Efficient thermally activated delayed fluorescence emitters with regioisomeric effects for red/near-infrared organic light-emitting diodes

Considerable efforts have been made to design efficient thermally activated delayed fluorescence (TADF) emitters for organic light-emitting diodes (OLEDs). However, the development of efficient red/near-infrared (NIR) TADF materials with emission wavelengths beyond 600 nm remains a great challenge due to serious non-radiative decay according to the energy-gap law. Herein, two novel red luminogens consisting of acenaphtho[1,2-b]pyrazine-8,9-dicarbonitrile (APDC) with para- or ortho-substituted cyano groups as acceptors (A) and triphenylamine (TPA) as donors (D), abbreviated as p-APDC-DTPA and o-APDC-DTPA, respectively, are designed and prepared. These luminogens are thermally stable and exhibit evident TADF characteristics. The impact of regioisomeric D-pi-A-pi-D structures on their TADF properties and electroluminescence (EL) behaivors is investigated and discussed, and o-APDC-DTPA is found to have better EL properties than p-APDC-DTPA. A non-doped OLED based on o-APDC-DTPA displays NIR light with an EL peak at 712 nm and achieves an external quantum efficiency (EQE) as high as 6.6%. The doped OLEDs employing p-APDC-DTPA and o-APDC-DTPA as emitters show red/deep red lights with EL peaks at 614-660 nm and exhibit remarkable EL performances with the highest EQEs of 10.5 and 19.0%, respectively. This work provides a reasonable design strategy and meaningful insights into the structure-property relationship for red/NIR TADF materials, which is conducive to exploring high-performance red/NIR OLEDs.