Kruppa S V, Bäppler F, Klopper W, Walg S P, Thiel W R, Diller R, Riehn C
Department of Chemistry, TU Kaiserslautern, Erwin-Schrödinger-Str. 52, D-67663 Kaiserslautern, Germany.
Department of Physics, TU Kaiserslautern, Erwin-Schrödinger-Str. 46, D-67663 Kaiserslautern, Germany.
Phys Chem Chem Phys. 2017 Aug 30;19(34):22785-22800. doi: 10.1039/c7cp04128d.
The binuclear complex Ag(dcpm) (dcpm = bis(dicyclohexylphosphino)methane) exhibits a structure with a close silver-silver contact mediated by the bridging ligand and thus a weak argentophilic interaction. Upon electronic excitation this cooperative effect is strongly increased and determines the optical and luminescence properties of the compound. We have studied here the ultrafast electronic dynamics in parallel in gas phase by transient photodissociation and in solution by transient absorption. In particular, we report the diverse photofragmentation pathways of isolated [Ag(dcpm)] in an ion trap and its gas phase UV photodissociation spectrum. By pump-probe fragmentation action spectroscopy (λ = 260 nm) in the gas phase, we have obtained fragment-specific transients which exhibit a common ultrafast multiexponential decay. This is fitted to four time constants (0.6/5.8/100/>1000 ps), highlighting complex intrinsic photophysical processes. Remarkably, multiexponential dynamics (0.9/8.5/73/604 ps) are as well found for the relaxation dynamics in acetonitrile solution. Ab initio calculations at the level of approximate coupled-cluster singles-doubles (CC2) theory of ground and electronically excited states of the reduced model system [Ag(dmpm)] (dmpm = bis(dimethylphosphino)methane) indicate a shortening of the Ag-Ag distance upon excitation by 0.3-0.4 Å. In C geometry two close-lying singlet states S (MC(dσ*-pπ), B, 4.13 eV) and S (MC(dσ*-pσ), A, 4.45 eV) are found. The nearly dark S state has not been reported so far. The excitation of the S state carries a large oscillator strength for the calculated vertical transition (266 nm). Two related triplets are calculated at T (3.87 eV) and T (3.90 eV). From these findings we suggest possible relaxation pathways with the two short time constants ascribed to ISC/IVR and propose from the obtained similar values in gas phase that the fast solution dynamics is dominated by intramolecular processes. A further relaxation by IC/IVR in the triplet manifold is likely to account for the observed intermediate time constants. For the acetonitrile relaxation dynamics additional modifications are invoked based on solvent-induced shifts of the energy levels and the possible formation of solvent and counterion exciplexes on a longer timescale.
双核配合物Ag(dcpm)（dcpm = 双（二环己基膦基）甲烷）呈现出一种结构，其中银 - 银之间通过桥连配体介导形成紧密接触，从而存在弱的亲银相互作用。在电子激发时，这种协同效应会显著增强，并决定了该化合物的光学和发光性质。我们在此通过瞬态光解离在气相中以及通过瞬态吸收在溶液中并行研究了超快电子动力学。特别地，我们报道了离子阱中孤立的[Ag(dcpm)]的多种光解离途径及其气相紫外光解离光谱。通过气相中的泵浦 - 探测光解离作用光谱（λ = 260 nm），我们获得了特定碎片的瞬态信号，这些信号呈现出共同的超快多指数衰减。这被拟合为四个时间常数（0.6/5.8/100/>1000 ps），突出了复杂的内在光物理过程。值得注意的是，在乙腈溶液中的弛豫动力学也发现了多指数动力学（0.9/8.5/73/604 ps）。对简化模型体系[Ag(dmpm)]（dmpm = 双（二甲基膦基）甲烷）的基态和电子激发态进行近似耦合簇单双激发（CC2）理论水平的从头算计算表明，激发后Ag - Ag距离缩短了0.3 - 0.4 Å。在C几何构型中发现了两个相邻的单重态S（MC(dσ* - pπ)，B，4.13 eV）和S（MC(dσ* - pσ)，A，4.45 eV）。到目前为止尚未报道近乎暗态的S态。对于计算得到的垂直跃迁（266 nm），S态的激发具有较大的振子强度。计算出两个相关的三重态，分别为T（3.87 eV）和T（3.90 eV）。基于这些发现，我们提出了可能的弛豫途径，将两个短时间常数归因于ISC/IVR，并从气相中获得的相似值推测快速的溶液动力学主要由分子内过程主导。在三重态多重态中通过IC/IVR的进一步弛豫可能解释了观察到的中间时间常数。对于乙腈的弛豫动力学，基于能级的溶剂诱导位移以及在更长时间尺度上可能形成的溶剂和抗衡离子激基复合物，提出了额外的修正。
