Synthesis of Selenium‐Doped Heteroacenes: Unveiling the External Heavy‐Atom Effect in Host Materials

The internal heavy‐atom effect (IHAE) has garnered considerable attention as a promising approach for developing highly efficient emitters in organic light‐emitting diodes (OLEDs). Nevertheless, the external heavy‐atom effect (EHAE) in host materials, despite being equally important, has been largely overlooked. In this study, we introduce a selenium‐doping strategy to unlock the potential of EHAE in host molecules. To demonstrate this approach, we developed a straightforward method for synthesizing structurally diverse pyridine‐fused, selenium‐containing heteroacenes via an intramolecular radical cyclization of 2‐(arylselanyl)pyridin‐3‐amine derivatives. This method facilitates the rapid construction of a novel host molecule, DCz‐BSeP, by incorporating two carbazole groups into the benzo[4,5]selenopheno[2,3‐b]pyridine (BSeP) core. Compared to its oxygen‐based (DCz‐BFP) and sulfur‐based (DCz‐BTP) counterparts, the introduction of selenium in DCz‐BSeP significantly enhances spin–orbit coupling and accelerates the reverse intersystem crossing rate of thermally activated delayed fluorescence (TADF) emitters by threefold, while also improving bipolar transport properties. These enhancements make DCz‐BSeP an ideal bipolar host for high‐performance, wide‐color‐gamut TADF‐OLEDs, with notably reduced efficiency roll‐off. Additionally, its successful application in phosphorescent OLEDs (Ph‐OLEDs) and TADF‐sensitized narrowband red fluorescence OLEDs (TSF‐OLEDs) highlights its versatility in advancing OLED technologies.