New Generation UV-A Filters: Understanding Their Photodynamics on a Human Skin Mimic

J Phys Chem Lett. 2021 Jan 14;12(1):337-344. doi: 10.1021/acs.jpclett.0c03004. Epub 2020 Dec 22.

Abstract

The sparsity of efficient commercial ultraviolet-A (UV-A) filters is a major challenge toward developing effective broadband sunscreens with minimal human- and eco-toxicity. To combat this, we have designed a new class of Meldrum-based phenolic UV-A filters. We explore the ultrafast photodynamics of coumaryl Meldrum, CMe, and sinapyl Meldrum (SMe), both in an industry-standard emollient and on a synthetic skin mimic, using femtosecond transient electronic and vibrational absorption spectroscopies and computational simulations. Upon photoexcitation to the lowest excited singlet state (S1), these Meldrum-based phenolics undergo fast and efficient nonradiative decay to repopulate the electronic ground state (S0). We propose an initial ultrafast twisted intramolecular charge-transfer mechanism as these systems evolve out of the Franck-Condon region toward an S1/S0 conical intersection, followed by internal conversion to S0 and subsequent vibrational cooling. Importantly, we correlate these 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.

MeSH terms

  • Biomimetic Materials / chemistry*
  • Humans
  • Models, Molecular
  • Molecular Conformation
  • Radiation-Protective Agents / chemistry*
  • Skin* / radiation effects
  • Ultraviolet Rays / adverse effects*

Substances

  • Radiation-Protective Agents