Electrochemical investigation of ultrathin compact 2-D layers started with a report Brdička[1]of adsorption of a solute at Hg-water. Many reports were summarized in reviews.[2],[3]  Scanning tunneling methods were applied, and electron transfer from surface attached ferrocene derivatives was examined as a function of distance from a metallic electrode.[4],[5]  However, as far as we know, there is no previous study on the electron transfer in the case of contacting a LB monolayer with an electrode at a solution-air interface. An electrochemical Langmuir-Blodgett trough that permits the examination of local redox processes in a layer floating on the surface of water with an STM-type tip ultramicroelectrode (UMC) was constructed. Material was polypropylene. Wilhelmy plate balance and barrier position were controlled by a software. The trough is located inside a Faraday cage. Water level in the trough was kept constant by a linear syringe pump. The working electrode tip was located in the water phase. Approaching the layer with the tip was possible in micrometer and finally in nanometer steps, until it entered into the surface layer. For testing purpose we performed voltammetry of 1,1´¾dicarbooctadecyloxyferrocene. When in solutions and with UMC, this Fc derivative displays  a reversible voltammogram. Stepwise approach of the tip from LB water phase towards the surface layer shows changes of the double layer and growth of a wave of Fc oxidation. The cyclic voltamogram has a hysteresis upon the reversal of the potential scan. The electrostatic repulsion of ferrocinium cation and a positive potential of the working electrode tip is most likely responsible for the current hysteresis. The tip electrode with the area of 9 μm² yielded the limiting current 300 pA. Details are in our recent publication.[6]

Scanning tunneling microscope (STM) [1] is an experimental device mostly known for direct obtaining of three-dimensional images of conductive solid surfaces with an atomic resolution. In 2003, Xu and Tao [2] introduced a new experimental technique based on the STM device for inspecting electric properties of single molecules. By repeated formation and breaking of a large number of junctions formed by STM metal (gold) tip and substrate electrodes with a molecule trapped in between, they were able to determine an electric conductance of a given molecule. Named an STM-based break junction (STM-BJ) technique, it has become the most common method used to study electronic properties of single‑molecule junctions. [3] In this work we demonstrate the ability of our highly‑sensitive STM-BJ setup to distinguish between two different states of conjugation (namely the aromatic conjugation and cross‑conjugation) on a pair of 4‑pyridyl‑ethynyl‑terminated representative model molecules. The variation of conjugation in probed systems is provided via core structure formed by one of two stable oxy‑derivatives of anthracene. Presented experimental method has been applied to examine the conjugate states of monomeric metalloporphyrin units in monolayers.