Isomeric Quinoxalinedicarbonitrile as Color-Managing Acceptors of Thermally Activated Delayed Fluorescent Emitters

Highly efficient yellow and red thermally activated delayed fluorescent (TADF) organic light-emitting diodes were developed using two quinoxalinedicarbonitrile units, quinoxaline-6,7-dicarbonitrile (6,7-DCQx) and quinoxaline-5,8-dicarbonitrile (5,8-DCQx) as electron acceptors, and t-butylcarbazole or 9,9-dimethylacridan as electron donors. The strong electron-withdrawing capability of the 5,8-DCQx and 6,7-DCQx acceptors enabled from yellow to red emission in the TADF emitters. Comparing 5,8-DCQx and 6,7-DCQx, a red-shifted emission by about 40 nm was observed in the 5,8-DCQx acceptor-based emitters, but the external quantum efficiency of the TADF devices was over 20% irrespective of the acceptor, proving the usefulness of the two acceptor moieties as the building blocks of the TADF emitters. Therefore, the quinoxalinedicarbonitrile acceptors are promising as the acceptor moiety for designing yellow or red TADF emitters.