Artificial Molecular Architectures Mimicking Photosynthetic Z Scheme – MolecularZScheme

Most of the energy found in the biosphere derives from the natural photosynthesis process. Mimicking this fundamental biological process represents a fantastic scientific challenge because it opens the possibility to produce fuels from sunlight at large scale with abundant and cheap raw materials such as water or carbon dioxide. This proposal involves fundamental science in the field of artificial photosynthesis, it is connected with solar energy which is a promising renewable energy source. So far, the majority of biomimetic molecular systems for artificial photosynthesis require sacrificial reagents to operate. Accordingly, the activation of low energy compounds into energy rich substances with sunlight generally consumes costly compounds and sometimes generates noxious by-products, restricting the economic interest. This limitation is due to the fact that it is difficult to generate both a strong oxidant and a strong reductant with a single photon of the visible spectrum. The use of water as electron source demands to generate both a strong oxidant and a strong reductant with sunlight. This project aims at developing new molecular materials to mimic the Z Scheme function of oxygenic photosynthesis for the first time. The concept proposed herein is at the forefront of what is accomplished today in artificial photosynthesis projects. It consists in electronically coupling two photoinduced charge separation processes brought about by two photons inside two distinct photomolecular systems. Similarly to natural photosynthesis, the Z scheme approach would enable to produce a high energy charge separated state, which would constitute a real energetic advantage to drive energy demanding chemical transformations such as water splitting or carbon dioxide reduction. In this project, two distinct approaches will be explored to mimic the Z Scheme. The first one consists in synthesizing and then linking two different classical homogenous photosystems such as S-D or S-A (S=sensitizer, D=electron donor and A=electron acceptor), whose photophysical properties will be first individually studied. One photosystem (mimic of PSI) will produce a strong reductant, while the other will generate a strong oxidant (mimic of PSII). The second strategy relies on the immobilization of a molecular architecture composed of a sensitizer tethered to a mimic of PSII on an inorganic semiconductor (such as TiO2). The pertinence and the feasibility of these two approaches are grounded on the fruitful collaboration of a synthetic group with a photophysicist team specialized in artificial photosynthesis and the results accumulated by these two teams on previous joint projects.