Orientation of 1-dodecyl-4-phenylpyridinium ions constituting an ionic liquid at the ionic liquid | water interface studied by second harmonic generation

Naoya Nishi, Ryoichi Ishimatsu, Masahiro Yamamoto, Takashi Kakiuchi

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A hydrophobic room-temperature ionic liquid (RTIL) of 1-dodecyl-4- phenylpyridinium (C 12 ppy + ) ions, the cations with high first hyperpolarizability, was prepared in combination with bis(pentafluoroethylsulfonyl)imide, and the orientation of C 12 ppy + at the RTIL|water and RTIL|air interfaces was analyzed using optical second harmonic generation (SHG). From polarization-dependence measurements and absolute phase measurements, it was found that C 12 ppy + ions at the RTIL|air interface are orientated with the main axis of 4-phenylpyridinium moiety (from phenyl to pyridinium direction) tilted at 53° from the surface normal (from RTIL to air direction) and that the dodecyl chain is protruding to the air. At the RTIL|water interface, it was suggested that C 12 ppy + is orientated at the tilt angle of 131° from the surface normal (from RTIL to water direction) with the dodecyl chain protruding away from the aqueous phase.

Original languageEnglish
Pages (from-to)12461-12466
Number of pages6
JournalJournal of Physical Chemistry C
Issue number33
Publication statusPublished - Aug 23 2007
Externally publishedYes


All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Energy(all)
  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films

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