Concise syntheses, polymers, and properties of 3-arylthieno[3,2- b ]thiophenes

Thieno[3,2-b]thiophenes (TT), having para-substituted phenyl groups at C-3, have been synthesized through a ring closure reaction, using P ₄S ₁₀, in moderate to high yields. Their absorbance studies displayed that the TT, having nitrophenyl group had the most red shift absorbance at 365 nm, which also showed the lowest optical band gap of 2.92 eV; the rest of the TTs had the absorbance between 300 and 302 nm. Cyclic voltammetry studies indicated that while all the TTs had the oxidation potentials above 1.0 V, the TT with dimethylaminophenyl group had the lowest oxidation potential of 1.33 V. The rest had the oxidation potentials between 1.6 and 1.99 V. The TTs were both electropolymerized and copolymerized with thiophene through Suzuki coupling reaction. Electropolymerized polymers indicated that while the polymer having strong electron donating dimethylaminophenyl group had the lowest oxidation potential of 0.97 V, the rest of the polymers displayed the potentials between 1.09 and 1.39 V. Their electronic band gaps varied between 1.86 and 2.46 eV. The CV-UV studies of the polymers, electro-deposited on ITO, showed absorbance maxima between 431 and 468 nm, and the lowest optical band gap was observed with the polymer having methoxyphenyl group (1.99 eV). The rest of the polymers had the optical band gaps between 2.05 and 2.19 eV. Regarding the copolymers, the one with methoxyphenyl group had the lowest oxidation potential of 0.75 V. They displayed absorption and emission maxima between 325 and 445 and 454-564 nm, respectively. Their optical and electronic band gaps varied between 2.0 and 2.5 eV. As the copolymer having strong electron donating methoxyphenyl group had the highest quantum yield, 0.64 eV, the one with strong electron withdrawing nitrophenyl group had the lowest quantum yield of 0.003 eV.