Synthesis of novel styryl-1,3,4-oxadiazoles and their photophysical properties

Current thesis study mainly covers the synthesis of various diarylsubstituted styryl-1,3,4-oxadiazole anilines and sulfonamides and their photophysical studies. As the main precursors, first, nitrobenzohydrazide (56) and cinnamoyl chloride derivatives (61a-e) were prepared and then converted to styryl-1,3,4-oxadiazole anilines bearing EWG and EDG groups (64a-e) efficiently over three steps. Later, styryl-1,3,4-oxadiazole sulfonamides (66a-o) were synthesized in high yields from the reaction of 64 derivatives with arylsulfonyl chlorides. All newly synthesized products (64a-e, 66a-o) were purified by chromatography or recrystallization and then, their structures were fully characterized using spectroscopic techniques including IR, 1H-NMR, 13C-NMR, and HRMS. Finally, the photophysical properties of 64 and 66 derivatives have been studied. Firstly, the absorption and fluorescence spectra of compounds 64a-e were measured in DMSO which provided best quantum yields. It was found that the fluorescence emission intensity increased with the introduction of EDG (64b and 64d) in comparison to EWG (64c). However, it was completely disappeared with the introduction of cyano group (EWG) (64e). Furthermore, a comparison study of fluorescence emission with regard to various arylsulfonyl groups on 66 derivatives revealed that fluorescence emission intensity and quantum yields diminished (moderate-low) by the effect of benzensulfonyl and tosyl groups, but disappeared by the introduction of nosyl group to 66c, f, i, l derivatives except in 66o.