Optical Excitations of Acceptor Substituted Poly-Thiophene Derivatives

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Abstract
We have studied acceptor substituted polythiophene derivatives in order to examine its usefulness as an intrinsic charge-trap under laser excitation. The polymers studied are the chemically prepared poly 3 - Butylethylether Thiophene (BETh) and the copolymer 3 - (4 - nitrobenzene 1,2 - ethen) Thiophene / BETh (1:3.5). We have established that the excitations which survive at long times in these polymers are: (a) bipolarons, which are doubly charged segments of the polymer accompanied by a significant bond alternation relaxation and having spin 0, and (b) triplet excitons, with zero charge and spin 1. When compared to unsubstituted polythiophene, it is noted that triplet excitons are much more efficiently photogenerated in these polythiophene derivatives.