一类[Os(II)(CO)3(tfa)(L)](L=O^O,O^N,N^N)配合物的结构和光谱特征

采用密度泛函理论以及B3LYP方法和单激发组态相互作用(CIS)方法分别优化了一系列[Os(II)(CO)3(tfa)(L)](tfa为三氟乙酸; L=O^O(1), O^N(2), N^N(3), 其中O^O为六氟乙酰丙酮, O^N为羟基喹啉, N^N为3-(三氟甲基)-5-(2-吡啶基)吡唑)配合物的基态和激发态结构. 利用含时密度泛函理论(TD-DFT)结合极化连续溶剂化模型(PCM)计算了配合物在CH2Cl2溶液中的吸收和发射光谱. 研究结果表明, 优化得到的几何结构参数和相应的实验值符合得非常好, 激发态几何构型相对基态变化较小, 这与实验上观察到的较小的斯托克斯频移现象一致. 配合物1-3的最低能吸收分别在342、431和329 nm, 其磷光发射分别在521、638 和488 nm. 配合物1-3的最高占据分子轨道和最低空轨道主要表现为L配体的π和π*轨道特征, 所以它们的最低能吸收归属于π-π*电荷跃迁, 并混有少量的金属到配体的电荷跃迁(MLCT)和配体之间电荷跃迁(LLCT)微扰, 且其高能吸收也表现为配体内部(IL)和配体间(LL)的电荷跃迁. 此外, 它们的磷光发射和吸收有相似的跃迁特征.

Structures and Spectroscopic Properties for a Series of [Os(II)(CO)3(tfa)(L)] (L=O^O,O^N,N^N) Complexes

The geometries, electronic structures and spectroscopic properties for a series of osmium(II) complexes [Os(II)(CO)3(tfa)(L)](tfa=trifluoroacetate; L=O^O (1), O^N (2),N^N (3), O^O=hexafluoroacetylacetonate, O^N=quinolinolate, N^N=3-(trifluoromethyl)-5-(2-pyridyl) pyrazole) were investigated theoretically. The Becke’s three parameter functional, the Lee-Yang-Parr (B3LYP) functional and single-excitation configuration interaction (CIS) methods were used to optimize the ground and excited states for complexes 1-3. The time-dependent density functional theory (TD-DFT) at B3LYP level with the polarized continuum model (PCM) was employed to obtain their absorption and phosphorescent emission spectra in CH2Cl2 based on their optimized ground and excited states geometries. The results revealed that the optimized structural parameters agreed well with the corresponding experimental results. There were slight structural differences between ground and excited states, and this was in agreement with the small Stokes-shift observed in the experiments. The lowest-lying absorptions were at 342, 431and 329 nm, and phosphorescent emissions were at 521, 638 and 488 nm for complexes 1-3, respectively. The highest occupied molecular orbitals (HOMO) and the lowest unoccupied molecular orbitals (LUMO) of 1-3 mainly manifest as characteristic π and π* orbitals of the L ligands. The lowest-lying absorptions were thus assigned to π-π* transitions with some metal to ligand charge transfer (MLCT) and ligand to ligand charge transfer (LLCT) contributions. High energy absorptions also had intraligand charge transfer (ILCT) and LLCT characteristics. The phosphorescence emissions of these complexes have similar transition properties to their absorptions.