Monolayers of a series of viologen derivatives and the electrochemical properties in Langmuir–Blodgett films

Abstract

The effects of a hydrocarbon layer on the electrochemical property of viologens were studied by immobilizing a series of symmetrically bis-alkylated viologens (C n V, n=12–18) on an indium–tin oxide electrode surface by using the Langmuir–Blodgett (LB) method. The electrochemical properties of viologen LB films were studied for different parameters; length of alkyl chains, the nature of counterions in the subphase, and deposition model (X- and Z-type LB films). Cyclic voltammetric measurements indicated that π-complex dimers were easily formed for viologens that had a ‘thin’ hydrocarbon barrier (CH 2=11 and 13) in Z-type LB films, but formed with difficulty for viologens that had a ‘thick’ barrier (CH 2≥15) and for all viologens in X-type LB films. A weak peak current and a small surface coverage of ‘electroactive’ viologens were observed for X-type LB films. For every viologen-modified In and Sn oxide (ITO) electrode, the reduced potential was negatively shifted; the thicker the barrier, the larger the shift.