Abstract
Understanding how deprotonation impacts the photophysics of UV filters is critical to better characterize how they behave in key alkaline environments including surface waters and coral reefs. Using anion photodissociation spectroscopy, we have measured the intrinsic absorption electronic spectroscopy (400–214 nm) and numerous accompanying ionic photofragmentation pathways of the benzophenone-4 anion ([BP4–H]−). Relative ion yield plots reveal the locations of the bright S1 and S3 excited states. For the first time for an ionic UV filter, ab initio potential energy surfaces are presented to provide new insight into how the photofragment identity maps the relaxation pathways. These calculations reveal that [BP4–H]− undergoes excited-state decay consistent with a statistical fragmentation process where the anion breaks down on the ground state after nonradiative relaxation. The broader relevance of the results in providing a basis for interpreting the relaxation dynamics of a wide range of gas-phase ionic systems is discussed.
Highlights
Understanding how deprotonation impacts the photophysics of UV filters is critical to better characterize how they behave in key alkaline environments including surface waters and coral reefs
Laser spectroscopy has been increasingly applied over recent years to characterize the intrinsic photophysics of UV filters to provide a more robust understanding of molecular-level sunscreen action.[1]
These experiments are important given that a number of aquatic environments are alkaline,[10,11] so that the understanding of how deprotonation affects photostability has important environmental implications
Summary
√ (w) aDetermined with mass accuracy >0.3 amu. bVery strong (vs), strong (s), moderate (m), weak (w), very weak (vw), and extremely weak (xw). cHCD fragment m/z 292 is observed to peak at 34% HCD energy, with a relative ion intensity of
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