Solvent effects on fluorescence spectroscopic properties of benoxaprofen, a cutaneous photosensitizer

Abstract

Absorption and fluorescence emission spectra of benoxaprofen (BXP), a cutaneous photosensitizer, have been measured in different solvents. The emission spectrum shifts to longer wavelength as the hydrogen-bonding ability and polarity of the solvent increase, even though the position of the absorption maximum remains similar except for the loss of the spectral structure. The red shift of the emission maximum is exceptionally large in water as compared with non-aqueous solution, indicating that specific solvent relaxation may occur around the excited BXP. In parallel with the red shift of the fluorescence spectrum, the fluorescence quantum yield is markedly decreased in water. The nature of the emitting species of BXP in water and its relationship to the fluorescence quenching are discussed.