A photoswitchable "turn-on" fluorescent chemosensor: Quinoline-naphthalene duo for nanomolar detection of aluminum and bisulfite ions and its multifarious applications.

Abstract A quinoline-naphthalene duo-based Schiff base probe (R) was synthesized and characterized by the usual spectroscopic and single-crystal X-ray crystallographic techniques. Probe R detects Al3+ and HSO3− ions via the fluorescent turn-on approach by dual pathways i.e., i) when probe R interacts with Al3+, the restriction of C N single bond rotation, blocking of both photoinduced electron transfer (PET) and C N isomerization were observed, and ii) when the sensor R interacts with HSO3−, imine (CH = N) bond was cleaved via hydrolysis and produced the respective aldehyde and amine behaving as a chemodosimeter. The binding stoichiometric ratio of R + Al3+ (1:1) was confirmed by Job’s plot, emission titration profile, NMR, and mass spectrometric analyses. This probe R is highly selective to both Al3+ -ions and HSO3− -ions, without any interference of other potentially competing cations and anions. Limit of detection (LOD) and quantification (LOQ) of R with Al3+ and HSO3− were downed to nanomolar concentrations, which is much lower than the recommended level of drinking water/food fixed by the World Health Organization (WHO). Furthermore, probe R was utilized in the detection of Al3+ and HSO3− ions in highly contaminated real samples, bioimaging in E. coli cells, multiple-targeting molecular logic gate, and in bovine serum albumin (BSA) binding.