Guanidinate Ligated Iridium (III) Complexes with Various Cyclometalated Ligands: Synthesis, Structure, and Highly Efficient Electrophosphorescent Properties with a

Guanidinate Ligated Iridium (III) Complexes with Various Cyclometalated Ligands: Synthesis, Structure, and Highly Efficient Electrophosphorescent Properties with a …-October 2012

Z Hou, VK Rai, M Nishiura, M Takimoto – Journal of Materials Chemistry C, 2013
We report the synthesis, structure, and electrophosphorescence properties of a series of heteroleptic iridium(III) complexes with various cyclometalated (C^N) ligands based on sterically demanding guanidinate ancillary ligand. The iridium(III) complexes contain two cyclometalated (C^N) ligands and one monoanionic guanidinate ancillary ligand [(NiPr)2C(NPh2)]. The reaction of the bis(C^N) iridium(III) chloride [(C^N)2Ir(μ-Cl)]2 with the lithium salt of guanidine ligand [Li{(NiPr)2C-N(Ph)2}] at 80 °C gave in 65-85% yield the corresponding heteroleptic [(C^N)2Ir{(NiPr)2C(NPh2)}] complexes with several different cyclometalated (C^N) ligands such as 2-phenylpyridine (ppy) (1), 2-(2,4-diflurophenyl)pyridine (dfppy) (2), 2-(p-tolyl) pyridine (tpy) (3), benzoquinoline (bzq) (4), 2-phenylbenzoxazole (box) (5), 2-phenylbenzothiazole (btz) (6), 2-(2′-benzothienyl)pyridine (btp) (7) and 1-phenylisoquinoline (piq) (8). These heteroleptic cyclometalated (C^N) iridium(III) complexes showed intense absorption bands in the UV region assignable to ligand-centered (π-π*) transitions and lower energy absorption bands that extended to the visible region are mainly derived from spin-forbidden ligand-centered (π-π*) transition as well as metal-to-ligand charge transfer (MLCT) transition. These complexes also showed intense emissions at room temperature, leading to λmax values from green (λ = 505 nm) to perfect red color (λ = 655 nm) with quantum yields (Φ) of 0.18 to 0.64 and phosphorescent lifetimes of 0.78 to 5.80 µs. Organic light-emitting diodes (OLEDs) were fabricated by the use of these complexes as phosphorescent dopants in various concentrations (5-100%) in a N,N’ dicarbazolylbiphenyl (CBP) host. High current efficiency (ηc; up to 125 cd/A) and power efficiency (ηp; up to 43.6 lm/W) were observed at appropriate conditions. Because of the steric hindrance of guanidinate ancillary ligand, no significant intermolecular interaction was observed in these complexes, thus leading to the reduction of self-quenching and triplet-triplet (T-T) annihilation at high luminance/currents in OLEDs…The size of each pixel was 5×5 mm2. The 35 electroluminescence (EL) spectra have been measured on a high- resolution spectrometer (Stellar net Blue-wave UV-VIS-NIR).