Rapid Proton-coupled Electron-transfer of Hydroquinone through Phenylenevinylene Bridges

We describe the synthesis of two oligo(phenylene vinylene)s (OPVs) with a hydroquinone moiety and a thiol anchor group:  4-(2‘,5‘-dihydroxystyryl)benzyl thioacetate and 4-[4‘-(2‘ ‘,5‘ ‘-dihydroxystyryl)styryl]benzyl thioacetate. Monolayers on gold of these molecules were examined by electrochemical techniques to determine the electron transfer kinetics of the hydroquinone functionality (H₂Q) through these delocalized tethers (“molecular wires”) as a function of pH. Between pH 4 and 9, rate constants were ca. 100-fold faster than for the same H₂Q functionality confined to the surface via alkane tethers. Also, in this same pH range rate constants were independent of the length of the OPV bridge. These new electroactive molecules in which the hydroquinone functionality is wired to the gold surface by means of OPV tethers should be useful platforms for constructing bioelectronic devices such as biosensors, biofuel cells, and biophotovoltaic cells with a fast response time.