title: Ladderlike oligomers; intramolecular hydrogen bonding, push-pull character, and electron affinity.
abstract: Symmetrical 2,5-bis(2-aminophenyl)pyrazines have been synthesized by application of the Stille coupling strategy. These cotrimers feature three important properties, namely strong intramolecular hydrogen bonding, push-pull character, and high electron affinity. The presence of intramolecular hydrogen bonds has been confirmed by 1H NMR, IR spectroscopy, and single-crystal X-ray diffraction. The hydrogen bond strength can be increased by substituting the amino groups with stronger electron-withdrawing functionalities. Despite the anticipated enhanced pi-conjugation through planarization, a hypsochromic shift was observed in the UV/Vis spectra, explained by a decrease in push-pull character. The electron affinity of the cotrimers was deduced from the first reduction potentials measured by cyclic voltammetry and is related to the electron-withdrawing character of the amino substituents. The results obtained have been compared with those of the corresponding 4-aminophenyl analogues and show that intramolecular hydrogen bonds can be used to design polymers with enhanced pi conjugation as well as a high electron affinity.
authors.affiliation: Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, The Netherlands.
authors.forename: K
authors.initials: K
authors.lastname: Pieterse
authors.forename: J A
authors.initials: JA
authors.lastname: Vekemans
authors.forename: H
authors.initials: H
authors.lastname: Kooijman
authors.forename: A L
authors.initials: AL
authors.lastname: Spek
authors.forename: E W
authors.initials: EW
authors.lastname: Meijer