Blue Phosphorescence from Mixed Cyano−Isocyanide Cyclometalated Iridium(III) Complexes

The synthesis, structure, and photophysical and electrochemical properties of cyclometalated iridium complexes
with ancillary cyano and isocyanide ligands are described. In the first synthetic step, cleavage of dichloro-bridged
dimers [Ir(N∧C)2(μ-Cl)]2 (N∧C = 2-phenylpyridine, 2-(2-fluorophenyl)pyridine, and 2-(2,4-difluorophenyl)pyridine)
by isocyanide ligands gave monomeric species of the types Ir(N∧C)2(RNC)(Cl) (RNC = t-butyl isocyanide, 1,1,3,3-tetramethylbutyl isocyanide, 2-morpholinoethyl isocyanide, and 2,6-dimethylphenyl isocyanide). In turn, the chloride
was replaced by cyanide giving Ir(N∧C)2(RNC)(CN). The X-ray structures for two of the complexes show that the
trans-pyridyl/cis-phenyl geometry of the parent dimer is preserved, with the ancillary ligands positioned trans to the
cyclometalated phenyls. The cyano complexes all display strong blue photoluminescence in ambient, deoxygenated
solutions with the first λmax ranging from 441 to 458 nm, quantum yields spanning 0.60 to 0.75, and luminescent
lifetimes of 12.0−21.4 μs. A lack of solvatochromism and highly structured emission indicate that the lowest energy
excited state is triplet ligand centered with some admixture of singlet metal-to-ligand charge-transfer character.