Dinuclear Iridium(III) Complexes Linked by a Bis(β‐diketonato) Bridging Ligand: Energy Convergence versus Aggregation‐Induced Emission

Abstract

AbstractNovel iridium(III)/iridium(III) and iridium(III)/platinum(II) dinuclear complexes, [{Ir(ppyFF)2}2(μ2‐L)] (4) and [{Ir(ppyFF)2}(μ2‐L){Pt(ppy)}] (5) [ppyFF = 2‐(2,4‐difluorophenyl)pyridine, ppy = 2‐phenylpyridine, L = 1,3‐bis(3‐phenyl‐3‐oxopropanoyl)benzene], linked by an L bridging ligand were prepared, and their photophysical properties were investigated in solution and in the solid state. The photophysical properties of mononuclear iridium(III) and platinum(II) complexes, [Ir(ppyFF)2(dbm)] (1) and [Pt(ppy)(dbm)] (2) bearing a dibenzoylmethane (dbm) ligand were also compared. Whereas the UV/Vis absorption spectra of 4 and 5 show independent light absorption at each metal‐centered moiety, the photoluminescence spectra of 4 and 5 display almost identical features, but very weak emissions in solution at both room temperature and 77 K. The weak emission in solution is found to mainly originate from a 3LX state of the L bridging ligand, which reflects the occurrence of efficient energy convergence from the triplet states of the Pt(ppy) and Ir(ppyFF) moieties to the 3LX state of L. By contrast, intense orange‐red emission, that is, aggregation‐induced emission, is produced in the solid state of 4 and 5. Inspection of the crystal‐packing structures of 5 reveals that strong intermolecular π–π interactions between the adjacent pyridine rings of ppyFF ligands in the Ir‐centered moieties are responsible for the emissive metal‐to‐ligand–ligand charge‐transfer [3M(LL)CT] state of the solid‐state dinuclear systems. The electrochemical properties of 4 and 5 further indicate that the first two reductions occur at the dbm moieties of the L bridging ligand linked to each metal center, which is consistent with the fact that the lowest‐energy excited state of the L bridging ligand dominates the excited‐state properties of 4 and 5 in solution.