New m -MTDATA skeleton-based hole transporting materials for multi-resonant TADF OLEDs.

Six new hole transporting materials based on the commercially available m -MTDATA core were synthesized by introducing different electron donating groups, such as methoxy, ethoxy and dimethylamino groups. To achieve the target compounds simple two-step synthesis was used by employing the Buchwald-Hartwig reaction. New derivatives were investigated experimentally and their thermal, optical, photoelectrical, and charge transporting properties were compared with the respective results of their commercial counterpart ( m -MTDATA). In solid-state and DCM solutions, target compounds and commercial m -MTDATA showed comparable ionization potential values. The compound with methoxy groups at the meta position showed a hole mobility of 1.06 × 10 -3 cm 2 V -1 s -1 at an electric field of 4.62 × 10 5 V cm -1 . These values exceed those reported for m -MTDATA. The synthesized derivatives were employed for the preparation of hole transporting layers in multi-resonant TADF OLEDs. Excellent colour purity and high maximum external quantum efficiency reaching 13.8% were achieved for OLEDs employing the synthesized hole-transporting material and the deep-blue MR-TADF emitter t -DABNA.