Unlocking intrinsic TADF in flexible crystalline covalent organic frameworks through nanopore confinement design

Abstract

Covalent organic frameworks (COFs) combine structural precision with synthetic versatility, yet their crystalline lattices intrinsically waste 75% of electro-generated excitons as non-emissive triplets. Thermally activated delayed fluorescence (TADF) could harvest these triplets, but its realization in ordered frameworks has been thwarted by a molecular paradox: the conformational flexibility required to minimize the singlet-triplet energy gap (ΔEST) is fundamentally incompatible with the rigidity needed to suppress non-radiative decay in a crystalline lattice. Here we introduce a nanopore-confinement strategy that resolves this dichotomy and unlocks intrinsic TADF in flexible COFs. By embedding conformationally locked donor-acceptor motifs directly into the COF backbone, the spatial constraints of the crystalline nanopores force donor-acceptor pairs into conformations that minimize ΔEST to 0.014 eV, while the rigid framework simultaneously curtails vibrational losses. This approach transforms COFs from passive scaffolds into active platforms for exciton management without compromising crystallinity, film integrity, or processability, yielding free-standing films with high photoluminescence quantum yields and enabling solution-processed OLEDs with competitive performance among crystalline porous emitters. Our work provides an effective strategy for functionalizing porous frameworks through precise manipulation of excited-state dynamics, opening avenues for flexible electronics, photocatalysis, and beyond. Covalent organic frameworks combine structural precision with synthetic versatility, though many systems have unfavorable photophysical properties. Here the authors unlock thermally activated delayed fluorescence, using flexible COFs