectrum (CDCl 3 , 500 MHz) of 3 11 . ................................ .................. 182 A 6 1 H NMR spectrum (CDCl 3 , 500 MHz) of 3 3 . ................................ .................... 182 A 7 1 H NMR spectrum (CDCl 3 , 500 MHz) of 3 2 . ................................ .................... 183 A 8 1 H NMR spectrum (CDCl 3 , 500 MHz) of 3 4 . ................................ .................... 183 A 9 1 H NMR spectrum (CDCl 3 , 500 MHz) of 3 12b . ................................ ................ 184 A 10 1 H NMR spectrum (CDCl 3 , 500 MHz) of 3 13 . ................................ .................. 184 A 11 1 H NMR spectrum (CDCl 3 , 500 MHz) of 3 15 . ................................ .................. 185 A 12 1 H NMR spectrum (CDCl 3 , 500 MHz) of 2 35 . ................................ .................. 185 A 13 1 H NMR spectrum (CDCl 3 , 500 MHz) of 3 16 . ................................ .................. 186 B 1 Carbon nuclear magnetic resonance ( 13 C NMR) spectrum (CDCl 3 , 500 MHz) of 3 1a . ................................ ................................ ................................ ............. 187 B 2 13 C NMR spectrum (CDCl 3 , 500 MHz) of 3 8 . ................................ ................... 187 B 3 13 C NMR spectrum (CDCl 3 , 500 MHz) of 3 9 . ................................ ................... 188 B 4 13 C NMR spectrum (CD Cl 3 , 500 MHz) of 3 10 . ................................ ................. 188 B 5 13 C NMR spectrum (CDCl 3 , 500 MHz) of 3 11 . ................................ ................. 189

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13 B 6 13 C NMR spectrum (CDCl 3 , 500 MHz) of 3 3 . ................................ ................... 189 B 7 13 C NMR spectrum (CDCl 3 , 500 MHz) of 3 2 . ................................ ................... 1 90 B 8 13 C NMR spectrum (CDCl 3 , 500 MHz) of 3 4 . ................................ ................... 190 B 9 13 C NMR spectrum (CDCl 3 , 500 MHz) of 3 12b . ................................ ............... 191 B 10 13 C NMR spectrum (CDCl 3 , 500 MHz) of 3 13 . ................................ ................. 191 B 11 13 C NMR spectrum (CDCl 3 , 500 MHz) of 3 15 . ................................ ................. 192 B 12 13 C NMR spectrum (CDCl 3 , 500 MHz) of 2 35 . ................................ ................. 192 B 13 13 C NMR spectrum (CDCl 3 , 500 MHz) of 3 16 . ................................ ................. 193

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14 LIST OF SCHEMES Scheme page 2 1 Synthesis of adenine terminated oligomers 2 1a and 2 2a . ............................... 51 2 2 Initial attempt to synthesize adenine terminated oligomers 2 2a . ....................... 52 2 3 Attempted synthesis of 2 16 . ................................ ................................ .............. 53 2 4 Attempted synthesis of 2 1c under Stille cross coupling conditions (R = 2 ethylhexyl). ................................ ................................ ................................ ......... 53 2 5 Possible coordination of deprotonated 2 15 to the Pd cat alyst under basic conditions. ................................ ................................ ................................ .......... 55 2 6 Synthesis of guanine containing oligomers 2 1c , 2 2c , and 2 25 . ...................... 56 2 7 Attempted synthesis of 2 30 . ................................ ................................ .............. 57 2 8 Synthesis of uracil containing oligomers 2 1d and 2 2d . ................................ .... 58 2 9 Attempted synthesis of 2 33 . ................................ ................................ .............. 58 3 1 Synthesis of Adenine Terminated Oligomer 3 1 . ................................ ................ 99 3 2 Synthesis of Guanine Terminated Oligomer 3 4 . ................................ .............. 100 3 3 Attempted synthesis of 3 12a . ................................ ................................ .......... 101 3 4 Attempted synthesis of 3 5 . ................................ ................................ .............. 102 3 5 Synthesis of 3 6 . ................................ ................................ ............................... 103 4 1 Synthesis of 4 1 RR . ................................ ................................ .......................... 139

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15 LIST OF ABBREVIATIONS 1 H NMR Proton nuclear magnetic resonance 13 C NMR Carbon nuclear magnetic resonance 2 AP 2 Aminopurine AFM Ato mic force microscopy AM 1.5 G Air mass 1.5 global BHJ Bulk heterojunction BOC tert Butyloxycarbonyl BTD B enzo[ c ][1,2,5]thiadiazole CV Cyclic voltammetry DART Direct analysis in real time DCM Dichloromethane (methylene chloride) DFT Density functional theory DMF N , dimethylformamide DMSO Dimethylsulfoxide DOX Doxorubicin DPP 2,5 D ihydropyrrolo [3,4 c ]pyrrole 1,4 dione DPV Differential pulse voltammetry DSC Differential scanning calorimetry EL E lectroluminescence EQE External quantum efficiency ESI Electrospray ionization HB Hydrogen bonding HOMO Highest occupied molecular orbital

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16 HPLC High performance liquid chromatography ITO Indium tin oxide LCST Lower Critical Solution Temperature LUMO Lo west unoccupied molecular orbital MO Mol ecular orbital MS Mass spectrometry NMR Nuclear magnetic resonance spectroscopy OFET Organic field effect transistor OLED Organic light emitting diode OPV Organic photovoltaic PCBM Phenyl C61 but yric acid methyl ester PCE Power conversion efficiency PV Photovoltaic SAXS Small angle X ray scattering SMDPPEH S mall m olecule di keto p yrrolo p yrrole e thyl h exyl d isubstituted TBA T hrombin binding aptamer TBT 4,7 D i(thiophen 2 yl)benzo[ c ][ 1,2,5]thiadiazole TDPPT 2,5 B is(2 ethylhexyl) 3,6 di(thiophen 2 yl) 2,5 dihydropyrrolo [3,4 c ]pyrrole 1,4 dione TFA Trifluoroacetic acid TGA Thermogravimetric analysis THF Tetrahydrofuran TLC Thin layer chromatography

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17 TOF Time of flight UV V is Ultraviolet visible spectroscopy WAXS Wide angle X ray scattering XRD X ray diffraction

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18 Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the D egree of Doctor of Philosophy STRUCTURE PROP ERTY FUNCTION RELATIONSHIPS OF INFORMATION RICH Pi CONJUGATED MOLECULES FOR ORGANIC EL ECTRONICS By Raghida Bou Zerdan August 2015 Chair: Ronald K. Castellano Major: Chemistry Organic semiconductive materials are promising candidates for device applications due to their pronounced optoelectronic properties displayed at the molecular level. However, these are rarely predictably reflected within devices, as the performance is profoundly influenced by the nanoscal e morphology of the organic film. Therefore, the ability of mutually controlling supramolecular architecture and tuning optoelectronic properties is of great importance, and r equire s a n optimized approach to conjugated supramolecular structures dictated by molecular design. Initial work focuses on developing synthetic methodologies for the incorporation conjugated materials to rationally optimize the corresponding optoelectronic characteristics. Structure property trend s have been established using purine and pyrimidine terminated oligomers. The absorption emission profiles, the redox behavior, and the estimated HOMO LUMO energies, correlate well with nucleobase an linker electronic structure: I ntroduction of an elec tron deficient moiety such as benzo[ c ][1,2,5] thiadiazole generates donor acceptor donor systems having lower optical gaps than terthiophene linked derivatives. Likewise, varying the nucleobase termini offers additional tunability with guanine oligomers

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19 di splaying most red shifted absorption maxima and highest oxidation potentials. The dimerization and association constant s between complementary adenine and uracil derivatives are evaluated using nonlinear regression analysis of 1 H NMR titration data . Expecte dly, their complementary association overpowers any self aggregation process. Future work will involve i ncorporation of nucleobase conjugated systems into organic devices. Throughout the studies the low solubility of the nucleobases was addres sed by installing rac 2 ethylhexyl (EtHx) groups. In additional work, the influence of the EtHx asymmetric carbon on the optical, electronic, morphological and photovoltaic properties of a diketopyrrolopyrrole conjugated oligomer (SMDPPEH) i s evalu ated. Therefore , three SMDPPEH stereoisomers ( RR , SS , and RS ), independently prepared , were studied alongside synthesized and commercially obtained isomeric mixtures. The different SMDPPEH stereoisomer compositions exhibit nearly identical optoelectronic p roperties in dilute solution, and amorphous films blended with PCBM. However, after thermal annealing, significant differences in molecular packing are observed for all compounds . All but the ( RS ) isomer showed a substantial increase in BHJ photovoltaic de vice performance after annealing, due to its higher degree of crystallization. Overall, the side chain chirality strongly impacts the thin film morphology and optical properties of SMDPPEH, but has modest effects on the photovoltaic performance of the mate rial as blends with PCBM.

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20 CHAPTER 1 INTRODUCTION Molecular Self A ssembly: from Nature to the Lab The inspiration and background of supramolecular chemistry originates from the interactions found in living biological systems. Sometimes extremely complex, o ther times exceptionally simple, Nature has developed a myriad of highly precise, hierarchical, selective and cooperative chemistry that allows functioning organisms to manage their dynamic equilibrium with their environment in order to nourish, breathe, r eproduce and react to external stimuli. 1 In this context, supramolecular chemistry has arisen in recent years as a new discipline that studies chemistry beyond the molecule as defined by its leading proponent Lehn, who received the Nobel Prize for his work in the area in 1987. 2 Supramolecular chemistry is characterized by t he assembly of pre programmed building blocks through weak non covalent interactions. Such non bonded interactions are characterized by much smaller energies than typical covalent bonds (50 100 k cal/mol); they range from purely electrostatic bonds (1 10 k c al/mol) to hydrogen bonding (1 20 k cal/mol), 3 k cal/mol) and even weaker interactions such as hydrophobic effects, and v an der Waals forces (~1 k cal/mol) , etc. (Figure 1 1). 3 As a result, these same interactions are wholly responsible for preserving the structural integrity of the end product. But at the same time, the notable advantage of non covalent associations is that, unlike covalent bond formation, they are reversible. Life as it is would be impossible if molecules bound to each other irrevocably. Complex physiological processes require both molecular association as well as dissociat ion. Only supramolecular chemistry can offer a deep understanding of this dynamic interchange between molecules. In addition, supramolecular chemistry also relies on specificity, the

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21 selective involvement of molecules that prevents biological systems from disintegrating into a cacophony of energetically costly, potentially harmful interactions. Most importantly, our ability to predict structural arrangements from combinations of the above mentioned interactions, let alone the functional outcomes, in the ass embled materials is still in its infancy stage. The grand challenge resides in the ability to predict how molecules aggregate in solution with a high degree of accuracy, interpret how a certain architecture is favored over the other, understand how these a ggregates consolidate themselves in th e solid state, and ultimately recognize how these intermolecular interactions within the bulk translate into desired physical and chemical properties suitable for functional materials. 4 Figure 1 1 . Schematic representation of different non covalent interactions . Biological organisms are devoid of these problems as natural systems ( e.g. , cells ) use nucleobase pairing among other interactions toward the formation of complex archite ctures . Some of the possible non covalent interactions are shown for the guanine

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22 nucleobase which represent a perfect building block for supramolecular assemblies given all the possible interactions it can be engaged in (Figure 1 2). 5 All nucleobases offer a similar plethora of potential non covalent interactions. Therefore, the integrity of the base pairing phenomenon is complemented by additional binding forces, adding more v alue to the use of nucleobase recogniti on in supramolecular chemistry. Figure 1 2 . Some of the possible non covalent interactions with the guanine nucleotide. Adapted from Sivakova, S.; Rowan, S. J., Chem. Soc. Rev. 2005, 34 , 9 21 , with permission from The Royal Society of Chemistry . Nucleobases Building Blocks for Supramolecular Chemistry One facet of supramolecular organic architectures that has advanced extensively in recent years is the engineering of diverse structures using nucleic acids. 6 By virtue of their H bonding capabilities, nucleobases are able to self assemble with high fidelity within a broad concentration range . Furthermore, their engagement into var ious non covalent interactions (Figure 1 1 and 1 2) adds value to their useful repertoire for supramolecular chemistry. Consequently, t his unique molecular recognition ability between the purine (adenine and guanine) and pyrimidine (cytosine, thymine, and uracil) rings has become widely used in the areas of nanotechnology, materials, and medicinal chemistry. 7 Such supramolecular materials

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23 have shown exceptional properties when compared to conventional polymeric mate rials, including simpler morphology control, stimuli responsiveness, efficient template ability, ease of functionalization, and remarkable physical/chemical properties. 7b Natural nucleobase pairs adenine thymine (or adenine uracil) and guanine cytosine inter act via 2 or 3 hydrogen bonds, respectively (Figure 1 3). While the Watson Crick base pairing is the dominant pattern (Figure 1 3), it is important to note that there are 28 other possible motifs that involve two hydrogen bonds which can be formed between the common nucleobases. 8 Figure 1 3 . Watson Crick base pairing. Among the five canonical nucleosides, the capacity to form stable and extensive self associations is limited to guanosine due to its unique hydrogen bonding donor a nd acceptor sites ( K GG ~ 10 2 10 4 M 1 in CDCl 3 ) . 8 The homo association of guanine is known to form dimers, ribbons, 9 or macrocycles. 7a, 10 Interestingly, the macrocycles can further stack in solution or i n the bulk as a result of their polarized aromatic surfaces. Cations play a critical role in stabilizing the hydrogen bonded macrocycles by occupying the central cavit y and neutralizing the electro static repulsion of inwardly pointing guanine O ( 6 ) oxygens. 7a, 11 The cation assisted assembly of guanosine, known as the G quartet (Figure 1 4), is one of the most studied case assembly since its discovery in 1962. 10 Renewed interest in the G quartet emerged in the early

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24 strands. 10 Since then, many reports appeared in the literature describing the different structural and functional aspects of the G quartet in different applications ranging from sensing, 12 drug delivery, 13 materials, 14 etc. Figure 1 4 . Cation in duced formation of a guanine, a G quartet , and a G quadruplex . For example , a selective potassium sensing oligonucleotide probe was designed from the guanine rich thrombin binding aptamer (TBA), a 15 mer oligonucleotide with the sequence d(GGTTGGTGTGGTTGG) (Figure 1 5a ). 15 TBA forms a chair type quadruplex structure upon binding to thrombin prote in, and this quadruplex incorporates K + to face (Figure 1 5b ) producing a specific excimer emission. This type of arrangement is highly selective for K + ion in the presence of other cations .

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25 Figure 1 5 . a) Chemical structure of the K + sensing oligonucleotide pyrene (PSO py); b) the expected quadruplex formation induced by K + . Adapted with p ermission from Nagatoishi, S.; Nojima, T.; Juskowiak, B.; Takenaka, S., Angew. Chem. Int. Ed. 2005, 44 , 5067 5070 . Copyright 2005 John Wiley and Sons. Another facet of the G quartet/quadruplex application was developed by Rivéra and co workers. 16 A n 8 aryl deoxyguanosine derivative (8ArG) (Figure 1 6 ) that self assembles in aqueous media into discrete supramolecular hexadecamers was designed for drug encapsulation at a biocompatible temperature. The H bonded agg regates supramolecular units engage in a temperature induced assembly to form solid nanoscopic globules of low polydispersity. Drug encapsulation was tested using Doxorubicin (D OX), a fluorescent anticancer agent, which can be monitored via emission measurements. The transition temperature was found to only increase by 2 °C in the presence of DOX, highlighting the potential versatility of this system to encapsulate different drug s with little to no effect o n the thermoresponsive properties. 16a b) a)

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26 Figure 1 6 . Formation of a hexadecamer by a guanine derivative in aqueous media; its stimuli responsive behavior enables the encapsulation of doxorubicin HCl (DOX) within the resulting microglobule. Adapted from Betancourt, J. E.; Subramani, C.; Serrano Velez, J. L.; Rosa Molinar, E.; Rotello, V. M.; Rivera, J. M., Chem. Commun. 2010, 46 , 8537 8539 , with permission from The Royal Society of Chemistry . Alth ough the self association constant of guanine is substantially high, the degree of interaction of guanine with cytosine is even higher ( K GC ~ 10 4 10 5 M 1 in CDCl 3 ). 8, 17 However, the reduced solubility of the guani ne derivatives has rendered synthetic access to such compounds strenuous . As a result, the G C motif has been scarcely employed in supramolecular chemistry. One of th e few examples reported showed photoinduced energy transfer occurring through the non cova lent interface of the G C pair bearing zinc porphyrin (II) and quinine as the electron donor and acceptor, respectively, with k ET = 8 × 10 8 s 1 . (Figure 1 7a). 17a, 18 The same group showed how electrostatic inter actions exist between a positively charged sapphyrin attached to a cytosine moiety, and the charged phosphate of the guanosine unit. These interactions induce the formation of the supramolecular complex

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27 (Figure 1 7b) and allow the selective transport of gu monophosphate across a membrane. 17a, 19 Figure 1 7 . a) Energy transfer between zinc porphyrin and quinine through G C Watson Crick interactions ; b) molecular receptor specific to th e guanosine. Despite the lower adenine and thymine/uracil association constant ( K AT/U ~ 10 2 M 1 in CDCl 3 ) with respect to guanine and cytosine ( K GC ~ 10 4 10 5 M 1 in CDCl 3 ), 8, 17 the A T/U interaction has been widel y used as a feasible tool for a variety of supramolecular systems. For instance, separately synthesized polyacrylic polymers, with appended adenine and thymine units (Figure 1 8a), 20 associated into a thermodynamically stable complex upon blending. The latter was physically cross linked via the A T base pairing generating supramolecular adhesives (Figure 1 8b). 20 a) b)

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28 Figure 1 8 . a) Copolymerization of n butyl acrylate and 4 (3 adenine 9 yl propanoyloxy)butyl acrylate or 4 ((3 (thymin lyl) propanoy l)oxy)butyl acrylate; b) r epresentation of adhesive formation . Adapted with permission from Cheng, S.; Zhang, M.; Dixit, N.; Moore, R. B.; Long, T. E., Macromol . 2012 , 45 , 805 812 . Copyright 2012 American Chemical Society. Access to a pH responsive drug de livery system based on the molecular recogni tion between adenine and uracil was reported by Zhu and coworkers. 21 This was achieved by pr eparing a hyperbranched copolymer H40 star PCLA:U PEG (Figure 1 9) in which the PCL core provides a hydrophobic environment for guaranteed base pairing even in aqueous media. These supramolecular copolymers spontaneously self assemble into micelles (Figure 1 9 ), where encapsulation and controlled drug release were demonstrated with the chemotherapeutic drug DOX. As a result of the slightly b )

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29 acidic nature of tumor sites and inflammatory tissues, the nucleobases tend to get protonated leading to micelle destru ction and efficient drug release. 21 The above examples illustrate the diversity of applications obtained by using the nucleobases as sel f assembly promoters, due to their high selectivity, extreme fidelity, large binding constants, and their dynamic, and tunable nature. Figure 1 9 . The schematic structure of supramolecular multiarm hyperbranched copolymer H40 star PCL A:U PEG. Adapted f rom Wang, D.; Chen, H.; Su, Y.; Qiu, F.; Zhu, L.; Huan, X.; Zhu, B.; Yan, D.; Guo, F.; Zhu, X., Polym. Chem. 2013, 4 , 85 94 , with permission from The Royal Society of Chemistry . Tuning the Optical and Electronic Properties of Nucleobases Despite their attr active features, most importantly their built in molecular recognition ability that imparts order in solution and the solid state, nucleobases have scarcely been considered for materials applications that rely on their optoelectronic properties. This is in part due to the level of the lowest electronically excited singlet state S 1 (~ 4.1 4.4 eV), the exceedingly low fluorescence quantum yields ( F ) (~10 6 10 4 ), and the extremely short S 1 state lifetime (~1 10 ps) of the purines and pyrimidines. 22 Typical approaches for remarkable improvements to the intrinsic fluorescence properties included tethering common fluorophores to the nucleobases (Figure 1 10a), 23 synthesizing expanded nucleobases bearing a fluorescent aromatic

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30 moiety instead of a natural nucleobase (Figure 1 10b), 24 conjugated surface of the nucleobases by simply adding a vinyl group 25 or an aromatic ring 26 (Figure 1 10c). Regardless of all the structural disturbances the modified nucleobases resemble the natural ones with respect to their molecular shape and hydrogen bonding pattern. Figure 1 10 . Fluorescent analogues of natur al nucleobases: a) Fluorophores tethered to the nucleobase, b) expanded nucleobases, and c) nucleobases with extended surfaces . 2 Aminopurine (2 AP), an isomer of adenine, is the simplest functional yet fluorescent nucleobase variant. 27 This molecule display s a high quantum yield (0.68 in water for the (deoxy)ribose), which prompt ed its widespread usage as an optical probe. 27 Despite that, 2 AP has not permeated traditional organic materials and related sensing applications. Along these lines acceptor) design can be extended to 2 AP and other purine derivatives in order to tune the optical and electronic characteristics of simple purines at the molecular level. 28 The addition of various electron accepting functional groups ( A = CN, CO 2 Me, and CONH n Bu) to the C8 position of the purine core to complement the amine based electron donors at C2 ( D 1 ) and C6 ( D 2 ) (NMe 2 ) resu lted in significantly improved photophysical properties with c) a) b)

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31 respect to the acceptor free purine ( A = H) (Figure 1 11a). As a result of the push pull effect, red shifted absorption maxima, enhanced Stokes shifts, and drastically improved fluorescence quant um yields were observed among other effects. Interestingly, modification of the optoelectronic properties of the purines did not affect their ability to self assemble ( via H bonding and stacking interactions) in the solid state (Figure 1 11b). 28a Figure 1 11 . 2 Cl 2 ; b) hydrogen stacking interactions in the X ray crystal structure of a purine where D 1 = NMe 2 , D 2 = NH 2 , and A = CO 2 Me . Reprinted with the permission of Butler, R. S.; Cohn, P.; Tenzel, P.; Abboud, K. A.; Castellano, R. K., J. Am. Chem. Soc. 2009, 131 , 623 633 . Copyright 2009 American Chemical Society. The extension of the donor acceptor character to purines has produced some of the most highly fluorescent isomorphic nucleoside analogs to date, making such approach a suitable strategy to impr ove the optical performance of otherwise non fluorescent nucleobases. These results rendered the purines suitable emissive components for blue violet UV emitting OLEDs. 29 Thus, two of the most highly fluorescent do nor acceptor purines, methyl 9 benzyl 2 ( dimethylamino) 9 H purine a) b)

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32 8 carboxylate 1 1 and 2 amino 9 benzyl 2 ( dimethylamino) 9 H purine 8 carboxylate 1 2 (Figure 1 12) were investigated by our group. M ultilayer OLEDs based on purine 1 2 displayed a m aximum external quantum efficiency (EQE) of 1.6%, and UV emission is obtained with maximum electroluminescence (EL) at a wavelength of = 393 nm (Figure 1 12). While OLEDs based on purine 1 1 show ed longer wavelength emission peaked at = 433 nm, and an increased maximum efficiency to 3.1% (Figure 1 12). The efficiencies of these OLEDs (based on 1 1 and 1 2 ) remain competitive for devic es with emission peak wavelengths below 450 nm. Figure 1 12 . Electro luminescence spectra of purines 1 1 (blue) and 1 2 (red) in solid state films (5 wt% in mCP) when excited at ex = 292 nm. Adapted from Yang, Y.; Cohn, P.; Eom, S. H.; Abboud, K. A.; ca stellano, R. K.; Xue, J., J. Mater. Chem. C 2013, 1 , 2867 2874 , with permission from The Royal Society of Chemistry . Nucleobases for Assembly and Optoelectronic Properties Control While a large amount of work has been focused on designing molecular structu res to optimize their optoelectronic properties, studies of the relationship between morphologies in blend structures and device performance are becoming more important

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33 and prerequisite for rationally improving performance. At this point, nucleobases emerg conjugated frameworks to generate novel opto and/or electroactive molecules. It is in these cases that an intimate system structure and function would exist to make the c onjugates unique for optoelectronic applications. To date, the concept has only been sparsely exploited, as most designs use nucleobases solely as a tool to control conjugated backbone, 6 therefore not contributing to the overall electronic properties of the resulting system. Figure 1 13 . a) A C 4 symmetric G quadruplex based on the GPDI conjugate b) Aliphatic substituents in the quadruplex are omitted fo r clarity. Reprinted with the permission of Wu, Y. L.; Brown, K. E.; Wasielewski, M. R., J. Am. Chem. Soc. 2013, 135 , 13322 13325 . Copyright 2013 American Chemical Society. One relevant example is the supramolecular arrangement of guanines in the design of organic electronics that was recently described by the Wasielewski group where the consequences of connecting the electron rich guanine (G) to a peripheral electron acceptor like perylene dicarboximide (PDI) was evaluated (Figure 1 13a). 30 Based on both NMR and SAXS/WAXS studies the G PDI aggregates in the presence of K + form C 4 symmetric octamers. Extended charge separation lifetime was observed in the G PDI quadruplex following photoexcitation (Figure1 13a). Photophysical and a) b)

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34 electrochemical measurements supported the hypothesis of charge delocalization or hopping th rough the non stacks of G pathways for hole and electron transport (Figure 1 13b). 30 Molecular Self A ssembly for Organic Electronics conjugated compounds that exhibit semiconductive properties are attractive candidates for the design of innovative, convenient, and high performance electronics. The performance and hence the value of organic electronic devices have increased sig nificantly over the last decade, evolving from a field with great promise for new materials and applications to a real industry with commercial products on the market. Breakthrough products include organic light emitting diodes used in many portable displa ys. Organic field effect transistors (OFETs) are also promising platforms with rapidly improved efficiencies. Organic photovoltaics (OPVs) represent an exciting technology of the future, not necessarily for replacing silicon based PVs, rather because of th eir flexibility, large area coverage, and low cost. conjugated systems come in two flavors: polymeric or oligomeric. Studies of low band gap polymers have previously conquered small molecules because of their unique optoelectronic properties, dis tinctive mechanical properties, and high device efficiencies. 31 However, due to their synthetic and purification flexibility, controlled molecular weight, sup erior batch to batch reproducibility, and no end group contaminants, small molecules have emerged as attractive surrogates to be used as active layers for organic semiconducting materials. 32 In addition, small molecules offer more flexibility for device fabrication; the latter involves either vacuum deposition or solution processing. 33 With that on board, focus throughout this dissertation will be on organic small molecules as they bear more

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35 relevance to the work discussed in the following chapters. On going resea rch in the field of organic electronics that implements conjugated molecules in the design and construction of novel semiconducting materials has suffered from lower stability, higher resistance and lower electric conductivity, as comp ared to inorganic semi conductors. As a result, critical scientific and engineering challenges have to be overcome in order to expand the functionality, availability , and sustainability of the world of organic electronics. One way to achieve this is to impr ove device reproducibility and performance by gaining control over the m orphology of the active layer. This can be accomplished by using non covalent interactions to govern the self assembly of organic electronic molecules into long range ordered pattern s . Figure 1 14 . a) Chemical structures of tetracene and its H bonded analog ue epindolidione ; b) i n the solid state, the molecules aggregate into H bonded pigment particles, which have markedly different optical properties than the isolated dye molecul es. Intermolecular hydrogen bonds between carbonyl groups and amine hydrogens are shown as dashed lines. To illustrate , small organic molecules, used as toners in inkjet printing (Figure 1 14 ), were selected to investigate the consequences of H b onding on fi eld effect hole mobilities. 34 Despite th e epindolidione limited conjugated surface in the aggregated pigment form (Figure 1 14a) , these molecules show an order of magnitude mobility increase ( h =1.5 cm 2 /V s) with respect to their non hydrogen bonded analog, the well a) b)

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36 known organic semiconductor tetracene ( h =0.1 cm 2 /V s) (Figure 1 14a ). On top of that, H bonding improved the air stability of these materials , ranging from substantial degradation within a few days for tetracene to no significant degradation for at least 140 days in the case of epindolidione. 34 Figure 1 15 . a) Molecular structures of the oli gothiophenes (MeBQ and MeLQ) that are either capable (PH) or incapable (PME) of hydrogen bond directed self assembly. Also shown is trimer rosette formation from phthalhydrazide (PH); b) illustration of the self assembly. U nfavorable morphologies for charg e transport may come as a result of random phase separation in bulk heterojunction (BHJ) active layers. In order to control the 3D molecular arrangements, and subsequently the performance of the OPV device, our con jugated electron donor system (D) with a hydrogen bonding unit (HB). 35 Upon H bonding (Figure 1 15b ), defined HB D aggregates might be formed which could further organize into columnar stacked architectures that are uniquely shape compatible with fullerene acceptors in an O PV blend. Thus, a systematic structure property relations hip study was performed using oligothiophene based chromophore s appended with a ph thalhydrazide HB unit (Figure 1 15a ) as well as an additional structurally and intrinsically similar, yet non H bondi ng a) b)

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37 compound (Figure 1 15a ). Devices fabricated via thermal vacuum deposition generated a two fold increase in power conversion efficiency for the HB derivative compared to the non H bonding control molecules. 35 The synergistic effect of H stacking may as well play an important role in controlling higher order structures to improve the electrical properties of OLEDs. B2PyMPM (Figure 1 16a) and its hydrogen bonding capable derivative B4PyMPM (Figure 1 16) were used to evaluate the consequences of the intermolecular C H N hydrogen bonds formed in vacuum deposited films. 36 Although the molecular shape, size, and electronic properties of these materials are quit e similar, a significant difference was observed in their molecular packing and long range order (Figure 1 16a). Consequently, the H bonded B4PyMPM exhibited a two orders of magnitude mobility increase ( e = 1.0 × 10 4 cm 2 /V s) with respect to the H bonding i ncapable derivative B2PyMPM ( e = 1. 6 × 10 6 cm 2 /V s). 36 Figure 1 16 . a) Chemical structure of B2PyMPM and B4PyMPM molecules; b) schematic illustration of the molecular orientation of the B2 and B4PyMPM molecules i n devices. The B4PyMPM molecules are bound by the intermolecular hydrogen bonds and form a stacked structure in the films. It is well documented that H stacking play a critical role in controlling the mole cular packing and orientation of a) b)

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38 conjugated molecules in solution and the solid state. Similarly, H bonding was shown to improve molecular stability and charge mobility in thin film device applications. However, intermolecular interactions by hyd rogen bonding can, in some cases, be destructive to the device performance due to unfavorable phase separation. Such outcomes have been observed in the case of dithienosilole based small molecules with different terminal groups (i.e., ester vs. amide group s) (Figure 1 17). 37 In comparison to the oligomers with ester terminal groups, those with amide terminal groups self assemble by h ydrogen bonding. The effect of molecular ordering and orientation on the charge transport ability of these molecules was investigated in OFET devices. The amide terminated derivative displayed one order of magnitude decrease in charge carrier mobility ( h max = 2.18 × 10 3 cm 2 ) with respect to the ester derivative ( h max = 1.37 × 10 2 cm 2 ). These results were attributed to the larger distance and the resulting morphology engendered by strong hydrogen bonding interactions. 37 Figure 1 17 . Chemical structure of dithienosilole based small molecules with different terminal groups (ester and amide groups); the amid e terminal groups can form hydrogen bonds.

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39 Likewise, the self complementary H bonding interactions between the amide functional groups of a dithieno[3,2 b ;2 ,3 d ]thiophene (DTT amide ) (Figure 1 18) derivative demonstrated lower performance in BHJ solar ce lls (PCE = 0.30 % when blended with PC 7 1 BM) in comparison with the one end capped with an ester group (DTT ester) (PCE = 1.15 %). 38 The unfavorable morphology induced by intermolecular hydrogen bonding led to improper phase separation, decreased cha rge transport, and consequently poor device performance. Figure 1 18 . Chemical structures of DTT ester and DTT amide with their corresponding PCEs from bulk heterojunction solar cells. While active layer morphology can have a serious impact on the perfo rmance of organic electronic devices; molecular self assembly, which offers controlled morphology, is not the sole criterion toward optimal device performance. A cautious approach must be adopted when considering strong intermolecular forces such as hydrog en bonding for material applications. The main question remains: is there an unexplored molecular structure that can mutually provide superstructural control and fine tuning of the application relevant parameters (i.e. energy levels) in solution, and the b ulk, then translate these changes into rationally improved device performance?

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40 Again, nucleobases seem like powerful building blocks for tuning optoelectronic properties and obtaining appropriate morphology to achieve efficient device s . Unfortunately, cons ideration of purines (e.g., adenine and guanine) and pyrimidines systems reveals challenges and opportunities unique from conventionally used heterocycles (e.g., carbazoles, thiophenes, pyridi nes, etc.). From the design and synthesis standpoint, challenges include the following: (1) What oligomer design best preserves the H bonding capabilities of the nucleobases? (2) Which synthetic methods can successfully introduce such highly coordinating ( i.e., to metals) and poorly soluble building blocks to frameworks? Regarding opportunities, it is intriguing to consider how the electronic structures of the nucleobases intensely studied over many years in the context of DNA charge transport 39 might result in base specific optical/electronic differences among conjugated oligomers. Role of Alkyl Chains in Organic Semiconducting Materials Various methods, such as thermal annealing, solvent anneal ing, and solvent additives have been used to optimize active layer structure and device performance. 40 From a molecular standpoint, e fforts conjugated systems for diverse applications in organic electronics have relied on we a k intermolecular forces (such as H bonding) building blocks . These stabilizing interactions are, however , associated with relatively strong 41 that are considered necessary for a high degree of int er molecular stacking and consequently efficient charge transport. Dissolution of ot herwise conjugated materials for synthesis, purification , and device fabrication requires judicious choice of pendent solubilizing groups. 42 Flexible, saturated

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41 hydrocarbon chains are typ ically introduced in order to promote favorable van der Waals interactions with polarizable organic solvents, hence weaken ing intermolecular 42b Branched non symmetrical alkyl chains are m ost frequently used for this purpose, since they are long enough to greatly enhance solubility and minimize undesired aggregations. 42b They even come pre installed on many commercially available building b conjugated oligomer/polymer synthesis. However, branched non symmetrical alkyl chains have a chiral center and thus mixtures of stereoisomers are formed in syntheses that begin from racemic starting materials. For molecules with two or more suc h side chains mixtures include enantiomers and diastereomers, although the isomeric complexity is generally ignored. 43 Despite th eir seemingly favorable outcomes, li pophilic chains are regarded as insulating materi als as they do not contribute to charge transport directly. Thus, f or applications that mutually rely on high degree of purity, good solution processability, surfaces, and appropriate active layer morphology (e.g., FETs, PVs, etc.), solubilizing groups emerge as important structural components for study a nd materi al/device optimization. Indeed, side chain type, 44 length, 45 branching, 45f, 45g, 46 placement, 32, 47 and stereochemistry 43, 48 have independently been shown to influence molecular packing, thin film morphology, charge carrier mobility, and device performance (Figure 1 19 ). The effects of the side chain placement were studied by varying the position of the n conjugated diketopyrrolopyrrole based molecule (DPP2T) (Figure 1 1 9 a). 32 Although the side chain position showed little influence on the optical properties in solution, a significant effect was observed on the

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42 optical, crystallization, and photovoltaic behavior of the molecules in thin films (Figure 1 1 9 a). The substitution position of the solubilizing chains influences device performance through changes in planarity, caused by steric hindrance, as well as changes in the orientation of the alkyl chains in the solid state. On the other hand, the role of alkyl chain branching position was stud ied in a series of naphthalene diimide (NDI) n type small molecules (Figure 1 1 9 b). 49 In this system, modulating the branching position of alkyl chains provided better solubility and resulted in dramatic differences in electron mobilities (Figure 1 1 9 b) despite the subtle changes in molecular packing. Figure 1 19 . Solubilizing group consequences on optoelectronic properties . Nonetheless , changing the type of solubilizing chains (i.e. branched non symmetrical, bulky, and linear) within a family of DPP derivatives , as shown in Figure 1 1 9 c, affected not only the pack ing level of these molecules, but also the electron density of the conjugated backbone in the case of the electron withdrawing BOC side chain . b) a) c ) e) d)

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43 This allow ed the adjustment of the electronic levels as well as the intermolecular interactions in organic solar cells, which ultimately led to differen ces in device performance (Figure 1 1 9 c). 44a Fr é chet and co workers reported the dependence of photovoltaic cells on the length of the alkyl chains in a DPP derivative by modulating the N alkyl substituents (Figure 1 1 9 e). 31 Such difference in performance was largely explained by the different crystal packing adopted by each derivative , reiterating the importance of side chains in the design of new organic semiconductors . All target compo unds described in this dissertation are poorly soluble due to stacking. Th is problem was resolved by introducing branched solubilizing groups, specifically the most commonly used 2 ethylhe xyl chain. However this pendent group has a chiral center, and therefore isomeric complexity is introduced. Stereoisomers and their mixtures usually exhibit different crystal structures and thereby different solid state properties that affect device perfor mance. Although numerous aspects and types of side chains have been tested over the years, the chirality of the popular 2 ethylhexyl has been ignored, until recently Nguyen and co workers reported a notable influence of alkyl chain conjugated oligomer crystallization behavior, thin film morphology, and consequently FET characteristics. Independent characterization of the three stereoisomers (RR, SS , and RS) of DPP(TBFu) 2 (Figure 1 1 9 d) as well as the shifted absorption, and several fold increase of the hole mobility (Figure 1 1 9 d) for the meso RS isomer versus the RR/SS isomers and the isomeric mixture. 43b To the best of our

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44 knowledge a similar analysis in the context of small molecule bulk heterojunction photovoltaics has not been performed. Motivation and Organization of Dissertation During the last decade, considerable in terest in organic semiconductive conjugated oligomers and polymers, has emerged as a result of their potential advantages over their inorganic counterparts. Many such systems exhibit promising optoelectronic properties at the molecul ar level. However, th ose properties are rarely predictably reflected within devices, as charge injection, separation, and conjugated organic molecules within a thin film active layer. D capable of mutually controlling supramolecular architecture and tuning optoelectronic properties (in solution and the solid state), represents a possible solution but also a significant challenge. The goal of this doctoral conjugated supramolecular structure through programmed self assembly dictated by molecular design. Chapter 2 describes how nucleobases are ind blocks by showing how their optoelectronic properties are nu cleobase dependent . Nucleobase containing conjugated oligomers have been synthesized and used to potential applications in organic electronics. Chapter 3 explore s the ability of complementary nucleobase conjugated oligomers to hydrogen bond in solution. Chapter 4 discusses the influence of the stereochemistry of a com monly used solubilizing chain, 2 ethylhexyl, on small molecule photovoltaics . Chapter 5 will provi de an overview of the thesis work, and f uture directions will be briefly discussed. Overall

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45 this dissertation discusses the structure property conjugated molecules for organic electronics .

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46 CHAPTER 2 SYNTHESI S, OPTICAL PROPERTIE S, AND ELECTRONIC ST RUCTURES OF NUCLEOBASE CONJUGATED OLIGOMERS a Introductory Remarks Research interests have been extensively focused on semiconductive organic molecules for applications in electronic and optoelectronic de vices including light emitting diodes, 50 field effect transistors, 51 solar cells, 52 photodetectors, 53 etc. 54 The conjugated organic molecules for these applications generally stems from their structural tunability, light absorption and emission characteristics, and solution processability, 55 etc. The org systems, in solution and in the bulk, into ordered suprastructures is of utmost importance for tuning optical and electronic properties and consequently device performance. 56 Control over the t hree dimensional conjugated materials involves appending biomolecules, i.e. amino acids, peptides, 57 nucleobases, 6 etc. due to their inherent ability to self assemble into well defined supramolecular structures. While the use of bioinspired building blocks has been extensively studied, there are significant knowledge gaps when it comes to building conjugated frameworks to mutually tune the optoelectronic properties and control the supramolecular assembly. 30, 58 Such an intimate relation system structure and function has, as far as we know, only been exploited in functional materials for simple purine derivatives by Bach, 59 Gottarelli, 9, 11a, 60 Spada, 6c, 7a, 11a, 11b, Adapted with permission from The Journal of Organic Chemistry , 2015 , 80 Copyright © 2015 American Chemical Society

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47 60a, 61 Davis, 7a, 10, 62 Rivéra, 16, 63 and Neogi. 6 4 Shown, for example (Figure 2 1), are the guanine ribbons described by Gottarelli for photodetectors, rectifiers, and transistors. 9, 11a, 60a, 65 Most notably, the work shows a clear dependence of device performa nce on active component supramolecular structure. Figure 2 1 . The guanosine ribbons of Gottarelli that comprise the active semiconductive layers of various optoelectronic devices. In addition to controlling solid state pa cking patterns, our lab has shown how purine photophysical properties can be altered upon modest structural perturbation to the system. 28 Such changes, particularly an increase in fluorescence quantum yield, rendered them suitable as emissive component for efficient blue violet UV light emitting devic es (refer to Chapter 1 for more details). 29 Along these lines, nucleobase conjugated systems could offer novel materials suitable for a broad range of optoelectronic applications. As an entry into such systems, reported here are the syntheses, optical properties, electronic structures , and complementary theoretical studies of two model families of nucleobase containing conjugated oligomers (Figure 2 2). Given the available nucleobase functionalization sites, various architectures are possible. However, linear conjugated oligomers have been selected as initial targets due to their synthetic accessibility. Moreover, the overall design preserves the

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48 heterocycles installed in terminal positions. The families ( 1 and 2 ) are distinguished by the intervening structure that consists of 4,7 bisthienylbenzothiadiazole (TBT) 66 or terthiophene (TTT), 33, 67 tracks that are (a) familiar f functional materials and (b) sufficiently long to afford molecules with semiconductive properties considered attractive for optoelectronic applications. To address the potentially low solubility of the oligomers, 2 ethylhexyl substituents are introdu ced in place of the sugars on the conjugated materials community, was selected on the basis of a qualitative organic solubility screen (vide infra). Experimental and theoretical (by DFT) analyses have since r evealed that the absorption, emission, emission lifetime, fluorescence quantum yields, and electronic properties respond in understandable ways to nucleobase and linker electronic structure. Figure 2 2 . Purine and pyrim idine containing conjugated targets. R = 2 ethylhexyl.

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49 Synthesis Selection of Solubilizing Group The poor solubility of the nucleobases in common organic solvents necessitated the addition of appropriate solubilizing groups, introduced to the N(9) positi on otherwise occupied by the sugar. To guide our selection, we conducted a series of qualitative solubility studies, in chloroform, of uracil substituted at position N(3) with linear (e.g., hexyl, octyl, dodecyl), branched symmetrical (e.g., 2 ethylbutyl), branched asymmetrical (e.g., 2 ethylhexyl), and cyclic (e.g., cyclohexylmethyl) alkyl chains (Table 2 1). The results confirmed that the most commonly used chiral 2 ethylhexyl group granted the best solubility among the choices. Despite the isomeric compl exity it introduces, this alkyl chain was employed for all of the targets considered in this work (Figure 2 2). The effect of the solubilizing group stereocenter is generally ignored, but its consequences conjugated molecule morphology and bulk heterojunction photovoltaic devices will be discussed in Chapter 4. In this work, targets bearing two 2 ethylhexyl groups (Figure 2 2) are assumed to exist as a mixture of stereoisomers, but the isomeric composition should not have an effect on photophysic al properties in dilute solution. 43 Table 2 1. Solubility of uracil derivatives in chloroform Structure Solubility in chloroform (mg/mL) 1 Hexyluracil 3 27 1 Octyluracil 4 94 1 Dodecyluracil 3 4 1 1 (2 Ethylhexyl)u racil 5 68 1 (2 Ethylbutyl)uracil 1 03 1 (Cyclohexylmethyl)uracil 1 49

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50 Adenine Terminated Oligomers Initial synthetic investigations related to 2 1a and 2 1b were performed by Pamela Cohn, a former graduate student in the Castellano laboratory. Using her findings, I reproduce d 2 1a and synthesize d 2 2a ( Scheme 2 1 ) . Accordingly, a solution of adenine 2 3 in DMF was treated with anhydrous K 2 CO 3 , followed by addition of rac 2 ethylhexyl bromide, yielding both N(7) and N(9) regioisomers of 2 4 in a 1:3 ratio (determined by 1 H NMR). The regiochemistry of the major product was confirmed by 1 H 13 C gHMBC NMR where correlation of C(4) (150.4 ppm) and C(8) (142.0 ppm) with the methylene protons (4.02 ppm) of the 2 ethylhexyl group were observed (Figure 2 3). Figure 2 3 . 1 H (bold) and 13 C (italics) chemical shifts (in ppm) and key 1 H 13 C gHMBC correlations for 2 4 . Bromination at C(8) was then pursued to introduce a handle for subsequent metal mediated cross coupling to expand the system. Unfortunately, conventional bromination conditions (Table 2 2) , 68 including the ones reported by Cohn (entry 4, Table 2 2) , either failed to generate the product 2 5 This challenging reaction was improved significantly under microwave conditions (100 W at 75 °C); a mixture of 2 4 and NBS in acetonitrile afforded 2 5 just 20 min.

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51 Scheme 2 1. Synthesis of adenine ter minated oligomers 2 1a and 2 2a . Starting material was recovered in attempts to couple 8 bromoadenine 2 5 to bis(tributylstannyl) terthiophene 2 11 to afford 2 1a in one step (Scheme 2 2). These observations prompted an iterative approach. Bromoadenine 2 5 was first reacted with 2 (tributylstannyl)thiophene, following a literature procedure, 69 to afford intermediate 2 6 in excellent yield. Subsequent bromination of the thiophenyl 2 position with NBS furnished 2 7 in good yield. Table 2 2 . Bromination of 2 4 entry a conditions yield (%) 1 68b Br 2 , NaOAc/HOAc, MeOH, THF 0 2 70 Br 2 , neat 7 3 68c Br 2 , sealed tube 20 4 NBS, MeCN 25 5 NBS, MeCN, MW, 75 °C, 20 min 45 50 a Lead references are given for the conditions used based on similar purine derivatives as starting materials.

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52 Scheme 2 2. Initial attempt to synthesize adenine terminated oligomers 2 2a . A final Suzuki coupling of 2 7 to boronic esters 2 8 and 2 9 , synthes ized according to literature procedures, 71 resulted in the formation of 2 1a 2 2a 2 10 was also isolated from the reaction of 2 7 and 2 8 in 30% yield. The Suzuki coupling was optimized by screening different palladium based catalysts. Better yields and fewer side products were obtained with those bearing bidentate ligands (e.g., Pd(dppf)Cl 2 ·CH 2 Cl 2 ) that enforce a cis geometry between the aryl fragments and facilitate reductive elimination in comparison to those with monodentate ligands (e.g., tri o tolylphosphine, dibenzylideneacetone (dba), etc.). Guanine Terminated Oligomers Synthesis of guanine derivatives 2 1c and 2 2c initially followed the adenine base d conjugated oligomer syntheses starting from guanine (Scheme 2 3). Alkylation of 2 amino 6 chloropurine 2 12 , obtained from treatment of guanine with POCl 3 in DMF, 72 with rac 2 ethylhexyl bromide afforded both N(7) and N(9) regioisomers of 2 13 in a 1:3 ratio (determined by 1 H NMR). The regiochemistry of 2 13 was confirmed by 1 13 C gHMBC NMR . Dilute acid hydrolysis of 2 13 furnished guanine intermediate 2 14 , which was subsequently brominated at C(8) with NBS to yield 2 15 . Unfortunately, cross coupling of 2 15 with 2 (tributylstannyl)thiophene under the Stille conditions 69 previously used for adenine intermediate 2 5 did not afford the target 2 16 .

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53 Scheme 2 3 . Attempted synthesis of 2 16 . Several cross coupling conditions were applied to 2 15 and either thienyl boron ic acid or stannylthiophene. These ranged from Stille couplings without (entry 1, Table 2 2) or with additives (entries 2 and 3, Table 2 2), to Suzuki couplings using conventional (entries 4 and 5, Table 2 2) and microwave heating (which yielded incomplete reactions) (entry 6, Table 2 2). Only Stille conditions (entry 3, Table 2 2) with triphenylbismuth (5%) 73 both successfully and reproducibly allowed cross coupling of 2 15 with stannylthiophene (affording 2 16 in 66% yield). Presumably, the longer Bi Pd bond (versus the P Pd bond) facilitates activation of the catalyst and reduces the reaction time. 73 The s ame conditions were attempted (Scheme 2 4) for coupling 2 15 and a bis(stannylthienyl)benzothiadiazole derivative 2 18 (prepared efficiently from 4,7 di(thiophen 2 yl)benzo[ c ][1,2,5]thiadiazole 2 17 ) to provide 2 1c directly; however, these conditions led to decomposition of the benzothiadiazole reagent. Scheme 2 4 . Attempted synthesis of 2 1c under Stille cross coupling conditions (R = 2 ethylhexyl).

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54 Table 2 3 . Optimization of the cross coupling conditions to prepare 2 16 Bromination of 2 16 followed by direct coupling to 2 8 / 2 9 (or their bis(stannyl) versions, of which bis(trimethylstannyl)benzo[ c ][1,2,5]thiadiazole has not been reported) was not pursued given the difficulty of achieving cross coupling reactions with the parent guanine derivatives (vide infra). As for the poorly performing Suzuki conditions (Table 2 2), the work of Shaughnessy, 76 et al. suggests that the deprotonation of the 10%) a Lead references are given for the conditions used based on similar purine derivatives as starting materials. b No reaction.

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55 acidic N(1) proton of the gua nine moiety to give a highly coordinating anion for the palladium catalyst (Pd(II) and Pd(0)) could be to blame (Scheme 2 5). Scheme 2 5 . Possible coordination of deprotonated 2 15 to the Pd catalyst under basic condition s. To circumvent the above challenges, we developed an alternative synthetic route using a protected guanine derivative (Scheme 2 6). Accordingly, compound 2 19 was 2 13 and benzyl alcohol in the presence of K 2 CO 3 and a catalytic amount of DABCO. 77 Bromination of 2 19 was then achieved using NBS in DMF to afford 2 20 eld; the 8 bromo derivative 2 20 then underwent Stille cross coupling with 2 (tributylstannyl)thiophene in the presence of triphenylbismuth to generate 2 21 bromination of 2 21 using NBS in THF/AcOH provided versati le intermediate 2 22 , which was reacted with 2 8 , 2 9 , and 2 2 3 under Suzuki cross coupling conditions to furnish 2 1b 2 2b 2 2 4 (55%) respectively. Final treatment of 2 1b , 2 2b , and 2 2 4 with BCl 3 in the presence of pentamethylben zene as a cation scavenger 78 afforded guanine derivatives 2 1 c , 2 2c , and 2 2 5 , correspondingly (Scheme 2 6).

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56 Scheme 2 6 . Synthesis of guanine containing oligomers 2 1c , 2 2c , and 2 2 5 . Uracil Terminated Oligomers Synthesis of uracil derivatives was initiated following the same app roach employed for the purines (Scheme 2 7). Uracil 2 2 6 was treated with K 2 CO 3 in DMSO, followed by addition of rac 2 ethylhexyl bromide at 40 °C, to generate the N(1) alkylated product 2 2 7 in modest yield 2 2 7 and N BS in DMF was stirred for 30 min at rt to afford 2 2 8 (tributylstannyl) thiophene generated the product 2 2 9 as a white solid in 63% yield after overnight heating at reflux.

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57 Scheme 2 7 . A ttempted synthesis of 2 30 . Table 2 4 . Bromination of 2 2 9 Entry a Conditions Product 1 THF, CH 3 COOH, NBS, 0 °C to rt 2 31 2 THF, NBS, 0 °C to rt 2 31 3 Br 2 , DCM 2 31 a Lead references are given for the conditions used based on similar purine derivativ es as starting materials. Bromination at C(5) of the thiophene ring of 2 2 9 did not proceed as expected and generated a dibrominated product 2 31 under several conditions (Table 2 3). To circumvent this issue, 4,7 bis(5 (trimethylstannyl) thiophen 2 yl)ben zo[ c ][1,2,5] thiadiazole 2 18 79 bis(tributylstannyl) terthiophene 2 11 80 were prepared following literature procedures, then subjected to Stille coupling with 5 bromouracil 2 2 8 to furnish the target compounds 2 1d and 2 2d in 70% and 50% yield, respectively (Scheme 2 8). The possibility of a straightforward synthetic approach for uracil, as opposed to adenine or guanine derivatives, speaks to a structural/electronic dependency that is not completely understood to date.

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58 Scheme 2 8. Synthesis of uracil containing oligomers 2 1d and 2 2d . Cytosine Terminated Oligomers Obviously absent from Figure 2 3 are cytosine derivatives that proved problematic to synthesize. Cytosine 2 3 2 was treated (Scheme 2 9) with tetrabutylammonium hydroxide in DMF at rt, followed by addition of rac 2 ethylhexyl bromide, to afford 1 (2 ethylhexyl) cytosine 2 3 3 81 Halogenation of 2 3 3 employing NBS in DMF at rt for 30 min resulted in the corresponding 5 bromo derivative 2 3 4 in moderate yields. 82 All attempts to extend the conjugation of c ytosine by adding a thienyl group at position C(5) failed to provide the desired product 2 3 5 using either Stille conditions 83 or other 84 reported approaches for cytosine derivatives. Iodination of C(5) represents a different alternative to access these targets as demonstrated in Chapter 3. Scheme 2 9. Attempted synthesis of 2 33 .

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59 Thermal Properties The thermal stability of the target compounds was evaluated by thermal gravimetric analysis (TGA), in consideration of their pertinence to potential future applications. The adenine derivati ves 2 1a and 2 2a showed loss of 5% of the original compound weight at relatively high temperatures, 239 and 394 °C, respectively (Figures 2 4). High thermal stability was also observed for 2 1b and 2 2b , which showed loss of 5% of the original compound we ight at 345 and 320 °C (Figures 2 4), respectively. On the other hand, 2 1c and 2 2c tended to trap solvent molecules, as evidenced by enhanced thermal stability upon longer vacuum drying of the solids prior to measurement (Figures 2 4). However, the major transitions of 2 1c and 2 2c seem to be comparable to 2 1b and 2 2b . Finally, compounds 2 1d and 2 2d exhibited good thermal stability with loss of 5% of the original compound weight at 283 and 352 °C, respectively (Figures 2 4). Figure 2 4 . The TGA for 2 1 and 2 2 compounds obtained at a heating rate of 10 °C/min under nitrogen .

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60 Optical Properties 2 and 2 in solution were collected to establish relationships between conjugated (and n ucleobase) structure and photophysical properties. Absorption spectra were measured in 1,4 dioxane ( E T (N) = 0.164) and DMF ( E T (N) = 0.386), 85 solvents with differing polarity and the ability to dissolv e the nucleobase terminated oligomers. In 1,4 dioxane, the absorption spectra of 2 5a and Table 2 4). The bands at shorter wavelength, 357, 363, 372, and 361 nm, correspond to * tr ansitions of the 2 1a , 2 1b , 2 1c , and 2 1d chromophores, respectively. The longest wavelength absorption bands at 494, 505, 513, and 503 nm are consistent with structure (vid e infra). Figure 2 5 . Absorption spectra (1.5 × 10 M) for 2 and 2 in a) 1,4 dioxane; and b) DMF . On the other hand, the absorption spectra of 2 2a , 2 2b , 2 2c , and 2 2d displayed a single band at 423, 416, 425, and 424 nm, respectively, whe n compared to a) b )

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61 the benzothiadiazole (BTD) derivatives 2 1 . In DMF, all absorption peaks were shifted to slightly longer wavelengths (Figure 2 5b and Table 2 4). This solvatochromism, in response to increased solvent polarity, is consistent with a larger dip ole moment of the chromophore in the excited state than in the ground state. It is noteworthy that 2 1a,b,d (Figure 2 6), 2 2a,b (Figure 2 7), 2 10 , 2 24 , and 2 2 5 clearly follow the B law for concentrations up to 20 30 × 10 M in 1,4 dioxane, which argues against aggregation in the ground state. Such is not necessarily the case for guanine derivatives 2 1c and 2 2c , and uracil derivative 2 2d (Figure 2 8), in 1,4 dioxane. W hen comparing the absorbance spectra of and in both 1,4 dioxane and DMF, guanine derivatives 2 1c and 2 2c exhibited the most redshifted absorption bands. These results are consistent with the stronger electron donating character of the guanine n ucleobase (guanine has the lowest calculated ionization potential among the nucleobases: 8.66, 7.95, and 7.52 V for uracil, adenine, and guanine, respectively 86 ); the observed absorbance red shift can also be due to aggregation in 1,4 dioxan e solution (vide infra). Overall, the nucleobase identity tunes the absorption maxima up to 20 nm within each series, best read out from the DMF absorption data. Furthermore, the molar extinction coefficient observed for the low energy absorption of 2 is reduced by at least a factor of 2 compared to that of the absorption of 2 (see Table 2 4). As for 2 10 , 2 24 , and 2 2 5 the same trend was observed upon changing to a more polar solvent, the maximum absorption peaks displayed a slight bathoch romic shifts from 420, 430 and 432 nm in 1,4 dioxane to 422, 432, 437 nm in DMF, correspondingly (Figure 2 9).

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62 Table 2 5 . Absorption Properties of 2 1 , 2 2 , 2 10 , 2 2 4 , and 2 2 5 in 1,4 Dioxane and DMF a compound 1,4 dioxane DMF abs max (nm) b 10 4 (M 1 cm 1 ) abs max (nm) b 10 4 (M 1 cm 1 ) 2 1a 494 2.9±0.1 493 1.9±0.2 2 1b 505 1.9±0.1 510 1.7±0.1 2 1c 513 0.20±0.08 516 2.1±0.5 2 1d 503 1.4±0.1 513 1.4±0.2 2 2a 423 4.1±0.2 428 4.5±0.4 2 2b 416 4.6±0.8 422 5.9±0.3 2 2c 425 0.70±0.04 434 4. 1±0.1 2 2d 424 3.0±0.1 426 3.9±0.2 2 10 420 1.8±0.1 422 0.69±0.2 2 24 430 1.3±0.04 432 1.4±0.4 2 2 5 432 1.1±0.07 437 1.2±0.3 a All measurements were performed at room temperature and at 15 × 10 6 M. b Lowest energy absorption maxima. abs max (nm) ± 1 n m.

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63 Figure 2 6. Absorption spectra and Beer Lambert plots in 1,4 dioxane for a) 2 1a ; b) 2 1b ; and c) 2 1d . a) b ) c )

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64 Figure 2 7. Absorption spectra and Beer Lambert plots in 1,4 dioxane for a) 2 2a ; and b) 2 2b . a) b )

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65 Figure 2 8. Absorption spectra and Beer Lambert plots in 1,4 dioxane for a) 2 1c ; b) 2 2c ; c) and 2 2d . a) b ) c )

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66 Figure 2 9 . Absorption spectra for 2 10 , 2 2 4 , and 2 2 5 in a) 1,4 dioxane; and b) DMF (15×10 6 M) . Figure 2 10 . a) Emission spectra in 1,4 dioxane for a) 2 1a d and 2 2a d (1 3 × 10 6 M ; ex = 476 nm for 2 1 ; ex = 430 nm for 2 2 ); and b) 2 10 , 2 2 4 , and 2 2 5 (1 3 × 10 6 M) . The emission spectra of 2 , 2 10 , 2 2 4 , and 2 2 5 in 1,4 dioxane showed single structureless bands at 618, 631, 640, and 640 nm, respectively (Figure 2 10 and Table 2 5). Unlike the absorbance, the emission profiles of 2 1c and 2 2c showed no signs of aggregation since the measurements are performed at lower concentrations. Vibrational progressions were observed in the emission spectra of 2 . The a ) b ) a ) b )

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67 structureless emi ssion spectra of 2 , 2 10 , 2 24 , and 2 2 5 suggest that the long wavelength emission arises from an internal charge transfer (ICT) state. Table 2 6 . Emission Properties of 2 1 , 2 2 , 2 10 , 2 2 4 , and 2 2 5 in 1,4 d ioxane a a All measurements were performed at room temperature. b All experiments were performed using opti cal ex = 476 nm for 2 1 ; ex = 430 nm for 2 2 ), so generally 5 10 × 10 6 M. c Fluorescence quantum yields are relative to the quantum yield of either Rhodamine B in absolute ethanol ( F = 0.49; for 2 1a d ) or Fluorescein in 0.1 M NaOH ( F = 0.79; for 2 2a d ). d Theoretical exponential decay curves are fitted with the instrument response function and the best fit is obtained when 2 = 0.9 1.1. e Fluorescence lifetime first order decay. f Fluorescence lifetime bi exponential decay with contribution percentage to the lifetime shown in parentheses. Larger Stokes shifts were observed for 2 , 2 10 , 2 2 4 , and 2 2 5 (124, 126, 127, 137 nm, 107, 158, and160 respectively) as compared to 2 (67, 64, 79, and 60 nm, respectively), thus reflecting more structural reorganization of 2 , 2 10 , 2 2 4 , and 2 2 5 upon photoexcitation. 87 The fluorescence quantum yields measured for 2 are strikingly lower than those for the 2 , 2 10 , 2 2 4 , and 2 2 5 oligomers (Table 2 5), which is in contrast with the band gap law. 88 This may result from the sulfur atoms of the terthiophene compound em max (nm) b Stokes shi ft (nm) F c F (ns) d k r = F / f × 10 7 (s 1 ) 2 1a 618 124 0.64 4.83 e 1.32 2 1b 631 126 0.38 3.92 e 0.97 2 1c 640 127 0.25 3.94 e 0.63 2 1d 640 137 0.33 5.95 e 0.55 2 2a 490,524 67 0.15 0.63 e 2.38 2 2b 480,513 64 0.11 0.50 (66%) f 0.87 (34%) 2.22 2 2 c 504,536 79 0.10 0.8 7 (52%) f 4.14 (48%) 1.12 2 2d 484,517 60 0.19 0.88 e 2.16 2 10 525 107 0.34 ND ND 2 2 4 588 158 0.37 ND ND 2 2 5 592 160 0.39 ND ND

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68 containing oligomers that promote intersystem crossing to the triplet manifold via 88a, 89 Further insight into the fluorescence behavior could be obtained from fluorescence lifetime measurements. Time res olved fluorescence decay profiles of all compounds were carried out in 1,4 dioxane. The decay dynamics were determined at an excitation wavelength of 375 nm, and the decays were monitored at the respective emission maxima, 570 nm for 2 , and 475 nm for 2 . The decay data for oligomers 2 could be fit to a single exponential, and these oligomers possessed similar and relatively long decay lifetimes ( F 5). In contrast, 2 showed much shorter lifetimes ( F the data for 2 2b,c were better fit using a double exponential decay function. The radiative decay rates ( k r ) for 2 calculated as k r = F / F are 7 s . The lifetimes and radiative decay rates for 2 are typical for conjugated oligomers with strongly allowed long axis polarized , * singlet excited states. 90 By contrast, compounds 2 have fluorescence lifetimes that are one order of magnitude lower than the benzothiadiazo le series, and the corresponding radiative rates are higher 7 s ). The significant difference in fluorescence lifetime and radiative rates for 2 and 2 likely reflects the fact that the singlet excited state in the TBT oligomers has a significant degree of charge transfer character, and it adds support to the notion that the BTD unit is a strong acceptor. 88a Electrochemical Properties The redox properties of 2 1a d and 2 2a d were investigated by cyclic voltammetry (CV) in DMF with NBu 4 PF 6 as the supporting electrolyte (Table 2 6). Differential pul se voltammetry (DPV) data was also obtained, as DPV offers better

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69 sensitivities than CV and leads to steeper peak onsets due to the sharper current response occurring near the E o region (due to the selective extraction of Faradaic current 91 ). The peak shapes seen in DPV also shed light on the redox behavior of the molecules. Compared to quasi reversible and irrever sible systems, truly reversible electrochemical events exhibit sharper, more symmetrical peaks. 91 The two foll owing equations were used to estimate the HOMO and LUMO levels from the DPV data: 91 92 E HOMO = ( E onset ox + 5.1) eV E LUMO = ( E onset red + 5.1) eV where E onset red and E onset ox are the onset oxidation and reducti on potentials measured for the compounds in solution versus the Fc/Fc + reference. Cyclic voltammetry revealed that the oligomers 2 and 2 undergo a single irreversible oxidation, commonly described in the literature for purine derivatives, 29a, 93 while the cyclic voltammograms of oligomers 2 1d and 2 2d indicated two irreversible ox idations within the accessible solvent window. Within the TBT series, adenine 2 1a and protected guanine 2 1b derivatives display three reversible or quasi reversible reduction bands. Meanwhile, 2 1c and 2 1d show only one reversible reduction observable w ithin the solvent window. Likewise, one or two reversible reduction bands are characteristic of 2 2a and 2 2b , while 2 2c and 2 2d possess only one irreversible reduction band. The strong electron accepting character of the BTD moiety was verified by the p ositive shift of the onsets of the reduction bands of oligomers 2 by ca. 0. 0. 640 V (DPV) with respect to their terthiophene analogues 2 , resulting in lower corresponding LUMO values for 2 (Table 2 -

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70 6). While the oxidation potentials and t he respective HOMO values of 2 and 2 are comparable, a certain degree of tunability of the HOMO level of the oligomer can be attained by changing the nucleobase structure from adenine, to 2 amino 6 (benzyloxy) 9H purine (protected guanine), to gu anine, or to uracil. Consistent with the literature, 94 for example, the redox potentials indicate that the unprotected guanine is the strongest electron donor among the nucleobases with the respective oligomers hav ing oxidation onsets at as low as 0.36 and 0.27 V vs Fc/Fc + (DPV values) for 2 1c and 2 2c , respectively (Table 2 6). Interestingly, the nucleobase structure has little effect on the reduction onsets and LUMO values in the TBT series demonstrating that the LUMO is dominated by the strong BTD acceptor. Although compounds within families 2 1 and 2 2 E g = 2 E g 2 ), the members differ slightly in their HOMO an d LUMO values speaking to optical and electronic tunability. Lastly worth noting, the electrochemical and optical data trends are consistent. Guanine derivatives 2 1b and 2 1c , for example, show the most bathochromically shifted absorbance bands and also t E g values. Likewise, both the E g 2 E g for 2 2 1 are reduced by 0.4 0.5 eV relative to 2 2 .

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71 Table 2 7 . Electronic Properties of 2 1 , 2 2 compound experimental DFT calculations a E onset ox (V) b 0.1 E onset red ( V) b 0.1 HOMO (eV) c 0.1 LUMO (eV) c 0.1 E g electrochemical (eV) 0.2 E g optical (eV) [DMF] d 0.2 HOMO (eV) LUMO (eV) E g (eV) 2 1a 0.51 1.40 5.61 3.70 1.91 2.14 5.50 3.21 2.29 2 1b 0.39 1.39 5.49 3.71 1.78 2.07 5.15 2.96 2.19 2 1c 0.36 1.41 5.46 3.69 1.77 2.01 5.16 2.92 2.24 2 1d 0.57 1.33 5.67 3.77 1.90 2.07 5.45 3.12 2.33 2 2a 0.48 1.81 5.58 3.29 2.29 2.48 5.40 2.60 2.80 2 2b 0.36 1.99 5.46 3.11 2.35 2.52 5.07 2.30 2.77 2 2c 0.27 2.05 5.37 3.05 2.32 2.43 5.07 2.25 2.82 2 2d 0.32 1.99 5.42 3.11 2.31 2.54 5.32 2.54 2.78 a All ethylhexyl groups have been replaced by methyl groups for the calcula tions. Geometry optimization and calculation of the HOMO and LUMO energies was performed at the B3LYP/6 31+G** level. b Energies are reported relative to Fc/Fc+ redox couple and are obtained from DPV experiments; the solvent employed is N,N dimethylformam ide (DMF) (0.1 mM TBAPF 6 at a 100 mV/s scan rate). c Estimated HOMO and LUMO energy levels (relative to vacuum) based on electrochemical potentials ( E 1/2 ox and E 1/2 red , respectively) determined in DMF (0.1 M TBAPF 6 at a 100 mV/s scan rate). d Determined b ased on UV absorption data in DMF.

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72 Electronic Structure Calculations The HOMO and LUMO energies of 2 and 2 were calculated, and the structural geometries were optimized at the B3LYP/6 31+G** level of theory (as implemented in Gaussian 09 95 ). In all cases, the 2 ethylhexyl groups were truncated to methyl groups to reduce computational time, since they do not significantly affect the equilibrium geometries or electronic properties. The oligomers are predicted to be quite planar. Using 2 1a and 2 2a as representative examples ( Figure 2 11 dihedral t of the oligomer conformations as global minima was possible through calculations using truncated versions, like 2 10 ( Figure 2 11). As illustrated in Figure 2 11, conformation 2 10d direction from the N(9) alkyl purine and the thiadiazole ring of BTD (dihedral angle = ~ 170°). Figure 2 11 . Computational analysis of oligomer conformations 2 10 based on B3LYP/6 31+G** calculations. 2 Et Hx groups have been truncated to methyl groups f or the calculations . A similar analysis was achieved with compound 2 2 9 , given the conformation of the thiophene relative to the BTD moiety is already known (Figure 2 12). In contrast to the purines, the thiophene ring is pointing towards the N(1) pend e nt group of the pyrimidine ring (dihedral angle C(6) C(5) S = 0.019°).

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73 Figure 2 12 . Computational analysis of oligomer conformations 2 2 9 based on B3LYP/6 31+G** calculations. 2 EtHx groups have been truncated to methyl groups for the calculations . R epresentative frontier MO plots are depicted in Figure s 2 1 3 ( 2 1 ) and 2 14 for ( 2 2 ) . The LUMO is concentrated on the benzothiadiazole unit, while the HOMO is conjugated backbone. The well separated HOMO and LUMO orbital coefficients indicate that the transition between them can be considered as a charge transfer transition. 96 For 2 2 , the MO constructs suggest that there is significant overlap between strongly delocalized HOMO and LUMO wave fu nctions. The electronic structure should result in a higher oscillator strength; this is reflected by the higher extinction coefficients for 2 mentioned earlier (Table 2 4). 97 As a result, both the 2 1 are decreased relative to 2 2 . The computed HOMO and LUMO energies, and E g values, of all compounds are summarized in Table 2 6 .

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74 Figure 2 13 . Calculated HOMO and LUMO plots for 2 1 a d based on B3LYP/6 31+G** calculations. 2 EtHx groups have been truncated to methyl groups for the calculations .

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75 Figure 2 14 . Calculated HOMO and LUMO plots for 2 2a d based on B3LYP/6 31+G** calculations. 2 EtHx groups have been truncated to methyl groups for the calculations .

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76 E g within each series of compounds (i.e., 2 and ) are based solely on the exchange of the nucleobase core; for 2 E g changes from 2.23, 2.19, to 2.33 eV by simply swap ping the nucleobase from adenine 2 1a , to guanine 2 1c , to uracil 2 1d , respectively. From the calculated energy levels of the parent nucleobases (Figure 2 15), the guanines (protected and unprotected) should be the strongest donors 94 and uracil should be the weakest; this theoretical observation is nicely reproduced in the experimental data (vide supra) where 2 1c 2 1d interaction. Figure 2 15 . Calculated HOMO and LUMO plots for subunits comprising the compounds investigated based on B3LYP/6 31+G** calcul ations. 2 EtHx groups have been truncated to methyl groups for the calculations .

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77 Conclusion The DNA/RNA bases (A, C, G, T/U) are unique building blocks to consider for conjugated materials design as they intimately merge electron function with predict able pairwise hydrogen bonding motifs. Toward developing bioinformed and functional conjugated materials, we have synthesized two families of nucleobase containing oligomers and fully characterized their photophysical and electronic properties with res pect to nucleobase and backbone structure. Synthetic approaches have been established to navigate the inherent synthetic challenges associated with building blocks in Pd catalyzed cross coupling reactions. Protocols have specifically allowed addition of three (A, G, U) of the nucleobase heterocycles to the terminal positions of standard thiophene containing conjugated sequences; attempts to prepare cytosine (C) derivatives will be discussed in the following chapter. containing conjugated oligomers have emerged from a combination of experimental spectroscopic data and DFT calculations. The absorption and emission properties, emission lifetime s, and fluorescence quantum yields respond in understandable ways to both nucleobase and backbone electronic structure. For example, guanine terminated derivatives (G TBT G and GTTT G) exhibit the most bathochromically shifted absorption, consistent with donating character compared to A and U. Despite TBT linked nucleobases are significantly improved over the terthiophene (TTT) family. The redo x behavior of the oligomers could be evaluated by CV and DPV, and the HOMO and LUMO energies estimated from the data show a dependence on the nature

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78 of the nucleobase and are in good agreement with electronic structure calculations performed at the B3LYP/6 31+G** level. conjugated oligomers that combine intrinsic light absorption and hydrogen bond directed self assembly properties are interesting candidates as organic solar cell materials. 35 With an understanding of how a structure can confer tunable optical and electronic properties to traditional on optoelectronic thin film structure and functi on. Work along these lines is underway and is reported in Chapter 3. Experimental General Methods Reagents and solvents were purchased from commercial sources and used without further purification unless otherwise specified. THF, diethyl ether, CH 2 Cl 2 , and DMF were degassed in 20 L drums and passed through two sequential purification columns (activated alumina; molecular sieves for DMF) under a positive argon atmosphere. Tetrakis(triphenylphosphine) palladium(0), trans bis(triphenylphosphine) palladium(II) bis(diphenylphosphino)ferrocene]dichloro palladium(II) (complex with dichloromethane, and [Pd(dppf)Cl 2 ·CH 2 Cl 2 ]) were purchased from Strem Chemicals or Sigma Aldrich and used as received. Thin layer chromatography (TLC) was performed on SiO 2 60 F254 aluminum plates with visualization by UV light or staining. Flash column chromatography was performed using SiO 2 Melting points (mp) were determined on an electrothermal melting point apparatus. 1 H( 13 C) NMR spectra were recor ded on 300(75) MHz or 500(125) MHz spectrometers as specified. Chemical shifts ( ) are given in parts per million (ppm) relative to TMS and

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79 referenced to residual protonated solvent (CDCl 3 : H 7.26 ppm, C 77.23 ppm; DMSO d 6 : H 2.50 ppm, C 39.50 ppm). Ab breviations used are s (singlet), d (doublet), t (triplet), q (quartet), quin (quintet), sep (septet), b (broad), and m (multiplet). Refer to J . Org. Chem . 201 5 , 80 , 1828 1840 to view the 1 H and 13 C NMR spectra. ESI and ESITOF MS spectra were recorded on FTICR and TOF spectrometers, respectively. EI , CI , and DIP CI MS spectra were recorded on a single quadrupole spectrometer. Microwave assisted reactions were carried out with a single mode cavity Discover Microwave Synthesizer (CEM corporation, NC). The following compounds have been prepared using literature procedures: 4,7 bis(4,4,5,5 tetramethyl 1,3,2 dioxaborolan 2 yl)benzo[ c ][1,2,5]thiadiazole 2 8 , 71a 2,5 bis(4,4,5,5 tetramethyl 1,3,2 dioxaborolan 2 yl)thiophene 2 9 , 71b 4,7 bis(5 (trimethylstannyl) thiophen 2 yl)benzo[ c ][1,2,5]thiadiazole 2 1 8 , 80 bis(trimethylstannyl) terthiophene 2 11 . 79 Synthesis of A denine T erminated O ligomers ( ± ) 9 (2 Ethylhexyl) 9H purin 6 amine (2 4) . Rac 2 ethylhexyl bromide (2.00 mL, 11.0 mmol) was added to a suspension of adenine 2 3 (1.00 g, 7.40 mmol) and K 2 CO 3 (3.11 g, 22.2 mmol) in dry DMF (50 mL). The resulting suspension was stirred for 20 h at rt under a rgon atmosphere. The insoluble solid was filtered, and the filtrate was evaporated to give a crude white solid which was purified by column chromatography with gradient elution (MeOH:CH 2 Cl 2 3:97 to 5:95) to afford the product as a white solid (1.06 g, 62%) . m.p. 153 156 °C; 1 H NMR (500 MHz, DMSO d 6 ): 8.12 (s, 1H), 8.11 (s, 1H), 7.17 (s, 2H), 4.03 (d, J = 7.5 Hz, 2H), 1.92 (sep, J = 6.5 Hz, 1H), 1.21 1.18 (m, 8H), 0.85 0.79 (m, 6H); 13 C NMR (125 MHz, DMSO d 6 ): 155.9, 152.3, 149.8, 141.2, 118.6, 46.3, 38. 8, 29.7, 27.8, 23.2, 22.3, 13.8, 10.2; HRMS (ESI) calcd for C 13 H 22 N 5 [M+H] + : 248.1875, found: 248.1876.

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80 ( ± ) 8 Bromo 9 (2 ethylhexyl) 9H purin 6 amine (2 5) . A suspension of NBS (0.76 g, 4.3 mmol) and 2 4 (0.50 g, 2.1 mmol) in dry CH 3 CN (5 mL) was irradiate d by microwave (100 W, 75 °C) for 20 min. The solvent was evaporated under reduced pressure and the crude solid was purified by column chromatography (EtOAc:hexanes, 1:1) to afford 2 5 as a pale yellow solid (0.32 g, 1.1 mmol, 50%): m.p. 167 168 °C; 1 H NMR (300 MHz, CDCl 3 ): 8.32 (s, 1H), 5.63 (s, 2H), 4.08 (d, J = 7.5 Hz, 2H), 2.08 2.04 (m, 1H), 1.30 1.25 (m, 8H), 0.93 0.84 (m, 6H); 13 C NMR (125 MHz, CDCl 3 ): 154.6, 153.0, 151.8, 127.6, 119.9, 48.5, 39.2, 30.4, 28.5, 23.8, 23.0, 14.0, 10.6; HRMS (ESI) ca lcd for C 13 H 21 BrN 5 [M+H] + : 326.0980, found: 326.0979. ( ± ) 9 (2 Ethylhexyl) 8 (thiophen 2 yl) 9H purin 6 amine (2 6) . 2 (Tributylstannyl)thiophene (0.50 mL, 1.6 mmol) was added to a solution of 2 5 (0.10 g, 0.31 mmol), and Pd(PPh 3 ) 2 Cl 2 (0.021 g, 0.031 mmol) in degassed THF (5 mL). The resulting mixture was heated to reflux for 16 h. The solvent was removed under reduced pressure. The crude mixture was purifie d by column chromatography (EtOAc:hexanes, 167 °C; 1 H NMR (300 MHz, CDCl 3 ): 8.36 (s, 1H), 7.56 (dd, J = 3.9; 1.2 Hz, 1H), 7.53 (dd, J = 5.1; 1.2 Hz, 1H), 7.19 (dd, J = 5.4; 3.9 Hz, 1H), 5.72 (s, 2H), 4.34 (d, J = 7.8 Hz, 2H), 1.96 1.92 (m, 1H), 1.26 1.17 (m, 8H), 0.83 0.78 (m, 6H); 13 C NMR (125 MHz, CDCl 3 ): 155.2, 152.8, 152.3, 145.7, 132.1, 128.7, 128.3, 128.0, 119.4, 47.7, 39.1, 30.3, 28.3, 23.8, 23.1, 14.1, 10.6; H RMS (ESI) calcd for C 17 H 24 N 5 S [M+H] + : 330.1752, found: 330.1754. ( ± ) 8 (5 Bromothiophen 2 yl) 9 (2 ethylhexyl) 9H purin 6 amine (2 7) . NBS (0.082 g, 0.46 mmol) was added over 2 h to a solution of 2 6 (0.10 g, 0.30 mmol) in THF

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81 (2 mL) and glacial AcOH (2 m L) at 0 °C. The solution was stirred for an additional 2 h at rt and was then diluted with EtOAc (50 mL). The organic layer was washed with H 2 O (3 × 25 mL) and brine, and was dried over Na 2 SO 4 (anhyd) to yield 2 7 as a beige solid (0.097 g, 78%): m.p. 150 °C (dec); 1 H NMR (300 MHz, CDCl 3 ): 0. 85 0.80 (m, 6H), 1.26 1.19 (m, 8H), 1.95 (m, 1H), 4.30 (d, J = 7.8 Hz, 2H), 5.64 (s, 2H), 7.14 (d, J = 3.9 Hz, 1H), 7.29 (d, J = 4.2 Hz, 1H), 8.36 (s, 1H); 13 C NMR (125 MHz, CDCl 3 ): 10.7, 14.2, 23.1, 23.9, 28.5, 30 .5, 39.2, 47.9, 116.3, 119.6, 128.3, 131.0, 134.1, 144.6, 152.4, 153.1, 155.3; HRMS (ESI) calcd for C 17 H 23 BrN 5 S [M+H] + : 410.0837, found: 410.0834. 8 (5 (Benzo[ c ][1,2,5]thiadiazol 4 yl)thiophen 2 yl) 9 (2 ethylhexyl) 9H purin 6 amine (2 10) and 8,8' (5,5' ( benzo[ c ][1,2,5]thiadiazole 4,7 diyl)bis(thiophene 5,2 diyl))bis(9 (2 ethylhexyl) 9H purin 6 amine) (2 1a) . In a dry round bottom flask under inert atmosphere, 2 9 (0.052 g, 0.13 mmol), K 2 CO 3 (0.32 g, 2.4 mmol), Pd(dppf)Cl 2 .CH 2 Cl 2 (0.018 g, 0.027 mmol), and aliquot 336 (2 drops) were dissolved in a degassed solution of 2 7 (0.12 g, 0.29 mmol) in toluene (6 mL). Then degassed water (2 mL) was added and the reaction vessel was heated to 85 °C for 18 h. The solvent was removed under reduced pressure and the res idue was dissolved in EtOAc (25 mL), washed with water (3 × 15 mL), and then dried over anhydrous Na 2 SO 4 . The solvent was removed under reduced pressure and the crude product was purified by silica gel column chromatography with gradient elution (MeOH:CH 2 C l 2 1:99 to 4:95). The mixture of 2 1a and 2 10 was further purified by precipitation from hexanes. 2 10 : Yellow solid (0.010 g, 30%): m.p. 185 °C (dec); 1 H NMR (300 MHz, CDCl 3 ): 8.38 (s, 1H), 8.21 (d, J = 4.2 Hz, 1H), 8.01 7.94 (m, 3H), 7.70 7.65 (m, 2H ), 5.59 (s, 2H), 4.43 (d, J = 7.8 Hz, 2H), 2.08 2.02 (m, 1H), 1.28 1.25 (m, 8H), 0.89 0.81 (m, 6H);

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82 13 C NMR (125 MHz, CDCl 3 ): 155.6, 154.6, 152.3, 152.1, 151.9, 151.9, 145.8, 142.4, 132.9, 129.7, 128.8, 128.3, 126.7, 126.0, 121.2, 48.0, 39.2, 29.8, 28.4, 23.8, 23.1, 14.1, 10.6; HRMS (ESI) calcd for C 23 H 26 N 7 S 2 [M+H] + : 464.1691, found: 464.1707. 2 1a : Mixture of stereoisomers as a red solid (0.045 g, 42%): 1 H NMR (500 MHz, DMSO d 6 ): 8.34 (s, 2H), 8.29 (d, J = 4.0 Hz, 2H), 8.18 (s, 2H), 7.87 (d, J = 4 Hz, 2H), 7.37 (s, 4H), 4.23 (d, J = 7.5 Hz, 4H), 1.94 1.90 (m, 2H), 1.23 1.20 (m, 16H), 0.81 0.72 (m, 12H); 13 C NMR (125 MHz, DMSO d 6 , gHMBC): 156.3, 153.4, 152.7, 152.5, 144.6, 141.2, 134.9, 129.0, 128.8, 127.0, 125.7, 119.5, 47.8, 39.2, 30.6, 28.5, 24.2, 2 3.0, 14.2, 11.0; HRMS (APCI) calcd for C 40 H 47 N 12 S 3 [M+H] + : 791.3209, found: 791.3184. 8,8' ([2,2':5',2'' Terthiophene] 5,5'' diyl)bis(9 (2 ethylhexyl) 9H purin 6 amine) (2 2a) . In a dry round bottom flask under inert atmosphere, 2 7 (0.18 g, 0.45 mmol), 9 (0.070 g, 0.22 mmol), K 2 CO 3 (0.50 g, 3.6 mmol), Pd(dppf)Cl 2 .CH 2 Cl 2 (0.03 g, 0.04 mmol), and aliquot 336 (2 drops) were dissolved in degassed toluene (6 mL), followed by addition of degassed water (2 mL). The reaction vessel was heated to 80 °C and stirred 18 h, filtered, and washed with CH 2 Cl 2 (15 mL). The product was further purified by precipitation from hexanes to afford the orange product as a mixture of stereoisomers (0.06 g, 40%): 1 H NMR (300 MHz, DMSO d 6 ): 8.17 (s, 2 H), 7.70 (d, J = 3.9 Hz, 2H), 7 .53 (d, J = 3.9 Hz, 2H), 7.33 (s, 4H), 7.49 (s, 2H), 4.37 (d, J = 7.5 Hz, 4H), 1.88 1.86 (m, 2H), 1.21 1.10 (m, 16H), 0.81 0.72 (m, 12H); 13 C NMR (75 MHz, DMSO d 6 ): 155.5, 152.7, 151.7, 143.2, 138.0, 135.3, 131.3, 128.7, 126.3, 125.4, 118.5, 46.7, 38.2, 29.6, 27.6, 23.3, 22.3, 13.8, 10.4; HRMS (APCI) calcd for C 38 H 46 N 10 S 3 [M+H] + : 739.3142, found: 739.3144.

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83 Synthesis of Guanine Terminated Oligomers ( ± ) 6 Chloro 9 (2 ethylhexyl) 9H purin 2 amine (2 13) . K 2 CO 3 (2.45 g, 17.7 mmol) was added to a solution of 6 chloro 9H purin 2 amine 2 12 (1.0 g, 5.9 mmol) in dry DMF (100 mL), then stirred at rt for 1 h. Racemic 2 ethylhexyl bromide was then added, and the solution was allowed to stir for 16 h. The solvent was removed under reduced pressure and the resulting cr ude mixture was purified by silica gel column chromatography with gradient elution (EtOAc:hexanes 30:70 to 50:50) to yield a white solid (0.92 g, 56 %): m.p. 107 °C (dec); 1 H NMR (500 MHz, CDCl 3 ): 7.71 (s, 1H), 5.32 (s, 2H), 3.95 (d, J = 7.0 Hz, 2H), 1.8 8 1.86 (m, 1H), 1.28 1.24 (m, 8H), 0.90 0.83 (m, 6H); 13 C NMR (125 MHz, CDCl 3 ): 159.2, 154.3, 151.2, 142.9, 125.2, 47.3, 39.6, 30.4, 28.5, 23.7, 23.0, 14.1, 10.5; HRMS (ESI) calcd for C 13 H 21 ClN 5 [M+H] + : 282.1485, found: 282.1472. ( ± ) 6 (Benzyloxy) 9 (2 e thylhexyl) 9H purin 2 amine ( 2 19 ) . A dry round bottom flask equipped with a condenser under inert argon atmosphere was charged with 2 13 (0.50 g, 1.8 mmol), K 2 CO 3 (0.25 g, 1.8 mmol), 1,4 diazabicyclo[2.2.2]octane (0.020 g, 0.18 mmol), and benzyl alcohol ( 3 mL). The reaction was heated to 80 °C and stirred 16 h. Then cooled to rt. The solvent was removed under reduced pressure. The crude product was purified by silica gel column chromatography with a gradient elution (EtOAc:hexanes 20:80 to 40:60) to yield a white solid (0.53 g, 84%): m.p. 102 104 °C; 1 H NMR (500 MHz, CDCl 3 ): 7.56 (s, 1H), 7.52 7.50 (m, 2H), 7.37 7.28 (m, 3H), 5.56 (s, 2H), 4.81 (bs, 2H), 3.94 (d, J = 7.0 Hz, 2H), 1.89 (sep, J = 6.5 Hz, 1H), 1.28 1.27 (m, 8H), 0.92 0.86 (m, 6H); 13 C NMR (1 25 MHz, CDCl 3 ): 161.1, 159.2, 154.7, 140.0, 136.7, 128.5, 128.4, 128.1, 115.7, 68.1, 47.1, 39.7, 30.4, 28.6, 23.8, 23.1, 14.2, 10.6; HRMS (ESI) calcd for C 20 H 28 N 5 O [M+H] + : 354.2294, found: 354.2300.

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84 ( ± ) 6 (Benzyloxy) 8 bromo 9 (2 ethylhexyl) 9H purin 2 a mine ( 2 20 ) . NBS (0.55 g, 3.1 mmol) was added portion wise to a solution of 2 19 (1.0 g, 2.8 mmol) and stirred at rt for 1.5 h. The reaction mixture was then poured into deionized water (20 mL), extracted with ethyl acetate (25 mL), washed with a solution of 5% Na 2 S 2 O 4 (15 mL), and dried over anhydrous Na 2 SO 4 . The solvent was removed under reduced pressure to yield 2 20 as a beige solid (1.04 g, 85%): m.p. 106 1 H NMR (500 MHz, CDCl 3 ): 7.50 7.48 (m, 2H), 7.36 7.30 (m, 3H), 5.52 (s, 2H), 4.86 (s, 2H), 3.93 (d, J = 8.0 Hz, 2H), 2.00 (sep, J = 6.5 Hz, 1H), 1.32 1.26 (m, 8H), 0.91 0.85 (m, 6H); 13 C NMR (125 MHz, CDCl 3 ): 159.8, 159.0, 155.6, 136.4, 128.5, 128.5, 128.2, 126.1, 115.9, 68.3, 48.1, 39.0, 30.4, 28.5, 23.8, 23.1, 14.1, 10.7; HRMS (ESI) calcd for C 40 H 52 Br 2 N 10 NaO 2 [M+Na] + : 887.2519, found: 887.2547. ( ± ) 6 (Benzyloxy) 9 (2 ethylhexyl) 8 (thiophen 2 yl) 9H pur in 2 amine ( 2 21 ) . Compound 2 20 (0.08 g, 0.2 mmol), Ph 3 Bi (0.03 g, 0.07 mmol), and Pd(PPh 3 ) 4 (0.04 g, 0.03 mmol) were dissolved in dry degassed xylenes (5 mL), along with 2 (tributylstannyl)thiophene (0.2 mL, 0.5 mmol). The reaction vessel was heated to r eflux for 10 min. The solvent was removed under reduced pressure. The crude product was purified by silica gel column chromatography (EtOAc:hexanes 10:90 to 40:60) to yield the product as a white solid (0.07 g, 97 %): m.p. 136 138 °C; 1 H NMR (500 MHz, CDCl 3 ): 7.53 7.51 (m, 3H), 7.44 7.43 (m, 1H), 7.36 7.33 (m, 2H), 7.31 7.28 (m, 1H), 7.13 7.11 (m, 1H), 5.59 (s, 2H), 4.86 (s, 2H), 4.21 (d, J = 7.5 Hz, 2H), 1.91 1.89 (m, 1H), 1.25 1.17 (m, 8H), 0.83 0.78 (m, 6H); 13 C NMR (125 MHz, CDCl 3 ): 160.7, 158.9, 15 6.5, 144.6, 136.7, 132.6, 128.6, 128.4, 128.1, 127.9, 127.8, 127.6, 115.4, 68.2, 47.4,

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85 38.9, 30.3, 28.3, 23.7, 23.0, 14.1, 10.6; HRMS (ESI) calcd for C 24 H 30 N 5 OS [M+H] + : 436.2166, found: 436.2187. ( ± ) 6 (Benzyloxy) 8 (5 bromothiophen 2 yl) 9 (2 ethylhexyl) 9H purin 2 amine ( 2 22 ) . In a dry round bottom flask under inert atmosphere, 2 21 (0.12 g, 0.28 mmol) was dissolved in dry THF (3 mL). To this solution, glacial HOAc (2 mL) was added and the contents of the reaction vessel were cooled to 0 °C in an ice wat er bath. Next, NBS (0.050 g, 0.30 mmol) was added and the reaction was slowly warmed to rt over 1.5 h. The solvent was removed under reduced pressure to yield the crude product, which was subsequently diluted with EtOAc (50 mL) and washed with saturated Na Cl solution (3 × 25 mL). The organic phase was dried over anhydrous Na 2 SO 4 , filtered, and evaporated to yield 2 22 as beige solid (0.13 g, 93%): m.p.: 129 131 °C; 1 H NMR (500 MHz, CDCl 3 ): 7.53 7.51 (m, 2H), 7.37 7.30 (m, 3H), 7.24 (d, J = 4.0 Hz, 1H), 7.07 (d, J = 4.0 Hz, 1H), 5.58 (s, 2H), 4.85 (s, 2H), 4.16 (d, J = 7.5 Hz, 2H), 1.94 1.86 (m, 1H), 1.25 1.22 (m, 8H), 0.84 0.80 (m, 6H); 13 C NMR (125 MHz, CDCl 3 ): 160.8, 159.0, 156.4, 143. 4, 136.6, 134.5, 130.5, 128.6, 128.5, 128.1, 127.6, 115.4, 115.2, 68.3, 47.4, 38.9, 30.3, 28.3, 23.7, 23.0, 14.1, 10.6; HRMS (ESI) calcd for C 24 H 29 BrN 5 OS [M+H] + : 516.1253, found: 516.1266. 8,8' (5,5' (Benzo[ c ][1,2,5]thiadiazole 4,7 diyl)bis(thiophene 5,2 d iyl))bis(6 (benzyloxy) 9 (2 ethylhexyl) 9H purin 2 amine) ( 2 1b) . In a dry round bottom flask under inert atmosphere, K 2 CO 3 (0.24 g, 1.8 mmol), aliquot 336 (2 drops), and Pd(dppf)Cl 2 .CH 2 Cl 2 (0.020 g, 0.020 mmol), 2 22 (0.050 g, 1.4 mmol) and 2 8 (0.11 g, 0 .22 mmol) were dissolved in degassed toluene (6 mL), followed by addition of degassed water (2 mL). The reaction was then heated to 80 °C for 17 h. The reaction

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86 mixture was diluted with EtOAc (75 mL). The organic layer was separated from the aqueous phase, and dried over anhydrous Na 2 SO 4 . The solvent was removed under reduced pressure to yield a crude red product, which was then precipitated from a mixture of CH 2 Cl 2 in hexanes to yield the red product as a mixture of stereoisomers (0.11 g, 97%): 1 H NMR (500 MHz, CDCl 3 ): 8.19(d, J = 4.0 Hz, 2H), 7.94 (s, 2H), 7.65 (d, J = 4.5 Hz, 2H), 7.56 7.52 (m, 4 H), 7.39 7.32 (m, 6 H), 5.62 (s, 4H), 4.86 (s, 4H), 4.31 (d, J = 7.5 Hz, 4H), 2.03 2.00 (m, 2H), 1.32 1.25 (m, 16H), 0.89 0.81 (m, 12H); 13 C NMR (125 MHz, CDCl 3 ): 160.8, 159.0, 156.6, 152.6, 144.4, 141.3, 136.7, 133.9, 128.7, 128.5, 128.3, 128.2, 128.1, 126.0, 125.9, 115.7, 68.3, 47.6, 39.1, 30.4, 28.4, 23.8, 23.1, 14.2, 10.7; HRMS (APCI) calcd for C 54 H 59 N 12 O 2 S 3 [M+H] + : 1003.4046, found: 1003.4026. 8,8' (5,5' (Benzo[ c ][1,2,5]thiadiazole 4,7 diyl)bis(thiophene 5,2 diyl))bis(2 amino 9 (2 ethylhexyl) 1H purin 6(9H) one) ( 2 1c) . In a dry round bottom flask under inert atmosphere, a solution of pentamethylbenzene (0.050 g, 0.32 mmol) and 2 1b (0.080 g, 0.080 mmol) i n dry degassed CH 2 Cl 2 (75 mL) was cooled to 78 °C and then a 1.0 M solution of BCl 3 in CH 2 Cl 2 (0.53 mL, 0.54 mmol) was added slowly over 15 min. The solution was stirred at 78 °C for 40 min, followed by the addition of methanol (25 mL) to quench the reac tion. The solvent was removed under reduced pressure to yield a crude purple solid 2 1c that was subsequently washed with DCM to remove impurities and afford the product as a mixture of stereoisomers (0.06 g, 95 %): 1 H NMR (500 MHz, DMSO d 6 ): 10. 85 (s, 2 H), 8.24 (s, 2 H), 8.22 (d, J = 3.5 Hz, 2H), 7.68 (d, J = 4.0 Hz, 2H), 6.72 (s, 4H), 4. 23 (d, J = 7.5 Hz, 4H), 1.88 1.86 (m, 2H), 1.23 1.20 (m, 16H), 0.82 0.75 (m, 12H); 13 C NMR (125 MHz, DMSO d 6 ): 156.1, 153.9, 153.2, 152.0,

PAGE 87

87 140.8, 139.5, 135.5, 133. 8, 128.5, 126.7, 126.3, 125.2, 47.0, 38.6, 30.1, 28.1, 23.7, 22.8, 14.2, 10.9; HRMS (APCI) calcd for C 40 H 46 N 12 NaO 2 S 3 [M+H] + : 845.2927, found: 845.2883. 8,8' ([2,2':5',2'' Terthiophene] 5,5'' diyl)bis(6 (benzyloxy) 9 (2 ethylhexyl) 9H purin 2 amine) ( 2 2b) . In a dry round bottom flask under inert atmosphere, a solution of 2 22 (0.10 g, 0.20 mmol), 2 9 (0.030 g, 0.10 mmol), K 2 CO 3 (0.22 g, 1.6 mmol), Pd(dppf)Cl 2 .CH 2 Cl 2 (0.020 g, 0.020 mmol), and aliquot 336 (2 drops) in degassed toluene (6 mL), and degassed wa ter (2 mL) was heated to 80 °C for 18 h. The solvent was removed under reduced pressure. The crude solid was dissolved in CH 2 Cl 2 , washed with water, and dried over anhydrous Na 2 SO 4 . The crude product was purified by silica gel column chromatography (EtOAc: hexanes 10:90 to 40:60) to afford 2 2b as an orange mixture of stereoisomers (0.05 g, 49%): 1 H NMR (500 MHz, CDCl 3 ): 7.53 (d, J = 6.5 Hz, 2H), 7.43 (d, J = 4.0 Hz, 2H), 7.38 7.34 (m, 4H), 7.32 7.31 (m, 2H), 7.18 (d, J = 4.0 Hz, 4H), 7.16 (s, 2H), 5.59 (s, 4H), 4.87 (s, 4H), 4.23 (d, J = 7.5 Hz, 4H), 1.97 (sep, J = 6.5 Hz, 2H), 1.29 1.26 (m, 16H), 0.87 0.81 (m, 12H); 13 C NMR (125 MHz, CDCl 3 ): 160.7, 158.9, 156.5, 144.0, 139.1, 136.7, 136.2, 131.7, 128.6, 128.5, 128.1, 128.0, 125.4, 124.2, 115.5, 68.2, 47.5, 39.9, 30.3, 28.4, 23.7, 23.1, 14.1, 10.6; HRMS (APCI) calcd for C 52 H 58 N 10 O 2 S 3 [M+H] + : 951.3979, found: 951.3987. 8,8' ([2,2':5',2'' Terthiophene] 5,5'' diyl)bis(2 amino 9 (2 ethylhexyl) 1H purin 6(9H) one) ( 2 2c) . In a dry round bottom flask under inert atmosphere, a solution of pentamethylbenzene (0.030 g, 0.18 mmol) and 2 2b (0.043 g, 0.045 mmol) in dry degassed CH 2 Cl 2 (15 mL) was cooled to 78 °C and then a 1.0 M solution of BCl 3 in CH 2 Cl 2 (0.27 mL, 0.27 mmol) was added slowly over 15 min. The solution was stirred at

PAGE 88

88 78 °C for 2 h, and then quenched with methanol (25 mL). The solvent was removed under reduced pres sure to yield a crude red solid that was subsequently washed with chloroform to remove impurities (0.03 g, 88%): 1 H NMR (500 MHz, DMSO d 6 ): 10.85 (s, 2H), 7.56 (d, J = 4.0 Hz, 2H), 7.50 7.44 (m, 4H), 6.70 (s, 4H), 4.17 (d, J = 7.5 Hz, 4H), 1.83 1.81 (m, 2H), 1.23 1.16 (m, 16H), 0.80 0.76 (m, 12H); 13 C NMR (75 MHz, DMSO d 6 ): 155.2, 154.3, 152.4, 139.6, 138.3, 135.1, 129.5, 128.4, 126.5, 125.3, 113.4, 46.8, 37.9, 29.4, 27.5, 23.1, 22.3, 13.8, 10.3; HRMS (APCI) calcd for C 38 H 46 N 10 O 2 S 3 [M+H] + : 771.3040, fou nd: 771.3007. (±) 8 (5 (Benzo[ c ][1,2,5]thiadiazol 4 yl)thiophen 2 yl) 6 (benzyloxy) 9 (2 ethylhexyl) 9 H purin 2 amine ( 2 24 ). In a dry round bottom flask under inert atmosphere, a solution of 2 22 (0.060 g, 0.13 mmol), 2 23 (0.030 g, 0.13 mmol), K 2 CO 3 (0.1 4 g, 1.0 mmol), Pd(dppf)Cl 2 CH 2 Cl 2 (0.02 g, 0.02 mmol), and aliquot 336 (2 drops) was heated to 80 °C overnight. The reaction vessel was cooled to rt, then t he solvent was removed under reduced pressure. The crude solid was dissolved in DCM , washed with wa ter, and dried over Na 2 SO 4 . The crude product was purified by silica gel column chromatography (EtOAc:hexanes 20:80) to afford the product as an orange solid (0.04 g, 55%): 1 H NMR (300 MHz, CDCl 3 ): 0.79 0.85 (m, 6H), 1.19 1.22 (m, 8H), 1.85 1.90 (m, 1H), 4.15 (d, J = 7.8 Hz, 2H), 4.87 (s, 2H), 5.58 (s, 2H), 7.06 7.08 (d, J = 3.9 Hz, 1H), 7.24 (d, J = 3.9 Hz, 1H), 7.30 7.38 (m, 3H), 7.49 7.54 (m, 2H); 13 C NMR (125 MHz, CDCl 3 ): 10.7, 14.2, 23.1, 23.8, 28.4, 30.4, 39.0, 47.6, 68.2, 115.6, 120.8, 125.8, 12 7.0, 128.1, 128.2, 128.3, 128.4, 128.4, 129.7, 133.7, 136.7, 141.4, 144.4, 152.1, 155.7, 156.6, 159.0, 160.8; HRMS (APCI) calcd for C 30 H 31 N 7 OS 2 [M+H] + : 570.2104, found: 570.2100.

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89 (±) 2 Amino 8 (5 (benzo[ c ][1,2,5]thiadiazol 4 yl)thiophen 2 yl) 9 (2 ethylhex yl) 1 H purin 6(9 H ) one ( 2 25 ). In a dry round bottom flask under inert atmosphere, a solution of pentamethylbenzene (0.030 g, 0.18 mmol) and 2 24 (0.02 g, 0.04 mmol) in dry degassed DCM (15 mL) was cooled to 78 °C and then a 1.0 M solution of boron trichl oride in methylene chloride (0.01 mL, 0.11 mmol) was added slowly over 15 min. The solution was stirred at 78 °C for 2 h, and then quenched with methanol (15 mL). The solvent was removed under reduced pressure to yield a crude orange solid that was subseq uently washed with chloroform to remove impurities (0.02 g, 99%): 1 H NMR (300 MHz, DMSO d 6 ): 0.74 0.82 (m, 6H), 1.11 1.23 (m, 8H), 1.85 1.88 (m, 1H), 4.23 (d, J = 7.8 Hz, 2H), 6.69 (s, 2H), 7.72 (d, J = 3.9 Hz, 1H), 7.82 (dd, J = 8.7, 6.9 Hz, 1H), 8.08 (d, J = 8.4 Hz, 1H), 8.19 8.22 (m, 2H), 10.85 (s, 1H) ; 13 C NMR (125 MHz, DMSO d 6 ): 10.4, 13. 7, 22.3, 22.2, 27.6, 29.5, 38.1, 46.8, 114.5, 120.7, 125.6, 125.9, 127.9, 128.0, 130.3, 132.3, 140.2, 140.2, 151.1, 152.9, 154.0, 154.8, 155.7; HRMS (APCI) calcd for C 23 H 25 N 7 OS 2 [M+H] + : 480.1635, found: 480.1655. Synthesis of U racil Terminated Oligomers ( ± ) 1 (2 Ethylhexyl)pyrimidine 2,4(1H,3H) dione ( 2 2 7 ) : A suspension of uracil 2 2 6 (2.00 g, 17.8 mmol), and anhydrous K 2 CO 3 (2.70 g, 19.6 mmol) in DMSO (20 mL), was stirred for 15 20 min. 2 ethylhexyl bromide (4.80 mL, 26.7 mmol) was added and the reaction mixture was stirred for 20 hours at 40 °C. The suspension was diluted with EtOAc, washed with H 2 O (20 mL x 2), and brine (20 mL x 2), and dried over Na 2 SO 4 . The organic layer was concentrated under reduced pressure and poured into cold hexane. The resulti ng precipitate was filtered and washed with hexane to afford compound 2 27 (0.8 g, 29 %) as a white solid: m.p. 80 82 °C; 1 H NMR (300 MHz, CDCl 3 ): 8.80 (s, 1H), 7.10 (d, J = 7.8 Hz, 1H), 5.68 (d, J = 7.8 Hz, 1H), 3.61 (d, J = 7.2

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90 Hz, 2H), 1.77 1.72 (m, 1H), 1.33 1.28 (m, 8H), 0.93 0.87 (m, 6H); 13 C NMR (75 MHz, CDCl 3 ): 164.1, 151.3, 145.0, 101.9, 52.4, 38.9, 30.2, 28.5, 23.5, 23.0, 14.1, 10.5; HR MS (ESI) calcd for C 12 H 20 N 2 O 2 [M+Na] + : 247.1417, found: 247.1426. ( ± ) 5 Bromo 1 (2 Ethylhexyl)pyrimidine 2,4(1H,3H) dione ( 2 2 8 ) : To a solution of 2 2 7 ( 0.50 g, 2.4 mmol) in dry DMF (20 mL), NBS ( 0.50 g, 2.6 mmol) was added. The reaction mixture was stir red for 15 minutes at rt. The solvent was removed under reduced pressure, and the resulting suspension was poured into cold hexanes. The resulting precipitate was filtered and washed with water to afford compound 2 2 8 as a white solid (0.7 g, 60 %): m.p. 1 56 158 °C; 1 H NMR (300 MHz, CDCl 3 ): 9.43 (s, 1H), 7.45 (s, 1H), 3.31 (d, J = 7.2 Hz, 2H), 1.75 1.71 (m, 1H), 1.32 1.28 (m, 8H), 0.93 0.88 (m, 6H); 13 C NMR (75 MHz, CDCl 3 ): 164.1, 155.2, 150.6, 144.3, 96.2, 52.8, 38.0, 30.1, 28.5, 23.0, 14.1, 10.5; HRMS (ESI) calcd for C 12 H 19 BrN 2 O 2 [M+H] + : 303.0703/305.0683, found: 303.0707/305.0685. ( ± ) 1 (2 Ethylhexyl) 5 (thiophen 2 yl)pyrimidine 2,4(1H,3H) dione ( 2 2 9 ) . 2 Tributylstannylthiophene (1.70 mL, 5.30 mmol) was added to a solution of 2 2 8 (0.40 g, 1.3 mmol) and Pd(PPh 3 ) 4 (0.10 g, 0.10 mmol) in dry and degassed 1,4 dioxane (30 mL), then stirred at 120 °C overnight. The reaction mixture was cooled to rt, then concentrated under reduced pressure. The crude product was purified by silica gel column chromatography (EtOAc:hexanes 20:80) to afford the title compound 2 2 9 as a white solid (0.30 g, 63%): m.p. 88 90 °C; 1 H NMR (500 MHz, CDCl 3 ): 8.85 (s, 1H), 7.46 (s, 1H), 7.42 (dd, J = 3.5, 1 Hz, 1H), 7.30 (dd, J = 5, 1 Hz, 1H), 7.10 (dd, J = 5.5, 4 Hz, 1H), 3.71 (d, J = 7.5 Hz, 2H), 1.82 1.80 (m, 1H), 1.40 1.29 (m, 8H), 0.95 0.89 (m, 6H); 13 C NMR (75 MHz, CDCl 3

PAGE 91

91 109.7, 52.7, 38.9, 30.1, 28.5, 23.5, 23.1, 14.1, 10.5; HRMS (ESI) calcd for C 16 H 22 N 2 O 2 S [M+Na] + : 329.1294, found: 329.1288. ( ± ) 5 (4,5 Dibromothiophen 2 yl) 1 (2 ethylhexyl)pyrimidine 2,4(1H,3H) dione ( 2 31 ) . NBS (0.15 g, 0.83 mmol) was added portionwise to a solution of (±) 1 (2 ethylhexyl) 5 (thiophen 2 yl)pyrimidine 2,4(1H,3H) dione 2 2 9 (0.25g, 0.76 mmol) in THF (10 mL) and AcOH (10 mL) at 0 °C. The reaction mixture was stirred for 30 minutes then warmed to rt, poured in water and extracted with DCM (3 × 25 mL). The organic layer was dried over Na 2 SO 4 , and concentrated under reduced pressure. The crude soli d was purified by column chromatography on silica gel (EtOAc:hexanes 20:80) to afford the product as a white solid (0.17 g, 45%): m.p. 150 152 °C; 1 H NMR (500 MHz, CDCl 3 ): 9.38 (s, 1H), 7.93 (s, 1H), 6.98 (s, 1H), 3.71 (d, J = 7.5 Hz, 2H), 1.82 (sep, J = 6 Hz, 1H), 1.43 1.25 (m, 8H), 0.94 0.88 (m, 6H); 13 C NMR (75 MHz, CDCl 3 ): 161.8, 150.1, 144.2, 132.3, 129.5, 114.4, 107.3, 106.9, 53.1, 39.1, 30.3, 28.6, 23.5, 23.1, 14.2, 10.6; HRMS (ESI) calcd for C 16 H 20 Br 2 N 2 O 2 S [M+Na] + : 486.9484, found: 486.9486. 5,5 ' (Benzo[ c ][1,2,5]thiadiazole 4,7 diylbis(thiophene 5,2 diyl))bis(1 (2 ethylhexyl)pyrimidine 2,4(1H,3H) dione) ( 2 1d) : Compound 2 2 8 (0.45 g, 1.5 mmol) and PdCl 2 (PPh 3 ) 2 (0.11 g, 0.15 mmol) were mixed in dry and degased 1,4 dioxane (8 mL), 2 11 (0.10 g, 0.8 3 mmol) was added to the solution and it was stirred at 100 °C overnight. The solvent was removed under reduced pressure and the crude was purified by silica gel column chromatography (EtOAc:hexanes 80:20) to afford the target compound 2 1d as a dark red s olid (mixture of stereoisomers) (0.28g, 50 %). 1 H NMR (500 MHz, DMSO d 6 ): 11.73 (s, 1H), 8.47 (s, 1H), 8.13 (d, J = 6.5 Hz, 1H), 8.06 (s,

PAGE 92

92 1H), 7.66 (d, J = 6.5 Hz, 1H), 3.73 (d, J = 11 Hz, 2H), 1.89 1.78 (m, 1H), 1.27 1.22 (m, 8H), 0.90 0.83 (m, 6H); 13 C NMR (150 MHz, DMSO d 6 ): 161.6, 151.7, 149.9, 141.6, 137.6, 135.9, 126.8, 125.3, 124.8, 123.3, 107.3, 51.6, 37.7, 29.3, 27.8, 22.8, 22.4, 13.9, 10.3; HRMS (ESI) calcd for C 38 H 44 N 6 O 4 S 3 [M+H] + : 745.2659, found: 745.2642. 5,5' ([2,2':5',2'' Terthiophene] 5, 5'' diyl)bis(1 (2 ethylhexyl)pyrimidine 2,4(1H,3H) dione) ( 2 2d) : Compound 2 2 8 (0.1 g, 0.3 mmol) and PdCl 2 (PPh 3 ) 2 (0.02 g, 0.03 mmol) were mixed in dry and degased 1,4 dioxane (8 mL), 2 1 8 (0.1 g, 2.0 mmol) was added to the solution and it was stirred at 100 °C overnight. The solvent was removed under reduced pressure and the crude was purified by silica gel column chromatography (EtOAc:hexanes 80:20) to afford the target compound 2 2d (mixture of stereoisomers) as a dark orange solid (0.08g, 70 %). 1 H NMR (300 MHz, CDCl 3 ): 8.47 (s, 1H), 7.47 (s, 1H), 7.33 (d, J = 4 Hz, 1H), 7.11 (d, J = 3.5 Hz, 2H), 3.72 (d, J = 6.5 Hz, 2H), 1.83 1.81 (m, 1H), 1.41 1.21 (m, 8H), 0.96 (m, 6H); 13 C NMR (75 MHz, CDCl 3 161.2, 149.8, 139.5, 137.1, 136.2, 132.4, 125.0, 124 .6, 123.7, 109.5, 52.9, 38.1, 30.2, 28.5, 23.6, 23.1, 14.2, 10.6; HRMS (ESI) calcd for C 36 H 44 N 4 O 4 S 3 [M+H] + : 693.2597, found: 693.2606. Attempted S ynthesis of C ytosine Terminated Oligomers ( ± ) 4 Amino 1 (2 ethylhexyl)pyrimidin 2(1H) one ( 2 3 3 ) . (Bu) 4 NOH (18 .0 mL, 72.0 mmol) was added to a suspension of cytosine 2 3 2 (2.00 g, 18.0 mmol) in DMF (200 mL), followed by dropwise addition of 2 ethylhexyl bromide (6.40 mL, 36.0 mmol) within 10 min. The mixture was stirred at rt overnight, then concentrated under red uced pressure, and precipitated from hexane. The resulting precipitate was filtered and washed with water to afford the product 2 3 3 (2.30 g, 57 %) as a white solid: m.p. 201 203 °C; 1 H NMR (300 MHz, CDCl 3 ): 7.50 (d, J = 6.9, 1H), 6.93 (bs, 2H), 5.61 (d, J =

PAGE 93

93 7.2 Hz, 1H), 3.51 (d, J = 7.2 Hz, 2H), 1.73 1.69 (m, 1H), 1.25 1.16 (m, 8H), 0.87 0.79 (m, 6H); 13 C NMR (75 MHz, CDCl 3 ): 164.7, 155.9, 146.4, 92.7, 52.3, 37.7, 29.6, 28.0, 23.0, 22.4, 13.9, 10.3; HRMS (ESI) calcd for C 12 H 21 N 3 O [M+H] + : 224.1757, foun d: 224.1767. ( ± ) 4 Amino 5 bromo 1 (2 ethylhexyl)pyrimidin 2(1H) one ( 2 3 4 ) . NBS (0.90 g, 5.0 mmol) was added to a solution of 2 3 3 (1.00 g, 4.50 mmol) in dry DMF (100 mL). The reaction mixture was then stirred for 2 h at rt. The solvent was concentrated u nder vacuum. The crude product was dissolved in DCM, washed with 5% Na 2 S 2 O 3 (20 mL), and brine (20 mL), then dried over Na 2 SO 4 . The organic layer was concentrated under reduced pressure and purified by column chromatography on silica gel (MeOH:DCM 5:95) to afford the product 30 as a pale yellow solid (0.60 g, 45 %): m.p. 131 133 °C; 1 H NMR (300 MHz, CDCl 3 ): 8.04 (s, 1H), 7.64 (s, 1H), 6.82 (s, 1H), 3.56 (d, J = 7.5 Hz, 2H), 1.75 1.71 (m, 1H), 1.25 1.18 (m, 8H), 0.86 0.80 (m, 6H); 13 C NMR (75 MHz, CDCl 3 ): 162.6, 155.5, 145.8, 86.7, 54.1, 38.6, 30.1, 28.5, 23.5, 23.1, 14.1, 10.5; HRMS (ESI) calcd for C 12 H 20 BrN 3 O [M+H] + : 302.0863/304.0843, found: 302.0866/304.0852. Photophysical Measurements and Additional Data Absorption M easurements Absorption spectra purines on a Perkin Elmer Lambda 25 dual beam absorption spectrometer and a Cary 100 Bio spectrophotometer using 1 cm quartz cells. All solvents were HPLC grade (purchased from Fisher) and stored over 4 Å molecular sieves . The absorption intensity at max was then plotted against the concentration in all cases to confirm, by linearity,

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94 Molar extinction coefficients ( ) were determined from the linear plot for each compound (where A = ). Steady State F luorescence and Q uantum Y ield M easurements Steady state fluorescence emission spectra were recorded on a SPEX Fluoromax spectrophotometer. The optical density of each compound was less than 0.1, and the sample concentration ranged from 5 10 M . Two additional precautions were taken: a) the optical density of the standard and the sample were matched within 0.002 absorbance units, and b) a 385 LP filter was used during the measurements ( ex = 320 nm). In numerous repeated experiments we have found excellent reproducibility and comparable data even without these precautions. The following equation was used to calculate the fluorescence quantum yield ( F ): F(x) = ( A s / A x )( x s )( x / s ) 2 F(s) A is the absorbance at the excitation wavelength, F is the area under the emission curve, and is the refractive index of the solvent used. Subscripts s and x refer to the standard and unknown, respectively. Quantum yields were calculated using quinine sulfate in 0.1 M H 2 SO 4 ( F = 0.577) as the standard. Fluorescence L ifetime M easurements in 1,4 dioxane Lifetime measurements were carried out using a PicoQuant FluoTime 100 compact fluorescence lifetime spectrometer. Samples for fluorescence lifetime measurements were prepared b y making ~ 5 M solutions of each compound in 1,4 dioxane for spectroscopy. Each compound was excited at 375 nm and the monochromater was set to the corresponding em(max) for each compound. After the measurement of each compound, a scattering agent (Lud ox ® AM 30 colloidal silica,

PAGE 95

95 30% wt. % suspension in water) was measured under the same parameters as the compound in order to find the instrument response time. The instrument response time along with the data collected for each sample was placed into the Picoharp to generate the fluorescence lifetime data. Deviations from the best fit are characterized by the reduced chi square statistic, 2 . The best results typically produce 2 s of 0.9 to 1.2. Electrochemistry Cyclic Voltammetry (CV) and Differential Pulse Voltammetry (DPV) measurements were performed for 2 1a , 2 1b , and 2 1c in an argon filled drybox (Vacuum Atmospheres) using a single compartment three electrode cell with a platinum flag as the counter electrode, a Ag/Ag + non aqueous reference electr ode calibrated versus Fc/Fc + in 0.1 M TBAPF 6 acetonitrile solutions (E 1/2 (Fc/Fc + ) = 0.10 V vs Ag/Ag + ), and a platinum disk (0.02 cm 2 ) as the working electrode. Tetrabutylammonium hexafluorophosphate (TBAPF 6 ) was purchased from Aldrich, recrystallized twic e from absolute ethanol and dried under vacuum. DMF was collected from an Innovative Technologies solvent system, sparged with Ar and passed over two columns of 5 Ã… activated sieves. The oligomer solid was dissolved to a concentration of 3.5 mM in a 0.1 M TBAPF 6 /DMF electrolyte. An EG&G Princeton Applied Research model 273A potentiostat/galvanostat was used under the control of Corrware II software from Scribner and Associates. The scan rate for CV was 50 mV/s. Cyclic Voltammetry (CV) and Differential Puls e Voltammetry (DPV) measurements were performed for 2 1d and 2 2a d using a single compartment three electrode cell under argon blanket with a platinum flag as the counter electrode, a silver wire quasi reference electrode calibrated versus Fc/Fc + in 0.1 M TBAPF 6 acetonitrile

PAGE 96

96 solutions (E 1/2 (Fc/Fc + ) = 0.10 V vs Ag/Ag + ), and a platinum disk (0.02 cm 2 ) as the working electrode. Tetrabutylammonium hexafluorophosphate (TBAPF 6 ) was purchased from Aldrich, recrystallized twice from absolute ethanol and dried un der vacuum. DMF was collected from an Innovative Technologies solvent system, sparged with Ar and passed over two columns of 5 Ã… activated sieves. The oligomer solid was dissolved to a concentration of 3.5 mM in a 0.1 M TBAPF 6 /DMF electrolyte. A Voltammet ric Analyzer potentiostat/galvanostat was used under the control of BAS CV 50W software from Bioanalytical Systems. The scan rate for CV was 50 mV/s. Computational Analysis Starting geometries were obtained from semi empirical calculations using the MM2 m ethod as implemented in Chem3D Pro v. 13.0.0.3015 for Windows. The ground state geometries, energies and orbital energies were then obtained from DFT calculations at the B3LYP/6 31+G** level as implemented in Gaussian 09, 95 accessed through the UF High Performance Computing Center. F requency calculations were performed at the same computational level, and no imaginary frequencies were found. Molecular orbital plots were made using GaussView v. 5.0.8 98 from the Gaussian output files.

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97 CHAPTER 3 SYNTHESIS, CHARACTERIZATION, AND COMPLEMENTARY HYDROGEN BONDING OF CONJUGATED NUCLEOBASE OLIGOMERS Introductory Remarks Nature employs simple molecular scaffolds with embedded genetic codes to nucleic acids, or peptides) have the inheren t ability to self assemble into well defined suprastructures. 1, 99 These attractive built in structural and functional molecular char acteristics have enticed chemists to make key strides in learning the fundamental rules of non covalent bonding. 2 The manipulation of these supramolecul ar interactions has helped them to build self assembling systems with modest to high degrees of complexity. 67a, 100 Although different classes of self associating biomolecules have been explored, 67a, 100 systems has been modestly considered. conjugated systems are the main focus of organic electronic applications (e.g, OPV, OFET, OLED) as a consequence of their semiconductive properties. In addition to the conjugated molecules on surface s or in the bulk is of utmost importance for a high performing organic device. 101 Accordingly, cooperative non covalent interactions have been introduced to achieve programmed self assembly, 34 35, 102 t renowned example; the double stran ded DNA, wherein the stacks of nucleobases allow charge transport to occur along their axis 103 while the size and geometry of the double helix is reinforced by directional and specific hydrogen bonding between the complementary purines and pyrimidines.

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98 In the pursuit of crea ting advanced materials that merge the complex molecular recognition motifs found in biomolecules with electronic properties suitable for device applications, nucleobases hold tremendous promise as potential scaffolds structurally (via non covalent interac tions) and electronically (as described in Chapter 2). The previously investigated nucleobase containing conjugated oligomers displayed a contribution of the nitrogen rich heterocycles to the optical and electronic properties of the systems (Chapter 2), in addition to a dependence of said properties on the nucleobase identity. 104 While nucleobases have th e inherent ability to self assemble into well defined suprastructures, their poor intrinsic photophysical properties, including visible light absorption and emission, 22 has prevented their entry into some electronic devices applications . However as discussed in Chapter 2, these downfalls can be o vercome by extending the nucleobase conjugated surface. Although compounds 2 1a d and 2 2a d have the potential to assemble utilizing a variety of non covalent interactions, their limited solubility presented an obstacle to studying their complementary self assembly. Therefore, more soluble variants of compounds 2 2a d were obtained by swapping a terminal nucleobase by a solubilizing group. Reported here is the synthesis of the natural nucleobases conjugated to a short oligothiophene fragment. Again, th e Watson Crick base pairing edges of the purines or pyrimidines are preserved by having the heterocycles installed in terminal positions (Figure 3 1). The sugar moieties are substituted by 2 ethylhexyl chains to improve solubility in common organic solvent s. In this work we also study the optical and electronic properties of all synthesized compounds, as well as the hydrogen bonding

PAGE 99

99 dimerization and hetero association processes between 3 1 and a uracil cap 2 2 7 by 1 H NMR, and analyze the binding isotherms b y adequate fitting programs in order to obtain the corresponding association constants in chloroform d . Synthesis Adenine Terminated Oligomer The synthesis of adenine terminated conjugated oligomer 3 1 is illustrated in Scheme 3 1. Suzuki coupling of 2 7 , obtained according to synthesis scheme 2 1, to commercially available boronic ester 3 7 generated the product 3 1 in 69% yield. Scheme 3 1 . S ynthesis of Adenine Terminated Oligomer 3 1 . Guanine Terminated Oligomer The synthesis of guanine terminated conjugated oligomer 3 4 followed the same protocol developed in Chapter 2. Two different routes were adopted to generate the target compound. Bot h benzyl and methyl protecting gro ups were evaluated to avoid represented in Scheme 3 2, wherein compound 3 8 was prepared in 80 94% yield by the reaction of 2 13 and sodi um methoxide in methanol. Upon reaction with NBS in DMF, compound 3 8 gave 52 90% yield of 3 9 , whose Stille cross coupling with 2 (tributylstannyl)thiophene in the presence of triphenylbismuth afforded 3 10 in good yield (82 94%). Subsequent bromination o f 3 10 using NBS in THF/AcOH provided intermediate 3 11 . Then, both protected guanine derivatives 2 22 and 3 11 were

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100 reacted with 3 7 under Suzuki cross coupling conditions to deliver 3 2 ( ) and 3 3 (46%), respectively. Treatment of 3 2 and 3 3 with BBr 3 in the presence of pentamethylbenzene as a cation scavenger afforded guanine derivative 3 4 (Scheme 3 2). Scheme 3 2 . S ynthesis of Guanine Terminated Oligomer 3 4 . Uracil Terminated Oligomer The synthesis of the urac il derivative proved to be troublesome. Initial attempts to synthesize (5'' hexyl [2,2':5',2'' terthiophen] 5 yl)trimethylstannane , to be used as a coupling partner with 2 2 8 , were not successful. Given that all efforts made towards the bromination of 2 2 9 (Scheme 2 7) failed to generate the desired product under several conditions (Table 2 3), we resorted to the iodination of 2 2 9 (Scheme 3 2). Likewise, we encountered the problem of diiodination. For instance, the usage of NIS as the iodo source generated exclusively 3 13 (Entry 1, Table 3 1). 105 However, under argon atmosphere, elemental iodine in the presence of CAN as the in situ oxidant, delivered a y ellow compound, believed to be 3 12 a . in very low yield (~10%), which was increased

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101 to 15% by running the reaction in the presence of aerial oxygen in order to re oxidize Ce(III), generated throughout the process, to Ce(IV) (Entry 2, Table 3 1). 106 The amount of yellow product obtained was further improved (18%) by reducing the equivalents of iodine by half (Entry 3, Table 3 1). Nonetheless, the best yield attained was obtained by replacing I 2 with lithium iodide in the presence of excess C AN (Entry 4, Table 3 1). Scheme 3 3 . Attempted s ynthesis of 3 12 a . Table 3 1 . Solubility of uracil derivatives in chloroform Entry a Conditions Product (yield) 1 105 NIS, TFA, DCE, 80 °C, 2 h 3 13 (56) 2 106 I 2 (1.2 eq), CAN (0.5 eq), MeCN, rt, 1 h 3 12 b (15%), 3 13 (32%) 3 107 I 2 (0.6 eq), CAN (0.5 eq), MeCN, rt, 1 h 3 12 b (18%), 3 13 (22%) 4 107 LiI (1.2 eq), CAN (2 eq), MeCN, rt, 1 h 3 12 b (20%), 3 13 (21%) a Lead references are given for the conditions used based on similar uracil derivatives as star ting materials. With the intention of avoiding basic Suzuki cross coupling conditions, the small amount of presumably 3 12 a in hand was subjected to Stille c onditions with (5' hexyl [2,2' bithiophen] 5 yl)trimethylstannane 3 14 , synthesized according to a literature procedure 108 (Scheme 3 4). Despite following the same successful conditions used to prepare 2 2 9 , this reaction failed to proceed (starting material was recovered). The unsuccessful coupling reaction pro mpted us to further investigate the yellow starting material. 1 H 13 C gHMBC NMR showed inconsistency in the chemical shift of C(5) of the thiophene ring (Scheme 3 3) , a downfield shift was observed, indicating the presence of an electron withdrawing group o n that position. Finally MS results proved the presence of a nitro group ( 3 12b ). More effort s will be devoted to obtaining the product 3 12a for

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102 further studies with its complementary adenine analogue. Protection of N(3 ) of uracil is currently under inves tigation as an entry to these targets. Scheme 3 4 . Attempted s ynthesis of 3 5 . Cytosine Terminated Oligomer To circumvent the previous challenges encountered with extending the conjugation of cytosine from the bromo deriv ative 2 3 4 , we investigated the iodination of the C(5) position of 2 3 3 as a possible alternative. Accordingly, intermediate 3 15 was obtained in the presence of iodine, and iodic acid in acetic acid in moderate yield (59%), but it failed to react with 2 ( tributylstannyl)thiophene under Stille conditions (not shown). However Suzuki coupling of 3 15 with thiophen 2 ylboronic acid was successful in THF/H 2 O, although the same reaction failed to proceed in a mixture of toluene/H 2 O. Subsequent iodination of 2 3 5 using NIS in DCE with a catalytic amount of TFA provided intermediate 3 1 6 , which was reacted with 3 7 under Suzuki cross coupling conditions to furnish 3 6 which was isolated as an inseparable mixture of product and starting material in a 5:1 ratio (Sche me 3 6).

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103 Scheme 3 5 . S ynthesis of 3 6 . Thermal Properties The thermal stability of the pure target compounds was evaluated by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) in order to und erstand the intrinsic properties of these materials and how they differ among nucleobases. The adenine derivative 3 1 showed loss of 5% of the original compound weight at relatively high temperature, 293 °C (Figure 3 1a). Although not observed with the sym metrical compound 2 2a , compound 3 1 showed loss of 20% of its original compound weight at around 348 ° C, which corresponds in mass to the loss of the ethylhexyl side chain. High thermal stability was also observed for 3 2 and 3 3 , which showed loss of 5% of the original compound weight at 301 and 331 °C (Figures 3 1a), respectively. Both 3 2 and 3 3 showed stepwise decomposition: W hile 3 2 showed loss of ~38% of its original compound weight at 456 °C, attributed to the loss of the benzyl group and the term inal hexylthiophene, compound 3 3 showed loss of ~40% at 446 °C ascribed to the loss of the terminal hexylbithiophene. On the other hand, 3 4 tended to

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104 trap solvent molecules, as evidenced by enhanced thermal stability upon longer vacuum drying of the soli ds prior to measurement (Figures 3 1a). Table 3 2 . Thermal properties of compounds 3 1 4 m aterial 5% Weight Loss (°C) T m ( °C ) a 3 1 293 135 3 2 303 116 3 3 331 101 3 4 229 a The 1 st heating scan cycles were employed to determine the thermal trans ition temperatures, at a scan rate of 10 °C/min, under N 2 atmosphere . Figure 3 1 . a) The TGA ; and b) DSC for 3 1 4 compounds operated at a heating r ate of 10 °C/min under nitrogen . DSC reveals a melting transition ( T m ) for three of the materials but no t for 3 4 (Figure 3 1b). These observations are an indirect evidence for the strong hydrogen bonding aggregation of 3 4 where the compound decomposes before melting. Likewise, the higher melting transition of 3 1 (135 ° C), relative to 3 2 (116 ° C) and 3 3 (101 ° C) (Table 3 2), speaks to the ability of adenine to self aggregate compared to 3 2 and 3 3 . Optical Properties The UV vis absorption spectra of 3 1 4 were collected in dilute solution (DMF; 20 × 10 6 M) (Figure 3 2); the corresponding data are listed in Table 3 3. All spectra b) a)

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105 displayed a single absorption band assigned to a * transition. When comparing the absorbance spectra of 3 1 4 , guanine 3 4 and protected guanine derivatives 3 2 and 3 3 presented very similar optical properties with a maximum absorbance ranging between 409 412 nm, whereas their onset remained unchange d, giving rise to identical optical gaps ( E opt = 2.60 eV ) . On the other hand, the absorption spectr um of 3 1 displayed a hypsochromically shifted band centered at 4 03 nm, along with a slightly blue shifted onset with respect to the other derivatives 3 2 4 . Therefore compound 3 1 displayed a faintly higher optical gap ( E opt = 2.65 eV ). Table 3 3 . Absorption Properties of 3 1 in DMF a compound abs max (nm) b abs onset (nm) c 10 4 (M 1 cm 1 ) E opt (eV) d 3 1 403 467 3.6 ± 0.03 2.65 3 2 412 477 4.0 ± 0.03 2.60 3 3 411 477 4.3 ± 0.02 2.60 3 4 409 476 3.2 ± 0.01 2.60 a All measurements were performed at room temperature and at 15 × 10 6 M. b Lo west energy absorption maxima. abs max (nm) ± 1 nm . c Onset of l o west energy absorption abs onset (nm) ± 1 nm . d E opt (eV) ± 1 nm . In all cases, the spectra follow the Beer Lambert law, over almost an order of magnitude increase in concentration (5 × 10 6 20 × 10 6 M), suggesting that the compounds 3 1 4 do not aggregate in solution at the concentrations used. Furth ermore, the intensity and molar extinction coefficient of 3 1 are within the same order of magnitude (See Table 3 3 ) .

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106 Figure 3 2 . Absorption spectra ( 20 × 10 M) for 3 1 in DMF . Electronic Properties The redox properties of 3 1 4 were investigated by cyclic voltammetry (CV) in DMF with NBu 4 PF 6 as the supporting electrolyte (Table 3 4). Due to the noisy onsets obtained from DPV measurements, CV data was used to determine the corresponding energy levels. The two following equations were again used to estimate the HOMO and LUMO levels. E HOMO = ( E onset ox + 5.1) eV E LUMO = ( E onset red + 5.1) eV where E onset red and E onset ox are the onset oxidation and reduction potentials measured for the compounds in solution versus the Fc/Fc + reference. The cyclic voltammograms of 3 1 4 showed the same features: a single irreversible oxidation, commonly observed for purine derivatives, 29a, 93a, 109 and an irreversible reduction band within the accessible solvent window. Give n the irreversibility moderate current response occurring at the onset, 91 the maximum peaks were used to

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107 determine the corresponding potentials. Guanine derivative 3 4 displayed the lowest oxidation potential at 0.36 V vs. Fc/Fc + (CV values) compared to its protected derivati ves 3 2 and 3 3 (0.69 V and 0.66 V respectively), resulting in a smaller energy gap despite comparable optical data (Table 3 4). Again experimental results were in agreement with literature reports regarding the ease of oxidation of unprotected guanine rel ative to the other nucleobases 94 (Table 3 4). While the reduction potentials and the respective LUMO values of 3 1 4 are approximate, the oxidation potentials and the equivalent HOMO levels differ depending on the nature of the nucleobase, giving access to a certain degree of tunability of the HOMO level of these oligomers. The HOMO and LUMO energies of 3 6 were calculated, and the structural geometries were optimized at the B3LYP/6 31+G** level of theory (as impl emented in Gaussian 09 95 ). I n all cases, the 2 ethylhexyl and the terminal hexyl groups were truncated to methyl groups to reduce computational time, since they do not significantly affect the equilibrium geometries or electronic properties. Oligomers 3 5 are quite planar ( Figure 3 cytosine derivative 3 6 angle is ~42 °. The conformations illustrated in Figure 3 4 represent the global minima assigned based on the calcula tions reported in Chapter 2 ( Figure 2 11 and 2 12). Likewise, the most favorable conformation of the cytosine derivative has been determined through calculations using truncated version 2 33 ( Figure 3 4 ) .

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108 Table 3 4 . Electronic Properties of 3 1 4 comp ound experimental DFT calculations a E max ox (V) b 0.1 E max red ( V) b 0.1 HOMO (eV) c 0.1 LUMO (eV) c 0.1 E g electro chemical (eV) 0. 2 E g optical d (eV) 0. 2 HOMO (eV) LUMO (eV) E g (eV) 3 1 0.77 1.48 5. 87 3. 62 2. 25 2.65 5. 32 2.29 3.03 3 2 0.6 9 1.48 5. 79 3. 62 2.17 2.60 5.1 5 2.16 2. 99 3 3 0.66 1.50 5. 76 3. 60 2.16 2.60 5.11 2.14 2.97 3 4 0.36 1.53 5. 46 3. 57 1. 90 2.60 5. 13 2.08 3.00 3 5 5. 28 2 . 28 3.00 3 6 5. 43 2 . 17 3.26 a All ethylhexyl and hexyl groups have bee n replaced by methyl groups for the calculations. Geometry optimization and calculation of the HOMO and LUMO energies was performed at the B3LYP/6 31+G** level. b Energies are reported relative to Fc/Fc + redox couple and are obtained from CV experiments; t he solvent employed is N,N dimethylformamide (DMF) ( 0.1 mM TBAPF 6 at a 100 mV/s scan rate) . c Estimated HOMO and LUMO energy levels (relative to vacuum) based on electrochemical potentials ( E 1/2 ox and E 1/2 red , respectively) determined in DMF (0.1 M TBAPF 6 at a 100 mV/s scan rate). d Determined based on UV absorption data in DMF .

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109 Figure 3 3 . Conformational analysis of 2 33 based on B3LYP/6 31G** calculations. 2 Et Hx groups have been truncated to methyl groups for the calculations . F rontier MO plots ar e presented in Figure 3 5 for 3 1 6 . The LUMO of the purine derivatives 3 1 4 conjugated terthiophene moiety, while the HOMO is distributed throughout the backbone with more contribution from the nucleobase . These observations corre late well with the electrochemical data (Table 3 4), as the LUMO is slightly affected by the changes in the purine structure, meanwhile more pronounced differences are found for the HOMO levels. This is not the case for the pyrimidine derivatives 3 5 and 3 6 . Uracil and cytosine contribute differently to the electronic structure of their corresponding oligomers ( 3 5 and 3 6 ) , hence the variations in both the HOMO and the LUMO with respect to each other. While uracil has more influence on the LUMO level, cyt osine contributes more to the HOMO which speaks to the difference in the electron donating and withdrawing character of the C(4) position of the pyrimidine ring (NH 2 vs. CO). The computed HOMO and LUMO energies, and E g values, of all compound s are summarized in Table 3 4.

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110 Figure 3 4 . Calculated HOMO and LUMO plots for 3 1 6 based on B3LYP/6 31G** calculations. 2 Et Hx and hexyl groups have been truncated to methyl groups for the calculations .

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111 Evaluation of Dimerization Constants Intere sted in analyzing quantitatively the intermolecular interactions between the complementary nucleobases, 1 H NMR dilution and titration experiments were carried out. However, before evaluating these hetero association equilibrium constants, the extent of sel f aggregation needed to be ascertained. 110 Considering a monomer dimer equilibrium system represented by Equation 3 1: M + M D ( 3 1) The dimerization constant characterizing this system can be expressed as follow s : ( 3 2) The chemical shifts for the relevant nuclei ( obs ), represented by E quation 3 3 as the weighted average of the shifts of monomer and dimer, was given by Gutowsky and Saika 111 as: ( 3 3) [M] 0 = [M] + 2[D] ( 3 4) where m is the monomer shift, d is the dimer shift, and [M], [D], and [M] o are monomer, dimer, and total concentration, respectively. f m and f d are mole fractions of M which are in the form of monomer and dimer, respective ly ( f m + f d = 1). The mole fractions can be expressed in terms of chemical shift according to Equations 3 5 and 3 6. f m = ( 3 5 ) f d = ( 3 6 ) Solving Equations 3 5 and 3 6 for [M] and [D] respectively, and inserting them into the equilibrium expression (Equation 3 2) gives Equation 3 7:

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112 ( 3 7) Assuming the presence of one dimeric form, Equations 3 5 and 3 6 are substituted into Equation 3 7 followed by taki ng the square root to generate Equation 3 8 ( 3 8) The numerical value of K dim is then obtained by knowing the values of d and m to a certain degree of accuracy. It is possible to find d at low temperature or high concentratio n or by just extrapolating a value for d from a plot of chemical shift vs. concentration. In contrast, m is determined at low concentration and/or high temperature. However, the sensitivity of the NMR instrument hinders the direct measurement of m . Ther efore, t he chemical shift obs as a function of total concentration [M] o can be estimated by fitting the three unknown parameters d , m , and K dim . The selected fitting program guesses a value for d , m , and K dim for each point in the dilution. Some preca utions should be taken into consideration when setting up concentration conditions for the dilution or titration experiments. Measurements below 20% a nd above 80% complexation ratio cause transfer of error from the complexation ratio into K , 112 and outside this saturation range the associated error increases exponentially. 112 Dilution studies, at concentrations ranging between 10 100 mM, were performed at room temperature fo r compound 2 2 7 (instead of 3 5 ) and 60 225 mM for adenine derivative 3 1 separately, in order to determine their extent of self aggregation. Thus , the intermolecular dimerization constants K dim of 2 2 7 and 3 1 were obtained by

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113 monitoring the N(3) H and NH 2 chemical shifts, respectively , by 1 HNMR. The K dim values were found to be 15 ± 1 .8 (20 60% bound) for 2 2 7 and 3 ± 0. 3 ( 20 40 % bound) for 3 1 (Figure 3 6). These values are the average of two runs calculated using standard software. 113 The lo w degree of self association of nucleobase derivatives 2 2 7 and 3 1 in chloroform are of the same order of magnitude and consistent with literature values commonly described for uracil and adenine derivatives. 41 Figure 3 5 . Concentration dependent 1 HNMR spectra for a) 2 2 7 and c) 3 1 ; 1 HNMR binding isotherm for b) 2 2 7 and d) 3 1 . Determination of Stoichiometry Nucleobases broadly employ a variety of cooperative and non covalent interaction s to hold the DNA double helix together and encode our genetic profiles . a) d) c) b)

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114 They nicely show a high degree of selectivity and fidelity in solution through the , it is reasonable to assume the pres ence of only one type of complex in the case of 2 2 7 and 3 1 . Given the dependence of the execution and analysis of supramolecular titrations on the stoichiometry of host and guest, 114 it is important to confirm the 1:1 stoichiometry between 2 2 7 and 3 1 before proceeding to the next step. Therefore , we can consider the basic equation for 2 2 7 and 3 1 complexation: H + G ( 3 9) Where H is the host ( 3 1 ), G is the guest ( 2 2 7 ), and is the complex ( 3 1 2 2 7 ) formed; a , b represent the stoichiometry shown in Equation 3 9. The Continuous Varia tion Method 115 or Job plot has gained substantial popularity with regards to determining assembly stoichiometry given its simplicity. The method consists of keepin g the total concentration of H ( ) and G ( ) constant and varying their relative proportions. 112 The x axis changes from concentration to mole fraction of H or G ( and such that: ( 3 10) Meanwhile the y axis can be any property ( P ) that correlates linearly with [ ] including absorbance, 116 conductivity, 117 NMR spectroscopy, 118 calorimetry, 119 etc. 120 Thus, the plot of P vs. yields the Job curve with a maximum at , which corresponds to the stoichiometry (Figure 3 7). 121 Due to the low degree of self association of 2 2 7 and 3 1 in chloroform (vide infra), 1 HNMR experiments were used to determine the stoichiometry and the bi nding isotherm. In this case, relatively high concentrations, as opposed to the lower

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115 concentration range used in UV vis experiments, were convenient for these investigations. 112 Given the fast exchange rate of 2 2 7 and 3 1 complexation equilibrium compared to the NMR time scale, the weight average chemical shift of the free host ( h ) and the complexed host ( c ) is detected and reported as obs . The modified Job plot, where ( obs h ) is plotted against the mole fraction , yielded a curve with a peak centered at 0.5 which corresponds to a = b , and in this case a 1:1 co mplexation of 2 2 7 and 3 1 (Figure 3 8). Figure 3 6 . Correlation between stoichiometry ( a , b ) and x coordinate at the maximum of the curve in a Job plot . Figure 3 7 . a) 1 H NMR spectra of 3 1 (50 mM) with increasing amount of 2 2 7 ( 5 0 mM) in CDCl 3 ; b) Job plot of 3 1 with 2 2 7 in CDCl 3 . b) a)

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116 Evaluation of the Association Constant Next, NMR titration experiments between 3 1 and 2 2 7 were performed in order to determine their association constant ( K a ). While uracil derivative 2 2 7 was used as the guest, ade nine derivative 3 1 was used as the host considering the reduced amount required to prepare the host solution. Once in hand, increasing volumes of 2 2 7 were added to a solution of complementary 3 1 . Worth noting, the guest solution 2 2 7 contained the host 3 1 as well, in order to keep the host concentration constant throughout the titration. Hence, the observed changes in the chemical shifts originate exclusively from the addition of the guest. Considering a 1:1 binding model, the system equilibrium, the corresponding association constant and the mass balance are represented by the following equations: H + G HG ( 3 11) K a = ( 3 12) [G] t = [G] + [HG ] ( 3 13) [H] t = [H] + [HG ] ( 3 14) Unfortunately, [HG] cannot be measured directly, therefore the mathematical model used to obtain the association constant is d eveloped from monitoring the change in the NMR chemical shift, which is given as a function of concentrations ( Equation 3 15) or mole fractions ( Equation 3 16) ( 3 15) ( 3 16) Combining the mole fraction notion with Equation 3 12 leads to Equation 3 17 that will prove useful in determin ing [G] and [HG] .

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117 ( 3 17) However, the free guest concentration is also unknown, but there is an alternative approach to solve this problem. It leads to a quadratic equation containing only the total concentrations ( and ) and the association constant ( K a ) as the unknown. Thus, representing the guest mole fraction by Equation 3 18 , followed by insertion in Equation 3 13 , then rear ranging yields a quadratic equation, when solved, generates the free guest concentration ( Equation 3 19). ( 3 18) ( 3 19) Alternatively, rearranging Equations 3 13 and 3 14 to isolate [H] and [G], respectively , and inserting them into Equation 3 12 , then rearranging yields another quadratic equation. The corresponding solution delivers the concentration of the complex ( Equation 3 20). ( 3 20) From Equation 3 20, we can establish solutions to Equations 3 15 a nd 3 16 that are dependent on the total concentrations ( and ), the association constant ( K a ), and the chemical shift ( obs ) that is changing during the course of the experiment. Now if we rearrange Equation 3 16, taking into consideratio n Equations 3 14 and 3 18 , we obtain Equation 3 21: ( ( 3 21)

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118 Inserting Equation 3 20 into 3 21 , it is now possible to describe the expected changes from the titration experiment of 2 2 7 and 3 1 , from two known ( and ) and two unknown ( K a and HG ) parameters. These two unknown parameters are usually obtained by non linear regression of the data obtained. This was readily achieved by using a program 113 that guesses K a , H , and HG for each point in the titration. Typically two different proton resonances ( N(3) H for 2 2 7 and NH 2 for 3 1 ) were monitored at the same time giving the corresponding data sets (Figure 3 9). The association constant fo r a single run was calculated as the mean values obtained for each of the signals followed during the titration, weighted by the observed changes in chemical shift. Figure 3 8 . Titration 1 HNMR spectra monitoring a) NH 2 of 3 1 and c) N(3) H of 2 2 7 ; b) 1 HNMR binding isotherm and global fitting for 2 2 7 and 3 1 . b) a) c)

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119 Thereby, the complementary nucleobases 2 2 7 and 3 1 , interacting via 2 hydrogen bonds, associate in deuterated chloroform with K a = 180 M 1 (Figure 3 9). This association constant derived in this w ork matched values reported in the literature for association between adenine and uracil derivatives. 41 On the other hand, a similar study was not possible with guanine derivative 3 4 and cy tosine 2 3 3 , due to the low solubility of these compounds in solvents that promote the formation of hydrogen bonding. The neat solutions of 3 4 and 2 3 3 are insoluble in deuterated chloroform. However, upon mixing in a 1:1 ratio, the solution becomes clear after being left overnight (Figure 3 10). These observations are attributed to the capping of the hydrogen bonding sites preventing formation of higher degree aggregates. Figure 3 9 . Deuterated chloroform solution of 3 4 , 2 33 and a 1:1 mixture of 3 4 and 2 33 .

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120 Conclusion Nucleobases nicely showcase the high degree of structural order that can be Combining this property with rationally optimizable optoelectronic prop erties will allow molecular and supramolecular structures to be tailored in ways not possible with more conventional building blocks. nucleobase containing oligomers and fully characterized their photophysical and electronic properties. Synthetic approaches, previously developed in our group, proved useful for the preparation of different architectures involving the adenine and guanine nucleobases, while pr ogress has been made toward expanding the chemistry of uracil and cytosine. Although the target compounds 3 5 and 3 6 were not obtained or could not be isolated in the desired degree of purity at this point, more efforts will be focused toward solving thes e problems. Nucleobase modulated optical, electronic, and thermal properties have been evaluated. Again, they showed dependence on the nature of the nucleobase. For instance, the guanine derivative displayed the lowest gap with respect to the other derivatives, consistent with its stronger electron donating character. Finally we showed that despite the alteration of their electronic structure, the persistence of the H bonding capabilities of the nucleobases, an d the fidelity of their molecular recognition selectivity remains intact. We have successfully developed some of the most useful synthetic approaches facilitating the introduction of nucleobases into conjugated systems. 104 In addition, general structur e property relationships have been established for nucleobase containing conjugated oligomers. 104 Future work involves investigation of the

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121 and charge transport behav ior. Experimental General Methods Reagents and solvents were purchased from commercial sources and used without further purification unless otherwise specified. THF, diethyl ether, CH 2 Cl 2 , toluene, and DMF , were degassed in 20 L drums and passed through tw o sequential purification columns (activated alumina; molecular sieves for DMF) under a positive argon atmosphere. Tetrakis(triphenylphosphine) palladium(0), and trans bis(triphenylpho sphine) palladium(II) chloride were purchased from Sigma Aldrich and use d as received. Thin layer chromatography (TLC) was performed on SiO 2 60 F254 aluminum plates with visualization by UV light or staining. Flash column chromatography was performed using SiO 2 1 H( 13 C) NMR spectra were recorded on 300(75) MHz or 500(125) MHz spectrometers as specified. Chemical shifts ( ) are given in parts per million (ppm) relative to TMS and referenced to residual protonated solvent (CDCl 3 : H 7.26 ppm, C 77.23 ppm; DMSO d 6 : H 2.50 ppm, C 39.50 ppm). Abbreviations used a re s (singlet), d (doublet), t (triplet), q (quartet), quin (quintet), sep (septet), b (broad), and m (multiplet). ESI and ESITOF MS spectra were recorded on FTICR and TOF spectrometers, respectively. EI , CI , and DIP CI MS spectra were recorded on a sin gle quadrupole spectrometer. The following compound have been prepared using literature procedures: (5' hexyl [2,2' bithiophen] 5 yl)trimethylstannane 3 14 . 108

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122 Synthesis of A denine Terminated Oligomers 9 (2 ethylhe xyl) 8 (5'' hexyl [2,2':5',2'' terthiophen] 5 yl) 9 H purin 6 amine (3 1) . In a dry round bottom flask under inert atmosphere, 2 7 (0.25 g, 0.60 mmol), 3 7 (0.25 g, 0.63 mmol), K 2 CO 3 (0.25 g, 1.8 mmol), and Pd(PPh 3 ) 4 (0.070 g, 0.060 mmol) were dissolved in degassed toluene (12 mL), followed by addition of degassed water (4 mL). The reaction vessel was heated to 80 °C and stirred 18 h, filtered, and washed with CH 2 Cl 2 (15 mL). The product was further purified by silica gel column chromatography with gradient elution (EtOAc:Hexanes 20:80 to 40:60) to afford the product as a yellow solid (0.24 g, 69%): 1 H NMR (500 MHz, CDCl 3 ): 8.34 (s, 1H), 7.48 (d, J = 3.9 Hz, 1H), 7.19 (dd, J = 16.3, 3.8 Hz, 2H), 7.03 (dd, J = 9.3, 3.6 Hz, 2H), 6.70 (d, J = 3.5 Hz, 1H), 6.04 (s, 2H), 4.37 (d, J = 7.7 Hz, 2H), 2.80 (t, J = 7.6 Hz, 2H), 2.05 1.95 (m, 1H), 1.69 ( quin , J = 7.9 Hz, 2H), 1.44 1 .15 (m, 1 6 H), 0.86 (ddt, J = 21.5, 14.0, 7.0 Hz, 9H); 13 C NMR (75 MHz, DMSO d 6 ): 154.0, 152.3, 151.1, 146.4, 145.9, 140.9, 138.5, 134.2, 1 30.0, 128.9, 125.6, 125.1, 124.0, 124.0, 123.9, 119.3, 110.1, 77.4, 77.2, 76.9, 48.0, 39.1, 31.7, 30.4, 30.4, 28.9, 28.4, 23.8 , 23 .1, 22.7, 14.2, 14.1, 10.6; HRMS (ESI) calcd for C 31 H 39 N 5 S 3 [M + H] + : 578.2440, found: 578.2431. Synthesis of G uanine T erminat e d O ligomer ( ± ) 9 (2 ethylhexyl) 6 methoxy 9H purin 2 amine (3 8) . ( ± ) 6 Chloro 9 (2 ethylhexyl) 9H purin 2 amine 2 13 (1.9 g, 6.7 mmol) was added to a solution of NaOMe (1.4 g, 27 mmol) in dry MeOH (25 mL), then stirred at rt overnight. The reaction mixt ure was then poured into deionized water (30 mL), extracted with chloroform (25 mL), and dried over anhydrous Na 2 SO 4 . The crude product was purified by recrystallization from hexanes to afford 3 8 as a white solid (1.7 g, 94%): 1 H NMR (500 MHz, CDCl 3 ): 7 .54 (s, 1H), 4.88 (s, 2H), 4.06 (s, 3H), 3.92 (d, J = 7.2 Hz, 2H), 1.87 ( quin , J = 6.6 Hz, 1H),

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123 1. 31 1.24 ( m , 8H), 0.86 (dt, J = 14.0, 7.2 Hz, 6H). ; 13 C NMR (125 MHz, CDCl 3 ): 161.6, 159.3, 154.3, 139.9 , 115.6, 53.9, 47.0, 39.7, 30.4, 28.5, 23.8, 23.0, 14 .1, 10.6; HRMS (ESI) calcd for C 14 H 23 N 5 O [M+H] + : 27 8 . 1975 , found: 278.1969 . ( ± ) 8 bromo 9 (2 ethylhexyl) 6 methoxy 9H purin 2 amine (3 9) . NBS (0.40 g, 2.2 mmol) was added portion wise to a solution of 3 8 (0.73 g, 2.0 mmol) and stirred at rt for 1 h. The reaction mixture was then poured into deionized water (20 mL), extracted with ethyl acetate (25 mL), washed with a solution of 5% Na 2 S 2 O 4 (15 mL), and dried over anhydrous Na 2 SO 4 . The solvent was removed under reduced pressure to yield 3 9 as a beige solid (0.79 g, 89%): 1 H NMR (500 MHz, CDCl 3 ): 4.86 (s, 2H), 4.05 (s, 3H), 3.93 (d, J = 7.6 Hz, 2H), 2.00 ( quin , J = 6.1 Hz, 1H), 1.35 1.22 (m, 8H), 0.87 (dt, J = 13.9, 7.3 Hz, 6H). ; 13 C NMR (125 MHz, CDCl 3 ): 160.5, 159.2, 155.3, 125.9, 115.9, 54.1, 48.2, 39 .1, 30.4, 28.5, 23.8, 23.1, 14.1, 10.7 ; HRMS (ESI) calcd for C 14 H 22 BrN 5 O [M+Na] + : 356. 10 80 , found: 356.1094 . ( ± ) 9 (2 ethylhexyl) 6 methoxy 8 (thiophen 2 yl) 9H purin 2 amine (3 10) . Compound 3 9 (0.79 g, 1.8 mmol), Ph 3 Bi (0.32 g, 0.73 mmol), and Pd(PPh 3 ) 4 (0.42 g, 0.36 mmol) were dissolved in dry degassed xylenes (25 mL), along with 2 (tributylstannyl)thiophene (1.4 mL, 4.4 mmol). The reaction vessel was heated to reflux for 15 min. The solvent was removed under reduced pressure. The crude product was puri fied by silica gel column chromatography (EtOAc:hexanes 10:90 to 20:80) to yield the product as a white solid (0.66 g, 84 %): 1 H NMR (500 MHz, CDCl 3 ): 7.53 (d, J = 3.6 Hz, 1H), 7.44 (d, J = 5.0 Hz, 1H), 7.12 (t, J = 4.3 Hz, 1H), 4.86 (s, 2H), 4.21 (d, J = 7.6 Hz, 2H), 4.08 (s, 3H), 1.9 5 1.89 ( m , 1H), 1.2 9 1.16 ( m , 8H), 0.83 0.78 (m, 6H); 13 C NMR (125 MHz, CDCl 3 ): 161.3, 159.2, 156.2, 144.6, 132.9, 128.0, 127.7 , 127.6 ,

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124 115.4 , 54.0, 47.5, 38.9, 30.3, 28.3, 23.8, 23.1, 14.2, 10.7; HRMS (ESI) calcd for C 18 H 25 N 5 OS [M+H] + : 3 60 . 1853 , found: 360.1850 . ( ± ) 8 (5 bromothiophen 2 yl) 9 (2 ethylhexyl) 6 methoxy 9H purin 2 amine (3 11) . Glacial HOAc (10 mL) was added to a solution of 3 10 (0.65 g, 1.5 mmol) in dry THF (10 mL). Then the contents of the reaction vessel were cooled to 0 °C in an ice water bath. Next, NBS (0.29 g, 1.6 mmol) was added and the reaction was slowly warmed to rt over 1.5 h. The solvent was removed under reduced pressure to yield the crude product, which was subsequently diluted with EtOAc (50 m L), washed with a solution of 5% Na 2 S 2 O 4 (25 mL), and with saturated NaCl solution (3 × 25 mL). The organic phase was dried over anhydrous Na 2 SO 4 , filtered, and evaporated. The crude product was purified by silica gel column chromatography (EtOAc:hexanes 1 0:90 to 40:60) to yield the product 3 11 as beige solid (0.55 g, 71 %): 1 H NMR (500 MHz, CDCl 3 ): 7.25 (s, 1H), 7.08 (d, J = 4.0 Hz, 1H), 4.86 (s, 2H), 4.17 (d, J = 7.7 Hz, 2H), 4.08 (s, 3H), 1.91 ( quin , J = 7.2 Hz, 1H), 1. 30 1.16 ( m , 8H), 0.82 (t, J = 7.4 Hz, 6H). ; 13 C NMR (125 MHz, CDCl 3 ): 161.2, 159.2, 156.0, 143.2, 134.5, 130.5, 127.3, 115.2, 115.1, 53.9, 47.4, 38.8, 30. 2, 28.2, 23.6, 22.9, 14.0, 10.5; HRMS (ESI) calcd for C 18 H 24 BrN 5 OS [M+H] + : 438. 0958 , found: 438.0970 . ( ± ) 9 (2 ethylhexyl) 8 (5'' hexyl [2,2':5',2'' terthiophen] 5 yl) 6 methoxy 9H purin 2 amine (3 3) . In a dry round bottom flas k under inert atmosphere, K 2 CO 3 ( 0.80 g, 5.8 mmol ), and Pd(PPh 3 ) 4 ( 0.22 g, 0.19 mmol ), 3 11 ( 0.8 0 g, 2.1 mmol ) and 3 7 ( 0.81 g, 1.9 mmol ) were dissolved in degassed toluene (17 mL), followed by addition of degassed water (4 mL). The reaction was then heate d to 110 °C for 17 h. The reaction mixture was diluted with DCM (75 mL). The organic layer was separated from the

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125 aqueous phase, and dried over anhydrous Na 2 SO 4 . The solvent was removed under reduced pressure to yield a crude dark orange product, which was then precipitated from a mixture of CH 2 Cl 2 in hexanes to yield the product as a mixture of stereoisomers ( 0.52 g, 46% ): 1 H NMR (500 MHz, CDCl 3 ): 7.42 (d, J = 3.9 Hz, 1H), 7.12 (dd, J = 13.0, 3.8 Hz, 2H), 7.00 (dd, J = 6.8, 3.6 Hz, 2H), 6.68 (d, J = 3.3 Hz, 1H), 4.92 (s, 2H), 4.23 (d, J = 7.5 Hz, 2H), 4.09 (s, 3H), 2.79 (t, J = 7.6 Hz, 2H), 1.98 ( quin , J = 7.7 Hz, 1H), 1.68 ( quin , J = 7.5 Hz, 2H), 1.41 1.1 2 (m, 14H), 0.91 0.80 (m, 9H); 13 C NMR (125 MHz, CDCl 3 ): 161.1, 158.8, 155.9, 146.0, 144.0, 139.5, 137.8, 134.6, 134.2, 131.1, 127.7, 125.1, 124.9, 123.7, 123.6, 115.3, 53.9, 47.5, 38.8, 31.6, 30.2, 30.2, 28.8, 28.2, 23. 6, 23.0, 22.6, 14.1, 14.0 , 10.5; HRMS (ESI) calcd for C 32 H 41 N 5 OS 3 [M + H]+: 608.2546, found: 608.2539. ( ± ) 6 (benzyloxy) 9 (2 ethylhexyl) 8 (5'' hexyl [2,2':5',2'' terthiophen] 5 yl) 9H purin 2 amine (3 2) . In a dry round bottom flask under inert atmosphere, K 2 CO 3 ( 0.46 g, 3.4 mmo l ), and Pd(PPh 3 ) 4 ( 0.13 g, 0.11 mmol ), 2 22 ( 0.58 g, 1.1 mmol ) and 3 7 ( 0.46 g, 1.2 mmol ) were dissolved in degassed toluene (15 mL), followed by addition of degassed water (3 mL). The reaction was then heated to 110 °C for 17 h. The reaction mixture was d iluted with EtOAc (75 mL). The organic layer was separated from the aqueous phase, and dried over anhydrous Na 2 SO 4 . The solvent was removed under reduced pressure. The curde product was precipitated several times from toluene:hexanes (cold) (1:1) to yield the product 3 2 as a yellow solid ( 0.53 g, 71 % ): 1 H NMR (500 MHz, CDCl 3 ): 7.53 (d, J = 7.4 Hz, 2H), 7.42 (d, J = 3.7 Hz, 1H), 7.36 (t, J = 7.4 Hz, 3H), 7.31 (t, J = 7.2 Hz, 1H), 7.15 (d, J = 3.6 Hz, 2H), 7.12 (d, J = 3.6 Hz, 2H), 7.01 (dd, J = 7.2, 3.6 Hz, 2H), 6.69 (d, J = 3.0 Hz, 1H), 5.60 (s, 2H), 4.87 (s, 2H), 4.2 4

PAGE 126

126 ( d, J = 7.5 Hz, 2H ), 2. 80 ( t , J = 7.5 Hz, 2 H), 2.00 1.93 (m, 1H), 1.68 ( quin , J = 7.5 Hz, 3H), 1. 40 1.20 ( m , 15H), 0.92 0.82 (m, 9H); 13 C NMR (125 MHz, CDCl 3 ): 160.7, 158.9, 156.6, 146.1, 144.2, 139.6, 137.9, 136.7, 134.7, 134.3, 131.2, 128.6, 128.5, 128.1, 128 .0, 125.2, 125.0, 123.8, 123.8, 123.7, 115.5, 68.2, 47.5, 38.9, 31.7, 30.3, 28.9, 28.4, 23.8, 23.1, 22.7, 14.2, 14.1, 10.6. ; HRMS (ESI) calcd for C 38 H 49 N 5 OS 3 [M + H] + : 684.2859, found: 684.2860. ( ± ) 2 amino 9 (2 ethylhexyl) 8 (5'' hexyl [2,2':5',2'' terthi ophen] 5 yl) 1,9 dihydro 6H purin 6 one (3 4) . In a dry round bottom flask under inert atmosphere, a solution of pentamethylbenzene ( 0.20 g, 1.3 mmol ) and 3 2 ( 0.30 g, 0.44 mmol ) in dry degassed CH 2 Cl 2 ( 17 mL ) was cooled to 78 °C and then a 1.0 M solution of BBr 3 in CH 2 Cl 2 ( 1.1 mL, 1.1 mmol ) was added slowly over 15 min. The solution was stirred at 78 °C for 2 h, followed by the addition of methanol (25 mL) to quench the reaction. The solvent was removed under reduced pressure to yield a crude orange soli d 3 4 that was subsequently washed with DCM to remove impurities and afford the product as a mixture of stereoisomers (0.14 g, 55 %): 1 H NMR (500 MHz, DMSO d 6 ): 10.76 (s, 1H), 7.53 (d, J = 3.9 Hz, 1H), 7.38 (dd, J = 15.3, 3.8 Hz, 2H), 7.20 (dd, J = 23.4, 3.6 Hz, 2H), 6.83 (d, J = 3.5 Hz, 1H), 6.60 ( b , 2H), 5. 70 ( b , 2 H), 4.17 (d, J = 7.6 Hz, 2H), 2.79 (t, J = 7.5 Hz, 2H), 1.81 ( quin , J = 6.9 Hz, 1H), 1.61 ( quin , J = 7.5 Hz, 2H), 1.36 1.0 6 (m, 15H), 0.89 0.75 (m, 9H); 13 C NMR (125 MHz, DMSO d 6 ): 155.9, 154.5, 153.1, 146.0, 140.3, 139.1, 137.4, 133.8, 133.6, 129.7, 128.7, 126.7, 126.2, 125.1, 124.9, 124.8, 114.2, 47.2, 38.4, 31.5, 31.4, 30.0, 29.8, 28.5, 28.0, 23. 6, 22.8, 22.5, 14.4, 14.2, 10.8; HRMS (ESI) calcd for C 31 H 39 N 5 OS 3 [M + H] + : 433.0441 , found: 433.0431 .

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127 Attempted S ynthesis of U racil Terminated O ligomer ( ± ) 1 (2 ethylhexyl) 5 (5 nitrothiophen 2 yl)pyrimidine 2,4(1 H ,3 H ) dione (3 12 b ) . Lithium iodide (0.34 g, 2.54 mmol), 2 2 9 (0.65 g, 2.1 mmol), and cerium ammonium nitrate (2.3 g, 0.65 mmol) were dissolved in MeCN (17 mL). The mixture was stirred for 1 h. After completion, the mixture was washed with Na 2 S 2 O 3 (saturated), dried over Na 2 SO 4 , filtered, and con centrated under reduced pressure. The crude product was purified by silica gel column chromatography (EtOAc:hexanes 20:80) to yield the product 3 12 as a yellow solid (0.16 g, 22 %): 1 H NMR (500 MHz, CDCl 3 ): 8.72 (s, 1H), 7.87 (d, J = 4.5 Hz, 1H), 7.68 ( s, 1H), 7.24 (d, J = 4.5 Hz, 1H), 3.77 (dd, J = 7.4, 2.6 Hz, 2H), 1.87 1.77 (m, 1H), 1.39 1.28 (m, 8H), 0.93 (dt, J = 20.3, 7.1 Hz, 6H); 13 C NMR (125 MHz, CDCl 3 ): 160.9, 151.2, 149.6, 142.0, 141.2, 128.3, 121.2, 107.7 , 53.4, 39.1, 30.1, 28.5, 23.5, 23. 1, 14.1 , 10. 5; HRMS (ESI) calcd for C 16 H 21 N 3 O 4 S [M+H] + : 352.4210 , found: 352.1337 . ( ± ) 5 (4,5 diiodothiophen 2 yl) 1 (2 ethylhexyl)pyrimidine 2,4(1 H ,3 H ) dione (3 13) . TFA (2.7 mL, 35 mmol) was added to a solution of 2 2 9 (0.54 g, 1.8 mmol), and N iodosucci nimide (0.48 g, 2.1 mmol). The reaction mixture was stirred for 2 h at 70 ° C. The cooled solution was washed with saturated NaHCO 3 solution (25 mL), then with H 2 O (25 mL). The organic layer was dried over Na 2 SO 4 . The crude product was purified by silica ge l column chromatography (EtOAc:hexanes 10:90) to afford the product as a pale yellow solid (0.54 g, 56%): 1 H NMR (500 MHz, CDCl 3 ): 8.83 (s, 1H), 7.68 (s, 1H), 7.23 (s, 1H), 3.71 (dd, J = 7.4, 1.7 Hz, 2H), 1.8 5 1.82 ( m , 1H), 1. 44 1.29 ( m , 8H), 0.91 (dt, J = 17.6, 7.1 Hz, 6H); 13 C NMR (125 MHz, CDCl 3 ): 161.5, 150.1, 145.0, 143.7, 138.2, 108.1, 53.0, 39.1, 30.3, 28.7, 23.6, 23.1, 14.2, 10.6 ; HRMS (ESI) calcd for C 16 H 20 I 2 N 2 O 2 S [M+H] + : 558. 9408 , found: 558.9403 .

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128 S ynthesis of C ytosine Terminated O ligomer ( ± ) 4 amino 1 (2 ethylhexyl) 5 iodopyrimidin 2(1 H ) one (3 15) . A suspension of 2 31 (1.5 g, 6.7 mmol), I 2 (1.5 g, 6.1 mmol), and iodic acid (2.0 g, 11 mmol) in acetic acid (45 mL) was stirred at 40 ° C for 16 h. The insoluble iodic acid was then filtered and d iscarded. A mixture of EtOAc/Et 2 O (1:1) was added to the reaction mixture and washed with H 2 O (3 × 50 mL), a saturated NaHCO 3 solution (3 × 50 mL), a saturated Na 2 S 2 O 3 solution (1 × 50 mL), and finally H 2 O again. The organic layer was dried over Na2SO4, fi ltered and concentrated under reduced pressure. The crude product was recrystallized from DCM:hexanes to yield a pale yellow solid 3 15 (1.9 g, 80%): 1 H NMR (500 MHz, CDCl 3 ): 8.91 (s, 1H), 7.49 (s, 1H), 5.57 (s, 1H), 3. 62 ( dd , J = 7 , 3 Hz, 2H), 1.80 ( qui n , J = 6.6 Hz, 1H), 1. 34 1 . 21 ( m , 8H), 0.9 0 0.8 6 (m, 6H). ; 13 C NMR (125 MHz, CDCl 3 ): 164.0, 155.7, 151.5, 55.4, 54.2, 38.7, 30. 2, 28.5, 23.5, 23.1, 14.2, 10.5; HRMS (ESI) calcd for C 12 H 20 IN 3 O [M + H] + : 3 50 . 0724, found: 350. 0723. ( ± ) 4 amino 1 (2 ethylhex yl) 5 (thiophen 2 yl)pyrimidin 2(1 H ) one (2 3 5 ) . T hiophen 2 ylboronic acid (2.4 g, 19 mmol), 3 15 (1.5 g, 4.3 mmol), Pd(PPh 3 ) 4 (0.57 g, 0.49 mmol), and Cs 2 CO 3 (5.0 g, 15 mmol) were dissolved in degassed THF (50 mL), followed by addition of degassed H 2 O (15 mL). The mixture was heated overnight at 66 ° C. The reaction vessel was cooled to rt. The mixture was extracted with DCM (25 mL), washed with brine (25 mL), and dried over Na 2 SO 4 . The crude product was purified by silica gel column chromatography (EtOAc) to yield the product 2 3 5 as light green solid (0.82 g, 63 %): 1 H NMR (500 MHz, CDCl 3 ): 9.09 (s, 1H), 7.34 (d, J = 5.1 Hz, 1H), 7.22 (s, 1H), 7.11 7.01 (m, 2H), 5.57 (s, 1H), 3.63 (d, J = 7.3 Hz, 2H), 1.83 ( quin , J = 6.0 Hz, 1H), 1.35 1.2 4 ( m , 8H), 0.89 0.83 (m, 6H); 13 C NMR (125 MHz, CDCl 3 ): 156.13, 145.55, 134.05, 128.22, 127.60, 126.69, 100.93, 54.07, 38.59, 30.31, 28.56, 23.63,

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129 23.16, 14.17, 10.57; HRMS (ESI) calcd for C 18 H 24 BrN 5 OS [M+H] + : 306.1635, found: 306.1631. ( ± ) 4 amino 1 (2 ethylhexyl) 5 (5 iodothiophen 2 yl)pyrimidin 2(1 H ) one (3 16) . TFA (1.3 mL, 16 mmol) was added to a solution of 2 3 5 (0.75 g, 2.4 mmol), and N iodosuccinimide (0.66 g, 2.9 mmol) in DCE (30 mL). The mixture was stirred for 2 h at 80 ° C, then poured in 20 mL of H 2 O. The org anic layer was separated, dried over Na 2 SO 4 , filtered, and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (MeOH:DCM 5:95) to yield the product as a pale yellow solid (0.46 g, 32%): 1 H NMR (500 MHz, CDCl3): 29 ( s , 1 H), 7.28 (d, J = 4 Hz, 1H), 6.77 (d, J = 3.6 Hz, 1H), 3.70 (d, J = 7.3 Hz, 2H), 1.9 0 1.8 6 (m, 1H), 1. 40 1.30 ( m , 8H), 0. 9 4 0.90 (m, 6H) ; 13 138.0, 129.3, 99.9, 54.2, 38.6, 30. 3, 28.6, 23.6, 23.2, 14.2, 10.5 ; HRMS (ESI) calcd for C 16 H 22 IN 3 OS [M+H]+: 306.1635, found: 306.1631. ( ± ) 4 amino 1 (2 ethylhexyl) 5 (5'' hexyl [2,2':5',2'' terthiophen] 5 yl)pyrimidin 2(1 H ) one (3 6) . Pd(PPh 3 ) 4 (0.10 g, 0.080 mmol), 3 16 (0.5 g, 0.84 mmol), 3 7 (0.41 g, 1.1 mmol), and Cs 2 CO 3 (0.82 g, 2.5 mmol) were dissolved in degassed THF (12 mL), followed by addition of degassed H 2 O (4 mL). The mixture was heated at 66 ° C for 16 h. The reaction mixture was diluted with DCM (50 mL). The organic layer was separated from the aqueous phase, and dried over anhydrous Na 2 SO 4 . The solvent was removed under reduced pressure, the crude product was purified by silica gel column chromatography (EtOAc) to yield the product 3 6 as a yellow solid (80% pure by NMR). 1 H NMR (500 MHz, CD 7.29 (s, 1H), 7.11 (d, J = 3.6 Hz, 1H), 7.05 (d, J = 3.8 Hz, 1H), 7.00 (dd, J = 6.2, 3.7 Hz, 2H), 6.96 (d, J = 3.7 Hz, 1H), 6.69 (d, J = 3.5 Hz, 1H),

PAGE 130

130 4.29 (d, J = 8.0 Hz, 1H), 3.68 (d, J = 7.3 Hz, 2H), 2.79 (t, J = 7.6 Hz, 2H), 1.91 1.81 (m, 2H), 1 .67 (q, J = 7.6 Hz, 2H), 1.34 1.25 (m, 16H), 0.92 0.87 (m, 9H) ; HRMS (ESI) calcd for C 30 H 39 N 3 OS 3 [M+H]+: 55 4 . 2328 , found: 554.2332 . Photophysical Measurements and Additional Data Absorption M easurements Absorption spectra were measured for 5, 10, 20, 40, a nucleobases on a Perkin Elmer Lambda 25 dual beam absorption spectrometer and a Cary 100 Bio spectrophotometer using 1 cm quartz cells. All solvents were spectroscopic grade (purchased from Fisher) and stored over 4 Ã… molecular si eves . The absorption intensity at max was then plotted against the concentration in all cases to Molar extinction coefficients ( ) were determined from the linear plot for each compound (where A = ). Electrochemistry Cyclic Voltammetry (CV) measurements were performed for 3 1 4 using a single compartment three electrode cell with a gold counter electrode, a Ag/Ag + reference electrode , and a platinum disk ( 0.02 cm 2 ) as the working electrode. Electrodes were purchased from either BASi, Inc. or CH Instruments Tetrabutylammonium hexafluorophosphate (TBAPF 6 ) was purchased from Aldrich, and kept dry under vacuum. DMF was collected from an Innovative Technologies solvent system, sparged with Ar and passed over two columns of 5 Ã… activated sieves. The oligomer solid was dissolved to a concentration of 2 mM in a 0.1 M TBAPF 6 /DMF electrolyte. Potential sweeps were controlled by a Princeton Applied Research Versastat II potentiostat . The scan rate for CV was 10 0 mV/s.

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131 Computational Analysis o f Oligomer Conformations Starting geometries were obtained from semi empirical calculations using the MM2 method as implemented in Chem3D Pro v. 13.0.0.3015 for Windows. The ground state geometries, energies and orbi tal energies were then obtained from DFT calculations at the B3LYP/6 31+G** level as implemented in Gaussian 09, 95 accessed through the UF High Performance Computing Center. Frequency calculations were performed at the same computational level, and no imaginary frequencies were found . Molecular orbital plots were made using GaussView v. 5.0.8 98 from the Gaussian output files. NMR experiments NMR D ilution s NMR dilutions were performed at 298 K on an Inova 500 spectrometer (500 MHz) in CDCl 3 , purchased from Cambridge Isotope Laboratories. A 100 and a 225 mM solution of 2 2 7 and 3 1 w ere respectively prepared in 400 L of CDCl 3 . By m icropipette , more deuterated solvent was added, in calculated amount s , into the NMR tube . The 1 H NMR experiments were continued until the dilutions yielded chemical shifts within the 20 80% saturation range. Dimerization constant s were calc ulated by nonlinear curve fitting methods for the dilutions induced chemical shifts of the uracil N(3)H peak in 2 2 7 and the adenine NH 2 peak in 3 1 . Each dilution was repeated at least twice. Job P lots ( Continuous Variation M ethod) The stoichiometry of th e host guest complex ( 3 2 7 ) method of continuous variation. Host 3 1 and guest 2 2 7 compounds were dissolved in CDCl 3 in NMR tubes, in which the combined total concentration of host and guest was

PAGE 132

132 kept constant. Normally, the molar fraction of host an d guest in the resulting solution in NMR tubes varied from 0 to 1 . The changes in chemical shifts ( molar fraction and plotted against molar fraction to obtain the Job plot. NMR T itrations NMR dilutions were performed at 298 K on an I nova 500 spectrometer (500 MHz) in CDCl 3 , purchased from Cambridge Isotope Laboratories. The host 3 1 was dissolved in 3 mL of CDCl 3 in a volumetric flask . 375 (10 mM) was added into an NMR tube. The remainder was used to disso lve the guest compound 2 2 7 (40 mM), so that the host concentration remained constant throughout the titration . By m icropipette , the host guest solution was added, in calculated amount, into the NMR tube which originally contain ed 375 3 1 . The 1 H NMR experiments were continued until no significant change in chemical shift was observed in successive 1 H NMR spectra. The b inding constant was calculated by nonlinear curve fitting methods based on the complexation induced chemical shifts of the ho st 3 1 ( adenine NH 2 peak ) and the guest 2 2 7 ( uracil N(3) H peak ) .

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133 CHAPTER 4 THE INFLUENCE OF SOL UBILIZING CHAIN STER EOCHEMISTRY ON SMALL MOLECULE PHOTOVOLTAI CS b Introductory Remarks conjugated organic semiconductors have emerged as high priority targets toward the design of future generations of functional materials for diverse solid state photonic, electronic and optoelectronic device applications. The potential advantage of conj ugated oligomers (COs) and polymers (CPs) is the variety of techniques available for device fabrication. 122 While traditional methods, such as vacuum deposition, include expensive manufacturing steps and generally require high temperature and high pressure (Figure 4 1), 123 solution processing is favored for large scale and low cost production performed under ambient conditions (Figure 4 1). 123 Although most of the conjugated backbones, the resulting device fabrication. 42b Therefore, d issolution of otherwise aggressively aggregating conjugated materials for thin film preparation from solution requires judicious choice of pendent solubilizing groups , 42 typically saturated hydrocarbon chains that promote favorable van der Waals interactions with polarizable organic solvents and weaken intermolecular interactions . 42b Ongoing research has demonstrated the significant impact of side chain type, 44, 124 length, 45, 125 126 branching, 45f, 45g, 46, 49, 127 placement, 32, 47, 128 and stereochemistry 43, 48 on applications that mutually rely on good solution Adapted with permission from Advanced Functional Materials , 201 4 , 24 , 5993 6004 C opyright © 2014 John Wiley and Sons.

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134 surfaces, and appropriate active layer morphology. 42b, 129 Figure 4 1 . Schematic p T diagram for preparative techniques for advanced materials . Reproduced from Yoshimura, M.; Suchanek, W.; Han, K. S. J. Mater. Chem. , 1999 , 9 , 77 82 , with permission from The Royal Society of Ch emistry . To address the low solubility characteristic of nucleobases , described in chapters 2 and 3 , rac 2 ethylhexyl groups were installed. 104 This branched alkyl chain is among the most commonly used solub ilizing groups in the organic materials communi ty 31, 130 131 132 and it even comes pre installed on many commercially available b uilding blocks for conjugated oligomer/polymer preparation. carbon atom, mixtures of stereoisomers (enantiomers and diastereomers) are formed in syntheses that begin from racemic starting materials , although the isomeric complexity is generally ignored. While the stereoirregularity presumably reduces crystallinity and

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135 improves solubility, 43b the ramifications for otherwise carefully performed structure property function studies involving organic systems, particularl y small molecules, have only recently come to light. 43b, 48 The motivation of the current work is to understand to what extent it is reasonable to ignore the stereochemistry of the EtHx solubilizing group, and the isomeric complexity it creates, for small conjugated molecule morphology and bulk heterojunction photovoltaic devices. Figure 4 2 . Conjugated polymers (a,b,c) and small molecules (d,e) prepared in stereocontrolled fashion with respect to their 2 ethylhexyl s ide chains. SMDPPEH 4 1 studied in the current work. For polymeric systems, the consequences of stereocontrol with respect to the EtHx side chain have been modestly evaluated. For example, ( R ) 2 ethylhexyl side chains biased the helical backbone conforma tion of polyfluorene homopolymers ( R ) PF2/6 (Figure 4 2 a), 133 leading to enhanced chiroptical pr operties in the solid state. For

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136 PProDOT ((2 S ) ethylhexyl) 2 (Figure 4 2 b), prepared by Reynolds and coworkers, 134 the chiral side chains further encouraged the formation of chiral aggregates in solution. Interestingly, the solid state electronic (electrochemical potentials, conductivity) and optical ( i.e., max , optical gap) properties of the enantiomerically pure polymer were essentially identical to PProDOT (ethylhexyl) 2 prepared from racemic EtHx starting materials. 134 Furthermore, the optically active narrow bandgap polymers ( RR ) and ( SS ) PTB5 (Figure 4 2c) formed chirally ordered architectures in the film state, re flected by the CD signals observed, otherwise absent from PTB5 (synthesized from racemic EtHx starting material). 48 However, in terms of thermal stability, absorption behavior, and frontier orbital energy levels, ( RR ) and ( SS ) PTB5 displayed equivalent properties to optically inactive PTB5, in addition to comparable performance in the context of organic photovoltaics. The slight d ifferences observed were ascribed to batch to batch reproducibility and variations in molecular weight of the polymers, 48 two is sues that can be technically ignored in the case of oligomer syntheses. One conclusion, although not stated by the authors, is that the effects of solubilizing chain stereochemistry are washed out in disperse polymer environments with respect to bulk thin film properties. In contrast, Nguyen and coworkers have recently reported a significant influence of EtHx stereoisomerism on conjugated oligomer crystallization behavior and consequently thin film morphology and FET characteristics. 43b Independent characterization of the three stereoisomers ( RR , SS , and RS ) of DPP(TBFu) 2 (isolated by chiral HPLC separation) (Figure 4 2d ) as well a s the as synthesized material (a roughly statistical mixture of stereoisomers) revealed greater planarity, smaller interplanar ( ) spacing, red shifted absorption, and several fold higher hole mobility

PAGE 137

137 for the centrosymmetric RS isomer versus the RR / SS i somers and the isomeric mixture. 43b To the best of our knowledge, a comparable analysis in the context of small molecule bulk heterojunction photovoltaics has not been performed. Reported here are the functional consequences of 2 ethylhexyl stereochemistry on the optical, electrical, morphological, and photovoltaic properties of SMDPPEH ( 4 1 ) (Figure 4 2e ), a well studied 130b, 135 and commercially available organic semiconductor. The requisite stereoisomers of the mater ial ( RR ( 4 1 RR ) , SS ( 4 1 SS ) , and RS SMDPPEH ( 4 1 RS ) ) have been independently synthesized and then characterized together with as synthesized (syn SMDPPEH 4 1 syn ) and commercially available (com SMDPPEH 4 1 com ) samples that are stereoisomeric mixtures. Our results show that side chain stereochemistry and stereoisomeric composition have measurable consequences on the morphology, charge transport characteristics, and photophysical properties of the active layer and the shape of the absorption spectra of the ne at materials, but have a limited effect on the overall photovoltaic performance in bulk heterojunction devices. Synthesis Five different SMDPPEH compositions were employed in this study: 4 1 com (sublimed, 97% (HPLC), commercially obtained from Sigma Aldric h and used without further purification), 4 1 syn (prepared from racemic reagents in our laboratory), and the pure stereoisomers (RR 4 1 RR , SS 4 1 SS and RS SMDPPEH 4 1 RS ) available through stepwise synthesis involving the independently prepared enan tiomer s of 2 ethylhexyl bromide 4 7 R and 4 7 S (Scheme 4 1). Our approach to 4 7 recognized that 2 ethylhexanol 4 5 , a suitable precursor, has been prepared in enantiomerically enriched form through chemical synthesis 134, 136 (and more recently via enzymatic

PAGE 138

138 reduction of 2 ethylidenehexan 1 ol). 137 We made small adjustments to a synthesis of 4 5 138 as shown for 4 7 R (Scheme 4 1). Acylation of ( R ) 4 benzyl 2 oxazolidinone 4 2 R with the in situ generated mixed anhydride derivative of hexanoic acid afforded 4 3 R in 6 0 96% . 139 Deprotonation with sodium bis(trimethylsilyl)amide followed by addition of ethyliodide gave 4 4 R in moderate yield s (4 0 75%) but excellent diastereopurity . 136 Worth noting, the yields of 4 4 R were increased from 40 to 75% upon passing the e thyliodide, prior to addition, through a short alumina column to remove any traces of hydrogen iodide. S ubsequent reduction using lithium borohydride yielded 2 ethylhexanol 4 7 R (54 90%). 136 Spectroscopic and analytical da ta for 4 7 R , including optical rotation, are identical to those reported in the literature. 134, 137, 140 Direct conversion to the bromide proved troublesome under a variety of conditions. 141 Replacement of the hydroxyl group with a bromine, via the Appel reaction, generated a mixture of 2 ethylhexyl bromide 4 7 R and 1,2 dibromooctane, for example. The desired product was difficult to isolate by column chromatography. Fortuna tely, conversion of 4 5 R first to the corresponding tosylate 4 6 R in 80% yield , 142 followed by treatment with lithium bromide gave 4 7 R cleanly in good yields (65 80%) . Preparation of 4 7 S from 4 2 S was performed similarly by a group member, Yu (Bill) Zhu . Synthesis of the SMDPPEH materials then followed the general approach pioneered by Nguyen and coworkers beginning from readily prepared dihydropyrrolo[3,4 c ]pyrrole 1,4 dione 4 8 (Scheme 4 1 ). 143 4 1syn , 4 1 RR , and 4 1 SS were prepared using (±) 2 ethylhexyl bromide, 4 7 R , and 4 7 S , respectively, as N alkylating agents. Only the synthesis of 4 1 RR is shown in Scheme 4 1. Reaction of 4 8

PAGE 139

139 with 4 7 R generated the alkylated product 4 9 RR in moderate yields ( 45 50%) . Bromination of the terminal thiophenes of 4 9 RR with N bromosuccinimide (NBS) and subsequent palladium catalyzed Suzuki coupling with commercially available boronic ester 3 17 generat ed 4 1 RR in amounts suitable for solution phase and thin film investigation. The synthesis, optical and thermal properties characterizations of 4 1 SS and 4 1 R S were performed by Yu Zhu. All five compounds were successfully analyzed by 1 H NMR, 13 C NMR, HRMS , and elemental analysis. Worth noting, 4 1syn and 4 1com showed no evidence by NMR of existing as isomeric mixtures. Scheme 4 1 . Synthesis of 4 1 RR .

PAGE 140

140 Isomeric Composition The stereoisomeric purity of 4 1 RR , 4 1 SS and 4 1 RS , as well as the isomeric composition of 4 1syn and 4 1com , were evaluated by chiral HPLC using the conditions established by Nguyen and coworkers . 43b Analysis of the independently synthesized isomers reveals just one major peak in each case confirming thei r excellent isomeric purity (~ 97%); the technique also provides the individual isomer retention times ( 4 1 SS = 50±1 min; 4 1 RS = 58±1 min; and 4 1 RR = 69±1 min) (Figure 4 3) . Figure 4 3 . Chiral HPLC analysis of 4 1 ( 8/92 i PrOH/hexane, eluting rate: 0. 8 mL/min, detecting wavelength: 350 nm )

PAGE 141

141 Analogous to the synthesis of DPP(TBFu) 2 , 43b preparation of SMDPPEH from (±) 2 ethylhexyl bromide should generate the SS , RS and RR stereoisomers in a statistically predicted 1:2:1 (25%, 50%, 25%) ratio, respectively. Three peaks are indeed detected for 4 1com in a nearly statistical area ratio of 24:48:28. For 4 1syn , the component ratios deviate slightly from the commercial material depending on the synthetic batch and final target purification protocol (e.g., batch # 1 (one chromatography column and two recrystallizations): 28:42:30; batch #2 (one chromatography column and one recrystallization): 26:41:33). While it is difficult to say whether the differences are statistically meaningful, the results should give pause to practitioners who assume that oligomer synthesis necessarily provides batch to systems containing two or more 2 EtHx substituents can easily vary depending on synthetic preparation and purification . Optical Properties The optical properties of 4 1 were fi rst eva luated in dilute solution (CHCl 3 ; 2.5 × 10 M 30 × 10 M). All fi ve share identi cal UV Vis absorption spectra ( Figure 4 4 and Table 4 1 ), confi rming that the c hiral side chain exerts no i nfl uence on the intrinsic electronic properties of the chromophores or their solution phase conformations. Linear Beer Lambert plots additionally confi rmed that no aggregation occurs at the considered concentrations (Figures 4 5 ). Three maxima are observab le in the UV visible region. The high energy absorption band ( = 384 nm) corresponds the thiophene and the central diketopyrrolopyrrole (DPP) units, 135b, 144 while the absorption in the visible region (maxima at 616 and 646 nm) is assigned as an intramolecular charge transfer transition. The extinction coefficients for these materials

PAGE 142

142 only vary slightly, and all show expectedly low optical gaps of 1.77 eV consistent with their strong donor acceptor character (Table 2 1) . 145 Figure 4 4 . Normalized absorbance spectra of 4 1 in CHCl 3 (20 × 10 6 M). Table 4 1 . Optical properties of 4 1 in CHCl 3 (20 × 10 6 M) Material a × 10 4 4 1syn 4 1com 4 1 SS 4 1 RR 4 1 RS a All measurements were performed at room temperature and at 15 × 10 6 M. b Lowest energy absorption maxima. abs max (nm) ± 1 nm.

PAGE 143

143 Figure 4 5 . Absorption spectra and Beer Lambert plots in CHCl 3 (2.5×10 6 M 30×10 6 M) for a) 4 1syn ; b) 4 1com ; c) 4 1 SS ; d) 4 1 RR ; e) 4 1 RS . Electronic Properties F ully consistent with the absorption data, representative SMDPPEH compositions ( 4 1sy n , 4 1com , and 4 1 RR ) have nearly identical electrochemical pote ntials (based on CV/DPV measurements) in dichloromethane with NBu 4 PF 6 as the a) b) c) d) e)

PAGE 144

144 supporting electrolyte and ferrocene as the internal reference ( Table 4 2). Cy clic voltammetry revealed that oligomers 4 1 undergo a single reversible reduction, and two reversibl e oxidations . The HOMO energies (average = 5.36 eV) and LUMO energies (average = 3.54 eV) are consistent with the reported data for SMDPPEH synthesized from racemic EtHx side chains. 130b, 146 The HOMO LUMO gaps ( average = 1.8 eV) estimated from the oxidation and reduction peak potentials are also consistent with the optical data (Table 4 1). Again, the matching voltammograms of 4 1sy n , 4 1com , and 4 1 RR ascertain the lack of influence of the c hiral side chain on t he intrinsic electronic properties of 4 1 in solution . Table 4 2 . Electronic properties of 4 1sy n , 4 1com , and 4 1 RR Thermal Properties The thermal properties of the SMDPPEH samples 4 1 were studied by thermogravime tric analysis (TGA) and differential scanning calorimetry (DSC) in order to understand the effect of isomeric composition and EtHx stereochemistry on the bulk behavior of the materials. All compounds show similar thermal stability with loss of 5% of their original weight at high temperature (341 343 °C; Figure 4 6a ).

PAGE 145

145 Figure 4 6 . a) TGA analysis of 4 1 samples; b) DSC analysis of 4 1 samples. DSC (Table 4 3; Figure 4 6b ) reveals a melting transition ( T m ) of ~ 160 °C for four of the materials; this is inc reased significantly to 180 °C for the meso compound 4 1 RS . An additional melting transition is found for the enantiomers 4 1 RR and 4 1 SS (at 156 and 155 °C, respectively) implicating the co existence of two different crystal phases. With the exception of 4 1 RS , the materials all crystallize upon cooling ( T c ) at ~ 130 °C. The higher T c for 4 1 RS (154 °C), taken together with its higher T m , speak to a greater crystallization tendency for this isomer formulation. This result is consistent with what was report ed for RS DPP(TBFu) 2 that showed the highest thermal transition temperatures and lowest solubility among its in dependently studied isomers. 43b 4 1 RS is accordingly also the least soluble of the SMDPPEH compositions in our hands. Table 4 3 . Thermal properties of 4 1 Material 5% Weight Loss [°C] T m [°C] a T c [°C] b 4 1 syn 342 158 126 4 1 com 341 159 133 4 1 SS 343 156/160 132 b 4 1 RR 343 155/160 127 b 4 1 RS 343 180 154 a The 2 nd and 3 rd heating and cooling scan cycles were employed to determine the thermal trans ition temperatures, at a scan rate of 10 °C/min, under N 2 atmosphere; b Although two crystallization peaks were expected for the enantiomers, they could not be resolved even upon changing the heating/cooling rate . a) b)

PAGE 146

146 Single Crystal Structure Attempts were mad e to grow single crystals in order to investigate the effect of crystal structure of 4 1syn was obtained by vapor diffusion using DCM and hexanes, while the pure stere oisomers 4 1 RR , 4 1 SS , and 4 1 RS crystals could not be procured in a good quality. The crystal structure of 4 1syn , shown in Figure 4 8a, exhibits both R and S configurations on each alkyl substituent and is represented by the average of the three stereois omers that is the meso structure. Such a mixture of stereoisomers creates disorder in the unit cell (Figure 4 7b). This disorder is denoted by the dots around the alkyl chains that represent the alternative positions of the carbon atoms of the flexible cha ins (Figure 4 7a). 4 1syn displays a needle like crystal morphology and exhibits a triclinic system. Intermolecular packing has a significant influence on the optoelectronic conjugated material in the solid state. Typically, the packing systems consists of layered structures with overlapping conjugated backbones leading 147 determined from the average interplane distance of the 2,5 bis(2 ethylhexyl) 3,6 di(thiophen 2 yl) 2,5 dihydropyrrolo[3,4 c ]pyrrole 1,4 dione (TDPPT) conjugated moiety, and was found to be 3.5 8 Å (Figure 4 7c). Interestingly, the molecules are slip stacked to position the electron deficient DPP core over a donor thiophene unit. The molecular conformation of 4 1syn was also obtained from the single crystal structure. The conformation of the conj ugated backbone, described by the dihedral angles of 8), was slightly twisted with dihedral angles ranging between 8 14°.(see Appendix C for more details).

PAGE 147

147 Figure 4 7. a) 4 1syn single crystal with C, O, N, and S atoms shown in grey, red, cyan and yellow res pectively; b) unit cell of 4 1syn . All the hydrogens are omitted for clarity. Unit cell axes a , b , and c are shown in red, green, and blue, conjugated backbone overlapping in the unit cell. Figure 4 8 . Conjugated backb one conformation of 4 1syn determined from the single crystal structure. a) b) c)

PAGE 148

148 Characterization of the SMDPPEH Compositions in the Solid State All solid state characterizations were conducted by Nate Shewmon, from the UF Department of Materials Science and Engi neering. X ray diffraction (XRD) was used to study the crystallinity of neat and blended (with PCBM) spin coated SMDPPEH thin films prepared on silicon substrates (pre coated with 25 nm thick PEDOT:PSS films to allow a direct comparison with films incorpor ated in photovoltaic devices, vide infra). For neat, unannealed films (Figure 4 9 a) a single, weak diffraction peak is observed for all five materials. The peaks for 4 1 syn (2 = 6.20°; d = 14.2 Å), 4 1 com (2 = 6.16°; d = 14.3 Å), and 4 1 RS (2 = 6.21°; d = 14.2 Å) are centered at similar 2 values. Of these three the 4 1 RS peak is most intense, supporting the DSC data with regards to the 4 1 SS (2 = 6.66°; d = 13.3 Å) and 4 1 RR (2 = 6.63°; d = 13. 3 Å) show expectedly nearly identical XRD spectra but a slightly tighter (by ~ 1 Å) molecular packing than the other three materials. After annealing (at 100 °C for 5 min), an increase in the degree of crystallization for all of the SMDPPEH materials is o bserved, accompanied by a 2 3 fold increase in diffraction intensity (Figure 4 9b). 4 1syn and 4 1com continue to exhibit identical XRD spectra, with a single peak centered at 2 = 6.00° ( d = 14.7 Å). Apparently, the differences in isomer composition between these two compounds have little effect on neat film crystallinity. Neat, annealed films of 4 1 SS and 4 1 RR again show expectedly similar behavior, but now with two peaks (2 d = 15.9 Å) and 2 = 6.36° ( d = 13.9 Å)) observed for each film. Implied are co existing crystal phases, a result consistent with the DSC data (vide supra). The difference in relative intensity for the two

PAGE 149

149 peaks between the 4 1 SS and 4 1 RR samples indicates a different fractional film coverage for the two phases, with both materials preferentially forming in the d = 15.9 Å phase while 4 1 RR forms slightly more of the d = 13.9 Å phase. Precedent 148 leads one to suspect that such differences might arise from the clockwise substrate rotation during spin co ating that was used here. Figure 4 9 . XRD spectra for spin coated films of (a,b) neat 4 1 or (c,d) 4 1 :PC 61 BM. Films (a,c) were not annealed, whereas films (b,d) were annealed at 100 °C for 5 minutes . At any rate, it appears that even for enantiomers t he film crystallinity can vary depending on subtle differences in film preparation. Interestingly, unlike the other four films, the 4 1 RS XRD peak shifts about half an angstrom to a smaller d spacing (2 = a) b) c) d)

PAGE 150

150 6.46°; d = 13.7 Å) upon annealing. Again, 4 1 RS sh ows the strongest peak intensity, indicating a higher degree of crystallization in the film. When blended in a 1:1 weight ratio with PCBM in solution, the spin coated fi lms of SMDPPEH are completely amorphous with the notable exception of the 4 1 RS :PCBM fi lm, which displays a weak, broad peak centered at 2 = 6.11° ( d = 14.4 Å) (Figure 4 9 c). The presence of PCBM along with rapid drying of the CHCl 3 solvent inhibits crystallization, 149 suggesting the effectiveness of the PCBM acceptor in interfering with SMDPPEH molecular packing. However, after annealing at 100 °C for 5 minut es a single XRD peak is present for each material (Figure 4 9 d ). The peaks for 4 1com and 4 1 RS are both centere d at 2 = 6.53° ( d = 13.5 Å), while a broader peak is centered at 2 = 6.36° ( d = 13.9 Å) for 4 1syn . The spectral differences here may be assig ned to differences in isomer composition between the 4 1syn and 4 1com materials. For 4 1 S S and 4 1 R R , a single peak for each is observed at 2 = 6.79° ( d = 13.0 Å ) and 2 = 6.84° ( d = 12.9 Å), respectively. Again, we would expect identical behavior betwee n the enantiomers, however small processing differences, for example the clockwise rotation of the spin coater, may contribute to the differen ces observed in peak intensity. Comparing the annealed neat films to the annealed fi lms blended with PCBM, it is c lear that PCBM can have a strong effect on the phase adopted by the different SMDPPEH isomers. Of the fi ve materials, the neat crystal structure appears to be maintained only by 4 1 RS after blending with PCBM, while the othe r four materials show a signifi c ant shift toward shorter d spacing upon PCBM addition.

PAGE 151

151 The thin film surface morphologies of the five SMDPPEH m aterials were investigated using atomic force microscopy (AFM). Neat, unannealed fi lms (Figure 4 8a e ) all show a random pattern , with a root me an sq uare (RMS) roughness for all five fi lms in the range of 1.0 1.3 nm. Upon annealing, large crystal formation is observed ( Figures 4 10 f j ). While t he surfaces of the annealed neat films of 4 1syn and 4 1com (Figures 4 10 f , g ) appear nearly identical , t h e annealed 4 1 SS and 4 1 RR fi lms (Figures 4 10 h , i ) both show noticeably larger domain features, and contain two different phases, consistent with the XRD data shown in Figure 4 7b. The anne aled neat fi lm of 4 1 RS (Figure 4 10 j) is signifi cantly fl atter tha n the others, with an RMS roughness of 3.3 nm. The 4 1syn , 4 1com , 4 1 SS , and 4 1 RR annealed fi lms show RMS roughnesses of 9.3, 8.1, 6.6, and 10.0 nm, respectively . Figure 4 10 . AFM images of neat unannealed (top) and annealed (bottom) spin coated films of (a,f) 4 1syn , (b,g) 4 1com , (c,h) 4 1 RR , (d,i) 4 1 SS , and (e,j) 4 1 RS , respectively. All images are 5 x 5 . Without any annealing, fi lms blended with PCBM are q uite flat and generally featureless, with RMS roughness of approximately 0.6 nm for all fi ve materials (Figure 4 11 a e ). After annealing, however, two dis tinct morphologies are observed for the 4 -

PAGE 152

152 1syn :PCBM, 4 1com :PCBM, and 4 1 RS :PCBM fi lms (Figures 4 11 f h) on one hand , and 4 1 RR :PCBM and 4 1 SS :PCBM fi lms on the other hand. The annealed blende d films were generally fl atter than the annealed neat fi lms, although less so for 4 1 RR and 4 1 SS isomers, with RMS roughnesses of 1.3, 1.5, 3.3, 7.4 and 1.0 nm for annealed 4 1syn :PCBM, 4 1com :PCBM, 4 1 SS :PCBM, 4 1 RR :PCBM, and 4 1 RS :PCBM fi lms, respective ly. In summary, very similar surface morpholog y is observed for unannealed films of all fi ve isomers; however, upon thermal annealing signifi cant differences are observed. The observed differences agree well with XRD data, and the techniques taken together suggest a number of different phases form depending on the isomer type and processing conditions. Figure 4 11 . AFM images of unannealed (top) and annealed (bottom) spin coated blended films ( 1:1 by weight with PCBM ) of (a,f) 4 1syn , (b,g) 4 1com , (c,h) 4 1 SS , (d,i) 4 1 RR , and (e,j) 4 1 RS . The scanning area is 5 x 5 for all images. Optical absorp tion spectra of SMDPPEH thin fi lms prepared on glass substrates (precoated with 25 nm thick PEDOT:PSS fi lms) are presented in Figure 4 1 2 . All films show th ree absorption bands cent ered at 400 nm, 635 nm and 720 nm. The first absorption peak is attributed to for both the thiophene and the central

PAGE 153

153 diketopyrrolopyrrole (DPP) units, 135b while the second and third peaks are attributed to intra and intermolecular charge transfer transition s, respectively. Given that neat unannealed fi lms of 4 1syn , 4 1 com , and 4 1 RS show similar absorption spectra ( Figure 4 1 2 a ), speaks to the greater ability of 4 1 RS to crystallize, thus dominating the crystal phases of 4 1syn and 4 1 com , with disordered regions containing the RR and SS SMDPPEH isomers in between. The se observations are supported by the XR D data (Figure 4 9 a). On the other hand, neat unannealed fi lms of 4 1 RR and 4 1 SS show slightly blue shifted abs orption peaks, with the shoulder at 600 nm becoming more prominent. As seen in the XRD analysis above, these fi lms crystallize into a different phase than the 4 1 RS containing films. After annealing, the spectral shape of the absorption from neat 4 1syn and 4 1 com fi lms is relatively unchanged ( Figure 4 1 2 b ), but a slight blue shift i s observed. Moreover, the 4 1 RS absorption spectrum no longer ma tches th ose of the isomeric mixtures, suggesting that the meso compound adopts a different phase, in agreement with XRD measurements. Again, after annealing, 4 1 SS and 4 1 RR films also show nearly identical absorption spectra. Taking the neat fi lm XRD and absorption data tog ether, before annealing, the RS SMDPPEH component of the isomer blends crystallizes the fastest, and thus dominates the absorption and XRD spectra of unannealed 4 1syn and 4 1 com fi lms. However, after annealing, the isomer blends take on a crystal structure that is different from bo th 4 1 RR and 4 1 SS fi lms on the one hand, and the 4 1 RS film on the other. It can be concluded that after annealing the isomer blends crystallize into a structure that incorporates all three of the isomers.

PAGE 154

154 F igure 4 1 2 . Absorption spectra for spin coated films of 4 1 on glass/PEDOT:PSS not annealed (a,c) and annealed (at 100 ° C for 5 minutes) (b,d) neat (a,b) and blended with PCBM (1:1 by weight) (c,d). The absorption spectra for unannealed 4 1 :PCBM blended f ilms are nearly identical ( Figure 4 1 2 c ) as a result of the low crystallinity of these fi lms. After annealing, however, all of the films are found to crystallize, resulting in differentiation of the absorption spectra ( Figure 4 1 2 d ). The most pronounced ch ange is observed for the annealed 4 1 RR and 4 1 SS :PCBM films, for which the 600 nm peak becomes dominant, while the peak at 700 nm is strongly suppressed. In agreement with the AFM and XRD results, the annealed 4 1 RS :PCBM film absorption spectrum resembles that of the 4 1syn and 4 1 com :PCBM fi lms, albeit with a reduction in intensity of the 700 nm a) b) c) d)

PAGE 155

155 peak. This peak has been previously assigned to intermolecular charge transfer in 4 1syn due to aggregate species, 135b and thus a reduction in its intensity may be interpreted as a reduction in crystallinity. However, such a conclusion is not supported by the AFM and XRD measurements in this work, which show that the surface morphology and degree of crystallization of annealed 4 1 RS :PCBM, 4 1syn :PCBM, and 4 1 com :PCBM fi lms are quite similar. Photovoltaic Device Performance In order to probe the effect of side chain stereochemistry on the optoelectronic propert ies of the SMDPPEH materials, photovoltaic devices were fabricated with the structure: indium tin oxide (ITO)/PEDOT:PSS/ 4 1 :PCBM/Al. Active layer formation was carried out in an id entical fashion to the fi lms analyzed above. Unannealed devices showed very similar performance with the exception of the 4 1 RS :PCBM device ( Table 4 4, Figure 4 1 3 a ,b ). For the other fo ur materials, relatively low fi ll factors (FF) of 34 36% presumably result from fast recombination of charge carriers in the amorphous blends due t o a lack of effi cient charge extraction pathways. External quantum effi ciencies (EQEs) in all four cases are also very similar ( Figure 4 1 3 b ); as the light absorption effi ciency was found to be the same, this suggests that the internal quantum effi ciencies are nearly identical. The stereochemical purity of the 2 ethylhexyl side chains is not expected to signifi cantly affect the electrical properties of the films when they are not allowed to crystallize. Thus, it is inferred that the more readily crystallizi ng 4 1 RS material begins to phase segregate from the PCBM without annealing, leading to enhanced charge extraction in the corresponding device and a signifi cantly higher FF of 45%.

PAGE 156

156 Table 4 4 . Characteristics of 4 1 photovoltaic devices Material Annealed V o c ( V ) J sc ( mA/cm 2 ) FF ( % ) PCE ( % ) 4 1 syn no 0.742 ± 0.005 5.4 ± 0.2 35 ± 1 1.4 ± 0.1 4 1 com no 0.742 ± 0.006 5.3 ± 0.2 34 ± 1 1.3 ± 0.1 4 1 SS no 0.756 ± 0.005 5.5 ± 0.2 36 ± 1 1.5 ± 0.1 4 1 RR no 0.752 ± 0.007 5.2 ± 0.4 35 ± 2 1.4 ± 0.2 4 1 RS no 0.740 ± 0.005 6.5 ± 0.2 45 ± 2 2.2 ± 0.2 4 1 syn yes 0.800 ± 0.005 7.3 ± 0.2 52 ± 1 3.0 ± 0.1 4 1 com yes 0.766 ± 0.005 7.5 ± 0.3 50 ± 1 2.9 ± 0.1 4 1 SS yes 0.705 ± 0.005 7.8 ± 0.3 52 ± 1 2.9 ± 0.1 4 1 RR yes 0.703 ± 0.005 7.6 ± 0.3 50 ± 1 2.7 ± 0.1 4 1 RS yes 0.688 ± 0.005 5.1 ± 0.2 55 ± 1 1.9 ± 0.1 For annealed devices ( Figures 4 1 3 c,d and Table 4 4 ) the performance is again quite similar for all of the devices except those featuring 4 1 RS . The most dramatic change after annealing for the other four material s is the increase in FF to 50 52%. Additionally, peak EQE increases from 30% for the unannealed devices up to 43 45% for the annealed devices, resulting in a relative increase in J SC by 35 45%. Clearly, the crystallization that occurs during the annealing step for the 4 1syn :PCBM, 4 1 com :PCBM, 4 1 SS :PCBM, and 4 1 RR :PCBM devices results in an improved photocurrent generation effi ciency. For these annealed devices, the EQE spectral shape matches the film absorption spectra above, with 4 1 RR and 4 1 SS showing stronger absorption from the 600 nm peak and 4 1syn and 4 1 com showing stronger absorption from the 700 nm peak. On balance, the spectral shift results in a similar short circuit current ( J SC ) of 7.3 7.8 mA/cm 2 for these four annealed devices. Differences in device performance for 4 1 RR and 4 1 SS may be related to differences in the degree of donor crystallization, as observed in the XRD data. A signifi cant reduction in open circuit voltage ( V OC ) is observed for 4 1 RR and 4 1 SS devices (0.703 V and 0.705 V, respectively) relative to 4 1syn and 4 1 com devices (0.800 V and 0.766

PAGE 157

157 V, respectively). If these differences in V OC resulted from a change in band gap ( E g ), we would expect to see a red shift of 30 50 nm in the absorption onset of the 4 1 RR and 4 1 SS dev ices relative to the 4 1syn and 4 1 com devices. A red shift is indeed observed in the onset of EQE, but only by approximately 5 10 nm. The discrepancy may arise from a difference in the relative shift of the optical and transport gaps. 150 Figure 4 1 3 . Characterization of 4 1 BHJ photovoltaic devices. (a,c) show current density under 1 sun AM1.5G illumination, (b,d) are EQE spectra. (a,b) were not annealed, while (c,d) were annealed at 100 ° C for 5 minutes. Unlike the other four devices, annealing of the 4 1 RS :PCBM device results in a reduction in EQE, and therefore a reduction in J SC . Differences in overall absorption canno t explain the reduction in EQE observed here, as peak EQE for the 4 1 RS :PCBM a) b) c) d)

PAGE 158

158 device is only 26% ( Figure 4 1 3 d ). Instead, some internal element of photocurrent generation effi ciency must be negatively affected by the annealed 4 1 RS morphology. O verall, we fi nd that the photovoltaic device performance is only weakly affected by the differences in morphology between the pure stereoisomers 4 1 SS / 4 1 RR and the stereoisomeric mixtures 4 1syn / 4 1 com . Shifted absorption spectra balance out to give appro ximately the same coverage of the solar spectrum. Moreover, although very different surface morphologies are observed with AFM, coincidently the ability of each of these materials to transport charges is only weakly affected. However, 4 1 RS devices perform much differently from those made with the other four materials. This isomer crystallizes more rapidly, resulting in differences in optimum fi lm processing. Most notably, while the PCE of the other devices improved upon mild thermal annealing at 100 °C, th e performance of the 4 1 RS :PCBM device deteriorated with the same treatment. It is expected that a more thorough optimization of processing conditions for this material could bring the overall effi ciency closer to that of the other four materials. Conclusi on The goal of the current work has been to evaluate the consequences of 2 ethylhexyl solubilizing group chirality, and the isomeric complexity it creates, conjugated molecule morphology and bulk heterojunction photovoltaic device performance. To this end, SMDPPEH, a commercially available organic semiconductor, was prepared in isomerically defined form from enantiomerically pure reagents. The crys tallization behavior and optoelectronic properties neat and as blends with PCBM of the three pure isomers ( 4 1 RR , 4 1 SS , and 4 1 RS ) were systematically compared to

PAGE 159

159 typical 1:1:2 isomer mixtures purchased commercially ( 4 1 com ) or prepared in the laborator y ( 4 1 syn ). Expectedly and gratifyingly, the enantiomers ( 4 1 RR , and 4 1 SS ) showed overall similar thin film morphology and absorption (neat and as blends; annealed or unannealed), and consequently bulk heterojunction device performance throughout the stud ies. Although different in these respects from the enantiomers, and despite small differences in isomer composition, 4 1 syn and 4 1 com showed similar morphologies and optoelectronic characteristics. All four SMDPPEH compositions were amorphous as 1:1 blend s with PCBM without post deposition thermal annealing, a situation where the crystallinity, and therefore stereochemical information, was lost. 4 1 RS was found to crystallize most readily of the pure isomers, in the presence and absence of PCBM, and conseq uently dominated the absorption and XRD profiles of the neat isomeric mixtures. Indeed, 4 1 RS maintained some crystallinity in the presence of PCBM prior to thermal annealing resulting in a 50 60% improvement in photovoltaic device performance relative to the other four compositions. After thermal annealing, 4 1 RR / 4 1 SS , 4 1 syn / 4 1 com , and 4 1 R S revealed different crystal structures and morphologies suggesti ng that the isomer mixtures ( 4 1 syn and 4 1 com ) adopted a phase that incorporated all three component s. Blending with PCBM had a strong effect on the crystal packing (by XRD), where again the more strongly crystallizing 4 1 R S dominated the profiles of the isomer mixtures. For 4 1 syn , 4 1 com , 4 1 SS , and 4 1 RR , a substantial increase in photovoltaic device performance was observed after thermal annealing, while 4 1 R S showed a decrease in device performance. Overall, the stereocenter affected the morphology of the active layer and

PAGE 160

160 the thin film absorption spectra, but had a relatively weak effect on the overa ll photovoltaic performance. The extent to which alkyl side chain stereochemistry should be considered an important tunable parameter in materials design is most certainly device/application dependent. To wit, Nguyen and coworkers demonstrated that while t he isolated stereoisomers of DPP(TBFu) 2 showed similar morphologies, RS DPP(TBFu) 2 displayed much higher FET mobility (before and after annealing) as a consequence of its crystal structure d omain shap e/size and smaller fi lm roughness (versus RR and SS DPP(TBFu) 2 ). The study conveys the importance of isomeric and the observation appears generally extendable to other conjugated systems. 43b Our wor k shows that the side chain chirality, while strongly impacting the thin film morphology an d optical properties of SMDPPEH , has modest effects on the photovoltaic performance of the material as blends with PCBM. While this does not mean that side chain ste reochemistry does not infl uence blend structure, it does suggest that the structural consequences lead to fortuitously compensatory optoelectronic effects in this context. Studies among additional classes of semiconductors will expose whether side chain ch irality can be employed to rationally improve OPV effi ciency or whether it can be Experimental General Methods Reagents and solvents were purchased from commercial sources and used without further purification unless otherwise specified. THF, Et 2 O, CH 2 Cl 2 , and DMF were degassed in 20 L drums and passed through two sequential purification columns

PAGE 161

161 (activated alumina; molecular sieves for DMF) under a positive argon atmosphere. 2 (5' Hexyl [2,2' bithiophen] 5 yl) 4,4,5,5 tetramethyl 1,3,2 dio bis(diphenylphosphino)ferrocene]dichloro palladium(II) (complex with dichloromethane, [Pd(dppf)Cl 2 CH 2 Cl 2 ]) were purchased from Sigma Aldrich and used as received. Thin layer chromatography (TLC) was performed on SiO 2 60 F 254 aluminum plates with visualization by UV light or staining. Flash column chromatography was performed particle size from Sigma Aldrich. Isomeric purity was determined by chiral H PLC analysis (Shimadzu) using Chiralpack IA column. Specific Optical rotations were obtained on a JASCO P 2000 Series Polarimeter (wavelength = 589 nm) and then corresponded to the literature. 500 (125) MHz 1 H ( 13 C) NMR were recorded on an INOVA 500 spectr ometer. Chemical shifts ( ) are given in parts per million (ppm) relative to TMS and referenced to residual protonated solvent purchased from Cambridge Isotope Laboratories, Inc. (CDCl 3 : H 7.26 ppm, C 77.16 ppm; DMSO d 6 : H 2.50 ppm, C 39.52 ppm). Abbreviations used are s (sing let), d (doublet), t (triplet), q (quartet), quin (quintet), hp (heptet), b (broad), and m ( multiplet). Refer to Adv. Funct. Mater. 2014 , 24 , 5993 6004 to view the 1 H and 13 C NMR spectra. ESI TOF , APCI TOF , and DART TOF MS spectra were recorded on an Agi lent 6210 TOF spectrometer with MassHunter software. EI MS (70 eV) spectra were recorded on a Thermo Scientific DSQ MS after sample introduction via GC with data processing on Xcalibur software (accurate masses are calculated with the CernoBioscience MassW orks software). MALDI TOF MS was performed on a AB Sciex TOF/TOF 5800 in reflectron mode while

PAGE 162

162 the data is processed with Data Explorer. Samples were prepared by mixing the molecule of interest in dithranol (DTL) and then applied onto the MALDI plate. Synt hesis of RR SMDPPEH (4 1 RR ) ( R ) 4 Benzyl 3 hexanoyloxazolidin 2 one (4 3 R ). 139 N Methylmorpholine (8.70 mL, 79.0 mmol) and ethylchloroformate (6.80 mL, 71.7 mmol) were added consecutively at 0 °C drop wise to a solutio n of hexanoic acid (8.50 mL, 68.3 mmol) in THF (200 mL). In a different flask, ( R ) 4 benzyloxazolidin 2 one 4 2 R (10.0 g, 56.4 mmol) and lithium chloride (3.59 g, 84.6 mmol) were dissolved in 50 mL of THF and cooled to 0 °C. Triethylamine (15.7 mL, 113 mmo l) was then added. After stirring for 1 h, the aforementioned activated anhydride solution was added slowly at 0 °C. The mixture was stirred for 3 hours and the temperature was allowed to slowly rise to rt. After stirring overnight, the solvent was removed under reduced pressure. The crude mixture was diluted with DCM, washed with 1N HCl solution (2 25 mL), brine (2 25 mL), and 5 % sodium carbonate solution (2 25 mL). It was then dried over Na 2 SO 4 and concentrated in vacuo to afford an oil which was purifie d by column chromatography (EtOAc:hexanes, [ ] 23 D (deg cm 3 g dm ) = 95.3° (1.2 g cm MeOH); lit[ ] 23 D (deg cm 3 g dm ) = 103.9° (0.6 g cm MeOH); 151 1 H NMR (500 MHz, CDCl 3 , ): 7.35 7.31 (m, 2H), 7.29 7.26 (m, 1H), 7.22 7.20 (m, 2H), 4.67 (ddt, J = 10; 7.5; 3 Hz, 1H), 4.21 4.15 (m, 2H), 3.30 (dd, J = 13.5; 3.5 Hz, 1H), 3.00 2.86 (m, 2H), 2.77 (dd, J = 13.5; 9.5 Hz, 1H), 1.72 1.68 (m, 2H), 1.38 1.36 (m, 4H), 0.93 0.90 (m, 3H); 13 C NMR (125 MHz, CDCl 3 , ): 173.5, 153.5, 135.4, 129.5, 129.0, 127.4, 66.2, 55.2, 38.0, 35.5, 31.3, 24.0, 22.5, 14.0; HRMS (ESI) m / z : [M+Na] + calcd for C 16 H 21 NNaO 3 298.1414; found: 298.1428.

PAGE 163

163 ( R ) 4 Benzyl 3 (( R ) 2 ethylhexanoyl)oxazolidin 2 one ( 4 4 R ) . 136 A solution of ( R ) 4 benzyl 3 hexanoyloxazolidin 2 one 4 3 R (3.00 g, 10.9 mmol) in THF (15 mL) was added drop wise to a solution of NaHMDS (1.0 M in THF) (16.3 mL, 16.3 mmol) at 78 °C. After 1 h, ethyliodide (2.60 mL, 32 .7 mmol) filtered through dry aluminum oxide, was added drop wise. The resulting mixture was allowed to stir at 40 °C for 16 h. The reaction was quenched by addition of a saturated solution of ammonium chloride at 30 °C, followed by evaporation of the or ganic solvent. The aqueous phase was extracted with CHCl 3 (2 25 mL), the organic extracts were dried over Na 2 SO 4 and the solvent was removed under vacuo . The residue was purified by column chromatography on silica gel (EtOAc:hexanes, 5:95) to afford the ti tle compound as a colorless oil (2.45 g, 8.07 mmol, 75%). [ ] 23 D (deg cm 3 g 1 dm 1 ) = 63.2° (1.0 g cm 3 DCM); 1 H NMR (500 MHz, CDCl 3 , ): 7.35 7.32 (m, 2H), 7.29 7.28 (m, 1H), 7.24 7.22 (m, 2H), 4.70 (ddt, J = 10.5; 7; 3.5 Hz, 1H), 4.13 4.19 (m, 2H), 3. 7 3 (tt, J = 7.8; 7.8; 6 Hz, 1H), 3.33 (dd, J = 13.5; 3.5 Hz, 1H), 2.70 (dd, J = 13.5; 10 Hz, 1H), 1.80 1.67 (m, 2H), 1.60 (ddd, J = 13.5; 7.5; 6 Hz, 1H), 1.53 1.46 (m, 1H), 1.28 (dddd, J = 21; 16; 9; 3.5 Hz, 4H), 0.96 (t, J = 7.5 Hz, 3H), 0.88 (t, J = 7 Hz, 3H); 13 C NMR (125 MHz, CDCl 3 , ): 177.0, 153.3, 135.6, 129.5, 129.0, 127.4, 66.0, 55.6, 44.2, 38.2, 31.3, 29.6, 25.6, 22.9, 14.1, 11.5; HRMS (ESI) m / z : [M+Na] + calcd for C 18 H 25 NNaO 3 : 326.1727; found: 326.1743. ( R ) 2 Ethylhexan 1 ol (4 5 R ). 136 To a mix ture of ( R ) 4 benzyl 3 (( R ) 2 ethylhexanoyl)oxazolidin 2 one 4 4 R (2.25 g, 7.40 mmol) and ethanol (0.50 mL, 8.10 mmol) in dry Et 2 O (20 mL) was added drop wise a 2.0 M solution of lithium borohydride in THF (4.40 mL, 8.90 mmol) at 0 °C. The reaction mixture was stirred at the same temperature for 3 h and quenched by adding brine solution (20 mL). The organic phase

PAGE 164

164 was washed with water (2 10 mL), dried over Na 2 SO 4 and the solvent was removed under reduced pressure. The crude product was purified by column ch romatography on silica gel (Et 2 O:pentane 50:50) to afford the product as a colorless oil (0.87 g, 6.67 mmol, 90%). [ ] 23 D (deg cm 3 g dm ) = 8.3° (1.0 g cm DCM); lit[ ] 23 D (deg cm 3 g dm ) = 3.1° (0.6 g cm DCM); 140 1 H NMR (500 MHz, CDCl 3 , ): 3.51 (d, J = 4.5 Hz, 2H), 1.76 (b, 1H), 1.38 1.26 (m, 8H) , 0.89 0.86 (m, 6H); 13 C NMR (125 MHz, CDCl 3 , ): 65.3, 42.1, 30.2, 29.2, 23.4, 23.2, 14.2, 11.2; 2 ethylhexan 1 ol (104 76 7) MS (GC EI) match score: 920; reverse match score: 927. ( R ) 2 Ethylhe xyl 4 methylbenzenesulfonate ( 4 6 R ). 142 To a stirred solution of ( R ) 2 ethylhexan 1 ol 4 5 R (5.00 mL, 32.0 mmol) and dry pyridine (7.70 mL, 95.9 mmol) in Et 2 O (50 mL) was added tosy lchloride (7.62 g, 40.0 mmol) at 0 °C, followed by addition of 4 dimethylaminopyridine (0.02 g, 0.16 mmol). The mixture was stirred at 4 °C for 48 h, then quenched with water with ice cooling, poured into 3 M HCl solution and extracted with Et 2 O (2 20 mL). The ethereal extract was washed with 1 M HCl solution (2 15 mL), water (2 15 mL), saturated solution of sodium NaHCO 3 (2 15 mL), and brine (2 15 mL), then dried over Na 2 SO 4 and concentrated under reduced pressure to give the crude that was used in the nex t step without further purification (7.28 g, 25.6 mmol, 80%). [ ] 23 D (deg cm 3 g 1 dm 1 ) = 8.8° (1.0 g cm 3 DCM); 1 H NMR (500 MHz, CDCl 3 , ): 7.79 (d, J = 8.5 Hz, 2H), 7.34 (d, J = 9 Hz, 2H), 3.92 (dd, J = 5.5; 2 Hz, 2H), 2.45 (s, 3H)1.5 (quin, J = 6 Hz, 1H), 1.35 1.28 (m, 2H), 1.27 1.18 (m, 2H), 1.16 1.10 (m, 2H), 0. 84 (t, J = 7.5 Hz, 3H), 0.79 (t, J = 7.5 Hz, 3H); 13 C NMR (125 MHz, CDCl 3 , ): 144.6, 133.1, 129.8, 127.9, 72.5, 39.0, 29.8, 28.6, 23.2, 22.8, 21.6, 13.9, 10.7; HRMS (ESI) m / z : [M+Na] + calcd for C 15 H 24 NaO 3 S: 307.1338; found: 307.1339.

PAGE 165

165 ( R ) 2 Ethylhexyl bro mide ( 4 7 R ). 142 ( R ) 2 Ethylhexyl 4 methylbenzenesulfonate 4 6 R (0.50 g, 1.80 mmol) was dissolved in dry acetone (5 mL), followed by addition of lithium bromide (0.23 g, 2.60 mmol). The mixture was refluxed overnight. The solvent was removed under reduced pressure. The crude product was dissolved in pentane, washed with water (2 10 mL), dried over Na 2 SO 4 , and the solvent was removed under reduced pressure to afford the product pure (0 .28 g, 1.44 mmol, 80%). [ ] 23 D (deg cm 3 g 1 dm 1 ) = 11.2° (1.0 g cm 3 DCM); 1 H NMR (500 MHz, CDCl 3 , ): 3.48 3.43 (m, 2H), 1.56 1.50 (m, 1H), 1.45 1.22 (m, 8H), 0.92 0.87 (m, 6H); 13 C NMR (125 MHz, CDCl 3 , ): 41.2, 39.2, 32.0, 29.0, 25.3, 23.0, 14.2, 11.0 ; HRMS (GC EI) m / z : [M] + calcd for C 8 H 17 Br : 192.0514; 194.0493; found: 192.0510; 194.0516 . 3,6 Di(thiophen 2 yl) 2,5 dihydropyrrolo[3,4 c ]pyrrole 1,4 dione ( 4 8 ). 143b A solution of t amyl alcohol (55 mL) and 2 thiophenecarbonitrile (5.00 mL, 53.7 mmol) was injected in one portion to a ro und bottom flask with potassium tert butylate (8.43 g, 75.2 mmol). The mixture was warmed to 110 °C and a solution of dimethyl succinate (2.32 mL, 17.7 mmol) in t amyl alcohol (14 mL) was added drop wise within 1 h. When the addition was completed, the rea ction was left stirring at the same temperature for 24 h. The mixture was next cooled to 65 °C, neutralized with acetic acid, and heated to reflux for another 10 min. The suspension was then filtered, and the black filter cake was washed with hot methanol and water (twice each) and dried under vacuum to afford the title product that was used in the next step without further purification (3.42 g, 11.4 mmol, 64%). 1 H NMR (500 MHz, DMSO d 6 , ): 11.26 (s, 2H), 8.21 (d, J = 3 Hz, 2H), 7.95 (dd, J = 4.2 Hz, 2H), 7.30 (dd, J = 4.5; 4 Hz, 2H); 13 C NMR (125 MHz, CDCl 3 , ):

PAGE 166

166 161.6, 136.2, 132.7, 131.3, 130.8, 128.7, 108.6; HRMS (APCI) m / z : [M+H] + calcd for C 14 H 8 N 2 O 2 S 2 : 301.0100; found: 301.0108. 2,5 Bis(( R ) 2 ethylhexyl) 3,6 di(thiophen 2 yl) 2,5 dihydropyrrolo[3,4 c ]pyrrole 1,4 dione ( 4 9 RR ). 152 Potassium carbonate (3.68 g, 26.6 mmol) was added to a solution of 3,6 di(thiophen 2 yl) 2,5 dihydropyrrolo[3,4 c ]pyrro le 1,4 dione 7 (2.00 g, 6.70 mmol) in dry DMF (60 mL), and the mixture was heated at 90 °C for 1 h. Then ( R ) 2 ethylhexyl bromide 4 7 R (4.75 mL, 26.6 mmol) was added and the mixture was stirred for 24 h at the same temperature. The suspension was then filt ered and the solvent removed under reduced pressure. The crude mixture was purified by column chromatography on silica gel (DCM). Then the residue was recrystallized from hexanes:DCM 9:1 to afford the title product as a red solid (1.58 g, 3.01 mmol, 45%). 1 H NMR (500 MHz, CDCl 3 , ): 8.88 (d, J = 3.7 Hz, 2H), 7.62 (d, J = 4.9 Hz, 2H), 7.27 (dd, J = 5; 4 Hz, 2H), 4.02 (quin, J = 7.1 Hz, 4H), 1.89 1.82 (m, 2H), 1.40 1.22 (m, 16H), 0.88 0.83 (m, 12H); 13 C NMR (125 MHz, CDCl 3 , ): 161.9, 140.6, 135.4, 130.6, 130 .0, 128.6, 108.1, 46.0, 39.2, 30.3, 28.5, 23.7, 23.2, 14.2, 10.6; HRMS (ESI) m / z : [M+Na] + calcd for C 30 H 40 N 2 O 2 S 2 : 547.2423; found: 547.2428. 3,6 Bis(5 bromothiophen 2 yl) 2,5 bis(( R ) 2 ethylhexyl) 2,5 dihydropyrrolo[3,4 c ]pyrrole 1,4 dione ( 4 10 RR ). 152 2,5 Bis(( R ) 2 ethylhexyl) 3,6 di(thiophen 2 yl) 2,5 dihydropyrrolo[3,4 c ]pyrrole 1,4 dione 4 9 RR (0.13 g, 0.25 mmol) and N bromosuccinimide (0.10 g, 0.54 mmol) were dissolved in dry CHCl 3 (6 mL), then the solution was pro tected from light and stirred at room temperature for 48 h. The mixture was poured into methanol, filtered, and washed with hot methanol twice to afford the pure product as a dark purple solid (0.14 g, 0.21 mmol, 81%). 1 H NMR (500

PAGE 167

167 MHz, CDCl 3 , ): 7.64 (d, J = 4 Hz, 2H), 7.22 (d, J = 4.5 Hz, 2H), 3.98 3.89 (m, 4H), 1.86 1.79 (m, 2H), 1.40 1.23 (m, 16H), 0.87 (dt, J = 10.5; 7.5 Hz, 12H); 13 C NMR (125 MHz, CDCl 3 , ): 161.5, 139.5, 135.5, 131.6, 131.3, 119.2, 108.1, 46.1, 39.2, 30.3, 28.5, 23.7, 23 .2, 14.2, 10.6; HRMS (DART) m / z : [M+H] + calcd for C 30 H 38 Br 2 N 2 O 2 S 2 : 681.0741; 683.0721; found: 681.0802; 683.0789. 2,5 Bis(( R ) 2 ethylhexyl) 3,6 bis(5'' hexyl [2,2':5',2'' terthiophen] 5 yl) 2,5 dihydropyrrolo[3,4 c ]pyrrole 1,4 dione ( 4 1 RR ). 3,6 Bis(5 brom othiophen 2 yl) 2,5 bis(( R ) 2 ethylhexyl) 2,5 dihydropyrrolo[3,4 c ]pyrrole 1,4 dione 4 10 RR (0.14 g, 0.21 mmol), 2 (5' hexyl [2,2' bithiophen] 5 yl) 4,4,5,5 tetramethyl 1,3,2 dioxaborolane 3 7 (0.20 g, 0.52 mmol), potassium carbonate (0.46 g, 3.33 mmol), a liquot 336 (2 drops), and Pd(dppf)Cl 2 CH 2 Cl 2 (0.03 g, 0.04 mmol) were added to a round bottom flask under argon atmosphere, followed by addition of degassed toluene (6 mL) and water (2 mL), and the mixture was heated at 80 °C for 24 h. The mixture was cool ed to rt. The solution was diluted with DCM (15 mL), washed with water (2 10 mL), then dried over Na 2 SO 4 , and the solvent was removed under reduced pressure. The crude product was purified by column chromatography on silica gel (DCM). Then the residue was recrystallized from hexanes:DCM (9:1) (0.11 g, 0.11 mmol, 53%). 1 H NMR (500 MHz, CDCl 3 , ): 8.94 (d, J = 4.5 Hz, 2H), 7.27 (d, J = 4 Hz, 2H), 7.19 (d, J = 4 Hz, 2H), 7.03 (dd, J = 6.5; 4 Hz, 2H), 6.70 (d, J = 3.5 Hz, 2H), 4.09 3.99 (m, 4H), 2.80 (t, J = 8 Hz, 4H), 1.97 1.89 (m, 2H), 1.69 (quin, J = 7.5 Hz, 4H), 1.41 1.29 (m, 30H), 0.90 (dt, J = 15; 7.5 Hz, 20H); 13 C NMR (125 MHz, CDCl 3 , ): 161.8, 146.6, 142.7, 139.4, 139.1, 136.9, 134.2, 134.2, 128.1, 125.9, 125.2, 124.6, 124.1, 124.0, 108.5, 46.1, 39.4, 3 1.7, 31.7, 30.5, 30.4, 28.9, 28.7, 23.8, 23.4, 22.7, 14.3, 14.2, 10.7; HRMS (MALDI) m / z : [M] + calcd for

PAGE 168

168 C 58 H 72 N 2 O 2 S 6 : 1021.3990; found: 1021.3986. Anal. calcd. for C 58 H 72 N 2 O 2 S 6 : C, 68.19; H, 7.10; N, 2.74; found: C, 67.93; H, 7.35; N, 2.74. Synthesis of s yn SMDPPEH (4 1syn) 2,5 Bis(2 ethylhexyl) 3,6 di(thiophen 2 yl) 2,5 dihydropyrrolo[3,4 c]pyrrole 1,4 dione (9). 152 9 was prepared analogously to 4 9 RR beginning from 4 8 (0.50 g, 1.66 mmol), rac 3 (bromomethyl)heptane ( 0.74 mL, 4.16 mmol), and K 2 CO 3 (0.92 g, 6.66 mmol) in DMF (15 mL). The product was obtained as a red solid (0.31 g, 0.58 mmol, 35%) . 1 H NMR (500 MHz, CDCl 3 , ): 8.88 (dd, J = 4; 0.5 Hz, 2H), 7.62 (dd, J = 4.5; 0.5 Hz, 2H), 7.27 (dd, J = 5; 4 Hz, 2H), 4.07 3.98 (m, 4H), 1.89 1.82 (m, 2H), 1.40 1.23 (m, 16H), 0.86 (dt, J = 12; 7.5 Hz, 12H); 13 C NMR (125 MHz, CDCl 3 , ): 161.9, 140.5, 135.4, 130.6, 130.0, 128.5, 1 08.0, 46.0, 39.2, 30.3, 28.5, 23.7, 23.2, 14.1, 10.6; HRMS (ESI) m / z : [M+Na] + calcd for C 30 H 40 N 2 O 2 S 2 : 547.2423; found: 547.2429. 3,6 Bis(5 bromothiophen 2 yl) 2,5 bis(2 ethylhexyl) 2,5 dihydropyrrolo[3,4 c ]pyrrole 1,4 dione (10). 152 10 was prepared analogously to 4 10 RR beginning from 4 9 RR (0.40 g, 0.76 mmol), and N bromosuccinimide (0.28 g, 1.56 mmol) in CHCl 3 (15 mL). The product was obtained as a purple solid (0.39 g, 0.56 mmol, 74%) . 1 H NMR (500 MHz, CDCl 3 , ): 8.6 4 (d, J = 4 Hz, 2H), 7.22 (d, J = 4.2 Hz, 2H), 3.92 (dt, J = 10.5; 5.5 Hz, 4H), 1.83 (quin, J = 6.5 Hz, 2H), 1.38 1.22 (m, 16H), 0.87 (dt, J = 10.5; 7.5 Hz, 12H) ; 13 C NMR (125 MHz, CDCl 3 , ): 161.5, 139.5, 135.5, 131.6, 131.3, 119.2, 108.1, 46.1, 39.2, 30. 3, 28.5, 23.7, 23.2, 14.2, 10.6; HRMS (DART) m / z : [M+H] + calcd for C 30 H 38 Br 2 N 2 O 2 S 2 : 681..0741; 683.0721 found: 681.0814; 683.0795. 2,5 Bis(2 ethylhexyl) 3,6 bis(5'' hexyl [2,2':5',2'' terthiophen] 5 yl) 2,5 dihydropyrrolo[3,4 c ]pyrrole 1,4 dione ( 4 1 syn). 4 1 syn was prepared analogously to 4 1 RR beginning from 10 (0.30 g, 0.45 mmol), 3 7 (0.42 g, 1.12 mmol), K 2 CO 3 (0.99

PAGE 169

169 g, 7.16 mmol), and Pd(dppf)Cl 2 (0.06 g, 0.09 mmol), and aliquot 336 (2 drops) in degassed toluene (9 mL) and water (3 mL). The product was obtained as a magenta solid (0.34 g, 0.33 mmol, 74%) . 1 H NMR (500 MHz, CDCl 3 , ): 8.94 (d, J = 4 Hz, 2H), 7.23 (d, J = 4 Hz, 2H), 7.16 (d, J = 3.5 Hz, 2H), 7.01 (t, J = 3 Hz, 2H), 6.69 (d, J = 3.5 Hz, 2H), 4.07 3.97 (m, 4H), 2.79 (t, J = 8 Hz, 4H), 1.94 1 .88 (m, 2H), 1.68 (quin, J = 7.5 Hz, 4H), 1.41 1.29 (m, 30H), 0.90 (dt, J = 14; 7.5 Hz, 20H); 13 C NMR (125 MHz, CDCl 3 , ): 161.7, 146.5, 142.6, 139.3, 139.0, 137.0, 134.2, 134.2, 128.0, 125.9, 125.1, 124.5, 124.1, 123.9, 108.4, 46.1, 39.4, 31.7, 31.7, 30.5 , 30.4, 28.9, 28.7, 23.9, 23.8, 23.3,22.7, 14.2, 10.7; HRMS (MALDI) m / z : [M] + calcd for C 58 H 72 N 2 O 2 S 6 : 1021.3990; found: 1021.3950. Anal. calcd. for C 58 H 72 N 2 O 2 S 6 : C, 68.19; H, 7.10; N, 2.74; found: C, 68.16; H, 7.31; N, 2.53. Solution B ased Characterization s Absorption M easurements A bsorption spectra were measured for at least six different concentrations (2.5 cuvettes. All solvents were spectrophotometric grade and purchased from Sigma Aldrich. The absorption in tensity at max was then plotted against the concentration in all cases to confirm, by linearity, that the Molar extinction coefficients ( ) were determined from the linear plot for each compound (where A = bc ). Electrochemi stry Cyclic Voltammetry (CV) and Differential Pulse Voltammetry (DPV) measurements were performed for 4 1syn , 4 1 com and 4 1 RR using a single compartment three electrode cell under argon blanket with a platinum flag as the

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170 counter electrode, a silver wire reference electrode, and a platinum disk (0.02 cm 2 ) as the working electrode. Tetrabutylammonium hexafluorophosphate (TBAPF 6 ) was purchased from Aldrich. DCM was collected from an Innovative Technologies solvent system, sparged with Ar and passed over two columns of 5 Å activated sieves. SMDPPEH solid was dissolved to a concentration of 3.5 mM in a 0.1 M TBAPF 6 /DMF electrolyte. A Voltammetric Analyzer potentiostat/galvanostat was used under the control of BAS CV 50W software from Bioanalytical Systems. T he scan rate for CV was 100 mV/s. Solid State Characterizations Thermal A nalysis Thermal gravimetric analysis (TGA) was performed on 4 1syn , 4 1 com , 4 1 SS , 4 1 RR , and 4 1 RS using a TA Instruments TGA Q5000 0121 V3.8 Build 256 at a heating rate of 10 °C/min using 1 3 mg of sample in a 100 L platinum pan (under nitrogen). The data was analyzed on Universal Analysis 2000 4.4A software. Differential Scanning Calorimetry (DSC) was performed on 4 1syn , 4 1 com , 4 1 SS , 4 1 RR , and 4 1 RS using a TA Instruments DSC Q 1000 0620 V9.9 at a heating/cooling rate of 10 °C/min using 1 3 mg of sample in a sealed aluminum pan, with respect to an empty aluminum reference pan. Three cycles of heating and subsequent cooling were performed, however, only the second full cycle is sh own. The data was analyzed on Universal Analysis 2000 4.4A software. X Ray E xperimental X Ray Intensity data were collected at 100 K on a Bruker DUO diffractometer using CuK radiation ( = 1.54178 Å), from an ImuS power source, and an APEXII CCD area dete ctor.

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1 71 Raw data frames were read by program SAINT 1 and integrated using 3D profilin g algorithms. The resulting data were reduced to produce hkl reflections and their intensities and estimated standard deviations. The data were corrected for Lorentz and p olarization effects and numerical absorption corrections were applied based on indexed and measured faces. The structure was solved and refined in SHELXT2014 , using full matrix least squares refinement. The non H atoms were refined with anisotropic the rmal parameters and all of the H atoms were calculated in idealized positions and refined riding on their parent atoms. The molecules are located on inversion centers thus a half molecule is appears in the asymmetric unit. The n hexyl group on C15 is diso rdered and is was refined in two parts with their site occupation factors dependently refined to 0.51(1) and 0.49(1) for the major and minor parts, respectively. Additionally, the ethyl and n butyl groups on C23 are disordered and also were refined in two parts with their site occupation factors dependently refined to 0.0.727(4) and 0.273(4) for the major and minor parts, respectively. The existence of both disordered regions lead to the conclusion that the molecules exist in all possible stereoisomers. In the final cycle of refinement, 4642 reflections (of which 3941 are observed with I > 2 (I)) were used to refine 411 parameters and the resulting R 1 , wR 2 and S (goodness of fit) were 4.64 %, 12.74 % and 1.077 , respectively. The refinement was carried out by minimizing the wR 2 function using F 2 rather than F values. R 1 is calculated to provide a reference to the conventional R value but its function is not minimized. SHELXTL2014 (2014). Bruker AXS, Madison, Wisconsin, USA.

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172 Thin Film C haracterizatio n UV vis absorption (thin film) measurements were carried out with a calibrated Newport 818 UV Si photodiode illuminated by a Newport Oriel Apex illuminator and monochromator system chopped at 400 Hz. The signal was detected using a Stanford Research Sy stems SR830 DSP lock in amplifi er. Atomic force microscopy was carried out using a Veeco Innova AFM in tapping mode with a silicon tip (radius 8 nm) at 325 kHz with a force constant of approximately 40 N/m. X ray diffraction measurements were performed using a the 2 mode using Cu K radiation Device Fabrication and C haracterizatio n Organic photovoltaic devices were fabricated on commercial indium tin oxide (ITO) coated glass substrates with a sheet resistance of 15 /square, while films for XRD and AFM analysis were fabricated o n Si(100) substrates. The substrates were sequentially sonicated for 15 minutes in detergent, water, acetone and isopropanol before UV ozone treatment for an additional 15 minutes. PEDOT:PSS (Clevios AI4083) was spin coated in air at 8000 rpm to form a 25 nm thick layer, which was annealed at 150 °C for 30 minutes in air before passing into a nitrogen glovebox (H 2 O 1 ppm). Photovoltaic active layers were spin coated from a 5:5 mg/mL solution of SMDPPEH:PC 61 BM in CHCl 3 at 500 rpm to form a 110 nm thick l ayer. Films were then passed into a vacuum chamber pumped down to 10 Torr, and a 100 nm Al cathode was evaporated through a shadow mask with thicknesses monitored by a quartz crystal monitor. The cross bar geometry was used to defi ne an active area of 4 mm 2 for the

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173 organic photovoltaic cells. After aluminum deposition, some devices were annealed at 100 °C for 5 minutes in a nitrogen glovebox, and then encapsulated with a UV curable epoxy layer to prevent degradation from exposure to ambient oxygen and wa ter before characterization in air. Devices were characterized under illumination from a 150W Xe arc lamp solar simulator with a KG1 filter, calibrated to 1 sun intensity using the AM1.5G spectrum. External quantum efficiency measurements were carried out with a calibrated Newport 818 UV Si photodiode illuminated by a Newport Oriel Apex illuminator and monochromator system chopped at 400 Hz. The photocurrent signal was detected using a Stanford Research Systems SR830 DSP lock in amplifier.

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174 CHAPTER 5 CONCLU SIONS AND FUTURE DIR ECTIONS conjugated oligomers can allow their molecular and supramolecular structures to be tailored in ways not provided by more conventional building blocks, 153 and their optoelectronic characteristics to be fine tuned. Synthesis, Optical Properties, and Electronic Structures of Nucleobase Containing Conjugated Oligomers conjugated materials, two families of nucleobase oligomers have been synthesized ( 2 1 and 2 2 ), and their optical and electronic properties were explored. The six purine terminate d ( 2 1a c and 2 2a c ) and two pyrimidine conjugated oligomers ( 2 1d and 2 2d ) served property trends. The absorption and emission profiles responded in un derstandable linker electronic structure. The electronic energy level of these systems showed dependence on the nature of the nucleobase within each family terthiophene (TTT) derivat ives 2 , fine tuning of the HOMO was achieved through replacing adenine ( 5.58 eV), by guanine ( 5.37 eV), or uracil ( 5.42 eV). Comparable behavior was observed for oligomers 2 bearing the 4,7 bisthienylbenzothiadiazole (TBT) spacer. On the other hand, the LUMO level showed more dependence on the core structure. Unlike 2 , intramolecular charge transfer governed the donor acceptor donor systems 2 created by introduction of the strong electron acceptor benzo[ c ][1,2,5]thiadiazole (BTD) ring , resulting in lower band gaps compared to the terthiophene linked nucleobases ( E ~1.8 eV vs. 2.4 eV based on electrochemical measurements). These results were in

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175 good agreement with theoretical calculations performed at the B3LYP/6 31+G** level. Overall, conjugated constructs to deliver tunable optoelectronic and stability characteristics. The synthetic protocols developed for the individual nucleobases can now be used to introduce a var iety of conjugated building blocks to provide appropriate optoelectronic properties, in addition to controlled assembly, needed for the construction of semiconductor based optoelectronic devices. Synthesis, Characterization, and Complementary Hydrogen Bo nding of Conjugated Nucleobase Oligomers Correlations between intermolecular order, solid state morphology, and material performance/efficiency are increasingly recognized for conjugated materials across a number of electronic architectures. 154 Supramolecular approaches are becoming popular strategies to gain control of chromophore ordering in solution and thin films. 35, 155 On that account, nucleobases emerge as potenti al scaffolds to approach well ordered conjugated architectures for potential optoelectronic applications. Given the low solubility of the previously studied nucleobase conjugated oligomers ( 2 1 and 2 2 ), more soluble versions were (and are currently being) synthesized (e.g., 3 1 ) in order to investigate the H bonding between the complementary nucleobases in extended conjugated systems in solution and the solid state. Consistent with previous results, the optoelectronic properties correlate well with the nature of the nucleobase as these nitrogen containing heterocycles contribute differently to the energy structure of the corresponding oligomers 3 1 . Theoretical calculations performed at the B3LYP/6 31+G** level were further evidence to these observations. Nucleobases have been extensively studied in solution, where much has been learned of their association

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176 behavior in different environments. 5, 17b, 41, 156 However, the effect of the extended conjugation on the H bonding capabilities of the nucleobases after the alteration of their electronic structure has not been fully investigated. Before exploring the heteroassociation between 3 1 and 2 2 7 , the self dimerization ability of the compounds was studied. Low self association constants were observed for both 3 1 and 2 2 7 ( K dim 17 M 1 ). For the assembly 3 1 2 2 7 , 1:1 binding stoichiometry was confirmed by Job plot analysis. The association constant ( K a ) was next determined by nonlinear regression analysis of 1 H NMR titration data. The value, 180 M 1 in CDCl 3 , is consistent with literature values for other adenine and uracil pairings. 41 These studies will permit a better understanding of how nucleobase structure can mutually confer tunability with respect to molecula r level structure, self assembly, and emergent electronic properties systems. The set of nucleobase containing conjugated oligomers was used as the basis for understanding the response of optoelectronic properties to nucleobase structural changes and solution phase self assembly. Future work will involve investigation of the ordering, film morphology, and device behavior. These studies will shed li ght on the complex relationships between molecular structure, solution phase and solid state supramolecular structure, and device performance, considering that nucleobases have not been investigated yet in device relevant settings where critical structure function relationships can be derived with respect to their base paired architectures. Also left unexplored, but worthy of future study, is the ability to tune conjugated oligomer

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177 optoelectronic properties post synthesis via protonation 157 and/or cation/metal coordination 158 of embedded nucleobases. In addition to edges capable of hydrogen bonding and surfaces capable of stacking, nucleobases are distinguished by multip le synthetic functionalization sites not available to conventional heterocycles, which gives the opportunity to consider more complex architectures that depart from traditional linear arrangements, as well as examining the possibility of having the Hoogste en H bonding faces exposed as opposed to the Watson Crick faces for H bond association. 159 Given the robust synthetic chemistry available to each nucleobase, it may even be possible to prepare hybrid systems, where the hydrogen bonded edges need not be identical. In this case the molecules will self assemble to form supramolecular polymers. The Influence of Solubilizing Chain Stereochemistry on Small Molecule Photovoltaics To improve the limit ed solubility of nucleobases derivatives, rac 2 ethylhexyl (EtHex) groups were introduced to the position otherwise occupied by the sugar. The choice of the solubilizing group was based on a series of solubility studies performed using uracil. The 2 ethylh exyl solubilizing chain, among the most popular in the literature, provided the best results among the other alkyl chains considered (Chapter 2). No doubt, the improved solubility is due to the chiral center that generates a mixture of stereoisomers, in sy ntheses that begin from racemic starting materials, and disrupts aggregation. Although side chains were long viewed as merely solubilizing insulating groups, recent work suggests that the type, size, topology and distribution of side chains can have a larg e impact on the solid state morphology, and charge transport properties

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178 of the materials and thus should also be fully explored in the design of new organic semiconductors. Typically, the stereochemistry of the 2 ethylhexyl side chain is ignored, and only recently has its ramifications for thin film based organic devices been exposed. 43b, 48 However, the effect of 2 ethylhexyl stereochemistry have not been investigated in the context of small molecule bulk heterojun ction photovoltaic device performance. Therefore we decided to study the functional consequences of the chiral chain on the optical, electrical, morphological, and photovoltaic properties of SMDPPEH ( 4 1 ) a well studied and commercially available organic s emiconductor. The pure stereoisomers have been synthesized and then characterized together with the commercially available sample and the one synthesized from racemic EtHex starting material. The isomeric composition did not have any effect on photophysic al properties in dilute solution. The set of pure enantiomers ( 4 1 RR and 4 1 SS ) showed expectedly similar thin film morphology and absorption properties while isomeric mixtures (available commercially and through synthesis from racemic alkylating agent) di splayed differences attributable to variations in isomeric composition. All 4 1 compounds showed nearly identical characteristics in spin coated amorphous films blended 1:1 with PCBM without thermal annealing. Bulk heterojunction photovoltaic devices were fabricated and investigated; all but the meso ( 4 1 RS ) isomer showed a substantial increase in device performance after annealing, presumable due to its higher degree of crystallization. This study showed that the side chain chirality, while strongly impact ing the thin film morphology and optical properties of 4 1 , has modest effects on the photovoltaic performance of the material as blends with PCBM. This means that side

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179 chain stereochemistry does indeed influence blend structure, but the structural consequ ences lead to unintentionally uniform optoelectronic effects in this context. Studies among additional classes of semiconductors will expose whether side chain chirality can be employed to rationally improve OPV efficiency or whether it can be

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180 APPENDIX A PROTON NUCLEAR RESON ANCE ( 1 H NMR) SPECTRA Figure A 1 . Proton nuclear magnetic resonance ( 1 H NMR) spectrum (CDCl 3 , 500 MHz) of 3 1a . Figure A 2 . 1 H NMR spectrum (CDCl 3 , 500 MHz) of 3 8 .

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181 Figure A 3 . 1 H NMR spectrum (CDCl 3 , 500 MHz) of 3 9 . Figure A 4 . 1 H NMR spectrum (CDCl 3 , 500 MHz) of 3 10 .

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182 Figure A 5 . 1 H NMR spectr um (CDCl 3 , 500 MHz) of 3 11 . Figure A 6 . 1 H NMR spectrum (CDCl 3 , 500 MHz) of 3 3 .

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183 Figure A 7 . 1 H NMR spectrum (CDCl 3 , 500 MHz) of 3 2 . Figure A 8 . 1 H N MR spectrum (CDCl 3 , 500 MHz) of 3 4 .

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184 Figure A 9 . 1 H NMR spectrum (CDCl 3 , 500 MHz) of 3 12b . Figure A 10 . 1 H NMR spectrum (CDCl 3 , 500 MHz) of 3 13 .

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185 Figur e A 11 . 1 H NMR spectrum (CDCl 3 , 500 MHz) of 3 15 . Figure A 12 . 1 H NMR spectrum (CDCl 3 , 500 MHz) of 2 3 5 .

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186 Figure A 13 . 1 H NMR spectrum (CDCl 3 , 500 MHz) of 3 16 .

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187 APPENDIX B CARBON NUCL EAR RESONANCE ( 1 3 C NMR) SPECTRA Figure B 1 . Carbon nuclear magnetic resonance ( 1 3 C NMR) spectrum (CDCl 3 , 500 MHz) of 3 1a . Figure B 2 . 1 3 C NMR spectrum (CDCl 3 , 500 MHz) of 3 8 .

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188 Figure B 3 . 1 3 C NMR spectrum (CDCl 3 , 500 MHz) of 3 9 . Figure B 4 . 1 3 C NMR spectrum (CDCl 3 , 500 MHz) of 3 10 .

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189 Figure B 5 . 1 3 C NMR spectrum (CDCl 3 , 500 MHz) of 3 11 . Figure B 6 . 1 3 C NMR spectrum (CDCl 3 , 500 MHz) of 3 3 .

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190 Figure B 7 . 1 3 C NMR spectrum (CDCl 3 , 500 MHz) of 3 2 . Figure B 8 . 1 3 C NMR spectrum (CDCl 3 , 5 00 MHz) of 3 4 .

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191 Figure B 9 . 1 3 C NMR spectrum (CDCl 3 , 500 MHz) of 3 12b . Figure B 10 . 1 3 C NMR spectrum (CDCl 3 , 500 MHz) of 3 13 .

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192 Figure B 11 . 1 3 C NMR sp ectrum (CDCl 3 , 500 MHz) of 3 15 . Figure B 12 . 1 3 C NMR spectrum (CDCl 3 , 500 MHz) of 2 3 5 .

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193 Figure B 13 . 1 3 C NMR spectrum (CDCl 3 , 500 MHz) of 3 16 .

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194 APPENDIX C SOLID STATE DATA Table C 1 . Crystal data and structure refinement for 4 1syn Identification code 4 1syn Empirical formula C58 H72 N2 O2 S6 Formula weight 1021.53 Temperature 100(2) K Wavelength 1.54178 Å Crystal system Triclinic Space group Unit cell dimensions a = 9.756 7(2) Å b = 10.5150(2) Å c = 14.3263(4) Å Volume 1338.04(5) Å 3 Z 1 Density (calculated) 1.268 Mg/m 3 Absorption coefficient 2.693 mm 1 F(000) 546 Crystal size 0.423 x 0.158 x 0.024 mm 3 Theta range for dat a collection 3.127 to 67.997°. Index ranges Reflections collected 14043 Independent reflections 4642 [R(int) = 0.0654] Completeness to theta = 67.679° 95.1 % Absorption correction Analytical Max. and min. transmission 0.9461 a nd 0.6235 Refinement method Full matrix least squares on F 2 Data / restraints / parameters 4642 / 7 / 411 Goodness of fit on F 2 1.077 Final R indices [I>2sigma(I)] R1 = 0.0464, wR2 = 0.1274 [3941] R indices (all data) R1 = 0.0538, wR2 = 0.1372 Extinction c oefficient n/a Largest diff. peak and hole 0.589 and 0.360 e.Å 3 R1 = (||F o | |F c ||) / |F o | wR2 = [ w(F o 2 F c 2 ) 2 ] / w F o 2 2 ]] 1/2

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195 S = [ w(F o 2 F c 2 ) 2 ] / (n p)] 1/2 w= 1/[ 2 (F o 2 )+(m*p) 2 +n*p], p = [max(F o 2 ,0)+ 2* F c 2 ]/3, m & n are constants . Table C 2 . Atomic coordinates ( x 10 4 ) and equivalent isotropic displacement parameters (Ã… 2 x 10 3 ) for 4 1syn . U(eq) is de fined as one third of the trace of the orthogonalized U ij tensor x y z U(eq) S(1) 1237(1) 4129(1) 3921(1) 31(1) S(2) 3590(1) 5508(1) 3950(1) 33(1) S(3) 6777(1) 9504(1) 2583(1) 40(1) O(1) 2691(2) 1036(2) 5772 (1) 35(1) N(1) 5271(2) 1940(2) 5866(1) 28(1) C(1) 3863(2) 899(2) 5561(1) 28(1) C(2) 4226(2) 206(2) 5000(1) 26(1) C(3) 3572(2) 1530(2) 4477(1) 26(1) C(4) 2019(2) 2346(2) 4330(1) 28(1) C(5) 911(2) 1830(2) 4533(2) 30(1) C(6) 528(2) 2849(2) 4350(2) 30(1) C( 7) 544(2) 4158(2) 4019(2) 30(1) C(8) 1804(2) 5447(2) 3747(2) 30(1) C(9) 1837(3) 6718(2) 3308(2) 35(1) C(10) 3286(3) 7724(2) 3121(2) 36(1) C(11) 4383(2) 7239(2) 3417(2) 30(1) C(12) 5980(2) 7924(2) 3313(2) 32(1) C(13) 7058(3) 7483(3) 3712(2) 41(1) C(1 4) 8513(3) 8430(3) 3435(2) 44(1) C(15) 8563(3) 9572(3) 2829(2) 40(1) C(16) 10029(9) 10694(12) 2414(12) 28(2) C(17) 9768(15) 12001(14) 1970(10) 24(2) C(18) 11254(9) 13231(10) 1688(7) 24(2) C(19) 11093(8) 14579(8) 1236(6) 32(2) C(20) 12584(7) 15779(6) 1051(5) 34(2) C(21) 12443(8) 17154(6) 647(5) 45(2) C(16') 9781(11) 10915(11) 2351(13) 40(4) C(17') 9519(17) 12254(18) 2030(12) 34(3) C(18') 10878(13) 13485(15) 1646(8) 52(3)

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196 C(19') 10603(14) 14796(11) 1358(6) 55(3) C(20') 11963(16) 16087(11) 973(6) 77(4) C(21') 11570(20) 17389(10) 706(5) 99(6) C(22) 5352(2) 3169(2) 6546(2) 32(1) C(23) 5660(3) 3077(3) 7576(2) 47(1) C(24) 5625(6) 4368(4) 8248(4) 49(1) C(25) 7141(5) 5503(4) 8376(3) 44(1) C(26) 7110(5) 6784(4) 9005(3) 49(1) C(27) 8654(6) 7928(5) 9 224(3) 70(1) C(28) 4425(7) 1766(5) 7847(3) 53(1) C(29) 4607(6) 1360(6) 8815(3) 56(1) C(24') 4470(20) 2010(17) 8094(12) 68(3) C(25') 5155(13) 2258(13) 9056(8) 48(2) C(26') 4125(14) 1044(12) 9553(9) 65(3) C(27') 2690(15) 967(17) 9672(12) 91(5) C(28') 6 252(15) 4611(7) 8064(8) 70(7) C(29') 5224(13) 5334(16) 8369(7) 68(3) Table C 3 . Bond lengths [ Å ] and angles [ ° ] for 4 1syn Bond Length S(1) C(7) 1.725(2) S(1) C(4) 1.739(2) S(2) C(8) 1.731(2) S(2) C(11) 1.737(2) S(3) C(12) 1.725(2) S(3) C(1 5) 1.737(2) O(1) C(1) 1.223(3) N(1) C(3)#1 1.397(3) N(1) C(1) 1.422(3) N(1) C(22) 1.464(3) C(1) C(2) 1.452(3) C(2) C(3) 1.389(3) C(2) C(2)#1 1.402(4) C(3) N(1)#1 1.397(3) C(3) C(4) 1.431(3)

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197 C(4) C(5) 1.385(3) C(5) C(6) 1.405(3) C(5) H(5A) 0.95 00 C(6) C(7) 1.376(3) C(6) H(6A) 0.9500 C(7) C(8) 1.447(3) C(8) C(9) 1.370(3) C(9) C(10) 1.408(3) C(9) H(9A) 0.9500 C(10) C(11) 1.375(3) C(10) H(10A) 0.9500 C(11) C(12) 1.446(3) C(12) C(13) 1.371(3) C(13) C(14) 1.414(3) C(13) H(13A) 0.9500 C(14 ) C(15) 1.348(4) C(14) H(14A) 0.9500 C(15) C(16) 1.531(4) C(15) C(16') 1.531(5) C(16) C(17) 1.526(14) C(16) H(16A) 0.9900 C(16) H(16B) 0.9900 C(17) C(18) 1.543(18) C(17) H(17A) 0.9900 C(17) H(17B) 0.9900 C(18) C(19) 1.522(9) C(18) H(18A) 0.9900 C(18) H(18B) 0.9900 C(19) C(20) 1.514(8) C(19) H(19A) 0.9900 C(19) H(19B) 0.9900 C(20) C(21) 1.522(8) C(20) H(20A) 0.9900 C(20) H(20B) 0.9900 C(21) H(21A) 0.9800 C(21) H(21B) 0.9800

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198 C(21) H(21C) 0.9800 C(16') C(17') 1.521(16) C(16') H(16C) 0.9 900 C(16') H(16F) 0.9900 C(17') C(18') 1.50(2) C(17') H(17C) 0.9900 C(17') H(17D) 0.9900 C(18') C(19') 1.494(15) C(18') H(18C) 0.9900 C(18') H(18D) 0.9900 C(19') C(20') 1.532(11) C(19') H(19C) 0.9900 C(19') H(19D) 0.9900 C(20') C(21') 1.547(16) C(20') H(20C) 0.9900 C(20') H(20D) 0.9900 C(21') H(21D) 0.9800 C(21') H(21E) 0.9800 C(21') H(21F) 0.9800 C(22) C(23) 1.544(3) C(22) H(22A) 0.9900 C(22) H(22B) 0.9900 C(23) C(24') 1.531(5) C(23) C(28) 1.534(4) C(23) C(24) 1.542(3) C(23) C(28') 1 .542(5) C(23) H(23A) 1.0000 C(23) H(23B) 1.0000 C(24) C(25) 1.497(6) C(24) H(24A) 0.9900 C(24) H(24B) 0.9900 C(25) C(26) 1.504(5) C(25) H(25A) 0.9900 C(25) H(25B) 0.9900 C(26) C(27) 1.530(6) C(26) H(26A) 0.9900

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199 C(26) H(26B) 0.9900 C(27) H(27A) 0.9800 C(27) H(27B) 0.9800 C(27) H(27C) 0.9800 C(28) C(29) 1.553(7) C(28) H(28A) 0.9900 C(28) H(28B) 0.9900 C(29) H(29A) 0.9800 C(29) H(29B) 0.9800 C(29) H(29C) 0.9800 C(24') C(25') 1.50(2) C(24') H(24C) 0.9900 C(24') H(24F) 0.9900 C(25') C(26') 1.544(15) C(25') H(25C) 0.9900 C(25') H(25F) 0.9900 C(26') C(27') 1.374(19) C(26') H(26C) 0.9900 C(26') H(26D) 0.9900 C(27') H(27D) 0.9800 C(27') H(27E) 0.9800 C(27') H(27F) 0.9800 C(28') C(29') 1.487(15) C(28') H(28C) 0.9900 C(28') H(28D) 0.9 900 C(29') H(29D) 0.9800 C(29') H(29E) 0.9800 C(29') H(29F) 0.9800 Bond Angle C(7) S(1) C(4) 92.31(10) C(8) S(2) C(11) 92.52(10) C(12) S(3) C(15) 92.49(12) C(3)#1 N(1) C(1) 111.44(16) C(3)#1 N(1) C(22) 128.41(17) C(1) N(1) C(22) 119.74(17)

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200 O(1) C(1) N( 1) 122.83(18) O(1) C(1) C(2) 133.41(19) N(1) C(1) C(2) 103.76(17) C(3) C(2) C(2)#1 109.6(2) C(3) C(2) C(1) 141.90(19) C(2)#1 C(2) C(1) 108.5(2) C(2) C(3) N(1)#1 106.69(17) C(2) C(3) C(4) 127.30(19) N(1)#1 C(3) C(4) 125.99(18) C(5) C(4) C(3) 124.40(19) C(5) C(4) S(1) 110.01(16) C(3) C(4) S(1) 125.55(16) C(4) C(5) C(6) 113.47(19) C(4) C(5) H(5A) 123.3 C(6) C(5) H(5A) 123.3 C(7) C(6) C(5) 113.19(19) C(7) C(6) H(6A) 123.4 C(5) C(6) H(6A) 123.4 C(6) C(7) C(8) 128.8(2) C(6) C(7) S(1) 111.02(16) C(8) C(7) S(1) 120 .16(17) C(9) C(8) C(7) 129.5(2) C(9) C(8) S(2) 110.50(16) C(7) C(8) S(2) 119.95(17) C(8) C(9) C(10) 113.3(2) C(8) C(9) H(9A) 123.3 C(10) C(9) H(9A) 123.3 C(11) C(10) C(9) 113.8(2) C(11) C(10) H(10A) 123.1 C(9) C(10) H(10A) 123.1 C(10) C(11) C(12) 130.2(2) C(10) C(11) S(2) 109.85(16) C(12) C(11) S(2) 119.95(18) C(13) C(12) C(11) 129.0(2) C(13) C(12) S(3) 110.21(17) C(11) C(12) S(3) 120.73(18)

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201 C(12) C(13) C(14) 113.0(2) C(12) C(13) H(13A) 123.5 C(14) C(13) H(13A) 123.5 C(15) C(14) C(13) 114.0(2) C(15) C(14) H (14A) 123.0 C(13) C(14) H(14A) 123.0 C(14) C(15) C(16) 122.2(6) C(14) C(15) C(16') 136.2(6) C(14) C(15) S(3) 110.20(18) C(16) C(15) S(3) 127.6(6) C(16') C(15) S(3) 113.5(6) C(17) C(16) C(15) 109.4(9) C(17) C(16) H(16A) 109.8 C(15) C(16) H(16A) 109.8 C(17) C(16) H(16B) 109.8 C(15) C(16) H(16B) 109.8 H(16A) C(16) H(16B) 108.2 C(16) C(17) C(18) 110.9(7) C(16) C(17) H(17A) 109.5 C(18) C(17) H(17A) 109.5 C(16) C(17) H(17B) 109.5 C(18) C(17) H(17B) 109.5 H(17A) C(17) H(17B) 108.0 C(19) C(18) C(17) 114.3(6) C(19) C(18) H(18A) 108.7 C(17) C(18) H(18A) 108.7 C(19) C(18) H(18B) 108.7 C(17) C(18) H(18B) 108.7 H(18A) C(18) H(18B) 107.6 C(20) C(19) C(18) 112.0(5) C(20) C(19) H(19A) 109.2 C(18) C(19) H(19A) 109.2 C(20) C(19) H(19B) 109.2 C(18) C(19) H(19B) 109.2 H(19A) C( 19) H(19B) 107.9 C(19) C(20) C(21) 112.8(5)

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202 C(19) C(20) H(20A) 109.0 C(21) C(20) H(20A) 109.0 C(19) C(20) H(20B) 109.0 C(21) C(20) H(20B) 109.0 H(20A) C(20) H(20B) 107.8 C(20) C(21) H(21A) 109.5 C(20) C(21) H(21B) 109.5 H(21A) C(21) H(21B) 109.5 C(20) C(21 ) H(21C) 109.5 H(21A) C(21) H(21C) 109.5 H(21B) C(21) H(21C) 109.5 C(17') C(16') C(15) 122.5(10) C(17') C(16') H(16C) 106.7 C(15) C(16') H(16C) 106.7 C(17') C(16') H(16F) 106.7 C(15) C(16') H(16F) 106.7 H(16C) C(16') H(16F) 106.6 C(18') C(17') C(16') 114.4 (9) C(18') C(17') H(17C) 108.6 C(16') C(17') H(17C) 108.6 C(18') C(17') H(17D) 108.6 C(16') C(17') H(17D) 108.6 H(17C) C(17') H(17D) 107.6 C(19') C(18') C(17') 113.5(8) C(19') C(18') H(18C) 108.9 C(17') C(18') H(18C) 108.9 C(19') C(18') H(18D) 108.9 C(17') C(18') H(18D) 108.9 H(18C) C(18') H(18D) 107.7 C(18') C(19') C(20') 115.5(9) C(18') C(19') H(19C) 108.4 C(20') C(19') H(19C) 108.4 C(18') C(19') H(19D) 108.4 C(20') C(19') H(19D) 108.4 H(19C) C(19') H(19D) 107.5 C(19') C(20') C(21') 111.4(9)

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203 C(19') C(20') H(20C) 109.3 C(21') C(20') H(20C) 109.3 C(19') C(20') H(20D) 109.3 C(21') C(20') H(20D) 109.3 H(20C) C(20') H(20D) 108.0 C(20') C(21') H(21D) 109.5 C(20') C(21') H(21E) 109.5 H(21D) C(21') H(21E) 109.5 C(20') C(21') H(21F) 109.5 H(21D) C(21') H(21F) 109.5 H(21E) C(21') H(21F) 109.5 N(1) C(22) C(23) 113.92(18) N(1) C(22) H(22A) 108.8 C(23) C(22) H(22A) 108.8 N(1) C(22) H(22B) 108.8 C(23) C(22) H(22B) 108.8 H(22A) C(22) H(22B) 107.7 C(28) C(23) C(24) 109.0(3) C(24') C(23) C(28') 117.1(9) C(24') C(23) C(22) 1 19.0(8) C(28) C(23) C(22) 107.5(3) C(24) C(23) C(22) 110.2(3) C(28') C(23) C(22) 103.7(5) C(28) C(23) H(23A) 110.0 C(24) C(23) H(23A) 110.0 C(22) C(23) H(23A) 110.0 C(24') C(23) H(23B) 105.2 C(28') C(23) H(23B) 105.2 C(22) C(23) H(23B) 105.2 C(25) C(24) C( 23) 111.1(4) C(25) C(24) H(24A) 109.4 C(23) C(24) H(24A) 109.4 C(25) C(24) H(24B) 109.4 C(23) C(24) H(24B) 109.4 H(24A) C(24) H(24B) 108.0 C(24) C(25) C(26) 111.5(3)

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204 C(24) C(25) H(25A) 109.3 C(26) C(25) H(25A) 109.3 C(24) C(25) H(25B) 109.3 C(26) C(25) H(2 5B) 109.3 H(25A) C(25) H(25B) 108.0 C(25) C(26) C(27) 113.3(4) C(25) C(26) H(26A) 108.9 C(27) C(26) H(26A) 108.9 C(25) C(26) H(26B) 108.9 C(27) C(26) H(26B) 108.9 H(26A) C(26) H(26B) 107.7 C(26) C(27) H(27A) 109.5 C(26) C(27) H(27B) 109.5 H(27A) C(27) H(27 B) 109.5 C(26) C(27) H(27C) 109.5 H(27A) C(27) H(27C) 109.5 H(27B) C(27) H(27C) 109.5 C(23) C(28) C(29) 116.7(5) C(23) C(28) H(28A) 108.1 C(29) C(28) H(28A) 108.1 C(23) C(28) H(28B) 108.1 C(29) C(28) H(28B) 108.1 H(28A) C(28) H(28B) 107.3 C(28) C(29) H(29A ) 109.5 C(28) C(29) H(29B) 109.5 H(29A) C(29) H(29B) 109.5 C(28) C(29) H(29C) 109.5 H(29A) C(29) H(29C) 109.5 H(29B) C(29) H(29C) 109.5 C(25') C(24') C(23) 103.2(11) C(25') C(24') H(24C) 111.1 C(23) C(24') H(24C) 111.1 C(25') C(24') H(24F) 111.1 C(23) C(24 ') H(24F) 111.1 H(24C) C(24') H(24F) 109.1 C(24') C(25') C(26') 105.5(9)

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205 C(24') C(25') H(25C) 110.6 C(26') C(25') H(25C) 110.6 C(24') C(25') H(25F) 110.7 C(26') C(25') H(25F) 110.6 H(25C) C(25') H(25F) 108.8 C(27') C(26') C(25') 115.1(11) C(27') C(26') H(2 6C) 108.5 C(25') C(26') H(26C) 108.5 C(27') C(26') H(26D) 108.5 C(25') C(26') H(26D) 108.5 H(26C) C(26') H(26D) 107.5 C(26') C(27') H(27D) 109.5 C(26') C(27') H(27E) 109.5 H(27D) C(27') H(27E) 109.5 C(26') C(27') H(27F) 109.5 H(27D) C(27') H(27F) 109.5 H(2 7E) C(27') H(27F) 109.5 C(29') C(28') C(23) 121.0(11) C(29') C(28') H(28C) 107.1 C(23) C(28') H(28C) 107.1 C(29') C(28') H(28D) 107.1 C(23) C(28') H(28D) 107.1 H(28C) C(28') H(28D) 106.8 C(28') C(29') H(29D) 109.5 C(28') C(29') H(29E) 109.5 H(29D) C(29') H (29E) 109.5 C(28') C(29') H(29F) 109.5 H(29D) C(29') H(29F) 109.5 H(29E) C(29') H(29F) 109.5 Symmetry transformations used to generate equivalent atoms: #1 x+1, y, z+1

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206 Table C 4 . Anis otropic displacement parameters ( Ã… 2 x 10 3 ) for 4 1syn . The anisotropic displacement factor exponent takes the form: 2 2 [ h 2 a* 2 U 11 + ... + 2 h k a* b* U 12 ] U 11 U 22 U 33 U 23 U 1 3 U 1 2 S(1) 22(1) 23(1) 38(1) 3(1) 4(1) 2(1) S(2) 23(1) 25(1) 42(1) 1(1) 1(1) 1(1) S(3) 26(1) 30(1) 50(1) 2(1) 6(1) 2(1) O( 1) 24(1) 31(1) 43(1) 6(1) 6(1) 7(1) N(1) 24(1) 23(1) 31(1) 3(1) 6(1) 6(1) C(1) 26(1) 24(1) 31(1) 0(1) 6(1) 6(1) C(2) 22(1) 21(1) 29(1) 1(1) 4(1) 3(1) C(3) 24(1) 24(1) 26(1) 2(1) 3(1) 5(1) C(4) 26(1) 23(1) 27(1) 1(1) 4(1) 3(1 ) C(5) 25(1) 25(1) 32(1) 2(1) 4(1) 4(1) C(6) 22(1) 28(1) 33(1) 1(1) 2(1) 4(1) C(7) 23(1) 27(1) 32(1) 0(1) 2(1) 3(1) C(8) 22(1) 25(1) 34(1) 2(1) 2(1) 0(1) C(9) 26(1) 27(1) 45(1) 1(1) 1(1) 4(1) C(10) 31(1) 22(1) 46(1) 0(1) 3(1) 1(1) C(11) 26(1) 23(1) 32(1) 3(1) 4(1) 2(1) C(12) 28(1) 28(1) 31(1) 8(1) 1(1) 2(1) C(13) 30(1) 42(1) 38(1) 2(1) 4(1) 3(1) C(14) 28(1) 52(2) 39(1) 3(1) 4(1) 4(1) C(15) 27(1) 43(1) 39(1) 12(1) 2(1) 1(1) C(16) 14(4) 23(3) 42(3) 8(2 ) 4(3) 5(3) C(17) 22(5) 26(5) 25(3) 2(3) 0(3) 10(3) C(18) 8(3) 23(3) 29(3) 3(2) 1(2) 5(2) C(19) 24(3) 29(3) 31(3) 7(2) 5(2) 2(2) C(20) 27(3) 23(3) 39(3) 2(2) 3(2) 1(2) C(21) 38(3) 29(3) 49(3) 11(2) 3(2) 1(3) C(16') 9(3) 62(9) 51( 6) 19(6) 2(3) 10(4) C(17') 18(5) 37(7) 36(3) 8(4) 5(3) 4(4) C(18') 23(5) 82(9) 34(4) 23(5) 4(3) 4(4) C(19') 45(5) 57(5) 29(3) 10(3) 8(3) 19(4) C(20') 84(8) 63(6) 44(4) 13(4) 19(5) 21(6) C(21') 133(12) 58(5) 46(4) 3(3) 3(5) 27( 6) C(22) 26(1) 24(1) 40(1) 6(1) 4(1) 6(1)

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207 C(23) 49(2) 54(2) 38(1) 11(1) 6(1) 27(1) C(24) 49(3) 47(2) 44(3) 18(2) 14(2) 22(2) C(25) 51(2) 35(2) 37(2) 2(1) 2(2) 11(2) C(26) 59(2) 31(2) 45(2) 4(1) 9(2) 6(2) C(27) 87(3) 47(2) 46(2) 1 (2) 8(2) 8(2) C(28) 63(3) 67(3) 32(3) 11(2) 9(2) 29(2) C(29) 84(3) 54(3) 33(2) 3(2) 6(2) 31(3) C(24') 60(5) 115(9) 33(4) 2(5) 9(4) 44(6) C(25') 51(6) 44(6) 49(6) 15(5) 3(4) 16(5) C(26') 63(7) 49(7) 73(8) 19(5) 9(6) 7(6) C(27') 61( 8) 88(10) 104(11) 25(9) 35(8) 1(7) C(28') 94(14) 144(18) 16(5) 1(7) 19(7) 100(15) C(29') 60(5) 115(9) 33(4) 2(5) 9(4) 44(6) Table C 5 . Hydrogen coordinates ( x 10 4 ) and isotropic displacement parameters (Ã… 2 x 10 3 ) for 4 1syn x y z U(eq) H(5A) 1105 878 4772 35 H(6A) 1402 2653 4445 36 H(9A) 968 6902 3147 42 H(10A) 3488 8652 2818 43 H(13A) 6850 6630 4130 49 H(14A) 9378 8275 3657 52 H(16A) 10417 10343 1929 34 H(16B) 10773 10920 2920 34 H(17A) 9148 11808 1402 29 H(17B) 9225 12255 242 6 29 H(18A) 11793 12959 1239 29 H(18B) 11868 13407 2260 29 H(19A) 10488 14819 1659 38 H(19B) 10562 14436 631 38 H(20A) 13136 15885 1650 41 H(20B) 13167 15556 602 41 H(21A) 13436 17892 540 67 H(21B) 11886 17392 1094 67

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208 H(21C) 11917 17063 45 67 H(16 C) 10124 10683 1787 48 H(16F) 10625 11143 2792 48 H(17C) 9123 12488 2573 41 H(17D) 8752 12086 1536 41 H(18C) 11260 13265 1091 62 H(18D) 11655 13643 2134 62 H(19C) 9829 14632 868 66 H(19D) 10202 14998 1913 66 H(20C) 12746 16266 1457 93 H(20D) 1236 1 15909 407 93 H(21D) 12456 18195 462 148 H(21E) 11188 17577 1268 148 H(21F) 10803 17219 219 148 H(22A) 6148 4002 6354 38 H(22B) 4401 3297 6523 38 H(23A) 6648 3010 7622 56 H(23B) 6534 2798 7540 56 H(24A) 5245 4100 8870 59 H(24B) 4940 4717 7986 59 H(25A) 7816 5162 8658 52 H(25B) 7534 5746 7751 52 H(26A) 6497 7163 8695 59 H(26B) 6629 6517 9607 59 H(27A) 8561 8732 9635 106 H(27B) 9129 8216 8633 106 H(27C) 9261 7570 9546 106 H(28A) 3474 1897 7848 63 H(28B) 4346 970 7347 63 H(29A) 3759 512 891 2 84 H(29B) 4651 2122 9323 84 H(29C) 5527 1191 8821 84 H(24C) 4261 1046 7772 81 H(24F) 3534 2176 8136 81 H(25C) 6169 2255 9001 57 H(25F) 5211 3165 9413 57

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209 H(26C) 4560 1137 10183 78 H(26D) 4101 156 9181 78 H(27D) 2120 171 9992 137 H(27E) 2234 845 9053 137 H(27F) 2693 1828 10057 137 H(28C) 6973 5166 7630 84 H(28D) 6822 4666 8633 84 H(29D) 5796 6295 8664 102 H(29E) 4523 4840 8827 102 H(29F) 4674 5344 7817 102 _______________________________________________ _______________________

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210 LIST OF REFE RENCES 1. Safont Sempere, M. M.; Fernández, G.; Würthner, F., Chem. Rev. 2011, 111 , 5784 5814. 2. Lehn, J. M., Angew. Chem. Int. Ed. 1988, 27 , 89 112. 3. Dodziuk, H., Supramolecular Chemistry What is This? In Introduction to Supramo lecular Chemistry , Springer Netherlands: 2002; pp 1 19. 4. Desiraju, G. R., J. Am. Chem. Soc. 2013, 135 , 9952 9967. 5. Sivakova, S.; Rowan, S. J., Chem. Soc. Rev. 2005, 34 , 9 21. 6. (a) Huang, K. W.; Wu, Y. R.; Jeong, K. U.; Kuo, S. W., Macromol. Rapid Commun. 2014, 34 , 1530 1536,(b) Jatsch, A.; Kopyshev, A.; Mena Osteritz, E.; Bäuerle, P., Org. Lett. 2008, 10 , 961 964,(c) Spada, G. P.; Lena, S.; Masiero, S.; Pieraccini, S.; Surin, M.; Samorì, P., Adv. Mater. 2008, 20 , 2433 2438,(d) Iwaura, R.; Hoeben, F . J. M.; Masuda, M.; Schenning, A. P. H. J.; Meijer, E. W.; Shimizu, T.; Central, T., J. Am. Chem. Soc. 2006, 128 , 13298 13304. 7. (a) Davis, J. T.; Spada, G. P., Chem. Soc. Rev. 2007, 36 , 296 313,(b) Wang, D.; Tong, G.; Dong, R.; Zhou, Y.; Shen, J.; Zhu, X., Chem. Commun. 2014, 50 , 11994 12017,(c) Sivakova, S.; Rowan, S. J., Chem. Commun. 2003 , 2428 2429,(d) Shimizu, T.; Iwaura, R.; Masuda, M.; Hanada, T.; Yase, K., J. Am. Chem. Soc. 2001, 123 , 5947 Macromol. 2012, 45 , 7665 7675,(f) McHale, R.; Patterson, J. P.; Zetterlund, P. B.; O'Reilly, R. K., Nat. Chem. 2012, 4 , 491 497. 8. Sivakova, S.; Rowan, S. J., Chem. Soc. Rev. 2005, 34 , 9 21. 9. Giorgi, T.; Grepioni, F.; Manet, I.; Mariani, P.; Masiero, S.; Mezzina, E.; P ieraccini, S.; Saturni, L.; Spada, G. P.; Gottarelli, G., Chem. Eur. J. 2002, 8 , 2143 2152. 10. Davis, J. T., Angew. Chem. Int. Ed. 2004, 43 , 668 698. 11. (a) Gottarelli, G.; Spada, G. P., Chem. Rec. 2004, 4 , 39 49,(b) Garbesi, A.; Gottarelli, G.; Maria, P.; Spada, G. P., Pure & Appl. Chem. 1993, 65 , 641 646,(c) Gubala, V.; Rivera Sánchez, M. d. C.; Hobley, G.; Rivera, J. M., Nucleic Acids Symposium Series 2007, 51 , 39 40. 12. (a) He, H. Z.; Chan, D. S. H.; Leung, C. H.; Ma, D. L., Nucleic Acids Research 2013, 41 , 4345 4359,(b) Laguerre, A.; Stefan, L.; Larrouy, M.; Genest, D.; Novotna, J.; Pirrotta, M.; Monchaud, D., J. Am. Chem. Soc. 2014, 136 , 12406 12414.

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211 13. Bryan, T.; Baumann, P., Mol. Biotechnol. 2011, 49 , 198 208. 14. (a) Abet, V.; Rodriguez, R. , New J. Chem. 2014, 38 , 5122 5128,(b) Adhikari, B.; Shah, A.; Kraatz, H. B., J. Mater. Chem. B 2014, 2 , 4802 4810,(c) González Rodríguez, D.; Janssen, P. G. A.; Martín Rapún, R.; De Cat, I.; De Feyter, S.; Schenning, A. P. H. J.; Meijer, E. W., J. Am. Che m. Soc. 2010, 132 , 4710 4719. 15. Nagatoishi, S.; Nojima, T.; Juskowiak, B.; Takenaka, S., Angew. Chem. Int. Ed. 2005, 44 , 5067 5070. 16. (a) Betancourt, J. E.; Subramani, C.; Serrano Velez, J. L.; Rosa Molinar, E.; Rotello, V. M.; Rivera, J. M., Chem. C ommun. 2010, 46 , 8537 8539,(b) Betancourt, J. E.; Rivera, J. M., J. Am. Chem. Soc. 2009, 131 , 16666 16668. 17. (a) Sessler, J. L.; Jayawickramarajah, J., Chem. Commun. 2005 , 1939 1949,(b) Fathalla, M.; Lawrence, C. M.; Zhang, N.; Sessler, J. L.; Jayawickr amarajah, J., Chem. Soc. Rev. 2009, 38 , 1608 1620. 18. Sessler, J. L.; Wang, B.; Harriman, A., J. Am. Chem. Soc. 1993, 115 , 10418 10419. 19. Kraus, G. A.; Wu, Y., J. Am. Chem. Soc. 1992, 114 , 8705 8707. 20. Cheng, S.; Zhang, M.; Dixit, N.; Moore, R. B.; Long, T. E., Macromol. 2012, 45 , 805 812. 21. Wang, D.; Chen, H.; Su, Y.; Qiu, F.; Zhu, L.; Huan, X.; Zhu, B.; Yan, D.; Guo, F.; Zhu, X., Polym. Chem. 2013, 4 , 85 94. 22. Nikogosyan, D. N.; Angelov, D.; Soep, B.; Lindqvist, L., Chem. Phys. Lett. 1996, 2 52 , 322 326. 23. Puri, N.; Chattopadhyaya, J., Nucleosides and Nucleotides 1999, 18 , 2785 2818. 24. Krueger, A. T.; Kool, E. T., J. Am. Chem. Soc. 2008, 130 , 3989 3999. 25. Nadler, A.; Strohmeier, J.; Diederichsen, U., Angew. Chem. Int. Ed. 2011, 50 , 53 92 5396. 26. (a) Dumas, A.; Luedtke, N. W., J. Am. Chem. Soc. 2010, 132 , 18004 18007,(b) Greco, N. J.; Tor, Y., J. Am. Chem. Soc. 2005, 127 , 10784 10785. 27. Wilhelmsson, L. M., Quar. Rev. Biophys. 2010, 43 , 159 183.

PAGE 212

212 28. (a) Butler, R. S.; Cohn, P.; Ten zel, P.; Abboud, K. A.; Castellano, R. K., J. Am. Chem. Soc. 2009, 131 , 623 633,(b) Butler, R. S.; Myers, A. K.; Bellarmine, P.; Abboud, K. A.; Castellano, R. K., J. Mater. Chem. 2007, 17 , 1863 1865. 29. (a) Yang, Y.; Cohn, P.; Dyer, A. L.; Eom, S. H.; Re ynolds, J. R.; Castellano, R. K.; Xue, J., Chem. Mater. 2010, 22 , 3580 3582,(b) Yang, Y.; Cohn, P.; Eom, S. H.; Abboud, K. A.; castellano, R. K.; Xue, J., J. Mater. Chem. C 2013, 1 , 2867 2874. 30. Wu, Y. L.; Brown, K. E.; Wasielewski, M. R., J. Am. Chem. Soc. 2013, 135 , 13322 13325. 31. Lee, O. P.; Yiu, A. T.; Beaujuge, P. M.; Woo, C. H.; Holcombe, T. W.; Millstone, J. E.; Douglas, J. D.; Chen, M. S.; Fréchet, J. M. J., Adv. Mater. 2011, 23 , 5359 5363. 32. Gevaerts, V. S.; Herzig, E. M.; Kirkus, M.; Hend riks, K. H.; Wienk, M. M.; Perlich, J.; Müller Buschbaum, P.; Janssen, R. A. J., Chem. Mater. 2014, 26 , 916 926. 33. Walker, B.; Kim, C.; Nguyen, T. Q., Chem. Mater. 2011, 23 , 470 482. 34. Vladu, M.; Kaltenbrunner, M.; Gsiorowski, J.; White, M. S.; Monkowius, U.; Romanazzi, G.; Suranna, G. P.; Mastrorilli, P.; Sekitani, T.; Bauer, S.; Someya, T.; Torsi, L.; Sariciftci, N. S., Adv. Mater. 2013, 25 , 1563 1569. 35. Schulze, B. M.; Shewmon, N. T.; Zhang, J.; Watkins, D. L.; Mudrick, J . P.; Cao, W.; Bou Zerdan, R.; Quartararo, A. J.; Ghiviriga, I.; Xue, J.; Castellano, R. K., J. Mater. Chem. A, 2014, 2 , 1541 1549. 36. (a) Yokoyama, D., J. Mater. Chem. 2011, 21 , 19187 19202,(b) Yokoyama, D.; Sasabe, H.; Furukawa, Y.; Adachi, C.; Kido, J ., Adv. Funct. Mater. 2011, 21 , 1375 1382. 37. Kim, K. H.; Yu, H.; Kang, H.; Kang, D. J.; Cho, C. H.; Cho, H. H.; Oh, J. H.; Kim, B. J., J. Mate. Chem. A 2013, 1 , 14538 14547. 38. Xiao, Z.; Sun, K.; Subbiah, J.; Ji, S.; Jones, D. J.; Wong, W. W. H., Sci. Rep. 2014, 4 , 1 7. 39. (a) Thazhathveetil, A. K.; Trifonov, A.; Wasielewski, M. R.; Lewis, F. D., J. Am. Chem. Soc. 2011, 133 , 11485 11487,(b) Genereux, J. C.; Barton, J. K., Chem. Rev. 2010, 110 , 1642 1662. 40. Guo, X.; Cui, C.; Zhang, M.; Huo, L.; Hua ng, Y.; Hou, J.; Li, Y., Energy Environ. Sci. 2012, 5 , 7943 7949.

PAGE 213

213 41. Camacho Garcia, J.; Montoro Garcia, C.; Lopez Perez, A. M.; Bilbao, N.; Romero Perez, S.; Gonzalez Rodriguez, D., Org. Biomol. Chem. 2015, 13 , 4506 4513. 42. (a) Naik, M. A.; Venkatrama iah, N.; Kanimozhi, C.; Patil, S., J. Phys. Chem. C 2012, 116 , 26128 26137,(b) Lei, T.; Wang, J. Y.; Pei, J., Chem. Mater. 2014, 26 , 594 603. 43. (a) Bou Zerdan, R.; Shewmon, N. T.; Zhu, Y.; Mudrick, J. P.; Chesney, K. J.; Jiangeng, X.; Castellano, R. K., Adv. Funct. Mater. 2014, 24 , 5993 6004,(b) Liu, J.; Zhang, Y.; Phan, H.; Sharenko, A.; Moonsin, P.; Walker, B.; Promarak, V.; Nguyen, T. Q., Adv. Mater. 2013, 25 , 3645 3650. 44. (a) Seo, J. H., Synth. Met. 2012, 162 , 748 752,(b) Subramaniyan, S.; Xin, H. ; Kim, F. S.; Shoaee, S.; Durrant, J. R.; Jenekhe, S. A., Adv. Funct. Mater. 2011, 1 , 854 860,(c) Henson, Z. B.; Zalar, P.; Chen, X.; Welch, G. C.; Nguyen, T. Q.; Bazan, G. C., J. Mater. Chem. A 2013, 1 , 11117 11120,(d) Fang, L.; Zhou, Y.; Yao, Y. X.; Diao , Y.; Lee, W. Y.; Appleton, A. L.; Allen, R.; Reinspach, J.; Mannsfeld, S. C. B.; Bao, Z., Chem. Mater. 2013, 25 , 4874 4880,(e) Zhang, Z. G.; Zhang, S.; Min, J.; Cui, C.; Geng, H.; Shuai, Z.; Li, Y., Macromol. 2012, 45 , 2312 2320,(f) Kwon, O.; Jo, J.; Walk er, B.; Bazan, G. C.; Seo, J. H., J. Mater. Chem. A 2013, 1 , 7118 7124,(g) Kroon, R.; Lundin, A.; Lindqvist, C.; Henriksson, P.; Steckler, T. T.; Andersson, M. R., Polymer 2013, 54 , 1285 1288,(h) Tang, A.; Lu, Z.; Bai, S.; Huang, J.; Chen, Y.; Shi, Q.; Zha n, C.; Yao, J., Chem. Asian. J. 2014, 9 , 883 892,(i) Ota, S.; Minami, S.; Hirano, K.; Satoh, T.; Ie, Y.; Seki, S.; Aso, Y.; Miura, M., RSC Adv. 2013, 3 , 12356 12365. 45. (a) Li, Y.; Chen, Y.; Liu, X.; Wang, Z.; Yang, X.; Tu, Y.; Zhu, X., Macromol. 2011, 4 4 , 6370 6381,(b) Min, J.; Luponosov, Y. N.; Gerl, A.; Polinskaya, M. S.; Peregudova, S. M.; Dmitryakov, P. V.; Bakirov, A. V.; Shcherbina, M. A.; Chvalun, S. N.; Grigorian, S.; Kaush Busies, N.; Ponomarenko, S. A.; Ameri, T.; Brabec, C. J., Adv. Energy Mat er. 2014, 4 , 1301234 1301244,(c) Fitzner, R.; Elschner, C.; Weil, M.; Uhrich, C.; Körner, C.; Riede, M.; Leo, K.; Pfeiffer, M.; Reinold, E.; Mena Osteritz, E.; Bäuerle, P., Adv. Mater. 2012, 24 , 675 680,(d) Cabanetos, C.; El Labban, A.; Bartelt, J. A.; Dou glas, J. D.; Mateker, W. R.; Fréchet, J. M. J.; McGehee, M. D.; Beaujuge, P. M., J. Am. Chem. Soc. 2013, 135 , 4656 4659,(e) Casey, A.; Ashraf, R. S.; Fei, Z.; Heeney, M., Macromol. 2014, 47 , 2279 2288,(f) Hendsbee, A. D.; Sun, J. P.; Rutledge, L. R.; Hill, I. G.; Welch, G. C., J. Mater. Chem. A 2014, 2 , 4198 4207,(g) Fu, B.; Baltazar, J.; Sankar, A. R.; Chu, P. H.; Zhang, S.; Collard, D. M.; Reichmanis, E., Adv. Funct. Mater. 2014, 24 , 3734 3744,(h) Osaka, I.; Saito, M.; Koganezawa, T.; Takimiya, K., Adv. M ater. 2014, 26 , 331 338,(i) Hendriks, K. H.; Li, W.; Wienk, M. M.; Janssen, R. A. J., Adv. Energy Mater. 2013, 3 , 674 679.

PAGE 214

214 46. (a) Li, Y.; Zou, J.; Yip, H. L.; Li, C. Z.; Zhang, Y.; Chueh, C. C.; Intemann, J.; Xu, Y.; Liang, P. W.; Chen, Y.; Jen, A. K. Y ., Macromol. 2013, 46 , 5497 5503,(b) Lei, T.; Wang, J. Y.; Pei, J., Acc. Chem. Res. 2014, 47 , 1117 1126,(c) Harschneck, T.; Zhou, N.; Manley, E. F.; Lou, S. J.; Yu, X.; Butler, M. R.; Timalsina, A.; Turrisi, R.; Ratner, M. A.; Chen, L. X.; Chang, R. P. H.; Facchetti, A.; Marks, T. J., Chem. Commun. 2014, 50 , 4099 4101,(d) Nakanishi, T.; Shirai, Y.; Yasuda, T.; Han, L., J. Polym. Sci., Part A: Polym. Chem. 2012, 50 , 4829 4839. 47. (a) Meager, I.; Ashraf, R. S.; Mollinger, S.; Schroeder, B. C.; Bronstein, H. ; Beatrup, D.; Vezie, M. S.; Kirchartz, T.; Salleo, A.; Nelson, J.; McCulloch, I., J. Am. Chem. Soc. 2013, 135 , 11537 11540,(b) Kumagai, J.; Hirano, K.; Satoh, T.; Seki, S.; Miura, M., J. Phys. Chem. B 2011, 115 , 8446 8452,(c) Fitzner, R.; Mena Osteritz, E .; Mishra, A.; Schulz, G.; Reinold, E.; Weil, M.; Körner, C.; Ziehlke, H.; Elschner, C.; Leo, K.; Riede, M.; Pfeiffer, M.; Uhrich, C.; Bäuerle, P., J. Am. Chem. Soc. 2012, 134 , 11064 11067,(d) Wu, Q.; Ren, S.; Wang, M.; Qiao, X.; Li, H.; Gao, X.; Yang, X.; Zhu, D., Adv. Funct. Mater. 2013, 23 , 2277 2284,(e) Yasuda, T.; Shinohara, Y.; Matsuda, T.; Han, L.; Ishi i, T., J. polym. Sci., Part A: Polym. Chem. 2013, 51 , 2536 2544. 48. Ikai, T.; Kojima, R.; Katori, S.; Yamamoto, T.; Kuwabara, T.; Maeda, K.; Takaha shi, K.; Kanoh, S., Polymer 2015, 56 , 171 177. 49. Zhang, F.; Hu, Y.; Schuettfort, T.; Di, C. a.; Gao, X.; McNeill, C. R.; Thomsen, L.; Mannsfeld, S. C. B.; Yuan, W.; Sirringhaus, H.; Zhu, D., J. Am. Chem. Soc. 2013, 135 , 2338 2349. 50. (a) Lee, C. W.; L ee, J. Y., Adv. Mater. 2013, 25 , 5450 5454,(b) Haldi, A.; Kimyonok, A.; Domercq, B.; Hayden, L. E.; Jones, S. C.; Marder, S. R.; Weck, M.; Kippelen, B., Adv. Funct. Mater. 2008, 18 , 3056 3062,(c) Zhu, M.; Yang, C., Chem. Soc. Rev. 2013, 42 , 4963 4976. 51. (a) Dong, H.; Fu, X.; Liu, J.; Wang, Z.; Hu, W., Adv. Mater. 2013, 25 , 6158 6183,(b) Yang, Y. S.; Yasuda, T.; Kakizoe, H.; Mieno, H.; Kino, H.; Tateyama, Y.; Adachi, C., Chem. Commun. 2013, 49 , 6483 6485,(c) Usta, H.; Facchetti, A.; Marks, T. J., Acc. Che m. Res. 2011, 44 , 501 510,(d) Murphy, A. R.; Fréchet, J. M. J., Chem. Rev. 2007, 107 , 1066 1096. 52. (a) Cao, W.; Xue, J., Energy Environ. Sci. 2014, 7 , 2123 2144,(b) Dennler, G.; Scharber, M. C.; Brabec, C. J., Adv. Mater. 2009, 21 , 1323 1338,(c) Yongsh eng, L.; Chen, C. C.; Hong, Z.; Gao, J.; Yang, Y.; Zhou, H.; Dou, L.; Li, G.; Yang, Y., Scientific Reports 2013, 3 , 1 8. 53. (a) Leem, D. S.; Lee, K. H.; Park, K. B.; Lim, S. J.; Kim, K. S.; Wan Jin, Y., ;; Lee, S., Appl. Phys. Lett. 2013, 103 , 043305 043 309,(b) Gong, X.; Tong, M.; Xia, Y.; Cai, W.; Moon, J. S.; Cao, Y.; Yu, G.; Shieh, C. L.; Nilsson, B.; Heeger, A. J., Science 2009, 325 , 1665 1667.

PAGE 215

215 54. (a) Beaujuge, P. M.; Ellinger, S.; Reynolds, J. R., Nat. Mater. 2008, 7 , 795 799,(b) Beaujuge, P. M.; Re ynolds, J. R., Chem. Rev. 2010, 110 , 268 320,(c) Kim, H. N.; Guo, Z.; Zhu, W.; Yoon, J.; Tian, H., Chem. Soc. Rev. 2011, 40 , 79 93. 55. (a) Zhang, L.; Colella, N. S.; Cherniawski, B. P.; Mannsfeld, S. C.; Briseno, A. L., ACS Appl. Mater. Interfaces 2014, 6 , 5327 5343,(b) Holcombe, T. W.; Norton, J. E.; Rivnay, J.; Woo, C. H.; Goris, L.; Piliego, C.; Griffini, G.; Sellinger, A.; Bredas, J. L.; Salleo, A.; Frechet, J. M., J. Am. Chem. Soc. 2011, 133 , 12106 12114,(c) Wang, S.; Oldham Jr., W. J.; Hudack Jr., R . A.; Bazan, G. C., J. Am. Chem. Soc. 2000, 122 , 5695 5709. 56. (a) Stupp, S. I.; Palmer, L. C., Chem. Mater. 2014, 26 , 507 518,(b) Huang, Y.; Kramer, E. J.; Heeger, A. J.; Bazan, G. C., Chem. Rev. 2014, 114 , 7006 7043. 57. (a) Wall, B. D.; Zacca, A. E.; Sanders, A. M.; Wilson, W. L.; Ferguson, A. L.; Tovar, J. D., Langmuir : the ACS journal of surfaces and colloids 2014, 30 , 5946 5956,(b) Tovar, J. D., Acc. Chem. Res. 2013, 46 , 1527 1537,(c) Schillinger, E. K.; Kümin, M.; Digennaro, A.; Mena Osteritz, E. ; Schmid, S.; Wennemers, H.; Bäuerle, P., Chem. Mater. 2013, 25 , 4511 4521,(d) Marty, R.; Szilluweit, R.; Sánchez Ferrer, A.; Bolisetty, S.; Adamcik, J.; Mezzenga, R.; Spitzner, E. C.; Feifer, M.; Steinmann, S. N.; Corminboeuf, C.; Frauenrath, H., ACS Nano 2013, 7 , 8498 8508,(e) Aida, T.; Meijer, E. W.; Stupp, S. I., Science 2012, 335 , 813 817,(f) Shaytan, A. K.; Schillinger, E. K.; Khalatur, P. G.; Mena osteritz, E.; Hentschel, J.; Borner, H. G.; Bäuerle, P.; Khokhlov, A. R., ACS nano 2011, 5 , 6894 6909,(g ) Stone, D. A.; Hsu, L.; Stupp, S. I., Soft Matter 2009, 5 , 1990 1993. 58. Shen, C.; Cramer, J. R.; Jacobsen, M. F.; Liu, L.; Zhang, S.; Dong, M.; Gothelf, K. V.; Besenbacher, F., Chem. Commun. 2013, 49 , 508 510. 59. (a) Zheng, Y.; Thai, T.; Reineck, P.; Qiu, L.; Guo, Y.; Bach, U., Adv. Funct. Mater. 2013, 23 , 1519 1526,(b) Anstaett, P.; Zheng, Y.; Thai, T.; Funston, A. M.; Bach, U.; Gasser, G., Angew. Chem. Int . Ed. 2013, 52 , 4217 4220,(c) Thai, T.; Zheng, Y.; Ng, S. H.; Mudie, S.; Altissimo, M.; Bach, U., Angew. Chem. Int . Ed. 2012, 51 , 8732 8735,(d) Lalander, C. H.; Zheng, Y.; Dhuey, S.; Cabrini, S.; Bach, U., ACS nano 2010, 4 , 6153 6161,(e) Zheng, Y.; Lalander, C. H.; Thai, T.; Dhuey, S.; Cabrini, S.; Bach, U., Angew. Chem. Int . Ed. 2011, 50 , 4398 4 402. 60. (a) Lena, S.; Brancolini, G.; Gottarelli, G.; Mariani, P.; Masiero, S.; Venturini, A.; Palermo, V.; Pandoli, O.; Pieraccini, S.; Samori, P.; Spada, G. P., Chem. Eur. J. 2007, 13 , 3757 3764,(b) Pham, T. N.; Masiero, S.; Gottarelli, G.; Brown, S. P ., J. Am. Chem. Soc. 2005, 127 , 16018 16019. 61. Lena, S.; Masiero, S.; Pieraccini, S.; Spada, G. P., Chem. Eur. J. 2009, 15 , 7792 7806.

PAGE 216

216 62. (a) Peters, G. M.; Skala, L. P.; Plank, T. N.; Hyman, B. J.; Reddy, G. N. M.; Marsh, A.; Brown, S. P.; Davis, J. T ., J. Am. Chem. Soc. 2014, 136 , 12596 12599,(b) Ma, L.; Harrell, J., W. A.;; Davis, J. T., Org. Lett. 2009, 11 , 1599 1602,(c) Kaucher, M. S.; Harrell, J., W. A.;; Davis, J. T., J. Am. Chem. Soc. 2005, 128 , 38 39. 63. (a) Martín Hidalgo, M.; Camacho Soto, K.; Gubala, V.; Rivera, J. M., Supramol Chem 2010, 22 , 862 869,(b) García Arriaga, M.; Hobley, G.; Rivera, J. M., J. Am. Chem. Soc. 2008, 130 , 10492 10493,(c) Betancourt, J. E.; Rivera, J. M., Org. Lett. 2008, 10 , 2287 2290. 64. (a) Li, J.; Sarkar, A.; Mo rkoc, H.; Neogi, A., J. Display Technol. 2009, 5 Appl. Phys. Lett. 2008, 92 , 0133091 0133093,(c) Neogi, A.; Li, J.; Neogi, P. B.; Sarkar, A.; Morkoc, H., Electron. Lett. 2004, 40 , 1605 1606. 65. (a) Rinaldi, R.; Branca, E.; Cingolani, R.; Masiero, S.; Spada, G. P.; Gottarelli, G., Appl. Phys. Lett. 2001, 78 , 3541 3543,(b) Maruccio, G.; Visconti, P.; Arima, V.; D'Amico, S.; Biasco, A.; D'Amone, E.; Cingolani, R.; Rin aldi, R.; Masiero, S.; Giorgi, T.; Gottarelli, G., Nano Lett. 2003, 3 , 479 483. 66. (a) Parker, T. C.; Patel, D. G.; Moudgil, K.; Barlow, S.; Risko, C.; Brédas, J. L.; Reynolds, J. R.; Marder, S. R., Mater. Horiz. 2015, 2 , 22 36,(b) Neto, B. A. D.; Lapis, A. A. M.; da Silva Júnior, E. N.; Dupont, J., Eur. J. Org. Chem. 2013, 2013 , 228 255. 67. (a) Jatsch, A.; Schillinger, E. K.; Schmid, S.; Bäuerle, P., J. Mater. Chem. 2010, 20 , 3563 3578,(b) Mishra, A.; Ma, C. Q.; Bäuerle, P., Chem. Rev. 2009, 109 , 1141 1276. 68. (a) Venkatesh, V.; Kumar, J.; Verma, S., CrystEngComm. 2011, 13 , 6030 6032,(b) Zhang, L.; Fan, J., ; ; Vu, K.; Hong, K.; Le Brazidec, J. Y.; Shi, J.; Biamonte, M.; Busch, D. J.; Lough, R. E.; Grecko, R.; Ran, Y.; Sensintaffar, J. L.; Kamal, A.; Lundgren, K.; Burrows, F. J.; Mansfield, R.; Timony, G. A.; Ulm, E. H.; Kasibhatla, S. R.; Boehm, M. F., J. Med. Chem. 2006, 49 , 5352 5362,(c) Fujii, T.; Saito, T.; Mori, S., Heterocycles 1988, 27 , 1145 1148. 69. Volpini, R.; Dal Ben, D.; Lambertucci, C.; Marucci, G.; Mishra, R. C.; Ramadori, A. T.; Klotz, K. N.; Trincavelli, M. L.; Martini, C.; Cristalli, G., Chem. Med. Chem. 2009, 4 , 1010 1019. 70. Venkatesh, V.; Kumar, J.; Verma, S., CrystEngComm 2011, 13 , 6030 6032. 71. (a) Amb, C. M.; Beaujuge, P. M .; Reynolds, J. R., Adv. Mater. 2010, 22 , 724 728,(b) Song, H.; Sun, B.; Gu, K. J.; Yang, Y.; Zhang, Y.; Shen, Q. D., J. App. Polym. Sci. 2009, 114 , 1278 1286.

PAGE 217

217 72. Luo, L.; Chen, G.; Li, Y., Heterocycles 2008, 75 , 2803 2808. 73. Arsenyan, P.; Ikaunieks, M .; Belyakov, S., Tetrahedron Lett. 2007, 48 , 961 964. 74. Can. J. Chem. 2011, 89 , 488 498. 75. Hobley, G.; Gubala, V.; Rivera Sánchez, M. D.; Rivera, J. M., Synlett. 2008, 2008 , 1510 1514. 76. Western, E. C.; Shaughnessy, K. H., J. Org. Chem. 2005, 70 , 6378 6388. 77. Stefan, L.; Guedin, A.; Amrane, S.; Smith, N.; Denat, F.; Mergny, J. L.; Monchaud, D., Chem. Commun. 2011, 47 , 4992 4994. 78. Yoshino, H. T., Y.; Saito, I.; Tsujii, M., Chem. Pharm. Bull. 1987, 35 , 3438 3441. 79. Li, Y.; Li, Z.; Wang, C.; Li, H.; Lu, H.; Xu, B.; Tian, W., J. Polym. Sci., Part A: Polym. Chem. 2010, 48 , 2765 2776. 80. Biniek, L.; Chochos, C. L.; Leclerc, N.; Boyron, O.; Fall, S.; Lévèque, P.; Heiser, T., J. Polym. Sci., Part A: Polym. Chem 2012, 50 , 1861 1868. 81. Noll , S.; Kralj, M.; Suman, L.; Stephan, H.; Piantanida, I., Eur. J. Med. Chem. 2009, 44 , 1172 1179. 82. Rai, D.; Johar, M., ;; Srivastav, N. C.; Manning, T.; Agrawal, B.; Kunimoto, D. Y.; Kumar, R., J. Med. Chem. 2007, 50 , 4766 4774. 83. Reigan, P.; Gbaj, A .; Stratford, I. J.; Bryce, R. A.; Freeman, S., Eur. J. Med. Chem. 2008, 43 , 1248 1260. 84. (a) Getmanenko, Y. A.; Kang, S. W.; Shakya, N.; Pokhrel, C.; Bunge, S. D.; Kumar, S.; Ellman, B. D.; Twieg, R. J., J. Mater. Chem. C 2014, 2 , 256 271,(b) Ahn, H. S .; An, G. I.; Rhee, H. J., Bull. Korean Chem. Soc. 2011, 32 , 1931 1935,(c) Park, J. W.; Lee, D. H.; Chung, D. S.; Kang, D. M.; Kim, Y. H.; Park, C. E.; Kwon, S. K., Macromol. 2010, 43 , 2118 2123. 85. Reichardt, C., Solvents and Solvent Effects in Organic Chemistry, Third Edition . Third ed.; Wiley VCH Verlag GmbH & Co. KGaA: 35032 Marburg Germany, 2004. 86. Mishra, D.; Pal, S., J. Mol. Struct.: THEOCHEM 2009, 902 , 96 102.

PAGE 218

218 87. Haid, S.; Marszalek, M.; Mishra, A.; Wielopolski, M.; Teuscher, J.; Moser, J. E. ; Humphry Baker, R.; Zakeeruddin, S. M.; Grätzel, M.; Bäuerle, P., Adv. Funct. Mater. 2012, 22 , 1291 1302. 88. (a) Patel, D. G.; Feng, F.; Ohnishi, Y. Y.; Abboud, K. A.; Hirata, S.; Schanze, K. S.; Reynolds, J. R., J. Am. Chem. Soc. 2012, 134 , 2599 2612,( b) Casper, T. J.; Meyer, J. V., J. Phys. Chem. 1983, 87 89. (a) Zhou, D. G.; Corbitt, T. S.; Parthasarathy, A.; Tang, Y.; Ista, L. K.; Schanze, K. S.; Whitten, D. G., J. Phys. Chem. Lett. 2010, 1 Silva, L. M.; Arnaut, L. G.; Becker, R. S., J. Chem. Phys. 1999, 111 , 542 7 5433. 90. (a) Amrutha, S. R.; Jayakannan, M., J. Phys. Chem. B 2008, 112 , 1119 1129,(b) Fakis, M.; Anestopoulos, D.; Giannetas, V.; Persephonis, P., J. Phys. Chem. B 2006, 110 , 24897 24902,(c) Walters, K. A.; Ley, K. D.; Cavalaheiro, C. S. P.; Miller, S . E.; Gosztola, D.; Wasielewski, M. R.; Bussandri, A. P.; van Willigen, H.; Schanze, K. S., J. Am. Chem. Soc. 2001, 123 , 8329 8342,(d) Hsu, J. H.; Fann, W.; Tsao, P. H.; Chuang, K. R.; Chen, S. A., J. Phys. Chem. A 1999, 103 , 2375 2380. 91. Dubois, C. J.; Abboud, K. A.; Reynolds, J. R.; Gaines, V., J. Phys. Chem. B 2004, 108 , 8550 8557. 92. (a) Thompson, B. C.; Kim, Y. G.; McCarley, T. D.; Reynolds, J. R., J. Am. Chem. Soc. 2006, 128 , 12714 12725,(b) van Mullekom, H. A. M.; Vekemans, J. A. J. M.; Meijer, E. W., Chem. Eur. J. 1998, 4 , 1235 1243. 93. (a) Teh, H. F.; Yang, X.; Gong, H.; Tan, S. N., Electroanalysis 2004, 16 , 769 773,(b) de los Santos Álvarez, N. D.; Ortea, P. M.; Pañeda, A. M.; Castañón, M. J. L.; Ordieres, A. J. M.; Blanco, P. T., J. Electro anal. Chem. 2001, 502 , 109 117. 94. (a) Delaney, S.; Barton, J. K., J. Org. Chem. 2003, 68 , 6475 6483,(b) Kane maguire, N. A. P.; Wheeler, J. F., Coord. Chem. Rev. 2001, 211 , 145 162,(c) Delaney, S.; Pascaly, M.; Bhattacharya, P. K.; Han, K.; Barton, J. K ., Inorg. Chem. 2001, 41 , 1966 1974,(d) Steenken, S.; Jovanovic, S. V., J. Am. Chem. Soc. 1997, 119 , 617 618,(e) Seidel, C. A. M.; Schulz, A.; Sauer, M. H. M., J. Phys. Chem. 1996, 100 , 5541 5553.

PAGE 219

219 95. Frisch, M. J. T., G. W.; Schlegel, H. B.; Scuser ia, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R .; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, M. J.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, Ö.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. , Gaussian 09, Revision D.01, Gaussian, Inc. , Wallingford CT, 2009 . 96. (a) Zhang, Z. G.; Liu, Y. L.; Yang, Y.; Hou, K.; Peng, B.; Zhao, G.; Zhang, M.; Guo, X.; Kang, E. T.; Li, Y., Macromol. 2010, 43 , 9376 9383,(b) Zhang, Z. G.; Zhang, K. L.; Liu, G.; Zhu, C. X.; Neoh, K. G., Macromol. 2009, 42 , 3 104 3111. 97. (a) Oberhumer, P. M.; Huang, Y. S.; Massip, S.; James, D. T.; Tu, G.; Albert Seifried, S.; Beljonne, D.; Cornil, J.; Kim, J. S.; Huck, W. T. S.; Greenham, N. C.; Hodgkiss, J. M.; Friend, R. H., J. Chem. Phys. 2011, 134 , 114901 114908,(b) Jes persen, K. G.; Beenken, W. J. D.; Zaushitsyn, Y.; Yartsev, A.; Andersson, M.; Pullerits, T.; Sundström, V., J. Phys. Chem. 2004, 121 , 12613 12617. 98. Dennington, R. K., T.; Millam, J., GaussView Version 5, Semichem Inc. Shawnee Mission KS, 2009 . 99. Alp er, J., Science 2002, 295 , 2396 2397. 100. (a) Elemans, J. A. A. W.; Rowan, A. E.; Nolte, R. J. M., J. Mater. Chem. 2003, 13 , 2661 2670,(b) González Rodríguez, D.; Schenning, A. P. H. J., Chem. Mater. 2011, 23 , 310 325,(c) Praveen, V. K.; Babu, S. S.; Vij ayakumar, C.; Varghese, R.; Ajayaghosh, A., Bulletin of the Chemical Society of Japan 2008, 81 , 1196 1211,(d) Avinash, M. B.; Govindaraju, T., Nanoscale 2014, 6 , 13348 13369. 101. Henson, Z. B.; Mullen, K.; Bazan, G. C., Nat. Chem. 2012, 4 , 699 704. 102. (a) Rest, C.; Kandanelli, R.; Fernandez, G., Chem. Soc. Rev. 2015, 44 , 2543 2572,(b) Jiang, L.; Gao, J.; Fu, Y.; Dong, H.; Zhao, H.; Li, H.; Tang, Q.; Chen, K.; Hu, W., Nanoscale 2010, 2 , 2652 2656. 103. Treadway, C. R.; Hill, M. G.; Barton, J. K., Chem. Phys. 2002, 281 , 409 428. 104. Bou Zerdan, R.; Cohn, P.; Puodziukynaite, E.; Baker, M. B.; Voisin, M.; Sarun, C.; Castellano, R. K., J. Org. Chem. 2015, 80 , 1828 1840.

PAGE 220

220 105. Sendula, R.; Orbán, E.; Hudecz, F.; Sági, G.; Jablonkai, I., Nucleosides, Nucleot ides and Nucleic Acids 2012, 31 , 482 500. 106. Das, B.; Krishnaiah, M.; Venkateswarlu, K.; Reddy, V. S., Tetrahedron Lett. 2007, 48 , 81 83. 107. Asakura, J.; Robins, M. J., J. Org. Chem. 1990, 55 , 4928 4933. 108. (a) Chen, C. Y.; Wu, S. J.; Wu, C. G.; C hen, J. G.; Ho, K. C., Angew. Chem. Int. Ed. 2006, 45 , 5822 5825,(b) Yin, J. F.; Chen, J. G.; Lu, Z. Z.; Ho, K. C.; Lin, H. C.; Lu, K. L., Chem. Mater. 2010, 22 , 4392 4399. 109. de los Santos Alvarez, N.; Ortea, P. M.; Paneda, A. M.; Castanon, M. J. L.; O rdieres, A. J. M.; Blanco, P. T., J. Electroanal. Chem. 2001, 502 , 109 117. 110. Chen, J. S.; Shirts, R. B., J. Phys. Chem. 1985, 89 , 1643 1646. 111. Gutowsky, H. S.; Saika, A., J. Chem. Phys. 1953, 21 , 1688 1694. 112. Hirose, K., Journal of Inclusion P henomena 2001, 39 , 193 209. 113. (a) Bisson, A. P.; Hunter, C. A.; Morales, J. C.; Young, K., Chem. Eur. J. 1998, 4 , 845 851,(b) Sanderson, J. M., University of Durham , http ://www.dur.ac.uk/j.m.sanderson/science/sheets/NMR_Fit_HH.pdf . 114. Thordarson, P., Chem. Soc. Rev. 2011, 40 , 1305 1323. 115. Harvey, A. E.; Manning, D. L., J. Am. Chem. Soc. 1950, 72 , 4488 4493. 116. Doiuchi, T.; Minoura, Y., Macromol. 1978, 11 , 270 27 4. 117. Tate, J. F.; Jones, M. M., J. Inorg. Nucl. Chem. 1960, 12 , 241 251. 118. (a) Loukas, Y. L., J. Pharm. Pharmacol. 1997, 49 , 944 948,(b) Fielding, L., Tetrahedron 2000, 56 , 6151 6170. 119. Addison, C. C.; Sheldon, J. C.; Smith, B. C., J. Chem. Soc . Dalton Trans. 1974 , 999 1002. 120. (a) Brown, T. L.; Gerteis, R. L.; Bafus, D. A.; Ladd, J. A., J. Am. Chem. Soc. 1964, 86 , 2135 2141,(b) Adachi, K.; Watarai, H., Chem. A Eur. J. 2006, 12 , 4249 4260,(c) Yan, F.; Copeland, R.; Brittain, H. G., Inorg. C him. Acta 1983, 72 , 211 216,(d) Ouhadi, T.; Hamitou, A.; Jerome, R.; Teyssie, P., Macromol. 1976, 9 , 927 931.

PAGE 221

221 121. Renny, J. S.; Tomasevich, L. L.; Tallmadge, E. H.; Collum, D. B., Angew. Chem. Int. Ed. 2013, 52 , 11998 12013. 122. (a) Brabec, C. J.; Durr ant, J. R., MRS Bulletin 2008, 33 , 670 675,(b) De Luca, G.; Pisula, W.; Credgington, D.; Treossi, E.; Fenwick, O.; Lazzerini, G. M.; Dabirian, R.; Orgiu, E.; Liscio, A.; Palermo, V.; Müllen, K.; Cacialli, F.; Samorì, P., Adv. Funct. Mater. 2011, 21 , 1279 1 295,(c) Hines, D. R.; Ballarotto, V. W.; Williams, E. D.; Shao, Y.; Solin, S. A., J. Appl. Phys. 2007, 101 , 024503. 123. Yoshimura, M.; Suchanek, W.; Han, K. S., J. Mater. Chem. 1999, 9 , 77 82. 124. Hollinger, J.; Seferos, D. S., Macromol. 2014, 47 , 5002 5009. 125. (a) Liu, X.; Kim, Y. J.; Ha, Y. H.; Zhao, Q.; Park, C. E.; Kim, Y. H., ACS Appl. Mater. Interfaces 2015, 7 , 8859 Özkut, M.; Algi, F.; Önal, A. M.; Cihaner, A., Org. Electron. 2012, 13 , 206 213,(c) Wang, X. Y.; Zhu ang, F. D.; Zhou, X.; Yang, D. C.; Wang, J. Y.; Pei, J., J. Mater. Chem. C 2014, 2 , 8152 8161,(d) Oliveira, E. F.; Lavarda, F. C., Mater. Res. 2014, 17 , 1369 1374. 126. Akkerman, H. B.; Mannsfeld, S. C. B.; Kaushik, A. P.; Verploegen, E.; Burnier, L.; Zoo mbelt, A. P.; Saathoff, J. D.; Hong, S.; Atahan Evrenk, S.; Liu, X.; Aspuru Guzik, A.; Toney, M. F.; Clancy, P.; Bao, Z., J. Am. Chem. Soc. 2013, 135 , 11006 11014. 127. (a) Lemaur, V.; Muccioli, L.; Zannoni, C.; Beljonne, D.; Lazzaroni, R.; Cornil, J.; Ol ivier, Y., Macromol. 2013, 46 , 8171 8178,(b) Lei, T.; Dou, J. H.; Pei, J., Adv. Mater. 2012, 24 , 6457 6461. 128. Speros, J. C.; Martinez, H.; Paulsen, B. D.; White, S. P.; Bonifas, A. D.; Goff, P. C.; Frisbie, C. D.; Hillmyer, M. A., Macromol. 2013, 46 , 5 184 5194. 129. (a) Mei, J.; Bao, Z., Chem. Mater. 2014, 26 , 604 615,(b) Yang, L.; Zhou, H.; You, W., J. Phys. Chem. C 2010, 114 , 16793 16800,(c) Yagai, S.; Suzuki, M.; Lin, X.; Gushiken, M.; Noguchi, T.; Karatsu, T.; Kitamura, A.; Saeki, A.; Seki, S.; Kik kawa, Y.; Tani, Y.; Nakayama, K. i., Chem. A Eur. J. 2014, 20 , 16128 16137.

PAGE 222

222 130. (a) Holcombe, T. W.; Yum, J. H.; Yoon, J.; Gao, P.; Marszalek, M.; Censo, D. D.; Rakstys, K.; Nazeeruddin, M. K.; Graetzel, M., Chem. Commun. 2012, 48 , 10724 10726,( b) Tamayo, A. B.; Dang, X. D.; Walker, B.; Seo, J.; Kent, T.; Nguyen, T. Q., Appl. Phys. Lett. 2009, 94 , 103301,(c) Lee, D. H.; Lee, M. J.; Song, H. M.; Song, B. J.; Seo, K. D.; Pastore, M.; Anselmi, C.; Fantacci, S.; De Angelis, F.; Nazeeruddin, M. K.; Gr äetzel, M.; Kim, H. K., Dyes Pigments 2011, 91 , 192 198,(d) Loser, S.; Bruns, C. J.; Miyauchi, H.; Ortiz, R. P.; Facchetti, A.; Stupp, S. I.; Marks, T. J., J. Am. Chem. Soc. 2011, 133 , 8142 8145,(e) Sahu, D.; Tsai, C. H.; Wei, H. Y.; Ho, K. C.; Chang, F. C .; Chu, C. W., J. Mater. Chem. 2012, 22 , 7945 7953,(f) Sun, Y.; Welch, G. C.; Leong, W. L.; Takacs, C. J.; Bazan, G. C.; Heeger, A. J., Nat. Mater. 2012, 11 , 44 48,(g) Mei, J.; Graham, K. R.; Stalder, R.; Reynolds, J. R., Org. Lett. 2010, 12 , 660 663,(h) P ark, J. K.; Kim, C.; Walker, B.; Nguyen, T. Q.; Seo, J. H., RSC Adv. 2012, 2 , 2232 2234,(i) Zhang, G.; Fu, Y.; Xie, Z.; Zhang, Q., Macromol. 2011, 44 , 1414 1420. 131. Zhang, H.; Welterlich, I.; Neudorfl, J. M.; Tieke, B.; Yang, C.; Chen, X.; Yang, W., Pol ym. Chem. 2013, 4 , 4682 4689. 132. (a) Lu, C.; Chen, W. C., Chem. Asian. J. 2013, 8 , 2813 2821,(b) Lee, Y. H.; Chen, W. C.; Yang, Y. L.; Chiang, C. J.; Yokozawa, T.; Dai, C. A., Nanoscale 2014, 6 , 5208 5216,(c) Dettinger, U.; Egelhaaf, H. J.; Brabec, C. J .; Latteyer, F.; Peisert, H.; Chassé, T., Chem. Mater. 2015, 27 , 2299 2308,(d) Fei, Z.; Ashraf, R. S.; Han, Y.; Wang, S.; Yau, C. P.; Tuladhar, P. S.; Anthopoulos, T. D.; Chabinyc, M. L.; Heeney, M., J. Mate. Chem. A 2015, 3 , 1986 1994. 133. Oda, M.; Noth Neher, D., Macromol. 2002, 35 , 6792 6798. 134. Grenier, C. R. G.; George, S. J.; Joncheray, T. J.; Meijer, E. W.; Reynolds, J. R., J. Am. Chem. Soc. 2007, 129 , 10694 10699. 135. (a) Akaba, T.; Yonezawa, K.; Kamioka, H.; Yasuda, T.; Han, L.; Moritomo, Y., Appl. Phys. Lett. 2013, 102 , 133901 133904,(b) Tamayo, A.; Kent, T.; Tantitiwat, M.; Dante, M. A.; Rogers, J.; Nguyen, T. Q., Energy Environ. Sci. 2009, 2 , 1180 1186. 136. Gemma, S.; Gabe llieri, E.; Sanna Coccone, S.; Martí, F.; Taglialatela Scafati, O.; Novellino, E.; Campiani, G.; Butini, S., J. Org. Chem. 2010, 75 , 2333 2340. 137. G. C. Bazan, L. Y., P. Zalar, T. Q. Nguyen, US Patent 2014, 8 729 221 B2 . 138. Evans, D. A.; Bartroli, J .; Shih, T. L., J. Am. Chem. Soc. 1981, 103 , 2127 2129. 139. Aquino, C.; Sarkar, M.; Chalmers, M. J.; Mendes, K.; Kodadek, T.; Micalizio, G. C., Nat. Chem. 2012, 4 , 99 104.

PAGE 223

223 140. Hodgson, D. M.; Kaka, N. S., Angew. Chem. Int. Ed. 2008, 47 , 9958 9960. 141 . (a) Tylleman, B.; Gbabode, G.; Amato, C.; Buess Herman, C.; Lemaur, V.; Cornil, J.; Gómez Aspe, R.; Geerts, Y. H.; Sergeyev, S., Chem. Mater. 2009, 21 , 2789 2797,(b) He, F.; Wang, W.; Chen, W.; Xu, T.; Darling, S. B.; Strzalka, J.; Liu, Y.; Yu, L., J. Am . Chem. Soc. 2011, 133 , 3284 3287,(c) Souza, B. S.; Leopoldino, E. C.; Tondo, D. W.; Dupont, J.; Nome, F., Langmuir : the ACS journal of surfaces and colloids 2012, 28 , 833 840. 142. Tamagawa, H.; Takikawa, H.; Mori, K., Eur. J. Org. Chem. 1999, 1999 , 973 978. 143. (a) Tamayo, A. B.; Tantiwiwat, M.; Walker, B.; Nguyen, T. Q., J. Phys. Chem. C 2008, 112 , 15543 15552,(b) Matthews, J. R.; Niu, W.; Tandia, A.; Wallace, A. L.; Hu, J.; Lee, W. Y.; Giri, G.; Mannsfeld, S. C. B.; Xie, Y.; Cai, S.; Fong, H. H.; Ba o, Z.; He, M., Chem. Mater. 2013, 25 , 782 789. 144. Farahat, M. E.; Wei, H. Y.; Ibrahem, M. A.; Boopathi, K. M.; Wei, K. H.; Chu, C. W., RSC Adv. 2014, 4 , 9401 9411. 145. T. Q. Nguyen, A. B. T., B. Walker, T. Kent, C. Kim, M. Tantiwiwat, US Patent 2010, 0326525 A1 . 146. Peet, J.; Tamayo, A. B.; Dang, X. D.; Seo, J. H.; Nguyen, T. Q., Appl. Phys. Lett. 2008, 93 , 163306 163309. 147. Liu, J.; Walker, B.; Tamayo, A.; Zhang, Y.; Nguyen, T. Q., Adv. Funct. Mater. 2013, 23 , 47 56. 148. Yamaguchi, T.; Kimura, T.; Matsuda, H.; Aida, T., Angew. Chem. 2004, 116 , 6510 6515. 149. Li, G.; Yao, Y.; Yang, H.; Shrotriya, V.; Yang, G.; Yang, Y., Adv. Funct. Mater. 2007, 17 , 1636 1644. 150. Braun, S.; Salaneck, W. R.; Fahlman, M., Adv. Mater. 2009, 21 , 1450 1472. 151. Yang, Z.; Jin, X.; Guaciaro, M.; Molino, B. F.; Mocek, U.; Reategui, R.; Rhea, J.; Morley, T., Org. Lett. 2011, 13 , 5436 5439. 152. Huo, L.; Hou, J.; Chen, H. Y.; Zhang, S.; Jiang, Y.; Chen, T. L.; Yang, Y., Macromol. 2009, 42 , 6564 6571. 153. Nielsen, C. B.; Turbiez, M.; McCulloch, I., Adv. Mater. 2013, 25 , 1859 1880.

PAGE 224

224 154. (a) Moulé, A. J.; Meerholz, K., Adv. Funct. Mater. 2009, 19 , 3028 3036,(b) Walker, B.; Tamayo, A. B.; Dang, X. D.; Zalar, P.; Seo, J. H.; Garcia, A.; Tantiwiwat, M.; Nguyen, T. Q., Adv. Funct. Mater. 2009, 19 , 3063 3069,(c) Salleo, A.; Kline, R. J.; DeLongchamp, D. M.; Chabinyc, M. L., Adv. Mater. 2010, 22 , 3812 3838,(d) Brocorens, P.; Van Vooren, A.; Chabinyc, M. L.; Toney, M. F.; Shkunov, M.; Heeney, M.; McCulloch, I.; Cornil, J.; Lazzaroni, R., Adv. Mater. 2009, 21 , 1193 1198. 155. (a) Kato, T.; Yasuda, T.; Kamikawa, Y.; Yoshio, M., Chem. Commun. 2009 , 729 739,(b) Hoeben, F. J. M.; Jonkheijm, P.; Meijer, E. W.; Schenning, A. P. H. J., Chem. Rev. 2005, 105 , 1491 1546,(c) Frattarell i, D.; Schiavo, M.; Facchetti, A.; Ratner, M. A.; Marks, T. J., J. Am. Chem. Soc. 2009, 131 , 12595 12612. 156. (a) Dunger, A.; Limbach, H. H.; Weisz, K., J. Am. Chem. Soc. 2000, 122 , 10109 10114,(b) Sartorius, J.; Schneider, H. J., Chem. A Eur. J. 1996, 2 , 1446 1452. 157. (a) Halder, A.; Halder, S.; Bhattacharyya, D.; Mitra, A., Phys. Chem. Chem. Phys. 2014, 16 , 18383 18396,(b) Yang, B.; Moehlig, A. R.; Frieler, C. E.; Rodgers, M. T., J. Phys. Chem. B 2015, 119 , 1857 1868. 158. (a) Li, J. P.; Wang, H. X.; Wang, H. X.; Xie, M. S.; Qu, G. R.; Niu, H. Y.; Guo, H. M., Eur. J. Org. Chem. 2014 , 2225 2230,(b) Amo Ochoa, P.; Zamora, F., Coord. Chem. Rev. 2014, 276 , 34 58,(c) Beobide, G.; Castillo, O.; Luque, A.; Perez Yanez, S., CrystEngComm 2015, 17 , 3051 3059 ,(d) Thomas Gipson, J.; Pérez Aguirre, R.; Beobide, G.; Castillo, O.; Luque, A.; Pérez Yáñez, S.; Román, P., Cryst. Growth. Des. 2015, 15 , 975 983. 159. Sessler, J. L.; Jayawickramarajah, J.; Gouloumis, A.; Torres, T.; Guldi, D. M.; Maldonado, S.; Stevens on, K. J., Chem. Commun. 2005 , 1892 1894.

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225 BIOGRAPHICAL SKETCH Raghida Bou Zerdan, known as Reggie in the United States, was born and raised in one of the smallest towns in Lebanon. She received her B.S. in chemistry from the Lebanese University in 2007 , then joined the graduate program at the American University of Beirut where she received her M.S. degree in organic chemistry in 2010, under the guidance of Prof. Makhlouf Haddadin. She was a small girl, from a small town, with big dreams. She crossed th e seas to pursue her Ph.D. studies in organic chemistry at the University of Florida under Prof. Ronald K. Castellano in 2010, and will graduate in August 2015. Beginning in September 2015, she will join Prof. Craig Hawker for a postdoctoral research posit ion at University of California, Santa Barbara.