Rational design of blue TADF host of various polarity according to cyano- group applicable to blue thermally activated delayed fluorescence emitter

Abstract

Although remarkable progress has been made in the field of blue organic light-emitting diodes (OLEDs), many challenges persist. In particular, the emitting material layer of an OLED is composed of a host and a dopant, and the host material has a significant influence on the device efficiency and lifetime along with the dopant. Therefore, in this study, 9-(2′-(dibenzo[b,d]furan-4-yl)-[1,1′-biphenyl]-3-yl)-9H-carbazole, 3′-(9H-carbazol-9-yl)-2-(dibenzo[b,d]furan-4-yl)-[1,1′-biphenyl]-3-carbonitrile, and 3′-(9H-carbazol-9-yl)-2-(dibenzo[b,d]furan-4-yl)-[1,1′-biphenyl]-4-carbonitrile were synthesised to investigate the changes in the device efficiency and lifetime through various properties such as the polarity of the host molecule and anionic bond dissociation energies (BDEs) according to the substitution position of the CN group. In addition, 2,4,6-tris(2-(3,6-di-tert-butyl-9H-carbazol-9-yl)phenyl)-1,3,5-triazine, a blue thermally activated delayed fluorescence dopant, was synthesised and evaluated. The roll-off at 5000 nit decreased from 30.2% to 21.9% depending on the polarity of the host molecule, whereas the lifetime increased from 7.95 to 15.5 h according to the anionic BDE of blue thermally activated delayed fluorescence hosts.