Three new donor–acceptor–donor type monomers bearing 2,7- or 3,6-linked carbazoles as the donor unit and diketopyrrolopyrrole as the acceptor unit were synthesized via a Suzuki cross coupling reaction.

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In this article, a series of benzothiadiazole and thiophene based donor-acceptor-donor (D-A-D) type monomers and their corresponding polymers, via potential cycling, were reported. Effect of increasing number of thiophene units in the electron rich donor segment on the electrochemical and photophysical properties of the monomers and their corresponding polymers were reported. Electrochemical and optical properties were determined by cyclic voltammetry, UV-Vis and emission spectrometry. Monomers with one, two and three thiophene units on both sides of benzothiadiazole (TBz, T2Bz, T3Bz) exhibited better conjugation and intramolecular charge transfer with increasing thiophene length. On the other hand, the inverse trend was observed in their corresponding polymers (PTBz, PT2Bz, PT3Bz). Blue shift of the absorption edge in polymer thin films resulted in wider optical bandgap (from 1.70 eV to 1.99 eV) with increasing donor/acceptor ratio on the polymer chain. Based on our experimental and theoretical studies, molecular weight or branching on these polymers together with degree of stiffness and conformational degree of freedom might be an explanation for these controversial observations.

A new copolymer of 3,4-ethylenedioxythiophene (EDOT) and 5-(2-ethylhexyl)-1,3-bis(9-methyl-9H-carbazol-3-yl)-5H-thieno [3,4-c]pyrrole-4,6-dione (CzPDICz) was electrochemically synthesized using different monomer feed ratios. The resulting copolymer films were investigated in terms of their electrochemical and electro-optical behaviors. Properties of the obtained copolymer films through different monomer feed ratios were compared to each other and to individual poly(ethylenedioxythiophene; PEDOT) and homopolymer of CzPDICz in order to observe the differences in the properties with respect to PEDOT and P(CzPDICz). Copolymers exhibited well adherence on the electrode surface with having non-diffusional redox process. The monomer feed ratios were prepared as 9:1; 4:1, and 1:1 (EDOT:CzPDICz) and changes in the electrochemical and spectroelectrochemical behavior were noted with increasing CzPDICz ratio in the monomer mixture. Although no appreciable change in the optical band gap values of the copolymers was noted as compared to PEDOT, the neutral blue copolymers exhibited grayish color in their semioxidized states and transparent green in their fully oxidized states.

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