Influence of solute charge and pyrrolidinium ionic liquid alkyl chain length on probe rotational reorientation dynamics

Jianchang Guo, Shannon M. Mahurin, Gary A. Baker, Patrick C. Hillesheim, Sheng Dai, Robert W. Shaw

Research output: Contribution to journalArticlepeer-review

20 Scopus citations

Abstract

In recent years, the effect of molecular charge on the rotational dynamics of probe solutes in room-temperature ionic liquids (RTILs) has been a subject of growing interest. For the purpose of extending our understanding of charged solute behavior within RTILs, we have studied the rotational dynamics of three illustrative xanthene fluorescent probes within a series of N-alkylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([Cnmpyr][Tf2N]) RTILs with different n-alkyl chain lengths (n = 3, 4, 6, 8, or 10) using time-resolved fluorescence anisotropy decay. The rotational dynamics of the neutral probe rhodamine B (RhB) dye lies between the stick and slip boundary conditions due to the influence of specific hydrogen bonding interactions. The rotation of the negatively charged sulforhodamine 640 (SR640) is slower than that of its positively charged counterpart rhodamine 6G (R6G). An analysis based upon Stokes-Einstein-Debye hydrodynamics indicates that SR640 adheres to stick boundary conditions due to specific interactions, whereas the faster rotation of R6G is attributed to weaker electrostatic interactions. No significant dependence of the rotational dynamics on the solvent alkyl chain length was observed for any of the three dyes, suggesting that the specific interactions between dyes and RTILs are relatively independent of this solvent parameter.

Original languageEnglish
Pages (from-to)1088-1096
Number of pages9
JournalJournal of Physical Chemistry B
Volume118
Issue number4
DOIs
StatePublished - Jan 30 2014

Funding

FundersFunder number
U.S. Department of Energy

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