Fluorescence Dynamics of Three UV-B Sunscreens |
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Authors: | Rajagopal Krishnan Thomas M Nordlund |
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Institution: | (1) Department of Physics, University of Alabama at Birmingham, CH 310, 1530 3rd Avenue South, Birmingham, AL 35294-1170, USA |
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Abstract: | Polarity of the surrounding medium affects the excited states of UV-B sunscreens. Therefore understanding excited state processes
in a mixed polarity model system similar to skin is essential. We report the excited state lifetimes, quantum yields, radiative
and non-radiative rates of three sunscreens. Among the three UV-B sunscreens studied, octyl salicylate emits from a single
excited state, while padimate O and octyl methoxy cinnamate show multiple states. The radiative rates of salicylate and cinnamate
are approximately constant, while that of padimate O depends strongly on solvent. The non-radiative rates of all sunscreens
vary with solvent polarity. Compared to salicylate and cinnamate, padimate O is complex to analyze because of its two emission
peaks and one peak’s strong dependence on the dielectric constant. High absorbance, broad absorption peak with small fluorescence
quantum yield, and low radiative rate make octyl methoxy cinnamate a superior UV-B sunscreen ingredient. The complexity in
excited-state analysis shows that the lifetimes of the sunscreens are critical parameters, in addition to absorbance and quantum
yield. Fluorescence lifetime substantiates the use of polystyrene nanospheres as a model host to study the photo-physical
properties of sunscreen in a heterogeneous environment. |
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Keywords: | Sunscreen Excited states Fluorescence UV-B Dynamics |
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