Multiscale Approach to the Structure and Spectra of Nile Red Adsorbed on Polystyrene Nanoparticles

The structure and absorption spectra of the Nile Red (NR) dye adsorbed on the surface of a polystyrene (PS) nanoparticle is studied by DFT/TDDFT based on the results of previous molecular dynamics (MD) simulations. From NR/PS surface structures obtained from MD simulations, relatively small clusters were constructed composed of the adsorbed NR molecule and the nearest PS fragments. These clusters were treated either explicitly by DFT/TDDFT or using the effective fragment potentials (EFP) model. The absorption and emission spectra of the NR/PS system calculated using the EFP model are very close to those calculated with the explicit environment, so that the EFP model can be recommended for use in multiple large-scale calculations. The calculated positions of the absorption and fluorescence bands are in good agreement with experiment.