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 .