title: Highly fluorescent crystalline and liquid crystalline columnar phases of pyrene-based structures.
abstract: A concept for highly ordered solid-state structures with bright fluorescence is proposed: liquid crystals based on tetraethynylpyrene chromophores, where the rigid core is functionalized with flexible, promesogenic alkoxy chains. The synthesis of this novel material is presented. The thermotropic properties are studied by means of differential scanning calorimetry (DSC), cross-polarized optical microscopy (POM), and X-ray diffraction. The mesogen possesses an enantiotropic Col(h) phase over a large temperature range before clearing. The material is highly fluorescent in solution and, most remarkably, in the condensed state, with a broad, strongly red shifted emission. Fluorescence quantum yields (Phi(F)) have been determined to be 70% in dichloromethane solution and 62% in the solid state. Concentration- and temperature-dependent absorption and emission studies as well as quantum-chemical calculations on isolated molecules and dimers are used to clarify the type of intermolecular interactions present as well as their influence on the fluorescence quantum yield and spectral properties of the material. The high luminescence efficiency in the solid state is ascribed to rotated chromophores, leading to an optically allowed lowest optical transition.
authors.affiliation: Laboratoire de chimie des polymères, CP 206/1, Université Libre de Bruxelles, Boulevard du Triomphe, 1050 Brussels, Belgium.
authors.forename: Anna
authors.initials: A
authors.lastname: Hayer
authors.forename: Véronique
authors.initials: V
authors.lastname: de Halleux
authors.forename: Anna
authors.initials: A
authors.lastname: Köhler
authors.forename: Abdel
authors.initials: A
authors.lastname: El-Garoughy
authors.forename: E W
authors.initials: EW
authors.lastname: Meijer
authors.forename: Joaquín
authors.initials: J
authors.lastname: Barberá
authors.forename: Julien
authors.initials: J
authors.lastname: Tant
authors.forename: Jeremy
authors.initials: J
authors.lastname: Levin
authors.forename: Matthias
authors.initials: M
authors.lastname: Lehmann
authors.forename: Johannes
authors.initials: J
authors.lastname: Gierschner
authors.forename: Jérôme
authors.initials: J
authors.lastname: Cornil
authors.forename: Yves Henri
authors.initials: YH
authors.lastname: Geerts