Solvent switching of intramolecular energy transfer in bichromophoric systems:: Photophysics of (2,2′-bipyridine)tetracyanoruthenate(II)/pyrenyl complexes
Solvent switching of intramolecular energy transfer in bichromophoric systems:: Photophysics of (2,2′-bipyridine)tetracyanoruthenate(II)/pyrenyl complexes
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DOI：
10.1021/ic034185x
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发表时间：
2003-09-08
影响因子：
4.6
通讯作者：
Campagna, S
中科院分区：
文献类型：
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作者：
Indelli, MT;Ghirotti, M;Campagna, S
合成了一个和两个芘基通过二亚甲基桥连接到[Ru（bpy）（CN）（4）]（2-）上的超分子体系[Ru（Pyr（n）bpy）（CN）（4）]（2-）（n = 1，2）.这些系统，其中包含一个高度solvatochromic金属配合物部分，已在水，甲醇和乙腈中的光物理性质进行了研究。在所有溶剂中，迅速和有效的单重态-单重态能量转移发生从芘到无机部分。另一方面，在三重态能级的能量转移是显著地依赖于溶剂的。在水中，钌基发色团的金属-配体电荷转移（MLCT）发射被完全淬灭，并在超快光谱中检测到快速（200 ps，n = 1）不可逆的三重态能量转移到芘单元。在乙腈中，MLCT发射几乎不受芘基发色团存在的影响，这意味着没有任何组分间三重态能量转移。在甲醇中，三重态能量转移导致激发态发色团之间的平衡，MLCT寿命显著延长。[Ru（Pyr（n）bpy）（CN）（4）]（2-）体系在甲醇中的研究提供了非常详细和自洽的图像：（i）初始形成的MLCT状态在0.5- 1.3ns（n = 1，2）内向平衡弛豫，如通过超快瞬态吸收和通过时间相关单光子计数两者所监测的。(ii)两个激发的发色团以260-450 ns（n = 1，2）的共同寿命衰减，如从MLCT发射（慢分量）和芘三重态吸收的衰减确定的。(iii)这些平衡寿命是完全一致的激发态分区的1 - 2 - 6%MLCT（n = 1-2），独立测量的发射衰减的指前因子。总而言之，结果表明，如何网站特定的溶剂效应可以用来控制的方向，在bichromophoric系统中的组件间的能量流。
The supramolecular systems [Ru(Pyr(n)bpy)(CN)(4)](2-) (n = 1, 2), where one and two pyrenyl units are linked via two-methylene bridges to the [Ru(bpy)(CN)(4)](2-) chromophore, have been synthesized. The photophysical properties of these systems, which contain a highly solvatochromic metal complex moiety, have been investigated in water, methanol, and acetonitrile. In all solvents, prompt and efficient singlet-singlet energy transfer takes places from the pyrene to the inorganic moiety. Energy transfer at the triplet level, on the other hand, is dramatically solvent dependent. In water, the metal-to-ligand charge transfer (MLCT) emission of the Ru-based chromophore is completely quenched, and rapid (200 ps for n = 1) irreversible triplet energy transfer to the pyrene units is detected in ultrafast spectroscopy. In acetonitrile, the MLCT emission is practically unaffected by the presence of the pyrenyl chromophore, implying the absence of any intercomponent triplet energy transfer. In methanol, triplet energy transfer leads to an equilibrium between the excited chromophores, with considerable elongation of the MLCT lifetime.The investigation of the [Ru(Pyr(n)bpy)(CN)(4)](2-)Systems in methanol provided a very detailed and self-consistent picture: (i) The initially formed MLCT state relaxes toward equilibrium in 0.5-1.3 ns (n = 1, 2), as monitored both by ultrafast transient absorption and by time-correlated single photon counting. (ii) The two excited chromophores decay with a common lifetime of 260-450 ns (n = 1, 2), as determined from the decay of MLCT emission (slow component) and of the pyrene triplet absorption. (iii) These equilibrium lifetimes are fully consistent with the excited-state partition of 12-6% MLCT (n = 1-2), independently measured from preexponential factors of the emission decay. Altogether, the results demonstrate how site-specific solvent effects can be used to control the direction of intercomponent energy flow in bichromophoric systems.