Strong two-photon absorption and two-photon excited fluorescence emission of heterofluorene derivatives

Two new chromophores: 2,8-bis[2-(4′-ethoxylphenyl)-5-(4′-styryl)-1,3,4-oxadiazole]dibenzothiophene (abbreviated as SO-G1) and 2,8-bis[(2-(4′-ethoxylphenyl)-5-(4′-styryl)-1,3,4-oxadiazole-N-ethylcarbazole (abbreviated as NO-G1) that exhibit strong two-photon absorption and enhanced two-photon excited fluorescence were synthesized based on “push-pull-core-pull-push” elongated molecules built from a rigid dibenzothiophene or carbazole. Both chromophores in different solvent are highly transparent across almost the whole visible spectrum region and possess highest fluorescence quantum yield of 0.89 for NO-G1 and 0.46 for SO-G1. Pumped by a visible wavelength (700-800 nm) of Ti: sapphire femto-second laser pulses, strong two-photon excited (TPE) fluorescence located at 440-510 nm with the TPE fluorescence emission cross-section (δTPF) being 21-8.2 times as much as that of fluorescein reference and strong two-photon absorption (TPA) cross-section (δTPA) of 454-377 GM have been observed.