A Reevaluation of the Photolytic Properties of 2-Hydroxybenzophenone-Based UV Sunscreens: Are Chemical Sunscreens Inoffensive?

The excited states of a set of popular sunscreen agents (2‐hydroxybenzophenone, oxybenzone, and sulisobenzone) are studied by using femto‐ and nanosecond time‐resolved spectroscopy. Upon excitation, the compounds undergo an ultrafast excited‐state intramolecular proton transfer (ESIPT) reaction as t...

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Bibliographic Details
Published in:Chemphyschem 2015-02, Vol.16 (3), p.628-633
Main Authors: Ignasiak, Marta T., Houée-Levin, Chantal, Kciuk, Gabriel, Marciniak, Bronislaw, Pedzinski, Tomasz
Format: Article
Language:English
Subjects:
benzophenones
Benzophenones - chemistry
excited-state intramolecular proton transfer (ESIPT)
Kinetics
Oxidation-Reduction
Phenols - chemistry
photochemistry
Photolysis
radicals
Spectrometry, Fluorescence
Sunscreening Agents - chemistry
sunscreens
Ultraviolet Rays
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Summary:The excited states of a set of popular sunscreen agents (2‐hydroxybenzophenone, oxybenzone, and sulisobenzone) are studied by using femto‐ and nanosecond time‐resolved spectroscopy. Upon excitation, the compounds undergo an ultrafast excited‐state intramolecular proton transfer (ESIPT) reaction as the major energy‐wasting process and the rate constant of this reaction is k=2×1012 s−1. The ESIPT yields a keto conformer that undergoes a fast, picosecond internal conversion decay. However, a photodegradative pathway is a monophotonic HO bond breakage that subsequently leads to trace yields of phenoxyl radicals. Because potentially harmful phenoxyl radicals are formed upon irradiation of sunscreen agents, care should be taken about their reactivity towards biologically relevant compounds. Excited state: Upon UV excitation, 2‐hydroxybenzophenone analogues undergo ultrafast excited‐state intramolecular proton transfer (ESIPT; see figure). Inefficient monophotonic HO bond breakage results in phenoxyl radical formation.
ISSN:1439-4235
1439-7641
DOI:10.1002/cphc.201402703