Ultrafast Excited-State Dynamics ef [Re(L)(CO)3(bpy)]n Complexes: Involvement of the Solvent
Ultrafast Excited-State Dynamics ef [Re(L)(CO)3(bpy)]n Complexes: Involvement of the Solvent
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DOI：
10.1021/jp101999m
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发表时间：
2010-06-10
影响因子：
2.9
通讯作者：
Chergui, Majed
中科院分区：
文献类型：
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作者：
El Nahhas, Amal;Cannizzo, Andrea;Chergui, Majed
用荧光上转换（FIUC）和紫外-维斯瞬态吸收（TA）研究了[Re（L）（CO）（3）（bpy）]（n）（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。还在[1-乙基-3-甲基-咪唑钥] BF 4离子液体中测量TA。配合物在540-550 nm处在零时间延迟下显示出非常宽的荧光带，其通过系统间交叉（ISC）衰减到pi pi* 配体内（（IL）-I-3）和Re（L）（CO）（3）-> bpy电荷转移（（CT）-C-3）激发态，衰减100-140 Is（取决于L）。第二发射衰减分量（1.1- 1.7ps）。在光谱的红色部分中明显可见的磷光，归因于（IL）-I-3 ->（CT）-C-3转换，使得来自最低（CT）-C-3状态的磷光作为在较长时间延迟下的唯一发射信号。三重态的转换是缓慢的DMF？比乙腈，与溶剂化时间相称。在长延迟时间的激发态吸收的充分分配是通过TD-DFT计算最低的三重态，显示，2，373 nm波段是唯一的诊断bpy减少CT激发态。可见光中的带是配体到金属电荷转移（LMCT）跃迁的线索。时间分辨的维斯吸收光谱表现出归因于（IL）-I-3 ->（CT）-C-3转化以及电子和振动弛豫的所有吸收特征的ps单位上升，以及仅373 nm ppi *（bpy（中心点-））带的类似于15 ps的上升，其在离子液体溶剂中减慢至类似于1 ns。有人提出，这种缓慢的弛豫主要源于重组的溶剂分子被发现非常接近的金属中心，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，并且这种效果很可能是其他类型的金属基分子络合物的操作。
Ultrafast excited-state dynamics of [Re(L)(CO)(3)(bpy)](n) (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 (FIUC) and UV - vis transient absorption (TA) with similar to 100 is time,resolution. TA was also measured in the [1-ethyl-3-methyl-imidazolium]BF4 ionic liquid. The complexes show a very broad fluorescence band at 540-550 nm at zero time delay, which decays with 100-140 Is (depending on L) by intersystem crossing (ISC) to pi pi* intraligand ((IL)-I-3) and a Re(L)(CO)(3) -> bpy charge-transfer ((CT)-C-3) excited states. A second emission decay component (1.1-1.7 ps). apparent in the red part of the spectrum, is attributed to (IL)-I-3 -> (CT)-C-3 conversion, leaving phosphorescence from the lowest (CT)-C-3 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,2 that the 373 nm band is the sole diagnostics of bpy reduction in the CT excited state. Bands in the visible are clue 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 (IL)-I-3 -> (CT)-C-3 conversion as well as electronic and vibrational relaxation, and a similar to 15 ps rise of only the 373 nm pi pi*(bpy(center dot-)) band which slows down to similar to 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 other classes of metal-based molecular complexes.