Side chain tuning of frontier orbitals in polymers of thieno[3,4-b]-pyrazine-based terthienyls

•Electropolymerization of thieno[3,4-b]pyrazine-based terthienyls gave polymeric thin films.•Materials produced exhibited band gaps ranging from 1.01 to 1.77 eV.•Band gaps and frontier orbitals can be tuned by choice of thieno[3,4-b]pyrazine side chains.

The tunability of the electronic and optical properties of thieno[3,4-b]pyrazine-based terthienyls utilizing electron-donating and electron-withdrawing side chains and their corresponding polymers have been investigated. As previously shown for the thieno[3,4-b]pyrazine monomers, the addition of electron-donating groups results in higher HOMO–LUMO energies in the oligomers and higher Eg values in the resulting polymers. Correspondingly, the use of electron-withdrawing groups provides reduced HOMO–LUMO energies and lower Eg values. The electronic effect of the side chains is diminished in comparison to the thieno[3,4-b]pyrazine analogs. However, the application of electron-withdrawing functionalized thieno[3,4-b]pyrazine-based terthienyls appears to be a promising approach for the production of low Eg materials.

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