Thieno[3,2-b]thiophene based electrochromic polymers: experimental cum theoretical appraisal of the EDOT position

Two thieno[3,2-b]thiophene based polymers (poly[2,5-bis(2,3-dihydro-thieno[3,4-b][1,4]dioxin-5-yl)thieno[3,2-b]thiophene] (P(2,5-BTE)) and poly[3,6-bis-(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)thieno[3,2-b]thiophene] (P(3,6-BTE))) were synthesized by an electrochemical method. By alternating the 3,4-ethylenedioxythiophene (EDOT) position along the polymer backbone we studied the electrochemical and optical properties by comparing the 2,5- and 3,6-positions on the thieno[3,2-b]thiophene unit. The theoretically calculated bandgaps and ultraviolet-visible spectrum peaks of the two dimers are in good agreement with the polar energy and peak range in the ultraviolet-visible and near-infrared (UV-Vis-NIR) spectrum, which helps us to comprehend the process of electrochemical polymerization and indicates that P(2,5-BTE) has a more conjugated structure than P(3,6-BTE). With the increase in voltage, both of the polymers gradually transform to their quinoid structures. Effective color tuning by changing the position of the EDOT units is the noteworthy property of P(2,5-BTE) and P(3,6-BTE), which makes them suitable electrochromic materials.