Electrochemical behaviour of methyl viologen in a matrix of paper

Methyl viologen (MV) has been incorporated into paper as an aqueous solution and in the viscous electrolyte polyAMPS, and the availability of the MV for electron-transfer has been investigated by cyclic voltammetry at a stationary platinum disc electrode. In this study, which is the first rigorous study of an electrochrome in paper, the variables of choice were scan rate, relative humidity and electrolyte composition. The implications of the incorporation of MV into paper are discussed in terms of electrochromism. It is concluded that (i) electrochemical generation of colour in the paper is feasible; (ii) the rate of colour formation in paper is likely to be very slow; (iii) the MV²⁺, MV^+· couple is fully electroactive in paper but (iv) the MV^o redox state is best avoided since its immediate product, a spin-paired radical–cation dimer formed via comproportionation, is slightly electro-inactive. Dimer also complicates the electrochemical interpretations.