Ecole Polytechnique Fédérale de Lausanne, Laboratoire de Spectroscopie Ultrarapide, ISIC-FSB, station 6, CH-1015 Lausanne, Switzerland.
J Phys Chem A. 2010 Jun 10;114(22):6361-9. doi: 10.1021/jp101999m.
Ultrafast excited-state dynamics of Re(L)(CO)(3)(bpy) (L = Cl, Br, n = 0; L = 4-ethyl-pyridine (Etpy), n = 1+; bpy = 2,2'-bipyridine) have been investigated in dimethylformamide (DMF) solution by fluorescence up-conversion (FlUC) and UV-vis transient absorption (TA) with approximately 100 fs time resolution. TA was also measured in the [1-ethyl-3-methyl-imidazolium]BF(4) ionic liquid. The complexes show a very broad fluorescence band at 540-550 nm at zero time delay, which decays with 100-140 fs (depending on L) by intersystem crossing (ISC) to a pipi* intraligand ((3)IL) and a Re(L)(CO)(3) --> bpy charge-transfer ((3)CT) excited states. A second emission decay component (1.1-1.7 ps), apparent in the red part of the spectrum, is attributed to (3)IL --> (3)CT conversion, leaving phosphorescence from the lowest (3)CT state as the only emission signal at longer time delays. The triplet conversion is slower in DMF than acetonitrile, commensurate with solvation times. Full assignment of the excited-state absorption at long delay times is obtained by TD-DFT calculations on the lowest triplet state, showing that the 373 nm band is the sole diagnostics of bpy reduction in the CT excited state. Bands in the visible are due to Ligand-to-Metal-Charge-Transfer (LMCT) transitions. Time-resolved UV-vis absorption spectra exhibit a units-of-ps rise of all absorption features attributed to (3)IL --> (3)CT conversion as well as electronic and vibrational relaxation, and a approximately 15 ps rise of only the 373 nm pipi*(bpy(*-)) band, which slows down to approximately 1 ns in the ionic liquid solvent. It is proposed that this slow relaxation originates mainly from restructuring of solvent molecules that are found very close to the metal center, inserted between the ligands. The solvent thus plays a key role in controlling the intramolecular charge separation, and this effect may well be operative in other classes of metal-based molecular complexes.
Re(L)(CO)(3)(bpy)（L = Cl、Br、n = 0；L = 4-乙基吡啶（Etpy）、n = 1+；bpy = 2,2'-联吡啶）在二甲基甲酰胺（DMF）溶液中的超快激发态动力学已通过荧光上转换（FlUC）和紫外可见瞬态吸收（TA）以约 100 fs 的时间分辨率进行了研究。TA 也在[1-乙基-3-甲基咪唑]BF(4)离子液体中进行了测量。该配合物在零延迟时在 540-550nm 处显示出非常宽的荧光带，该荧光带通过系间窜越（ISC）以 100-140fs（取决于 L）衰减至 pi内配位（3）IL 和 Re（L）（CO）（3）-> bpy 电荷转移（3）CT 激发态。在光谱的红色部分明显出现的第二个发射衰减分量（1.1-1.7ps）归因于（3）IL->（3）CT 转换，使来自最低（3）CT 态的磷光成为较长时间延迟时的唯一发射信号。三重态转换在 DMF 中比在乙腈中慢，与溶剂化时间一致。通过对最低三重态进行 TD-DFT 计算，获得了长时间延迟下的激发态吸收的完全分配，表明 373nm 带是 CT 激发态中 bpy 还原的唯一诊断带。可见光中的带归因于配体到金属电荷转移（LMCT）跃迁。时间分辨的紫外可见吸收光谱显示出所有吸收特征的单位 ps 上升归因于（3）IL->（3）CT 转换以及电子和振动弛豫，以及 373nm pipi（bpy（*-））带的约 15ps 上升，该带在离子液体溶剂中缓慢至约 1ns。据推测，这种缓慢的弛豫主要源自非常靠近金属中心的溶剂分子的重排，插入配体之间。因此，溶剂在控制分子内电荷分离中起着关键作用，这种效应在其他类别的金属基分子配合物中可能很有效。
