Ultra-low-temperature reversible thermochromism and contactless bacterial sensing by chalcone-functionalized polydiacetylene

Polydiacetylenes are a class of conjugated polymers exhibiting unique color and fluorescence transformations. Here, we report the synthesis and remarkable chromatic properties of polymerized diacetylene displaying a chalcone headgroup. Specifically, the exposure of drop-casted chalcone-diacetylene films to HCl allowed diacetylene polymerization through modulating the ion-pair interactions and hydrogen bonding between adjacent chalcone residues. The HCl-treated chalcone-polydiacetylene films displayed reversible thermochromism even at very low temperatures (down to −50 °C). In addition, the polymerized films exhibit specific color and fluorescence transformations selectively induced by ammonia vapor, ascribed to scavenging of the HCl residues and resultant “blending” of the distinctive colors/fluorescence of both chalcone moieties and the polydiacetylene network. The ammonia sensing capabilities of the HCl-treated chalcone-polydiacetylene films were employed for high-sensitivity visible detection of bacterial growth and food spoilage, in varied temperatures and under various humidity conditions. Notably, the simple synthesis, sensitive chromatic response of the chalcone-polydiacetylene-HCl films and the demonstrated feasibility of visual early detection of food spoilage in a broad temperature range furnish significant practical advantages compared to existing food monitoring technologies.