Broadband femtosecond fluorescence spectroscopy of [Ru(bpy)3]2+
Broadband femtosecond fluorescence spectroscopy of [Ru(bpy)3]2+
复制标题
DOI：
10.1002/anie.200600125
复制
发表时间：
2006-01-01
影响因子：
16.6
通讯作者：
Chergui, Majed
中科院分区：
文献类型：
--
作者：
Cannizzo, Andrea;van Mourik, Frank;Chergui, Majed
金属-聚吡啶配合物的激发态动力学在太阳能转换[1-3]和信息存储[4]等多种应用中非常重要，因为它们可以由光和氧化还原触发。三联吡啶钌 ([Ru (bpy) 3] 2+) 是此类配合物的原型，其研究已成为大多数光化学应用的基础。这些配合物由于金属中心轨道和配体 π 轨道之间的电荷转移而表现出跃迁，通常称为金属到配体电荷转移（MLCT）。 [Ru (bpy) 3] 2+ 的飞秒瞬态吸收研究表明，激发单线态 1MLCT 态（最大吸收波长 450nm）时，超快系间窜越 (ISC) 在 < 100 fs 内发生，导致形成具有接近单位量子产率的三线态 3MLCT 态。[5, 6] 从 300 fs 开始，瞬态吸收光谱保持不变。[5] 3MLCT 态在室温下的水溶液中辐射衰变到基态，寿命为 600 ns。[2,3,7]然而，复合体内的能量处理和振动弛豫问题仍然是一个争论的话题。事实上，根据文献[5, 6]，400 nm 激发对应于振动松弛 3MLCT 状态上方 % 8500 cmÀ1 的过剩能量，[8] 该能量将在 % 300 fs 内消散。[5, 6] 为了解决这个问题，Bhasikuttan 等人[9]在与 1MLCT（500 和 575 nm）和 3MLCT（620 nm）预期发射波长相对应的单一波长下进行了荧光上转换研究。他们的结果被解释为快速 ISC 到 3MLCT 状态，然后在 0.6 到 1 ps 的时间尺度上进行振动冷却。由于3MLCT态的辐射率较低，在他们的实验中无法观察到3MLCT态的发射。然而，单波长检测并不能产生弛豫动力学的完整图像。因此，Browne 等人[10]实施了皮秒宽带检测技术并观察到以 520 nm 为中心的发射带，他们将其归因于 1MLCT 态。不幸的是，他们无法以所使用的时间分辨率（% 3 ps）捕获3MLCT状态内弛豫动力学的细节。在此，我们首次报告了440-690 nm范围内的多色飞秒荧光上转换实验，分辨率为110Æ 10 fs，以捕获导致[Ru (bpy) 3] 2+ 3MLCT状态稳态发射的早期弛豫过程。实验程序和数据分析在参考文献[11]和支持信息中进行了解释。图 1a 显示了在 400 nm (25000 cm-1) 激发时获得的典型二维光谱。 %21 600 cm-1 处的点是水的拉曼线。尽管在 t= 0 时存在 15 000–20 000-cm-1 区域中的荧光，但其寿命非常短，在 200 fs 内会聚到 16 000-17 500-cm-1 (575-680nm) 区域中的微弱发射。固定光谱
The excited-state dynamics of metal–polypyridine complexes are of great importance in applications as diverse as solarenergy conversion [1–3] and information storage [4] because they can be photo-and redox-triggered. Ruthenium trisbipyridine ([Ru (bpy) 3] 2+) is the prototype for this class of complexes, the study of which has formed the basis for most photochemical applications. These complexes exhibit transitions due to charge transfer between the metal-centered dorbital and the ligand π orbital, commonly known as metal-to-ligand charge transfer (MLCT). Femtosecond transient-absorption studies on [Ru (bpy) 3] 2+ have shown that upon excitation of the singlet 1MLCT state (absorption maximum 450nm), ultrafast intersystem crossing (ISC) occurs in< 100 fs, leading to the formation of the triplet 3MLCT state with near-unity quantum yield.[5, 6] From 300 fs onwards, the transient-absorption spectrum remains unchanged.[5] The 3MLCT state decays radiatively to the ground state with a lifetime of% 600 ns in aqueous solution at room temperature.[2, 3, 7] However, the issue of energy disposal and vibrational relaxation within the complex is still a subject of debate. Indeed, a 400-nm excitation corresponds to an excess energy of% 8500 cmÀ1 above the vibrationally relaxed 3MLCT state,[8] which would be dissipated in% 300 fs, according to the literature.[5, 6] To address this issue, Bhasikuttan et al.[9] carried out a fluorescence-upconversion study at single wavelengths that correspond to those at which the 1MLCT (500 and 575 nm) and the 3MLCT (620nm) emissions are expected. Their results were interpreted in terms of fast ISC to the 3MLCT state followed by vibrational cooling on a timescale of 0.6 to 1 ps. The emission by the 3MLCT state could not be observed in their experiment owing to its low radiative rate. However, single-wavelength detection does not produce a complete picture of the relaxation dynamics. Consequently, Browne et al.[10] implemented a picosecond broadband detection technique and observed an emission band centered at520 nm, which they attributed to the 1MLCT state. Unfortunately, they could not capture the details of the relaxation dynamics within the 3MLCT state with the time resolution (% 3 ps) used.Herein we report for the first time a polychromatic femtosecond fluorescence-upconversion experiment in the 440–690 nm range, with a resolution of 110Æ 10 fs to capture the early relaxation processes leading to the steady-state emission of the 3MLCT state of [Ru (bpy) 3] 2+. The experimental procedure and the data analysis are explained in reference [11] and in the Supporting Information. Figure 1a shows a typical 2D spectrum obtained upon excitation at 400 nm (25000 cmÀ1). The spot at% 21 600 cmÀ1 is the Raman line of water. Although fluorescence in the 15 000–20 000-cmÀ1 region was present at t= 0, it was very short-lived, converging within 200 fs to a weak emission in the 16 000–17 500-cmÀ1 (575–680nm) region. Spectra at fixed