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)BAR approximately 9.1 X 10(3)) has one of the longest pi-conjugation lengths known for poly(alkythiophenes) and high conductivity. The low molecular weight fraction (M(w)BAR approximately 4.3 X 10(3)) has a shorter conjugation length and 2 orders of magnitude lower conductivity (approximately 10(-2) S/cm) at room temperature. Thermal gravimetric analysis studies show that the polymer is stable in nitrogen up to 380-degrees-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.