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

测量了Ru(Bpy)_3^&lt；2+&gt；，Ru(Phen)_3^&lt；2+&gt；Os(Bpy)_3^&lt；2+&gt；和Os(Phen)_3^&lt；2+&gt；在水-乙醇-二氧六环混合溶剂中的无辐射衰变速率。在Ru(II)络合物中，根据温度依赖性的测量结果，我们将无辐射衰减率分为两个非辐射过程：一个是直接到达基态的路径(IC路径)，另一个是到达^3MLCT态以上的金属中心态的路径(MC路径)。相反，在Os(II)络合物中，IC路径占主导地位。结果表明，在分子轨道上没有观察到同位素效应。对于IC路径，在水中观察到很大的同位素效应，而在酒精中观察到轻微的同位素效应。在水中加入乙醇时，随着乙醇摩尔分数的增加，反应速率常数呈非线性下降。为了解释观察到的溶剂对速率的影响，我们提出了一个新的无辐射跃迁到…的模型此外，基态取代了电荷转移到溶剂的机理：络合物的配体之间的水分子可能接受激发能量，随后能量耗散到所包含的水预先与之结合的外部分类周围的溶剂团簇。所含溶剂与配位体之间的相互作用随着所含溶剂与外部溶剂团簇相互作用的变化而变化。因此，金属络合物向包裹体水分子的能量传递系数kappa随溶剂的微观结构而变化，这是因为包裹体与外部溶剂团簇之间的相互作用是由外层团簇的氢键强度决定的。在酒精中，由于所包含的醇分子只有一个羟基，分子必须重新定位以将激发能耗散到外部的溶剂团簇。因此，卡帕应该很小。较少

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