Photo-oxidation of phenylazonaphthol dyes and their reactivity analysis in the gas phase and adsorbed on cellulose fibers states using DFT and TD-DFT

摘要

Reactivity of gaseous 1-arylazo-2-naphthol dyes and their complexes with cellulose, after adsorption on cellulose, towards singlet molecular oxygen, ~1O2 are investigated based on frontier molecular orbital theory. Results reveal that electrophilic reactions may occur predominately for the studied species, with the oxidizing agent ~1O2 as electrophile. The -SO3 functionalized l-arylazo-2-naphtol tautomers (soft nucleophiles) and their complexes with the cellulose are shown to be less reactive towards ~1O2 and under thermodynamic control; while the -SO3H functionalized l-arylazo-2-naphtol tautomers (hard nucleuphiles) and their cellulose complexes are fairly reactive and under kinetic control. According to the frontier molecular orbital theory, the sites more vulnerable for ~1O2 attack (the atomic positions and double bounds) are similar for both azo dyes and their complexes with cellulose. Thermodynamic study reveals that the photo-oxidation reactions are exothermic and spontaneous, except for cycloaddition of hydrazone tautomers. TD-DFT calculations confirm the decolorization and color fading phenomenon during the photo-decomposition reaction.