L'oxydation du A-éthylcarbazole par FeCl3 conduit à la formation quantitative du dimère. Cette oxydation est l'étape déterminante des trois étapes élémentaires mises en jeu dans le processus. L'oxydation du 3-octylthiophène dans les mêmes conditions, conduit à la formation très rapide de haut polymère à partir du couplage d'espèces actives oligomères, l'étape lente de la polymérisation étant l'oxydation du monomère. La copolymérisation des deux monomères par FeCl3 permet d'obtenir des matériaux dont la solubilité et le thermochromisme varient en fonction de la composition et sont donc modulables.

Chemical oxidation of N-ethylcarbazole by FeCl3 quantitatively yields dimer. Oxidation is the rate-determining step among the three elementary reactions involved in the process, Oxidation of 3-octylthiophene in the same conditions, leads to the formation very rapidly of high molecular weights through the coupling of oligomeric active species. Copolymerization of the monomers by FeCl3 gives rise to materials whose solubility and thermochromism depend on the composition and therefore can be tuned.

Temperature-dependent UV-visible absorption measurements in the solid state and in solution have been performed on poly(3-butoxy-3'-decyl-2,2'-bithiophene) (PBDBT), poly(3-dodecyl-2, 2'-bithiophene) (PBT12), poly(3-(octyloxy)-4-methylthiophene) (POMT), and poly(3-dodecylthiophene) (PT12). These measurements revealed the existence of two different types of thermochromism which are correlated to the substitution pattern of the polymers. A ''two-phase'' thermochromic behavior was found in POMT and PT12 and was related to the formation of delocalized conformational defects (twistons) upon heating. The formation of such twistons is made possible by the presence of sterically demanding substituents between each consecutive repeat unit. In contrast, the partially substituted structure of PBDBT and PBT12 allows only the formation of localized conformational defects along the polymer backbone leading to a continuous and monotonic blue shift of the absorption maximum upon heating.

Two categories of thermochromic polythiophene derivatives have been identified, which are dependent upon the nature and the position of the substituents. A molecular mechanism is proposed that can explain the thermally induced optical transitions observed in these materials.

Temperature dependent optical absorption measurements have revealed important thermochromic effects in poly(3-dodecylthiophene) and poly[(3-octyloxy)-4-methylthiophene] between 25 and 150 °C which are related to a conformation transition of the conjugated polymer from a co-planar structure to a non-planar form. This conformational transition is caused by an increase of the repulsive intrachain steric interactions upon heating which then force the thiophene backbone to adopt a non-planar conformation. On the other hand, as observed with poly(3-octyloxythiophene), if the thermally induced disorder in the side chains does not lead to large steric interactions, the polymer can keep a highly conjugated structure even at high temperatures whereas, if the steric interactions are too strong (e.g. as in poly(3,3′-dihexyl-2,2′-bithiohene), no co-planar conformation can take place.

Temperature-dependent optical absorption measurements have revealed important thermochromic effects in poly(3-dodecylthiophene) and poly(3-octyloxy-4-methylthiophene) between 25 and 150-degrees-C which are related to a planar to non-planar transition of the main polymer chain. This conformational transition is caused by an increase of the repulsive intrachain steric interactions upon heating, which then force the thiophene backbone to adopt a non-planar conformation. On the other hand, as observed with poly(3-octyloxythiophene), if the side chains do not lead to large steric interactions, the polymer can maintain a highly conjugated structure even at high temperatures while, if the steric interactions are too strong (e. g. poly(3,3'-dihexyl-2,2'-bithiophene)), no co-planar conformation can be adopted.

Die Makromolekulare Chemie, Rapid CommunicationsVolume 14, Issue 8 p. 461-464 Article Thermochromic properties of polythiophenes: Cooperative effects Claudine Roux, Claudine Roux Départment de Chimie, Université de Montréal, Montréal Québec, H3C 3J7, CanadaSearch for more papers by this authorKarim Faid, Karim Faid Départment de Chimie, Université de Montréal, Montréal Québec, H3C 3J7, CanadaSearch for more papers by this authorMario Leclerc, Corresponding Author Mario Leclerc Départment de Chimie, Université de Montréal, Montréal Québec, H3C 3J7, CanadaDépartment de Chimie, Université de Montréal, Montréal Québec, H3C 3J7, CanadaSearch for more papers by this author Claudine Roux, Claudine Roux Départment de Chimie, Université de Montréal, Montréal Québec, H3C 3J7, CanadaSearch for more papers by this authorKarim Faid, Karim Faid Départment de Chimie, Université de Montréal, Montréal Québec, H3C 3J7, CanadaSearch for more papers by this authorMario Leclerc, Corresponding Author Mario Leclerc Départment de Chimie, Université de Montréal, Montréal Québec, H3C 3J7, CanadaDépartment de Chimie, Université de Montréal, Montréal Québec, H3C 3J7, CanadaSearch for more papers by this author First published: August 1993 https://doi.org/10.1002/marc.1993.030140801Citations: 16AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume14, Issue8August 1993Pages 461-464 RelatedInformation

Temperature-dependent UV-visible absorption measurements have revealed reversible thermochromic effects (a 0.95-eV shift in the maximum of absorption) in amorphous poly[3-(octyloxy)-4-methylthiophene] (POMT). The presence of a solid-state "phase" transition was also confirmed by infrared and calorimetric analyses. All these experimental results are consistent with a conformational transition of the conjugated polymer chain from a coplanar (rod) structure at room temperature to a nonplanar (coil) form at 150-degrees-C. According to theoretical calculations, the less conjugated form of POMT can be related to the presence of a torsion angle of +/- 45-degrees between each consecutive repeat unit.

Waveguiding and refractive index measurements were performed at a number of wavelengths in the red and near infrared region of the spectrum by grating coupling into a series of polythiophenes, poly[3-tetradecylthiophene] (PT14), poly[3-decylthiophene] (PT10) and poly[3-hexylthiophene] (PT6) films. The dispersion in the refractive index was compared to the Kramers-Kronig analysis of the absorption spectra. A decrease of the refractive indices with increasing number of side-chains was found due to a volume dilution effect of the optically active main chain.