Photophysical Properties of Heteroleptic Iridium Complexes Containing Carbazole‐Functionalized β‐Diketonates

Abstract

Twelve iridium complexes with general formula of Ir(C;N)(2)(LX) [C;N represents the cyclometalated ligand, i.e. 2-(2,4-difluorophenyl) pyridine (dfppy), 2-phenylpyridine (ppy), dibenzo{f, h}quinoxaline (DBQ); LX stands for beta-diketonate, i.e. acetyl acetonate (acac), 1-(carbazol-9-yl)-5,5-dimethylhexane-2,4-diketonate (CBDK), 1-(carbazol-9-yl)-5,5,6,6,7,7,7-heptafluoroheptane-2,4-diketonate (CHFDK), 1-(N-ethyl-carbazol-3-yl)-4,4,5,5,6,6,6-heptafluorohexane-1,3-diketonate (ECHFDK)] are synthesized, characterized and their photophysical properties are systemically studied. In addition, crystals of Ir(DBQ)(2)(CHFDK) and Ir(DBQ)(2)(acac) are obtained and characterized by single crystal X-ray diffraction. The choice of these iridium complexes provides an opportunity for tracing the effect of the triplet energy level of ancillary ligands on the photophysical and electrochemical behaviors. Data show that if the triplet energy level of the beta-diketonate is higher than that of the Ir(C;N)(2) fragment and there is no superposition on the state density map, strong (3)LC or (3)MLCT-based phosphorescence can be obtained. Alternatively, if the state density map of the two parts are in superposition, the (3)LC or (3)MLCT-based transition will be quenched at room temperature. Density functional theory calculations show that these complexes can be divided into two categories. The lowest excited state is mainly determined by C;N but not beta-diketonate when the difference between the triplet energy levels of the two parts is large. However, when this difference is very small, the lowest excited state will be determined by both sides. This provides a satisfactory explanation for the experimental observations.

Functional IrIII Complexes and Their Applications

“…We reported the synthesis, photophysical, and electrochemical properties of a series of iridium complexes with different b-diketonates with a range of triplet energy levels as the ancillary ligand. [29] The effect of the triplet energy level of b-diketonates on the properties of iridium complexes was examined. Strong …”

Organometallic Materials for Electroluminescent and Photovoltaic Devices

“…The computations also suggest that the phosphorescent emission wavelengths could be blue-shifted by introducing π electron-withdrawing groups and by suppressing the π-conjugation in the C^N ligand. Liu et al (2008) also investigated the photophysical properties of heteroleptic iridium complexes containing carbazole-functionalized β-diketonates. The authors have studied the influence of the triplet energy level of the ancillary carbazole-containing ligand on the photophysical and electrochemical behavior, and found that the superposition of the state density map of the triplet energy levels between the β-diketonate and the Ir(C^N) 2 fragment is the key factor to obtain strong 3 LC or 3 MLCT-based phosphorescence and high photophysical performance.…”

(Acetylacetonato-κ2O,O′)bis[2-(5-methyl-3-phenylpyrazin-2-yl-κN1)phenyl-κC1]iridium(III)

“…For background to organic light-emitting diodes based on phosphorescent complexes, see: Baldo et al (1998Baldo et al ( , 2000; Hwang et al (2005); Liu et al (2008); Tsuboyama et al (2003). For the synthesis, see: Zhang et al (2003Zhang et al ( , 2005.…”

“…In recent decades, organic light-emitting diodes (OLEDs) based on phosphorescent complexes have attracted increasing attention due to their potential applications in full-color flat panel displays (Baldo et al, 1998(Baldo et al, , 2000. Among these phosphorescent complexes, iridium cyclometalates often exhibit favorable photoproperties for OLEDs including short phosphorescent lifetimes, high quantum efficiencies and good stability (Liu et al, 2008;Hwang et al, 2005;Tsuboyama et al, 2003). Zhang et al (2005) demonstrated a high efficiency yellow OLED using [Ir(mdpp) 2 (acac)] [mdpp = 2-(5-methyl-3-phenylpyrazine-2-yl)phenyl, Hacac = acetylacetone] as the dopant.…”