Synthesis of solvatochromic cyanine dyes having a benzo[a]quinolizinium ring

Abstract

New stilbazolium cyanine-type dyes were synthesized by the base-catalysed aldol-type condensation of 2-methylbenzo[a]quinolizinium perchlorate with hydroxy-substituted benzaldehyde derivatives. The long wavelength absorption band of the deprotonated form of the dyes underwent a remarkable hypsochromic shift as the solvent polarity increased, and the pronounced negative solvato-chromism extended over the whole visible region.