Simulation and UV-visible spectra of organic dyes in subcritical and supercritical carbon dioxide

Ab initio calculations have been used to adapt the AMBER force field to three organic dyes (CI disperse red 82, CI disperse blue 60 and CI disperse yellow 211) that are interesting for industrial textile dying processes in supercritical carbon dioxide. For each dye molecule in carbon dioxide solution, Molecular Dynamics simulations with periodic boundary conditions have been performed for three thermodynamic conditions (278 K, 50 atm; 278 K, 400 atm; 373 K, 400 atm) to obtain structural, thermodynamical and dynamical properties. From the red dye/CO2 and the blue dye/CO2 trajectories, one hundred of uncorrelated configurations have been extracted to compute the UV/vis absorption spectra with the INDO/CIS method. Quantitative agreement with the experimental trend has been observed for the lowest absorption band spectral shift between 278 K, 50 atm and supercritical conditions at 373 K, 400 atm for the red dye/CO2 system.