Weingartz Nicholas P, Mara Michael W, Roy Subhangi, Hong Jiyun, Chakraborty Arnab, Brown-Xu Samantha E, Phelan Brian T, Castellano Felix N, Chen Lin X
Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States.
Chemical Science and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States.
J Phys Chem A. 2021 Oct 14;125(40):8891-8898. doi: 10.1021/acs.jpca.1c07201. Epub 2021 Oct 1.
Interactions between metal centers in dimeric transition metal complexes (TMCs) play important roles in their excited-state energetics and pathways and, thus, affect their photophysical properties relevant to their applications, for example, photoluminescent materials and photocatalysis. Here, we report electronic and nuclear structural dynamics studies of two photoexcited pyrazolate-bridged [Pt(ppy)(μ-Rpz)]-type Pt(II) dimers (ppy = 2-phenylpyridine, μ-Rpz = 3,5-substituted pyrazolate): [Pt(ppy)(μ-Hpz)] () and [Pt(NDI-ppy)(μ-Phpz)] (, NDI = 1,4,5,8-naphthalenediimide), both of which have distinct ground-state Pt-Pt distances. X-ray transient absorption (XTA) spectroscopy at the Pt L-edge revealed a new d-orbital vacancy due to the one-electron oxidation of the Pt centers in and . However, while a transient Pt-Pt contraction was observed in , such an effect was completely absent in , demonstrating how the excited states of these complexes are determined by the overlap of the Pt (d) orbitals, which is tuned by the steric bulk of the pyrazolate R-groups in the 3- and 5-positions. In tandem with analysis of the Pt-Pt distance structural parameter, we observed photoinduced electron transfer in featuring a covalently linked NDI acceptor on the ppy ligand. The formation and subsequent decay of the NDI radical anion absorption signals were detected upon photoexcitation using optical transient absorption spectroscopy. The NDI radical anion decayed on the same time scale, hundreds of picoseconds, as that of the d-orbital vacancy signal of the oxidized Pt-Pt core observed in the XTA measurements. The data indicated an ultrafast formation of the charge-separated state and subsequent charge recombination to the original Pt(II-II) species.
二聚体过渡金属配合物（TMCs）中金属中心之间的相互作用在其激发态能量学和途径中起着重要作用，因此会影响其与应用相关的光物理性质，例如光致发光材料和光催化。在此，我们报告了两种光激发的吡唑盐桥连的[Pt(ppy)(μ-Rpz)]型Pt(II)二聚体（ppy = 2-苯基吡啶，μ-Rpz = 3,5-取代的吡唑盐）的电子和核结构动力学研究：[Pt(ppy)(μ-Hpz)]（）和[Pt(NDI-ppy)(μ-Phpz)]（，NDI = 1,4,5,8-萘二酰亚胺），两者具有不同的基态Pt-Pt距离。在Pt L边的X射线瞬态吸收（XTA）光谱揭示了由于和中Pt中心的单电子氧化而产生的一个新的d轨道空位。然而，虽然在中观察到了瞬态Pt-Pt收缩，但在中完全没有这种效应，这表明这些配合物的激发态是如何由Pt(d)轨道的重叠决定的，而这种重叠是由3-和5-位吡唑盐R基团的空间位阻调节的。与Pt-Pt距离结构参数的分析相结合，我们在具有共价连接在ppy配体上的NDI受体的中观察到了光诱导电子转移。使用光学瞬态吸收光谱在光激发时检测到了NDI自由基阴离子吸收信号的形成和随后的衰减。NDI自由基阴离子在与XTA测量中观察到的氧化Pt-Pt核的d轨道空位信号相同的时间尺度上，即数百皮秒内衰减。数据表明电荷分离态的超快形成以及随后向原始Pt(II-II)物种的电荷复合。
