Bicarbazole based donor-acceptor compound as a host for thermally activated delayed fluorescent emitter

A bicarbazole based donor-acceptor compound, 4,4′-([3,4′-bicarbazole]-9,9′-diyl)dibenzonitrile (4CN34BCz), was synthesized as a host material for thermally activated delayed fluorescent emitter and the device performances of the green devices with the synthesized host and (4s,6s)-2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN) delayed fluorescent emitter were investigated. 4CN34BCz with CN unit at para-position could effectively assist delayed fluorescent emission of 4CzIPN and achieved a high external quantum efficiency of 20.8% compared to 13.8% of the similar host with CN unit at meta-position because the orientation of the CN functional group at para position of the benzonitrile was favourable for charge balance in the emitting layer.