Functionalization at C2, C3, and C4 of quinolines: Discovery of water-soluble betaine dyes of C3 quinolinium derivatives with solvatochromic and pH-sensitive properties

Abstract

During functionalization at C2, C3, and C4 of quinoline, we came across a one-step metal free synthesis of C3 quinolinium derivatives of mesomeric betaine dyes. Some mesomeric betaine dyes had solvatochromic properties, and were sensitive to pH and solvates in the water. Certain betaine dyes had different properties in acidic and basic environments; the reversible interconversion between yellow (neutral or basic condition) and colorless (acidic condition) forms of the dye occurs by pH change. The changes in UV absorbance intensities of the dyes in the presence of cyclodextrins indicated the inclusion complex formation between cyclodextrins and dyes. The betaine dyes were partially dissolved in water due to the presence of positive and negative charges in the molecule. These betaine dyes did not exhibit cytotoxic activity, hence may be used in biological research.