Intramolecular-locked triazatruxene-based thermally activated delayed fluorescence emitter for efficient solution-processed deep-blue organic light emitting diodes

Developing efficient deep blue thermally activated delayed fluorescence (TADF) emitters for solution-processed organic light emitting diodes (OLEDs) remains a formidable challenge. Herein, three new TADF emitters, namely FTAT-MBO, FTAT-HBO and FTAT-FBO, are designed and synthesized by incorporating intramolecular-locked triazatruxene with deep highest occupied molecular orbital and high triplet level as the electron donor and the boron-fused units with different substituents of methyl, hydrogen, and fluorine as the electron acceptors. Three compounds show blue emission (445–473 nm) with photoluminescence quantum yields up to 90% and bandwidths down to 54 nm. They also exhibit distinct TADF effect with small singlet − triplet energy splitting (ΔEST) below 0.2 eV and short delay fluorescence lifetimes (down to 1.8 μs). Solution-processed TADF OLEDs based on FTAT-MBO and FTAT-HBO as emitters displayed deep blue emission with the maximum external quantum efficiency (EQE) and Commission Internationale de l’éclairage (CIE) coordinates of 10.2% and (0.15, 0.08); 11.4% and (0.15, 0.12); respectively, while the solution-processed sky-blue OLEDs based on FTAT-FBO achieved the maximum EQE of 17.5% and CIE coordinates of (0.15, 0.25). This study demonstrates the potential of the intramolecular-locked triazatruxene donor unit to construct efficient TADF materials for the fabrication of solution-processed deep-blue to sky-blue OLEDs.