Cyclometallated rhodium(iii) complexes have been underexplored as photosensitisers due to their low-lying d-d excited states, which result in weak visible-light absorption and non-emissive properties, coupled with a modest heavy atom effect that limits reactive oxygen species (ROS) generation. In this work, a series of cyclometallated rhodium(iii) polypyridine complexes appended with two rhodamine units [Rh(N^C)2(bpy-diRho)](PF6)3 was rationally designed as Type I photosensitisers. These complexes exhibited intense absorption in the visible region and moderate rhodamine fluorescence in solution upon photoexcitation. Time-resolved transient absorption spectroscopy revealed a long-lived rhodamine-based triplet excited state as the lowest-lying excited state in this hybrid system, which is attributed to the presence of the rhodium(iii) centre and is responsible for ROS photosensitisation. Notably, these rhodium(iii) complexes efficiently generated superoxide anion (O2˙-) and hydroxyl (HO˙) radicals via the Type I pathway upon photoirradiation, likely via intramolecular electron transfer between the two adjacent excited rhodamine units within the complex to form radical cation and anion. Cellular colocalisation studies demonstrated that these complexes predominantly accumulated in mitochondria, where the photosensitised ROS triggered significant mitochondrial dysfunction, resulting in their outstanding photocytotoxicity under both normoxic and CoCl2-induced hypoxic conditions. Further mechanistic investigations revealed that the photoinduced mitochondrial ROS generation triggered cancer cell death via gasdermin D-mediated pyroptosis. This rhodium(iii)-dirhodamine system further explores the utilisation of rhodium(iii) complexes as phototheranostic agents and underscores their potential in this role.
Rational design and atomically precise synthesis of efficiently low-valent single atom catalysts, particularly those in which isolated transition-metal centers are directly coordinated to highly electronegative oxygen atoms embedded within layered double hydroxide (LDH) or oxyhydroxide matrices, are pivotal for surmounting the kinetic bottlenecks of the oxygen evolution reaction (OER). In the present work, low-valent molybdenum single atoms (Mo SAs) are successfully anchored onto NiFe LDH (LSAMo-NiFe LDH) through a low-temperature solution-phase reduction process, resulting in a unique unsaturated and electron-rich Mo-O3 coordination configuration. Under identical mass loadings, LSAMo-NiFe LDH outperforms both pristine NiFe LDH and commercial IrO2 in alkaline media, delivering substantially higher intrinsic activity. The boost stems from robust electronic interactions between low-valent Mo SAs and the NiFe LDH lattice, which synergistically optimizes the local electronic structure. Remarkably, when architecturally engineered into a 3D monolithic electrode on nickel foam, this electrode achieves an ultra-low overpotential of 158 mV at 10 mA cm-2, ranking it among the most active single-atom-based OER electrocatalysts yet reported. Post-characterization analyses corroborate that LSAMo-NiFe LDH retains its atomic architecture and stoichiometry after prolonged operation. Importantly, operando electrochemical characterization further reveals that the lattice oxygen mechanism pathway serves as the primary redox partner during the OER. Theoretical calculations reveal that the low-valent Mo SAs enhance OER activity and identify the rate-determining steps in the OER process. The present work delivers a universal blueprint for high-performance, low-valent monoatomic catalysts: craft under-coordinated metal centers whose electron density is precisely modulated by adjacent, highly electronegative ligands.
The first examples of a M(EAr iPr6)3 complex [Ar iPr6 = C6H3-2,6-(C6H2-2,4,6- i Pr3)2] of any metal with any donor, E = O, S, NH, PH, have been isolated from the two-electron reduction of 1,3,5,7-cyclooctatetraene by the Ln(II) complexes Ln(SAr iPr6)2 [Ln = La, Nd]. Two equiv. of Ln(SAr iPr6)2 react with C8H8 to form the (C8H8)2--ligated Ln(III) complexes, Ln(SAr iPr6)(C8H8). Surprisingly, the second product of this reaction is the tris(terphenylthiolate), Ln(SAr iPr6)3, a complex expected to be too sterically crowded to exist. A computational study showed that interligand London dispersion effects (LDEs) in Ln(SAr iPr6)3 are responsible for approximately half of the dissociation energy of the thiolate ligands. Overall, the results demonstrate that the (SAr iPr6)1- ligand platform has a wide range of electronic and steric flexibility in rare-earth metal complexes.
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