Simple Synthesis of Red Iridium(III) Complexes with Sulfur-Contained Four-Membered Ancillary Ligands for OLEDs

Abstract

Phosphorescent iridium(III) complexes have been widely researched for the fabrication of efficient organic light-emitting diodes (OLEDs). In this work, three red Ir(III) complexes named Ir-1, Ir-2, and Ir-3, with Ir-S-C-S four-membered framework rings, were synthesized efficiently at room temperature within 5 min using sulfur-containing ancillary ligands with electron-donating groups of 9,10-dihydro-9,9-dimethylacridine, phenoxazine, and phenothiazine, respectively. Due to the same main ligand of 4-(4-(trifluoromethyl)phenyl)quinazoline, all Ir(III) complexes showed similar photoluminescence emissions at 622, 619, and 622 nm with phosphorescence quantum yields of 35.4%, 50.4%, and 52.8%, respectively. OLEDs employing these complexes as emitters with the structure of ITO (indium tin oxide)/HAT-CN (dipyra-zino[2,3-f,2′,3′-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile, 5 nm)/TAPC (4,4′-cyclohexylidenebis[N,N-bis-(4-methylphenyl)aniline], 40 nm)/TCTA (4,4″,4″-tris(carbazol-9-yl)triphenylamine, 10 nm)/Ir(III) complex (10 wt%): 2,6DCzPPy (2,6-bis-(3-(carbazol-9-yl)phenyl)pyridine, 10 nm)/TmPyPB (1,3,5-tri(mpyrid-3-yl-phenyl)benzene, 50 nm)/LiF (1 nm)/Al (100 nm) achieved good performance. In particular, the device based on complex Ir-3 with the phenothiazine unit showed the best performance with a maximum brightness of 22480 cd m−2, a maximum current efficiency of 23.71 cd A−1, and a maximum external quantum efficiency of 18.1%. The research results suggest the Ir(III) complexes with a four-membered ring Ir–S–C–S backbone provide ideas for the rapid preparation of Ir(III) complexes for OLEDs.

Orange to red iridium(iii) complexes possessing good electron mobility with a pyrimidine-4-carboxylic acid ligand for high-performance solution-processed OLEDs with an EQE over 31%

“…The bond lengths of Ir-C (1.987-2.030 Å), Ir-N (2.029-2.148 Å) and Ir-O (2.151-2.171 Å) match with those of other similar Ir(III) complexes. [26][27][28]…”

Two Novel Neutral Cyclometalated Iridium(III) Complexes Based on 10,11,12,13-Tetrahydrodibenzo[a,c]phenazine for Efficient Red Electroluminescence

“…Red emission is one of the important primary colors for display applications, and has aroused tremendous interest. Designing and fabricating novel, efficient, red iridium(III) complexes are of great significance and practical values [ 21 , 22 ].…”

Organic molecules with inverted singlet-triplet gaps

“…Therefore, the maximum internal quantum efficiency (IQE) of a fluorescent OLED is only 25%, and consequently the external quantum efficiency (EQE) is limited to about 5%. In turn, the IQEs of phosphorescent OLEDs can theoretically reach 100% by capturing both singlet and triplet excitons as a consequence of strong spin-orbit coupling (SOC) effect induced by heavy atoms ( Figure 1B ) ( Bernhard et al, 2002 ; Chi and Chou, 2010 ; Zhou et al, 2014 ; Mao et al, 2021 ). Nonetheless, the utilization of precious metals brings problems of high cost and environmental pollution.…”