Donor Arylmethylation toward Horizontally Oriented TADF Emitters for Efficient Electroluminescence with 37% External Quantum Efficiency

Designing thermally activated delayed fluorescence (TADF) emitters with high horizontal orientation dipole ratios (Θ//) is regarded as one of the key measures to achieve high light outcoupling efficiency and thus efficient organic light‐emitting diodes (OLEDs). Herein, donor arylmethylation is presented to construct horizontally oriented TADF emitters. Two compounds PFDMAC‐TRZ and DPFDMAC‐TRZ are designed and synthesized through Friedel‐Crafts arylmethylation of their parent TADF molecule DMAC‐TRZ with 9‐phenyl‐9‐fluorenol. The 9‐phenyl‐9‐fluorene substituents endow PFDMAC‐TRZ and DPFDMAC‐TRZ with similar excited states and emission characteristics as DMAC‐TRZ due to the unique σ–π conjugation. Impressively, with an arylmethylated donor, PFDMAC‐TRZ and DPFDMAC‐TRZ show an enhanced horizontal orientation dipole ratio of 78% and 81%, respectively. Green TADF OLED based on DPFDMAC‐TRZ reaches a maximum external quantum efficiency of 37.0% and power efficiency of 124.5 lm W−1, which represents one of the most efficient green OLEDs reported so far. This work provides a facile yet powerful strategy to design and construct horizontally oriented luminogens for high‐performance optical devices. A strategy of donor arylmethylation for enhancing horizontal dipole orientation of thermally activated delayed fluorescence emitters is presented. The resulting emitter achieves a higher horizontal dipole ratio of 81% and superior electroluminescence performance with a maximum external quantum efficiency of 37.0% and power efficiency of 124.5 lm W−1.