Rational Design, Synthesis, and Characterization of Deep Blue Phosphorescent Ir(III) Complexes Containing (4′-Substituted-2′-pyridyl)-1,2,4-triazole Ancillary Ligands

On
the basis of the results of frontier orbital considerations, 4-substituted-2′-pyridyltriazoles
were designed to serve as ancillary ligands in 2-phenylpyridine main
ligand containing heteroleptic iridium­(III) complexes that display
deep blue phosphorescence emission. The iridium­(III) complexes, Ir1–Ir7, prepared using the new ancillary
ligands, were found to display structured, highly quantum efficient
(Φp = 0.20–0.42) phosphorescence with emission
maxima in the blue to deep blue 448–456 nm at room temperature.
In accord with predictions based on frontier orbital considerations,
the complexes were observed to have emission properties that are dependent
on the electronic nature of substituents at the C-4 position of the
pyridine moiety of the ancillary ligand. Importantly, placement of
an electron-donating methyl group at C-4′ of the pyridine ring
of the 5-(pyridine-2′-yl)-3-trifluoromethyl-1,2,4-triazole
ancillary ligand leads to an iridium­(III) complex that displays a
deep blue phosphorescence emission maximum at 448 nm in both the liquid
and film states at room temperature. Finally, an OLED device, constructed
using an Ir-complex containing the optimized ancillary ligand as the
dopant, was found to emit deep blue color with a CIE of 0.15, 0.18,
which is close to the perfect goal of 0.15, 0.15.