Facile non‐radiative decay of low‐lying metal‐centered (MC) d‐d excited states has been well documented to pose a significant obstacle to the development of phosphorescent NiII complexes due to substantial structural distortions between the d‐d excited state and the ground state. Herein, we prepared a series of dinuclear Ni2II,II complexes by using strong σ‐donors, carbene‐phenyl‐carbene (CNHC^Cphenyl^CNHC) pincer ligands, and prepared their dinuclear Pt2II,II and Pd2II,II analogues. Dinuclear Ni2II,II complexes bridged by formamidinate/α‐carbolinato ligand exhibit short Ni‐Ni distances of 2.947‐3.054 Å and singlet metal‐metal‐to‐ligand charge transfer (1MMLCT) transitions at 500‐550 nm. Their 1MMLCT absorption energies are red‐shifted relative to the Pt2II,II and Pd2II,II analogues at ~450 nm and ≤420 nm respectively. One‐electron oxidation of these Ni2II,II complexes produces valence‐trapped dinuclear Ni2II,III species, which are characterized by EPR spectroscopy. Upon photoexcitation, these Ni2II,II complexes display phosphorescence (τ=2.6‐8.6 μs) in the NIR (800‐1400nm) spectral region in 2‐MeTHF and in solid state at 77 K, which is insensitive to π‐conjugation of the coordinated [CNHC^Cphenyl^CNHC] ligand. Combined with DFT calculations, the NIR emission is assigned to originate from the 3dd excited state. Studies have found that the dinuclear Ni2II,II complex can sensitize the formation of singlet oxygen and catalyze the oxidation of cyclo‐dienes under light irradiation.

中文翻译：

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具有金属-金属-配体电荷转移激发态和近红外发射的双核环金属化钳形镍(II)络合物


低位金属中心（MC）d-d激发态的容易非辐射衰变已被充分记录，由于d-d激发态和d-d激发态之间的严重结构扭曲，对磷光NiII配合物的开发构成了重大障碍基态。在此，我们通过使用强σ-供体卡宾-苯基-卡宾（CNHC^C苯基^CNHC）钳配体制备了一系列双核Ni2II,II配合物，并制备了它们的双核Pt2II,II和Pd2II,II类似物。由甲脒/α-羰基配体桥接的双核 Ni2II,II 配合物表现出 2.947-3.054 Å 的短 Ni-Ni 距离以及在 500-550 nm 处的单线态金属-金属-配体电荷转移 (1MMLCT) 跃迁。它们的 1MMLCT 吸收能相对于 Pt2II,II 和 Pd2II,II 类似物分别在 ~450 nm 和 ≤420 nm 处发生红移。这些 Ni2II,II 配合物的单电子氧化产生价态捕获的双核 Ni2II,III 物质，并通过 EPR 光谱进行表征。光激发后，这些 Ni2II,II 配合物在 2-MeTHF 中的 NIR (800-1400nm) 光谱区和 77 K 的固态下显示磷光 (τ=2.6-8.6 μs)，这对配位的 π 共轭不敏感。 [CNHC^C苯基^CNHC]配体。结合 DFT 计算，近红外发射被指定为源自 3dd 激发态。研究发现双核Ni2II,II配合物在光照射下可以敏化单线态氧的形成并催化环二烯的氧化。