Fluorescent Nano pH Indicators Based on Supramolecular Interactions

Highly hydrophilic switchable dyes are widely applied [1] as optical pH indicators. On the other hand, the basic chromophoric structure of such indicators commonly consists of extended olefinic or aromatic structures, where lipophilic properties are dominating [2], and special measures are necessary for solubilisation in water, such as the introduction of a charge and the attachment of hydrophilic substituents to the periphery. However, the lipophilicity of the core still remains and may cause problems such as aggregation in solutions with high ionic strengths. Further problems arise for permanently coloured solutions where the change in the colour of the indicator is difficult to see. It would be of interest to apply lipophilic indicators directly to the aqueous phase.