Flash Photolysis of Vat Dyes

A brief outline is given of the methods which have been used to investigate the procesaea occurring when fading and phototendering take place. The results obtained using model systems and the technique of flash photolysis are extended in this work to the more complex problem of commercial vat dyes in solution. It is shown that closely similar species exist in these latter solutions, namely the semiquinone radical and radical‐ion, and that the reactions taking place on light absorption, as well as the behaviour of the radicals under various conditions, are similar to those obtained for simple quinones. Active tenderers are found to yield, on illumination, greater amounts of radicals with longer lifetimes than inactive dyes. These results are considered to be a justification for using the above methods to help understand the practical case of vat dyes on fibres.