Ab initio studies of excited state properties of chromophores in tunable biological environments

Naturally evolved light-harvesting complexes are assembled from highly evolutionarily-conserved sequences of amino acids that form functional chemical pockets for chromophores. A systematic understanding of why particular chemical sequences in peptides are ideal for facilitating charge transfer between chromophores has yet to be developed. Here, we explain the impact of amino acid mutations on fluorescence and absorption, using the excited state electronic structure of molecular systems computed with time-dependent density functional theory and the ab initio GW-Bethe Salpeter equation (GW/BSE) approach, approximately accounting for the protein environment. We find that combinations of amino acid chemistries surrounding the chromophore orchestrate unique collective oscillations that tune excited state energies and lifetimes. Our results provide insight into the role of the chemical pocket with site-specific amino acid mutations on charge transfer in natural light harvesting materials.