The geometry, electronic structures and electronic spectra of different type stilbene derivatives (D-π-D,A-π-A,D-π-A) are systematically studied by AM1 and INDO/CI methods. On the basis of correct UV-vis spectra, the position and strength of two- photon absorption can be predicted. Nonlinear third- order optical susceptibilities and two-photon absorption cross-sections was calculated using a program of Sum-over-states expression complied by the present authors. The influence of various substituents on two- photon absorption cross-sections are discussed micromechanically.

Key words: STYRENE P, ELECTRONIC SPECTROSCOPY, TWO PHOTON ABSORPTION