Explicit solvent effects on the visible absorption spectrum of a photosynthetic pigment: Chlorophyll-c2 in methanol

The explicit solvent effects on the light absorption properties of a photosynthetic pigment are analyzed from a combined study using Monte Carlo simulation and quantum mechanical Density-Functional Theory calculations. The case considered is chlorophyll-c2 in methanol and excellent results are obtained for both position and intensities in the entire visible region. Explicit solvent molecules are essential for describing the absorption spectrum. Analysis is also made of the coordination of the Mg atom, the influence of solute–solvent hydrogen bonds, the existence and location of dark states for internal conversion mechanisms and the adequacy of the four-state model for classifying the transitions.