Static and dynamic electronic spectroscopy at the interface between water and chemically modified self-assembled monolayers

I. Benjamin and J. Vieceli

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

Molecular dynamics computer simulations are used to study the static and dynamic electronic spectroscopy of a chromophore located at the interface between water and self-assembled organic monolayers terminated by either a methyl group or chlorine atom. The roughness and polarity of the monolayer surfaces are varied to determine the dependence of the spectroscopy on the surface composition. Equilibrium trajectories are used to calculate the static electronic spectrum relative to the gas phase and non-equilibrium trajectories are used to monitor the dynamic solvent response immediately following an electronic transition. Relative to bulk water, the interfaces with methyl-terminated monolayers are less polar, while interfaces with chlorine-terminated monolayers are more polar. This is understood in terms of the contribution from each component of the system to the solvation energy. The dynamic solvent response at each interface studied is slower than bulk water. The rate of water relaxation is correlated with the polarization of interfacial water molecules due to the monolayer.