Exciplex dynamics and emission from nonbonding energy levels in electronic polymer blends and bilayers

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Abstract
Photoexcited bound exciplexes generated at interfaces in bilayers and blends of hole and electron transporting polymers are unusual and differ from bound excitons formed by photoexcitations of bulk polymers. We present a unique exciplex system we found present for interfaces involving a π molecular orbital on one polymer with a nonbonding N-orbital on another polymer. The exciplex emission occurs in an unexpected energy region intermediate to that of emission of each of the isolated layers. Our data show that the photophysics of this exciplex differs from that of excimers and aggregates. The exciplex emission has greater similarity to exciton emission than excimer emission, reflecting the role of symmetry breaking at the interface of two dissimilar polymers. We present the first temperature and wavelength dependent studies of exciplex photoluminescence decays and propose a model based on the unique role of the nonbonding orbital in these N-containing polymers. We demonstrate that this type of exciplex is characteristic of a broad class of materials.