Deep-red iridium(iii) complexes cyclometalated by phenanthridine derivatives for highly efficient solution-processed organic light-emitting diodes
Two deep-red emitting iridium complexes, [(TP-BQ)2Ir(acac) and (TPA-BQ)2Ir(acac)], with 6-phenanthridine derivatives as cyclometalating ligands were designed and synthesized. The relationship between the structures and their photophysical, electrochemical and electrophosphorescent properties was investigated. The introduction of a phenanthridine moiety enlarges the π conjugation and causes the peak emissions to red-shift to ca. 660 nm. Meanwhile, the bulky ligands sufficiently protect the emissive core from the intermolecular interaction to decrease triplet–triplet annihilation (TTA). The solution-processed electroluminescent devices with a single emissive layer using (TPA-BQ)2Ir(acac) as the triplet emitter achieve a maximum external quantum efficiency (EQE) of 5.2% with the emission peak at 682 nm.