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

Abstract

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–π–A–π–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.