Synthesis and electrochromic properties of asymmetric viologen derivatives

Viologen has become a prominent focus of research in electrochromism due to its facile molecular structure modification, diverse color transitions, low driving voltage, and high coloration efficiency. In this study, asymmetric viologen derivatives (Pentyl-V and Heptyl-V) were synthesized through N-alkylation reactions using 1,2-bis(4-pyridyl) ethylene as the pyridine backbone. Subsequently, these derivatives were used to fabricate electrochromic gels, which were integrated with ITO-coated conductive glass to assemble electrochromic devices. Finally, the spectroelectrochemical, and electrochromic properties of the devices were comprehensively studied. Among these two electrochromic devices based on asymmetric viologen derivatives, the viologen derivative Heptyl-V, which has a longer alkyl chain substituent, demonstrates a significant optical contrast (30.3%) at 521 nm, a fast response time (coloring/ bleaching time of 21.1 s and 4.9 s), and a satisfactory coloring efficiency (180.4 cm²/C). The gel electrochromic device, based on asymmetric viologen derivatives, offers advantages such as a simple preparation process, low energy consumption, and high coloring efficiency. It holds potential for application in fields such as smart windows, electrochromic displays, and wearable electronics.