ELECTRON EJECTION AND ELECTRON-CAPTURE BY PHENOLIC COMPOUNDS
ELECTRON EJECTION AND ELECTRON-CAPTURE BY PHENOLIC COMPOUNDS
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DOI：
10.1021/j100620a003
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发表时间：
1973-01-01
影响因子：
--
通讯作者：
HAYON, E
中科院分区：
文献类型：
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作者：
FEITELSON, J;HAYON, E
研究了对甲酚、对羟基苯丙酸、酪胺和酪氨酸的无空气水溶液在长波吸收带照射下的闪光光解。考察了光解离为苯氧基、溶剂化电子和氢原子的情况。在典型的三重态猝灭剂2，4-己二烯存在下的实验表明，这些酚类化合物在25℃的水溶液中的光电子发射是从长寿命激发态发生的，可能是这些分子的三重态激发态。测定了苯氧基自由基的瞬时吸收光谱、消光系数和衰减动力学。用脉冲辐解法研究了这四种物质对水合电子的反应性。研究发现，反应速率常数与羟基和氨基的质子化状态有关。观察到了这些酚类化合物与eaq~+和H原子(光解或辐解产生)反应的瞬时吸收光谱，xmax~350 nm。当酚类物质被强光激发到第一个单激发态时，会产生苯氧基自由基和溶剂化电子(可能还有氢原子)。这种酚类物质的光解已经在稳态和闪光光解中得到了研究。2-3Land和Porter2描述了苯氧基自由基在400 nm附近具有非常特征的尖锐吸收带，GrosSweiner等人3发现水合电子(xmax~710 nm)与苯氧基自由基同时形成。酚类化合物光电离的激发态(单重态或三重态)前体的性质尚未确定。此外，当被激发的苯酚分子释放电子到水溶液中时，基态的酚类物质起到电子清除剂的作用(见下文)。这种与溶剂化电子的反应性似乎在很大程度上取决于苯酚环上侧链的性质。
The flash photolysis of air-free aqueous solutions of p-cresol, p-hydroxyphenylpropionic acid, tyramine, and tyrosine was studied on illumination of their long-wavelength absorption bands. The photodissociation into phenoxyl radicals, solvated electrons, and hydrogen atoms was examined. Experiments in the presence of 2, 4-hexadiene, a typical triplet quencher, showed that the photoelectron ejection of these phenolic compounds in aqueous solution at 25 takes place from a long-lived excited state, probably the triplet excited states of these molecules. The transient absorption spectra, extinction coefficients, and decay kinetics of the phenoxyl radicals were determined. The reactivity of all four substances toward hydrated electrons was studied by pulse radiolysis. The reaction rate constants were found to be dependent on the state of protonation of the hydroxyl and the amino groups. The transient absorption spectra due to the reactionof eaq~ and H atoms (produced by photolysis or radiolysis) with these phenolic com-pounds were observed, with Xmax~ 350 nm. It is shown that eaq~ and H atoms add predominantly to the phenol ring of the compounds examined.When phenolic substances are excited by high-intensity light flashes to their first singletexcited state, phenoxyl radicals and solvated electrons (possibly also hydrogen atoms) are produced. Such photodissociations of phenolic substances have been studied in the steady state1 and by flash photolysis. 2-3 Land and Porter2 have described the phenoxyl radical with its very characteristic sharp absorp-tion band in the vicinity of 400 nm, and Grossweiner, et al., 3 have found that hydrated electrons (Xmax~ 710 nm) are formed simultaneously with the phenoxyl radical. The nature of the excited state (singlet or triplet) precursor of the photoionization of phenolic compounds has not been defined as yet. Furthermore, while excited phenol mole-cules release electrons into aqueous solutions, phenolic substances in their groundstate act as electron scavengers (see below). Thisreactivity with solvated electrons seems to depend to a great extent on the nature of the side chain on the phenol ring.