A study on the conformation-dependent colorimetric response of polydiacetylene supramolecules to external triggers

Polydiacetylene (PDA) supramolecules exhibit a conformation-dependent colorimetric response to external triggers. They transition from the blue phase, the planar backbone conformation, to the red phase, which exhibits a twisted nonplanar conformation. Therefore, PDAs act as sensors for the changes in their chain conformations caused by external triggers. Here we demonstrate how the colorimetric response of PDA vesicles to triggers is affected by having an initial purple phase, an intermediate phase with a twisted ribbon-like conformation, instead of blue. We obtained purple PDA vesicles at room temperature in aqueous conditions. Once exposed to external triggers, these vesicles gave a colorimetric response at lower exposure levels than blue-phase PDA vesicles. Their already nonplanar conformation makes the complete conformational transition easier. We also report the supramolecular interactions that govern the conformation transition in the PDA vesicle system by using various PDA vesicles and external triggers. Within the scope investigated, we show that inter- and intra-chain interactions play a crucial part in causing chain distortions and structural rearrangements of the PDA backbone, in addition to the repulsive-ionic head group interactions. These results broaden the understanding of supramolecular interactions that make PDAs such interesting systems for research and also highlight the possibility of utilizing PDAs prepared at intermediate phases for customized sensing applications.