X-ray Structures, Photophysical Characterization, and Computational Analysis of Geometrically Constrained Copper(I)−Phenanthroline Complexes

A series of three geometrically constrained C2-symmetric Cu(I) mono-phenanthroline complexes were characterized
by X-ray structural analysis, and their photophysical properties were investigated by absorption and emission
spectroscopy. Visible light excitation yielded metal-to-ligand charge-transfer (MLCT) excited states with luminescence
lifetimes up to 155 ns. Ultrafast transient absorption spectroscopy provided further insights into the excited-state
dynamics and suggests for all three complexes the formation of a phenanthroline radical anion. In agreement with
electrochemical measurements, the data further indicate that coordinative rearrangements are involved in nonradiative
deactivation of the excited states. According to time-dependent density functional theory calculations (B3LYP/6-31G**), the major MLCT transitions are polarized along the C2 axis of the complex and originate predominantly
from the copper dxz orbital. The computational analysis identifies an excited-state manifold with a number of close-lying, potentially emissive triplet states and is in agreement with the multiexponential decay kinetics of the MLCT
luminescence. The relationship between structural and photophysical data of the studied Cu(I) mono-phenanthroline
complexes agrees well with current models describing the photophysics of the related Cu(I) bis-diimine complexes.

本研究对三个几何受限的C₂对称单菲咯啉合铜(I)配合物（Cu(I) mono-phenanthroline complexes）进行了X射线结构分析表征，并通过吸收与发射光谱法研究了其光物理性质。可见光激发可产生金属-配体电荷转移（metal-to-ligand charge-transfer, MLCT）激发态，其发光寿命最高可达155 ns。超快瞬态吸收光谱进一步揭示了该系列配合物的激发态动力学过程，结果表明三种配合物均会生成菲咯啉自由基阴离子（phenanthroline radical anion）。与电化学测试结果一致，上述实验数据进一步证实配位重排参与了激发态的无辐射失活过程。根据含时密度泛函理论（time-dependent density functional theory）计算（B3LYP/6-31G**），主要的MLCT跃迁沿配合物的C₂轴极化，且主要起源于铜的dxz轨道。计算分析识别出一个包含多个近简并、具备潜在发光特性的三重态的激发态流形，其结果与MLCT发光的多指数衰减动力学特征相符。本研究中所考察的单菲咯啉合铜(I)配合物的结构与光物理数据之间的关联，与当前描述相关双亚胺合铜(I)配合物（Cu(I) bis-diimine complexes）光物理行为的模型吻合良好。