Department of Chemistry and Biochemistry, University of Texas at El Paso, El Paso, Texas 79968, USA.
J Chem Phys. 2022 Aug 21;157(7):074306. doi: 10.1063/5.0094380.
In this computational study, the electronic structure changes along the oxidative and reductive quenching cycles of a homoleptic and a heteroleptic prototype Cu(I) photoredox catalyst, namely, [Cu(dmp)] (dmp = 2,9-dimethyl-1,10-phenanthroline) and [Cu(phen)(POP)] (POP = bis [2-(diphenylphosphino)phenyl]ether), are scrutinized and characterized using quasi-restricted orbitals (QROs), electron density differences, and spin densities. After validating our density functional theory-based computational protocol, the equilibrium geometries and wavefunctions (using QROs and atom/fragment compositions) of the four states involved in photoredox cycle (S, T, D, and D) are systematically and thoroughly described. The formal ground and excited state ligand- and metal-centered redox events are substantiated by the QRO description of the open-shell triplet metal-to-ligand charge-transfer (MLCT) (dL), D (dL), and D (dL) species and the corresponding structural changes, e.g., flattening distortion, shortening/elongation of Cu-N/Cu-P bonds, are rationalized in terms of the underlying electronic structure transformations. Among others, we reveal the molecular-scale delocalization of the ligand-centered radical in the MLCT (dL) and D (dL) states of homoleptic [Cu(dmp)] and its localization to the redox-active phenanthroline ligand in the case of heteroleptic [Cu(phen)(POP)].
在这项计算研究中，我们详细研究和描述了均配型和杂配型铜（I）光氧化还原催化剂原型[Cu(dmp)]（dmp=2,9-二甲基-1,10-菲咯啉）和[Cu(phen)(POP)]（POP=双[2-(二苯基膦基)苯基]醚）在氧化和还原猝灭循环中电子结构的变化，使用准限制轨道（QROs）、电子密度差和自旋密度。在验证了我们基于密度泛函理论的计算方案后，我们系统而彻底地描述了光氧化还原循环（S、T、D 和 D）中涉及的四个状态的平衡几何形状和波函数（使用 QROs 和原子/片段组成）。通过对开壳三重态金属-配体电荷转移（MLCT）（dL）、D（dL）和 D（dL）物种的 QRO 描述以及相应的结构变化（例如，平面扭曲、Cu-N/Cu-P 键的缩短/伸长），证实了配体中心自由基的形式基态和激发态的配体和金属中心氧化还原事件，这些变化可以根据潜在的电子结构转化来合理化。除其他外，我们揭示了均配型[Cu(dmp)]的 MLCT（dL）和 D（dL）态中配体中心自由基的分子尺度离域化及其在杂配型[Cu(phen)(POP)]中向氧化还原活性菲咯啉配体的局部化。
