title: Pyrrolidinium ionic liquid crystals.
abstract: N-alkyl-N-methylpyrrolidinium cations have been used for the design of ionic liquid crystals, including a new type of uranium-containing metallomesogen. Pyrrolidinium salts with bromide, bis(trifluoromethylsulfonyl)imide, tetrafluoroborate, hexafluorophosphate, thiocyanate, tetrakis(2- thenoyltrifluoroacetonato)europate(III) and tetrabromouranyl counteranions were prepared. For the bromide salts and tetrabromouranyl compounds, the chain length of the alkyl group C(n)H(2n+1) was varied from eight to twenty carbon atoms (n = 8, 10-20). The compounds show rich mesomorphic behaviour: highly ordered smectic phases (the crystal smectic E phase and the uncommon crystal smectic T phase), smectic A phases, and hexagonal columnar phases were observed, depending on chain length and anion. This work gives better insight into the nature and formation of the crystal smectic T phase, and the molecular requirements for the appearance of this highly ordered phase. This uncommon tetragonal mesophase is thoroughly discussed on the basis of detailed powder X-ray diffraction experiments and in relation to the existing literature. Structural models are proposed for self-assembly of the molecules within the smectic layers. In addition, the photophysical properties of the compounds containing a metal complex anion were investigated. For the uranium-containing mesogens, luminescence can be induced by dissolving them in an ionic liquid matrix. The europium-containing compound shows intense red photoluminescence with high colour purity.
authors.affiliation: Katholieke Universiteit Leuven, Department of Chemistry, Celestijnenlaan 200F, PO Box 2404, 3001 Leuven, Belgium.
authors.forename: Karel
authors.initials: K
authors.lastname: Goossens
authors.forename: Kathleen
authors.initials: K
authors.lastname: Lava
authors.forename: Peter
authors.initials: P
authors.lastname: Nockemann
authors.forename: Kristof
authors.initials: K
authors.lastname: Van Hecke
authors.forename: Luc
authors.initials: L
authors.lastname: Van Meervelt
authors.forename: Kris
authors.initials: K
authors.lastname: Driesen
authors.forename: Christiane
authors.initials: C
authors.lastname: Görller-Walrand
authors.forename: Koen
authors.initials: K
authors.lastname: Binnemans
authors.forename: Thomas
authors.initials: T
authors.lastname: Cardinaels