Spin dynamics of organic acids and bases in their nonphosphorescent and short-lived excited triplet states

1.通过时间分辨电子顺磁共振（EPR）、紫外吸收和荧光光谱的测量，研究了质子化对反式-3-苯乙烯基吡啶（StP）和反式-4，4 '-联吡啶基乙烯（DPE）在甲醇-水混合溶剂中激发态的影响.通过对这些谱的分析，得出单质子化对StP和DPE最低激发三重态（T_1）的零场分裂参数和子能级布居率的各向异性影响不大的结论。单质子化使荧光态的衰减速率常数减小，荧光量子产率增加。这些实验结果表明，单质子化导致三个T_1子能级的系间交叉率下降。这些结果可以用最低激发单重态中^1nπ^* 和^1ππ^* 态之间的电子振动混合来解释.反式对甲氧基肉桂酸酯是化妆品防晒剂中最广泛使用的紫外线吸收剂。为了在皮肤护理防晒剂中有效地作为UV保护化合物，UV吸收剂必须能够无害地将吸收的UV能量转化为振动能量。反式肉桂酸及其酯类化合物的失活机理一直是人们研究的热点。然而，对CA及其酯类化合物的T_1态的性质知之甚少。这是因为它们的磷光性很弱，T_1寿命很短。在本研究中，通过测量77 K下刚性有机玻璃和拉伸聚乙烯醇薄膜中的时间分辨EPR和荧光，研究了去质子化对反式对甲基肉桂酸激发态的影响。去质子化对零场分裂参数影响不大。然而，三重态次能级动力学变化的去质子化。

1. The effects of protonation on the excited states of trans-3-styrylpyridine (StP) and trans-4,4'-dipyridylethylene (DPE) have been studied through measurements of the time-resolved electron paramagnetic resonance (EPR), UV absorption, and fluorescence spectra in methanol-water mixtures at 77 K. From the analysis of these spectra it is concluded that the single protonation appears to have little effect on the zero-field splitting parameters and the anisotropy in the sublevel populating rates of the lowest excited triplet (T_1) states of StP and DPE. The decay rate constants of the fluorescent states decrease and fluorescence quantum yields increase on single protonation. These experimental results suggest that the single protonation causes a decrease in the intersystem crossing rates for the three T_1 sublevels. These results are explained in terms of the vibronic mixing between the ^1nπ^* and ^1ππ^* states in the lowest excited singlet state.2. The esters of trans-p-methoxycinnamic acid are the most widely used UV absorbers in cosmetic sunscreens. To be effective as a UV protective compound in skin-care sunscreens, the UV absorber must be able to harmlessly transform the absorbed UV energy into vibrational energy. The deactivation mechanism of trans-cinnamic acids (CAs) and their esters have been an object of continuous interest for many years. However, the property of the T_1 states of CAs and their esters is poorly known. This is because of their weakly phosphorescent character and short T_1 lifetimes. In the present research, the effects of deprotonation on the excited states of trans-p-methylcinnamic acid have been studied through measurements of the time-resolved EPR and fluorescence in rigid organic glasses and in stretched poly(vinyl alcohol) films at 77 K. The deprotonation appears to have little effect on the zero-field splitting parameters. However, the triplet sublevel kinetics changes on deprotonation.