Solvatochromic Dyes as Solvent Polarity Indicators
نویسنده
چکیده
This review compiles positively and negatively solvatochromic compounds which have been used to establish empirical scales of solvent polarity by means of UV/vis/near-IR spectroscopic measurements in solution-with particular emphasis on the E ~ ( 3 0 ) scale derived from negatively solvatochromic pyridinium N-phenolate betaine dyes. This requires a short discussion of the concept of solvent polarity and how empirical parameters of solvent polarity can be derived and understood in the framework of linear free-energy relationships. The preconditions for the occurrence of solvatochromism, and further requirements of solvatochromic compounds for them to be useful as solvent polarity indicators will be discussed. In addition to spectroscopically based single parameters of solvent polarity, multiparameter treatments of solvent effects by means of solvatochromic parameters will also be mentioned. The mutual interrelation between some of the more important W/vis/near-IR spectroscopically derived solvent scales, and their correlations with solvatochromic multiparameter equations will be exemplarily given.
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