Synthesis and characterization of β-substituted 3,4-ethylenedioxy terthiophene monomers for conducting polymer applications

• 3′-Functionalized 2,5-bis[(3,4-ethylenedioxy)thien-2-yl] thiophene were prepared.
• Quantum yield of the each monomer indicates possible electrochromic applications.
• The absorption of the polymers was in the range of 300–800 nm in film.
• The AFM analysis of the polymers confirm the roughness of the films.

2,5-Bis[(3,4-ethylenedioxy)thien-2-yl] thiophene monomers bearing 3′-hydroxymethylene (2), 3′-hydroxyethylene (3), 3′-acetoxyethyl (4) and 3′-acetoxyl (5) functions were prepared in a short bidirectional synthesis using Kumada–Corriu or Stille chemistry. The newly prepared monomers are stable enough in organic solvents at RT in the absence of acids and can be safely stored without exclusion of oxygen, at 4 °C in the dark. The chloroform solutions of 2–5 exhibit a blue-shifted λmax in the range of 345–352 nm, when compared to 2,5-bis[(3,4-ethylenedioxy)thien-2-yl] thiophene (1). Smaller shifts were observed in the fluorescence spectra where all λmax values were centered in the range of 438–440 nm, similar to the parent unsubstituted 1 (439 nm) with fluorescence quantum yields φf = 2.2–2.8%, that was roughly half of the monomer 1 reference value (4.8%). Cyclic voltammetry was employed to investigate the electrochemical behaviour of the monomers. Polymer films deposited by repeated potential cycling show oxidation potentials ranging from 320 to 540 mV. AFM analysis shows that these polymers display large active surface because of their roughness. All the polymers exhibit a broad absorption spectrum with a λmax ranging from 464 nm to 533 nm.

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