Orange-glowing iron at room temperature Many photoactive coordination compounds contain precious metals. Replacing ruthenium with more–earth-abundant iron has been a long-sought goal, but iron compounds generally relax too rapidly after light absorption to channel the energy productively. Kjær et al. prepared an iron compound with an excited state stable enough to emit light for nanoseconds, or that could engage in bimolecular electron transfer (see the Perspective by Young and Oldacre). Targeting a ligand-to-metal rather than metal-to-ligand charge-transfer state was key to the achievement, as was the octahedral coordination environment rigidly enforced by two tridentate carbene ligands. Science, this issue p. 249; see also p. 225 Targeting ligand-to-metal instead of metal-to-ligand charge transfer extends iron’s photoactivity to a nanosecond time frame. Iron’s abundance and rich coordination chemistry are potentially appealing features for photochemical applications. However, the photoexcitable charge-transfer states of most iron complexes are limited by picosecond or subpicosecond deactivation through low-lying metal-centered states, resulting in inefficient electron-transfer reactivity and complete lack of photoluminescence. In this study, we show that octahedral coordination of iron(III) by two mono-anionic facial tris-carbene ligands can markedly suppress such deactivation. The resulting complex [Fe(phtmeimb)2]+, where phtmeimb is {phenyl[tris(3-methylimidazol-1-ylidene)]borate}−, exhibits strong, visible, room temperature photoluminescence with a 2.0-nanosecond lifetime and 2% quantum yield via spin-allowed transition from a doublet ligand-to-metal charge-transfer (2LMCT) state to the doublet ground state. Reductive and oxidative electron-transfer reactions were observed for the 2LMCT state of [Fe(phtmeimb)2]+ in bimolecular quenching studies with methylviologen and diphenylamine.

中文翻译：

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具有纳秒寿命的电荷转移激发铁络合物的发光和反应性

室温下发橙色光的铁 许多光活性配位化合物含有贵金属。用地球上含量更高的铁代替钌是一个长期追求的目标，但铁化合物通常在光吸收后松弛得太快，无法有效地引导能量。Kjær 等人。制备了一种激发态足够稳定的铁化合物，可以在纳秒内发光，或者可以参与双分子电子转移（参见 Young 和 Oldacre 的观点）。靶向配体到金属而不是金属到配体的电荷转移状态是这一成就的关键，两个三齿卡宾配体严格执行的八面体配位环境也是如此。科学，这个问题 p。249; 另见第。225 靶向配体到金属而不是金属到配体的电荷转移将铁的光活性扩展到纳秒时间范围。铁的丰度和丰富的配位化学是光化学应用的潜在吸引力特征。然而，大多数铁配合物的光激发电荷转移状态受到皮秒或亚皮秒失活的限制，通过低位金属中心状态导致电子转移反应效率低下和完全缺乏光致发光。在这项研究中，我们表明铁（III）通过两个单阴离子面部三卡宾配体的八面体配位可以显着抑制这种失活。得到的复合物 [Fe(phtmeimb)2]+，其中 phtmeimb 是{苯基[三(3-甲基咪唑-1-亚基)]硼酸盐}-，显示出强的、可见的、室温光致发光和 2。通过自旋允许从双配体到金属电荷转移 (2LMCT) 状态到双基基态的转变，实现了 0 纳秒的寿命和 2% 的量子产率。在用甲基紫精和二苯胺进行双分子淬灭研究中，观察到 [Fe(phtmeimb)2]+ 的 2LMCT 状态的还原和氧化电子转移反应。