Prediction of photofading of N‐β‐hydroxyethylamino‐o‐nitrophenyl derivatives: a theoretical study

Abstract

AbstractUntil now, the lightfastness of hair dyes had not been investigated using all‐valence molecular orbital methods. The results of calculations are used to obtain the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) frontier electron density, which can reflect the propensity for electrophilic or nucleophilic attack at an atom in a molecule. Using semi‐empirical quantum chemical methods AM1 and PM3, we have calculated the reactivity rates , superdelocalisability and electron density distribution in the tested dyes. We have found that the photooxidation of hair dyes (photochemical decomposition of hair dyes) and derivatives of N‐β‐hydroxyethylamino‐o‐nitrobenzene occurs through the degradation of the N‐β‐hydroxyethylamine substituent and on C2 or C4 atom (C4–NO2) in the process of electrophilic reaction with singlet oxygen 1O2 or nucleophilic reaction on the C1 carbon atom of the aromatic ring, with the use of superoxide anion radical O2●. The structures of the dyes were optimised using MM+, DM and AM1 or PM3 until constant energy value was realised with a 0.01 kcal/mol convergence criterion.