Structure, dynamics and electronic spectrum of N,N'-Diethyl-p-Nitroaniline at water interfaces. A Molecular Dynamics Study

David Michael and Ilan Benjamin

Department of Chemistry, University of California, Santa Cruz, California 95064

The adsorption of N,N'-diethyl-p-nitroaniline (DEPNA) - a common chromophore probe of liquid polarity at the water liquid/vapor interface and at the water/1,2-dichloroethane (DCE) interface - is studied using molecular dynamics computer simulations. The adsorption energetics, orientation and reorientation dynamics are examined. The electronic absorption line shapes at the two interfaces, in bulk DCE and in bulk water are calculated and are found to be in reasonable agreement with experiments. Including many-body polarizable liquid potentials in the calculations at the water/DCE interface is found to improve the results. The role of surface roughness is examined by repeating the calculations for an artificially smooth water/DCE interface.