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

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 (S 1 ), these Meldrum-based phenolics undergo fast and efficient nonradiative decay to repopulate the electronic ground state (S 0 ). We propose an initial ultrafast twisted intramolecular charge-transfer mechanism as these systems evolve out of the Franck−Condon region toward an S 1 /S 0 conical intersection, followed by internal conversion to S 0 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.

Towards developing novel and sustainable molecular light-to-heat converters

“…The femtosecond (fs) TEAS setup and procedure used to explore the photodynamics of the barbiturics has been detailed previously, 32,54–57 and only information specific to the present experiment is reported here. Separate samples of CDBA, CBA, and MeCDBA, (coumaryl series) and of FBA and FDBA (ferulyl series) were prepared to 1 mM concentration in DMSO and dioxane (Fisher Chemicals).…”

“…The TVAS setup and experimental technique employed in this work have also been reported in detail previously 32,58 and, again, only information specific to the current experiments is reported. TVAS measurements of CBA and CDBA were undertaken in DMSO at 30 mM concentration, using the same sample delivery system as for the TEAS studies, but with a 150 μm thick spacer (to achieve a change in optical density ΔOD of ∼0.002) and a maximum pump–probe delay of 2.5 ns.…”

Fewest switches surface hopping with Baeck-An couplings

“…Indeed, thanks to Send and Furche 10 , S 1 /S 0 nonadiabatic coupling vectors for TDDFT are now a common feature of several quantum chemistry software programs. Our own research protocol has been to run TDDFT dynamics until the energy S 1 /S 0 gap drops below some threshold (about 0.1 eV), stop the trajectory propagation there, and assume that point to be the hopping point 34 . Here, we were interested in testing whether the TD-BA model would allow going beyond this protocol, with actual hoppings to the ground state.…”

“…Ethylene is a crucial prototype 32 for internal conversion in various systems as diverse as protonated Schiff bases 33 , substituted polyenes 34 , and purine bases 35 . In turn, fulvene poses the challenge of S 1 ↔S 0 recurrences at an extended crossing seam with both peaked and sloped conical intersections 36 .…”

Investigation of the Antioxidant and UV Absorption Properties of 2-(2’-hydroxy-5’-methylphenyl)-benzotriazole and Its Ortho-Substituted Derivatives via DFT/TD-DFT

“…Biological systems depend on solar radiation for energy to sustain life. Unfortunately, chronic exposure to solar ultraviolet radiation (UVR) is responsible for health problems such as premature aging, erythema, skin cancers and sunburn [1] [2] [3] [4] [5]. Melanin (naturally occurring UV-absorbing pigment in the human skin) provides the first line of defense to the harmful effects of UVR but does not provide enough shield against high levels of UVR.…”