Influence of counterion on the electrochromic performance of water-soluble naphthalene diimides.

Amino acid appended naphthalene diimides (NDIs) undergo a reversible colourless-to-dark transition following reduction and are therefore suitable candidates for use in electrochromic devices. Alkali hydroxides can be used to deprotonate the carboxylic acid groups on the NDI, rendering the compounds water soluble. This avoids the use of organic solvents in device fabrication. We have found the electrochromic properties of the NDI varies significantly depending on the alkali hydroxide used to solubilise the material. We have also shown that the counterion used (i.e. Li+, Na+, K+, Cs+) influences the self-assembly of the aggregates formed by the NDI. As these aggregates are known to affect the ability of the NDI to form and stabilise the coloured radical anion, it can be theorised that the structures formed in the presence of different counterions are directly impacting the performance of our materials. Therefore, we hope to use SANS to probe the structural differences that arise in the presence of different counterions to justify the electrochromic properties of the resulting devices. The results from this experiment will allow for further optimisation and help guide future device construction.