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 cm² V^-1 s^-1 at an electric field of 4.62 × 10⁵ 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.