Solvation dynamics of coumarin 153 in dimethylsulfoxide-water mixtures: Molecular dynamics simulations

We present results of molecular dynamics simulations of solvation dynamics of coumarin 153 in dimethylsulfoxide (DMSO)-water mixtures of different compositions (x(D)=0.00, 0.25, 0.32, 0.50, 0.75, and 1.00) using an all-atom model for the solute probe. Results are reported for the global solvation responses of the simulated systems, as well as for the separate contributions from each cosolvent and the individual solute-site couplings to water and DMSO. The solvation dynamics is predominantly given by DMSO's contribution, even at low (25%) DMSO content, because of the preferential solvation of the probe. We find that the water molecules are only mildly coupled to the charge transfer in the coumarin, resulting in a small, largely diffusive, water relaxation component. Simulation results, including solvation responses, characteristic times, and Stokes shifts are compared with recent fluorescence upconversion experimental measurements showing good agreement for the relaxation but significant differences for the shifts. (C) 2003 American Institute of Physics.