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.