ELECTRONIC-SPECTRA OF DIPOLAR SOLUTES AT LIQUID LIQUID INTERFACES - EFFECT OF INTERFACE STRUCTURE AND POLARITY/

Molecular dynamics computer simulations are used to elucidate the role of solvent polarity and interface structure in determining the electr onic absorption and fluorescence line shapes for model dipolar solutes at the interface between water and one of four different organic liqu ids, The different organic liquids represent a range of molecular stru cture and polarity: 1-octanol, 1,2-dichloroethane, n-nonane, and carbo n tetrachloride. The solute is represented by two rigidly connected Le nnard-Jones spheres, The different electronic states correspond to dif ferent charges on the two Lennard-Jones centers, In each interfacial s ystem, different choices of solute charge distribution and solute loca tion relative to the interface (including the bulk region) are conside red and provide insight into different microscopic factors that influe nce the electronic line shape. For the water/ 1,2-dichloroethane and w ater/CCl4 interfaces, all of the calculations are repeated while the i nterface is externally constrained to be smooth in order to investigat e the role of surface roughness. The calculated electronic line shapes are Gaussians whose peak positions reflect solvent polarity, interfac e structure, and probe location. Their widths are in general agreement with the prediction of linear response theory. Although continuum ele ctrostatic models predict qualitatively correct behavior, they miss in teresting interfacial effects. (C) 1997 American Institute of Physics.