**3. Photoactive chromophore**

Synthetic porphyrin derivatives have been widely used to mimic the natural chlorophyll pigments to convert light energy into chemical energy. [Ru(bpy)3]2+ presents an absorption band in the region around 450 nm corresponding to a metal to ligand charge transfer (MLCT) band with an extinction coefficient of about 13,000M−1cm−1. Upon irradiation in the MLCT band, the input light energy is converted into a (d6) → (d5π\*) excited state, which in turn relaxes to form the lowest triplet state (3MLCT) in less than a picosecond. The oxidation potential of [Ru(bpy)3]3+ is similar to oxidized photosystem II primary donor in natural photosynthesis, therefore making it a suitable candidate to reproduce the oxidation reactions performed by the natural system.
