Multicolored and high optical contrast flexible electrochromic devices based on viologen derivatives

Three viologen derivatives: 1,1′- (4-indolyphenyl) -4,4′-bipyridine dihexafluorophosphate (2IV), 1,1′- (4-phenothiazinylphenyl) -4,4′- bipyridine dihexafluorophosphate (2PV) and 1,1′-(4-benzimidazolylphenyl)-4,4′-bipyridine dihexafluorophosphate (2BV) were synthesized. The electrochemical and electrochromic properties of these viologen derivatives were investigated. The flexible and rigid electrochromic devices (ECD) were prepared by using the synthesized viologen derivatives as active materials. The structure of the device is ITO-PET (or ITO-glass)/ electrochromic gel film/ ITO-PET (or ITO-glass). The flexible and rigid ECDs exhibited reversible color changes under applied voltage. Upon applied voltage from 0.0 V to −1.0 V, 2IV-based flexible ECD exhibited optical contrast 61.2% at 695 nm, 2PV-based flexible ECD exhibited optical contrast 60.8% at 715 nm and 2BV-based flexible ECD exhibited optical contrast 53.1% at 574 nm.