title: Metal ion modulated torsion angle in a ditopic oligothiophene ligand: toward supramolecular control of π conjugation.
abstract: A π-conjugated oligomer bearing two 15-crown-5-containing styryl moieties connected at the inner β positions of the terminal thiophene nuclei can adopt either a U or a Z shape depending on the structures of its complexes with magnesium and barium ions. We show that barium cations lead to the formation of a mononuclear complex in solution, which causes the system to fold into the U shape. Magnesium ions lead to the same effect at low concentration, but force the ligand to adopt the Z-shaped geometry at high concentrations favoring formation of a binuclear complex. These geometrical reorganizations in solution are accompanied by profound changes in spectroscopic properties, which can be rationalized in terms of variations in the extent of electron delocalization along the oligothiophene backbone. The effects are analyzed by mass spectrometry and (1)H NMR, UV/Vis absorption, and fluorescence spectroscopy in the steady-state and time-resolved regimes. The experimental results are compared to data calculated by using MOPAC2007 with the PM6 Hamiltonian including the COSMO solvation model.
authors.affiliation: Department of Chemistry, M. V. Lomonosov Moscow State University, Leninskie Gory, 119992 Moscow, Russia.
authors.forename: Elena
authors.initials: E
authors.lastname: Lukovskaya
authors.forename: Alla
authors.initials: A
authors.lastname: Bobylyova
authors.forename: Yuri
authors.initials: Y
authors.lastname: Fedorov
authors.forename: Anton
authors.initials: A
authors.lastname: Maksimov
authors.forename: Alexander
authors.initials: A
authors.lastname: Anisimov
authors.forename: Olga
authors.initials: O
authors.lastname: Fedorova
authors.forename: Gediminas
authors.initials: G
authors.lastname: Jonusauskas
authors.forename: Frédéric
authors.initials: F
authors.lastname: Fages