Static and Dynamic Electrolyte Effects on Excited State Intramolecular Electron Transfer and Excited State Solvation
In a solution of an electrolyte in a liquid of low permittivity after excitation of molecules which exhibit either a large Stokes shift (coumarins) or undergo an intramolecular electron transfer (DMABN) process, the fast solvent longitudinal dielectric relaxation, τ1= (ɛ∞/ɛs) τD (few picosecond in non associative liquids) is succeeded by nanosecond time scale translational relaxation of the “ionic atmosphere”.
In such solutions one may assume that single ions, ion pairs, triple ions and larger aggregates are present. At an electrolyte concentration range of 0.005M–0.5M dissolved in neat liquid with permittivities of 4.5–7 most of the salt is present as ion-pairs. The dissolved electrolyte ionic relaxation time measured by time resolved fluorescence was found to be inversely dependent on the electrolyte concentration and linearly dependent on the ion size. Thus new ways of probing medium effects on excited state behavior are opened.
KeywordsElectrolyte Concentration Steady State Fluorescence Reorganization Energy Static Dielectric Constant Ionic Atmosphere
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