Bis-Cyclometalated Iridium(III) Complexes Bearing Ancillary Guanidinate Ligands. Synthesis, Structure, and Highly Efficient Electroluminescence

Abstract

We report the synthesis, structure, and photophysical and electroluminescent (EL) properties of a series of heteroleptic bis(pyridylphenyl)iridium(III) complexes with various ancillary guanidinate ligands. The reaction of the bis(pyridylphenyl)iridium(III) chloride [(ppy)(2)Ir(μ-Cl)](2) with the lithium salt of various guanidine ligands Li{(N(i)Pr)(2)C(NR(1)R(2))} at 80 °C gave in 60-80% yield the corresponding heteroleptic bis(pyridylphenyl)/guanidinate iridium(III) complexes having a general formula of [(ppy)(2)Ir{(N(i)Pr)(2)C(NR(1)R(2))}], where NR(1)R(2) = NPh(2) (1), N(C(6)H(4)(t)Bu-4)(2) (2), carbazolyl (3), 3,6-bis(tert-butyl)carbazolyl (4), N(C(6)H(4))(2)S (5), N(C(6)H(4))(2)O (6), indolyl (7), NEt(2) (8), N(i)Pr(2) (9), N(i)Bu(2) (10), and N(SiMe(3))(2) (11). These heteroleptic cyclometalated (C^N) iridium(III) complexes showed intense absorption bands in the UV region assignable to π-π* transitions and weaker metal-to-ligand charge-transfer transitions extending to the visible region. These complexes also showed intense emissions at room temperature. Their photoluminescence spectra were influenced to some extent by the ancillary guanidinate ligands, giving λ(max) values in the range of 528-560 nm with quantum yields (Φ) of 0.16-0.37 and lifetimes of 0.61-1.43 μs. Organic light-emitting diodes were fabricated by the use of these complexes as dopants in various concentrations (5-100%) in a N,N'-dicarbazolylbiphenyl host. High current efficiency (η(c); up to 137.4 cd/A) and power efficiency (η(p); up to 45.7 lm/W) were observed under appropriate conditions. Their high EL efficiency may result from efficient trapping and radiative relaxation of the excitons formed in the EL process. Because of the steric hindrance of the guanidinate ligands, no significant intermolecular interaction was observed in these complexes, thus leading to the reduction of self-quenching and triplet-triplet annihilation at high currents. The EL emission color could be changed in the range of green to yellow by choosing appropriate guanidinate ligands.

Functionalization of phosphorescent emitters and their host materials by main-group elements for phosphorescent organic light-emitting devices

“…110 nm with the emission maximum at around 540 nm. 452 Compared to those of (ppy) 2 Ir(acac) (l em = 516 nm, t = 1.6 ms, F P = 0.34), 28 the emission peaks of these Ir(III) complexes are red-shifted (e.g. Hou et al firstly used an amidinate unit N,N 0 -diisopropylbenzamidinate (dipba) as an ancillary ligand to replace the acac ligands in (ppy-type) 2 Ir(acac) complexes (Fig.…”

“…Hou et al firstly used an amidinate unit N,N 0 -diisopropylbenzamidinate (dipba) as an ancillary ligand to replace the acac ligands in (ppy-type) 2 Ir(acac) complexes (Fig. Devices [ITO/NPB (30 nm)/5 wt% dopant:CBP 452 With an optimized structure of ITO/NPB (35 nm)/15 wt% Ir-dipIp:TPBI (25 nm)/TPBI (30 nm)/ LiF (0.5 nm)/Al, the yellow-emitting device exhibits an outstanding performance with a peak EQE of 25.3% and a PE of 93.6 lm W À1 , which are the highest value obtained by yellow PHOLEDs so far. [447][448][449][450] Theoretical calculation results indicate that the N atoms of the dipba ligand make significant contributions to the HOMOs of the concerned complexes because of the stronger p-bonding ability of the dipba ligand than that of acac, resulting in greatly raised HOMO levels which are also confirmed by the experimental results.…”

Structural Mimics of Phenyl Pyridine (ppy) – Substituted, Phosphorescent Cyclometalated Homo and Heteroleptic Iridium(III) Complexes for Organic Light Emitting Diodes – An Overview

“…Virendra Kumar et al ., reported the synthesis, structural characterization, photophysical, electrochemical, and EL properties of bis(pyridylphenyl)iridium(III) complexes (232‐242, Figure ) with various ancillary guanidinate ligands . These phosphorescent complexes can serve as excellent emitting materials for OLEDs, exhibiting both η C and η P under appropriate conditions.…”

Electrochemiluminescence of iridium complexes with ammonia in dimethylformamide and its analytical application for ammonia detection

“…All the optimized geometries were confirmed to be potential energy minima by vibrational frequency calculation in the presence of only real frequencies [32,33]. The DFT/B3LYP/6-31G Ã has been found to be an accurate formalism for calculating the structural and optical properties of the iridium complexes [34,35]. Fig.…”