Diverse colorimetric changes of polydiacetylenes with cationic surfactants and their mechanistic studies

Polydiacetylenes (PDAs), a family of conjugated polymers, are known to show stimulus-induced apparent blue-to-red transitions, which have led to the development of a variety of PDA-based chemosensors. However, in most cases, recognition sites were introduced at the terminal ends of PDAs, therefore, recognition processes on the surface of PDAs have been the primary stimulations to induce blue to red colorimetric changes. In this study, we reported that diverse colorimetric changes can be observed for PDA based sensors in which penetration of cationic surfactant into PDAs bearing benzoic acid groups can cause not only the typical blue to red change but also blue to violet, blue to yellow or blue to orange color change. We systematically demonstrated that these novel findings can be used effectively to discriminate different cationic surfactants by using three different PDAs. Furthermore, theoretical calculations and transmission electron microscope (TEM) images also confirm these unique colorimetric changes. These results suggest a new direction in which to design colorimetric sensors based on PDA polymers.