Iridium(III) Complexes Bearing a Formal Tetradentate Coordination Chelate: Structural Properties and Phosphorescence Fine-Tuned by Ancillaries.

Synthesis of the multidentate coordinated chelate N3C-H, composed of a linked functional pyridyl pyrazole fragment plus a peripheral phenyl and pyridyl unit, was obtained using a multistep protocol. Preparation of Ir(III) metal complexes bearing a N3C chelate in the tridentate (κ), tetradentate (κ), and pentadentate (κ) modes was executed en route from two nonemissive dimer intermediates [Ir(κ-N3CH)Cl] () and [Ir(κ-N3C)Cl] (). Next, a series of mononuclear Ir(III) complexes with the formulas [Ir(κ-N3C)Cl(py)] (), [Ir(κ-N3C)Cl(dmap)] (), [Ir(κ-N3C)Cl(mpzH)] (), and [Ir(κ-N3C)Cl(dmpzH)] (), as well as diiridium complexes [Ir(κ-N3C)(mpz)(CO)(H)] () and [Ir(κ-N3C)(dmpz)(CO)(H)] (), were obtained upon treatment of dimer with pyridine (py), 4-dimethylaminopyridine (dmap), 4-methylpyrazole (mpzH), and 3,5-dimethylpyrazole (dmpzH), respectively. These Ir(III) metal complexes were identified using spectroscopic methods and by X-ray crystallographic analysis of representative derivatives , , and . Their photophysical and electrochemical properties were investigated and confirmed by the theoretical simulations. Notably, green-emitting organic light-emitting diode (OLED) on the basis of Ir(III) complex gives a maximum external quantum efficiency up to 25.1%. This result sheds light on the enormous potential of this tetradentate coordinated chelate in the development of highly efficient iridium complexes for OLED applications.