Synthesis and Characterization of Phosphorescent Cyclometalated Iridium Complexes

Abstract

The preparation, photophysics, and solid state structures of octahedral organometallic Ir complexes with several different cyclometalated ligands are reported. IrCl3.nH2O cleanly cyclometalates a number of different compounds (i.e., 2-phenylpyridine, 2-(p-tolyl)pyridine, benzoquinoline, 2-phenylbenzothiazole, 2-(1-naphthyl)benzothiazole, and 2-phenylquinoline), forming the corresponding chloride-bridged dimers, CwedgeN2Ir(mu-Cl)2IrCwedgeN2 (CwedgeNis a cyclometalated ligand) in good yield. These chloride-bridged dimers react with acetyl acetone (acacH) and other bidentate, monoanionic ligands such as picolinic acid (picH) and N-methylsalicylimine (salH), to give monomeric CwedgeN2Ir(LX) complexes (LX = acac, pic, sal). The emission spectra of these complexes are largely governed by the nature of the cyclometalating ligand, leading to lambda(max) values from 510 to 606 nm for the complexes reported here. The strong spin-orbit coupling of iridium mixes the formally forbidden 3MLCT and 3pi-pi* transitions with the allowed 1MLCT, leading to a strong phosphorescence with good quantum efficiencies (0.1-0.4) and room temperature lifetimes in the microsecond regime. The emission spectra of the CwedgeN2Ir(LX) complexes are surprisingly similar to the fac-IrCwedgeN3 complex of the same ligand, even though the structures of the two complexes are markedly different. The crystal structures of two of the CwedgeN2Ir(acac) complexes (i.e., CwedgeN = ppy and tpy) have been determined. Both complexes show cis-C,C', trans-N,N' disposition of the two cyclometalated ligands, similar to the structures reported for other complexes with a "CwedgeN2Ir" fragment. NMR data (1H and 13C) support a similar structure for all of the CwedgeN2Ir(LX) complexes. Close intermolecular contacts in both (ppy)2Ir(acac) and (tpy)2Ir(acac) lead to significantly red shifted emission spectra for crystalline samples of the ppy and tpy complexes relative to their solution spectra.

Diarylboron‐Based Asymmetric Red‐Emitting Ir(III) Complex for Solution‐Processed Phosphorescent Organic Light‐Emitting Diode with External Quantum Efficiency above 28%

“…On the whole, the incorporation of diarylboron moieties has greatly influenced the emission properties of these Ir(III) complexes. Remarkable emission redshifts of these diarylboron‐based asymmetric Ir(III) complexes with significantly improved PLQYs have been observed, since the related symmetric Ir(III) complexes without the diarylboron substituent usually show green or green‐yellow emissions with PLQYs less than 0.4 35, 36. In detail, when introducing the diarylboron unit to the thiazole ring, the resulted complex BThThIr displayed longer emission wavelength both in the THF solution and TCTA film, and also its emission lifetimes (τ p ) were the longest (Table 1 and Figure S6, Supporting Information).…”

Highly phosphorescent perfect green emitting iridium(iii) complex for application in OLEDs

“…4,5 A large number of iridium complexes have been utilized for this purpose, which are mostly based on the cyclometalating ligand 2-phenylpyridine (ppy) with an auxiliary ligand such as acetylacetonate (acac) or picolinate (pic). [6][7][8][9][10] Several groups have demonstrated tuning of the phosphorescence wavelength from blue to red by functionalization of the ligands with electron withdrawing and electron donating substituents. [11][12][13] Nevertheless, no attempts were made to tune the colour purity by decreasing the emission bandwidth, which of course is attractive for both fundamental research and practical applications.…”

High efficiency phosphorescent organic light emitting diodes using triplet quantum well structure

“…8,11 Other than these, host and dopant materials were found to have a great impact on the recombination efficiency of PHOLEDs. 9,[12][13][14] Another way to get high efficiency in OLED is to confine excitons inside an emitting layer using a multilayer quantum well structure. 15,16 There have been several reports about quantum well structure which can confine holes or excitons within an emitting layer.…”

“…6,8,9,[11][12][13][14] It was reported by He et al that the efficiency of green PHOLEDs could be doubled using a double layer emitting structure. 6 The use of an effective hole or exciton blocking layer could also enhance the recombination efficiency of PHOLEDs.…”