Indelli M T, Ghirotti M, Prodi A, Chiorboli C, Scandola F, McClenaghan N D, Puntoriero F, Campagna S
Dipartimento di Chimica, Università di Ferrara, 44100 Ferrara, Italy.
Inorg Chem. 2003 Sep 8;42(18):5489-97. doi: 10.1021/ic034185x.
The supramolecular systems Ru(Pyr(n)bpy)(CN)(4) (n = 1, 2), where one and two pyrenyl units are linked via two-methylene bridges to the Ru(bpy)(CN)(4) 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) 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.
已合成超分子体系Ru(Pyr(n)bpy)(CN)(4)（n = 1, 2），其中一个和两个芘基单元通过两个亚甲基桥连接到Ru(bpy)(CN)(4)发色团上。这些体系含有高度溶剂化显色金属络合物部分，已在水、甲醇和乙腈中研究了其光物理性质。在所有溶剂中，都发生了从芘到无机部分的快速且高效的单重态-单重态能量转移。另一方面，三重态能级的能量转移强烈依赖于溶剂。在水中，基于钌的发色团的金属-配体电荷转移（MLCT）发射完全淬灭，并且在超快光谱中检测到快速（n = 1时为200皮秒）不可逆的三重态能量转移到芘单元。在乙腈中，MLCT发射实际上不受芘基发色团存在的影响，这意味着不存在任何组分间的三重态能量转移。在甲醇中，三重态能量转移导致激发发色团之间达到平衡，MLCT寿命显著延长。对Ru(Pyr(n)bpy)(CN)(4)体系在甲醇中的研究提供了一幅非常详细且自洽的图景：（i）通过超快瞬态吸收和时间相关单光子计数监测，最初形成的MLCT态在0.5 - 1.3纳秒（n = 1, 2）内弛豫至平衡。（ii）从MLCT发射（慢组分）和芘三重态吸收的衰减确定，两个激发发色团以260 - 450纳秒（n = 1, 2）的共同寿命衰减。（iii）这些平衡寿命与从发射衰减的预指数因子独立测量的12 - 6%的MLCT激发态分配完全一致。总之，结果表明如何利用位点特异性溶剂效应来控制双发色团体系中组分间能量流动的方向。
