The materials at the centre of the study are covalent organic frameworks, or COFs, a class of substances that has captivated chemists for the better part of two decades. COFs are constructed from organic molecules stitched together by strong covalent bonds into extended, ordered lattices riddled with pores measured in nanometres. This marriage of crystalline precision and internal void space makes them tantalising candidates for everything from electronic devices and chemical sensors to energy storage systems. Yet there has always been a catch. In their pristine form, most COFs are electrical insulators, and the standard remedy has been post-synthetic doping, in which external substances are introduced to supply the electrons or holes needed for conduction. That remedy comes at a price, because dopants can disrupt the framework’s structure, diminishing its crystallinity, its porosity and its long-term stability.

The CiQUS researchers, working across three groups led by Manuel Souto, Diego Peña and Francisco Rivadulla, proposed a fundamentally different route. Rather than injecting charge carriers after the framework has been assembled, they designed the building blocks to carry them from the outset. The key ingredients are neutral trioxotriangulene radicals, often abbreviated TOT, a family of organic molecules distinguished by a highly delocalised spin and a remarkable resistance to degradation. Because these radicals are stable in their neutral state, they can be woven into the framework as genuine structural components rather than added later as guests, and their unpaired electrons stand ready to serve as charge carriers without the need for counterions or any other external chemical species.

The results reported in the journal Angewandte Chemie International Edition are striking on several fronts. The radical-embedded framework crystallised into an ordered lattice and exhibited genuine semiconducting behaviour, with room-temperature electrical conductivity ranking among the highest values ever recorded for a neutral, non-doped COF. Crucially, the material did not sacrifice the property that makes COFs so attractive in the first place. The framework retained a specific surface area exceeding 1,200 square metres per gram, a figure that speaks to an internal landscape of pores preserved intact despite the electronic functionality now built into its walls.

What distinguishes this approach from earlier attempts to electrify COFs is the intimate integration of function and structure. The TOT radicals are not additives suspended within the pores or molecules grafted onto the surface as an afterthought. They are part of the molecular backbone itself, positioned by design so that their unpaired electrons can participate in charge transport. The ordered arrangement of these radical units throughout the framework creates pathways along which charges can move, turning the entire crystalline edifice into a conduit for electricity. In conventional doped systems, by contrast, the charge carriers and the framework often coexist uneasily, with the dopant acting as an intruder whose presence is tolerated rather than celebrated.

The significance of the achievement lies in the simultaneous preservation of three properties that chemists have historically struggled to reconcile: electrical conductivity, crystallinity and porosity. Materials that conduct well tend to be dense and disordered; materials that are porous and crystalline tend to be insulating. By embedding stable radicals into the framework’s architecture, the Spanish team has demonstrated that these attributes need not be mutually exclusive. The study further shows that the framework can be modified by selecting different molecular components and linkages, offering chemists a tunable dial for adjusting the electronic properties of the resulting materials. That modularity is one of the great promises of COF chemistry, and the new work suggests it can now be extended into the semiconducting regime without compromise.

The practical implications stretch across a remarkably broad technological canvas. Conductive, porous and crystalline organic frameworks could serve in electronics, where their processability and structural diversity offer advantages over rigid inorganic semiconductors. They could underpin spintronics, a field that exploits electron spin rather than charge alone, since the embedded radicals carry intrinsic spin character. Their porosity makes them natural candidates for sensors, where target molecules can diffuse into the material and modulate its electrical response, and for electrochemical devices where ion and electron transport must be coordinated. Energy storage looms particularly large on the horizon, because the TOT units can reversibly accept electrons, a property that points toward their use as active materials in batteries. The researchers are careful to note that these applications remain prospects for future investigation rather than demonstrated realities, but the foundational chemistry is now in place.

Behind the paper lies a story of interdisciplinary synergy within a single research centre. Synthesising a COF is a synthetic chemist’s challenge, demanding the precise design of molecular building blocks and the control of polymerisation conditions; characterising its electronic behaviour is a physicist’s task, requiring careful measurement of conductivity and charge transport; and understanding how structure governs function demands expertise spanning both. The groups of Souto, Peña and Rivadulla contributed complementary perspectives on the design, synthesis, characterisation and property studies of the new materials. The collaboration also extended beyond Spain’s borders, drawing in scientists at the CICECO-Aveiro Institute of Materials at the University of Aveiro in Portugal, whose contributions helped complete the picture of the framework’s structure and behaviour.

The work has already attracted attention beyond the specialist literature. Chemical & Engineering News, the news magazine of the American Chemical Society, recently highlighted the study as a new route to producing semiconducting COFs without dopants, a signal that the broader chemistry community regards the strategy as more than an incremental advance. Published under the title Semiconducting Covalent Organic Frameworks Based on Spin-Delocalized Trioxotriangulene Neutral Radicals, the paper arrives at a moment when demand is surging for organic electronic materials that can be manufactured cheaply, tuned molecularly and deployed in applications where silicon cannot follow. CiQUS, which holds María de Maeztu Unit of Excellence accreditation and CIGUS recognition from the Xunta de Galicia, and receives support from the European Union through the Galicia FEDER 2021–2027 Programme, has positioned itself at the forefront of that effort. If the radical-embedded framework approach proves general, the era of doping organic semiconductors may be drawing to a close, replaced by materials that carry their own charge, pore by pore, bond by bond.

Subject of Research: Dopant-free semiconducting covalent organic frameworks based on spin-delocalized trioxotriangulene neutral radicals

Article Title: New strategy to produce porous organic semiconductors without doping

Article References: New strategy to produce porous organic semiconductors without doping. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: covalent organic frameworks, COFs, organic semiconductors, trioxotriangulene radicals, dopant-free conductivity, charge transport, porosity, crystallinity, energy storage, spintronics, CiQUS, Angewandte Chemie