Robust Sandwich‐Structured Thermally Activated Delayed Fluorescence Molecules Utilizing 11,12‐Dihydroindolo[2,3‐a]carbazole as Bridge

• Published in: Angewandte Chemie International Edition 2025-01, Vol.64 (1), p.e202414488-n/a
• Main Authors: Lan, Xia, Zeng, Jiajie, Chen, Jinke, Yang, Tao, Dong, Xiaobin, Tang, Ben Zhong, Zhao, Zujin
• Format: Article
• Language: English
• Subjects: electroluminescence; organic light-emitting diodes; sandwich structures; thermally activated delayed fluorescence; through-space interactions
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202414488

Constructing folded molecular structures is emerging as a promising strategy to develop efficient thermally activated delayed fluorescence (TADF) materials. Most folded TADF materials have V‐shaped configurations formed by donors and acceptors linked on carbazole or fluorene bridges. In this work, a facile molecular design strategy is proposed for exploring sandwich‐structured molecules, and a series of novel and robust TADF materials with regular U‐shaped sandwich conformations are constructed by using 11,12‐dihydroindolo[2,3‐a]carbazole as bridge, xanthone as acceptor, and dibenzothiophene, dibenzofuran, 9‐phenylcarbazole and indolo[3,2,1‐JK]carbazole as donors. They hold outstanding thermal stability with ultrahigh decomposition temperatures (556–563 °C), and exhibit fast delayed fluorescence and excellent photoluminescence quantum efficiencies (86 %–97 %). The regular and close stacking of acceptor and donors results in rigidified molecular structures with efficient through‐space interaction, which are conducive to suppressing intramolecular motion and reducing reorganized excited‐state energy. The organic light‐emitting diodes (OLEDs) using them as emitters exhibit excellent electroluminescence performances, with maximum external quantum efficiencies of up to 30.6 %, which is a leading value for the OLEDs based on folded TADF emitters. These results demonstrate the proposed strategy of employing 11,12‐dihydroindolo[2,3‐a]carbazole as bridge for planar donors and acceptors to construct efficient folded TADF materials is applicable. Novel efficient thermally activated delayed fluorescence molecules with regular folded sandwich configurations are constructed using 11,12‐dihydroindolo[2,3‐a]carbazole as bridge, xanthone as acceptor, and dibenzothiophene, dibenzofuran, 9‐phenylcarbazole and indolo[3,2,1‐JK]carbazole as donors. They can function efficiently as emitters in organic light‐emitting diodes, providing high electroluminescence efficiencies of up to 30.6 %.