Nonlinear optical signature of nanostructural transition in ionic liquids

The homologous series of the ionic liquids 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [CnC1im][NTf2] (n = 2,4,6,8 and 10) was studied by polarization-resolved second harmonic scattering (SHS). analysis polarization plots clearly demonstrates that SHS response is dominated an octupolar contribution. Orientational correlations are observed on nanometer scale in all investigated liquids, even for shortest alkyl chain length. A radial distribution nonlinear optical sources evidenced. sharp transition from short to longer range occurs between with n 4 6, signature dominating role taken chains. technique therefore provides structural observation at scales well-below diffraction limit these findings open new interesting perspectives domain.