Molecular Design for Octupolar Nonlinear Optical Systems: An ab Initio Study of First Hyperpolarizabilities of Symmetrically Heteroaromatic-Substituted Triazines

Abstract

An ab initio coupled perturbed Hartree−Fock study has been performed to investigate the hyperpolarizabilities β of a series of heteroaromatic-substituted sym-triazines in the frame of a tensorial formalism. Effects of donor or acceptor substitution and electron correlation on the octupolar triazines have also been explored. Geometric effects have been considered in a set of calculations by using fully optimized and planar structures. It is found that the effects of the deviations from the planarity on β are very small. Octupolar triazines containing pyrrole derivatives have larger β than the corresponding analogues containing furan and thiophene derivatives, and NO2 or NH2 substitution strongly affects β of octupolar benzene-substituted triazine. An additive model is introduced to evidence specific contributions to β arising from the multipolar symmetry. The β tensor of a multipolar system is dissected into two separate tensor representation, an additive term β A representing the tensorial sum of the dipo...