Blue to True-Blue Phosphorescent Ir^{III Complexes Bearing a Nonconjugated Ancillary Phosphine Chelate}: Strategic synthesis, photophysics, and device integration

We report the design and synthesis of Ir^III complexes functionalized with substituted pyridyl cyclometalate or azolate chromophores, plus one newly designed nonconjugated phosphine chelate, which not only greatly restricts its participation in the lowest-lying electronic transition but also enhances the coordination strength. These two key factors lead to fine-tuning of the phosphorescence chromaticity toward authentic blue and simultaneously suppress, in part, the nonradiative deactivation. This conceptual design presents a novel strategy in achieving heretofore uncommon, high-efficiency blue and true-blue phosphorescence. The fabrication of the organic light-emitting devices (OLEDs) employing phosphorescent dopants [Ir(dfpbpy)₂(P^∧N)] (1b) and [Ir(fppz)₂(P^∧N)] (3) was successfully made, for which the abbreviations (dfpbpy)H, (fppz)H, and (P^∧N)H represent 2-(4,6-difluorophenyl)-4-tert-butylpyridine, 3-(trifluoromethyl)-5-(2-pyridyl)pyrazole, and 5-(diphenylphosphinomethyl)-3-(trifluoromethyl)pyrazole, respectively. Of particular interest is the 3-doped OLEDs, which exhibit remarkable maximum efficiencies of 6.9%, 8.1 cd A⁻¹, and 4.9 lm W⁻¹, together with a true-blue chromaticity CIE_x,y = 0.163, with 0.145 recorded at 100 cd m⁻².