1-(Chloro-1-pyrrolidinylmethylene)pyrrolidinium tetrafluoroborate

We investigated the temperature dependence of the intermolecular vibrational dynamics of pyrrolidinium-based ionic liquids (ILs) with 10 different anion species using femtosecond Raman-induced Kerr effect spectroscopy. The features of the temperature-dependent vibrational spectra vary with the different anions. In the case of the ILs with spherical top anions, such as tetrafluoroborate and hexafluorophosphate, and trifluoromethanesulfonate, the spectral intensity in the low-frequency region below 50 cm-1 increases with rising temperature, while that in the high-frequency region above 50 cm-1 remains almost unchanged. Similar temperature-dependent features were also found in the bis(fluorosulfonyl)amide and bis(perfluoroalkylsulfonyl)amide salts. However, the difference spectra at respective temperature relative to 293 K indicate that the spectra of the bis(fluorosulfonyl)amide and bis(perfluoroalkylsulfonyl)amide salts are more temperature-sensitive in the low-frequency region below 50 cm-1 compared to those of the tetrafluoroborate, hexafluorophosphate, and trifluoromethanesulfonate salts. The spectra of 1-butyl-1-methylpyrrolidinium-based ILs with dicyanamide and tricyanomethide anions show a characteristic temperature dependence; in addition to an increase of the spectral intensity in the low-frequency region below 50 cm-1, a red shift of the spectra in the high-frequency side above 50 cm-1 was observed with increasing temperature. This implies that the librational motions of planar dicyanamide and tricyanomethide anions contribute substantially to the low-frequency spectra. We also compared the temperature-dependent low-frequency spectra of 1-butyl-1-methylpyrrolidinium- and 1-(2-methoxyethyl)-1-methylpyrrolidinium-based ILs with some anions. Although the spectral shapes are slightly different in the range of 70-150 cm-1, which can be attributed to the intramolecular vibrational modes of the cations, the temperature dependence of the spectral shapes is quite similar, indicating that the ether substitution in the cation side groups has little effects on the temperature dependence of the low-frequency spectra. The fragilities of the ILs were also estimated from the temperature-dependent viscosities and the glass-transition temperatures. The fragility parameter seems to be correlated with the temperature dependence of the first moment of the low-frequency spectral bands mainly arising from the intermolecular vibrations of the ILs.

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.

Aggregation studies of anionic surfactant sodium dodecyl sulphate (SDS) was investigated in aqueous 1-butyl-3-methylimidazolium chloride [bmim]Cl and N-butyl-N-methyl pyrrolidinium tetrafluoroborate [bmp]BF4 ionic liquid (IL) solutions respectively. Systems were studied by surface tension, conductance, UV-VIS absorption/emission spectroscopy and dynamic light scattering. Critical micelle concentration (CMC) values gradually decreased with increasing IL concentration which indicates synergistic interaction between ILs and SDS. Gibbs free energy change results demonstrated spontaneous micellization induced by ILs; however the effect of ILs were not similar to the corresponding regular salts (NaCl and NaBF4). Aggregation number (n) of micelles, determined by fluorescence quenching method, indicate that the 'n' values increase with increasing ILs concentration, induced by the oppositely charged IL cation. Size of the micelles, determined by dynamic light scattering studies, increased with increasing ILs concentration, which were due to the formation of larger aggregates; the aggregates are considered to be comprised of the anionic surfactant with a substantial proportion of ILs cation as the bound counter ions. Such studies are considered to shed further light in the fundamentals of IL induced micellization as well as in different practical applications.