Sorting Out the Relative Contributions of Electrostatic Polarization, Dispersion, and Hydrogen Bonding to Solvatochromic Shifts on Vertical Electronic Excitation Energies

Conventional polarized continuum model calculations of solvatochromic shifts on electronic excitation energies using popular quantum chemical programs (e.g., Gaussian or Turbomole) include the noninertial and inertial bulk-solvent polarization, which will be called electrostatics, but not dispersion interactions and specific effects like hydrogen bonding. For the n→π* excitation of acetone in several solvents, we estimated the nonelectrostatic contributions in two ways: (i) the vertical excitation model (VEM) of Li et al. (Int. J. Quantum Chem. 2000, 77, 264), but updated to use TD-DFT corrected linear response with SMD atomic radii, and (ii) in the case of acetone in water, ensemble averaging over supermolecule calculations with up to 12 explicit solvent molecules selected from a molecular dynamics trajectory, with the explicit solvent surrounded by a continuum solvent. The TD-DFT VEM calculations carried out with the M06 density functional for 23 solvents result in a dispersion contribution to the red of 261-356 cm(-1) and a hydrogen-bonding contribution to the blue of up to 289 cm(-1).