Geometries of two thioester analogs of the PYP chromophore (shown in Figure ) solvated in water were obtained from previous work by Milanese et al. based on molecular dynamics (MD) simulations in TIP3P water. The two analogs are, respectively, the neutral transthiophenyl-p-coumarate, (1), and the anionic form of it (2). 19 solvated structures of 1 and 2 in water were obtained from Ref. 23 and were used in this study without further modifications. Additionally, MD simulations of 1 and 2 in chloroform (CHCl 3 ) and in dimethyl sulfoxide (DMSO) were performed to test solvent effects on absorption spectra, as well as investigate the implication of applying the exciton model for systems where the absorption spectra of the solute and solvent are partially overlapping. In the case of the solvent being CHCl 3 the MD simulations were performed using the Amber14 package. The solutes were solvated in a cubic box with a radius from the solutes of 20 Å. The general Amber force field (GAFF) was used for the chromophore analogs and CHCl 3 parameters from Cieplak et al. were used to model the solvent. To equilibrate the systems, 1000 steps of initial minimization followed by 1000 steps of minimization of the solvent keeping the solute fixed with harmonic positional restraints were performed. After minimization, three MD equilibration steps were performed using a stepwise procedure starting by heating the system to 300 K over 20 ps with constant volume, after which the systems were allowed to equilibrate at 300 K for 10 ps. The last equilibration step consisted of a 200 ps MD at 300 K using periodic boundary conditions to assure that the system was completely equilibrated.