Optical Spectroscopy of Hydrophobic Sunscreen Molecules Adsorbed to Dielectric Nanospheres¶

Abstract

Fluorescence and absorption spectra of hydrophobic sunscreens, weakly fluorescent octyl methoxycinnamate, moderately fluorescent octyl salicylate and highly fluorescent 2-ethylhexyl-4-(dimethylamino)benzoate (padimate O) adsorbed to dielectric microspheres in aqueous suspension, have been compared with spectra in organic solution. The fluorescence of adsorbed salicylate and padimate is enhanced compared with fluorescence in methanol: about a factor of 6 and 30 in terms of fluorescence yield per molecule of salicylate and padimate, respectively. Cinnamate, which has a low fluorescence yield, does not show a comparable fluorescence enhancement. The fluorescence amplification is independent of sphere diameter from 30 to 1500 nm, at least for salicylate. The enhancement, as well as the location of absorption spectral peaks, is consistent with a low-dielectric constant environment of the molecules, in spite of the presumed location near the interface between polystyrene (epsilon = 2.4-3.8) and water (epsilon = 78). The adsorbed state of these sunscreens represents a proposed improved in vitro model for the environment of sunscreens in vivo, as well as a general model for chromophores in heterogeneous environments.

Ultraviolet resonance Raman spectroscopy as a robust spectroscopic tool for in situ sunscreen analysis

“…OCS, OCT and OMC exhibit some fluorescence, BZ3 at 324 nm excitation shows a little bit of fluorescence, but OCY and BZ3 at 288 nm excitation show no fluorescence. OCS and OMC have been shown previously to be fluorescent [43]. OCT is expected to be fluorescent, since it has an identical chromophore to OCS (Scheme 1).…”