SPECTROSCOPIC AND ELECTROCHEMICAL STUDIES OF ORIENTED MONOLAYERS ON ELECTRODE SURFACES

A series of electrochemical and Raman studies were undertaken to investigate the effects of orientation of electroactive species on their electrochemical behavior. Raman, resonance Raman, surface-enhanced Raman scattering, and surface-enhanced resonance Raman scattering techniques provided information essential for determining species orientation on electrode surfaces. The paradigm compounds employed were a series of derivatized viologens. Synthesis of these compounds involved the incorporation of long alkyl chains, rendering them surface-active and capable of incorporation into various kinds of oriented systems at interfaces. Orientation control was effected by the use of three techniques which provided a hierarchy of progressively more stringently oriented systems. Viologens were incorporated into vesicles, spontaneously self-assembled systems, and Langmuir-Blodgett (LB) monolayer arrays. Whereas the ordering and orientation control was probably least effective in vesicles, a maximal ordering could be attained in LB systems. Analysis of the experimental findings indicates that the systems studied show varied behavior and a complex interaction of the important variables operative during electrochemical processes. The extent of orientation present in specific preparations, the electrochemical potentials, the presence of counterions, the density of monolayer packing, and the exact structures (relative contributions of alkyl chains and of the viologen moiety) were all found to influence the behavior observed. © 1990.