Ultrafast photogeneration of inter-chain charge pairs in polythiophene films

Photoexcitation dynamics in films of polythiophenes with different side gro ups were studied by transient absorption spectroscopy using 80 fs pulses. W e show that inter-chain charge pairs (CP) are generated with similar to 20% efficiency in a polymer with short inter-chain distance (similar to 4 Angs trom) within 100 fs after photoexcitation. We discuss two mechanisms for in ter-chain charge separation: (i) electron or hole transfer from an initiall y excited intra-chain singlet state or (ii) optical excitation of mixed exc iton-charge transfer states, which quickly evolve to inter-chain CPs. (C) 2 000 Elsevier Science B.V, All rights reserved.