Covalent-organic frameworks (COFs) are usually insulating materials. But a group of researchers in Galicia, Spain, now reports a simple way to make semiconducting COFs. The team made the new materials from neutral building blocks—instead of by adding dopants, a strategy used previously to try to modify COFs’ electronic properties. The new COFs can be tuned easily, opening the possibility of applications in electronics, spintronics, and energy storage (Angew. Chem., Int. Ed. 2026, DOI: 10.1002/anie.6104022).
Currently, researchers create conductive COFs by adding charge-carrying dopants. But that approach can compromise the crystallinity, porosity, structure, and stability of the materials, explains one of the study’s lead authors, Manuel Souto Salom of the Center for Research in Biological Chemistry and Molecular Materials at the University of Santiago de Compostela. In this case, the researchers devised “a new synthetic strategy for developing semiconducting COFs while preserving structure and porosity,” he says. The secret lies in using persistent radicals such as trioxotriangulene, a relatively long-lived compound featuring unpaired electrons.
The problem with using persistent radicals in synthesis is structural: they “require bulky protective groups, which inhibit the planarity, close stacking, and reversible assembly needed for crystalline COFs,” explains Safiya Khalil Alhashmi, an expert in reticular materials at New York University Abu Dhabi, who wasn’t involved in the study. But trioxotriangulene is flat and “stabilized through extensive spin delocalization, [which] produces a substantially more ordered and conductive [covalent-organic] framework,” she adds. This approach creates a crystalline semiconductive COF “without dopants or counterions [to] disrupt crystallinity and obstruct pores.” Overall, it’s an “all-in-one, simple material” ready for electronic transport with a low band gap, Khalil says.
“This demonstrates that neutral radicals generate charge carriers while preserving the crystallinity and porosity of the COF,” says Souto Salom. He adds that the COFs made this way exhibit the highest ever electrical conductivity for a nondoped, neutral COF.
Another advantage is that they’re modular materials. “In the world of COFs, changing the building blocks is only one option,” Khalil says. “Many other variations are possible, [including altering] linkage chemistry, radical spacing, stacking, interlayer distance, and film orientation.” Tuning these parameters creates a vast performance landscape, she adds. And replacing trioxotriangulene with other radicals could lead to larger conductivities and maybe magnetic properties, Souto Salom says, referring to recent reports.
In addition to applications in electronics where semiconductors are well established, this dopant-free semiconducting COF might also be used to build better batteries. “Trioxotriangulene units could reversibly accept electrons while lithium or sodium ions enter the [COF] pores, providing ion channels and preventing dissolution of the active molecules,” Khalil says. That idea is supported by earlier work indicating that trioxotriangulene holds promise for use in lithium-ion batteries.
Overall, this semiconducting COF is “particularly attractive for batteries, sensors, and electrochemical devices, where electronic conduction and chemical accessibility must work together,” Khalil says.
