Colour and Constitution of Anthraquinonoid Dyes. Part 1‐Modified PPP Calculations and Substituent Effects

Abstract

Calculation of the –electronic excitation energies of anthraquinonoid dyes has been carried out by means of the Pariser–Parr–Pople (PPP) method with the variable β, γ approximation. A good linear correlation between the observed and calculated values for the first – * excitation was found for a series of amino– and hydroxy–anthraquinone dyes. The effect of substituents on the colour of different dyes was studied on the basis of these calculated results. The intramolecular charge–transfer character of the first – * transition was supported. The parameters used in this calculation can be adapted to estimate the colour of any anthraquinonoid dye.