CONFORMATION-DEPENDENT MOLECULAR OPTICAL NONLINEARITIES IN BISNAPHTHOL DERIVATIVES

The 'vibrational technique' has been applied to measure first-order an d second-order molecular nonlinearities beta and gamma of bisnaphthol derivatives constrained in a non-coplanar conformation and containing electron donor and acceptor groups. The vibrational chemical shifts ob served in the IR spectra of model molecules show that in solution a co nformational equilibrium exists with only one conformer favouring elec tron injection by the oxygen lone pair into the aromatic ring, with th e consequent increase of the weight of a quinoid structure. It follows that the hyperpolarizabilities are conformationally dependent and may show temperature dependence. The same spectroscopic approach to the b isnaphthol derivatives shows that the conformationally dependent role of the electron injecting property of the oxygen is more relevant than the inter-ring electron hopping between p(z) orbitals.