Solvent and Methyl Group Effects on the Electronic Spectral Properties of Azo-2-Naphthol Dye

The influence of solvent polarity on the absorption pattern of azo-2-naphthol dyes,1-(4-methylphenylazo)-2-naphthol (MPAN) and 1-phenylazo-2-naphthol (PAN) have been studied using a UV-Visible spectrophotometer in polar and non-polar solvents. Analysis of the spectral data obtained revealed two types of effects - the polar effect (tPE) and the non-polar effect (tNPE) - exhibited when polar and non-polar solvents are used respectively. These effects can affect differently, the direction of shift in the wavelength (λmax) of electronic absorption of azo-2-naphthol dyes bathochromically or hypsochromically. Linear solvation energy relationships (LSER) have been used to quantify the interactions between solvents and dyes. The overall solute-solvent interaction had contributions from polarizability/dipolarity, hydrogen bond donor (HBD) and hydrogen bond acceptor (HBA) abilities.