Metachromatic behaviour of dyes in solvents of low dielectric constant

Abstract

The metachromasy induced in a series of equimolar dye solutions in n-butanol+cyclohexane by increasing the proportion of cyclohexane is most marked over the range of solvent compositions where the long-range electrical forces in solution are most evident. The metachromasy induced by increasing the dye concentration in given solvent mixtures is greater the lower the dielectric constant of the mixture. Similar metachromasy has been induced in chloroform (containing 1% ethanol to prevent the formation of phosgene) and anisole. But it is less marked though still comparable in extent to that in the mixed solvents of similar dielectric constant. This evidence supports the view that the metachromatic behaviour of dyes should be attributed primarily to interaction between dye ions and counter-ions.