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（UV）过滤剂，常被添加至防晒配方中，尽管其光稳定性欠佳。由于当前UVA波段（320–400 nm）可用的光防护替代方案寥寥无几，因此其添加仍属必要。为更深入地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），探究了溶剂（包括润肤剂）、浓度以及皮肤表面温度在UVA辐射（~350 nm）光激发后对其激发态弛豫机制的影响。各体系的激发态寿命存在细微差异，但所有溶液与温度组合的TEAS光谱特征在定性层面均保持一致。除TEAS测试外，研究人员还使用模拟太阳光辐照含阿伏苯宗的紫外线过滤剂/润肤剂混合物，并采用稳态紫外-可见光谱追踪其降解过程。研究人员还针对代表性油相（高浓度混合物）开展了防晒系数（Sun Protection Factor, SPF）与UVA防护系数（UVA Protection Factor, UVA-PF）评估，此类油相可用于制备水包油型防晒霜。研究发现，此类混合物的长期光防护效能存在显著的浓度依赖性，而基态漂白偏移现象可将该依赖性与超快光动力学过程关联起来。该多技术联用方案有望实现阿伏苯宗长期行为（数分钟至数小时）与其超快光物理过程（飞秒至纳秒）的关联，从而填补基础光物理/光化学与商业化防晒配方设计之间的研究空白。