Novel electrochromic-fluorescent bi-functional devices based on aromatic viologen derivates

Highlights: • Aromatic viologen derivates exhibit vivid colors under applied bias. • These derivates have similar PL property with electrofluorochromic material. • ECDs of these derivates could achieve high transmittance change (over 69%) during electrochromic process. • ECDs reveal long cyclic stability over thousands cycles. Novel electrochromic-fluorescent dual functional devices based on aryl substituted viologen derivates were fabricated and characterized. The devices containing four viologen derivates, had both electrochromic and fluorescent switching properties. They were designed and functionally synthesized by introducing benzene, naphthalene, anthracene and benzothiadiazole rings between two pyridine rings, which endowed these viologen derivates with unique photoelectric properties. Devices consisted of benzene viologen, naphthalene viologen and benzothiadiazole viologen revealed exceptional electrochromic properties, of vivid color changes, high optical contrast and fast response time under applied bias. In addition, owing to the increased conjugated π-framework degree of our designed compounds, compared to conventional viologens, the fabricated devices could all achieve intense fluorescence emission. Notably, outstanding cyclic stability of electrochromic devices over thousands cycles made these aromatic viologen derivates promising candidates for new generation electrochromic-fluorescent applications.