A simple and dual responsive efficient new Schiff base chemoreceptor for selective sensing of F- and Hg2+: application to bioimaging in living cells and mimicking of molecular logic gates

A novel colorimetric hydrazine-functionalized Schiff base chemoreceptor, NPMP, was synthesized following a simple one-step Schiff base condensation pathway. NPMP showed selective colorimetric change from faint yellow to yellowish orange in the presence of biologically ubiquitous fluoride (F-). It also showed a 'turn off' fluorescent response in the presence of F- that could effectively distinguish it from all anions tested except acetate. Acetate (OAc-) caused a weak response, while other anions like chloride, bromide, iodide, phosphate, hydrogen sulfate and nitrate did not have any observable effect on the NPMP receptor (E)-4-nitro-2-((2-(perfluorophenyl) hydrazono) methyl) phenol. Recognition of F- in the presence of NPMP can be explained in light of multiple H-bonding interactions, as well as acid-base interactions between host receptor and guest F-. Interestingly, NPMP also showed enormous potential as a staining agent in determining the presence of low levels of intracellular fluoride. Moreover, it was found that in NPMP/F- solutions, incorporation of Hg2+ showed observable optical changes, revealing that this compound is a smart material. Optical responses of NPMP can mimic a molecular logic gate (INHIBIT gate). This can be interpreted as a combination of an AND gate with a NOT function. It also represented a potential 'Write-Read-Erase-Read' memory function reflecting multi-writing ability.