Multi-resonant thermally activated delayed fluorescence emitters based on tetracoordinate boron-containing PAHs: colour tuning based on the nature of chelates

Multi-resonant thermally activated delayed fluorescence (MR-TADF) materials have attracted considerable attention recently. The molecular design frequently incorporates cycloboration. However, to the best of our knowledge MR-TADF compounds containing nitrogen chelated to boron are still unknown. Reported herein is a new class of tetracoordinate boron-containing MR-TADF emitters bearing C<<^>>N<<^>>C- and N<<^>>N<<^>>N-chelating ligands. We demonstrate that the replacement of the B-C covalent bond in the C<<^>>N<<^>>C-chelating ligand by the B-N covalent bond affords an isomer, which dramatically influences the optoelectronic properties of the molecule. The resulting N<<^>>N<<^>>N-chelating compounds show bathochromically shifted absorption and emission spectra relative to C<<^>>N<<^>>C-chelating compounds. The incorporation of a tert-butylcarbazole group at the 4-position of the pyridine significantly enhances both the thermal stability and the reverse intersystem crossing rate, yet has a negligible effect on emission properties. Consequently, high-performance hyperfluorescent organic light-emitting diodes (HF-OLEDs) that utilize these molecules as green and yellow-green emitters show a maximum external quantum efficiency (eta(ext)) of 11.5% and 25.1%, and a suppressed efficiency roll-off with an eta(ext) of 10.2% and 18.7% at a luminance of 1000 cd m(-2), respectively.

Automated summary

Multi-resonant thermally activated delayed fluorescence (MR-TADF) materials have attracted attention for their potential application in high-performance organic light-emitting diodes (HF-OLEDs). This study introduces a new class of tetracoordinate boron-containing MR-TADF emitters with different chelating ligands, showcasing how structural modifications can significantly impact the optoelectronic properties of the molecules. The incorporation of specific functional groups enhances the thermal stability and performance of the compounds for efficient device applications.