A new insight into the origin of eumelanin chromophore

umelanins, the chief photoprotective pigments in men and mam-mals, owe their black color to an unusual broadband absorption spectrum whose origin is still a conundrum. The contributions of structural and redox disorder in particular have still remained uncharted.We report herein a new entry to eumelanin chromophore dynam-ics based on a comparative spectrophotometric investigation of the oxidation mixtures of a collection of eumelanin precursors featuring different substituents, molecular size and shape. The obtained results uncovered the impact of the structural scaffold on eumelanin opti-cal properties, disproving the widespread assumption of a universal monotonic chromophore. Moreover, intermolecular interactions leading to redox equilibration and stacking were found to play an im-portant role in chromophore broadening in an oxidation independent manner.Based on these data, eumelanin chromophore buildup can be described as a three- step process involving the rapid generation of oxidized oligomers (melanochromes) (step I), followed by a slow oxidant- independent band broadening (step II) leading eventually to scattering (step III).1Although the relevance of these results to eumelanin optical prop-erties in vivo within the melanosomes remains to be assessed, the new background of structure- property relationships emerging from this study may guide the rational design of eumelanin- inspired functional materials tailored to specific biomedical, dermocosmetic or technolog-ical application