Mechanisms of photoinduced protolytic interactions of 2,5-diphenyloxazoleortho-hydroxy derivatives in media of various acidities

The mechanism of photoinduced intra- and intermolecular protolytic interactions ofortho-hydroxy derivatives of 2,5-diphenyloxazole in an aqueous alcohol medium was studied over a wide range of acidity from pH ∼13 toH ₀ of ∼−7. The spectral parameters of protolytic forms and equilibrium constants were obtained, and rate constants for the primary photochemical processes (excited-state intra- and intermolecular proton transfer reactions) were evaluated. It was shown that the spectral characteristics of oxazoleortho-hydroxy derivatives in an acidic medium are formed as a result of competition and interchange of intra- and intermolecular protolytic interactions. The phototautomeric form in strongly acidic solutions was found to be produced by dissociation of the cationic form with the protonated oxazole ring.