Analysis of photofading of phenylazo-indole and phenylazo-N-ethanolaniline disperse dyes on poly(ethylene terephthalate) fabric using the PM5 method

The photofading behaviors of phenylazo-N-(ethanol)aniline and phenylazo-indole, nitrohetarylazo-N-substituted aniline disperse dyes on poly(ethylene terephthalate) (PET) substrate were analyzed using the Kubelka-Munk (K/S) parameters of the dyed fabrics exposed to a carbon arc in air. The initial experimental slopes (KPET) of fading on PET were estimated from the time profiles of the K/S values at the λmax. The rates (k0,i) of reaction of these dyes with 1O2 were estimated by frontier orbital theory using the PM5 method. The photosensitivities (fi) of the dyes were estimated from the KPET assuming that the KPET values are proportional to the product of k0,i and fi. Dyes with small fi values, irrespective of their k0,i values, possess excellent lightfastness (LF), while dyes with larger fi values possess poorer LF. The validity of estimating k0,i values by the MO method was confirmed experimentally by analyzing the mutually photosensitized fading behaviors of combination dyeings.