Syntheses and UV/Vis-Spectroscopic Properties of Hydrophilic 2-, 3-, and 4-Pyridyl-Substituted Solvatochromic and Halochromic PyridiniumN-Phenolate Betaine Dyes as New Empirical Solvent Polarity Indicators
Syntheses and negative solvatochromism of nine new hydrophilic 2-, 3-, and 4-pyridyl-substituted pyridinium N-phenolate betainedyes 3−11 are described. These were produced in order to obtain zwitterionic dyes better soluble in water and other aqueous media (such as binary water/solvent mixtures, aqueous ionophore solutions) than the rather hydrophobic standard betainedyes 1 and 2, which have been