Determining the photostability of avobenzone in sunscreen formulation models using ultrafast spectroscopy

Avobenzone is an ultraviolet (UV) filter that is often included in sunscreen formulations despite its lack of photostability. Its inclusion is necessary due to few existing alternatives for photoprotection in the UVA region (320 – 400 nm). To better understand and predict the photostability of avobenzone, ultrafast transient electronic absorption spectroscopy (TEAS) has been used to study the effects of solvent (including emollients), concentration and skin surface temperature on its excited-state relaxation mechanism, following photoexcitation with UVA radiation (~350 nm). Subtle differences between the excited-state lifetimes were found between the systems, but the TEAS spectral features were qualitatively the same for all solution and temperature combinations. Alongside TEAS measurements, UV filter/emollient blends containing avobenzone were irradiated using simulated solar light and their degradation tracked using steady-state UV-visible spectroscopy. Sun protection factor (SPF) and UVA protection factor (UVA-PF) assessments were also carried out on representative oil phases (higher concentration blends), which could be used to formulate oil-in-water sunscreens. It was found that there was an apparent concentration dependence on the long-term photoprotective efficacy of these mixtures, which could be linked to the ultrafast photodynamics by the presence of a ground-state bleach offset. This combination of techniques show potential for correlating long-term behaviours (minutes to hours) of avobenzone with its ultrafast photophysics (femtoseconds to nanoseconds), bridging the gap between fundamental photophysics/photochemistry and commercial sunscreen design.阿伏苯宗（Avobenzone）是一种紫外线（ultraviolet, UV）滤光剂，尽管其光稳定性欠佳，仍常被添加于防晒配方之中。鉴于UVA波段（320–400 nm）内现有光防护替代方案寥寥无几，阿伏苯宗的添加实属必要。为深入理解并预测阿伏苯宗的光稳定性，研究人员采用超快瞬态电子吸收光谱（ultrafast transient electronic absorption spectroscopy, TEAS），针对经约350 nm的UVA辐射光激发后，溶剂（包括润肤剂）、浓度以及皮肤表面温度对其激发态弛豫机制的影响开展了研究。结果表明，不同测试体系间的激发态寿命存在细微差异，但所有溶液体系与温度组合的TEAS光谱特征在定性层面均保持一致。除TEAS测量外，研究人员还通过模拟太阳光对含阿伏苯宗的UV滤光剂/润肤剂混合物进行辐照，并采用稳态紫外-可见光谱追踪其降解过程。同时，针对可用于制备水包油型防晒霜的代表性油相（高浓度混合物），研究人员开展了防晒因子（Sun Protection Factor, SPF）与UVA防护因子（UVA Protection Factor, UVA-PF）评估。研究发现，此类混合物的长期光防护功效存在显著的浓度依赖性，而基态漂白偏移现象可将该浓度依赖性与超快光动力学过程建立关联。这种多技术联用的研究方法，为建立阿伏苯宗长期行为（分钟至小时级）与其超快光物理过程（飞秒至纳秒级）之间的关联提供了可能，填补了基础光物理/光化学与商业化防晒配方设计之间的研究空白。