Theoretical Studies of Third Hyperpolarizabilities for π-Conjugated Organic Systems with Intra- and Inter-Molecular Charge-Transfer Effects

Abstract

The origin of the macroscopic third nonlinear optical effects is the microscopic third hyperpolarizabilities (γ_ykl) at the molecular level. In this paper, (i) the time-dependent perturbation theory (=TDPT), (ii) the time-independent perturbation theory (=Rayleigh-Schrödinger perturbation theory =RSPT), and (iii) the coupled-Hartree-Fock (CHF) theory are applied to calculate the γ values. In order to investigate the spatial contributions of γ, the schematic diagrams of the transition moments in the TDPT three type approximation, and the plots of third derivatives of the Mulliken charge densities (γ density analysis) in the CHF method are introduced. Two types of new nonlinear systems are proposed. One is the charge-transfer complex utilizing intermolecular interations. It is found thast this system possesses a large γ component in the column direction. The other one is the polymer with polar side chains constructed from donor and acceptor molecules. The contribution of the side chain is found to be as large as that of the main chain.