Studies on Conjugated Polymers: Preparation, Spectroscopic, and Charge-Transport Properties of a New Soluble Polythiophene Derivative: Poly(3′,4′dibutyl-2,2′:5′2″-terthiophene)

A new polythiophene derivative has been synthesized by chemical oxidative polymerization of 3′,4′-dibutyl-2,2′:5′2″-terthiophene (DBTT). The new polymer, poly(DBTT), contains two soluble fractions of differing molecular weights both of which were characterized by X-ray diffraction, IR, NMR, UV-vis-NIR, photoluminescence, and ESR spectroscopies, as well as magnetic susceptibility and charge-transport measurements. The molecular weights of both fractions were determined by gel permeation chromatography. The high molecular weight fraction (M_w ~ 9.1 × 10³) has one of the longest π-conjugation lengths known for poly(alkylthiophenes) and high conductivity. The low molecular weight fraction (M_w ~ 4.3× 103) has a shorter conjugation length and 2 orders of magnitude lower conductivity (~10⁻² S/cm) at room temperature. Thermal gravimetric analysis studies show that the polymer is stable in nitrogen up to 380 °C. Variable-temperature charge-transport data (conductivity and thermopower) for both doped polymer fractions indicate p-type metallic behavior. These results are compared to previously characterized polythiophenes.