Fundamentals of the photocatalytic activity of conjugated polymers for hydrogen evolution reaction: optical and thermodynamic aspects

Harvesting sunlight is a convenient approach to meet the global demand of energy, a process that makes use of a suitable photo-electro-catalyst to convert solar energy into chemical fuels[1]. In this context, conjugated polymers have emerged as a subclass of materials with potential applicability as photocatalysts for hydrogen evolution reaction (HER). [2] In this work, we use density functional theory-based methods to evaluate the thermodynamic and optical properties of a set of conjugated polymers containing fluorene, cyclopenthathiophene or thiophene-based donor units and benzothiadiazole-based acceptor units. Optimizations and frequencies were held in Gaussian 09 [3] at the M06/6-31G* level of theory, whereas the excitation, solvation and electronic energies were obtained with the 6-311G** basis set. Our preliminary results show that the polymers containing benzo(triazole-thiadiazole) or benzo(triazole-selenodiazole) acceptor units present a broad absorption spectrum and a suitable reduction potential for photocatalytic HER. In particular, PFO-DSeBTrT has maximum peak at 950 nm, while showing a hydrogen binding free energy (0.02 eV) that is lower in absolute values than Pt (-0.10 eV).