The accurate prediction of lineshapes of chromophores in aqueous solution from first principles is highly challenging, as polarization effects of the environment, vibronic effects, and explicit solute-solvent interactions have to be accounted for. We have recently introduced an efficient approach for modelling these challenging systems, by combining an ensemble sampling of solute-solvent conformations with a zero-temperature Franck-Condon shape function computed for the chromophore embedded in a frozen solvent pocket. Here, we apply this approach to study the origin of the broad absorption spectra of the PYP and GFP chromophore in aqueous solution. We find that solvent polarization effects play an important role in broadening the spectra and that these effects cannot be recovered using a classical description of the solvent environment, making a quantum mechanical treatment of large parts of the solvent environment necessary. Furthermore, nuclear quantum effects are found to be crucial in correctly capturing the strength of hydrogen bonding between the chromophore and its solvent environment, leading to additional broadening of spectral features. We also investigate the role of ions on optical absorption spectra of the GFP chromophore, finding that ions disrupt the hydrogen bonding network between the chromophore and its environment, causing shifts in the computed absorption spectra. Finally, we investigate the role of the solvent environment on optical spectra for a fully dynamic approach to computing the optical response function based on open quantum system approaches, which allow for a rigorous coupling between the chromophore and its environment. We find that solvent polarization effects can strongly enhance certain vibronic features in both linear and ultrafast non-linear spectra and can only be captured by a fully quantum mechanical description of the first solvation shell.

New methods for revealing the effects of solvent in optical spectroscopy

2019 Fall National Meeting

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