Photoacoustic studies of non-radiative relaxation of excited states in melanin.

Photoacoustic measurements made at various chopping frequencies on dense acqueous melanin suspensions have revealed a significant dependence upon pH and redox state. It is shown that such behaviour, differing from the simple predictions of the Rosencwaig-Gersho theory, can be explained in terms of finite carrier diffusion and recombination times. The implications of these findings with respect to the amorphous semiconductor model proposed to describe the dynamic role of epidermal melanin are discussed. From the experimental data, values of physical parameters were calculated which allow a qualitative correlation between chemical states and electronic behaviour and, consequently, some aspects of the molecular biology of the melanosome, founded on a rigorous base.