Effect of the Alkyl Chain Length on the Rotational Dynamics of Nonpolar and Dipolar Solutes in a Series of N-Alkyl-N-Methylmorpholinium Ionic Liquids

Abstract

Rotational dynamics of two dipolar solutes, 4-aminophthalimide (AP) and 6-propionyl-2-dimethylaminonaphthalene (PRODAN), and a nonpolar solute, anthracene, have been studied in N-alkyl-N-methylmorpholinium (alkyl = ethyl, butyl, hexyl, and octyl) bis(trifluoromethansulfonyl)imide (Tf2N) ionic liquids as a function of temperature and excitation wavelength to probe the microheterogeneous nature of these ionic liquids, which are recently reported to be more structured than the imidazolium ionic liquids (Khara and Samanta, J. Phys. Chem. B2012, 116, 13430-13438). Analysis of the measured rotational time constants of the solutes in terms of the Stokes-Einstein-Debye (SED) hydrodynamic theory reveals that with increase in the alkyl chain length attached to the cationic component of the ionic liquids, AP shows stick to superstick behavior, PRODAN rotation lies between stick and slip boundary conditions, whereas anthracene exhibits slip to sub slip behavior. The contrasting rotational dynamics of these probe molecules is a reflection of their location in distinct environments of the ionic liquids thus demonstrating the heterogeneity of these ionic liquids. The microheterogeneity of these media, in particular, those with the long alkyl chain, is further evidence from the excitation wavelength dependence study of the rotational diffusion of the dipolar probe molecules.

Interaction and dynamics of (alkylamide + electrolyte) deep eutectics: Dependence on alkyl chain-length, temperature, and anion identity

“…Similar effects of alkyl chain have also been observed in studies with RTILs. 40,82 The anion dependence of ν em obtained by using DMASBT (τ life ∼ 0.5 ns) and C153 (τ life ∼ 4 ns) is shown in Table I where representative results for (CH 3 CONH 2 + LiX) DEs at 303 K are presented along with the radii 35,83 of the ions considered. Note the extent of anion dependence of ν em is larger for low lifetime probe.…”

Effect of ionic liquids on the conformation of a porphyrin-based viscometer

“…12,13 Possibilities for using neat ILs to control intermolecular interactions have been suggested primarily for cyanine dye self-assemblies. 14 Studies on viscosity of ILs using fluorescent dyes has been a subject of interest, [15][16][17] and the use of fluorescent probes for understanding the structure of ILs, in general, has been recently reviewed. 18 In addition, it was shown that the viscosity of molecular organic media could control the conformation of a conjugated porphyrin dimer (PD), resulting in an array of conformations with two distinct extremes: a planar and a twisted conformation (Fig.…”

Microheterogeneity in imidazolium and piperidinium cation‐based ionic liquids: 1D and 2D NMR studies

“…Many specific features have been observed due to heterogeneous nature of RTILs including the significant difference between their bulk viscosity and micro viscosity, the spatial solvation, and rotational dynamics and other interesting photo physical process of the solute in RTILs . Samanta et al have also shown how the existence of the domain structure of ILs through fluorescence correlation spectroscopy . Role of cation symmetry and tuning the microheterogeneity through size effect of the constituent ions is currently a fascinating area of experimental and computational investigation in IL field …”