Determination of relaxation paths in the manifold of excited states of Pt(2-thpy)₂ and [Ru(bpy)₃]²⁺ by time-resolved excitation and emission
Determination of relaxation paths in the manifold of excited states of Pt(2-thpy)₂ and [Ru(bpy)₃]²⁺ by time-resolved excitation and emission
复制标题
通过时间分辨激发和发射确定 Pt(2-thpy)2 和 [Ru(bpy)3]2⁺ 激发态流形中的弛豫路径
DOI：
10.1021/ic960565p
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发表时间：
1997
影响因子：
4.6
通讯作者：
H. Yersin
中科院分区：
文献类型：
--
作者：
Josef J. E. Schmidt;J. Strasser;H. Yersin
Pt（2-thpy）d2和[Ru（bpy）d2] d2作为过渡金属配合物的代表，具有几cm <$的最低三重态的零场分裂（zfs），表现出一系列通常不为人所知的发射衰减特性的时间依赖性。这些都是由相对缓慢的自旋晶格弛豫（slr）过程决定的。因此，人们发现[Ru（bpy）<$] 2 <$$>和Pt（2-thpy）<$2在T = 1.3 K时的发射衰减分别为220和600 ns，这两种化合物都是由从第二激发态到最低激发态的弛豫过程控制的，而最低激发态本身的发射衰减分别为230和110 μs。根据这些明显不同的发射衰减时间观察到的两个最低激发态（相同的化合物），它是可能的，以获得更详细的洞察到不同的状态的性质，通过应用光谱高分辨和时间分辨发射光谱技术。特别是，这种更深层次的洞察力来自于记录第二激发态的高质量低温发射光谱的可能性，迄今为止还没有
知道的此外，从Pt（2-thpy）双金属间化合物的slr速率随温度的变化关系可以得出结论：在低温下，slr的直接过程占主导地位，而当T > 2.3K时，Orbach过程变得越来越重要。对于[Ru（bpy）<$] 2 <$，情况类似，但是当T > 6 K时，Orbach过程增长。本研究的重点是首次引入时间分辨激发光谱方法，利用激光共振器的特殊性质研究电子和振动激发态流形中弛豫路径的细节。特别是，它可以显示-不应用亚皮秒时间分辨率-在脉冲激发后，弛豫发生在每个三重态子能级的振动势能超曲面内。三重态子能级之间的交叉不会通过激发振动态发生，而是在达到零点振动能级之后发生。然而，这种选择性的弛豫路径时，失去了一个更高的单态被激发。此外，这种新的方法提供了一系列进一步的激发态性质的访问。
Pt(2-thpy)₂ and [Ru(bpy)₃]²⁺, studied as representatives of transition metal complexes with zero-field splittings (zfs) of the lowest triplets of several cm⁻¹, exhibit a series of generally not-well known time dependencies of emission decay properties. These are strongly determined by relatively slow spin-lattice relaxation (slr) processes. Thus, one finds emission decays for [Ru(bpy)₃]²⁺ and Pt(2-thpy)₂ of 220 and 600 ns at T = 1.3 K, respectively, which are in both compounds controlled by relaxation processes from the second to the lowest excited state, while the lowest state itself emits with a long decay of 230 and 110 μs, respectively. According to these distinctly different emission decay times observed for the two lowest excited states (of the same compound), it is possible to gain a more detailed insight into the properties of the different states by applying the techniques of spectrally highly resolved and time-resolved emission spectroscopy. In particular, this deeper insight results from the possibility to register high-quality low-temperature emission spectra also of the second excited state, hitherto not
known. Moreover, from the temperature dependencies of the slr rates in Pt(2-thpy)₂, it is concluded that at low temperature the direct process of slr dominates, while for T > 2.3 K the Orbach process becomes increasingly important. For [Ru(bpy)₃]²⁺ the situation is similar, but the Orbach process grows in for T > 6 K. It is the highlight of the present investigation that the specific properties of slr can be used to study details of relaxation paths in the manifold of the electronically and vibrationally excited states by introducing - for the first time - the method of time-resolved excitation spectroscopy. In particular, it can be shown - without applying a sub-picosecond time resolution - that after a pulsed excitation the relaxations occur within the vibrational potential hypersurfaces of each triplet sublevel. A crossing between the triplet sublevels does not occur via excited vibrational states, but it takes place after the zero-point vibrational levels are reached. However, this selectivity of the relaxation paths is lost when a higher lying singlet is excited. Moreover, this new method provides access to a series of further excited state properties.