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, comp rising 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-alkylthio phene)s. A generic trend depicting decreasing Stokes shift in the fluoresce nce spectra with increasing pendant alkyl chain length was observed. The in corporatibn of the acetylenic spacer also resulted in a significant red shi ft in the absorption spectra in comparison to poly(3-alkylthiophene) s, cor responding to an increase in effective conjugation over the entire series o f polymers. These polymers, upon doping with iodine or ferric chloride, gav e electrical conductivity in the range of 10(0) to 10(-4) S cm(-1). Thermoc hromism studies showed a blue shift in absorption peak as the temperature c hanges from 25 to 180 degrees C. The influence of alkyl chain length and th e adetylenic spacer on the conductivity and UV-VIS absorption is also discu ssed. In situ electrochemical doping studies were monitored using UV-VIS-ne ar infrared absorption spectroscopy and showed the evolution of polaron ban ds at around 1.4 eV.