We report a joint theoretical and experimental study of several new thiophene-based poly(azomethine)s. Hybrid density functional theory (DFT) method was used to calculate the optimized geometry and electronic structure of poly(azomethine)s. Theoretical band gaps of the new thiophene-based poly(azomethine)s were in the range 2.33−2.67 eV, which are smaller than that of the phenylene-based polymer. The variation of the backbone ring (fluorene, carbazole, or naphthalene) or donor/acceptor side group on the phenylene ring significantly affected the dihedral angles and resulted in the variation of electronic properties (ionization potential, electron affinity, and band gap) of the poly(azomethine)s. Five soluble new conjugated poly(azomethine)s derived from the polymerization of 2,5-diformyl-3-hexylthiophene (DFHT) with various diamines were prepared and characterized. The optical and electrochemical band gaps of the polymer films were in the ranges 2.21−2.28 and 2.13−2.24 eV, respectively. The trend of the effect of the backbone ring or side chain on the experimental electronic properties is in good agreement with the theoretical results. Our study demonstrates how the electronic properties of conjugated poly(azomethine)s can be tuned by the backbone ring or side group, which could be important for electronic or optoelectronic applications of the materials.

Theoretical and experimental characterization of relatively small band gap methine-bridged poly(3,4-ethylenedioxythiophene)(PEDOT) derivatives is reported. AM1 and the modified extended Hückel theory were used to explore the ground-state geometric and electronic structures of poly[(3,4-ethylenedioxythiophene-2,5-diyl) methine] (PEDOT-M). The bond length alteration in PEDOT-M was found to be smaller than that in the reported methine-bridged polythiophene, and this resulted in a significantly lower band gap of 0.48 eV in PEDOT-M. The structure and properties of the methine-bridged PEDOT were further verified by synthesis of poly[(3,4-ethylenedioxythiophene-2,5-diyl)-benzylidene] (PEDOT-B) and poly[(3,4-ethylenedioxythiophene-2,5-diyl)-(p-methoxybenzylidene)] (PEDOT-MB). These polymers were found to be highly dehydrogenated and to contain a conjugated backbone of alternating aromatic and quinoid ethylenedioxythiophene segments. The optical and electrochemical band gaps of PEDOT-B are 0.87 and 1.05 eV, respectively, while those of PEDOT-MB are 0.86 and 1.01 eV. The methoxy substitution of PEDOT-MB results in a smaller ionization potential and electron affinity than those of PEDOT-B. The theoretical and experimental results show that methine-bridged PEDOT is a small band gap polymer.

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