High Color Purity Deep-Blue Multi-Resonance TADF Material with Narrowband Emission Toward BT.2020 Standard

Due to higher exciton energy, the deep-blue organic light-emitting diodes (OLEDs) are the most challenging among trichromatic emitters. In this work, three novel blue emitters with multi-resonance (MR) effects are reported based on N,N,5,9-tetraphenyl-5,9-dihydro-5,9-diaza-13b-boranaphtho[3,2,1-de]anthracen-7-amine (PAB) skeleton, incorporating fluorine and methyl groups. Compound 2FPAB and MePAB exhibit ultra-pure deep-blue emission peaks at 436 and 448 nm respectively. The device based on MePAB achieves a maximum external quantum efficiency of 19.8% with an ultralow CIEy value of 0.046 and a full-width-at-half-maximum (FWHM) of 29 nm in the bottom emitting device. Additionally, the peripheral cladding of fluorine atoms extends the conjugation framework and slightly enhances the electron acceptance character of the boron atom at the ortho-position. This leads to a redshift in the emission spectrum and enhanced photoluminescence quantum yield (PLQY) of up to 93% for MePABF. Furthermore, the potential application of MePAB as a deep-blue sensitizer for MePABF is examined by fabricating a TADF-sensitized-TADF (TST) device. The results show a significantly reduced efficiency roll-off and improved device performance, with a maximum external quantum efficiency (EQEmax) of 25.1% and a FWHM of 29 nm.