Abstract
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.
Highlights
Photoprotection from harmful ultraviolet (UV) radiation exposure is a key problem in modern society
While many articles exist exploring the presence and extraction of MAAs,[4,13−16] experimental information pertaining to their ultrafast photophysics and photochemistry within the first few picoseconds following photoexcitation is, to the best of our knowledge, lacking
MAAs have been recently suggested as suitable synthetic replacements in commercial products and studied both through steady-state absorption measurements and theoretically,[20] as extraction or synthesis yields only small quantities of the natural MAAs.[1,21,22]
Summary
We shall first focus on the transient absorption spectra (TAS) of ACyO in the polar solvents acetonitrile and methanol (Figure 2). The spectral responses differ between ACyO in acetonitrile and methanol, the former showing vibrational cooling to a minimum of the S1 potential in 2.8 ps, while in the latter, the initial time constant of 330 fs is attributed to geometry relaxation and solvent rearrangement, followed by vibrational cooling within 3.4 ps, again leading to a long-lived population in the S1 minimum This is consistent with our own, as well as previously reported theoretical work.[20] Combined, this suggests that excited-state properties of cyclohexenonebased systems prevent effective repopulation of the electronic ground state on an ultrafast time-scale due to the S1/S0 CI being energetically inaccessible (see the Supporting Information). This work highlights the need to extend these measurements to MAAs themselves, experiments which are currently underway in our laboratory
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