title: Highly functionalized dimeric tetraethynylethenes and expanded radialenes: strong evidence for macrocyclic cross-conjugation.
abstract: A selection of dimeric tetraethynylethenes (TEEs) and perethynylated expanded radialenes, containing different donor/acceptor substitution patterns, have been prepared and fully characterized. The first X-ray crystal structure of an expanded [6]radialene, with twelve peripheral 3,5-di(tert-butyl)phenyl substituents, is presented. This macrocycle, the all-carbon core of which is isomeric with fullerene C60, adopts a non-planar, "chair-like" conformation. Also a TEE dimer, carrying N,N-dimethylaniline donor substituents, has been subjected to an X-ray crystallographic analysis. The electronic properties were studied by UV/Vis spectroscopy and electrochemistry, providing fundamental insight into mechanisms of pi-electron delocalization in the acyclic and macrocyclic chromophores. Donor or donor-acceptor-substituted dimeric TEE derivatives show very strong absorptions extending over the entire UV/Vis region; their longest wavelength absorption bands have high charge-transfer character. Macrocyclic cross-conjugation in the expanded radialenes becomes increasingly efficient with increasing donor-acceptor polarization. A dual, strongly solvent-polarity-dependent fluorescence was observed for a tetrakis(N,N-dimethylaniline)-substituted dimeric TEE; this interesting emission behavior is explained by the twisted intramolecular charge-transfer (TICT) state model. Donor-substituted expanded radialenes display huge resonance-enhanced third-order nonlinear optical coefficients.
authors.affiliation: Laboratorium für Organische Chemie, ETH-Zentrum, Zürich, Switzerland.
authors.forename: M B
authors.initials: MB
authors.lastname: Nielsen
authors.forename: M
authors.initials: M
authors.lastname: Schreiber
authors.forename: Y G
authors.initials: YG
authors.lastname: Baek
authors.forename: P
authors.initials: P
authors.lastname: Seiler
authors.forename: S
authors.initials: S
authors.lastname: Lecomte
authors.forename: C
authors.initials: C
authors.lastname: Boudon
authors.forename: R R
authors.initials: RR
authors.lastname: Tykwinski
authors.forename: J P
authors.initials: JP
authors.lastname: Gisselbrecht
authors.forename: V
authors.initials: V
authors.lastname: Gramlich
authors.forename: P J
authors.initials: PJ
authors.lastname: Skinner
authors.forename: C
authors.initials: C
authors.lastname: Bosshard
authors.forename: P
authors.initials: P
authors.lastname: Günter
authors.forename: M
authors.initials: M
authors.lastname: Gross
authors.forename: F
authors.initials: F
authors.lastname: Diederich