Photoelectronic properties of synthetic melanins

Melanins are ubiquitous natural pigments, formed by oxidation and polymerization of catechols, whose absorption spectra increase monotonically from 700 to 250 nm. An investigation of their optical and photoelectric properties, reported here, shows that melanins can be described as an amorphous network of nanometre-sized conjugated clusters, where photogenerated electron-hole pairs undergo either geminate recombination or dissociation, depending on the photon energy.