Photoredox-Catalyzed Reduction of Halogenated Arenes in Water by Amphiphilic Polymeric Nanoparticles

Challenges and Future Perspectives in Photocatalysis: Conclusions from an Interdisciplinary Workshop

Photocatalysis is a versatile and rapidly developing field with applications spanning artificial photosynthesis, photo-biocatalysis, photoredox catalysis in solution or supramolecular structures, utilization of abundant metals and organocatalysts, sustainable synthesis, and plastic degradation. In this Perspective, we summarize conclusions from an interdisciplinary workshop of young principal investigators held at the Lorentz Center in Leiden in March 2023. We explore how diverse fields within photocatalysis can benefit from one another. We delve into the intricate interplay between these subdisciplines, by highlighting the unique challenges and opportunities presented by each field and how a multidisciplinary approach can drive innovation and lead to sustainable solutions for the future. Advanced collaboration and knowledge exchange across these domains can further enhance the potential of photocatalysis. Artificial photosynthesis has become a promising technology for solar fuel generation, for instance, via water splitting or CO2 reduction, while photocatalysis has revolutionized the way we think about assembling molecular building blocks. Merging such powerful disciplines may give rise to efficient and sustainable protocols across different technologies. While photocatalysis has matured and can be applied in industrial processes, a deeper understanding of complex mechanisms is of great importance to improve reaction quantum yields and to sustain continuous development. Photocatalysis is in the perfect position to play an important role in the synthesis, deconstruction, and reuse of molecules and materials impacting a sustainable future. To exploit the full potential of photocatalysis, a fundamental understanding of underlying processes within different subfields is necessary to close the cycle of use and reuse most efficiently. Following the initial interactions at the Lorentz Center Workshop in 2023, we aim to stimulate discussions and interdisciplinary approaches to tackle these challenges in diverse future teams.

Unravelling the Effect of Water Addition in Consecutive Photocatalysis with Naphthalene Diimide

We describe the effect of water addition in the catalyst performance for a C-H functionalization of benzene. Improved yields and selectivity were achieved in a consecutive photoredox catalysis in contrast to the reaction without water. Mechanistic analysis demonstrated this is due to a better catalyst stability and faster kinetic rather than a change in the different steps of the mechanism. The addition of water constitutes a convenient approach to improve catalyst performance, and it was also observed with other catalysts.

Direct C-H Trifluoromethylation of (Hetero)Arenes in Water Enabled by Organic Photoredox-Active Amphiphilic Nanoparticles

Photoredox-catalyzed chemical conversions are predominantly operated in organic media to ensure good compatibility between substrates and catalysts. Yet, when conducted in aqueous media, they are an attractive, mild, and green way to introduce functional groups into organic molecules. We here show that trifluoromethyl groups can be readily installed into a broad range of organic compounds by using water as the reaction medium and light as the energy source. To bypass solubility obstacles, we developed robust water-soluble polymeric nanoparticles that accommodate reagents and photocatalysts within their hydrophobic interior under high local concentrations. By taking advantage of the high excited state reduction potential of N-phenylphenothiazine (PTH) through UV light illumination, the direct C-H trifluoromethylation of a wide array of small organic molecules is achieved selectively with high substrate conversion. Key to our approach is slowing down the production of CF3 radicals during the chemical process by reducing the catalyst loading as well as the light intensity, thereby improving effectiveness and selectivity of this aqueous photocatalytic method. Furthermore, the catalyst system shows excellent recyclability and can be fueled by sunlight. The method we propose here is versatile, widely applicable, energy efficient, and attractive for late-stage introduction of trifluoromethyl groups into biologically active molecules.

Visible-Light Photoredox Catalysis in Water

The use of water in organic synthesis draws attention to its green chemistry features and its unique ability to unveil unconventional reactivities. Herein, literature about the use of water as a reaction medium under visible-light photocatalytic conditions is summarized in order to highlight challenges and opportunities. Accordingly, this Synopsis has been divided into four different sections focused on (1) the unconventional role of water in photocatalytic reactions, (2) in-/on-water reactions, (3) water-soluble photocatalysts, and (4) photomicellar catalytic systems.