Acid-responsive polydiacetylene-Na plus assemblies with unique red-to-blue color transition

Polydiacetylenes (PDAs), conjugated and stimuli-responsive polymers, are of interest for colorimetric sensing technologies. Commercially available PDAs with carboxylic headgroup do not show any colorimetric response to acid. To achieve acid-responsive property, the headgroups of PDAs are often modified with some functional moieties, involving complicated synthetic processes. This contribution presents a facile approach to develop acid-responsive materials via coassembly of PDA and excess sodium hydroxide (NaOH). After low-temperature incubation and photopolymerization, the mixtures of 10,12-tricosadiynoic acid (TCDA) and NaOH develop into red -phase poly (TCDA-Na + ) assemblies. A unique red-to-blue color transition occurs when the poly (TCDA-Na + ) assemblies are exposed to hydrogen chloride (HCl) acid both in aqueous solution and gas phase. Increasing the concentrations of NaOH and TCDA monomer during the selfassembly process affects the molecular organization and morphologies of the resultant poly (TCDA-Na + ) assemblies, which in turn govern the sensitivity to acid. The results of this study offer a simple and inexpensive method for developing acid-responsive PDAs, extending their colorimetric sensing applications.