Imidazole-based probe for the “light-up” detection of hypochlorite ion based on protonation-deprotonation strategy: Applications in real samples

Hypochlorite is one of the most potent among the reactive oxygen species owing to its importance in living organisms besides as a bleaching agent in industry, as well as potable water disinfectant. The harmful effects of its under and over expressions to the living systems has necessitated the development of reliable and sensitive sensing probes for real sample monitoring to keep check on its level in industrial/environmental/biological samples. Though a number of reaction based fluorescent probes have been reported, there is a shortage of reversible probes. To fill this void, the present study aims to develop reversible sensing probe. A simple Imidazole based donor-π-acceptor molecular probe has been synthesised. It discloses its pH sensitivity by forming cationic and anionic species at low and high pH values respectively, which consequently affects the magnitude of intramolecular charge transfer (ICT) process. The probe not only exhibits pH sensitivity, but also selectively detects hypochlorite ions employing deprotonation-protonation strategy. The probe which otherwise is weakly emissive in mixed solvent system “lights-up” on interaction with hypochlorite ions which is attributed to the more ordered assembling of the anionic state of the probe as compared to the free probe for which X-ray structure has revealed disordered assembling in solution. Interestingly, the sensing of hypochlorite is reversible with a little precedence in literature over a large number of reports on irreversible reaction based sensing of hypochlorite. The reversible sensing probes contribute significantly to the cost-effective molecular recognition processes. The real-sample application of the probe and the construction of ready to use paper strips for the on-site detection without using expensive equipment has also been explored.