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

A series of viologens has been synthesised, characterised and tested for th eir suitability as redox chromophores in electrochromic devices. These viol ogens contain a phosphonic acid moiety and are irreversibly adsorbed at a t ransparent nanoporous-nanocrystalline TiO2 electrode. An electrochromic dev ice consisting of a sandwich of a viologen-modified TiO2 electrode/electrol yte (gamma-butyrolactone, 0.05M LiClO4, 0.05M ferrocene)/conducting glass s hows excellent electrochromic properties: fast switching times (1-2 s), lar ge changes in absorbance, high colouration efficiencies (up to similar to 2 00 cm(2)/C) and good long-term stability( > 10 000 cycles). Further, the co lour 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 Scie nce B.V. All rights reserved.