Contribution of Nitro Gtoup on the Anomalous Photofading of Some Azo Disperse Dyes

The behavior of photofading, of some azodisperse dyes containing nitr, group has been examined on polyester and o n polyamide films, The contributionof nitro group on the an, 4-nitro-4-hydroxy, malous photofading, of thesedyeswas discussed, 4rNitro-2 -hydroxy-4-, 4-nitro-2, , 4-dihydroxy-and 4-nitro-4-N-biscyan, ethyl in, az, benzenes, n p, lyamide fade It is observe thst there by light easier th he corresponding P ed deri is a correlation between the basicity of a dye and its sensitivity to the anomaleus photofading. Anomolous fading of a dye proceeds easily when it is less basic, and 4-nitro-4 -N, N-diethylaminoazobenzene dp. es not show the c, . haracter. The spec3. fioc anomqlous fading of 4-nitroazobenzenes on polyamide may be explained by the assumption that the nitro group can be photoreduced to amino group prior to photooxidation of azo group to azoxy group.2-Nitroazobenzenes on polyester and on polyamide fade by light much more easily than the corresponding 4-nitro derivatives. In anaerobic coRdition, 4-nitroazobenzenes are more resitant to fading than that in normal condition, however, the fading of 2-nitro-azobenzenes does not change practically in both conditions. The anomalous fading of 2-nitroazobenzenes is position specific and may be explained by the assumption that intramolecular photo-oxidation of azo group to azoxy group Proceeds exc usively by 2-nitro group. The behavior of fading of 2, 4-dinitroazobenZeneS has also been examined and discussed.