Bottom-up excited state dynamics of two cinnamate-based sunscreen filter molecules

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Peperstraete, Yoann ; Staniforth, Michael ; Baker, Lewis A. ; Rodrigues, Natércia D. N. ; Cole-Filipiak, Neil C. ; Quan, Wen-Dong ; Stavros, Vasilios G. (2016)

Methyl-E-4-methoxycinnamate (E-MMC) is a model chromophore of the commonly used commercial sunscreen agent, 2- ethylhexyl-E-4-methoxycinnamate (E-EHMC). In an effort to garner a molecular-level understanding of the photoprotection mechanisms in operation with E-EHMC, we have used time-resolved pump-probe spectroscopy to explore E-MMC’s and E-EHMC’s excited state dynamics upon UV-B photoexcitation to the S1 (11ππ*) state in both the gas- and solution-phase. In the gas-phase, our studies suggest that the excited state dynamics are driven by non-radiative decay from the 11ππ* to the S3 (11nπ*) state, followed by de-excitation from the 11nπ* to the ground electronic state (S0). Using both a non-polar-aprotic solvent, cyclohexane, and a polar-protic solvent, methanol, we investigated E-MMC and EEHMC’s photochemistry in a more realistic, ‘closer-to-shelf’ environment. A stark change to the excited state dynamics in the gas-phase is observed in the solution-phase suggesting that the dynamics are now driven by efficient E/Z isomerisation from the initially photoexcited 11ππ*state to S0.
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    French state for financing his studies. M. S. and N. D. N. R. thank 19 D. Shimada, R. Kusaka, Y. Inokuchi, M. Ehara and T. Ebata, the Engineering and Physical Sciences Research Council (EPSRC) Phys. Chem. Chem. Phys., 2012, 14, 8999.

    for postdoctoral and doctoral funding respectively. L. A. B. and 20 M. D. Horbury, L. A. Baker, W. D. Quan, S. E. Greenough W. D. Q. thank the EPSRC for providing studentships under grant and V. G. Stavros, Phys. Chem. Chem. Phys., 2016, 18, 17691.

    EP/F500378/1, through the Molecular Organisation and Assembly 21 M. Staniforth and V. G. Stavros, Proc. Math. Phys. Eng. Sci., in Cells Doctoral Training Centre. N. C. C. F. thanks the Lever- 2013, 469, 20130458.

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