Selenophene, thiophene, and furan functionalized π-extended viologen derivatives for tunable all-in-one ECDs

π-Extended viologen derivatives of SHP, THP and FHP with selenophene, thiophene and furan units between two pyridine moieties, respectively, as chromophores, were synthesized. Compared with conventional viologen of DHP using bipyridines as the chromophore, the three compounds of SHP, THP, and FHP possess extended conjugation lengths and narrowed bandgaps. All-in-one electrochromic devices (ECDs) were assembled using these four viologen derivatives and investigated systematically. Due to the different electronic properties of the chromophores, the devices exhibited different colored states, blue, blue-violet, magenta and red. Furthermore, the electrochromic response of SHP, THP, and FHP extended into near-infrared (NIR) region due to the long conjugation as compared with that of DHP. Further, the ECDs possessing SHP, THP and FHP displayed faster response speed and relatively higher coloration efficiency than that of DHP. Among them, ECD based on FHP has shown the most excellent stability, which retains 95.7% optical contrast of its initial state after continuous working for 20000 cycles. Additionally, upon applying a switching potential, electrofluorochromic (EFC) properties of the devices based on THP and FHP were observed. This study revealed structure-property relations and demonstrated that manipulation of chromophores offers an effective route to obtain multicolor and multifunctional ECDs, which provides potential applications for colorful displays and smart windows.