You are combining two important trends – microfluidic systems that allow for continuous organic syntheses and energy transfer via light rather than heat. Where lies the most relevant advantage of your approach compared to conventional methods?
The use of microreactors provides definitely a strong advantage for photochemical transformations as it allows to ensure a homogeneous irradiation profile of the entire reaction solution. Due to the Bouguer-Lambert-Beer limitation, light is rapidly absorbed within the solution making it difficult to scale photochemical transformations in classical reactors. Such reactors would witness a decreased efficiency since the center of the reactor has almost no access to light. Consequently, prolonged reaction times are often needed to reach full conversion. Furthermore, this also results into overirradiation of your product and can lead to byproduct formation.
The approach of my group has always gravitated around a desire to solve real application problems for organic synthetic chemistry. The difficulty of scaling photochemical transformations was one of the major motivational drivers at the outset of my independent research career. We have approached that by developing continuous-flow photomicroreactors. Once that was solved you typically start seeing other issues, e.g. what about the use of solar energy to drive such reactions? Last year we published a paper in Angewandte Chemie (Angewandte Chemie International Edition 2017, 56 (4), 1050-1054; VIP article) which addresses this issue. The paper describes the development of luminescent solar concentrator photomicroreactor. Our reactor allows to harvest both direct and diffuse light, downconvert it to a narrow spectral range and deliver the luminescent photons to the embedded microflow channels. In that fashion, like natural photosynthetic systems in the tree leaf, we are able to increase solar light harvesting. Hence, the channels witness 7x more photons than any other alternative. Moreover, since we downconvert all the energy, we match the color of the light with the needs of the photocatalytic transformation. This means that non-useful energy can be converted in useful energy (energy-matching).
Now one thing that we could NOT handle at that point were big fluctuations in light, e.g. by passing clouds. This affects off course the photochemistry in the channels: less light means less conversion and thus varying light conditions result in a highly fluctuating reaction outcome. Recently, we have solved this by developing a self-optimization protocol which can automatically adjust the flow rates to ensure a constant conversion within the reactor (Green Chemistry 2018, DOI: 10.1039/c8gc00613j). The solution is extremely cheap and solves the problem efficiently. I believe this discovery brings us again one step closer towards a chemical industry which can be run on solar energy.
What would be the most relevant application that you envision for your work?
We want to develop cheap and accessible technological solutions for important chemical problems. Most of our work has focused on the development of new synthetic methodology and technology for photoredox catalysis. We hope that the technology we develop in the lab will eventually be used in the industry to prepare e.g. pharmaceuticals. Currently, we are working together with researchers from the pharmaceutical industry and with technology developers to get our technology into real applications.
But we do more than only photochemistry, we work also on technological solutions for C–H activation chemistry, enzyme catalysis and electrochemistry.
What do you like most about your research?
The interdisciplinary aspect of our research is really interesting. It is only when you see a problem from different angles that you can come up with a solution which satisfies the needs of the individual disciplines. Importantly, it also provides me with inspiration to solve problems which are otherwise difficult to solve. As an example: one key experiment in the mechanistic investigation of photocatalytic transformations is the so-called Stern-Volmer quenching study. This is an experiment which cost my students a lot of time to obtain reliable data. A day to a full week was unfortunately no exception, much to their frustration and despair. To address this issue, we have developed an automated protocol where we can do these measurements in a highly controlled fashion. This allowed us not only to reduce the experimental time to less than an hour but also to increase the accuracy of the obtained results. These results are now automatically send via email to the student allowing to devote their time to more productive tasks.
Learn more about Timothy Noel's research at ACHEMA:
"Visible-light photoredox catalysis in flow - towards a sustainable production of pharmaceuticals"
Thursday, 14 June 2018, 13.30 h, Hall 4 Room Europa