Organoisocyanides with high σ-donor/π-acid ratio, stabilize higher oxidation state of transition metals and create rugged organometallics. Little has been explored on the steric and electronic effect of aryl isocyanides on cyclometalated iridium(III). We report synthesis, photophysics and electrochemical properties of 11 new luminescent cationic biscyclomtalated bis-(aryl isocyanide)iridium(III) complexes. Three different aryl isocyanides with various degree of steric bulk–2,6-dimethylohenyl isocyanide (CNArdmp), 2,6-diisopropylphenyl isocyanide (CNArdipp) and 2-naphthyl isocyanide (CNArnap) were incorporated in synchronized with four cyclometalating ligands with differential π–π* energy–2-phenylpyridine (ppy), 2,4-difluorophenylpyridine (F2ppy), 2-benzothiphenylpyridine (btp) and 2-phenylbenzothizole (bt). Five of them, [(ppy)2Ir(CNArdmp)2]OTf (1a), [(F2ppy)2Ir(CNArdmp)2]PF6 (2a), [(btp)2Ir(CNArdipp)2]PF6 (3b), [(btp)2Ir(CNArnap)2]PF6 (3c) and [(bt)2Ir(CNArdmp)2]PF6 (4a) were crystallographically characterized. All new complexes show wide redox window with reduction potentials pitch in a narrow range of 2.02–2.37 V, while oxidation potentials vary in a wide region of 0.97–1.48 V. Efficient structured emission spans from blue-region for [(F2ppy)2Ir(CNAr)2]PF6 class of complexes (417 nm for 2a with lifetime 41 μs and quantum yield of 0.37) to orange region for [(btp)2Ir(CNAr)2]PF6 class of complexes (581 nm for 3c with quantum yield 1%). To the best of our knowledge, this is the lowest emission energy that was achieved for biscyclometalted bis(aryl isocyanide) iridium(III). Substitution of flanking –CH3 groups of CNAr ligand with bulkier –CH(CH3)2 has minimal effect on the steric and electronic properties. 2-naphthyl isocyanide (CNArnap) effectively participates in the excited states of few the complexes. UV-vis absorption profile, variable temperature emission study and lifetime measurement predict a ligand centered (LC) lowest energy excited state with very little contribution from metal-to-ligand charge transfer (MLCT) states for most of the compounds described here.

Influencing excited states of iridium(III) cyclometalates by various aryl isocyanides and cyclometalating ligands

251st National Meeting (2016)

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