Research Center, Shiseido Company Ltd., Hayabuchi, Tsuzuki-ku, Yokohama 224-8558, Japan.
Photochem Photobiol Sci. 2012 Oct;11(10):1528-35. doi: 10.1039/c2pp25101a.
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 (S(1)) and triplet (T(1)) states of DOMBM were determined by measuring fluorescence and phosphorescence spectra in ethanol at 77 K. The energy level of the T(1) 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 S(1) → T(1) intersystem crossing is negligible and the deactivation process is predominantly internal conversion to the ground state for DOMBM.
二辛基 4-甲氧基苄叉丙二腈（DOMBM）是光不稳定的 4-叔丁基-4'-甲氧基二苯甲酮（BMDBM）的有效稳定剂。与最广泛使用的 UV-B 吸收剂辛基甲氧基肉桂酸（OMC）相比，DOMBM 在 BMDBM 存在下更能保持其 UV-B 吸收率。通过在乙醇中于 77 K 测量荧光和磷光光谱，确定了 DOMBM 的最低激发单线态（S(1)）和三重态（T(1)）能级。DOMBM 的 T(1)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 BMDBM 向 DOMBM 的三重态-三重态能量转移。通过乙基碘的外部重原子效应观察到 DOMBM 的磷光和 EPR 信号太弱，无法在 77 K 的乙醇中直接激发观察到。EPR 光谱通过使用二苯甲酮作为三重态敏化剂进行观察。DOMBM 在室温下的乙醇中的荧光量子产率较小。在室温下的时间分辨热透镜实验中仅观察到快组分，这归因于 DOMBM 激发态释放的热量。这些结果表明，S(1)→T(1)系间窜越的量子产率可以忽略不计，DOMBM 的失活过程主要是内部转换到基态。
