Department Chemie und Pharmazie, Physikalische Chemie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstraße 3, 91058, Erlangen, Germany.
Departamento de Química Inorgánica, Analítica y Química Física, Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Pabellón 2, Ciudad Universitaria, C1428EHA, Buenos Aires, Argentina.
Chemistry. 2022 Jul 20;28(41):e202200269. doi: 10.1002/chem.202200269. Epub 2022 Jun 13.
We report high-valent iron complexes supported by N-heterocyclic carbene (NHC)-anchored, bis-phenolate pincer ligands that undergo ligand-to-metal charge transfer (LMCT) upon photoexcitation. The resulting excited states - with a lifetime in the picosecond range - feature a ligand-based, mixed-valence system and intense intervalence charge transfer bands in the near-infrared region. Upon oxidation of the complex, corresponding intervalence charge transfer absorptions are also observed in the ground state. We suggest that the spectroscopic hallmarks of such LMCT states provide useful tools to decipher excited-state decay mechanisms in high-valent NHC complexes. Our observations further indicate that NHC-anchored, bis-phenolate pincer ligands are not sufficiently strong donors to prevent the population of excited metal-centered states in high-valent iron complexes.
我们报告了由 N-杂环卡宾（NHC）锚定的双酚配体支持的高价铁配合物，这些配合物在光激发下会发生配体到金属的电荷转移（LMCT）。由此产生的激发态 - 寿命在皮秒范围内 - 具有基于配体的混合价系统和近红外区域中强烈的分子内电荷转移带。在配合物被氧化后，在基态也观察到相应的分子内电荷转移吸收。我们认为，这种 LMCT 态的光谱特征为解析高价 NHC 配合物中的激发态衰减机制提供了有用的工具。我们的观察结果进一步表明，NHC 锚定的双酚配体不是足够强的供体，无法阻止高价铁配合物中激发的金属中心态的占据。
