Isomeric effects of poly-viologens on electrochromic performance and applications in low-power electrochemical devices

Electrochromic (EC) behaviors of poly-viologens are tuned by selecting positions (ortho (o), meta (m), and para (p)) of the benzene rings linked to 4,4'-bipyridine. All-in-one type EC devices (ECDs) are conveniently fabricated by adding poly-viologens to highly conductive solid-state polymeric gel electrolytes. The maximum transmittance contrast (triangle T) of the o-poly-viologen based ECD is much lower than that of the other isomers, and its bleaching is not reversible, whereas a large triangle T and high stability are achieved with the m- and p-poly-viologens. Considering the high solubility of the m-poly-viologen in ion gels, it is anticipated to have a larger hydrodynamic size, leading to low diffusivity (similar to 1.1 x 10(-12) cm(2)/s for cationic and similar to 2.7 x 10(-12) cm(2)/s for anionic current). As a result, the m-poly-viologen ECD shows a superior memory effect and long-lasting colored state without voltage supply. This feature allows us to demonstrate a low-power ECD based on the m-poly-viologen, which only requires similar to 3.54 mu W/cm(2) to maintain the transmittance below 30%. The results indicate that adjusting the isomeric molecular structure of poly-viologen EC chromophores is an effective way to control their EC performance.

Automated summary

The EC behaviors of poly-viologens can be adjusted by selecting different isomers, with meta and para isomers achieving high stability and transmittance contrast. The solubility of the meta isomer in ion gels leads to a larger hydrodynamic size and lower diffusivity.