Electron-deficient conjugated materials

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The development of new conjugated materials with tailored properties is in high demand for applications in organic electronics. This has led to conjugated materials receiving a great deal of research attention over the last few decades. One efficient method to prepare these novel conjugated small molecules and polymers is the incorporation of p-block elements into conjugated systems. In Chapter 2, a new phosphafluorene is synthesized and copolymerized to produce a donor-acceptor (D-A) conjugated copolymer PPF-BDTT. Direct post-polymerization modification of PPF-BDTT was performed on the phosphorus center to prepare the phosphine sulfide polymer PPF-BDTT-S and phosphine gold chloride polymer PPF-BDTT-Au. These D-A polymers have been fully characterized, and their applications in organic solar cells was also investigated. In Chapter 3, three air-stable difuran small molecules were synthesized by the incorporation of phosphorus, germanium, and silicon. The good stability is partially due to the σ*-π* conjugation interaction between p-block elements and the pi systems. These molecules show strong absorption in the UV region and intense emissions. The phosphorus bridged difuran was also copolymerized with fluorene to produce a D-A conjugated polymer. In Chapter 4, bithiazole (BTz) was functionalized with a 9-borabicyclononane (BBN) moiety to produce a boronium molecule BTz-BBN. With similar synthetic methods, two conjugated organoboronium polymers PFOBPy-BBN and PFOBTz-BBN were developed, which demonstrated a novel method to prepare conjugated boronium polymers in high yield. PFOBPy-BBN and PFOBTz-BBN were studied optically and electrochemically. In Chapter 5, benzothiophene dioxide was selected to prepare the non-fullerene acceptor ITBC with an acceptor-donor-acceptor structure. The strong electron-withdrawing sulfonyl acceptor units lead to extended UV-Vis absorption and low frontier molecular orbital energy levels with a narrow bandgap. A power conversion efficiency of 4.17 % was achieved by fabricating organic solar cells with polymer FTAZ as the donor and ITBC as the acceptor. In Chapter 6, a chlorinated bifuran small molecule ClBF was synthesized, and a series of random copolymers (PNDI-ClBFx) using ClBF and naphthalene diimide were prepared. These polymers exhibit strong and broad absorption, and the low-lying frontier energy levels of PNDI-ClBFx are suitable as polymer acceptors in all-polymer solar cells applications.

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Organic chemistry