Asymmetrically twisted anthracene derivatives as highly efficient deep-blue emitters for organic light-emitting diodes

Deep-blue emission is particularly important for applications of organic light-emitting diodes (OLEDs) in full colour flat-panel displays and solid-state lighting resources. Two asymmetrically twisted anthracene derivatives, 4,5-diphenyl-1,2-bis(4-(10-phenylanthracen-9-yl)phenyl)-1H-imidazole (DPA-PIM) and 1,2-bis(4-(10-phenylanthracen-9-yl)phenyl)-1H-phen-anthro[9,10-d]imidazole (DPA-PPI), for deep-blue OLEDs have been designed and synthesized. The asymmetrically twisted conformations between anthracene and imidazole units in compounds efficiently interrupt molecular π-conjugation and inhibit π-π intermolecular interactions, resulting in high thermal stability and efficient deep-blue emission. The two anthracene derivatives in non-doped OLEDs exhibited blue emission. In particular, the non-doped device based on DPA-PIM achieved an external quantum efficiency (EQE) of 6.5% with CIE coordinates of (0.15, 0.08). In addition, the two emitters in doped devices achieved high EQEs of over 5.0% and much purer blue emission with CIE coordinates of (0.15, 0.06) for DPA-PPI and (0.15, 0.05) for DPA-PIM, which nearly match the CIE coordinates of the European Broadcasting Union (EBU) blue standard of (0.15, 0.06).