Photophysical properties of pyrene in interaction with the surface of melanin particles

Melanins perform their biological activity (photoprotection and light enhanced chemical reactivity) under the form of porous aggregates on which ions and neutral molecules can be adsorbed. For this reason, the photochemistry of natural and synthetic melanins must be investigated in the framework of the physico-chemical theory of the heterogeneous reactions and a detailed knowledge of the surface properties, is therefore, necessary. In this work, some surface characteristics of melanin particles have been investigated taking advantage of the photophysical behaviour of pyrene, a dye widely used in studies of the interface properties of micelles and colloidal semiconductors. Our fluorescence study has allowed to obtain valuable informations regarding the micro-environmental polarity of the melanin surface (that influences the vibronic structure of the emission spectra), the excimer formation, the lifetimes of the emissions and the kinetics of quenching by Cu2+.