Localized excitation effect on dipole moments of oligophenylenevinylenes in their excited Franck–Condon state

Abstract

The results from electrooptical absorption measurements (EOAM) on the ground and excited Franck–Condon state dipole moments of oligophenylenevinylenes in 1,4-dioxane and cyclohexane are presented. The dipole moments of quadrupolar dyes in the ground state are not equal zero. This means that one of the functional end groups of these molecules is not on the axis or on the plane with the central part of the molecule. Such a conclusion is confirmed by the quantum-chemical and semi-empirical recalculations. Owing to disorder in the ground-state geometry of the dyes the π–π conjugated system is located on mostly the plane part of the molecule and in the main this part absorbs the light. The localized excitation effect causes the large change of the dipole moments of quadrupolar molecules upon excitation to the Franck–Condon excited state. Due to an efficient intramolecular charge transfer the new oligophenylenevinylenes must have significant non-linear optical properties.