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首页> 外文期刊>Coordination chemistry reviews >Charge transfer-excited state emission spectra of mono- and bi-metallic coordination complexes: Band shapes, reorganizational energies and lifetimes
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Charge transfer-excited state emission spectra of mono- and bi-metallic coordination complexes: Band shapes, reorganizational energies and lifetimes

机译：单金属和双金属配位化合物的电荷转移激发态发射光谱：能带形状，重组能和寿命

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摘要

The low energy sidebands of an emission spectrum contain information about the difference between the ground and the excited state molecular structures. The structural information that can be extracted from the sideband intensities and structure decreases as the component bandwidths increase, but there is significant structural information in the sidebands of the charge transfer emission spectra of even the relatively broad (Δν_(1/2) ～ 1000 cm~(-1)) charge transfer (CT) emission spectra of transition metal complexes in frozen solutions. A Gaussian band shape model for the contributions of vibronic components is described and applied to the analysis of transition metal CT emission band shapes in frozen solution. The uncertainties of this approach are examined with respect to the emission spectra calculated from reported resonance-Raman (rR) parameters; such calculated spectra reproduce the frozen solution emission spectra of [Ru(bpy)_3]~(2+) and [Ru(NH_3)_4bpy]~(2+) very well. Patterns of excited state distortions can be expressed in terms of variations in the vibrational reorganizational energies, λ_k (proportional to the squared displacements), of the normal modes that correlate with the differences in excited and ground state geometries. The excited state distortions usually correspond to displacements in a large number of ground state molecular vibrational modes (more than 11 for the Ru-bpy complexes), and the bandwidths characteristic of CT spectra in frozen solutions preclude their resolution in frozen solution spectra. Thus, the convolution of the overlapping spectral contributions of these individual distortion modes results in a vibronic sideband that is broad and sometimes weakly structured, and the variations of the sideband amplitude provides information about variations in molecular structure for a series of closely related complexes. The emission sidebands can readily be converted into a reorganizational energy profile (emrep) in which the variations in amplitude are more readily interpreted in terms of molecular distortions and in which the contributions from the distortions in the highest frequency vibrational modes are more evident. This approach has been used to analyze the patterns of variations of the vibronic sideband structure of the frozen solution CT emission spectra of [Ru(L)_4(bpy]~(2+), [Ru(bpy)_2PP]~(2+), [{(bpy)_2Ru}_2PP]~(4+) (bpy, 2,2'-bipyridine; PP, a tetraazapolypyridyl bridging ligand) and cyanide-bridged Cr(Ⅲ)/Ru(Ⅱ) complexes. The observed emission energies of the bpy complexes span a range of about 8000 cm~(-1) and the vibronic sideband amplitudes tend to decrease appreciably (over about a two-fold range for the [Ru(L)_4bpy]~(2+) complexes) and systematically with decreasing emission energy in each class of these complexes. This attenuation of the vibronic sideband intensities is ascribed to the increases in ground state-excited state configurational mixing with decreasing energy differences between the states and to the large electronic matrix elements. The variations in emreps also suggest that there is a great deal of excited state-excited state configurational mixing (probably ligand field/metal to ligand CT) in most, but not all, [Ru(L)_4bpy]~(2+) complexes and relatively little such configurational mixing between the different MLCT valence isomer excited states of the [{(bpy)_2Ru}_2PP]~(4+) complexes.
机译：发射光谱的低能边带包含有关基态和激发态分子结构之间差异的信息。可以从边带强度和结构中提取的结构信息随着组件带宽的增加而减小，但是即使在相对较宽的（Δν_（1/2）〜1000 cm）的电荷转移发射谱的边带中也存在大量的结构信息。 〜（-1））冻结溶液中过渡金属配合物的电荷转移（CT）发射光谱。描述了高斯能带形状模型，用于振动成分的贡献，并将其用于分析冷冻溶液中过渡金属CT发射能带形状。根据从报告的共振拉曼（rR）参数计算出的发射光谱，检查了这种方法的不确定性。这样计算出的光谱非常好地再现了[Ru（bpy）_3]〜（2+）和[Ru（NH_3）_4bpy]〜（2+）的冻结溶液发射光谱。激发态畸变的模式可以用与激发态和基态几何结构差异相关的正常模态的振动重组能λ_k（与平方位移成比例）来表示。激发态畸变通常对应于大量基态分子振动模式中的位移（对于Ru-bpy络合物而言，大于11），并且在冷冻溶液中CT光谱的带宽特征妨碍了它们在冷冻溶液光谱中的分辨。因此，这些单个畸变模式的重叠光谱贡献的卷积导致宽泛的，有时结构较弱的振动电子边带，并且边带振幅的变化提供了一系列紧密相关的配合物的分子结构变化信息。发射边带可以很容易地转换成重组能量分布图（emrep），其中振幅变化更容易根据分子畸变来解释，并且在最高频率振动模式中畸变的贡献更加明显。该方法已用于分析冷冻溶液的[Ru（L）_4（bpy]〜（2 +），[Ru（bpy）_2PP]〜（2+）的电子束边带结构的变化模式。 ），[{（bpy）_2Ru} _2PP]〜（4 +）（bpy，2,2'-联吡啶； PP，四氮杂吡啶基桥联配体）和氰化物桥联的Cr（Ⅲ）/ Ru（Ⅱ）配合物。 bpy配合物的发射能量跨度在8000 cm〜（-1）范围内，并且电子束边带振幅趋于明显降低（[Ru（L）_4bpy]〜（2+）配合物的大约两倍范围内） ），并且系统地降低了这些复合物中的每一类的发射能量，振动边带强度的这种衰减归因于基态激发态构型混合的增加，而状态之间的能量差减小了，而大型电子矩阵元素也是如此。 emrep的变化也表明存在大量的激发态-激发态构型混合（可能是配体场/ [Ru（L）_4bpy]〜（2+）络合物中的大多数（但不是全部）络合物中，并且[[（（bpy）_2Ru} _2PP]的不同MLCT价异构体激发态之间的这种构型混合相对较少〜（4+）个复合物。

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