Highly twisted bipolar emitter for efficient nondoped deep-blue electroluminescence

Abstract

Three novel bipolar deep-blue emitters, 1-(4-(tert-butyl)phenyl)-2-(4-(9,9-diphenylacridin-10(9H)-yl)phenyl)-1H-phenanthro[9,10-d]imidazole (DPACTPI), 1-(4-(tert-butyl)phenyl)-2-(4′-(9,9-diphenylacridin-10(9H)-yl)-[1,1′-biphenyl]-4-yl)-1H-phenanthro[9,10-d]imidazole (DPACPhTPI) and 2-(4-(9,9-diphenylacridin-10(9H)-yl)phenyl)-1-(4-(trifluoromethyl)phenyl)-1H-phenanthro[9,10-d]imidazole (DPACFPPI), employing the donor 9,9-diphenyl-9,10-dihydroacridine (DPAC) and the acceptor, phenanthroimidazole, were designed and synthesized. The highly twisted conformations between DAPC and phenanthroimidazole in the molecules efficiently interrupt molecular π-conjugation and inhibit π-π intermolecular interactions, resulting in good thermal stability and efficient deep-blue emission. The three phenanthroimidazole derivatives in non-doped OLEDs exhibited deep-blue emission. In particular, DPACPhTPI-based nondoped device showed an excellent performance with maximum external quantum efficiency (EQE) of 3.50%, maximum current efficiency (CE) of 1.38 cd/A, maximum power efficiency (PE) of 1.40 lm/W and CIE coordinate of (0.156, 0.047), which is among the best results for OLEDs with a similar color. The high radiative exciton utilization could be resulted from hybridized local and charge transfer (HLCT).