Researchers at Nanjing University of Posts & Telecommunications have developed a nanopore-confinement technique that unlocks intrinsic thermally activated delayed fluorescence in flexible crystalline covalent organic frameworks, according to a study published August 15, 2026, in Nature Communications.
Standard covalent organic framework lattices waste 75% of electro-generated excitons as non-emissive triplets. While thermally activated delayed fluorescence (TADF) can harvest those triplets, doing so in ordered crystalline frameworks has been obstructed by a molecular trade-off: minimizing the singlet-triplet energy gap requires conformational flexibility, yet suppressing non-radiative decay requires structural rigidity.
The researchers resolved this conflict by embedding conformationally locked donor-acceptor motifs directly into the framework backbone. The spatial constraints inside the crystalline nanopores force donor-acceptor pairs into conformations that shrink the singlet-triplet energy gap to 0.014 electron volts, while the rigid framework simultaneously suppresses vibrational energy losses.
The approach turns the frameworks into active exciton management platforms without compromising crystallinity, film integrity, or material processability. This produces free-standing films with high photoluminescence quantum yields and enables solution-processed organic light-emitting diodes that deliver competitive performance among crystalline porous emitters.
Xiang-Chun Li, Hao Sun, Weijie Yang, Weizhe Luo, Zuqiang Wang, Qinchen Jiang, Chuanrui Wu, Qiaoyu Wang, and Wen-Yong Lai conducted the research at the State Key Laboratory of Flexible Electronics, Institute of Advanced Materials, and School of Chemistry and Life Sciences in Nanjing, China. The team received funding from the National Key Research and Development Program of China, the National Natural Science Foundation of China, and the Basic Research Program of Jiangsu Province.
