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Linking Electronic Relaxation Dynamics and Ionic Photofragmentation Patterns for the Deprotonated UV Filter
Natalie G K Wong1, Conor D Rankine2, Caroline E H Dessent1
1Department of Chemistry, University of York, Heslington, York, YO10 5DD, U.K.
The Journal of Physical Chemistry Letters
|March 15, 2021
Summary
Deprotonation significantly affects UV filter photophysics in alkaline waters. Benzophenone-4 anion fragmentation reveals excited-state decay pathways, crucial for understanding environmental behavior.
Area of Science:
- Photochemistry
- Environmental Chemistry
- Spectroscopy
Background:
- UV filters are crucial for sun protection but their environmental fate, especially in alkaline conditions like surface waters and coral reefs, requires deeper understanding.
- Deprotonation can alter the photophysical properties and degradation pathways of UV filters.
Purpose of the Study:
- To investigate the impact of deprotonation on the photophysics of UV filters.
- To characterize the electronic spectroscopy and photofragmentation of the benzophenone-4 anion ([BP4-H]-).
- To elucidate the excited-state decay mechanisms of ionic UV filters.
Main Methods:
- Anion photodissociation spectroscopy was employed to measure absorption electronic spectroscopy (400-214 nm).
- Relative ion yield plots were used to identify excited states (S1 and S3).
- Ab initio potential energy surface calculations were performed to map relaxation pathways.
Main Results:
- The intrinsic absorption electronic spectroscopy of the benzophenone-4 anion was determined.
- Bright S1 and S3 excited states were located.
- Calculations showed [BP4-H]- undergoes statistical fragmentation on the ground state after nonradiative relaxation.
Conclusions:
- The excited-state decay of benzophenone-4 anion follows a statistical fragmentation process.
- Understanding these pathways is vital for assessing UV filter behavior in alkaline aquatic environments.
- The findings offer a framework for interpreting relaxation dynamics in similar gas-phase ionic systems.
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