title: Donor-substituted cyanoethynylethenes: pi-conjugation and band-gap tuning in strong charge-transfer chromophores.
abstract: An extensive series of silyl-protected cyanoethynylethenes (CEEs) and N,N-dimethylanilino donor-substituted CEEs have been synthesized. More extended chromophores were constructed by selective silyl deprotection and subsequent oxidative acetylenic coupling. The strong electron-accepting nature of the CEEs was revealed by a combination of 13C NMR spectroscopic and electrochemistry measurements. Donor-substituted CEEs display strong intramolecular charge-transfer (CT) character, resulting in intense, bathochromically shifted CT bands in the UV/Vis spectrum. Their structural diversity establishes them as suitable models for the study of pi-conjugation and band gap tuning in strong charge-transfer chromophores. The extent of pi-conjugation in the donor-substituted CEEs was investigated by a combination of ground-state techniques, such as X-ray crystallography, electrochemistry, B3 LYP calculations, and NMR spectroscopy. The comparison of these ground-state results with the features observed in the UV/Vis spectra reveals that-contrary to expectations-more extensive pi-conjugation can lead to larger band gaps in molecules with strong donor and acceptor moieties.
authors.affiliation: Laboratorium für Organische Chemie, ETH-Hönggerberg, HCI, 8093 Zürich, Switzerland.
authors.forename: Nicolle N P
authors.initials: NN
authors.lastname: Moonen
authors.forename: William C
authors.initials: WC
authors.lastname: Pomerantz
authors.forename: Robin
authors.initials: R
authors.lastname: Gist
authors.forename: Corinne
authors.initials: C
authors.lastname: Boudon
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Gisselbrecht
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Kawai
authors.forename: Atsushi
authors.initials: A
authors.lastname: Kishioka
authors.forename: Maurice
authors.initials: M
authors.lastname: Gross
authors.forename: Masahiro
authors.initials: M
authors.lastname: Irie
authors.forename: François
authors.initials: F
authors.lastname: Diederich