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A Theoretical Study of Carbon-Based Functionalized Materials by Reed Nieman, B.S. a Dissertation in Chemistry Submitted to the G

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A Theoretical Study of Carbon-Based Functionalized Materials by Reed Nieman, B.S. a Dissertation in Chemistry Submitted to the G A Theoretical Study of Carbon-Based Functionalized Materials by Reed Nieman, B.S. A Dissertation In Chemistry Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY Approved Clemens Krempner, Ph.D. Chair of Committee Hans Lischka, Ph.D. Adelia J. A. Aquino, Ph.D. Mark Sheridan Dean of the Graduate School May, 2019 Copyright 2019, Reed Nieman Texas Tech University, Reed Nieman, May 2019 ACKNOWLEDGMENTS I would first like to thank my advisor, Dr. Hans Lischka, whose passion for science and dedication to his work are truly inspiring. Working with him on my various projects has been a tremendous learning experience these past several years. One of his foremost characteristics that I have made an attempt to emulate is his tireless attention to detail, no matter how seemingly small, as all contributing parts are significant to a finished product. Finally, I have always been able to rely on his patience and encouragement to see through any difficult moment in a project. I would also like to thank Dr. Adelia Aquino who first saw potential in me when I did my undergraduate research project with her. She provided my first lessons in performing computational chemistry calculations and I still fondly remember sitting at her side hurriedly taking notes and trying to keep up as she quickly went through commands. Her constant kindness and support over the years is very much appreciated. I am very grateful too for Dr. Clemens Krempner for not only serving as the chairperson of my committee, but for going above and beyond in, among other things, helping me to secure several of my fellowships. I also thank Dr. Anita Das, and Nadeesha Jayani Silva for being good group members and great friends. I am thankful as well to Megan Gonzalez and Dr. Veronica Lyons for their friendship and support, without which graduate school would not have been nearly as colorful let alone bearable. I am also very thankful for my family and their unending encouragement even through our lowest moments. I acknowledge and thank our collaborators, specifically Dr. Francisco Machado with whom I worked closely while he was visiting. Thanks is also given to the groups of Dr. Toma Susi at the University of Vienna and Dr. Sergei Tretiak at Los Alamos National Laboratory for their excellent work and contributions. Finally, I gratefully acknowledge the following for helping to fund my education: the National Science Foundation, Texas Tech University for the Provost Scholarship and Doctoral Dissertation Completion Fellowship, the AT&T Foundation for the AT&T President’s Fellowship, and the Community Foundation of West Texas for the Lubbock Achievement Rewards for College Scientists Chapter (ARCS) Memorial Scholarship. ii Texas Tech University, Reed Nieman, May 2019 TABLE OF CONTENTS ACKNOWLEDGMENTS ii ABSTRACT vi LIST OF TABLES viii LIST OF FIGURES xiii LIST OF ABBREVIATIONS xxi I. BACKGROUND 1 1.1 Graphene 2 1.2 Organic Photovoltaic Bulk Heterojunctions and Electronic Excited 4 States 1.3 Radical Character in Polycyclic Aromatic Hydrocarbons 6 1.4 Bibliography 10 II. THEORETICAL METHODS 16 2.1 Density Functional Theory 18 2.2 Second-Order Møller-Plesset Perturbation Theory 22 2.3 Second-Order Algebraic Diagrammatic Construction 25 2.4 Basis Set Superposition Error and the Counterpoise Correction 27 Method 2.5 Environmental Simulation Approaches 29 2.6 Multiconfigurational Self-Consistent Field 31 2.7 Multireference Configuration Interaction 32 2.8 Multireference Averaged Quadratic Coupled-Cluster 34 2.9 Bibliography 36 III. SINGLE AND DOUBLE CARBON VACANCIES IN PYRENE AS FIRST MODELS FOR GRAPHENE DEFECTS: A SURVEY OF THE 38 CHEMICAL REACTIVITY TOWARD HYDROGEN 3.1 Abstract 39 3.2 Introduction 40 3.3 Computational Details 44 3.4 Results and Discussion 45 3.4.1 Potential Energy Scan 45 3.4.2 Geometry Optimizations 49 3.4.3 Energetic Stabilities 52 3.5 Conclusions 59 3.5 Acknowledgments 61 3.7 Bibliography 61 IV. STRUCTURE AND ELECTRONIC STATES OF A GRAPHENE 63 DOUBLE VACANCY WITH EMBEDDED SI DOPANT 4.1 Abstract 64 4.2 Introduction 65 4.3 Computational Details 66 iii Texas Tech University, Reed Nieman, May 2019 4.4 Results and Discussion 68 4.4.1 The Pyrene-2C+Si Defect Structure 68 4.4.2 The Circumpyrene-2C+Si Defect Structure 71 4.4.3 The Graphene-2C+Si Defect Structure 73 4.4.4 Natural Bond Orbital Analysis 73 4.4.5 Molecular Electrostatic Potential 79 4.4.6 Electron Energy Loss Spectroscopy 80 4.5 Conclusions 82 4.5 Acknowledgments 83 4.7 Bibliography 83 V. THE CRUCIAL ROLE OF A SPACER MATERIAL ON THE EFFICIENCY OF CHARGE TRANSFER PROCESSES IN ORGANIC 87 DONOR-ACCEPTOR JUNCTION SOLAR CELLS 5.1 Abstract 88 5.2 Introduction 89 5.3 Methods 92 5.3.1 Experimental 92 5.3.1.1 Bilayer Solar Cells Fabrication 92 5.3.1.2 Device Characterization 93 5.3.2 Computational Details 93 5.4 Results and Discussion 95 5.4.1 Experimental Observations 95 5.4.2 Analysis of Energy Levels 98 5.4.3 Characterization of Electronic States 102 5.5 Conclusions 104 5.6 Acknowledgments 106 5.7 Bibliography 106 VI. BENCHMARK AB INITIO CALCULATIONS OF POLY(P- PHENYLENEVINYLENE) DIMERS: STRUCTURE AND EXCITON 111 ANALYSIS 6.1 Abstract 112 6.2 Introduction 112 6.3 Computational Details 116 6.4 Results and Discussion 119 6.4.1 Structural Description 119 6.4.2 Excited States 124 6.5 Conclusions 133 6.6 Bibliography 134 VII. THE BIRADICALOID CHARACTER IN RELATION TO SINGLET/TRIPLET SPLITTINGS FOR CIS-/TRANS- DIINDENOACENES AND TRANS- 139 INDENOINDENODI(ACENOTHIOPHENES) BASED ON EXTENDED MULTIREFERENCE CALCULATIONS iv Texas Tech University, Reed Nieman, May 2019 7.1 Abstract 140 7.2 Introduction 141 7.3 Computational Details 143 7.4 Results and Discussion 146 7.4.1 Trans-diindenoacenes 146 7.4.2 Cis-diindenoacenes 152 7.4.3 Trans-indenoindenodi(acenothiophenes) 156 7.5 Conclusions 160 7.6 Bibliography 161 169 VIII. CONCLUDING REMARKS APPENDICES A. ADDITIONAL TABLES AND FIGURES NOT INCLUDED IN CHAPTER III 174 B. ADDITIONAL TABLES AND FIGURES NOT INCLUDED IN CHAPTER IV 181 C. ADDITIONAL TABLES AND FIGURES NOT INCLUDED IN CHAPTER V 189 D. ADDITIONAL TABLES AND FIGURES NOT INCLUDED IN CHAPTER VI 198 E. ADDITIONAL TABLES AND FIGURES NOT INCLUDED IN CHAPTER VII 216 v Texas Tech University, Reed Nieman, May 2019 ABSTRACT This dissertation will examine the electronic properties of several materials used in state-of-the art technology and ongoing scientific investigation by means of high-level ab initio quantum chemical calculations. In this way, the application of such calculations to graphene reactivity and defects, organic photovoltaic processes, and excited states and biradical character of polycyclic aromatic hydrocarbons (PAH) is presented. Graphene reactivity and defect characterization is currently the source of intense scrutiny. The reactivity of pristine graphene and single and double carbon vacancies toward a hydrogen radical was assessed using complete active space self-consistent field theory (CASSCF) and multireference configuration interaction singles and doubles (MR-CISD) calculations using a pyrene model. While all carbon centers formed stable, novel C-H bonds, the single carbon defect was found to be most stabilizing thanks to the dangling bond at the six-membered ring. Bonding at this carbon center shows interaction with several closely-spaced electronic excited states. A rigid scan was also used to show the dynamic landscape of the potential energy surfaces of these structures. Double carbon vacancy pyrene and circumpyrene were used to investigate the structure and electronic states of an intrinsic silicon impurity in graphene by density functional theory (DFT) methods. The ground state was found to be low spin, non-planar and D2 symmetric with a nearby low spin, planar state with D2h symmetry. Characterization with natural bond orbital (NBO) analyses showed that the hybridization in the non-planar structure is sp3 and sp2d in the planar structure. Charge transfer from the silicon dopant to the surrounding carbon atoms is demonstrated via analysis with natural charges and molecular electrostatic potential (MEP) plots. Experiment shows drastically enhanced power conversion efficiency (PCE) in a bulk heterojunction (BHJ) device consisting of poly(3-hexylthiophene-2, 5-diyl) (P3HT), terthiophene (T3), and fullerene (C60). This BHJ scheme was investigated using DFT and several environmental models. The state-specific (SS) environment was found to best reproduce the experimental findings showing that initial photoexcitation of a local, bright exciton at P3HT was able to decay through several charge transfer (CT) bands of P3HT→C60 and T3→C60 character explaining the increased PCE. The spectra calculated vi Texas Tech University, Reed Nieman, May 2019 for the isolated system and linear response (LR) environment were very similar to each other and showed the initial photoexcitation at P3HT decayed instead into bands of local C60 excitonic states quenching the CT states. Crucial benchmark calculations of the structure and electronic excited states missing from the current literature were performed for oligomers of poly(p- phenylenevinylene) (PPV) dimers using high-level scaled opposite-spin (SOS) second- order Møller-Plesset (SOS-MP2) and second-order algebraic diagrammatic construction (SOS-ADC(2)) calculations. Comparisons were also made to DFT methods. The dimer structures were studied in two conformations: sandwich-stacked and displaced; the latter exhibited greater stacking interactions. Good agreement was found between the cc-pVQZ and aug-cc-pVQZ basis sets and the cc-pVTZ basis. Comparisons of the interaction energies were made to the complete basis set limit. Basis set superposition error was also accounted for. The excited state spectra presented a varied and dynamic picture that was analyzed using transition density matrices and natural transition orbitals (NTOs).
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