Evaluating the Fluorescence Quenching of Troxerutin for Commercial UV Sunscreen Filters

2-Phenylbenzimidazole-5-sulfonic acid (PBSA) and disodium phenyl dibenzimidazole tetrasulfonate (DPDT) are commercially available ultraviolet (UV) sunscreen filters that are known to undergo radiative relaxation following the absorption of UV light. The release of high-energy photons from this relaxation can be detrimental to human health; therefore, fluorescence quenchers need to be incorporated in commercial sunscreen formulations containing PBSA or DPDT. Troxerutin is a fluorescence quencher utilized for DPDT commercially. Here, its ability to quench the fluorescence of both PBSA and DPDT is evaluated using a dual-pronged approach by breaking down the multicomponent problem into its constituent parts. First, PBSA and DPDT's femtosecond to nanosecond photodynamics are uncovered in solution and on the surface of a human skin mimic to ascertain a benchmark. Second, these results are compared to their photodynamics in the presence of troxerutin. A significant reduction in the fluorescence lifetime is observed for both PBSA and DPDT on a human skin mimic with the addition of troxerutin, which is attributed to a Dexter energy transfer (DET) or Förster resonance energy transfer (FRET) quenching mechanism. This finding demonstrates the hitherto unseen fluorescence quenching mechanism of troxerutin on a human skin mimic and its role in quenching the fluorescence of commercial UV sunscreen filters through a DET or FRET mechanism.