Mexoryl SX (terephthalylidene-3,3′-dicamphor-10,10′-disulfonic acid, Ecamsule) is a water-soluble UV-A absorber. The near-IR phosphorescence spectrum of singlet oxygen generated by photosensitization with Mexoryl SX was not observed in air-saturated water. On the other hand, the time-resolved near-IR phosphorescence spectrum was observed in oxygen-saturated phosphate buffer (pH 7.4). The quantum yield of the singlet oxygen generation ( Φ Δ ) was determined to be 0.0021 ± 0.0005. The ability of Mexoryl SX as a photosensitizer is quite low. The question arises as to the quite low Φ Δ value. No phosphorescence was detectable from Mexoryl SX in ethanol at 77 K. We elucidated the nature of the lowest excited triplet (T 1 ) state of Mexoryl SX using a time-resolved EPR technique, because this technique is powerful for the study of short-lived and nonphosphorescent T 1 molecules. The strong time-resolved EPR signals were observed. This fact shows that a considerable proportion of the lowest excited singlet (S 1 ) state molecules undergoes intersystem crossing (ISC) to the T 1 state and the deactivation process of the T 1 state is mainly radiationless. The observed zero-filed splitting parameters, T 1 lifetime, and S 1 → T 1 ISC anisotropy suggest that the T 1 state can be regarded as a 3 nπ * – 3 ππ * mixing state in character and the two unpaired electrons in the T 1 state do not localize on (4-methylbenzylidene)camphor, a closely related component. Although the shorter T 1 lifetime (47 ns) prevents T 1 state quenching by ground-state oxygen, the 3 nπ * character may contribute something to the low Φ Δ value.

中文翻译：

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Mexoryl SX 的短寿命和非磷光三重态，一种 UV-A 防晒霜

Mexoryl SX (terephthalylidene-3,3'-dicamphor-10,10'-disulfonic acid, Ecamsule) 是一种水溶性 UV-A 吸收剂。在空气饱和的水中未观察到由 Mexoryl SX 光敏产生的单线态氧的近红外磷光光谱。另一方面，在氧饱和磷酸盐缓冲液 (pH 7.4) 中观察到时间分辨近红外磷光光谱。单线态氧产生的量子产率 (Φ Δ ) 被确定为 0.0021 ± 0.0005。Mexoryl SX 作为光敏剂的能力非常低。问题是关于相当低的 Φ Δ 值。在 77 K 的乙醇中未检测到 Mexoryl SX 的磷光。我们使用时间分辨 EPR 技术阐明了 Mexoryl SX 的最低激发三重 (T 1 ) 态的性质，因为这种技术对于研究短寿命和非磷光 T 1 分子非常有效。观察到强烈的时间分辨 EPR 信号。这一事实表明，相当大比例的最低激发单重 (S 1 ) 态分子经历系统间穿越 (ISC) 到 T 1 态，并且 T 1 态的失活过程主要是无辐射的。观察到的零场分裂参数、T 1 寿命和 S 1 → T 1 ISC 各向异性表明 T 1 态可以被视为一个 3 nπ * – 3 ππ * 混合态和 T 中的两个未配对电子1 状态不定位于密切相关的成分（4-甲基亚苄基）樟脑。尽管较短的 T 1 寿命 (47 ns) 可防止基态氧对 T 1 态猝灭，但 3 nπ * 特性可能对低 Φ Δ 值有所贡献。