Photophysical and electron-transfer properties of a few 2,6-dimethyl-4-arylpyrylium derivatives

Abstract

Photophysical and electron transfer properties of pyrylium salts 1-4 were investigated. The photophysical properties include absorption and fluorescence spectra, quantum yields, fluorescence lifetimes and phosphorescence spectra. Laser flash photolysis of 1-4 in degassed dichloromethane led to the formation of transients assigned to the triplets of these molecules. The quantum yields of triplet formation and the extinction coefficients of the triplet-triplet absorption were determined. Electron transfers to the excited states of 1-4 from biphenyl were studied by fluorescence quenching and laser flash photolysis. The intermediate radical ions formed in the electron transfer reactions were characterized. In the case of 1-3, only the singlet excited states were involved in electron transfer reactions, whereas, in the case of 4, the singlet as well as the triplet excited states act as electron acceptors. Involvement of the triplet in the electron transfer reactions, led to higher Φ_ion and lower k_bet values in the case of 4. Thus, suitable modification of the structure of pyrylium salts can lead to molecules with very good photoelectron transfer properties.