VIBRONIC STRUCTURE IN THE OPTICAL-ABSORPTION SPECTRA OF PHENYLENE VINYLENE OLIGOMERS - A JOINT EXPERIMENTAL AND THEORETICAL-STUDY

We present a joint experimental and theoretical investigation of the o ptical absorption spectra of phenylene vinylene oligomers, The vibroni c structure, which is clearly observed in the experimental spectra, is well described by a simple model based on the Frank-Condon approximat ion but requires the use of at least two effective modes coupled to th e electronic states, Using a fitting procedure, we deduce the displace ment of the B-1(u) excited state potential energy curve relative to th at of the ground state and compare it to the results of recent Hartree -Fock semi-empirical calculations. Such information is of prime import ance in the description of the frequency-dependent linear as well as n onlinear optical responses.