Design and Synthesis of Novel Compounds Based on Dithienylpyrrole Systems Containing Azobenzene Units and Their Electrochemical and Optical Properties as well as Their Processable Conducting Polymers

Two dithienylpyrroles based on azo dyes, namely 2,5’-dimethyl-[4-(2,5-di-thiophen-2-yl-pyrrol-1- yl)-phenyl]azobenzene (1) and 2,5’-dimethyloxy-[4-(2,5-di-thiophen-2-yl-pyrrol-1-yl)-phenyl] azobenzene (2), were synthesized and their corresponding polymers (P1 and P2) were successfully obtained via electropolymerization. The monomers have lower oxidation potentials (0.75 V and 0.80 V vs. Ag/AgCl for 1 and 2, respectively) when compared to their analogous. Both monomers exhibited photoisomerism properties under irradiation at 360 nm. During the irradiation process, for example, the color of monomer 2 changes from yellow to greenish yellow. The electroactive polymer films have well-defined and reversible redox couples with a good cycle stability in both aqueous and organic solutions. The polymer films also exhibited electrochromic behaviors; color changes from yellowish green to dark green for the P1 (λma= 435 nm and Eg= 2.31 eV) and from mustard color to green for P2 (λmax= 430 nm and Eg= 2.34 eV). Furthermore, the soluble polymers demonstrated different hues of yellow and green colors. The electrochemical and optical properties of a novel conducting copolymer called poly(3,4- ethylenedioxythiophene-co-1)-(P(EDOT-co-1)) are reported. Electrochemically synthesized P(EDOTco- 1) based on the azo dye has a well-defined and reversible redox couple (0.37 V vs. Ag/AgCl) with good cycle stability. The copolymer film exhibits high conductivity (13 S/cm) as well as electrochromic behavior (magenta when neutralized and transmissive sky blue when oxidized). Furthermore, electrooptically active copolymer film has a low band gap of 1.79 eV with a π−π* transition at 555 nm.