Syntheses and W-visible spectroscopic properties of two new hydrophilic 2,6-di(carbamoyl)-substituted solvatochromic pyridinium N-phenolate betaine dyes

Syntheses and negative solvatochromism of two 2,6-di(carbamoyl)-substituted pyridinium. N-phenolate betaines dyes, 3 and 4, are described for the purpose of obtaining more hydrophilic zwitterionic dyes which are better soluble in water and other aqueous media (such as binary water-solvent mixtures or aqueous ionophore solutions) than the rather hydrophobic standard betaine dyes I and 2, which have been used to establish an empirical scale of solvent polarity, called the E-T(30) or E-T(N) scale. Copyright (C) 2003 John Wiley Sons, Ltd.