Using Simple Fused‐Ring Thieno[2,3‐d]pyrimidine to Construct Orange/Red Ir(III) Complexes: High‐Performance Red Organic Light‐Emitting Diodes with EQEs up to Nearly 28%

Abstract In this article, a promising molecular design strategy for obtaining highly efficient orange/red iridium complexes by utilizing simple fused‐ring thieno[2,3‐d]pyrimidine derivatives as the cyclometalated ligands is reported. The introduction of a pyrimidine moiety lowers the lowest unoccupied molecular orbital (LUMO) energy levels and consequently narrows the HOMO–LUMO (HOMO = highest occupied molecular orbital) energy gaps to obtain orange/red emissions. As a result, a series of phosphorescent iridium complexes, namely, PMD‐Ir‐1, PMD‐Ir‐2, PMD‐Ir‐3, and PMD‐Ir‐4, with emission peaks in the range of 578–614 nm are obtained. Notably, phosphorescent organic light‐emitting diodes (PhOLEDs) utilizing PMD‐Ir‐2 and PMD‐Ir‐3 as emitters exhibit orange and red emissions with maximum external quantum efficiencies up to 24.5% and 27.6%, respectively. These results clearly demonstrate that the thieno[2,3‐d]pyrimidine‐based iridium complexes have great potential for fabricating high‐performance orange/red OLEDs.