Acceptor Moieties with Extended Conjugation for Semiconducting Polymers
Abstract
The field of semiconducting conjugated polymers has grown tremendously over the past few decades with innovations expanding the use of conjugated polymers into several devices such as transistors, light emitting diodes, and biocompatible electronics. For transistor devices, charge carrier mobility has rivaled the performance of amorphous silicon. The intrinsic properties of organic materials make them extremely attractive for further development and application. Organic materials are synonymous with terms such as lightweight, robust, flexible, and stretchable. A major advantage of conjugated polymers is their ability to be rendered solution processable with the alluring potential for large-area green manufacturing of electronic devices. However, these properties often fall short of their potential. Often strain engineering is often employed for favorable mechanical properties of polymer thin films. Incorporation of acceptor-acceptor (A-A) type moieties into donor-acceptor (D-A) type conjugated polymers becomes a new strategy to tune their electronic properties. In this work, we first demonstrate an efficient convergent route to prepare isoindigo-based A-A type building blocks - bis-isoindigos - via the palladium-catalyzed oxidative coupling. Bis-isoindigo-based polymers show high planarity and delocalized frontier molecular orbitals with lowered LUMO and intact HOMO energy levels, in comparison with their corresponding mono-isoindigo counterparts. Moreover, fluorine substitution on donors only lowers HOMO levels of Bis-IID polymers. This study asserts that the D-A-A strategy is effective in selectively tuning FMO energy levels of conjugated polymers, complementary to the D-D-A approach for the HOMO energy level tuning. Finally, we investigated the effect ofisomer structure has on the properties of conjugation polymers utilizing diazines to decouple the effects of spatial arrangement from heteroatom placement. These studies highlight the significant impact of side-chain sequence regioisomerism on aggregation behaviors, morphologies, and subsequently charge transport properties of donor-acceptor type conjugated polymers.
Degree
Ph.D.
Advisors
Mei, Purdue University.
Subject Area
Energy|Engineering|Condensed matter physics|Electrical engineering|Materials science|Optics|Physics
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