The effects of cyclic terminal groups in di- and tri-arylmethane dyes. Part 3. Consequences of unsymmetrical substitution in Malachite Green

Abstract

A comprehensive series of novel, unsymmetrical Malachite Green dyes containing different amino substituents has been prepared and the electronic absorption spectra have been determined. In general, the structurally unsymmetrical dyes display electronic symmetry. Hypsochromic shifts and reduced intensity of the λ_max(x) absorption bands were generally observed for the dyes containing the N-methylpiperazino group, consistent with the reduced ability of the heterocyclic moiety to stabilise the cationic system by conjugation. In solvents of increasing acidity, the dyes exhibit variable spectral responses because of the differing basicities of the terminal amino groups.