Highly Effective Thermally Activated Delayed Fluorescence Emitters Based on Symmetry and Asymmetry Nicotinonitrile Derivatives.

In this study, we developed two thermally activated delayed fluorescence (TADF) emitters, and , to apply to organic light-emitting diodes (OLEDs). These emitters involve indolocarbazole (ICz) donor units and nicotinonitrile acceptor units with a twisted donor-acceptor-donor (D-A-D) structure for small singlet (S) and triplet (T) state energy gap (Δ) to enable efficient exciton transfer from the T to the S state. Depending on the position of the cyano-substituent, has a symmetric structure by introducing donor units at the 3,5-position of isonicotinonitrile, and has an asymmetric structure by introducing donor units at the 2,6-position of nicotinonitrile. These emitters have different properties, such as the maximum luminance () value. The of reached over 10000 cd m. The external quantum efficiency () was 14.8% for and 14.9% for , and both achieved a low turn-on voltage () of less than 3.4 eV.