Taheri Atefeh, Meyer Gerald J
Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, USA.
Dalton Trans. 2014 Dec 21;43(47):17856-63. doi: 10.1039/c4dt01683a.
The metal-to-ligand charge transfer (MLCT) excited states of two related heteroleptic Ru(ii) compounds Ru(bpy)2(deeb) and Ru(bpy)2(deebq), where bpy is 2,2'-bipyridine, deeb is 4,4'-(CO2CH2CH3)2-2,2'-bipyridine and deebq is 4,4'-(CO2CH2CH3)2-2,2'-biquinoline, were characterized in fluid acetonitrile by temperature dependent photoluminescence spectroscopies as well as quenching by iodide ions. Photoluminescence emanates from a manifold of thermally equilibrated excited states referred to as the thexi states. Evidence for activated internal conversion to a 4(th) MLCT excited state was garnered from an Arrhenius analysis of temperature dependent lifetime data. The activation energy was found to be 550 cm(-1) for Ru(bpy)2(deeb)* and 1200 cm(-1) for Ru(bpy)2(deebq). The pre-exponential factor abstracted from the Arrhenius analysis of the Ru(bpy)2(deebq) data suggested that ligand field excited states might be populated, however there was no evidence for ligand loss photochemistry under the conditions studied. The excited states were found to quench iodide by a dynamic process in good agreement with the Stern-Volmer model. Transient absorption data showed that the quenching mechanism was electron transfer to generate an iodine atom and a reduced ruthenium compound as products. The quenching rate constants abstracted from temperature dependent Stern-Volmer quenching data were corrected for diffusion and activated complex formation to yield electron transfer rate constants that were found to increase markedly with temperature. An Arrhenius analysis of the electron transfer data revealed that electron transfer from iodide to the d-orbitals of the excited state was an activated process with an Ea of 2400 cm(-1) for Ru(bpy)2(deeb) and 3300 cm(-1) for Ru(bpy)2(deebq).
两种相关的异质 Ru(ii) 化合物 Ru(bpy)2(deeb) 和 Ru(bpy)2(deebq) 的金属 - 配体电荷转移 (MLCT) 激发态，其中 bpy 为 2,2'-联吡啶，deeb 为 4,4'-(CO2CH2CH3)2-2,2'-联吡啶，deebq 为 4,4'-(CO2CH2CH3)2-2,2'-联喹啉，在流动乙腈中通过变温光致发光光谱以及碘离子猝灭进行了表征。光致发光源自一系列热平衡激发态，称为thexi态。通过对变温寿命数据的阿仑尼乌斯分析，获得了向第四重 MLCT 激发态的活化内转换的证据。发现 Ru(bpy)2(deeb) * 的活化能为 550 cm(-1)，Ru(bpy)2(deebq) * 的活化能为 1200 cm(-1)。从 Ru(bpy)2(deebq) * 数据的阿仑尼乌斯分析中提取的指前因子表明可能存在配体场激发态，然而在所研究的条件下没有配体损失光化学的证据。发现激发态通过动态过程猝灭碘离子，这与斯特恩 - 沃尔默模型高度吻合。瞬态吸收数据表明猝灭机制是电子转移，生成碘原子和还原的钌化合物作为产物。从变温斯特恩 - 沃尔默猝灭数据中提取的猝灭速率常数针对扩散和活化络合物形成进行了校正，以得到电子转移速率常数，发现其随温度显著增加。对电子转移数据的阿仑尼乌斯分析表明，从碘离子到激发态d轨道的电子转移是一个活化过程，Ru(bpy)2(deeb) 的Ea为 2400 cm(-1)，Ru(bpy)2(deebq) 的Ea为 3300 cm(-1)。
