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Nature as Model

26 Aug | By Biophotonics.World
Nature as Model
Image source: Leibniz IPHT
By: Sven Döring

Linda Zedler, Maria Wächtler and Benjamin Dietzek are investigating the basics of artificial photosynthesis 


How Light Keeps
Chemical Reactions Moving 

Researchers visualize ultrashort chemical reactions in a time-resolved manner and thus provide fundamental findings for the sustainable production of hydrogen from sunlight and water 

In order to supply people worldwide with climate-friendly energy, hydrogen is considered the fuel of the future. Attempts to produce it in an environmentally friendly way from sunlight and water have so far been unproductive. Linda Zedler and her team from the research department "Functional Interfaces" have now developed a method to decipher basic processes in order to investigate new materials for the use of solar energy following nature's example. Using a combination of spectroscopic and electrochemical techniques, the scientists can for the first time show the mechanisms by which complex, multi-step light-driven processes operate. 

"Up to now, we have perceived light-driven processes as a hundred meter run, where you hear the starter's gun and then only see the finish photo again," explains Benjamin Dietzek, who heads the research department. Following the model of photosynthesis in nature, chemical reactions are triggered by light in such multi-step photocatalytic processes. Due to the extremely short lifespan of these intermediates, it has not yet been possible to investigate how these reactions take place and which factors influence the reactivity of intermediates. The research team is now showing new approaches to analyze this reactivity. 

Processes that researchers previously overlooked 

"It is a fundamental advance that we have managed to look at the dynamics of the processes triggered by light in an intermediate product," reports Maria Wächtler, who was involved in researching the process. "The first hurdle we cleared was to be able to produce these very reactive intermediates in sufficient concentration at all." Only then did the researchers gain access to the process after the start of photoinduction, which they had previously been blind to. 

In order to make such ultrashort chemical reactions visible on a time-resolved basis the researchers combine spectroelectrochemical methods with quantum chemical simulations. "We have thus developed a method that can in principle be applied to all multi-step photocatalytic processes," says Benjamin Dietzek. It enables scientists to gain a better understanding of the entire catalytic activity by providing insights into the sequence of multi-step multi-electron transfer cascades, which has previously not been understood until now. These take place in the respiratory chain as well as in natural and artificial photosynthesis or in solar cells. The method thus opens up new possibilities for researching highly active and stable photocatalysts for the production of hydrogen and a climate-friendly energy supply of the future. 

The work was carried out within the Collaborative Research Center Sonderforschungsbereich, SFB "CataLight" ("Light-driven Molecular Catalysts in Hierarchically Structured Materials – Synthesis and Mechanistic Studies"), in which teams of scientists from Leibniz IPHT and the universities of Jena and Ulm are developing molecular catalyst systems for the light-controlled production of hydrogen and oxygen from water based on the model of natural photosynthesis. 

The vision: artificial chloroplasts 

The research of "CataLight" focuses on the constructive interaction between molecular photocatalysts and their polymer-based environment, which allow a high degree of control over reactivity but are relatively unstable compared to photocatalytically active metal oxides. "We want to find a new way to stabilise such molecular photocatalysts and make repair methods accessible," said CataLight spokesperson Sven Rau from the University of Ulm. "We look at how nature does it," adds Benjamin Dietzek, "and integrate the molecular components into soft matter in order to establish new concepts for photocatalytic water splitting." The goal? "Using the energy of sunlight to split water with molecular machines", says Sven Rau. "We want to provide a mechanistic understanding of the interactions of light-driven molecular catalysts with structured soft materials." However, intensive research is required before basic research on the chemical process can lead to the long-term goal of producing artificial chloroplasts. "We want to recreate processes that nature has developed over millions of years," stresses Maria Wächtler. "Photosynthesis is highly complex, with several systems interacting. To efficiently imitate this with simplified systems is a great challenge. But we are convinced that the photocatalytic approach to produce hydrogen can be a technological solution." 

Publication: Linda Zedler et al., Unraveling the Light-Activated Reaction Mechanism in a Catalytically Competent Key Intermediate of Multifunctional Molecular Catalyst for Artificial Photosynthesis, Angewandte Chemie, 58 (37), 2019, https://doi.org/10.1002/anie.201907247 

Source: Leibniz IPHT


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