Effect of charge on the rotation of prolate nitroxide spin probes in room-temperature ionic liquids

O'Brien, Meghan H.; Ranganathan, Radha; Merunka, Dalibor; Stafford, Alexander K.; Bleecker, Steven D.; Perić, Miroslav (2024) Effect of charge on the rotation of prolate nitroxide spin probes in room-temperature ionic liquids. Journal of Molecular Liquids, 404 . ISSN 01677322

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Abstract

We have studied the rotational diffusion of two prolate nitroxide probes, the doubly negatively charged peroxylamine disulfonate (Frémy's salt - FS) and neutral di-tert-butyl nitroxide (DTBN), in a series of 1-alkyl-3-methylimidazolium tetrafluoroborate room-temperature ionic liquids (RTILs) having alkyl chain lengths from two to eight carbons using electron paramagnetic resonance (EPR) spectroscopy. Though the size and shape of the probes are reasonably similar, they behave differently due to the charge difference. The rotation of FS is anisotropic, and the rotational anisotropy increases with the alkyl chain length of the cation, while the rotation of DTBN is isotropic. The hyperfine coupling constant of DTBN decreases as a function of the alkyl chain length and is proportional to the relative permittivity of ionic liquids. On the other hand, the hyperfine coupling constant of FS increases with increasing chain length. These behaviors indicate the location of each probe in RTILs. FS is likely located in the polar region near the network of charged imidazolium ions. DTBN molecules are predominately distributed in the nonpolar domains.

Item Type:

Article

Uncontrolled Keywords:

electron paramagnetic resonance; rotational diffusion; nitroxide radicals; rotational anisotropy; hyperfine coupling constant; room-temperature ionic liquids

Subjects:

NATURAL SCIENCES > Physics > Condensed Matter Physics
NATURAL SCIENCES > Chemistry > Physical Chemistry

Divisions:

Division of Physical Chemistry

Projects: