A Perspective on Femtosecond Pump–Probe Spectroscopy in the Development of Future Sunscreens

Abstract

Given the negative impacts of overexposure to ultraviolet radiation (UVR) on humans, sunscreens have become a widely used product. Certain ingredients within sunscreens are responsible for photoprotection and these are known, collectively herein, as ultraviolet (UV) filters. Generally speaking, organic UV filters work by absorbing the potentially harmful UVR and dissipating this energy as harmless heat. This process happens on picosecond time scales and so femtosecond pump–probe spectroscopy (FPPS) is an ideal technique for tracking this energy conversion in real time. Coupling FPPS with complementary techniques, including steady-state spectroscopy and computational methods, can provide a detailed mechanistic picture of how UV filters provide photoprotection. As such, FPPS is crucial in aiding the future design of UV filters. This Perspective sheds light on the advancements made over the past two years on both approved and nature-inspired UV filters. Moreover, we suggest where FPPS can be further utilized within sunscreen applications for future considerations.

Theoretical Insights into the Ultrafast Deactivation Mechanism and Photostability of a Natural Sunscreen System: Mycosporine Glycine

“…We have employed different levels of theory: TD-DFT using the ωB97XD functional; RI-ADC(2); and MS-CASPT2. Regarding the TD-DFT calculations, the ωB97XD functional was used as it successfully described the energy of the electronic states and nonradiative deactivation process in similar systems. ,,,− …”

“…However understanding of the mechanisms of the relaxation dynamics in mycosporines and MAAs is still in its infancy. 24 Herein, we report on a systematic investigation of the photochemical mechanisms for radiationless excited-state deactivation of the most stable conformer of mycosporineglycine (abbreviated as MyG henceforth). This system has an absorption maximum at 310 nm in water solvent medium 26 and possesses a cyclohexenone ring linked with an amino acid, glycine (Figure 1).…”

“…In contrast to the crucial photoprotection role that they have, rare reports in the literature are devoted to the fundamental root of the photophysical nature of these systems especially involving the cyclohexenone core. − Recent studies on MAAs clearly show that the excited electronic states are very short-lived, decaying rapidly to repopulate the ground electronic state. However understanding of the mechanisms of the relaxation dynamics in mycosporines and MAAs is still in its infancy. , …”

“…However understanding of the mechanisms of the relaxation dynamics in mycosporines and MAAs is still in its infancy. 24 , 25 …”

Examining the substituent effect on mycosporine-inspired ultraviolet filters

“…[7][8][9][10][11] With this in mind, research into understanding the fundamental photochemistry and photophysics of current organic UV filters as well as for novel alternatives is crucial to the development of sunscreens with improved safety profiles. 12 Toxicological studies and the monitoring of biological endpoints are also essential to assess the true safety of a candidate organic UV filter. Recently, there has been a considerable interest in biomimetic molecules for use as organic UV filters in sunscreens.…”