Highly Efficient Orange-Red Thermally Activated Delayed Fluorescence Compounds Comprising Dual Dicyano-Substituted...

The π-conjugation of molecules has a large influence on their excited state properties, especially for red thermally activated delayed fluorescence (TADF) materials. Two orange-red TADF compounds comprising dual dicyano-substituted pyrazine/quinoxaline acceptors have been designed and synthesized. TPA-2DCNQ (3,3'-((phenylazanediyl)bis(4,1-phenylene))bis(2-phenylquinoxaline-6,7-dicarbonitrile) with extended π-conjugated quinoxaline as the acceptor exhibits higher photoluminescence quantum yields (ca. 0.67-0.71) in doped films. A smaller energy splitting (ΔE_st ) between the first singlet excited state and triplet excited state is also achieved, indicating that extending the π-conjugation of the acceptor rationally is an effective approach to designing highly efficient long-wavelength TADF materials. Devices with TPA-2DCNQ as the emitter display maximum external quantum efficiencies (EQEs) of 12.6-14.0 %, which are more than twice those of devices containing TPA-2DCNPZ (6,6'-((phenylazanediyl)bis(4,1-phenylene))bis(5-phenylpyrazine-2,3-dicarbonitrile).