Ir(III) phosphorescent complexes with the ligands attaching pyridyl group to 4-position of dibenzo[b,d]thiophene-S,S-dioxide/dibenzo[b,d]thiophene unit and their efficient solution-processed OLEDs

Abstract

Through attaching pyridyl ring to 4-position of dibenzo[b,d]thiophene-S,S-dioxide and dibenzo[b,d]thiophene, two ppy-type ligands have been developed. With the obtained ligands in one-pot reaction, three Ir(III) complexes have been synthesized as symmetric Ir-1 with two dibenzo[b,d]thiophene-S,S-dioxide units, unsymmetric Ir-2 with both dibenzo[b,d]thiophene-S,S-dioxide and dibenzo[b,d]thiophene units and symmetric Ir-3 with two dibenzo[b,d]thiophene units. Photophysical results show that their phosphorescent wavelengths fall in the order of Ir-2 (585 nm) ˃ Ir-1 (567 nm) ˃ Ir-3 (543 nm) in solution and their phosphorescent quantum yields (Φp) fall in the same order with ca. 0.83 for Ir-2, 0.68 for Ir-1 and 0.53 for Ir-3, indicating the advantage of constructing unsymmetric Ir(III) complexes. Solution-processed OLEDs based on the unsymmetric complex Ir-2 can show the highest electroluminescent (EL) efficiencies with the external quantum efficiency (ηext) of 16.6%, a maximum current efficiency (ηL) of 51.1 cd A − 1 and a maximum power efficiency (ηP) of 38.7 lm W − 1, indicating its great potential in the EL field. These encouraging results can provide critical information for developing highly efficient phosphorescent emitters based on dibenzo[b,d]thiophene-S,S-dioxide and dibenzo[b,d]thiophene groups.