Optical Excitations in Aggregates, Films and Crystals of Conjugated Oligomers and Polymers

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This grant is funded jointly by the Materials Theory Program in the Division of Materials Research and the Theoretical and Computational Chemistry Porgram in the Chemistry Division. The theoretical research focuses on thin films of pi-conjugated polymers and their associated oligomers. These materials are receiving widespread attention as the active components for organic-based field effect transistors and organic light emitting diodes (OLED's). Despite the many experiments designed to reveal the mechanism(s) by which oligomer/polymer films produce light, a fundamental understanding of light emission (and absorption) is far from complete. In this grant a strategy is implemented to theoretically investigate light absorption and emission in oligomer and polymernanoaggregates, films and crystals. The focus will be primarily on oligo-phenylenevinylene (OPVn) and oligo-thiophene (Otn) and their parent polymers. The anaylsis will be based on herringbone aggregates with molecular packing derived from known crystal structures. The Hamiltonian includes intermolecular (excitonic) interactions, linear excition-vibrational coupling with multiple intramolecular modes, and the influence of point and structural defects. The two-particle approximation will be employed to reduce the basis set to a tractable size for numerical analysis without sacrificing accuracy. %%% This grant is funded jointly by the Materials Theory Program in the Division of Materials Research and the Theoretical and Computational Chemistry Program in the Chemistry Division. This fundamental research on the electronic and optical properties of organic materials may lead to a new understanding of polymeric (plastic) optoelectronics and their possible applications as devices. ***