NONLINEAR-OPTICAL PROPERTIES OF NOVEL THIOPHENE DERIVATIVES - EXPERIMENTAL AND AB-INITIO TIME-DEPENDENT COUPLED PERTURBED HARTREE-FOCK STUDIES

We report in this paper experimental and theoretical studies of the no nlinear optical properties of a new class of compounds which differ fr om traditional second-order molecules in the sense that a commonly use d electron donor chromophore is replaced by a thiophene ring. The mole cular second-order nonlinear optical coefficients, beta, as determined by the electric field-induced second-harmonic generation technique, f or 2-nitro-1-(2-thienyl)ethene and 4-nitro-1-(2-thienyl)-1,3-butadiene are, respectively, 1 and 3 times that of para-nitroaniline. Ab initio time-dependent coupled perturbed Hartree-Fock results are in agreemen t with the experimental findings. A Mulliken population analysis indic ates that the sulfur atom in the thiophene ring acts as an electron do nor. Both the experimental and the theoretical results confirm that a thiophene ring acts as an efficient donor, giving rise to highly effic ient second-order nonlinear optical properties. We also show that with this type of chromophore one can use a thiophene oligomer, in place o f a thiophene monomer, to amplify the nonlinearity.