期刊
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
卷 143, 期 38, 页码 15800-15811出版社
AMER CHEMICAL SOC
DOI: 10.1021/jacs.1c07345
关键词
-
资金
- Independent Research Fund Denmark [9059-00003B]
- Swiss National Science Foundation [200021_178760, 206021_157687]
- Swiss National Science Foundation (SNF) [206021_157687] Funding Source: Swiss National Science Foundation (SNF)
Introducing pyrene units into the diisocyanide ligand backbone significantly enhances the luminescence quantum yield and MLCT lifetime of a chromium(0) isocyanide complex by nearly two orders of magnitude. The enlarged pi-conjugation system in the ligand leads to a strongly delocalized MLCT state, reducing nonradiative relaxation despite a redshift of the emission wavelength. Luminescence properties of the complex exhibit a unique solvent polarity-dependent behavior, indicating two competing mechanisms for MLCT deactivation.
There is a long-standing interest in iron(II) complexes that emit from metal-to-ligand charge transfer (MLCT) excited states, analogous to ruthenium(II) polypyridines. The 3d(6) electrons of iron(II) are exposed to a relatively weak ligand field, rendering nonradiative relaxation of MLCT states via metal-centered excited states undesirably efficient. For isoelectronic chromium(0), chelating diisocyanide ligands recently provided access to very weak MLCT emission in solution at room temperature. Here, we present a concept that boosts the luminescence quantum yield of a chromium(0) isocyanide complex by nearly 2 orders of magnitude, accompanied by a significant increase of the MLCT lifetime. Pyrene units in the diisocyanide ligand backbone lead to an enlarged pi-conjugation system and to a strongly delocalized MLCT state, from which nonradiative relaxation is less dominant despite a sizable redshift of the emission. While the pyrene moiety is electronically coupled to the core of the chromium(0) complex in the excited state, UV-vis absorption and 2D NMR spectroscopy show that this is not the case in the ground state. Luminescence lifetimes and quantum yields for our pyrenyl-decorated chromium(0) complex exhibit an unusual bell-shaped dependence on solvent polarity, indicative of two counteracting effects governing the MLCT deactivation. These two effects are identified as predominant deactivation either through an energetically nearby lying metal-centered state in the most apolar solvents, or alternatively via direct nonradiative relaxation to the ground state following the energy gap law in more polar solvents. This is the first example of a 3d(6) MLCT emitter to benefit from an increased pi-conjugation network.
作者
我是这篇论文的作者
点击您的名字以认领此论文并将其添加到您的个人资料中。
推荐
暂无数据