Computational Design of (B)Chl Models: Structural and Chemical Modifications toward Enriched Properties

The functional units of natural photosynthetic systems control the process of converting sunlight into chemical energy. In this article, we explore a series of chemically and structurally modified bacteriochlorophyll and chlorophyll pigments through computational chemistry to evaluate their electronic spectroscopy properties. More specifically, we use multiconfigurational and time-dependent density functional theory methods, along with molecular dynamics simulations, to compute the models' energetics both in an implicit and explicit solvent environment. Structural modifications aimed at reducing the planarity of the macrocycle through alkyl-bridge anchoring reveal the significant role of the curvature in fine-tuning spectral properties, which mimics protein scaffold effects on naturally occurring pigments. Furthermore, chemical substitutions with a carbonyl group show potential for expanding absorption spectra toward the blue region, while incorporating an additional double bond decreases absorption efficiency. These insights lay the groundwork to design novel synthetic pigments, with potential applications in artificial light-harvesting systems and more efficient photovoltaic devices.