The harmful effects of overexposure to ultraviolet (UV) radiation on humans has been widely reported in the literature. To prevent these effects, sunscreens with UV-filters as the active ingredients are often used. However, some of the current organic UV-filters used in sunscreen formulations have several human- and eco-toxicity concerns. In order to overcome these challenges, focus is now on nature (plant and microbial) inspired UV-filters. Sinapate ester derivatives have been reported to offer photoprotection against the damaging effect of ultraviolet radiation exposure in plants. These compounds absorb in the UV-A region of the electromagnetic spectrum, where many commercial UV-filters are currently lacking.<br/>In the present work, two derivatives of sinapate esters, coumaryl meldrum (shown in figure caption) and sinapoyl meldrum were investigated for their energy dissipation mechanism in caprylic capric triglyceride (an emollient currently used in the formulation of sunscreen products in cosmeceutical industries) and by deposition of the resulting mixture on synthetic skin mimic using ultrafast transient electronic and vibrational absorption spectroscopies complemented with electronic structure calculations. This provides a close-to-real formulation and application environment for UV-filters. The results of our studies revealed that following photoexcitation, these candidate UV-filters undergo efficient non-radiative decay which includes twisted intramolecular charge transfer, internal conversion, and vibrational cooling to repopulate the electronic ground state. Importantly, we correlate our findings to their long-term photostability upon irradiation with a solar simulator and conclude that these molecules surpass the basic requirements of an industry standard UV-filter.

Unravelling the ultrafast energy dissipation mechanism of plant based UV-A filters in close to sunscreen realistic environment

ACS Spring Meeting 2021

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