A series of twenty four 1‐alkyl(aralkyl)‐3‐methylimidazolium hexafluorophosphates and bis(trifluoromethyl‐sulfonyl)imides are prepared and the influence of structural variations in the imidazolium cation and the identity of the anion on physical properties (phase transition, density, viscosity, and surface tension) of the ionic liquids is determined.

An improved method for the preparation of 1-alkyl-3-methylimidazolium hexafluorophosphates provides a series of room-temperature ionic liquids (RTILs) in which the 1-alkyl group is varied systematically from butyl to nonyl. For competitive solvent extraction of aqueous solutions of alkali metal chlorides with solutions of dicyclohexano-18-crown-6 (DC18C6) in these RTILs, the extraction efficiency generally diminished as the length of the 1-alkyl group was increased. Under the same conditions, extraction of alkali metal chlorides into solutions of DC18C6 in chloroform, nitrobenzene, and 1-octanol was undetectable. The extraction selectivity order for DC18C6 in the RTILs was K+ > Rb+ > Cs+ > Na+ > Li+. As the alkyl group in the RTIL was elongated, the K+/ Rb+ and K+/Cs+ selectivities exhibited general increases with the larger enhancement for the latter. For DC18C6 in 1-octyl-3-methylimidazolium hexafluorophosphate, the alkali metal cation extraction selectivity and efficiency were unaffected by variation of the aqueous-phase anion from chloride to nitrate to sulfate.

Using optically heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES) with 40 fs laser pulses, the transient birefringence in the room-temperature ionic liquids (RTILs), 1-alkyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)imides, [C n mim]NTf2 with n = 2, 4, 5, 6, 8, 10 (C2, C4, C5, C6, C8, C10), has been studied at room temperature and ambient pressure. Near zero delay, the OHD-RIKES response is dominated by the instantaneous electronic response. The nuclear response appears as a shoulder on the electronic response. Between 0 and 1 ps, the nuclear response is dominated by the intermolecular vibrational (nondiffusive) response. For C4, C5, C6, and C8, the 1/e time of the pseudo-exponential tail of the intermolecular response decreases with viscosity, in accord with the hydrodynamic model for vibrational dephasing. Superimposed on the OHD-RIKES response for C4, C5, and C6 is a coherent oscillation with a frequency of ∼140 cm-1. The intermolecular vibrational spectra for these RTILs obtained from the reduced OHD-RIKES data by using a Fourier transform procedure extend from 0 to 200 cm-1 and are bimodal with a low-frequency component at ∼22 cm-1 and a high-frequency component at ∼84 cm-1. The relative contribution of the high-frequency component to the total band increases in going from C2 to C5 and remains constant for C5, C6, and C8. The behavior of the reduced spectral densities is consistent with increasing order in the liquid. It is proposed that the 140 cm-1 oscillation arises from collective motions of locally ordered domains in the liquid.

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L-cysteine derivatives induce and modulate the optical activity of achiral cadmium selenide (CdSe) and cadmium sulfide (CdS) quantum dots (QDs). Remarkably, N-acetyl-L-cysteine-CdSe and L-homocysteine-CdSe as well as N-acetyl-L-cysteine-CdS and L-cysteine-CdS showed "mirror-image" circular dichroism (CD) spectra regardless of the diameter of the QDs. This is an example of the inversion of the CD signal of QDs by alteration of the ligand's structure, rather than inversion of the ligand's absolute configuration. Non-empirical quantum chemical simulations of the CD spectra were able to reproduce the experimentally observed sign patterns and demonstrate that the inversion of chirality originated from different binding arrangements of N-acetyl-L-cysteine and L-homocysteine-CdSe to the QD surface. These efforts may allow the prediction of the ligand-induced chiroptical activity of QDs by calculating the specific binding modes of the chiral capping ligands. Combined with the large pool of available chiral ligands, our work opens a robust approach to the rational design of chiral semiconducting nanomaterials.