[Synthesis and spectral properties of stilbene derivatives as two-photon absorption materials].

Three stilbene derivatives with good coplanarity and enhanced charge delocalization in the conjugated molecular system, 4,4'-bis(diphenylammino-trans-styryl)biphenyl (BPSBP), 4,4'-bis(diethylamino-trans-styryl) biphenyl (BESBP) and 4,4'-bis(9-carbazyl-trans-styryl)-biphenyl (BCSBP), were designed, synthesized and characterized by infra-red spectroscopy, hydrogen nuclear magnetic resonance and elemental analysis. Experimental results reveal that the strongest one-photon absorption peaks appear between 350 and 400 nm, which is the energy region of two near infrared photons. The obvious solvatochromism was observed in five different polar solvents and the corresponding one-photon absorption and fluorescence emission spectra validate the character of intramolecular symmetric charge transfer. Two-photon fluorescence spectra show that both one- and two-photon processes share the same emission mechanism although they have different excitation processes and selection rules. The quadratic dependence of fluorescence intensity on excitation intensity indicates a real two-photon absorption process. The two-photon absorption cross section was measured via two-photon induced upconversion fluorescence method. The large values of two-photon absorption cross section, 892 GM, 617 GM and 483 GM for BPSBP, BESBP and BCSBP respectively, were obtained at 800 nm wavelength from a femtosecond laser source, which means potential applications in two-photon absorption fields.