Influence of fluorine substitution position on electrochromic and capacitive properties of hybrid conjugated polymer

Fluorine atom as side chain substituted conjugated polymer exhibits enhanced photoelectric performance due to the intra- and inter-molecular interaction. However, the strong molecular aggregation due to the existence of fluorine atom inhibits the doping ion transport in conjugated polymer. Here, two fluorine substituted hybrid conjugated polymers, poly(BisTh-o-2F) and poly(BisTh-p-2F), based on para-phenylene and thiophene were prepared by electrochemical method. The molecular structure difference of the two hybrid conjugated polymers is the substitution position of fluorine atom. The two hybrid conjugated polymers exhibit similar redox property and optical absorption region. During oxidation process, the colors of the two hybrid conjugated polymers turn from dark red to blue. Kinetic studies demonstrate that fluorine atom ortho-substituted poly(BisTh-o-2F) possesses faster response time than that para-substituted poly(BisTh-p-2F) due to the decreased molecular aggregation. However, poly(BisTh-p-2F) exhibits higher optical contrast than poly(BisTh-o-2F) under different wavelengths. The charge-discharge experiments demonstrate that poly(BisTh-o-2F) possesses much higher specific capacitance than poly(BisTh-p-2F). And, the energy storage states of the two conjugated polymers could be monitored by the color variation, demonstrating they possess great application potential in electrochromic supercapacitor.