Zimmer Peter, Burkhardt Lukas, Friedrich Aleksej, Steube Jakob, Neuba Adam, Schepper Rahel, Müller Patrick, Flörke Ulrich, Huber Marina, Lochbrunner Stefan, Bauer Matthias
Department Chemie, Universität Paderborn , Warburger Straße 100, 33098 Paderborn, Germany.
Institute of Physics, University of Rostock , Albert-Einstein-Str. 23, 18059 Rostock, Germany.
Inorg Chem. 2018 Jan 2;57(1):360-373. doi: 10.1021/acs.inorgchem.7b02624. Epub 2017 Dec 13.
Four homo- and heteroleptic complexes bearing both polypyridyl units and N-heterocyclic carbene (NHC) donor functions are studied as potential noble metal-free photosensitizers. The complexes [Fe(L1)(terpy)][PF], [Fe(L2)][PF], [Fe(L1)(L3)][PF], and [Fe(L3)][PF] (terpy = 2,2':6',2″ terpyridine, L1 = 2,6-bis[3-(2,6-diisopropylphenyl)imidazol-2-ylidene]pyridine, L2 = 2,6-bis[3-isopropylimidazol-2-ylidene]pyridine, L3 = 1-(2,2'-bipyridyl)-3-methylimidazol-2-ylidene) contain tridentate ligands of the C^N^C and N^N^C type, respectively, resulting in a Fe-NHC number between two and four. Thorough ground state characterization by single crystal diffraction, electrochemistry, valence-to-core X-ray emission spectroscopy (VtC-XES), and high energy resolution fluorescence detected X-ray absorption near edge structure (HERFD-XANES) in combination with ab initio calculations show a correlation between the geometric and electronic structure of these new compounds and the number of the NHC donor functions. These results serve as a basis for the investigation of the excited states by ultrafast transient absorption spectroscopy, where the lifetime of the MLCT states is found to increase with the NHC donor count. The results demonstrate for the first time the close interplay between the number of NHC functionalities in Fe(II) complexes and their photochemical properties, as revealed in a comparison of the activity as photosensitizers in photocatalytic proton reduction.
研究了四种同时带有多吡啶单元和N-杂环卡宾（NHC）供体功能的同配和异配配合物，作为潜在的无贵金属光敏剂。配合物[Fe(L1)(terpy)][PF]、[Fe(L2)][PF]、[Fe(L1)(L3)][PF]和[Fe(L3)][PF]（terpy = 2,2':6',2″-三联吡啶，L1 = 2,6-双[3-(2,6-二异丙基苯基)咪唑-2-亚基]吡啶，L2 = 2,6-双[3-异丙基咪唑-2-亚基]吡啶，L3 = 1-(2,2'-联吡啶)-3-甲基咪唑-2-亚基）分别包含C^N^C型和N^N^C型三齿配体，导致Fe-NHC数量在两个到四个之间。通过单晶衍射、电化学、价层到芯层X射线发射光谱（VtC-XES）和高能量分辨率荧光检测X射线吸收近边结构（HERFD-XANES）结合从头算计算对基态进行了全面表征，结果表明这些新化合物的几何结构和电子结构与NHC供体功能的数量之间存在相关性。这些结果为通过超快瞬态吸收光谱研究激发态奠定了基础，研究发现MLCT态的寿命随NHC供体数量的增加而延长。在光催化质子还原中作为光敏剂的活性比较中揭示了Fe(II)配合物中NHC官能团数量与其光化学性质之间的密切相互作用，这是首次得到证实。
