The design and synthesis of molecular compounds capable of storing and shuttling electrons is required for advanced technological applications, including solar energy conversion, small molecule activation, water splitting and the reduction of carbon dioxide. We have synthesized a series of dipyrido[3,2-a:2’,3’-c]phenazine derivatives that were systematically designed to store electrons by photo-irradiation. In the case of the derivative 9,11,20,22-tetraaza-tetrapyridopentacene (TATPP), the number of electrons stored could be varied by controlling the pH. Photo-irradiation of TATPP using energy ≤ 3.35 eV in an acidic medium led to the formation of (TATPPH (-)), a two-electron carrying species, whereas in a basic medium, the species (TATPPH2), a four-electron species, was formed. Exposure of carbon dioxide to either TATPPH(-) or TATPPH2 led to the formation of formic acid, and was confirmed by gas chromatography-mass spectroscopy and nuclear magnetic resonance spectroscopy. In addition to the experimental findings, favorability of formic acid production was investigated using restricted Hartree-Fock 6-31G(d,p) calculations. According to the computational calculations it was found that the reaction is thermodynamically favorable with a Gibbs free energy, ΔG298 of -12.91 KJ/mol.

Conversion of carbon dioxide to formic acid mediated by light driven electron storage systems

253rd National Meeting (2017)

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