NILE RED AS A SOLVATOCHROMIC DYE FOR MEASURING SOLVENT STRENGTH IN NORMAL LIQUIDS AND MIXTURES OF NORMAL LIQUIDS WITH SUPERCRITICAL AND NEAR CRITICAL FLUIDS

Nlle Red was used as a solvatochromic probe to measure the solvent strength of 85 pure liquids and the results were compared to solvent strength scales from the better known Rei-chardt's Et(26) and Et(30)dyes. Nile Red Is also soluble in some pure supercritical fluids and in polar mixtures of supercritical fluids and modifiers. The solvent strength of mixtures of organic modifiers In CO2, Freon-13, and Freon-23 was measured as a function of modifier concentration with Nlle Red and other solvatochromic dyes. Nlle Red exhibits large shifts in the wavelength of Its absorption maximum allowing subtle changes In solvent strength with fluid composition to be quantified, and It Is stable In very strong acids. Relative scales of solvent strength comparing different modifiers added to C02 are presented and compared to a wide range of normal liquids. © 1990, American Chemical Society. All rights reserved.