Max Planck Institute for Chemical Energy Conversion, Stiftstrasse 34-36, Mülheim an der Ruhr, 45470, Germany.
Institute of Chemical Research of Catalonia (ICIQ), Avinguda Països Catalans 16, 43007, Tarragona, Spain.
Chemistry. 2018 Apr 25;24(24):6464-6472. doi: 10.1002/chem.201800330. Epub 2018 Apr 14.
We report the light-induced electronic and geometric changes taking place within a heteroleptic Cu photosensitizer, namely [(xant)Cu(Me phenPh )]PF (xant=xantphos, Me phenPh =bathocuproine), by time-resolved X-ray absorption spectroscopy in the ps-μs time regime. Time-resolved X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analysis enabled the elucidation of the electronic and structural configuration of the copper center in the excited state as well as its decay dynamics in different solvent conditions with and without triethylamine acting as a sacrificial electron donor. A three-fold decrease in the decay lifetime of the excited state is observed in the presence of triethylamine, showing the feasibility of the reductive quenching pathway in the latter case. A prominent pre-edge feature is observed in the XANES spectrum of the excited state upon metal to charge ligand transfer transition, showing an increased hybridization of the 3d states with the ligand p orbitals in the tetrahedron around the Cu center. EXAFS and density functional theory illustrate a significant shortening of the Cu-N and an elongation of the Cu-P bonds together with a decrease in the torsional angle between the xantphos and bathocuproine ligand. This study provides mechanistic time-resolved understanding for the development of improved heteroleptic Cu photosensitizers, which can be used for the light-driven production of hydrogen from water.
我们通过皮秒到微秒时间范围内的时间分辨 X 射线吸收光谱报告了杂配 Cu 敏化剂[(xant)Cu(Me phenPh )]PF（xant=xantphos，Me phenPh =bathocuproine）中发生的光诱导电子和几何变化。时间分辨 X 射线吸收近边结构（XANES）和扩展 X 射线吸收精细结构（EXAFS）分析使我们能够阐明铜中心在激发态下的电子和结构构型及其在不同溶剂条件下的衰减动力学，其中包括三乙胺作为牺牲电子供体的情况。在存在三乙胺的情况下，观察到激发态衰减寿命缩短了三倍，这表明在后一种情况下存在还原猝灭途径的可行性。在金属到电荷配体转移跃迁过程中，观察到激发态的 XANES 光谱中出现了明显的预边特征，表明 Cu 中心周围四面体中 3d 态与配体 p 轨道的杂化增强。EXAFS 和密度泛函理论表明，Cu-N 键显著缩短，Cu-P 键伸长，xantphos 和 bathocuproine 配体之间的扭转角减小。这项研究为开发改进的杂配 Cu 敏化剂提供了机制性的时间分辨理解，可用于光驱动水制氢。
