Two symmetrical 2,5-bis[4-(2-arylvinyl)phenyl]-1,3,4-oxadiazoles that exhibit strong two-photon absorption and enhanced two-photon excited fluorescence were designed and synthesized based on “push-core-pull-core-push” molecules built from embedding electron-transporting 1,3,4-oxadiazole in aromatic conjugated system through Wittig-Horner reaction. Pumped by nanosecond laser at 800 nm, strong up-conversion emissions with the central wavelength at 507 and 475 nm in the solution of CHCl₃ have been observed. Their two-photon absorption cross-sections obtained by nonlinear transmission method are 1.07× 10^－46 and 6.6×10^－47 cm⁴•s•photon^－1. A very effective energy transfer from the excited terminal units to the π-conjugated bridging units of the two symmetrical D-π-A-π-D chromophores make the dominant contribution to the two-photon absorption and two-photon excited fluorescence.

Key words: 1,3,4-oxadiazole derivative, two-photon excited fluorescence, two-photon absorption cross- section