On the basis of INDO-SCI program, we have designed a program to calculate the nonlinear second-order polarizability β~i~j~k and β~μ according to the SOS expression. The electronic spectra and second- order nonlinear optical properties of 1,2-diamino-4,5-dinitrobezene 1 and 1,3-diamino-4,5-dinitrobezene 2 were studied. The calculated results indicate that molecule 1 possesses second-order nonlinear optical polarizability comparable to that of molecule 2. Because the dipole moment of 1 is much larger than that of 2, so the value of μβ of 1 is much larger than that of 2. Based on the studied above, the electronic spectra and second-order nonlinear optical properties of 2,3-bis(β-phenylethenyl0-5,6-dicyanopyrazine and 2,3-bis(β- thienylethenyl)-5,6-dicyanopyrazine derivatives were studied as well. It is found that all these compounds possess two low-lying excited electronic states that are very close to each other in energies, both contributing to the second-order nonlinear optical polarizability in an additive fashion. These derivatives are good candidates as chromophores due to their absorption <413 nm and large μβ values.

Key words: CHARGE TRANSFER, NON LINEAR OPTICS, POLARIZABILITIES, ELECTRON SPECTROSCOPY, PYRAZINE P, NITROBENZENE P, INTERMEDIATE NEGLECT OF DIFFERENTIAL OVERLAP APPROXIMATION (IND