Photophysical and photocatalytic properties of corrophyll and chlorophyll

Tetrapyrrolic macrocycles are well known photosensitizers, absorbing light in the ultraviolet and visible region. The quantum efficiency of these naturally occurring compounds in optical processes, and the possibility of altering their behavior by modifying its constituent features, make them promising candidates for applications as Dye Sensitized Solar Cells (DSSC) and photocatalytic reactions. The time-dependent density-functional theory (TD-DFT) were used to study the optical and redox properties of chlorophyll and corrin-related molecules (corrophyll). The influence of the substituents and metallic atoms in their properties have been investigated. Our results show lower reduction potentials for corrophyll molecules compared with chlorophyll. The optical absorbance spectra of corrophyll without a metallic atom at their central rings shows a significant blue-shift, as compared to their chlorophyll counterparts. The presence of Co(I) ion species at the corrophyll core leads to oxidation potentials below than that of water, which puts corrophyll ahead of traditional chlorophyll pigments as photocatalysts. We show that the substituents and the ions coordinated to the macrocycles play an important role in this phenomena. These findings show the great potential of tuning the spectroscopic and reactive properties of tetrapyrrole macrocycles for applications in photocatalysis and optoelectronic devices, while keeping their essential structural features intact.