Photophysical behaviour of ground state anion and phototautomer of 3-hydroxyflavone in liposome membrane

Abstract

A detailed account of the photophysical behaviour of the phototautomer (PT) and the ground state anion (A⁻) of 3-hydroxyflavone in liposome membrane at various membrane conditions is presented. A quenching study with a hydrophilic quencher Ag⁺ suggests that the phototautomeric emission generates from the fraction of 3HF that is located at the inner hydrophobic core, whereas the ground state anionic emission is from the fraction that resides near the water-accessible surface site. However, the biexponential nature of fluorescence decays of both the forms indicates that there is local heterogeneity in the distribution. Temperature dependence studies and experiments in the presence of ethanol reveal that, as the membrane becomes more fluid, redistribution of 3HF takes place between the two sites leading to increase in A⁻ population. The temperature dependence of the fluorescence anisotropy change of PT shows good correlation with the phase change and shows a sharp drop at the transition temperature, whereas the corresponding change in the case of A⁻ is gradual.