Changing absorption intensity ratios for methylene violet Bernthsen in normal alcohols and at different temperatures

Abstract

Absorption spectra of methylene violet Bernthsen (MVB) are reported, obtained in normal alcohols, methanol through 1-octanol, and at different temperatures, 15 °C to 75 °C. Two distinct absorption intensities are apparent. The 565 nm intensity increases relative to the 598 nm intensity as alcohol chain length increases. For each solvent, increasing temperature causes similar intensity ratio effects. Computational spectra of MVB in methanol indicates a decrease in hydrogen-bonding as temperature increases with a corresponding loss of intensity in the low energy peak consistent with the experimental observations. Hydrogen-bonding is indicated as playing a role in the alcoholic solvent effects.