Two novel neutral and ionic Ir(III) complexes based on the same bipolar main ligand: a comparative study of photophysical properties and the application 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 and 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. And the devices of Ir-2 show good performance 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 an donor-acceptor type of ligand into transition metal complexes has potential applications in constructing an efficient emitter in OLEDs with excellent performances