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Tracking the picosecond deactivation dynamics of a photoexcited iron carbene complex by time-resolved X-ray scattering
Chemical Science ( IF 7.6 ) Pub Date : 2017-10-31 00:00:00 , DOI: 10.1039/c7sc02815f Denis Leshchev 1, 2, 3 , Tobias C. B. Harlang 4, 5, 6, 7, 8 , Lisa A. Fredin 5, 6, 7, 9 , Dmitry Khakhulin 10, 11, 12 , Yizhu Liu 5, 7, 13, 14, 15 , Elisa Biasin 8, 16, 17, 18, 19 , Mads G. Laursen 8, 16, 17, 18, 19 , Gemma E. Newby 1, 2, 3 , Kristoffer Haldrup 8, 16, 17, 18, 19 , Martin M. Nielsen 8, 16, 17, 18, 19 , Kenneth Wärnmark 5, 7, 13, 14, 15 , Villy Sundström 4, 5, 6, 7 , Petter Persson 5, 6, 7, 9 , Kasper S. Kjær 4, 5, 6, 7, 8 , Michael Wulff 1, 2, 3
Chemical Science ( IF 7.6 ) Pub Date : 2017-10-31 00:00:00 , DOI: 10.1039/c7sc02815f Denis Leshchev 1, 2, 3 , Tobias C. B. Harlang 4, 5, 6, 7, 8 , Lisa A. Fredin 5, 6, 7, 9 , Dmitry Khakhulin 10, 11, 12 , Yizhu Liu 5, 7, 13, 14, 15 , Elisa Biasin 8, 16, 17, 18, 19 , Mads G. Laursen 8, 16, 17, 18, 19 , Gemma E. Newby 1, 2, 3 , Kristoffer Haldrup 8, 16, 17, 18, 19 , Martin M. Nielsen 8, 16, 17, 18, 19 , Kenneth Wärnmark 5, 7, 13, 14, 15 , Villy Sundström 4, 5, 6, 7 , Petter Persson 5, 6, 7, 9 , Kasper S. Kjær 4, 5, 6, 7, 8 , Michael Wulff 1, 2, 3
Affiliation
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Recent years have seen the development of new iron-centered N-heterocyclic carbene (NHC) complexes for solar energy applications. Compared to typical ligand systems, the NHC ligands provide Fe complexes with longer-lived metal-to-ligand charge transfer (MLCT) states. This increased lifetime is ascribed to strong ligand field splitting provided by the NHC ligands that raises the energy levels of the metal centered (MC) states and therefore reduces the deactivation efficiency of MLCT states. Among currently known NHC systems, [Fe(btbip)2]2+ (btbip = 2,6-bis(3-tert-butyl-imidazol-1-ylidene)pyridine) is a unique complex as it exhibits a short-lived MC state with a lifetime on the scale of a few hundreds of picoseconds. Hence, this complex allows for a detailed investigation, using 100 ps X-ray pulses from a synchrotron, of strong ligand field effects on the intermediate MC state in an NHC complex. Here, we use time-resolved wide angle X-ray scattering (TRWAXS) aided by density functional theory (DFT) to investigate the molecular structure, energetics and lifetime of the high-energy MC state in the Fe–NHC complex [Fe(btbip)2]2+ after excitation to the MLCT manifold. We identify it as a 260 ps metal-centered quintet (5MC) state, and we refine the molecular structure of the excited-state complex verifying the DFT results. Using information about the hydrodynamic state of the solvent, we also determine, for the first time, the energy of the 5MC state as 0.75 ± 0.15 eV. Our results demonstrate that due to the increased ligand field strength caused by NHC ligands, upon transition from the ground state to the 5MC state, the metal to ligand bonds extend by unusually large values: by 0.29 Å in the axial and 0.21 Å in the equatorial direction. These results imply that the transition in the photochemical properties from typical Fe complexes to novel NHC compounds is manifested not only in the destabilization of the MC states, but also in structural distortion of these states.
中文翻译：
通过时间分辨X射线散射跟踪光激发的铁卡宾络合物的皮秒失活动力学
近年来，已经看到了用于太阳能应用的新型以铁为中心的N-杂环卡宾（NHC）配合物的开发。与典型的配体体系相比，NHC配体为Fe络合物提供了寿命更长的金属到配体电荷转移（MLCT）状态。这种增加的寿命归因于NHC配体提供的强配体场分裂，这会提高金属居中（MC）态的能级，从而降低MLCT态的失活效率。在当前已知的NHC系统中，[Fe（btbip）2 ] 2+（btbip = 2,6-bis（3- tert-丁基-咪唑-1-基吡啶）是一种独特的络合物，因为它具有短暂的MC状态，寿命长达几百皮秒。因此，该复合物允许使用来自同步加速器的100 ps X射线脉冲对NHC复合物中中间MC态的强配体场效应进行详细研究。在这里，我们使用时间分辨广角X射线散射（TRWAXS）借助密度泛函理论（DFT）来研究Fe-NHC络合物[Fe（btbip ）2 ] 2+激励到MLCT歧管后。我们将其确定为260 ps以金属为中心的五重奏（5MC）状态，并且我们完善了激发态配合物的分子结构，从而验证了DFT结果。我们还使用有关溶剂的流体动力学状态的信息，首次将5 MC状态的能量确定为0.75±0.15 eV。我们的结果表明，由于NHC配体引起的配体场强增加，从基态跃迁到5 MC态时，金属与配体之间的键扩展了异常大的值：轴向为0.29Å，轴向为0.21Å。赤道方向。这些结果表明，光化学性质从典型的Fe配合物向新型NHC化合物的转变不仅表现为MC状态的不稳定，而且表现为这些状态的结构变形。
更新日期：2017-11-08
中文翻译：
通过时间分辨X射线散射跟踪光激发的铁卡宾络合物的皮秒失活动力学
近年来，已经看到了用于太阳能应用的新型以铁为中心的N-杂环卡宾（NHC）配合物的开发。与典型的配体体系相比，NHC配体为Fe络合物提供了寿命更长的金属到配体电荷转移（MLCT）状态。这种增加的寿命归因于NHC配体提供的强配体场分裂，这会提高金属居中（MC）态的能级，从而降低MLCT态的失活效率。在当前已知的NHC系统中，[Fe（btbip）2 ] 2+（btbip = 2,6-bis（3- tert-丁基-咪唑-1-基吡啶）是一种独特的络合物，因为它具有短暂的MC状态，寿命长达几百皮秒。因此，该复合物允许使用来自同步加速器的100 ps X射线脉冲对NHC复合物中中间MC态的强配体场效应进行详细研究。在这里，我们使用时间分辨广角X射线散射（TRWAXS）借助密度泛函理论（DFT）来研究Fe-NHC络合物[Fe（btbip ）2 ] 2+激励到MLCT歧管后。我们将其确定为260 ps以金属为中心的五重奏（5MC）状态，并且我们完善了激发态配合物的分子结构，从而验证了DFT结果。我们还使用有关溶剂的流体动力学状态的信息，首次将5 MC状态的能量确定为0.75±0.15 eV。我们的结果表明，由于NHC配体引起的配体场强增加，从基态跃迁到5 MC态时，金属与配体之间的键扩展了异常大的值：轴向为0.29Å，轴向为0.21Å。赤道方向。这些结果表明，光化学性质从典型的Fe配合物向新型NHC化合物的转变不仅表现为MC状态的不稳定，而且表现为这些状态的结构变形。
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