Preparation of Conjugated Gels of Regioregular HT Sexi(3-n-octylthiophene) and Related Star Molecules

Abstract

We present new kinds of conducting gels of octylthiophene. Contrary to the gels previously obtained in our laboratory, they present two “high” gelation thresholds (i.e., related to high crosslink ratios). Consequently, systems close to the gelation threshold can be prepared with accuracy. Furthermore, they are calibrated and regioregular: The length and the regioregularity of the chain segments between adjacent cross-links are fully controlled. They are prepared by chemical polycondensation of monodisperse regioregular [(head-to-tail (HT)] oligo(octylthiophene)s with tribromobenzene. For the preparation of these gels, two kinds of regioregular oligomers are synthesized: linear (from dimer to hexamer) and “star” oligo(octylthiophene)s. The two star oligomers are made of a benzene ring trisubstituted in meta positions by a regioregular (HT) segment of respectively six (E6) and twelve (E12) octylthiophenes. The structural properties of the oligomers are studied by 1H and 13C NMR spectroscopy; information concerning their conformation is reported. The optical properties (UV−vis absorption and fluorescence) of the star oligomers are compared with that of the linear oligomers. A linear evolution of the energy of the fluorescence transitions of the linear regioregular oligo(octylthiophene)s with the reverse of thiophene number is demonstrated for the first time. The Stille coupling chosen to prepare the gels from the oligomers is studied to determine the experimental conditions allowing both the good solubility of large clusters formed during the gel preparation and the good yield of the coupling reaction. A first series of 14 networks is reported. It is characterized by two gelation thresholds that are very high, as expected, but very close one from another. A strategy is proposed to increase the distance between the two gelation thresholds in the coming series.