Synthesis and Characterization of New Dithienosilole Based Copolymers

Abstract

2-Ethylhexyl substituted dithienosilole based soluble polymers including thiophene (1) and bithiophene (2) units were synthesized via Stille coupling reaction. The presence of 2-ethylhexyl substituents on the silole ring gave solubility property to the polymers in common solvents. According to gel permeation chromatography measurements, the weight average molecular weights of the polymers 1 and 2 were found to be as 70,977 with a polydispersity index of 2.30 and 110,439 with a PDI of 1.42, respectively. Fluorescent polymers in toluene solution have maximum emisssion bands at 634 nm for the polymer 1 and 613 nm for the polymer 2. Chemical and electrochemical doping of the polymers in the solution and in the film forms were monitored by using ultraviolet-visible spectroscopic technique. The polymers exhibited chromic (chemochromic and electrochromic) properties. While the colors of the neutral polymer films are purple for the polymer 1 and reddish brown for the polymer 2, both polymers are transparent sky blue at their oxidized states. The bandgaps of polymers in film forms were calculated as 1.81 eV for the polymer 1 and 1.92 eV for the polymer 2. Also, electrochromic device applications of the polymers were done. Electrochemical and optical behaviors of the polymers demonstrated that they can be good candidates for optoelectronic applications.