As mentioned above, the overall goal was to develop a combined photo(electro)lyzer able to oxidize water to oxygen and reduce nitrogen to ammonia. The oxidation part has been focused on the development of a supramolecular system which self assemble through weak interactions based on a photosensitizer able to harvest light and on a catalyst able to split water into oxygen. The ability of this system (made of perylene molecules surrounding a Ruthenium catalyst) to split water was demonstrated in 2018, with a paper published by Bonchio et al.On the other hand this structure is disorganized and self-assemble without a particular order, giving rise to potential non-radiative decay pathways that might be a limitation factor for a performative catalysis. Taking into account this argument, we decided to make a more ordered structure. In particular, we decided to lock the molecules of light harvesters in an ordered structure that can be tuned by changing the number of units efficiently. Another fair point of my research was the study of less demanding oxidative reactions that can be coupled to the reduction reaction, that is the center of our study.In particular we decided to focus on acid bromide splitting, which products are very useful storage sources to employ in fuel cells. This system is based, similarly, on a supramolecular aggregate made of several organic molecules (perylenes) packed through weak bonds that can be tuned if needed. The work has been submitted and accepted and it is going to be published soon. At the same time the reductive part was developed, taking into account the demanding kinetic associated to the process. Indeed, reduction of nitrogen to ammonia is a 6electron 6proton reaction. While is a thermodynamic favored process, from the point of view of the kinetic is problematic and requires a good catalyst. A very straightforward way to overcome the barrier is the concerted transfer of protons and electrons to nitrogen through the mean of a catalyst. This process can be very feasible if coupled with the power of sunlight. One good example of this is a paper published by Peters et al in 2022. In this particular study it was ruled in the possibility to run nitrogen reduction through the employment of a small organic molecule that in principle was only employed as electrons source for photocatalysts (namely, sacrificial electron donor). We started from that paper to study the mechanism behind the catalysis. The conclusion of the work points towards the fact that the small organic molecule is the responsible of the efficient catalysis. The paper related has been submitted and it will be published soon. At the same time, in the same directions, three different routes have been explored in parallel. All the three routes point towards the direction of using a light that is green shifted. First of all, ruthenium/Iridium metal based light harvesters were coupled with a Tungsten based catalyst for nitrogen reduction. At the same time two other routes were explored photo(electro)chemically, being the light absorbing source in the two cases respectively a Molybdenum based system which has excited state properties that favor a long lived state; and a green light absorbing organic molecule, which was firstly employed in oxygen evolution (namely perylene), with a non reducing excited state that can be tuned by the access to a dianionic state
