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

Abstract

Until 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 frEfalse(Nfalse), superdelocalisability SrEfalse(Nfalse) 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.

A review of developments in industrial hair colorant actives for oxidative dyes

“…Metallising one of the aforementioned acid dyes after application to hair to create aluminium or iron complexes led to greater wash‐off resistance than the oxidative dyeing, presumably through a combination of increased bulk and relatively low water solubility compared with direct dyes employed in temporary colorants. Computational modelling of the electronic properties of direct dyes has been brought to bear on better understanding the impact of substituents on their photostability 187 . No such work has yet been published in connection with oxidative coupling products.…”

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

“…46 Literature suggests that the photodegradation of ohydroxyazo dyes occurs in the hydrazone form, and the singlet oxygen is the oxidant. 47,48 It leads to a hyperoxide form being obtained, decomposing through homolysis or heterolysis to quinone, and to an ionic form of the diazonium residue (X-p-diazonium ion).…”