Electrochromics by intramolecular redox switching of single bonds

Two moieties of mono- and trimethincyanines as well as those of styryl dyes were connected by a saturated alkyl tether made from compounds 3a-c, 5, 7, and 9a,b. In most cases, cyclic voltammetry and spectroelectrochemistry for these dyes together with the data for their monomeric models 4, 6, 8, and 10 reveal electrochemically irreversible transfer of two electrons but chemically reversible reaction and discoloration both on reduction and oxidation. Discoloration is interpreted as intramolecular formation of a single bond, which on redox breaking regenerates the starting colored species. Therefore, the investigated dyes exemplify a new general principle for electrochromics.