Logic gate behavior and intracellular application of a fluorescent molecular switch for the detection of Fe3+ and cascade sensing of F− in pure aqueous media

The nature and coordination sites of a Schiff base 3,3'-(1E,1'E)-(1,3-phenylenebis(azan-1-yl-1-ylidene))bis(methan-1-yl-1-ylidene)dinaphthalen-2-ol (APHN), are tuned by its selective reduction to design a highly efficient fluorescent probe 3,3'-(pyridine-2,6-diylbis(azanediyl))bis(methylene)dinaphthalen-2-ol (RAPHN). The structures of APHN, RAPHN and RAPHN-Fe3+ complex have been satisfactorily modeled by density functional theory (DFT) and time dependent-DFT (TD-DFT) calculations. The probe RAPHN worked as Fe3+ and F- induced turn On-Off-On probe in pure aqueous medium. The fluorescence nature of probe in the presence and absence of Fe3+/ F- is regulated by the set of mechanisms viz. -CH=N isomerization and LMCT. The 2:1 (M: L) binding stoichiometry has been established from fluorescence Job’s plot and further substantiated by HR–MS studies. The limit of detection of RAPHN for Fe3+ and RAPHN-Fe3+ for F- have been found to be 2.49 × 10–7 M and 1.09 × 10–7 M, respectively. The probe RAPHN caused no cytotoxicity in gut tissue of Drosophila even at the higher concentration. The probe exhibits an excellent bioimaging application for detection of Fe3+ and F- in gut tissue of Drosophila. A combinatorial logic gate has been constructed for the proper understanding of the working principle of RAPHN.