INTRAMOLECULAR PROTON-TRANSFER REACTION IN AN EXCITED-STATE IN A SERIES OF ORTHO-HYDROXY DERIVATIVES OF 2,5-DIARYLOXAZOLE

Spectral and luminescent properties of some ortho-hydroxy derivatives of 2,5-diaryloxazole were examined in aprotic solvents of different po larity. A reaction of intramolecular photoinduced proton transfer is t ypical for these compounds in an excited state. The effects of solvent polarity and basicity and molecular structure of the compounds on the efficiency of photoinduced proton transfer were considered. It was fo und that this efficiency in ortho-hydroxy derivatives of 2,5-diaryloxa zole depends mainly on an increase in acidity of the hydroxy group in the transition to the excited state. It was suggested that fluorescenc e quenching in a reaction product of intramolecular photoinduced proto n transfer (in a phototautomeric form) makes the main contribution to a decrease in emission efficiency of the examined ortho-hydroxy deriva tives of diaryloxazole, as compared with their analogues without intra molecular hydrogen bonds.