Femtosecond fluorescence and intersystem crossing in rhenium(I) carbonyl-bipyridine complexes
Femtosecond fluorescence and intersystem crossing in rhenium(I) carbonyl-bipyridine complexes
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DOI：
10.1021/ja710763w
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发表时间：
2008-07-16
影响因子：
15
通讯作者：
Chergui, Majed
中科院分区：
文献类型：
--
作者：
Cannizzo, Andrea;Blanco-Rodriguez, Ana Maria;Chergui, Majed
利用飞秒荧光上转换技术和多色探测研究了[Re（L）（CO）（3）（bpy）]（n）（L = Cl，Br，1，n = 0; L = 4-Et-Pyridine，n = 1+）在乙腈溶液中单重态电荷转移B（1）A'态激发时的超快电子振动弛豫.此外，用TD-DFT计算了各发射态的能量、性质和分子结构。发光的特征在于在非常短的时间内具有宽的荧光带，并且在较长的时间内从a（3）A“态演变为稳态磷光光谱。通过对数据的分析，我们可以识别出三种光谱成分。前两个的特征在于衰变时间τ（1）= 85-150 fS和τ（2）= 340-1200 fs，取决于L，并且分别被识别为来自初始激发单重态的荧光和来自更高三重态（B（3）A”）的磷光。第三个分量对应于来自最低a（3）A”态的长寿命磷光。此外，发现荧光衰减时间（τ（1））对应于到两个发射三重态的系间穿越（ISC）时间。τ（2）对应于三重态之间的内转换。DFT结果表明，ISC涉及电子交换正交，主要是重新本地化，分子轨道，从而总电子动量守恒。令人惊讶的是，测得的ISC率与配体L的自旋-轨道耦合常数成反比，但我们发现ISC时间和Re-L模式的振动周期之间存在明显的相关性，这表明后者可能介导ISC在一个强烈的非绝热制度。
Ultrafast electronic-vibrational relaxation upon excitation of the singlet charge-transfer b(1)A' state of [Re(L)(CO)(3)(bpy)](n) (L = CI, Br, 1, n = 0; L = 4-Et-pyridine, n = 1+) in acetonitrile was investigated using the femtosecond fluorescence up-conversion technique with polychromatic detection. In addition, energies, characters, and molecular structures of the emitting states were calculated by TD-DFT. The luminescence is characterized by a broad fluorescence band at very short times, and evolves to the steady-state phosphorescence spectrum from the a(3)A'' state at longer times. The analysis of the data allows us to identify three spectral components. The first two are characterized by decay times tau(1) = 85-150 fS and tau(2) = 340-1200 fs, depending on L, and are identified as fluorescence from the initially excited singlet state and phosphorescence from a higher triplet state (b(3)A"), respectively. The third component corresponds to the long-lived phosphorescence from the lowest a(3)A" state. In addition, it is found that the fluorescence decay time (tau(1)) corresponds to the intersystem crossing (ISC) time to the two emissive triplet states. tau(2) corresponds to internal conversion among triplet states. DFT results show that ISC involves electron exchange in orthogonal, largely Re-localized, molecular orbitals, whereby the total electron momentum is conserved. Surprisingly, the measured ISC rates scale inversely with the spin-orbit coupling constant of the ligand L, but we find a clear correlation between the ISC times and the vibrational periods of the Re-L mode, suggesting that the latter may mediate the ISC in a strongly nonadiabatic regime.