Nonlinear Optical Materials Based on Benzobisthiazole. Electronic Structure/Molecular Architecture/Polarizability/Hyperpolarizability Relationships Derived from π-Electron Theory

Abstract

ABSTRACTFactors contributing to the polarizability (αij) and frequencydoubling hyperpolarizability (βijk) of 2-(p-dimethylaminophenyl)-6-(pnitrophenyl) benzo(l,2-d:4,5-d′ )blsthiazole (DNBT) are analyzed via perturbation theory and the PPP-SCF-MECI π-electron model Hamiltonian. While the observable part of β (βvec) is clearly identifiable with a small number of charge transfer excitations along the molecular dipole direction, a (and by inference, the second-order hyperpolarizability γ) is more closely related to the overall size (volume) of the π-electron cloud. As a consequence, βvec is far more sensitive to molecular distortions which affect donor-acceptor charge transfer interactions than is π. The more sensitive frequency dependence of βvec can be understood in terms of the three-photon character of this nonlinearity.