Full-Color Sterically Shielded Boron Difluoride Emitters with Efficient and Ultrapure Electroluminescence via Sensitized Fluorescence

Emitters with narrowband emissions are essential to improve the color purity of organic light-emitting diodes (OLEDs). Boron difluoride (BF) derivatives have preliminarily exhibited small full width at half-maximum (FWHM) values in electroluminescent devices, which, however, still face formidable challenges in recycling triplet excitons and realizing full-color emissions covering the whole visible spectra. Here, a systematic molecular engineering on the aza-fused aromatic emitting core and peripheral substitutions is made, affording a family of full-color BF emitters spanning from blue (461 nm) to red (635 nm), with high photoluminescence quantum yields of >90% and a small FWHM of 0.12 eV. The device architectures are delicately manipulated to form effective thermally activated sensitizing emissions, first affording the highest maximum external quantum efficiency of >20% for BF-based OLEDs with negligible efficiency roll-off.