Optical properties of molecules in solution via hybrid TDDFT/MM simulations

The optical properties of molecules in complex environments were investigated within hybrid time-dependent density functional theory / molecular mechanics (TDDFT/MM) simulation studies. The potential energy surface in the excited state is described within time-dependent density functional theory (TDDFT). The solvent is described through a molecular mechanics approach and the effects due to the inhomogeneities of the electric field of the solvent molecules are fully included. The results for different systems including both n --> pi* and pi --> pi* transitions are discussed. We apply this TDDFT/MM technique to the study of the properties of the ground state and of the first excited singlet state of two different systems: acetone in water and aminocoumarins in water and acetonitrile. Our approach yields quantitative information on the solvent-induced shifts, both batho- and hypsochromic, of the electronic absorption spectra, and on the effect of a protic and an aprotic solvent on the spectral shift. (C) 2004 Wiley Periodicals, Inc.