Electrochemical and spectroelectrochemical study of 7,7 '-diapo-(7E,7 ' Z)- diphenylcarotene

Self-assembled monolayers (SAMs) formed by adsorption of thiols onto gold p rovide a flexible method to study the electrochemical reactivity of 7,7'-di apo-(7E, 7'Z)-diphenylcarotene (DDC) on such barrier monolayers. Barrier pr operties of three kinds of SAMs (long-chain n-alkanethiols, omega -substitu ted alkanethiols, and 4-mercaptopyridine) were investigated. The influence of the omega -functional group and the thickness (chain length in n-alkanet hiols) of the monolayer on the electrochemical reaction of DDC was explored . Electron transfer between solution species and the modified-gold electrod e can occur either by tunneling through the monolayer or by approaching the electrode at "pinholes" or defects in the monolayer. Compared to the behav ior on bare gold electrodes, the thiol monolayers cause a barrier effect fo r the reaction of DDC and the adsorption of polymeric products on the Au el ectrode surface. With increasing chain length of alkanethiol molecules, a s tronger barrier effect to the adsorption of polymeric products is observed. DDC and its electrochemical reaction products (including the radical catio ns and polymers) were also studied by simultaneous optical and electrochemi cal techniques.