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

The effects of a hydrocarbon layer on the electrochemical property of violo gens were studied by immobilizing a series of symmetrically bis-alkylated v iologens (CnV, n = 12-18) on an indium-tin oxide electrode surface by using the Langmuir-Blodgett (LB) method. The electrochemical properties of violo gen 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 sr-complex dimers were easily formed for viologens that had a 'thin' hydrocarbon barri er (CH2 = 11 and 13) in Z-type LB films, but formed with difficulty for vio logens that had a 'thick' barrier (CH2 greater than or equal to 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. Fo r every viologen-modified In and Sn oxide (ITO) electrode, the reduced pote ntial was negatively shifted; the thicker the barrier, the larger the shift . (C) 2000 Elsevier Science S.A. All rights reserved.