The photophysical properties of closely-coupled, binuclear complexes formed by connecting two ruthenium(II) bis(2,2â²:6â²,2â³-terpyridine) complexes via an alkynylene group are compared to those of the parent complex. The dimers exhibit red-shifted emission maxima and prolonged triplet lifetimes in deoxygenated solution. Triplet quantum yields are much less than unity and the dimers generate singlet molecular oxygen with low quantum efficiency. Temperature dependence emission studies indicate coupling to higher-energy triplet states while cyclic voltammetry shows that the metal centres are only very weakly coupled but that extensive electron delocalisation occurs upon one-electron reduction. The radiative rate constants derived for these dimers are relatively low, because the lowest-energy metal-to-ligand, charge-transfer states possess increased triplet character. In contrast, the rate constants for nonradiative decay of the lowest-energy triplet states are kept low by extended electron delocalisation over the polytopic ligand. The poor triplet yields are a consequence of partitioning at the second triplet level.
通过一个炔基连接两个双(2,2â²:6â²,2â³-三
吡啶)
钌(II)络合物而形成的紧密耦合双核络合物的光物理特性与母体络合物的光物理特性进行了比较。在脱氧溶液中,二聚体显示出红移发射最大值和延长的三重态寿命。三重量子产率远低于统一值,二聚体产生单线分子氧的量子效率较低。与温度相关的发射研究表明,三重态与高能量的三重态耦合,而循环伏安法表明,
金属中心的耦合非常弱,但在单电子还原时会发生广泛的电子析出。这些二聚体的辐射速率常数相对较低,因为能量最低的
金属-
配体电荷转移态具有更高的三重态特性。与此相反,由于电子在多位
配体上的分散扩展,最低能量三重态的非辐射衰变速率常数保持在较低
水平。较低的三重态产率是第二三重态分区的结果。