A Luminescent Probe Study of Water/Acetonitrile Mixtures

Abstract

Luminescence spectra for 1.0 × ^10-2 mol dm^-3 solutions of salicylic acid in water, acetonitrile and water/acetonitrile mixtures have been determined. In the wavelength range 300-600 nm, all spectra showed a single broad emission band. The variations of the wavelength of maximum luminescence intensity (λ_max) and luminescence band half-width (Δ_½) with solvent composition are similar to the composition dependence of these parameters observed previously for solutions of salicylic acid in water/alcohol mixtures.

The invariance of Δ_½ with acetonitrile content up to approximately 15 mole% supports earlier conclusions that up to c. 15 mole% acetonitrile is accommodated within cavities in the water structure. The rapid increase in near 15 mole% acetonitrile provides further evidence for a progressive destruction of the water structure as the acetonitrile content is increased beyond c. 15 mole%.