Mechanism of a photoinduced solvent-assisted transfer of a proton to a specified remote target
Mechanism of a photoinduced solvent-assisted transfer of a proton to a specified remote target
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DOI：
10.1021/jp000046e
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发表时间：
2000-06-29
影响因子：
2.9
通讯作者：
Varma, CAGO
中科院分区：
文献类型：
--
作者：
de Bekker, EJA;Geerlings, JD;Varma, CAGO
本文研究了7-羟基-8-（N-吗啉甲基）喹啉（HMMQ）、2-羟基-1-（N-吗啉甲基）萘（HMMN）和7-羟基喹啉（7-HQ）溶液荧光的稳态和动态性质随温度、溶剂组成和溶质中OH基团氘代的变化。溶剂为纯正己烷、纯1，4-二氧六环、纯四氢呋喃或具有质子接受组分的二元混合物。观测结果的分析导致HMMQ在液体溶液中的光化学和光物理行为的方案，不同于以前的。溶剂在HMMQ的多步光诱导烯醇-酮互变异构反应中的催化作用已经很清楚。当溶剂中含有质子受体（S）时，HMMQ在基态有两种形式，即分子内氢键的裸露形式和分子内氢键中的质子也与S氢键结合的复合物。只有后者表现出光诱导的烯醇-酮互变异构。这两种形式都通过质子隧穿转化为两性离子形式，质子隧穿仅在通过激发沉积的过量能量的振动弛豫之前进行。与S的复合物中的部分多余能量用于破坏分子内H键并使质子化侧基旋转运动。总结了主要结论。
Stationary and dynamic properties of the fluorescence of liquid solutions of 7-hydroxy-8-(N-morpholinomethyl)-quinoline (HMMQ), 2-hydroxy-1-(N-morpholinomethyl)-naphthalene (HMMN), and 7-hydroxyquinoline (7-HQ) have been studied as a function of temperature, solvent composition, and deuteration of the OH group in the solute. The solvents were neat n-hexane, neat 1,4-dioxane, neat tetrahydrofurane, or binary mixtures with a proton-accepting component. The analysis of the observations leads to a scheme for the photochemical and photophysical behavior of HMMQ in liquid solutions that differs from previous ones. It is now clear how solvents act in the catalysis of the multistep photoinduced enol-keto tautomerization of HMMQ. There are two forms of HMMQ in the ground state when the solvent contains proton accepters (S), namely a bare form with an intramolecular H-bond and a complex in which the proton in the intramolecular H bond is also H-bonded to S. Only the latter exhibits photoinduced enol-keto tautomerization. Both forms are converted to a zwitterionic form by proton tunneling that proceeds only prior to vibrational relaxation of the excess energy deposited viith the excitation. Part of the excess energy in the complex with S is used to break the intramolecular H bond and to set the protonated side group into rotational motion. The main conclusions are summarized.