The geometry of the monomer is optimized at the theoretical level of B3LYP/6-31G(d,p) in a mixed solution (details of the solvent and dielectric constants are listed in Table in the supporting information (SI)). The D3 version of Gramme's dispersion with Becke-Johnson damping is employed. The subsequent calculations of ground-state vibrational frequencies and excited-state gradient are finished with respect to the same DFT exchange-correlation (XC) functional.