Photoprotection from harmful ultraviolet (UV) radiation exposure is a key problem in modern society. Mycosporine-like amino acids found in fungi, cyanobacteria, macroalgae, phytoplankton, and animals are already presenting a promising form of natural photoprotection in sunscreen formulations. Using time-resolved transient electronic absorption spectroscopy and guided by complementary ab initio calculations, we help to unravel how the core structures of these molecules perform under UV irradiation. Through such detailed insight into the relaxation mechanisms of these ubiquitous molecules, we hope to inspire new thinking in developing next-generation photoprotective molecules.

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Microorganisms require protection against the potentially damaging effects of ultraviolet radiation exposure. Photoprotection is, in part, provided by mycosporine-like amino acids (MAAs). Previous reports have proposed that nonradiative decay mediates the impressive photoprotection abilities of MAAs. In this letter, we present the first ultrafast dynamics study of two MAAs, shinorine and porphyra-334. We demonstrate that, in aqueous solution, these MAAs relax along their S1 coordinates toward the S1/S0 conical intersection within a few hundred femtoseconds after photoexcitation and then traverse the conical intersection and vibrationally cool in approximately 1 ps through heat transfer to the solvent. This new insight allows a quintessential component of microbial life to be unraveled and informs the development of molecular photon-to-heat converters for a myriad of applications.

Light-to-heat conversion materials generate great interest due to their widespread applications, notable exemplars being solar energy harvesting and photoprotection. Another more recently identified potential application for such material is in...