Coloured electrochromic windows based on nanostructured TiO2 films modified by adsorbed redox chromophores

A series of viologens has been synthesised, characterised and tested for their suitability as redox chromophores in electrochromic devices. These viologens contain a phosphonic acid moiety and are irreversibly adsorbed at a transparent nanoporous-nanocrystalline TiO2 electrode. An electrochromic device consisting of a sandwich of a viologen-modified TiO2 electrode/electrolyte (gamma-butyrolactone, 0.05M LiClO4, 0.05M ferrocene)/conducting glass shows excellent electrochromic properties: fast switching times (1-2 s), large changes in absorbance, high colouration efficiencies (up to similar to 200 cm(2)/C) and good long-term stability( > 10 000 cycles). Further, the colour changes from transparent or a faint yellow to either a deep blue or a deep green, depending on the nature of the viologen. (C) 1999 Elsevier Science B.V. All rights reserved.