Novel Ir(III) Complexes with NHC-Based Ancillary Ligands for Efficient Nondoped OLEDs

Abstract

Nondoped organic light-emitting diodes (OLEDs) are of paramount importance for display and lighting applications owing to their advantages of facile fabrication and outstanding stability. However, nondoped OLEDs achieving extraordinary electroluminescence (EL) performance and low turn-on voltage (V on) remain sparse. Here, three Ir(III) complexes featuring N-heterocyclic carbene (NHC) auxiliary ligands functionalized with electron-deficient aromatic sulfonyl or phosphine oxide groups are reported as promising emitters for nondoped OLEDs. All Ir(III) complexes exhibit green emission with relatively high neat film efficiency. Although the photoluminescence spectra of three complexes reveal similarities, there are distinct differences in the nondoped EL performance. The nondoped device N3 based on tBu-Ir-ISO displays the most eminent EL performances and presents a low V on of 2.1 V, a power efficiency of 30.7 lm W–1, and a maximum current efficiency of 27.0 cd A–1, which can be attributed to steric hindrance and balanced carrier-transporting ability induced by electron-deficient substituents. Moreover, doped devices D1–D3 also realize excellent EL performance. It is believed that the strategy reported herein is a simple and efficient way of constructing excellent Ir(III) complexes for nondoped phosphorescent OLEDs.

Synthesis of N-Heterocyclic Carbene Complexes by Oxidative Addition of 4-Iodo-imidazolium Salts Followed by an Unusual Rearrangement

“…Over the last 3 decades, the development of transition-metal complexes bearing N-heterocyclic carbene ligands (NHCs) has rapidly advanced, starting with the preparation of the first stable-free NHC by Arduengo in 1991 . NHC metal complexes have been employed as catalysts − for substrate recognition, in supramolecular chemistry, as antibacterial agents, , and in OLEDs …”

“…1 NHC metal complexes have been employed as catalysts 2−5 for substrate recognition, 6 in supramolecular chemistry, 7 as antibacterial agents, 8,9 and in OLEDs. 10 Classical NHC metal complexes of type I (Figure 1) are usually prepared by C2 deprotonation of suitable azolium salts followed by subsequent or in situ metalation of the C2 position. 11−13 Complexes bearing abnormal NHC ligands (aNHCs) of type II (Figure 1) feature the carbene−metal bond at the C4 or C5 position of the diaminoheterocycle.…”

Theoretical investigation of the influence of heterocycles on the radiative and non-radiative decay processes of iridium(iii) complexes

“…N-heterocyclic moieties, as the scaffold materials for incorporating chelating ligands into Ir(III), have sparked significant interest because the corresponding Ir(III) complexes exhibit excellent performances and chemical stabilities. [18][19][20][21] Recently, Lee et al chose phenylpyridine-ligand-based and phenylimidazole-based Ir(III) complexes as CT complex-forming materials. White OLEDs could be constructed by doping these Ir(III) complexes into the host material, which exhibited both blue emission and yellow emission with a quantum efficiency of 13.7%.…”