In a groundbreaking advance poised to reshape sustainable chemical synthesis, researchers at the Center for Research in Biological Chemistry and Molecular Materials (CiQUS) have unveiled a novel photocatalytic system that leverages red light and reusable covalent organic frameworks (COFs). This innovative platform addresses long-standing challenges in photocatalysis by employing a low-energy light source combined with a recyclable heterogeneous catalyst, marking a significant step forward in green chemistry and opening new avenues in complex molecule construction.
Photocatalysis, the acceleration of chemical reactions via light activation, has gained immense traction in recent years for its potential to perform transformations under milder and more environmentally benign conditions than traditional methods. However, conventional photocatalysts often suffer from limitations related to their homogeneous nature—they dissolve in reaction media, making recovery and reuse cumbersome. Furthermore, many catalysts are activated by blue or ultraviolet light, forms of high-energy radiation that can degrade sensitive substrates, penetrate only superficially into reaction mixtures, and demand substantial energy inputs, hindering scalability and applications in biological contexts.
Addressing these constraints, the CiQUS team developed a unique photocatalytic approach utilizing red light, a wavelength of substantially lower energy that penetrates deeper into reaction systems and reduces energy consumption. Central to this advance is the integration of COFs—highly tunable, crystalline porous polymers constructed from organic monomers linked by robust covalent bonds. Unlike metal-organic frameworks (MOFs), COFs are entirely organic, enabling precise molecular design, exceptional chemical stability, and modular optoelectronic properties which are advantageous for light-harvesting applications.
The researchers synthesized a bespoke COF incorporating benzothiadiazole-based photoactive units, conferring strong absorption in the red region of the visible spectrum and efficient generation of excited states capable of initiating catalytic cycles. This structural design facilitates the creation of reactive intermediates necessary to drive chemical transformations while ensuring that the catalytic material remains a solid phase. The solid-state nature allows for straightforward recovery and reuse—remarkably, the catalyst demonstrated consistent activity through at least six cycles without noticeable degradation, an achievement that significantly enhances its practical viability compared to conventional homogeneous photocatalysts.
To demonstrate the versatility and efficacy of their system, the researchers selected the direct C(sp²)–H sulfonylation of anilines as a model transformation. This reaction introduces sulfone functionalities—structural motifs that are essential in many pharmaceuticals and bioactive molecules, known for enhancing molecular stability and modulating biological interactions. By enabling sulfonylation under mild, red-light-driven conditions with minimal catalyst loading, the approach showcases a clean, direct, and broadly applicable synthetic route that aligns with principles of atom economy and sustainability.
The research underscores the remarkable synergistic collaboration between CiQUS groups specializing in organic synthesis, photocatalysis, and COF design. This internal dynamic ecosystem, nurtured by the CiQUS-Synergy program, embodies the forefront of interdisciplinary innovation, combining deep expertise in materials engineering with synthetic methodology development. Such collaborative workflows foster accelerated discovery and refinement of novel catalytic platforms capable of addressing complex challenges in modern chemistry.
In contrast to many existing photocatalytic systems demanding blue or ultraviolet light, the adoption of red light offers substantial practical advantages. Red light is less damaging to functional groups, enabling the preservation of delicate molecular architectures during transformations. Its superior penetration also makes it highly suited for reactions on larger scales or in heterogeneous media where diffusional limitations can curtail efficiency. Additionally, red light sources often exhibit greater energy efficiency and lower operational costs, enhancing the overall sustainability profile of photocatalytic processes.
The versatility of COFs as heterogeneous photocatalysts advanced by this study also highlights the untapped potential of these materials for diverse chemical applications. The finely tuneable pore sizes and surface functionalities inherent to COF architectures enable precise control over substrate-catalyst interactions, while their crystalline nature supports stable electronic environments conducive to efficient charge transfer. Progress in incorporating robust photoactive fragments expands the landscape of accessible photocatalytic properties, facilitating innovations not only in chemical synthesis but also in fields such as environmental remediation and solar energy harvesting.
Of particular note is the environmentally friendly aspect of catalyst recycling. Traditional homogeneous photocatalysts generate significant amounts of chemical waste or require elaborate filtration and purification steps, limiting their practicality and commercial appeal. The ability to recover and reuse a red-light-active COF catalyst without compromising performance reduces both material costs and environmental impact, aligning with the global demand for greener chemical technologies and sustainable materials management.
The implications of this research extend beyond synthetic organic chemistry. The use of red light-responsive COFs suggests promising applications in biomedicine, where the moderate energy of red light avoids harmful effects associated with ultraviolet exposure and can penetrate biological tissues more effectively. This could enable novel photoactivated therapeutic strategies or diagnostic tools capitalizing on the selectivity and stability of COF-based materials.
Published in the Journal of the American Chemical Society, the study sets a new benchmark for combining advanced material design with sustainable photochemical processes. By demonstrating the efficacy of benzothiadiazole-based COFs as recyclable catalysts activated by low-energy red light, the research not only challenges prevailing paradigms in photocatalysis but also paves the way for further explorations into tailored organic frameworks optimized for a wide range of photochemical and photophysical functions.
This work also reinforces the importance of fostering interdisciplinary and collaborative research environments that bring together materials science, organic chemistry, and photophysics. The CiQUS center’s integrative approach, supported by regional and European funding programs, exemplifies how strategic investment in cross-disciplinary teams can accelerate the discovery of innovative solutions to pressing scientific and technological challenges, especially those related to sustainability and energy efficiency.
In conclusion, the synergy of recyclable COF materials with red-light photocatalysis introduced by CiQUS researchers represents a transformative advance in sustainable chemistry. Their findings redefine the capabilities of heterogeneous photocatalysts, enabling efficient, mild, and environmentally considerate synthesis of valuable chemical entities. The broad applicability, coupled with the potential to extend this platform into biological and industrial realms, heralds a new era where light-driven catalysis harmonizes with principles of green chemistry to meet future demands.
Subject of Research: Covalent organic frameworks as recyclable heterogeneous photocatalysts driven by red light for sustainable organic synthesis.
Article Title: Red-Light-Driven C(sp2)–H Sulfonylation of Anilines Using a Recyclable Benzothiadiazole-Based Covalent Organic Framework
News Publication Date: 13-Oct-2025
Web References:
DOI:10.1021/jacs.5c12697
Image Credits: Illustration by Eugenio Vázquez Sentís
Keywords
Covalent organic frameworks; Photocatalysis; Sustainable chemistry; Red light; Benzothiadiazole; Heterogeneous catalysis; Sulfonylation; Organic synthesis; Recyclable catalysts; Green chemistry; Photochemical reactions; Molecular materials
