Two-photon absorption and two-photon excited fluorescence of 1,3,4-oxadiazole derivatives

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 X 10(-46) and 6.6 x 10(-17) cm(4.)s(.)photon(-1). A very effective energy transfer from the excited terminal units to the pi-conjugated bridging units of the two symmetrical D-pi-A-pi-D chromophores make the dominant contribution to the two-photon absorption and two-photon excited fluorescence.