Short-lived and Nonphosphorescent Triplet state of Mexoryl SX, a UV-A Sunscreen
Short-lived and Nonphosphorescent Triplet state of Mexoryl SX, a UV-A Sunscreen
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Mexoryl SX（一种 UV-A 防晒霜）的短寿命非磷光三重态
DOI：
10.1007/s00723-020-01198-x
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发表时间：
2020
影响因子：
1
通讯作者：
Yuta Shamoto， Ryohei Shimizu， Mikio Yagi，Nozomi Oguchi-Fujiyama，Jasmin Kang， Azusa Kikuchi
中科院分区：
文献类型：
--
作者：
Shogo Kitasaka;Mikio Yagi;Azusa Kikuchi;Yuta Shamoto， Ryohei Shimizu， Mikio Yagi，Nozomi Oguchi-Fujiyama，Jasmin Kang， Azusa Kikuchi
Mexoryl SX（对苯二甲叉-3，3 ′-二樟脑-10，10 ′-二磺酸，Ecamethyl）是一种水溶性紫外线吸收剂。在空气饱和的水中没有观察到Mexoryl SX光敏化产生的单线态氧的近红外磷光光谱。另一方面，在氧饱和的磷酸盐缓冲液（pH 7.4）中观察到时间分辨的近红外磷光光谱。单线态氧产生的量子产率（ΦΔ）被确定为0.0021 ± 0.0005。Mexoryl SX作为光敏剂的能力很低。问题在于相当低的ΦΔ值。在77 K下，Mexoryl SX在乙醇中没有检测到磷光。我们利用时间分辨EPR技术阐明了Mexoryl SX的最低激发三重态（T1）的性质，因为这种技术对于研究短寿命和非磷光T1分子是非常有效的。观察到强的时间分辨EPR信号。这一事实表明，相当大比例的最低激发单重态（S1）分子经历了系统间穿越（ISC）到T1态，T1态的失活过程主要是无辐射的。零场分裂参数、T1寿命和S1→ T1 ISC的各向异性表明，T1态的特征是3 n π*-3ππ* 混合态，T1态中的两个未成对电子不局限于与其密切相关的组分（4-甲基苯亚甲基）樟脑上.虽然较短的T1寿命（47 ns）阻止了基态氧对T1态的猝灭，但3 n π* 特性可能对低的ΦΔ值有所贡献。
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 (ΦΔ) 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 lowΦΔvalue. No phosphorescence was detectable from Mexoryl SX in ethanol at 77 K. We elucidated the nature of the lowest excited triplet (T1) state of Mexoryl SX using a time-resolved EPR technique, because this technique is powerful for the study of short-lived and nonphosphorescent T1molecules. The strong time-resolved EPR signals were observed. This fact shows that a considerable proportion of the lowest excited singlet (S1) state molecules undergoes intersystem crossing (ISC) to the T1state and the deactivation process of the T1state is mainly radiationless. The observed zero-filed splitting parameters, T1lifetime, and S1→ T1ISC anisotropy suggest that the T1state can be regarded as a3nπ*–3ππ*mixing state in character and the two unpaired electrons in the T1state do not localize on (4-methylbenzylidene)camphor, a closely related component. Although the shorter T1lifetime (47 ns) prevents T1state quenching by ground-state oxygen, the3nπ*character may contribute something to the lowΦΔvalue.