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

Novel iridium(III)/iridium(III) and iridium(III)/platinum(II) dinuclear complexes, [{Ir(ppyFF) 2 } 2 (μ 2 ‐ L )] ( 4 ) and [{Ir(ppyFF) 2 }(μ 2 ‐ 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 3 LX 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 3 LX 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 [ 3 M(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.