ELECTROCHEMICAL INVESTIGATIONS OF THE LATERAL DIFFUSION AND ELECTRON HOPPING IN LANGMUIR MONOLAYERS AT THE AIR-WATER-INTERFACE

A purposefully designed microelectrode is positioned at the air-water interface where it functions as a one-dimensional line electrode, probing the dynamics of lateral processes in Langmuir monolayers. This report focuses on the comparison of fluidity and the mechanisms of lateral charge transport in two monolayer systems consisting of transition metal complexes. Octadecylferrocene monolayers are liquid-like where diffusivity of the individual molecules decreases with surface concentration. Electrochemical measurements reveal a liquid/gas phase transition and a value of critical temperature. Osmium tris(diphenylphenanthroline) perchlorate forms aggregates on the water surface. Lateral charge transport in this case is only possible when the monolayer is compressed above 6 mN/m, at which point electron hopping becomes a viable mechanism of charge propagation. Further compression of the monolayer leads to an increase in the apparent diffusion coefficient, an effect related to the increasing extent of electroactivity of the osmium sites in the monolayer. These measurements are interpreted in terms of the first order rate constant of electron hopping.