Luminescence properties of [Ir(C^N)(N^N)] complexes: relations between DFT computation results and emission band-shape analysis data.

Luminescence properties of two series of [Ir(C^N)(N^N)] complexes bearing deprotonated 1-phenyl-1-pyrazole or 1-(2,4-difluorophenyl)-1-pyrazole as cyclometalating C^N ligands and different α-diimines (2,2'-bipyridine, 1,10-phenanthroline and their derivatives) as ancillary N^N ligands have been studied in acetonitrile solutions at room temperature and in 77 K methanol/ethanol (1 : 1) matrices. Ligand and temperature induced changes in the nature of the emissive *[Ir(C^N)(N^N)] species result in well-pronounced changes in their emission properties like emission wavelength, emission quantum yields and emission lifetimes. Depending on the nature of the coordinated C^N and N^N ligands and/or the measurement temperature, the investigated luminophores exhibit emissions arising from the intraligand transitions localized within the N^N ligand or from the metal-to-ligand charge-transfer transitions involving the Ir(C^N) and N^N moieties as confirmed by means of the DFT computations. The computed DFT energies of the excited *[Ir(C^N)(N^N)] states and outer/inner reorganization energies associated with the S ← *[Ir(C^N)(N^N)] transitions remain in nice agreement with those available from the performed emission band-shape analyses. The observed agreement implies ordinary DFT computations at the B3LYP/LANL2DZ/6-31G(d,p) level of theory, even performed neglecting the spin-orbit phenomena, as enough accurate in the quantitative prediction of the most important parameters characterizing the investigated [Ir(C^N)(N^N)] luminophores.