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

Abstract

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 (Δ 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 Δ 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 (∼1.1 × 10 −12 cm 2 /s for cationic and ∼2.7 × 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 ∼3.54 μW/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. • Three isomeric poly-viologens are designed and synthesized for electrochromic (EC) chromophores. • Poly-viologens with a larger hydrodynamic size exhibit a lower diffusivity and a higher memory effect. • EC devices with meta -poly-viologens consume very low power of ∼3.54 μW/cm 2 to maintain colored state.