Abstract
We present a joint theoretical and experimental characterization of the absorption and photoluminescence spectra of oligo-paraphenylenevinylenes containing from 2 to 5 phenylene rings, Attention is paid to the emission spectra and their vibronic progressions in order to shed light on the geometry relaxation phenomena in the lowest singlet excited state, The results indicate that the relaxation energy in the excited state increases with inverse chain length. For long conjugated chains, the relaxation energy of the bound electron-hole pair is extrapolated to be of the order of 0.14 eV and the most significant part of the geometry deformations are found to spread over a length of about 20 Angstrom. (C) 1997 Elsevier Science B.V.