Aza-Arenes for Promoting Efficient Stable Molecular WOCs

In todays science, one of the most challenging and demanding tasks is the development of new materials that can be utilized to make renewable and clean energy from abundant and easily accessible resources. Water and light afford an opportunity be converted as raw materials in artificial photosynthesis, a process where water splitting is used electrochemically to generate energy. One major obstacle is the development of robust and long-living water oxidation catalysts that efficiently produce molecular oxygen. Works have been aimed on the development of homogenous catalyst systems that can readily produce molecular oxygen via a defined pathway. The major challenge is the evolution of highly stable systems that can be immobilized on anode surfaces to drive water splitting catalysis in a controlled manner. Typical homogenous systems can suffer from an oxidative degeneration of the ligand sphere triggered by rough oxidation conditions leading to the decomposition of the complex. By introducing a special ligand sphere, several improvements in comparison to conventionally applied systems will be expected. In this coherence, aza-arenes are appealing ligands as a variation in number and position of the nitrogen-atoms can accomplish multinuclear and macromolecular catalysts (linear polymers or toroidal systems). Primarily, the formation of macromolecular structures will impinge positively on the thermodynamic stability of the catalysts. Additionally, toroidal structures that are built up from six building blocks have their active sites oriented inwards. The hole will act as size discriminator and only allows potential substrates to penetrate inside the hole for the transformation. Moreover, potential (deactivating) interferences between solvent molecules, counteranions or impurities and the WOC will be avoided. All in all, the geometry of the WOC will improve the turnover number (TON) and frequency (TOF) of the catalyst when generating elemental oxygen from water. This, in combination with an enhanced stability of macromolecular WOCs, will be beneficial for an immobilization of the catalysts into solid supports (anodes and photoanodes) that can be integrated in photo-electrochemical cells to successfully achieve an artificial photosynthetic system.