Synthesis, photophysical, electrochemical and electroluminescence studies of red emitting phosphorescent Ir(III) heteroleptic complexes

Abstract

Five heteroleptic, cyclometalated (C $$^{\wedge }$$ N) Iridium(III) complexes of acetylacetone (acac) and 1-phenyl-isoquinoline (piq) derivatives, Ir(acac)(piq) $$_{2}$$ , Ir(acac)(2,4-difluoro-piq) $$_{2}$$ , Ir(acac)(4-trifluoromethyl-piq) $$_{2}$$ , Ir(acac)(4-N,N-dimethyl-piq) $$_{2}$$ , Ir(acac)(4-acetyl-piq) $$_{2}$$ , were synthesized and characterized. The ( $$\text {C}^{{\wedge }}\text {N})_{2}$$ Ir(acac) complexes in toluene showed phosphorescence ( $$\uplambda _{\max }= 598$$ nm to 658 nm) with quantum yields (0.1 to 0.32) and microsecond lifetimes (0.43 to 1.9 $$\upmu $$ s). The complexes were non-luminescent in thin films due to self-quenching but luminescent when lightly doped (5%) in a host organic material, 4,4 $$^\prime $$ -Bis(N-carbazolyl)-1,1 $$^\prime $$ -biphenyl (CBP). The HOMO levels determined using cyclic voltammetric oxidation potentials were in the range −5.48 to −5.80 eV. Electroluminescence properties and performance of the Ir complexes doped in CBP (active layer) were studied in a multilayer (ITO/F4TCNQ/TPD/doped CBP/BCP/LiF/Al) organic light emitting device (OLED). The electroluminescense (EL) spectra of the device matched with the phosphorescent spectra of the Ir complexes. The turn-on voltage at $$\sim $$ 4.5 V, maximum brightness of 7600 cd/ $$\hbox {m}^{2}$$ and current efficiency of $$\sim $$ 7.0 cd/A at a brightness of $$\sim $$ 100 cd/ $$\hbox {m}^{2}$$ indicate that these are promising OLED materials. Synopsis. Heteroleptic, cyclometalated (C $$^{\wedge }$$ N) Iridium(III) complexes of acetylacetone (acac) and 1-phenyl-isoquinoline were synthesized and their photophysical, electrochemical and electroluminescence properties were studied. The OLED of Ir complex as emitting material showed turn-on voltage at $$\sim $$ 4.5 V, maximum brightness of 7600 cd/ $$\hbox {m}^{2}$$ and current efficiency of $$\sim $$ 7.0 cd/A at a brightness of $$\sim $$ 100 cd/ $$\hbox {m}^{2}$$ .