Conformation-dependent molecular optical nonlinearities in bisnaphthol derivatives

The vibrational technique was applied to measure 1st-order and 2nd-order mol. nonlinearities b and g of bisnaphthol derivs. constrained in a noncoplanar conformation and contg. electron donor and acceptor groups. The vibrational chem. shifts obsd. in the IR spectra of model mols. show that in soln. a conformational equil. exists with only one conformer favoring electron injection by the oxygen lone pair into the arom. ring, with the consequent increase of the wt. of a quinoid structure. Thus the hyperpolarizabilities are conformationally dependent and may show temp. dependence. The same spectroscopic approach to the bisnaphthol derivs. shows that the conformationally dependent role of the electron injecting property of the oxygen is more relevant than the inter-ring electron hopping between pz orbitals