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The Carbene Cannibal: Photoinduced Symmetry-Breaking Charge Separation in an Fe(III) N-Heterocyclic Carbene
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2021-07-15 , DOI: 10.1021/jacs.1c03770 Nidhi Kaul 1 , Reiner Lomoth 1
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2021-07-15 , DOI: 10.1021/jacs.1c03770 Nidhi Kaul 1 , Reiner Lomoth 1
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Photoinduced symmetry-breaking charge separation (SB-CS) processes offer the possibility of harvesting solar energy by electron transfer between identical molecules. Here, we present the first case of direct observation of bimolecular SB-CS in a transition metal complex, [FeIIIL2](PF6) (L = [phenyl(tris(3-methylimidazol-1-ylidene))borate]−). Photoexcitation of the complex in the visible region results in the formation of a doublet ligand-to-metal charge transfer (2LMCT) excited state (E0–0 = 2.13 eV), which readily reacts with the doublet ground state to generate charge separated products, [FeIIL2] and [FeIVL2]2+, with a measurable cage escape yield. Known spectral signatures allow for unambiguous identification of the products, whose formation and recombination are monitored with transient absorption spectroscopy. The unusual energetic landscape of [FeIIIL2]+, as reflected in its ground and excited state reduction potentials, results in SB-CS being intrinsically exergonic (ΔGCS° ∼ −0.7 eV). This is in contrast to most systems investigated in the literature, where ΔGCS° is close to zero, and the charge transfer driven primarily by solvation effects. The study is therefore illustrative for the utilization of the rich redox chemistry accessible in transition metal complexes for the realization of SB-CS.
中文翻译：
卡宾食人族：Fe(III) N-杂环卡宾中的光致对称破坏电荷分离
光致对称破坏电荷分离 (SB-CS) 过程提供了通过相同分子之间的电子转移来收集太阳能的可能性。在这里，我们展示了第一个直接观察过渡金属络合物中双分子 SB-CS 的案例，[Fe III L 2 ](PF 6 ) (L = [苯基(三(3-甲基咪唑-1-亚基))硼酸盐] - )。复合物在可见光区的光激发导致形成双配体到金属电荷转移 ( 2 LMCT) 激发态 ( E 0–0 = 2.13 eV)，它很容易与双基态反应产生电荷分离产物，[Fe II L 2 ] 和 [FeIV L 2 ] 2+，具有可测量的笼逃逸率。已知的光谱特征允许明确识别产物，其形成和重组由瞬态吸收光谱监测。[Fe III L 2 ] +不寻常的能量景观，如其基态和激发态还原电位所反映的那样，导致 SB-CS 本质上是放能的（Δ G CS ° ~ -0.7 eV）。这与文献中研究的大多数系统形成对比，其中 Δ G CS° 接近于零，电荷转移主要由溶剂化效应驱动。因此，该研究说明了利用过渡金属络合物中丰富的氧化还原化学来实现 SB-CS。
更新日期：2021-07-28
中文翻译：
卡宾食人族：Fe(III) N-杂环卡宾中的光致对称破坏电荷分离
光致对称破坏电荷分离 (SB-CS) 过程提供了通过相同分子之间的电子转移来收集太阳能的可能性。在这里，我们展示了第一个直接观察过渡金属络合物中双分子 SB-CS 的案例，[Fe III L 2 ](PF 6 ) (L = [苯基(三(3-甲基咪唑-1-亚基))硼酸盐] - )。复合物在可见光区的光激发导致形成双配体到金属电荷转移 ( 2 LMCT) 激发态 ( E 0–0 = 2.13 eV)，它很容易与双基态反应产生电荷分离产物，[Fe II L 2 ] 和 [FeIV L 2 ] 2+，具有可测量的笼逃逸率。已知的光谱特征允许明确识别产物，其形成和重组由瞬态吸收光谱监测。[Fe III L 2 ] +不寻常的能量景观，如其基态和激发态还原电位所反映的那样，导致 SB-CS 本质上是放能的（Δ G CS ° ~ -0.7 eV）。这与文献中研究的大多数系统形成对比，其中 Δ G CS° 接近于零，电荷转移主要由溶剂化效应驱动。因此，该研究说明了利用过渡金属络合物中丰富的氧化还原化学来实现 SB-CS。
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