Fluorescence and time resolved photoacoustics of the

photoprotective pigment pheomelanin

L. Brancaleon, P.R. Crippa, C. Viappiani

Dept. of Physics, University of Parma

43100 Parma, Italy

Summary

A spectroscopical study was performed on synthetic pheomelanin with the aim to improve at a molecular level the knowledge of the photophysiological properties of such a protective epidermal pigment.

Both absorption and fluorescence spectra show a rather complex behaviour dependent upon pH changes. The time-resolved photoacoustic calorimetry gives values of quantum yields for non radiative relaxation of the optically exited states, that agree with the fluorescence data. Such high values (about 0.97), suggest that pheomelanin, like the black eumelanin, relaxes mainly through thermal transition, leaving only a little part of the electronic energy available for photochemical reaction putatively involved in pathological changes as solar eritheme and skin cancer.