Electrochemical Characterization And Application Studies Of Porphyrin On Self-assemblied Monolayers

Self-assembled monolayers (SAMs) is the ideal model to study the surface and interfacial phenomena. It is of interest and importance for the researches on electron transfer (ET) process. Additionally, it has been widely applied in the electronic and optical devices, chemical sensors, biological sensors, catalysis and other research fields, so it has been the focus of considerable research activity. SAMs provided a perfect technique to research interfacial phenomenon and accurately control its characteristics at molecule level. Owning to the favorable optoelectronic properties and biologically activity of porphyrins, the porphyrin and their metal complexes play an important role in the ET of biomembranes and other investigations, as known as the "life of pigment." Porphyrins and their metal chelates have been widely applied in catalysis, molecular recognition, photo-electron conversions, memorial material and medicinal fields. In this paper, porphyrins are effectively combined with self-assembled monolayer technique to construct functional ordered ultrathin films—monolayer and multiplayer films. The physical and chemical characteristics of porphyrin SAMs, electrocatalytic activity for the hydroquinon have been investigated by a variety of electrochemical methods, such as electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM).Due to the biological importance of hydroquinone, it is particular significance to detect in acetic acid buffer solution. Moreover, hydroquinone plays a very important role in environmental chemistry. The reports on hydroquinone are much more. However, the study of using cobalt porphyrin self-assembly film on the electrode is rather little, especially in acetic acid buffer solution of hydroquinone in catalytic. Cobalt porphyrin modified on the gold electrodes by self-assembly technology, electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM) were employed to investigate the SAMs, and then the modified electrode was proved to have efficient and convenient detecting for hydroquinone in acetic acid buffer solutions when use the redox couple Fe(CN)₆^3-/4- as"reporter ion". We have studied the electrochemical response of the organic-inorganic multilayers film by using CV, SECM, and EIS. Multilayers film of nanostructured gold particles (AuNPs) has been fabricated based on the layer-by-layer (LBL) technique by using a self-assembled monolayer of 5,15-di-[p-(6-mercaptohexyl)-phenyl]-10,20-diphenyl porphyrin(trans-PPS₂)/AuNPs/(5-[p-(6-mercapto-dodecaoxy)-phenyl]-10,15,20-triphenyl cobalt porphyrin as physical cross-link points in the multilayers. Using the high sensitivity of the electron transfer of ferricyanide to the modification of the gold surface with multilayers film, we selected this reaction as a probe to study the different modification stages on this modified electrode. SECM images of bare and the different modification stages showed a very good resolution with different topographies. Based on a comparison with the results of the experiments, a reasonable agreement can be obtained. That means a conjunction of these techniques.