Two novel neutral and ionic Ir(iii) complexes based on the same bipolar main ligand: A comparative study of their photophysical properties and applications in solution-processed red organic light-emitting diodes

Using 4-(5-(4-(dimesitylboranyl)phenyl)pyridin-2-yl)-N,N-diphenylaniline (BNpppy) as a cyclometalated ligand, 1,10-phenanthroline or 2,4-pentanedione (acac) as the ancillary ligand, respectively, two novel iridium(iii) complexes (Ir-1 and Ir-2) were successfully synthesized and their photoelectric properties have been investigated in detail. The incorporation of electron-accepting dimesitylboron (Mes2B) moieties and electron-donating triphenylamine moieties into iridium(iii) complexes has been demonstrated with benign photophysical and electronic properties. The solution-processed OLEDs were fabricated using these two iridium(iii) complexes, respectively. The devices of Ir-2 show good performances compared to those of Ir-1 with a maximum luminance of 7916 cd m-2, a maximum external quantum efficiency (EQE) of 2.48% and a maximum current efficiency of 3.99 cd A-1. These results indicate that the introduction of a donor-acceptor type of ligand into transition metal complexes has potential applications in constructing an efficient emitter in OLEDs with excellent performances.