Intramolecular C-H Activation as an Easy Toolbox to Synthesize Pyridine-Fused Bipolar Hosts for Blue Organic Light-Emitting Diodes.

The development of high-performance blue organic light-emitting diodes (OLEDs) remains a challenging task. While exploiting new blue emitters has attracted great interest, developing host materials that considerably determine device performance obviously lags behind. Herein, we present an ease of access to the structurally diverse benzoheteroaromatic-fused pyridine skeletons by the iridium-catalyzed intramolecular C-H/C-H coupling reaction, which unlocks an unparalleled opportunity to rapidly assemble a library of pyridine-fused bipolar host materials. As an illustrated example, the benzo[4,5]thieno[2,3-b]pyridine skeleton (BTP) has been made to a pseudo-symmetric host (DCz-BTP). The merging of a pyridine fragment enables strong intermolecular interactions, leading to satisfactory bipolar transporting properties. Utilizing DCz-BTP as the host, blue thermally activated delayed fluorescent OLEDs (TADF-OLEDs) exhibit a low turn-on voltage of 2.8 V and a high maximum external quantum efficiency (EQE ) of 29.0 % and blue TADF-sensitized florescent OLEDs (TSF-OLEDs) give an EQE as high as 20.5 %, revealing the potential of the BTP skeleton for the construction of high-performance host materials.