Poly[3,3′-dialkyl-2,2′-(ethyne-1,2-diyl)bis(thiophene)]:: electrically conducting and fluorescent polymers incorporating a rigid acetylenic spacer

A series of poly [3,3'-dialkyl-2,2'-(ethyne-1,2-diyl)bis(thiophene)]s, comprising a rigid carbon-carbon triple bond between two bithiophene repeating units, were synthesized. The improved rigidity of the polymer backbone led to an increased fluorescent quantum yield in comparison to poly(3-alkylthiophene)s. A generic trend depicting decreasing Stokes shift in the fluorescence spectra with increasing pendant alkyl chain length was observed. The incorporatibn of the acetylenic spacer also resulted in a significant red shift in the absorption spectra in comparison to poly(3-alkylthiophene) s, corresponding to an increase in effective conjugation over the entire series of polymers. These polymers, upon doping with iodine or ferric chloride, gave electrical conductivity in the range of 10(0) to 10(-4) S cm(-1). Thermochromism studies showed a blue shift in absorption peak as the temperature changes from 25 to 180 degrees C. The influence of alkyl chain length and the adetylenic spacer on the conductivity and UV-VIS absorption is also discussed. In situ electrochemical doping studies were monitored using UV-VIS-near infrared absorption spectroscopy and showed the evolution of polaron bands at around 1.4 eV.