A chelating diisocyanide ligand for cyclometalated Ir(III) complexes with strong and tunable luminescence

We report the synthesis, structural characterisation and detailed photophysical description of three cationic cyclometalated iridium(III) complexes (2-4) bearing a chelating diisocyanide as the ancillary ligand (1 = 2,2''-diisocyano-1,1':3',1''-terphenyl). All compounds display irreversible reduction and oxidation potentials and emit from a triplet excited state centred on the cyclometalating ligands with lifetimes of several dozen microseconds, as commonly observed for other iridium(III) isocyanide complexes and further confirmed by DFT calculations. Room-temperature photoluminescence can be tuned from blue to orange upon variation of the cyclometalating ligands, and the related quantum yields range from around 30% in acetonitrile solution to nearly 80% in solid-state, as for complex 3 embedded in a 1% w/w poly(methyl methacrylate) matrix.