A Water Soluble 2-Phenyl-5-(pyridin-3-yl)-1,3,4-oxadiazole Based Probe: Antimicrobial Activity and Colorimetric/Fluorescence pH Response

The growing demand of responsive tools for biological and biomedical applications pushestowards new low-cost probes easy to synthesize and versatile. Current optical probes are theranostictools simultaneously responsive to biological parameters/analyte and therapeutically operating.Among the optical methods for pH monitoring, simple small organic molecules including multifunc-tional probes for simultaneous biological activity being highly desired by scientists and technicians.Here, we present a novel pH-responsive probe with a three-ring heteroaromatic pattern and a flexiblecationic chain. The novel molecule shows real-time naked-eye colorimetric and fluorescence responsein the slightly acidic pH range besides its excellent solubility both in the organic phase and in water.In addition, the small probe shows significant antibacterial activity, particularly againstEscherichia coli.Single-crystal X-ray study and density functional theory (DFT) calculations rationalize the moleculespectroscopic response. Finally, molecular dynamics (MD) elucidate the interactions between theprobe and a model cell membrane.