Electrochemical Properties of Langmuir-Blodgett Mixed Films Consisting of a Water-Soluble Porphyrin and a Phospholipid

Films of a water-soluble tetracationic porphyrin (TMPyP) and an insoluble phospholipid (DMPA), in a molar ratio TMPyP:DMPA ) 1:4, were transferred onto optically transparent indium tin oxide (ITO) electrodes, and cyclic voltammetry and visible spectroscopy were used to detected and quantify the presence of porphyrin on the ITO supports. We found the surface density of porphyrin deposited ranges from that corresponding to a monolayer of porphyrin monomers lying parallel to the electrode surface to the total amount of porphyrin (partially as dimer) present in the compressed monolayer at the air-water interface. Also, the electrochemical properties of the films were analyzed in terms of experimental variables including the nature and concentration of the electrolyte and the scan rate, used to obtain the voltammetric recordings. When the reduction of TMPyP is a two-electron process and the salt concentration moderate, porphyrin remains anchored to the phospholipid film, which makes the system highly stable and reversible in successive oxidation-reduction cycles.