Photophysical characterization of cinnamates
Photophysical characterization of cinnamates
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DOI：
10.1039/b909695g
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发表时间：
2009-01-01
影响因子：
3.1
通讯作者：
Albinsson, Bo
中科院分区：
文献类型：
--
作者：
Karpkird, Thitinun Monhaphol;Wanichweacharungruang, Supason;Albinsson, Bo
采用实验和理论相结合的方法研究了5种甲氧基取代肉桂酸2-乙基己酯的物理化学性质。结果表明，荧光量子产率随苯环取代方式的不同而变化。甲氧基取代的Meta位得到强的荧光，而帕拉取代的化合物强烈淬灭。这一观察结果可以与相应的变化在紫外吸收光谱;两个最低的pi pi* 状态分裂的间甲氧基取代的肉桂酸酯，但几乎退化的帕拉化合物。半经验量子力学计算证实了所观察到的状态顺序和实验确定的非辐射衰变活化能的差异。这种“元效应”也保留在三甲氧基取代的化合物2-乙基己基-2，4，5-和2，4，6-三甲氧基肉桂酸酯中，导致前者的强荧光和相对高的非辐射衰变势垒，而后者的弱荧光和相对低的非辐射衰变势垒。所获得的信息显示了商业防晒剂2-乙基己基-对甲氧基肉桂酸酯（OMC）的性能可能如何改进。
The photophysical properties of five methoxy-substituted 2-ethylhexylcinnamates were studied with experimental and theoretical methods. It was found that the fluorescence quantum yields varied strongly with the substitution pattern of the phenyl ring. A methoxy substitution at the meta position gave strong fluorescence, whereas the para substituted compounds were strongly quenched. This observation could be correlated to corresponding changes in the UV absorption spectra; the two lowest pi pi* states were split for the meta-methoxy substituted cinnamate but almost degenerate for the para compound. Semi-empirical quantum mechanical calculations confirmed both the observed state order and the difference in the experimentally determined activation energies for non-radiative decay. This "meta-effect" was also preserved in the trimethoxy-substituted compounds, 2-ethylhexyl-2,4,5- and 2,4,6-trimethoxycinnamate, resulting in strong fluorescence and relatively high barrier for non-radiative decay in the former and weak fluorescence and relatively low barrier for non-radiative decay in the latter. The obtained information shows how the performance of the commercial sunscreen agent, 2-ethylhexyl-para-methoxycinnamate (OMC) might be improved.