Molecular association of pentanols in n-heptane VI: Betaine dye probe

The penta t-butyl-substituted betaine dye 4-[2,4,6-tri(4-t-butylphenyl)pyridinium-1-yl]-2,6-di(4-t-butylphenyl)phenolate has been used to probe the polarities of binary mixtures of three pentanols in n-heptane. The longest-wavelength intramolecular CT absorption band of the betaine dye in the visible region exhibits a strong negative solvatochromism, even in a minute change in the concentration of pentanols. The polarity parameters of the substituted dye in the binary mixtures are calculated from the measured λmax values, they are then converted to the well-known ET(30) values of the non-substituted standard betaine dye. The plots of the normalized polarity scale, ETN against mole fractions x of pentanols show nonlinearity in the low concentration range of pentanol for which x < 0.105; however, in the high concentration range (x > 0.105), the plots are linear.