Excited-State Bond Contraction and Charge Migration in a Platinum Dimer Complex Characterized by X-ray and Optical Transient Absorption Spectroscopy
Excited-State Bond Contraction and Charge Migration in a Platinum Dimer Complex Characterized by X-ray and Optical Transient Absorption Spectroscopy
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X 射线和光学瞬态吸收光谱表征铂二聚体复合物中的激发态键收缩和电荷迁移
DOI：
10.1021/acs.jpca.1c07201
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Chen, Lin X.
中科院分区：
文献类型：
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作者：
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.
二聚体过渡金属络合物(TMC)中金属中心之间的相互作用在其激发态能级和途径中起着重要的作用，从而影响其在光致发光材料和光催化等方面的应用。在这里，我们报道了两种光激发光型吡唑桥联[Pt(Ppy)(μ-R2pz)]2型铂(II)二聚体(ppy=2-苯基吡啶，μ-R2pz=3，5-取代吡唑醇)的电子和核结构动力学研究：[PT(Ppy)(μ-2pz)]2(1)和[Pt(ndi-ppy)(μ-Ph2pz)]2(2，ndi=1，4，5，8-萘二酰亚胺)，两者具有不同的基态铂距离。X射线瞬时吸收谱(XTA)表明，由于铂中心1和2的单电子氧化，产生了一个新的d轨道空位。然而，虽然在2中观察到了瞬时的铂-铂收缩，但在1中完全没有这种影响，这表明这些配合物的激发态是如何由铂(Dz2)轨道的重叠决定的，而重叠是由3-和5-位的吡唑基R-基团的空间体积所调节的。在分析铂-铂距离结构参数的同时，我们观察到在ppy配体上存在一个共价连接的NDI受体的光致电子转移。利用光学暂态吸收光谱检测了光激发下NDI自由基阴离子吸收信号的形成和随后的衰减。NDI自由基阴离子的衰变与XTA测量中观察到的被氧化的铂-铂核的d轨道空位信号的衰变时间相同，为数百皮秒。数据表明，电荷分离态的超快形成和随后的电荷复合形成了原始的铂(II-II)物种。
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-R2pz)]2-type Pt(II) dimers (ppy = 2-phenylpyridine, μ-R2pz = 3,5-substituted pyrazolate): [Pt(ppy)(μ-H2pz)]2(1) and [Pt(NDI-ppy)(μ-Ph2pz)]2(2, 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 LIII-edge revealed a new d-orbital vacancy due to the one-electron oxidation of the Pt centers in1and2. However, while a transient Pt–Pt contraction was observed in2, such an effect was completely absent in1, demonstrating how the excited states of these complexes are determined by the overlap of the Pt (dz2) 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 in2featuring 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.