Discrete Solvent Reaction Field Calculations for One- and Two-Photon Absorptions of Solution-Phase Dimethylaminonitrostilbene Molecule.

Based on the configurations generated by molecular dynamics (MD) simulations using the on-the-fly density-functional tight-bonding (DFTB) force field, we investigated performance of the discrete solvent reaction field (DRF) model coupled to time-dependent density functional theory (TD-DFT) for solvatochromic effect of one- and two-photon absorption phenomena. Dimethylaminonitrostilbene (DANS) molecule solvated in chloroform, dichloromethane, and dimethyl sulfoxide solvents was selected as a model system for our research purpose. For every selected MD/DFTB configuration, within the context of the DRF, solute molecule is represented by TD-DFT and solvent molecules are described by atomic charges and polarizabilities. The calculated one-photon absorption energies reproduce well the positive solvatochromic behavior of solvated DANS and are in good agreement with available experimental data. For the two-photon absorption cross section, even though our approach overshot the experimental data by about 20% in absolute magnitude, experimentally observed solvatochromic change was captured qualitatively in this work. At last, we examined the contributions of atomic charges and polarizabilities of solvent molecules to the solvatochromic shifts of properties of interest.