Electrochemical Quartz Crystal Microbalance, Voltammetry, Spectroelectrochemical, and Microscopic Studies of Adsorption Behavior for (7<i>E</i>,7‘<i>Z</i>)-Diphenyl-7,7‘-diapocarotene Electrochemical Oxidation Product

Abstract

Polymeric products, which are formed by reaction of the dications of (7E,7‘Z)-diphenyl-7,7‘-diapocarotene (I) generated by electrochemical oxidation in dichloromethane with the neutral carotenoid, are adsorbed on various electrode surfaces. An apparent average molar mass of 5400 g/(mol electrons) was calculated from simultaneous electrochemical quartz crystal microbalance (EQCM) measurements, and the green, fiber-like structure observed by optical microscopy confirms the formation of polymers. X-ray microanalysis of the surface composed of an uneven, layered structure indicates that electrolyte counter anions PF6- are associated with the deposited material. Cathodic stripping voltammetry indicates that the film thickness ranges from 0.16 to 0.84 μm as the charge increases from 10.0 to 51.1 μC. Cation radicals of I show no adsorption behavior nor do the dications of carotenoids terminally substituted with one cyclohexene ring (V) or containing a triple bond at C15 (IV). Apparently a diphenyl-substituted carotenoid containing only double bonds in the backbone is required to observe this unusual behavior.