Posokhov Y. Protolytic reactions in excited state and spectral-luminescent properties of ortho-hydroxy derivatives of 2,5-diaryl-1,3-oxazole and 2,5-diaryl-1,3,4-oxadiazole

The aim of the work was to elucidate how molecular structure of the studied compounds and acidity of media influence on character of exited state intramolecular proton transfer reaction (ESIPT). The subject of the work was the spectral-luminescent properties of several ortho-hydroxy derivatives of 2,5-diaryl-1,3-oxazole and 2,5-diaryl-1,3,4-oxadiazole. It has been shown that the fluorescent properties of the investigated compounds are determined by the exited state intramolecular proton transfer reaction (ESIPT). Rate constants of the ESIPT were obtained. It has been concluded that the rates of the ESIPT are determined by the increase of protonodonor-group acidity on exitation. The connection between the character of electron density redistribution in phototautomer form on excitation and the efficiency of phototautomer quenching has been found. It has been estimated that in acidic media phototautomer is formed by the hydroxy group dissociation of the cationic forms with protonated oxazole cycle