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

Abstract

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.