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

Abstract

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 λ max values, they are then converted to the well-known E T(30) values of the non-substituted standard betaine dye. The plots of the normalized polarity scale, E T N 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.