Pyrrolidinium Ionic Liquid Crystals

• Published in: Chemistry : a European journal 2009-01, Vol.15 (3), p.656-674
• Main Authors: Goossens, Karel, Lava, Kathleen, Nockemann, Peter, Van Hecke, Kristof, Van Meervelt, Luc, Driesen, Kris, Görller‐Walrand, Christiane, Binnemans, Koen, Cardinaels, Thomas
• Format: Article
• Language: English
• Subjects: ionic liquids; liquid crystals; metallomesogens; pyrrolidinium cations; uranium
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200801566

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 CnH2n+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. Het N‐alkyl‐N‐methylpyrrolidiniumkation werd gebruikt voor de bereiding van ionische vloeibare kristallen, waaronder een nieuw type uraniumhoudend metallomesogeen. Er werden pyrrolidiniumzouten met bromide‐, bis(trifluoromethylsulfonyl)imide‐, tetrafluoroboraat‐, hexafluorofosfaat‐, thiocyanaat‐, tetrakis(2‐thenoyl‐trifluoroacetonato)europaat(III)‐ en tetrabromouranyl‐anionen gesynthetiseerd. In het geval van de bromidezouten en de tetrabromouranylverbindingen werd de ketenlengte gevarieerd van acht tot twintig koolstofatomen (n=8, 10, 11, 12 ,13, 14, 15, 16, 17, 18, 19, 20). De verbindingen vertonen een rijk mesofasegedrag, van hooggeordende smectische fasen (de kristal‐smectische E fase en de zeldzame kristal‐smectische T fase) over smectische A fasen tot hexagonaal kolomvormige fasen, afhankelijk van de ketenlengte en het anion. Dit werk geeft een beter inzicht in de aard en vorming van de kristal‐smectische T fase, en de moleculaire vereisten voor het