Résumé
A series of small-sized model π-conjugated oligomers have been prepared from thienylene and phenylene or dimethylor dimethoxy-substituted phenylene units. Crystallographic data for the methoxylated compound show a quasi-planar conformation with a non-covalent S–O interaction. The resulting strong conjugation in the gas phase has also been highlighted by UV/photoelectron spectroscopy and theoretical calculations (DFT). Indeed, for these compounds there is a large energy gap ΔEπ arising from the interaction between the molecular orbitals of the isolated thienylene-phenylene species. This can be explained in terms of the energies of the two π orbitals of the dimethoxyphenylene unit, the shape of these molecular orbitals in a three-orbital interaction diagram and by the presence of the S···O interaction which re- Introduction π-Conjugated organic polymers have received much attention for several years because of the large variety of applications directly associated with the existence of an extended conjugated π-system along the polymer backbone. They have attracted much interest in the design of electronic and optoelectronic devices such as organic field-effect transistors (OFET), organic light-emitting diodes (OLED) or solar cells because of their remarkable electronic and electro- optical properties[1,2] which are easy to tune as a result of their molecular and supramolecular chemistry. Among the more notable examples, the regioregular poly(3-alkylthiophene) exhibits excellent chain planarity and extended conjugation lengths as a result of its head-to-tail regiochemistry,[ 3] leading to highly conjugated sheets with high field- [a] Hétérochimie Moléculaire et Macromoléculaire, UMR CNRS 5076, Ecole Nationale Supérieure de Chimie de Montpellier, 8, rue de l'Ecole Normale, 34296 Montpellier Cedex 05, France E-mail: lere@enscm.fr [b] Equipe de Chimie-Physique, IPREM-UMR CNRS 5254 Avenue de l'Université, B. P. 1155, 64013 Pau Cedex, France E-mail: jean-marc.sotiro@univ-pau.fr [c] Laboratoire des Agrégats Moléculaires et Matériaux Inorganiques, UMR CNRS 5072, Université Montpellier II, 2 Place Eugène Bataillon, 34095 Montpellier Cedex 5, France Supporting information for this article is available on the WWW under http://www.eurjoc.org or from the author. Eur. J. Org. Chem. 2007, 4019–4031 © 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 4019 duces the inter-ring angle between the two aromatic cycles. The nature of the sulfur–oxygen interaction, discussed from a theoretical point of view, is mainly electrostatic, the orbital contribution from the only correctly directed orbitals nO σ and σ*S–C being slightly stabilising. These results show extensive conjugation of the π system corroborated by a small HOMO– LUMO gap. These studies, carried out in the solid state and in the gas phase, show how important it is to combine thienylene and dialkoxyphenylene fragments to obtain oligomers with a strong electronic delocalisation. Thus, these compounds are of interest in the fields of electronic and optoelectronic devices.