The photodegradation of avobenzone (AV), the only ultraviolet filter molecule approved by the Food and Drug Administration to absorb UVA radiation, is an important problem in sunscreen formulations. In this paper, the photophysics and photostability of AV in various solvent systems and in aqueous micelles are studied. AV in its keto-enol tautomer functions as an effective UVA protection agent. AV is highly susceptible to photoinduced diketonization in both nonpolar solvents and in aqueous aggregates but is considerably more stable in polar, protic solvents like methanol. By studying its stability in different surfactant solutions, we show that incorporation of AV into sodium dodecylsulfate (SDS) micelles can achieve stability levels comparable to neat methanol. Steady-state spectral shifts, fluorescence anisotropy, and time-resolved fluorescence decay measurements are all consistent with AV experiencing a polar environment after micellar encapsulation. It is proposed that AV is encapsulated in the palisade layer of the SDS micelles, which allows access to water molecules that facilitate the re-formation of the enol form after photon absorption and relaxation. Although the detailed mechanism of AV tautomerization remains unclear, this work suggests that tuning the chemical microenvironment of AV may be a useful strategy for improving sunscreen efficacy.

中文翻译：

---

溶剂和胶束封装对阿伏苯宗的光稳定性的影响。

阿伏苯宗（AV）的光降解是食品和药物管理局批准的唯一吸收UVA辐射的紫外线滤光片分子，是防晒配方中的一个重要问题。本文研究了各种溶剂体系和水性胶束中AV的光物理性质和光稳定性。酮-烯醇互变异构体中的AV可作为有效的UVA保护剂。在非极性溶剂和水性聚集体中，AV对光诱导的二酮化反应都非常敏感，但在极性质子溶剂（如甲醇）中则非常稳定。通过研究其在不同表面活性剂溶液中的稳定性，我们表明将AV掺入十二烷基硫酸钠（SDS）胶束中可以达到与纯甲醇相当的稳定性水平。稳态光谱偏移，荧光各向异性，和时间分辨的荧光衰减测量结果均与胶束封装后的AV经历极性环境一致。建议将AV封装在SDS胶束的栅栏层中，从而允许进入水分子，从而促进光子吸收和弛豫后烯醇形式的重新形成。尽管AV互变异构的详细机制仍不清楚，但这项工作表明，调整AV的化学微环境可能是提高防晒功效的有用策略。它允许进入水分子，促进光子吸收和弛豫后烯醇形式的重新形成。尽管AV互变异构的详细机制仍不清楚，但这项工作表明，调整AV的化学微环境可能是提高防晒功效的有用策略。这使得在光子吸收和弛豫之后，可以访问有助于烯醇形式重新形成的水分子。尽管AV互变异构的详细机制仍不清楚，但这项工作表明，调整AV的化学微环境可能是提高防晒功效的有用策略。