High-performance D-A-D type electrochromic polymer with π spacer applied in supercapacitor

pi-spacer as well as its substituted groups could take part in tuning the properties of molecules, such as optical absorption, molecular configuration, film morphology and charge transport. In the paper, 3,4-dihexoxythiophene regarded as pi-spacer was used to design the D-pi-A-pi-D type conjugated polymer poly(4,7-bis(5-(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-3,4-bis(hexyloxy)thiophen-2-yl)benzo[ c][1,2,5]thiadiazole) (poly(BT-Th-EDOT)) with green color at neutral state and blue color at oxidation state. The introduction of pi-spacer makes BT-Th-EDOT polymerize at lower potential. Moreover, its substituted groups hanging out of the conjugated block endow molecular configuration with a degree of local torsion, making poly(BT-Th-EDOT) film possess porous micromorphology. Due to molecular structure modification, the polymer exhibits improved electrochromic performance compare to control polymer PBDT without pi-spacer including 46% optical contrast in visible region, 0.4 s response time and 271 C-1 cm(2) coloration efficiency. Remarkably, the optical contrast of 46% in visible region is one of the highest values among the neutral green polymers. Besides, poly(BT-Th-EDOT) modified electrode shows the higher specific capacitance compare to PBDT, because of the porous morphology providing larger surface area and more transport channels for ions. These satisfactory dual functions make electrochromic supercapacitor device based on poly(BT-Th-EDOT) possess different colors at charge and discharge processes, resulting in the energy storage state could be monitored by naked eye. These results demonstrate that the performance of D-A-D type polymer as well as film morphology could be optimized by the modulation of pi-spacer structure.