An artificial photosynthetic system for photoaccumulation of two electrons on a fused dipyridophenazine (dppz) – pyridoquinolinone ligand

Increasing the efficiency of molecular artificial photosynthetic systems is mandatory for the construction of functional devices for solar fuels production. Decoupling the light-induced charge separation steps from the catalytic process is a promising strategy, which can be achieved thanks to the introduction of suitable electron relay units performing charge accumulation. We report here on a novel ruthenium tris-diimine complex able to temporarily store two electrons on a fused dipyridophenazine-pyridoquinolinone π-extended ligand upon visible-light irradiation in the presence of a sacrificial electron donor. Full characterization of this compound and of its singly- and doubly-reduced derivatives thanks to resonance Raman, EPR and DFT studies allowed to localize the two electron-storage sites and to relate charge photoaccumulation with proton-coupled electron transfer processes.