An insight into the mechanism of the cellulose dyeing process, part 1: Modelling azo-systems in azo-linked aromatics and dyes

Abstract

Molecular modelling has been used to model the three-dimensional structure of azo-containing aryl systems and in particular, azo-dyes such as Procion Red MX-5B. These simulations look in detail at the dynamics of the azo-linkage and the effect of an ortho -phenol function. In this paper we show that the planar arrangement of the C-N=N-C potentially delocalised sp 2 -hybridised system is not encountered exactly in the systems examined; a transoid -arrangement of the azo-linkage allows dihedrals to approach close to 180°, however, a cisoid -arrangement can engender greater deformation producing dihedrals around 30° away from planarity. Hence, intra-molecular repulsions are capable of easily distorting the azo-linkages producing a range of dihedral geometries which depend strongly on other substituents around the molecular framework.