The effect of solute-solvent interaction on the radiationless relaxation rate of the ^3MLCT states of tris(alpha, alpha'-diimine)metal(II) complexes

测定了Ru(bpy)_3^<2+>、Ru(phen)_3^<2+>、Os(bpy)_3^<2+>和Os(phen)_3^<2+>在水-醇和-二氧六环混合溶剂中的无辐射衰变速率。在Ru（II）配合物中，我们根据温度依赖性的测量结果将无辐射衰变率分为两个非辐射过程：一个是直接到基态的路径（IC路径），另一个是到^3MLCT态以上的金属中心态的路径（MC路径）。相反，IC路径在Os（II）配合物中占主导地位。通过使用氘化溶剂，发现在MC路径上没有观察到同位素效应。对于IC路径，在水中观察到较大的同位素效应，而在醇中观察到轻微的同位素效应。当乙醇加入水中时，反应速率常数随乙醇摩尔分数的增加呈非线性降低。为了解释所观察到的溶剂对速率的影响，我们提出了一种新的无辐射跃迁到基态的模型，而不是电荷转移到溶剂的机制：在配合物的配体之间包含的水分子可能接受激发能，然后能量耗散到与所包含的水预先结合的外部周围溶剂团。所含溶剂与配体的相互作用随所含溶剂与外溶剂簇相互作用的变化而变化。因此，随着溶剂微观结构的变化，金属配合物向包合水分子传递的能量传递系数kappa也随之变化，因为包合溶剂与外溶剂团簇之间的相互作用是由外溶剂团簇的氢键强度改变的。在醇中，由于所包含的醇分子只有一个OH，分子必须重新定向以将激发能分散到外部溶剂簇。因此kappa应该很小。少

The radiationless decay rates of Ru(bpy)_3^<2+>, Ru(phen)_3^<2+> Os(bpy)_3^<2+> and Os(phen)_3^<2+> were measured in water-alcohol and -dioxane mixted solvents. In the Ru(II) complexes, we divided the radiationless decay rate into two non-radiative processes from the results of the measurements for the temperature dependence : one is the path to the ground state directly (IC path) and another is the path to the metal center state above the ^3MLCT state (MC path). On the contrary, the IC path is predominant in Os(II) complexes. By using the deuterated solvent, it has been revealed that no isotope effect is observed in the MC path. For the IC path, a large isotope effect on the rate was observed in water while a slight isotope effect was observed in alcohol. On adding alcohol to water, the rate constant decreased nonlinearly With increase of mole fraction of alcohol. In order to explain the observed solvent effect on the rates, we proposed a new model for the radiationless transition to … More the ground state as below instead of the mechanism of charge-transfer-to-solvent : the water molecule included between ligands of the complex may accept the excitation energy followed by the energy dissipation toward the cluster of outer sorrounding solvents with which the included water combines in advance. The interaction between the included solvent and the ligands varies accompanying with the change in the interaction between the included solvent and the outer solvent cluster. Therefore, the transmission coefficient, kappa, of the energy tranefer from the metal complex to the included water molecule is change with the microscopic structure of solvent, since the interaction between the included solvent and the outer solvent cluster is changed by the strength of the hydrogen bond of the outer cluster. In alcohol, since the included alcohol molecule have only one OH,the molecule must reorientate to dissipate the excitation energy to the outer solvent cluster. Thus the kappa should be small. Less