Synthesis and optical properties of fused aromatic thienopyrazine based π-conjugated polymers

Two new polythieno[3,4-b]pyrazine derivatives, poly-10,12-bis(4-hexylthiophen-2-yl)dibenzo[f,h] thieno[3,4-b]quinoxaline (PDBTQ) and poly-8,10-bis(4-hexylthiophen-2-yl)acenaphtho[1,2-b]thieno[3,4-e]pyrazine (PATP) were synthesized by electrochemical polymerization and their electrochemical properties reported. Electroactivity of the monomer and electrochemical redox behavior of its polymers were investigated by cyclic voltammetry. Spectroelectrochemical analysis was performed and the band gaps of the polymers were determined as 2.0 eV and 1.2 eV from the onset of the π–π* transitions of PDBTQ and PATP, respectively. The polymer PDBTQ shows multicolored electrochromic behavior with five distinct states—orange (0.0 V), yellow (+0.30 V), brown (+0.50 V), green (+0.65 V), blue-gray (0.80 V); PATP has two distinct colors—transmissive gray (0.0 V) and green (+0.80 V). The polymers revealed superior optical contrast in the near-infrared (NIR) region with fast switching times of less than 1 s