A Design Strategy for Multiple Resonance-Induced Pure Violet Thermally Activated Delayed Fluorescence Emitters with a Narrow Emission Band

This study proposes a novel approach to develop highly efficient, narrow-emitting violet materials based on boron and oxygen polycyclic aromatic hydrocarbon multiple resonance structure. Herein, B-2OCz is developed by fusing indole with a 5,9-dioxa-13bboranaphtho[3,2,1-de]anthracene (DOBNA) core to enhance its thermally activated delayed fluorescence (TADF) properties and molecular rigidity. On the other hand, the B-2OCz-Si is decorated with a bulky tetraphenylsilyl substituent. B-2OCz-Si exhibits exceptional features such as violet emission at 397 nm, a very small full width at half maximum of 16 nm, and 82% of photoluminescence quantum yield. The B-2OCz-Si devices achieve a high external quantum efficiency of over 15%, violet emission with a peak wavelength of 423 nm, and color coordinates of (0.156, 0.037). Furthermore, the B-2OCz-Si is used as an electron transport type host material for phosphorescent organic light-emitting diodes (PhOLEDs), based on its high triplet energy and TADF properties. As compared to the conventional triazine based host materials, these newly developed DOBNA-based materials display superior device lifetime performance. All these potential aspects corroborate that this new class of DOBNA-based materials can work as a promising host material for PhOLEDs and violet-emitting fluorescent devices.