Sky-blue tri-cyclometalated heteroleptic iridium (III) phosphors: Influence of ancillary ligand

Two sky-blue tri-cyclometalated heteroleptic iridium complexes with the Ir(C"N)2(C1"N1) framework, namely M1 and M2, were developed with(3,5-bis(trifluoromethyl)phenyl)pyridine (cf3ppy) as the main cyclometalating ligand and 3-(1-benzyl-1H-1,2,3-triazol-4-yl)pyridine (pt) or 2 ',6 '-difluoro-2,3 '-bipyridine (dfbpy) as the ancillary cyclometalating ligand. The effect of the C1"N1 ancillary ligand on the photophysical, thermal, electrochemical properties as well as the device performances were studied comparatively. It was revealed that the ancillary ligand pt favored to suppress the longer-wavelength vibronic band intensity and thus enhanced the blue color purity of the tris-cyclometalated iridium complex M1. Sky-blue phosphorescent organic light-emitting diodes (OLEDs) were fabricated with these iridium phosphors as doped emitter. The M1-based OLED exhibited better performance with improved color purity and reduced intensity at long-wavelength vibronic band, and a maximum current efficiency and external quantum efficiency of 28.2 cd/A and 12.5 %. This study provides a valid molecular design strategy to control the intensity of the shoulder vibronic sub-band for optimized color purity of cyclometalated iridium phosphors.