Azo Dye Molecules Research Articles

Influence of fluorine-containing substituents on the energy of intermolecular interactions and the heat of evaporation of disperse azo dyes

The heats of evaporation of some fluorine-containing disperse azo dyes have been determined by electronic absorption spectroscopy. The introduction of fluorine or fluorine-containing substituents into azo dye molecules decreases the energy of intermolecular interactions and correspondingly the heat of evaporation of dyes by 10–40 kJ mol −1 as compared with dyes without fluorine. Such dyes may therefore be recommended for gas-phase methods of dyeing and printing. The energy of orientation-induction interactions is the main contribution to the heat of evaporation.

The Use of Azo Dyes in Guest-Host Displays

Abstract Azo dye molecules are cylindrically shaped, and therefore, due to their resemblance to liquid crystal molecules, would seem to be suitable for use in guest-host mixtures. The dichroic ratio of a dye in a given nematic host depends on the molecular length of the dye molecules, the order parameter of the liquid crystal host and its molecular dimensions. It is possible to obtain a guest-host mixture with an order parameter which is higher than that of the pure host. Lateral substitution of mono-azo dyes lowers the order parameter, whilst lateral substitution of the corresponding bis-and tris-azo molecules results in only a slight change in their order parameter. The stability of these compounds to light is poor, and depends on the wavelength for maximum absorption, and on the host material. Whilst lateral substitution increases the fastness of azo compounds when used for textile dying, this is not the case when they are employed with liquid crystal mixtures. The kinetics of degradation are zero orde...