Energy transfer in a conjugated polymer with reduced inter-chain coupling

Energy transfer in spin-coated films and solutions of poly(dioctylphenylthiophene) with bulky side chains has been studied by femtosecond pump-probe spectroscopy, polarisation anisotropy and excitation annihilation. A red shift of stimulated emission spectra with time and a gradual decay of anisotropy are observed in him and solution and attributed to excitation migration towards lower-energy sites. At high-excitation intensities singlet-singlet annihilation with time-independent rate dominates the decay of excited-state population in the film for short times. It is concluded that energy migration in film, which results in effective excitation trapping and nonradiative decay, is a three-dimensional process, while in solution a one-dimensional intra-chain energy migration is much more limited. (C) 1998 Elsevier Science B.V. All rights reserved.