Optical Excitations in Conjugated Oligomer and Polymer Aggregates: A Computational Approach

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0071802SpanoThis grant supports the theoretical work of this mid-career PI on light absorption and emission from conjugated polymer films. The work here is focussed on the absorption and emission of light by aggregates of the model compounds, oligo- (p-phenylenevinylene) and oligo-thiophene and their derivatives. The analysis is broadly divided between two aggregate packing motifs: (i) edge-to-face packing, which leads to cyclic tetramers (pinwheels) as well as the large herringbone lattices, and (ii) cofacial packing, which leads to p stacks. The aggregate eigenstates are vibrationally dressed excitons, determined primarily by the competition between the delocalizing influence of intermolecular energy (and/or charge) transfer and the localizing influence of intramolecular excited state nuclear relaxation. The primary objective is to understand how exciton-vibrational coupling and the degree of charge separation influence photophysical properties.%%% This grant supports the work of this midcareer theoretical chemist in a comprehensive study of the phenomena of light emission and absorption in conjugated polymer films.It is expected that soon the light-emitting diodes and other optoelectronic devices will be made out of conjugated polymer films. This will show up, most likely, in flat panel displays. Polymer films can be made to lase via optical pumping although there is hope that they may lase electrically as well. Despite the many experiments designed to uncover the mechanism, by which they produce light, a fundamental understanding of light emission in polymer films is far from complete largely because of the complicating presence of strong intermolecular interactions. The research here will attempt to address these and other related issues***