Photophysical Properties of Dioctyl 4-Methoxybenzylidenemalonate: UV-B Absorber
Photophysical Properties of Dioctyl 4-Methoxybenzylidenemalonate: UV-B Absorber
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4-甲氧基亚苄基丙二酸二辛酯的光物理性质：UV-B 吸收剂
DOI：
10.1039/c2pp25101a
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发表时间：
2012
期刊：
影响因子：
--
通讯作者：
N. Oguchi-Fujiyama
中科院分区：
文献类型：
--
作者：
Azusa Kikuchi;Kenji Shibata;Ryo Kumasaka;Mikio Yagi;小口 希，宮沢和之，菊地あづさ，八木幹雄;N. Oguchi-Fujiyama
4-甲氧基亚苄基丙二酸二辛酯 (DOMBM) 是光不稳定的 4-叔丁基-4'-甲氧基二苯甲酰甲烷 (BMDBM) 的有效稳定剂。 DOMBM 在 BMDBM 存在下保持 UV-B 吸光度方面优于最广泛使用的 UV-B 吸收剂甲氧基肉桂酸辛酯 (OMC)。通过测量77 K乙醇中的荧光和磷光光谱，确定了DOMBM的最低激发单重态（S1）和三重态（T1）态的能级。DOMBM的T1态能级低于BMDBM，高于OMC。通过测量电子顺磁共振（EPR）和时间分辨磷光光谱证明了从 BMDBM 到 DOMBM 的三重态-三重态能量转移。 DOMBM的磷光和EPR信号太弱，在77 K乙醇中直接激发无法观察到磷光光谱。利用碘乙烷的外部重原子效应观察磷光光谱。使用二苯甲酮作为三重态敏化剂观察 EPR 光谱。室温下，DOMBM 在乙醇中的荧光量子产率很小。在室温下的时间分辨热透镜实验中，仅观察到由于 DOMBM 激发态释放的热量而产生的快分量。这些结果表明，S1 → T1 系间窜越的量子产率可以忽略不计，并且 DOMBM 的失活过程主要是内部转换到基态。
Dioctyl 4-methoxybenzylidenemalonate (DOMBM) is an effective stabilizer for photolabile 4-tert-butyl-4′-methoxydibenzoylmethane (BMDBM). DOMBM is superior to the most widely used UV-B absorber, octyl methoxycinnamate (OMC), at preserving its UV-B absorbance in the presence of BMDBM. The energy levels of the lowest excited singlet (S1) and triplet (T1) states of DOMBM were determined by measuring fluorescence and phosphorescence spectra in ethanol at 77 K. The energy level of the T1 state of DOMBM is lower than that of BMDBM and is higher than that of OMC. The triplet–triplet energy transfer from BMDBM to DOMBM was demonstrated by measuring the electron paramagnetic resonance (EPR) and time-resolved phosphorescence spectra. The phosphorescence and EPR signals of DOMBM are too weak to be observed through the direct excitation in ethanol at 77 K. The phosphorescence spectrum was observed by using external heavy atom effects of ethyl iodide. The EPR spectrum was observed by using benzophenone as a triplet sensitizer. The fluorescence quantum yield of DOMBM is small in ethanol at room temperature. Only the fast component, due to the heat released from the excited state of DOMBM, was observed in the time-resolved thermal lensing experiments at room temperature. These results show that the quantum yield of the S1 → T1 intersystem crossing is negligible and the deactivation process is predominantly internal conversion to the ground state for DOMBM.