Pressure-induced crystallization of 1-butyl-3-methylimidazolium hexafluorophosphate

We have investigated the pressure-induced crystallization of 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) associated with the conformational changes of [bmim](+) by Raman spectroscopy. [bmim](+) has trans-trans and gauche-trans (GT) conformers of the butyl side chain at ambient pressure. Our result revealed that liquid to solid-phase transition occurs at 0.20.4GPa region, where the GT conformer becomes dominant. We found that the GT dominant state continues up to 4GPa.