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Laser Flash Photolysis Studies of the UVA Sunscreen Mexoryl SX
Author(s) -
Cantrell Ann,
McGarvey David J.,
Mulroy Louise,
Truscott T. George
Publication year - 1999
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1999.tb08138.x
Subject(s) - flash photolysis , photochemistry , quantum yield , quenching (fluorescence) , chemistry , triplet state , singlet oxygen , acetonitrile , nanosecond , ultrafast laser spectroscopy , absorption (acoustics) , singlet state , phosphorescence , absorption spectroscopy , excited state , oxygen , laser , analytical chemistry (journal) , materials science , fluorescence , molecule , reaction rate constant , atomic physics , optics , organic chemistry , kinetics , physics , quantum mechanics , composite material
The results of a nanosecond laser flash photolysis investigation of the UVA sunscreen Mexoryl* SX in various solvent environments and within a commercial sunscreen formulation are reported. To the best of our knowledge this is the first laser flash photolysis study of a commercial suncare formulation. In each of these environments kinetic UV‐visible absorption measurements following nanosecond 355 nm laser excitation reveals a short‐lived species with a solvent‐dependent absorption maximum around 470–500 nm and a solvent‐dependent lifetime of ?50–120 ns. This transient absorption is attributed to the triplet state of Mexoryl* SX on the basis that it is quenched by molecular oxygen leading to the formation of singlet oxygen in acetonitrile. The singlet oxygen quantum yield (φ Δ ), determined by comparative time‐resolved near‐infrared luminescence measurements and extrapolated to the limit of complete triplet state quenching, is estimated as 0.09 ± 0.03 in acetonitrile. In aqueous solution the shorter triplet state lifetime combined with lower ambient oxygen concentrations precludes significant triplet state quenching. For the commercial sunscreen formulation there was no observable difference in the measured triplet lifetime between samples exposed to oxygen or argon, suggesting that the singlet oxygen quantum yield in such environments is likely to be orders of magnitude lower than that measured in acetonitrile.