Finite field study on nonlinear optical properties of substituted ketene N,S-acetals

The nonlinear optical properties of title compounds calculated by AM1/finite field (AM1/FF) approach are discussed based on their crystal parameters. The origins of large molecular first hyperpolarizabilities β and good transparency of the compounds are explained well through the aromatic character enhancement in the excited state and the short conjugation length in the ground state. Results show that the difference of β values obtained by two experimental methods (Solvatochromic and Hyper Rayleigh Scattering) is due to the molecular quasi two dimension character and the octupolar components’ contribution. The calculation has also demonstrated that the change of β xxx caused by different donor substituents is linearly related with the Hammett substituent constant σ +.