Two new pyrimidine-based iridium complexes with triphenylamine and tetraphenylsilane, namely (TPAPr)2 IrAcac and (TPSPr)2 IrAcac, were fully synthesized and characterized. Both of the targeted iridium complexes exhibit excellent thermal stability and high photoluminescence quantum yields. Compared to (TPAPr)2 IrAcac, (TPSPr)2 IrAcac achieved its highest PLQY and current efficiency (CE) at higher dopant concentration probably because of its bulky tetraphenylsilane group, which can effectively suppress the concentration quenching. However, according to DFT studies, (TPSPr)2 IrAcac shows faster non-radiative transitions due to the presence of more excited-state distortions than (TPAPr)2 IrAcac. As a result, Green phosphorescent polymer light-emitting diodes (PLEDs) containing (TPAPr)2 IrAcac and (TPSPr)2 IrAcac as dopants exhibit exceptional device performance with peak CE values of 38.24 and 36.06 cd A-1 , respectively. (TPAPr)2 IrAcac exhibited a superior efficiency than (TPSPr)2 IrAcac because of its high Φp , low RMSD value, and efficient energy transfer from the host to the guest. More importantly, the PLEDs based on (TPAPr)2 IrAcac and (TPSPr)2 IrAcac show stable phosphorescent emission with Commission Internationale de L'Eclairage (CIE) coordinates of (0.313, 0.497) and (0.299, 0.483), respectively. This work points out a viable method for creating phosphorescent iridium complexes based on pyrimidine for high-efficiency organic light-emitting diodes (OLEDs).
Keywords: OLED; iridium complex; pyrimidine; tetraarylsilane; triphenylamine.
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