Blue to True-Blue Phosphorescent Ir^III Complexes Bearing a Nonconjugated Ancillary Phosphine Chelate: Strategic Synthesis, Photophysics, and Device Integration

Abstract

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(wedge)N)] (1b) and [Ir(fppz)(2)(P(wedge)N)] (3) was successfully made, for which the abbreviations (dfpbpy)H, (fppz)H, and (P(wedge)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).

Novel Cationic 2-Phenylpyridine-based Iridium(III) Complexes Bearing an Ancillary Phosphine Ligand: Synthesis, Photophysics and Crystal Structure

“…The synthetic procedure is shown in Scheme 1. The properties of the chloride salts are nearly consistent with those of the PF 6 -salts discussed herein.…”

“…, reflecting that the π-accepting character of the phosphine group increased the associated MLCT energy levels, resulting in a blue-shift emission. 6 The substituents in the main ligand showed a hypsochromic shift on the order of ppy → dfppy → dfmppy, and revealed that difluorination on the 2,4-positions of the phenyl ring led to a significant blue-shift, whereas methylation on the pyridine group caused a small blue-shift of the emission maximum. 22 The emission peaks were next examined in a variety of solvents, but little solvatochromism was observed as shown in Table 2.…”

Theoretical study on the electronic structures and phosphorescent properties of a series of iridium(III) complexes with the different positional N-substitution in the pyridyl moiety

“…In fact, there are also several of strategies to tune the emission color or efficiency of the Ir(III) complexes, such as designing new cyclometalating ligands, ancillary ligands, or attaching different substituents [24][25][26][27]. It is noted that electron deficient and/or higher field strength L\widehatX ancillaries, such as pyridylazolate and imidodiphosphinate, and phosphorus-containing chelates, such as benzyl phosphine and phosphine substituted pyrazole, are very suitable for the construction of blue-or even bluish-green-emitting Ir(III) metal phosphors [28][29][30][31].…”

A theoretical investigation on the electronic structures and phosphorescent properties of three heteroleptic iridium(III) complexes with different substituted ancillary groups

“…Thus, as for iridium-containing emitters, the internal quantum efficiency of about 100% is higher than that based on fluorescence [14], because they are capable of harvesting both singlet and triplet excitons, while fluorescent emitters are limited to singlet excitons [15,16]. It is well known that phosphorescent iridium(III) complexes can realise emission in the full visible spectra by modifying the ligand structure and/or incorporation of ancillary ligands [17,18]. The introduction of electron-donating or electron-withdrawing substituents to the coordinated ligands is the most common approach to tune the emission energy [19][20][21][22].…”