Unravelling the mysteries behind orcein dye: from orcinol-based synthesis to molecular degradation

This study aims to identify the various reasons behind the wide range of colours of orchil dye. The first step was to study the impact of synthesis parameters on colour and chemical composition variation, while the second step aimed to study chemical degradation with the artificial ageing protocol. Variation in reactant concentration, ammonia level and O 2 availability led to red-orange or purple-coloured solutions. HPLC-DAD-MS, UV-Vis absorption and reflectance analysis enabled both molecular identification and objective colour characterisation of each solution. Thanks to PLS regression, the contribution of the relative content of each molecule to observed colour of the dye could be determined. Finally, accelerated light-ageing experiments assessed the stability of the synthesised dyes. Molecules responsible for the purple hue (β- and γ-orceins) were found to be significantly more sensitive to photodegradation than those associated with red-orange shades (α-orceins).