ABSTRACT GARCIA, ROSALVA CASTREJON. Design, Synthesis, and Characterization of Oligo- and Poly-(N-heteroacene)s for Organic Electronics. (Under the direction of Dr. Christopher B. Gorman). In an era of information technology, there is a demand for light-weight, low-cost, and flexible devices that consume less power and generate less heat. One strategy to achieve these properties comprises of complementary circuits which are composed of both p- and n-type organic semiconductors. Currently, there is an abundance of p-type organic molecules and a shortage of n-type organic molecules. The development of n-type organic molecules lags from its counterpart due to issues arising from ambient stability, charge-carrier mobility, and energy alignment. These limitations can be ameliorated through molecular, process, and interface engineering. However, there are synthetic challenges that restrict the pool of n-type materials. To overcome this shortage, a handy addition to the synthetic tool box is the Buchwald-Hartwig amination. While this synthetic method has expanded the library of N-heteroacenes for an evaluation of their structure-property relationships, the yields can be low with long reaction times. In this work, we have developed an approach for the synthesis of novel N-heteropentacenes. Our approach consists of a palladium-mediated cross-coupling, to obtain the precursor, followed by an acid-mediated cyclization, to furnish the N-heteropentacenes. Furthermore, the building blocks for the synthesis of the precursor have been designed to optimize the electronics to favor the cross-coupling and the cyclization. As a result of the design and the optimization of the synthesis, novel N-heteropentacene derivatives have been synthesized and characterized in this work. Outstanding features in the synthesis of the N-heteropentacene derivatives are the ease of the synthetic routes, purification which does not require column chromatography, and high yields (>78%) under short reaction times (< 2 h.). This approach can be applied to the synthesis of oligo- and poly-(N-heteroacene)s, once solubility and stability issues are addressed. Altogether, this method augments the pool of N-heteroacenes to investigate structure-property relationships with the intention to better understand and address the challenges of n-type organic semiconductors. © Copyright 2018 by Rosalva Castrejon Garcia All Rights Reserved Design, Synthesis, and Characterization of Oligo- and Poly-(N-heteroacene)s for Organic Electronics by Rosalva Castrejon Garcia A dissertation submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy Chemistry Raleigh, North Carolina 2018 APPROVED BY: _______________________________ _______________________________ Dr. Christopher B. Gorman Dr. Leslie Sombers Committee Chair _______________________________ _______________________________ Dr. David Shultz Dr. Jan Genzer DEDICATION This work is dedicated to my parents Francisco and Maria Castrejon and my fiancé Mark Bokhart for their unconditional support and encouragement. ii BIOGRAPHY Rosa was born on November 03, 1991 in Whiteville, North Carolina to Francisco and Maria Castrejon. In middle and high school, Rosa developed a passion for chemistry, mathematics, and computer science. To learn more about each subject, Rosa interned in the Department of Chemistry at Duke University as a NC Project SEED Intern, placed 1st and 2nd at regional and state level competitions, respectively, for the Future Business Leaders of America, and learned HTML coding. With these experiences, Rosa decided to pursue her post-secondary studies in Chemistry at Wake Forest University (WFU) in Winston-Salem, NC where she obtained a Bachelor of Science degree in Chemistry with a concentration in materials and a Bachelor of Arts degree in Spanish in the Spring of 2014. At WFU, her undergraduate research was focused on the synthesis and characterization of thiophene ligands and metal complexes for the uptake and release of metal ions upon an electrochemical response. Upon graduation, she decided to pursue a doctoral degree in the Department of Chemistry at North Carolina State University in Raleigh, NC under the supervision of Professor Christopher B. Gorman in the Fall of 2014. iii ACKNOWLEDGEMENTS First and foremost, I would like to thank my parents for all their encouragement during the difficult transition from high school to college. I would also thank the many mentors that I have had throughout the years. These mentors include Dr. Mirela Risden, Mr. Ken Cutler, Mr. Greene, Ms. Faye McNeil, Dr. Ronald Noftle, Dr. Cynthia Day, and Dr. Christa Collier. I would like to thank my advisor Dr. Gorman and former and current lab mates. I would also like the members in the Castellano, Pierce, and Shultz groups for allowing me to use their instruments. I would to thank Maria Moreno, Wendy Bunce, Katie Elliot, Emily Milks, Catherine Lull, and Jackie Hughes for their assistance in placing orders with third-party vendors and other administrative support. I would like to thank the undergraduates who assisted me carry out experiments. I would also like to thank my friends and my roommates. Lastly, I thank my fiancé Dr. Mark Bokhart for his unconditional support. iv TABLE OF CONTENTS LIST OF TABLES ................................................................................................................... ix LIST OF FIGURES .................................................................................................................. x LIST OF SCHEMES.............................................................................................................. xiv Chapter 1. Introduction ......................................................................................................... 1 1.1. Organic Electronic Devices ........................................................................................... 1 1.1.1. Organic Light-Emitting Diodes (OLEDs) .............................................................. 1 1.1.2. Organic Field-Effect Transistors (OFETs) ............................................................. 2 1.1.3. Organic Solar Cells (OSCs) .................................................................................... 3 1.1.4. Organic Resistive Memories (ORMs) .................................................................... 4 1.2. Small Organic Molecules ............................................................................................... 5 1.2.1. Acenes ..................................................................................................................... 5 1.2.1.1. Background ...................................................................................................... 5 1.2.1.2. Electronic Structure ......................................................................................... 5 1.2.1.3. Molecular Packing ........................................................................................... 7 1.2.1.4. Solubility and Stability .................................................................................. 10 1.2.2. N-Heteroacenes ..................................................................................................... 16 1.2.2.1. Background .................................................................................................... 16 1.2.2.2. Electronic Structure ....................................................................................... 17 1.2.2.3. Molecular Packing ......................................................................................... 17 1.2.2.4. Solubility and Stability .................................................................................. 18 1.3. Organic Polymers......................................................................................................... 19 1.4. Previous Work ............................................................................................................. 20 v 1.5. Research Goals............................................................................................................. 22 Chapter 2. Optimization of the Synthesis and Cyclization of the Precursor Molecules 23 2.1. Introduction .................................................................................................................. 23 2.2. Results and Discussion ................................................................................................ 23 2.2.1. Design of Reactions .............................................................................................. 23 2.2.2. Optimization of the Coupling with meta-Linkages .............................................. 23 2.2.2.1. Pd-Mediated Cross-Coupling......................................................................... 23 2.2.2.1.1. Model Reactions ..................................................................................... 25 2.2.2.1.2. Preliminary Polymerizations ................................................................... 29 2.2.2.2. Nucleophilic Aromatic Substitution .............................................................. 36 2.2.2.2.1. Preliminary Polymerizations ................................................................... 37 2.2.3. Optimization of the Cyclization with meta-Linkages ........................................... 40 2.2.4. Optimization of the Coupling with para-Linkages ............................................... 47 2.2.4.1. Model Reactions