Effect of the sulphonic group position on the properties of monoazo dyes

The colour properties of monoazo dyes, analogues of C.I. Direct Red 23 (CI 29160), containing a sulphonic acid group in the diazo component have been examined. Optimisation of the molecule geometric structure was carried out by the AM1 method, while the absorption maximum positions were calculated by the PPP-MO method. The calculated and found values are in good agreement. It has been found that the position of the sulphonic acid group significantly affects the molecule spatial structure and thereby the coupling effect.