Peripheral Selenium Modification of Multi‐Resonance Thermally Activated Delayed Fluorescence Molecules for High‐Performance Blue Organic Light‐Emitting Diodes

Abstract Multi‐resonance thermally activated delayed fluorescence (MR‐TADF) molecules have attracted much attention in the academia owing to their unique photoelectrical properties. However, MR‐TADF emitters usually show slow reverse intersystem crossing (RISC) rate, resulting in high efficiency roll‐off of organic light‐emitting diodes (OLEDs) and seriously limiting their further development. Here, a peripheral selenium (Se) modification is presented for MR‐TADF molecules to promote the RISC process while keeping the narrowband emission for high‐performance blue OLEDs. Compared to the parent molecules (NBN and tBuNBN), SeNBN and SetBuNBN exhibited narrower full‐width at half maximum (FWHM) value of 23 nm and more obvious delayed fluorescence properties with a high efficiency of delayed fluorescence up to 86%, shorter delayed lifetime of 2.4 µs as well as a faster RISC rate of 3.34×10⁵ s⁻¹. Therefore, high‐performance OLEDs based on these two Se modified MR‐TADF emitters are achieved with a high maximum external quantum efficiency (EQE) up to 25.5% and extremely suppressed efficiency roll‐offs of 3.9% at 100 cd m⁻² and 24.4% at 1000 cd m⁻². This work demonstrated that the introduction of peripheral Se atom can achieve high‐performance organic semiconductors with both narrowband emission and fast RISC rate constant for high‐performance organic optoelectronic devices.