Distant Nanostructures Interacting upon an External Stimulus

Introduction: Transport phenomena have profoundly been influenced by the development of nanotechnology. We have investigated a system comprising of two discrete covalently surface-confined monolayers, in which one of them can supply an important component to the other, by exposing to a mass transport phenomenon their external surfaces. Materials and methods: In a glove box under a N2 atmosphere some SiO2 and Si(100) freshly cleaned substrates were covalently coated with a trichloro[4- (chloromethyl)phenyl]silane monolayer. Then some monolayer were reacted with a solution of 5,10,15,20-tetrakis(4-hydroxyphenil)-21H,23H-porphyne, H2THPP, and some others with a solution of 4-(2-pyridylazo)resorcinol, PAR. Then the PAR_SAMs molecules were quantitatively complexed with Cu2+ ions in a 1:1 ratio. The covalently immobilized monolayers were characterized by XPS, AFM and UV-vis. Results: Two H2THPP_SAM and Cu_PAR_SAM+ monolayers were fixed in a particular Teflon set-up, put in a cuvette and covered with an acidic solution (starting pH = 1.88). Then successive aliquots of a NaOH solution have been added. There are UV-vis evidences that the -OH ions activated a controlled Cu2+ mass transfer from the Cu_PAR_SAM+ to the H2THPP_SAM. Discussion: The monolayers setup exhibits many optically active states. We have shown that these systems can communicate among themselves and exchange mass upon a precise external input. Therefore, for the first time it has been reported a guided transfer of Cu2+ cations between two molecular interfaces, specifically from a Cu_PAR_SAM+ to a H2THPP_ SAM. This transfer was carried out in an aqueous environment and driven by a fine tuning of an external trigger (-OH-). It has been possible to read the physical states of the overall system that, in turn, represent the answer (output) to the chemical OH- stimulus. For the first time, the protonation and complexation equilibria of monolayers have been described. Moreover, we trust that this archetypal setup may represent the platform for the development of advanced interfacial communication systems based on optically active monolayers.