Prediction of the photofading of 1‐H or 1‐ethyl derivatives of 3‐cyano‐6‐hydroxy‐4‐methyl‐5‐(p‐X‐phenylazo)‐2‐pyridone dyes and their azo‐hydrazone tautomerism: A theoretical study

The lightfastness calculations for photofading of monoazo pyridone dyes were performed. For this purpose, all‐valence molecular orbital method PM3 was applied. Frontier electron density distribution on the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) was examined. The obtained parameters seem to reflect the tendency for an electrophilic attack with a singlet oxygen (1O2) atom or a nucleophilic attack with superoxide anion (O2●─) on a particular atom in a molecule. Reactivity indicators for superdelocalisability (SrEN) and electron density distribution in ground and excited state were calculated. Superdelocalisabilities enable the fastness values to be explained in different chemical molecules depending on tautomeric forms in which they may occur. [ABSTRACT FROM AUTHOR]