Rational design and characterization of novel phosphorescent rhenium(I) complexes for extremely high-efficiency organic light-emitting diodes

Three novel neutral tricarbonyl rhenium(I) [Re(I)] complexes (Re-PTIP, Re-TPIP and Re-TTIP) with donor–acceptor structures were designed and synthesized. Their photophysical and electrochemical properties were investigated in detail. These Re(I) complexes showed an orange emission with a high photoluminescence quantum efficiency of 9–18%. Organic light-emitting diodes (OLEDs) with the structure ITO/2-TNATA (4,4′,4′′-tris(N-(naphthalen-2-yl)-N-phenyl-amino)triphenylamine, 5 nm)/NPB (1,4-bis[(1-naphthylphenyl)amino]-biphenyl, 40 nm)/TCTA (4,4′,4′′-tris(N-carbazolyl)tri phenylamine, 10 nm)/CBP (4,4′-bis(carbazol-9-yl)biphenyl): 8% Re(I) complex (30 nm)/Bepp2 (bis[2-(2-hydroxyphenyl)-pyridine]beryllium, 40 nm)/LiF (0.5 nm)/Al (100 nm) were fabricated to evaluate the potential application of these Re(I) complexes. Excellent device performances (current efficiency: 26.0–36.5 cd A−1, power efficiency: 20.1–31.7 lm W−1 and external quantum efficiency: 9.8–12.0%) were achieved. In particular, OLEDs with Re-TTIP as the dopant emitter showed the best performance with a maximum current efficiency of 36.5 cd A−1, a maximum power efficiency of 31.7 lm W−1 and a maximum external quantum efficiency of 12.0% with low efficiency roll-off, which were among the best data for the Re(I)-based OLEDs reported so far. Our findings indicate the great potential of neutral tricarbonyl Re(I) complexes as phosphorescent emitting materials in OLEDs.