Unexpected Role of Ru(II) Orbital and Spin Contribution on Photoinduced Ligand Exchange: New Mechanism To Access the Photodynamic Therapy Window
Unexpected Role of Ru(II) Orbital and Spin Contribution on Photoinduced Ligand Exchange: New Mechanism To Access the Photodynamic Therapy Window
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DOI：
10.1021/acs.jpcc.9b01576
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发表时间：
2019-04-25
影响因子：
3.7
通讯作者：
Turro, Claudia
中科院分区：
文献类型：
--
作者：
Loftus, Lauren M.;Al-Afyouni, Kathlyn F.;Turro, Claudia
合成了一系列12个含三齿三联吡啶配体（tpy = 2，2 '：6'，2“-三联吡啶）和各种二齿辅助配体L的[Ru（tpy）（L）-（CH_3CN）]（n+）型Ru（II）配合物，并评价了它们光解含腈药物模型CH_3CN的能力。虽然所选择的双齿配体在基态下围绕金属中心显示出类似程度的空间体积，但1-12的光取代效率变化约一个数量级。含有最多给电子双齿配体8-11的配合物在水中表现出较大的配体交换量子产率值。配合物8-11还具有基态和最低能量的三重态金属-配体电荷转移（（MLCT）-M-3）激发态之间的最小能隙。此外，密度泛函理论计算表明，在很大程度上的配体特征是存在于其最高占据分子轨道（HOMO）和在其（MLCT）-M-3激发态。这些结果表明，配体混合影响了金属中心在激发态的π-背键能力，增加了腈配体解离的量子产率。配体交换的量子产率与激发态金属中心上的Mulliken自旋密度和基态HOMO中Ru（d）特征的百分比之间存在线性关系。这些发现，驱动的π捐赠辅助配体的存在下，增强激发态的反应性，可以用来设计新的配合物具有更高的量子产率的含腈药物和生物探针的释放，而不影响其在黑暗中的稳定性。
A series of 12 Ru(II) complexes of the type [Ru(tpy)(L)-(CH3CN)](n+), 1-12, containing the tridentate tpy ligand (tpy = 2,2':6',2 ''-terpyridine) and various bidentate ancillary ligands, L, were synthesized and evaluated for their ability to photodissociate CH3CN, a model for nitrile-containing drugs. Although the bidentate ligands chosen display a similar degree of steric bulk around the metal center in the ground state, the photosubstitution efficiencies of 1-12 vary by approximately an order of magnitude. The complexes containing the most electron-donating bidentate ligands, 8-11, exhibit the larger quantum yield values for ligand exchange in water. Complexes 8-11 also possess the smallest energy gap between the ground state and the lowest energy triplet metal-to-ligand charge transfer ((MLCT)-M-3) excited state. In addition, density functional theory calculations indicate that a large degree of ligand character is present in their highest occupied molecular orbitals (HOMOs) and in their (MLCT)-M-3 excited states. These results show that ligand mixing affects the pi-backbonding ability of the metal center in the excited state, increasing the quantum yields of nitrile ligand dissociation. Linear relationships were observed between the quantum yield of ligand exchange and both the Mulliken spin density on the metal center in the excited state and the percent of Ru(d) character in the ground state HOMO. These findings, driven by the presence of pi-donating ancillary ligands that enhance excited state reactivity, can be used to design new complexes with higher quantum yields for the release of nitrile-containing drugs and biological probes without affecting their stability in the dark.