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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Role of Hydrogen-Bonded Adducts in Excited-State Proton-Transfer Processes
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Role of Hydrogen-Bonded Adducts in Excited-State Proton-Transfer Processes

机译：氢键加合物在激发态质子转移过程中的作用

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摘要

The protonated cation of 2-(2'-hydroxyphenyl)benzimidazole becomes a very strong acid in its first excited singlet state (C~*). We studied the proton-transfer process from C~* to the bases water, methylurea (MU), and dimethyl sulfoxide (DMSO) i acetonitrile solution by means of fluorescence and UV-vis absorption spectroscopy. We found that the process occurs via a 1:1 hydrogen-bonded adduct between the photoacid C~* and the base. We determined the photophysical properties of the adducts with the three bases and the equilibrium constants of formation of various adducts in the ground and excited states. The proton transfer takes place by dissociation of the adduct, in a unimolecular or bimolecular process involving a second molecule of the base. The unimolecular dissocaiotn takes place for teh adducts formed with DMSO and MU, but not for the adduct formed with water. The bimolecular dissociation occurs for the adducts formed with water and MU. In this process, the entity that finally accepts the proton is a cluster of two molecules of the base. We conclude that only one molecule of water is not able to accept the proton donated by the photoacid, a cluster of two molecules of water being required. This cluster is formed in two consecutive steps. First the adduct between the photoacid and one molecule of water is formed, subsequently followed by the reaction of the addcut with a second molecule of water.
机译：2-（2'-羟基苯基）苯并咪唑的质子化阳离子在其第一个激发单线态（C〜*）时变成非常强的酸。我们通过荧光和紫外可见吸收光谱研究了从C〜*到质子转移到碱水，甲基脲（MU）和二甲亚砜（DMSO）和乙腈溶液中的过程。我们发现该过程是通过光酸C〜*与碱之间的1：1氢键加合物发生的。我们确定了具有三个碱基的加合物的光物理性质，以及在基态和激发态下各种加合物形成的平衡常数。质子转移通过加合物的解离而发生，涉及分子的第二个分子的单分子或双分子过程。单分子分解发生在与DMSO和MU形成的加合物上，而不是与水形成的加合物上。与水和MU形成的加合物发生双分子解离。在此过程中，最终接受质子的实体是两个碱基的分子的簇。我们得出的结论是，只有一个分子的水不能接受光酸捐赠的质子，需要两个分子的水簇。该群集是在两个连续的步骤中形成的。首先在光酸和一个水分子之间形成加合物，然后使加成产物与第二个水分子反应。

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