Neutral heteroleptic mononuclear iridium(III) complexes with (2,4-difluoro)phenylpyridine and different pyridine-1,2,4-triazole ligands were synthesized and fully characterized. We investigated the effects of substituents in the 5-position of the triazole ring on the photophysical and electrochemical behavior. Increasing the electron-withdrawing capabilities generally leads to a lowering of the HOMO level with a consequent slight widening of the HOMO-LUMO gap and a blue shift in emission. The complexes reported exhibit high emission quantum yields and long luminescent lifetimes, typical of iridium(III) complexes, and most of them show reversible redox processes in solution. Also, many of the complexes reported here have been obtained as single crystals suitable for X-ray crystallography. Two of the complexes were further tested as phosphorescent dyes in OLED devices and showed high external quantum efficiencies (~7%) and color points better than the "standard" for blue iridium(III) bis[(4,6-difluorophenyl)pyridinato-N,C2']picolinate (FIrpic). We also report the full electrochemical investigation of FIrpic in different solvents.

The Class III (delocalized) intervalence radical anions of 1,4-dinitrobenzene, 2,6-dinitronaphthalene, 2,6-dinitroanthracene, 9,9-dimethyl-2,7-dinitrofluorene, 4,4'-dinitrobiphenyl, and 1,5-dinitronaphthalene show charge-transfer bands in their near-IR spectra. The dinitroaromatic radical anions have comparable but slightly larger electronic interactions (H(ab) values) through the same aromatic bridges as do the corresponding dianisylamino-substituted radical cations. H(ab) values range from 5410 cm(-)(1) (1,4- dinitrobenzene) to 3400 cm(-)(1) (9,9-dimethyl-2,7-dinitrofluorene), decreasing as the number of bonds between the nitro groups increases, except for the 1,5-dinitronaphthalene radical-anion, which has a coupling similar to that of 9,9-dimethyl-2,7-dinitrofluorene. All charge-transfer bands show vibrational fine structure. The vertical excitation energies (lambda(v)) were estimated from the vibrational components, obtained by simulation of the entire band. The large 2H(ab)/lambda(v) values confirm these radicals to be Class III delocalized mixed-valence species. Analysis using Cave and Newton's generalized Mulliken-Hush theory relating the transition dipole moment to the distance on the diabatic surfaces suggests that the electron-transfer distance on the diabatic surfaces, d(ab), is only 26-40% of the nitrogen-to-nitrogen distance, which implies that something may be wrong with our analysis.