Redox active electrochromic polymers from low oxidation monomers containing 3,4-ethylenedioxythiophene (EDOT)

Here we report the synthesis of several new low oxidation monomers with the external rings being 3,4-ethylenedioxythiophene (EDOT). These monomers were prepared via NiCI2(dppp) catalyzed Grignard coupling in good yields and were found to exhibit low oxidation potentials with the lowest having an onset of 0.14 V for 2,2′:5′,2″-ter(3,4-ethylenedioxythienyl)thiophene (TER-EDOT). The polymers were found to be stable electrical conductors and were found to exhibit band gaps ranging from 1.4 eV for trans-1,2-bis(2-(3,4-ethylenedioxy)thienyl)vinylene (BEDOT-V) to 2.5 eV for the series of 3,6-bis(2-(3,4-ethylenedioxy)-thienyl)N-substituted carbazoles (BEDOT-NCz). BEDOT-V was found to be opaque purple in the reduced state and transmissive sky blue in the oxidized state while the BEDOT-NCzʹs are transmissive yellow in the reduced state, green upon mild oxidation and deep opaque blue in the oxidized state. Both the BEDOT-V and BEDOT-NCzʹs were found to exhibit fast response times and high contrast ratios upon redox stepping, thereby proving them useful for electrochromic coatings.