Analysis of the solvatochromic behavior of the disubstituted triphenylmethane dye brilliant green.

The coincident spectral components of the main visible absorption band of the triphenylmethane dye Brilliant Green can be resolved using a nonlinear least-squares fitting routine. This analysis reveals two Gaussian components, with centers near 600 and 630 nm, that possess additional spectral characteristics with a pronounced sensitivity to the dye's microenvironment. In particular, both the ratio of the heights of these Gaussian peaks and the ratio of their areas exhibit an inverted dependence on solvent dielectric constant, i.e., a reversal of solvatochromic behavior in media of low polarity. Such an absorption spectrum analysis facilitates the use of triphenylmethane dyes that lack symmetric trisubstitution of the phenyl rings as environment-sensitive spectroscopic probes. We demonstrate further the utility of this approach through the spectrophotometric determination of the critical micelle concentration of the anionic surfactant sodium dodecyl sulfate using Brilliant Green as an optical probe.