Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, USA.
Dalton Trans. 2011 Apr 21;40(15):3830-8. doi: 10.1039/c0dt01447h. Epub 2011 Jan 17.
The oxidation of iodide to diiodide, I(2)˙(-), by the metal-to-ligand charge-transfer (MLCT) excited state of Ru(deeb)(3), where deeb is 4,4'-(CO(2)CH(2)CH(3))(2)-2,2'-bipyridine, was quantified in acetonitrile and dichloromethane solution at room temperature. The redox and excited state properties of Ru(deeb)(3) were similar in the two solvents; however, the mechanisms for excited state quenching by iodide were found to differ significantly. In acetonitrile, reaction of Ru(deeb)(3) and iodide was dynamic (lifetime quenching) with kinetics that followed the Stern-Volmer model (K(D) = 1.0 ± 0.01 × 10(5) M(-1), k(q) = 4.8 × 10(10) M(-1) s(-1)). Excited state reactivity was observed to be the result of reductive quenching that yielded the reduced ruthenium compound, Ru(deeb(-))(deeb)(2), and the iodine atom, I˙. In dichloromethane, excited state quenching was primarily static (photoluminescence amplitude quenching) and Ru(deeb(-))(deeb)(2) formed within 10 ns, consistent with the formation of ion pairs in the ground state that react rapidly upon visible light absorption. In both solvents the appearance of I(2)˙(-) could be time resolved. In acetonitrile, the rate constant for I(2)˙(-) growth, 2.2 ± 0.2 × 10(10) M(-1) s(-1), was found to be about a factor of two slower than the formation of Ru(deeb(-))(deeb)(2), indicating it was a secondary photoproduct. The delayed appearance of I(2)˙(-) was attributed to the reaction of iodine atoms with iodide. In dichloromethane, the growth of I(2)˙(-), 1.3 ± 0.4 × 10(10) M(-1) s(-1), was similar to that in acetonitrile, yet resulted from iodine atoms formed within the laser pulse. These results are discussed within the context of solar energy conversion by dye-sensitized solar cells and storage via chemical bond formation.
碘化物氧化为二碘化物，I(2)˙(-)，通过金属到配体电荷转移（MLCT）激发态的Ru(deeb)(3)，其中 deeb 是 4,4'-(CO(2)CH(2)CH(3))(2)-2,2'-联吡啶，在室温下的乙腈和二氯甲烷溶液中进行了定量。Ru(deeb)(3)的氧化还原和激发态性质在两种溶剂中相似；然而，发现碘化物对激发态的猝灭机制有很大的不同。在乙腈中，Ru(deeb)(3)与碘化物的反应是动态的（寿命猝灭），动力学符合 Stern-Volmer 模型（K(D) = 1.0 ± 0.01 × 10(5) M(-1)，k(q) = 4.8 × 10(10) M(-1) s(-1)）。观察到激发态反应性是还原猝灭的结果，生成还原的钌化合物Ru(deeb(-))(deeb)(2)和碘原子 I˙。在二氯甲烷中，激发态猝灭主要是静态的（光致发光幅度猝灭），并且Ru(deeb(-))(deeb)(2)在 10 ns 内形成，这与基态中形成离子对一致，这些离子对在可见光吸收后迅速反应。在两种溶剂中都可以对 I(2)˙(-)进行时间分辨。在乙腈中，I(2)˙(-)生长的速率常数为 2.2 ± 0.2 × 10(10) M(-1) s(-1)，发现比Ru(deeb(-))(deeb)(2)的形成慢约一个因子，表明它是二级光产物。I(2)˙(-)的延迟出现归因于碘原子与碘化物的反应。在二氯甲烷中，I(2)˙(-)的生长，1.3 ± 0.4 × 10(10) M(-1) s(-1)，与乙腈中的生长相似，但源于激光脉冲内形成的碘原子。这些结果在染料敏化太阳能电池的太阳能转换和通过化学键形成的储能的背景下进行了讨论。
