LAUSR

Significance The black–brown eumelanin pigment plays a major role in humans’ photoprotection against high-energy UV photons by dissipating radiation into heat before harmful radical reactions can damage tissue. Due to the high degree of the disorder of the pigment and the ultrafast timescale energy dissipation, the main photoprotection mechanism is not well understood. Here, we apply a suite of ultrafast optical spectroscopy methods to eumelanin and one of its key building blocks, DHICA. We found that photoprotection has a two-step mechanism; Excited states relax to lower energies extremely rapidly due to electronic interactions among neighboring molecules, and then partial proton transfer occurs from the catechol hydroxy groups to the solvent.