coated with a transparent nanostructured film 14 of tio 2 having a redox chromophore 15 adsorbed thereon the redox chromophore 15 is bis 2 phosphonoethyl 4 4 bipyridinium dichloride prepared as described in the example 0058 fig2 and 3 illustrate an ec system 10 according to the invention comprising the first glass substrate 11 with the layer 13 and the modified tio 2 film 14 shown in fig1 and a second glass substrate 22 having a conductive layer 23 of fluorine doped tin oxide coated thereon the second glass substrate 22 has a 0 25 cm border 24 of epoxy resin deposited thereon with a small gap 25 which is sealed after addition of the electrolyte electron donor solution 16 described above it will be observed that construction of the ec system 10 according to the invention is simple and utilises low cost and non toxic materials these are particularly attractive features in the context of the large scale manufacture of the ec system 10 it should also be noted that due to surface roughness of the order of 500 for a 4 u03bcm film no spacer is required in an ec system of the invention in prior art electrochromic systems a dielectric spacer must be.