Electrochromic behaviors and applications of tetrasubstituted thienoviologen derivatives

Electrochromic materials have been widely used in various parts of life due to their advantages of energy conservation and rich colors. In this work, a series of novel viologen derivatives (tetrasubstituted thienoviologen derivatives, a–f) were designed and synthesized as electrochromic materials by decorating 4,4′,4″,4‴-(thiophene-2,3,4,5-tetrayl)tetrapyridine with different N-substituents (alkyl, benzyl and aryl). Electrochromic devices based on a–f exhibited a low working voltage of −1.4 V. The N-substituents markedly affected their electrochromic performance. The compounds with alkyl and benzyl substituents performed better than the compound with aryl substituent. Among them, compound c with benzyl substituent performed best with a high optical contrast (66 %), a high coloration efficiency (389 cm²/C), good cycling stability, and fast response time. Besides, compound c was also applicable to sodium carboxymethyl cellulose hydrogel ECD with good cycling stability and a broad absorption band (500–700 nm) in the visible region. The applications of compound c in electronic tags, functional displays and smart windows were explored, indicating it's a promising ECM with wide application prospects.