Syntheses, Structures and Second-order Nonlinear Optical Behavior of (E)-N-(4-Nitrobenzylidene)-3,4-dimethylaniline and (E)-N-(3-Nitrobenzylidene)-3,4-dimethylaniline

(E)-N-(4-Nitrobenzylidene)-3,4-dimethylaniline (1) and (E)-N-(3-nitrobenzylidene)-3,4-dimethylaniline (2) have been synthesized, and their crystal structures have been determined by X-ray diffraction analysis. Linear optical characteristics have been evaluated experimentally using UV/Vis spectroscopy and theoretically using the configuration interaction (CI) method. The maximum one-photon absorption (OPA) wavelengths of the studied compounds are shorter than 450 nm, giving rise to good optical transparency in the visible and near IR regions. The ab initio quantum-mechanical calculations (finite field second-order Moller-Plesset perturbation theory) of the investigated molecules have been carried out to compute the electric dipole moment (mu) and the first hyperpolarizability (beta) values. The ab initio results suggest that the title compounds might have microscopic second-order nonlinear optical (NLO) behavior with non-zero values.