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

Abstract

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