Steady-state and time-resolved fluorescence were used to investigate the solvation of coumarin 153 (C153) and coumarin 343 (C343) in methanol + ethaline binary solutions, a deep eutectic solvent composed of a 1:2 molar ratio choline chloride + ethylene glycol. In addition, time-resolved anisotropy decays were used to determine the solute’s rotational reorientation time as a function of viscosity. Measurements were made in solutions covering the entire range of mole fraction. Viscosity measurements were used to characterize the bulk solvent properties, and as expected, addition of methanol resulted in an decreased viscosity, showing an exponential decrease with mole fraction, up to ∼50-fold at xMeOH = 1.0. Probe rotational reorientation times were found to be biexponential at xMeOH < 0.3 for C153 and xMeOH < 0.5 for C343 and monoexponential at richer methanol content. In proportion to viscosity, C153 and C343 average rotation times decreased ∼30-fold from xMeOH = 0 to 0.9 and showed a power law dependence of ∼η0.85. Rotation times approached the stick boundary limit on dilution with methanol. Time-resolved Stokes shifts quantified the solvation dynamics and were nearly single exponential for C153 but were clearly biexponential for C343. Solvation times also tracked with viscosity according to a power law dependence, with exponents of 0.3 and 0.4 for C153 and C343, respectively. The dilution effect of methanol was not linear in proportion to the viscosity change and alone cannot account for the change in solvation. Dilution also showed a different correlation to solvation than did temperature variations to govern the viscosity change.
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21 July 2021
Research Article|
July 19 2021
Assessing rotation and solvation dynamics in ethaline deep eutectic solvent and its solutions with methanol
Special Collection:
Chemical Physics of Deep Eutectic Solvents
Mary M. LaRocca
;
Mary M. LaRocca
1
Department of Chemistry and Biochemistry, SUNY Brockport
, Brockport, New York 14420, USA
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Gary A. Baker
;
Gary A. Baker
2
Department of Chemistry, University of Missouri-Columbia
, Columbia, Missouri 65211, USA
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Mark P. Heitz
Mark P. Heitz
a)
1
Department of Chemistry and Biochemistry, SUNY Brockport
, Brockport, New York 14420, USA
a)Author to whom correspondence should be addressed: mheitz@brockport.edu. Telephone: 585-395-5586
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a)Author to whom correspondence should be addressed: mheitz@brockport.edu. Telephone: 585-395-5586
Note: This paper is part of the JCP Special Topic on Chemical Physics of Deep Eutectic Solvents.
J. Chem. Phys. 155, 034505 (2021)
Article history
Received:
May 12 2021
Accepted:
June 28 2021
Citation
Mary M. LaRocca, Gary A. Baker, Mark P. Heitz; Assessing rotation and solvation dynamics in ethaline deep eutectic solvent and its solutions with methanol. J. Chem. Phys. 21 July 2021; 155 (3): 034505. https://doi.org/10.1063/5.0056653
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