Achieving Highly Efficient Deep-blue OLEDs by Introducing Intramolecular Hydrogen Bonds to Tune the Properties of Multiple Resonance Emitters

Multi-resonance thermally activated delayed fluorescence (MR-TADF) materials are considered a class of organic materials with exceptional electronic and optical properties, which make them promising for the applications in organic light-emitting diodes (OLEDs). However, the steric repulsion from the spatially-close hydrogens would twist the multi-resonance skeletons to cause the potential spectral broadening issues. Herein, pyridine and pyrimidine as aromatic-heterocyclic-core are introduced to stiffen the MR framework and minimize the emission spectral broadening by an intramolecular locking strategy. Planarizing the molecular skeleton is achieved due to enhancement of intramolecular interactions (hydrogen bonds) and alleviating the hydrogen steric repulsion. In addition, as a first multiple resonance material with heteroatoms-core, the introduction of pyridine and pyrimidine not only maintains the conventional MR properties of the emitters, but also endows the emitters with tunable emission spectra. Thanks to the overall superior properties brought by the hydrogen‐bonds promoted molecular rigidity, our proof-of-concept molecules, Py-BN and Pm-BN, exhibit deep-blue TADF emission with ultra-narrow full width at half maximum (FWHM) of 14 and 13 nm and Commission Internationale de L’Eclairage (CIE) coordinates of (0.16, 0.03) and (0.16, 0.04), respectively. The OLED developed using them as the emitters demonstrate electroluminescence FWHM of 21 and 24 nm and achieve a high external quantum efficiencies (EQEs) of 15.8% and 5.8%, respectively.