Reactivity in self-assembled monolayers: Effect of the distance from the reaction center to the monolayer-solution interface

Monolayers containing a reactive-p-nitrophenyl ester group at different levels with respect to the monolayer interface have been self-assembled on a gold surface. Analysis of grazing angle IR spectra, surface plasmon resonance (SPR), and wettability measurements suggests disordered organization of the alkane chains in the monolayers. Kinetics of monolayer reactions with external reagents (alkylamines) have been studied and compared with those of the same process in bulk medium. Burying of a reaction center under the surface and other structural changes of monolayers were shown to have only a minor effect on the rates of reaction, implying that these monolayers could be easily penetrated by guest molecules. The higher reaction rates with monolayers than in bulk solution are possibly due to a weak binding of the external reagent to the monolayer prior to reaction.