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J. Phys. Chem. C 2007, 111, 16362-16371
Noncovalent Intramolecular Interactions in the Monomers and Oligomers of the Acceptor and Donor Type of Low Band Gap Conducting Polymers Alimet Sema O 2 zen,* Canan Atilgan, and Gursel Sonmez† Materials Science and Engineering Program, Faculty of Engineering and Natural Sciences, Sabanci UniVersity, 34956, Tuzla, Istanbul, Turkey ReceiVed: June 6, 2007; In Final Form: July 30, 2007
Intramolecular interactions of noncovalent nature in the conjugated oligomers of co-thiophene-thieno[3,4b]pyrazine-thiophene and co-thiophene-benzo[c]1,2,5-thiadiazole-thiophene are studied quantum mechanically. S‚‚‚N contacts are identified by the existence of topological bond critical points (bcp’s) along the bond path by means of atoms-in-molecules (AIM) theory. The planarity of the oligomers is attributed to the observed ring critical points among the thiophene and pyrazine or thiadiazole rings. Similar systems, obtained by replacing the thiophene by pyrrole and pyrazine by ethylenedioxy, are further studied with AIM analysis. The extent of the contribution of intramolecular interactions to the intrinsic conductivity of the conjugated polymers is investigated by extrapolating the oligomer band gap values from the time-dependent density functional theory excitation energies and density functional theory HOMO-LUMO gaps and is found to be in excellent agreement with measured experimental values, where values are present. Pyrrole substitution leads to the lowest band gap value (
