Solvatochromic studies on reversed-phase liquid chromatographic phases .1. Synthesis and solvent effects of a new merocyanine dye, 4,6-dichloro-2-[2-(1-methyl-4-pyridinio)vinyl]-phenolate

A new merocyanine dye with a stilbazolium betaine structure has been synthesized and characterized by its UV-visible absorption. This compound, 4,6-dichloro-2-[2-(1-methyl-4-pyridinio)vinyl]phenolate (DCMPVP), has an absorption wavelength shift of 166 nm across 13 polar solvents, with peak positions ranging from 454.8 nm in water to 620.9 nm in ethyl acetate, Correlation of the absorption energy of DCMPVP by least-squares fitting with the Kamlet-Taft dipolarity/polarizability, pi*, and hydrogen-bond-donating ability, alpha, yields a regression equation of Delta E(max) (kcal/mol) = (9.0 +/- 1.1)pi* + (10.1 +/- 0.5)alpha + (41.8 +/- 0.8), The pK(a) value of 6.26 is lower than those for other non-chlorinated derivatives of stilbazolium dyes. This dye is a suitable indicator for a variety of neutral and weak acidic media, including chromatographic phases.