Investigation of bipyridilium and Prussian blue systems for their potential application in electrochromic devices

Analogues of 1,1'-dimethyl-4,4'-bipyridilium, 'paraquat' or methyl viologen, have been investigated. A series of symmetrical 1,1'-di-alkyl-4,4'-bipyridilium, methyl to n-nonyl viologen, were synthesised. Electrochemical and spectroelectrochemical data in aqueous solution are reported. With the exception of n-heptyl, n-octyl and n-nonyl viologens, all the compounds in the series were successfully incorporated into films of the sulphonated perfluorinated polyether Nafion. Iso-propyl, iso-butyl, allyl and cinnamyl viologens were also synthesised. Electrochemical data in aqueous solution are reported and the influence of size/conformation of the molecules on incorporation into Nafion has been investigated. The incorporation of methyl viologen into two other solid electrolytes, DAIS and Flemion, has also been investigated and a comparison of the results is presented. 1,1'-Ethylene-2.,2'-dipyridilium, 'diquat', and its benzo-15-crown-5 and 1,2-dimethyloxybenzene derivatives were the second group of compounds to be investigated. Diquat has many similar properties to paraquat and thus it was striking that the electrochromic properties of diquat had not been previously reported. The thesis presents new electrochemical and spectroelectrochemical data for diquat and its derivatives in aqueous solution. Iron(III) hexacyanoferrate(II), Prussian blue, is an important and well studied electrochromic system. The present work surveys analogous transition metal hexacyanoferrates for electrochromic properties. Results are presented for the thin film deposition of metal hexacyanoferrates onto ITO glass working electrodes. Electrochemical and spectroelectrochemical data are reported. Finally practical devices using the electrochromic systems studied above were constructed. An electrochromic device utilising, Prussian blue and Nafion is described and its optical switching behaviour is characterised and compared to a device containing only Prussian blue. Methyl viologen is also introduced into the device. (author)