Blue Phosphorescence with High Quantum Efficiency Engaging the Trifluoromethylsulfonyl Group to Iridium...

Incorporation of an electron-withdrawing -SO₂CF₃ substituent to cyclometalating C^N-phenylpyridine (ppy) ligand resulted in an expected blue-shifted phosphorescence in the corresponding homoleptic Ir(ppySCF) complex, showing the emission of λ_em = 464 nm at 300 K. One of its heteroleptic derivatives, modified by a pyrazolyl borate LX ligand, Ir(ppySCF)(bor), exhibited further blue-shifted phosphorescence of λ_em = 460 nm at 300 K. Cyclic voltammograms (CVs) and density-functional theory (DFT) calculations supported the efficacy of the electron-withdrawing capability of the SO₂CF₃ substituent lowering HOMO energy and obtained widened bandgaps and resumed blue emissions for all of the iridium complexes studied. The homoleptic complexes of both substituents, Ir(ppySCF) and Ir(ppySF), reached the higher quantum yields (Φ_PL) of (0.89 and 0.72), respectively. Similarly, emission quantum yields (Φ_PL) of the heteroleptic derivatives were reported to be (0.75, 0.83, and 0.87) for Ir(ppySCF)(acac), Ir(ppySCF)(bor), and Ir(ppySCF)(pic), respectively. Emission kinetics support the enhanced quantum efficiency when k_r and k_nr values are compared between Ir(ppySCF) and Ir(ppySF), and both values favorably contribute to attaining a higher quantum efficiency for Ir(ppySCF). Among solution-processed multilayered devices having an ITO/PEDOT:PSS/TCTA:Ir dopant (10:1, w/w)/TmPyPB/Liq/Al structure, a heteroleptic dopant, Ir(ppySCF)(bor), exhibited better device performance, reporting an external quantum efficiency (EQE) of 1.14%, current efficiency (CE) of 2.31 cd A^-1, and power efficiency (PE) of 1.21 lm W^-1, together with blue chromaticity of CIE_x,y = (0.16, 0.32).