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

Marenich, A. V.; Cramer, C. J.; Truhlar, D. G.
J. Chem. Theor. Comput. 2010, 6, 2829 (doi:10.1021/ct100267s).

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 with SMD atomic radii, and, (ii) in the case of acetone in water, ensemble averaging over supermolecule calculations with up to twelve 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.