Fluorescence studies of solvation and solvation dynamics in ionic solutions

Journal Article · Thu Nov 14 04:00:00 EST 1991 · Journal of Physical Chemistry; (United States)

DOI:https://doi.org/10.1021/j100176a016· OSTI ID:7017641

Chapman, C F; Maroncelli, M ^[1]

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1. Pennsylvania State Univ., University Park (United States)

The authors have employed steady-state and time-resolved emission spectroscopy to study static and dynamic aspects of the solvation of polar aromatic solutes in ionic solution. Several common solvatochromic probe molecules (Cu102, Cu153, Prodan, 4-AP) were examined in a wide range of ionic solutions consisting of a variety of salts (mainly Li{sup +}, Na{sup +}, Mg{sup 2+}, Ca{sup 2+}, Sr{sup 2+}, Ba{sup 2+} perchlorates) in a number of nonaqueous solvents (tetrahydrofuran, acetone, propylene carbonate, acetonitrile, dimethylformamide, dimethyl sulfoxide, methanol, 1-propanol, and formamide). The presence of ions causes shifts in the spectra of these probe solutes similar to those observed in pure solvents of varying polarity. As a function of increasing salt concentration or time, the primary spectral change is a frequency shift with little accompanying change in the spectral shape or width. The ionic solvation dynamics measured by time-resolved fluorescence take place on a 1-10ns time scale. The kinetics are significantly dependent on excitation wavelength, especially for excitation on the red edge of the absorption spectrum. The rate of spectral shift is proportional to salt concentrations and inversely proportional to viscosity for concentrations of 1 M or less. When these two factors are accounted for, the observed solvation rates are found to decrease with solvent polarity and decrease with the charge-to-size ration of the cation. A number of the above results are inconsistent with the commonly used description of solute-ion interactions in terms of a diffuse ion atmosphere. To rationalize the observations the authors propose a model based on equilibrium among a limited set of solvates distinguished by the number of cations in the first solvation shell of the probe.

• OSTI ID: 7017641
• Journal Information: Journal of Physical Chemistry; (United States), Journal Name: Journal of Physical Chemistry; (United States) Vol. 95:23; ISSN 0022-3654; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ALKALI METAL COMPOUNDS
ALKALINE EARTH METAL COMPOUNDS
AROMATICS
BARIUM COMPOUNDS
CALCIUM COMPOUNDS
CHARGED PARTICLES
CHLORINE COMPOUNDS
DATA
DISPERSIONS
EMISSION SPECTROSCOPY
EXPERIMENTAL DATA
FLUORESCENCE SPECTROSCOPY
HALOGEN COMPOUNDS
INFORMATION
IONS
LITHIUM COMPOUNDS
MAGNESIUM COMPOUNDS
MIXTURES
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC SOLVENTS
OXYGEN COMPOUNDS
PERCHLORATES
RESOLUTION
SODIUM COMPOUNDS
SOLUTIONS
SOLVATION
SOLVENTS
SPECTROSCOPY
STEADY-STATE CONDITIONS
STRONTIUM COMPOUNDS
TIME RESOLUTION
TIMING PROPERTIES
VISCOSITY