Langmuir-Blodgett (LB) deposition methodology has applications ranging from chemical sensing to synthesis of complex multilayer structures. The interactions of metal ions with mono- and multilayer amphiphiles have been investigated extensively. Copper, Cadmium, and Ruthenium have received relatively little attention as a subphase constituent. These metal ions are of interest because of the potential to control their oxidation states reversibly, once they are incorporated into a monolayer structure that is deposited on an electrode surface.In the first part of the project, we report on the formation and organization of a Cu2+-complexed octadecylphosphonic acid (ODPA) monolayer formed by LB deposition. The formation of the Cu-complexed monolayer is seen to depend sensitively on subphase pH and Cu2+ concentration and it is possible to form a monolayer containing regions of complexed and free ODPA. From pressure-area isotherm data for these monolayers we can determine the equilibrium constant and free energy of formation for the Cu2+-ODPA complex. For the second part of this project, we modified the surface of Indium Tin Oxide (ITO). ITO has been used extensively as a transparent conductor. The surface chemistry of ITO is amenable to reactions similar to those used to modify silica, but a long-standing issue has been understanding the density and robustness of the ITO surface-modification. We report on the formation of chemically bound Cd2+-complexed ODPA monolayer formed on a Langmuir trough and deposited using LB methodology onto an ITO surface, either in its native form or functionalized with phosphonate (RPO32-). The organization of the Langmuir monolayer depends on the pH and [Cd2+] in the aqueous subphase on which it is formed and on the functionalization of the ITO surface. We probe the permeability of the resulting LB-support interface electrochemically and the motional freedom characteristic of chromophores contained within the monolayer using fluorescence recovery after photobleaching (FRAP). Our data demonstrate that, without modification of the ITO surface, the monolayer is significantly permeable by the electrophores used (ferrocene and Ru3+), and surface modification to produce covalently bound phosphonate functionality results in a monolayer that is impermeable to the electrophores. FRAP studies reveal a relatively rigid monolayer aliphatic chain region for deposition on either native or modified ITO, suggesting direct Cd2+-ITO interactions. We have also used Ru3+ as a metal ion for the fabrication of ODPA monolayers. The motivation for the use of Ru3+ is that it can be converted reversibly between several oxidation states, resulting in changes in ODPA monolayer properties. We show that Ru3+ can be changed to Ru2+ without loss of the monolayer. The CV data for this monolayer points to complex electrode morphology, with consequent complexity in the order and permeability of the adsorbed monolayer.
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