Ultrafast fluorescence detection in tris(2,2′-bipyridine)ruthenium(II) complex in solution:: Relaxation dynamics involving higher excited states
Ultrafast fluorescence detection in tris(2,2′-bipyridine)ruthenium(II) complex in solution:: Relaxation dynamics involving higher excited states
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DOI：
10.1021/ja026135h
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发表时间：
2002-07-17
影响因子：
15
通讯作者：
Okada, T
中科院分区：
文献类型：
--
作者：
Bhasikuttan, AC;Suzuki, M;Okada, T
利用飞秒荧光上转换光谱研究了一种过渡金属配合物——三（2,2'-联吡啶）钌（II），[Ru(bpy)₃]²⁺的激发态动力学。这些分子中的弛豫动力学对于理解与界面电子转移相关的各种超快过程非常重要，特别是在半导体纳米粒子中。尽管有一些实验和理论研究，但一直缺少对该分子中弗兰克 - 康登单重激发态的直接观测。在这项研究中，首次观测到了[Ru(bpy)₃]²⁺的弗兰克 - 康登激发单重态的发射，其寿命估计为40±15飞秒。在较长波长处观察到具有快速上升成分的双指数衰减，表明系统中存在不止一种发射态。通过详细的数据分析，提出在410nm激发时，从较高激发的（¹）（MLCT）态到振动热三重态的交叉发生，系间窜越时间常数为40±15飞秒。由于强自旋 - 轨道耦合，提出了三重态中的较高能级与单重态的混合。这提高了三重态内振动热态的辐射速率常数kᵣ，促进了发射光子的上转换。具有发射性的振动激发三重态经历振动冷却，衰减时间在0.56 - 1.3皮秒范围内，并弛豫到长寿命的三重态。[Ru(bpy)₃]²⁺中较高激发态弛豫动力学的结果对于解释过渡金属配合物的非平衡较高激发敏化态在电子注入和其他超快过程中的作用是有价值的。
The excited-state dynamics of a transition metal complex, tris(2,2'-bipyridine)ruthenium(II), [Ru(bpy)(3)](2+), has been investigated using femtosecond fluorescence upconversion spectroscopy. The relaxation dynamics in these molecules is of great importance in understanding the various ultrafast processes related to interfacial electron transfer, especially in semiconductor nanoparticles. Despite several experimental and theoretical efforts, direct observation of a Franck-Condon singlet excited state in this molecule was missing. In this study, emission from the Franck-Condon excited singlet state of [Ru(bpy)(3)](2+) has been observed for the first time, and its lifetime has been estimated to be 40 +/- 15 fs. Biexponential decays with a fast rise component observed at longer wavelengths indicated the existence of more than one emitting state in the system. From a detailed data analysis, it has been proposed that, on excitation at 410 nm, crossover from higher excited (1)(MLCT) states to the vibrationally hot triplet manifold occurs with an intersystem crossing time constant of 40 +/- 15 fs. Mixing of the higher levels in the triplet state with the singlet state due to strong spin-orbit coupling is proposed. This enhances the radiative rate constant, k(r), of the vibrationally hot states within the triplet manifold, facilitating the upconversion of the emitted photons. The vibrationally excited triplet, which is emissive, undergoes vibrational cooling with a decay time in the range of 0.56-1.3 ps and relaxes to the long-lived triplet state. The results on the relaxation dynamics of the higher excited states in [Ru(bpy)(3)](2+) are valuable in explaining the role of nonequilibrated higher excited sensitizer states of transition metal complexes in the electron injection and other ultrafast processes.