Methylene Spacer Mediated Detection Switch Between Copper and Zinc Ions by Two Coumarin‐Pyrene Based Chemosensors

Abstract

Pyrene linked‐coumarin based fluorescent chemosensors L1 and L2 are utilized for the selective detection of Cu2+ and Zn2+ ions, respectively. Both chemosensors differed by a methylene spacer that connects the coumarin and pyrene rings through an imine group. The inclusion of methylene spacer dramatically changed the detection profiles of two chemosensors. While L1 showed fluorescence “turn‐off” response towards the Cu2+ ion; L2 showed “turn‐on” emission enhancement with the Zn2+ ion. Both chemosensors illustrated nano‐molar detection limits and were selective even in the presence of other competing metal ions. The 1 : 1 stoichiometry between a chemosensor and Cu2+/Zn2+ ion was supported by the binding studies, Job's plot, NMR spectral titrations, mass spectra and density functional theory (DFT) studies. The detection ability of both chemosensors was utilized by fabricating the filter paper test‐strips as well as polystyrene films for quick and visual monitoring of these ions in different water samples. Chemosensor L2 was further utilized for the “turn‐on” detection of Zn2+ ion in HepG2 cells whereas solution generated L2‐Zn species functioned as a secondary chemosensor for the detection of cystine, an important amino acid.

Coumarin‐Based Reversible Fluorescent Chemosensors for the Sequential Detection of Copper and Citrate Ions

“…Therefore, the present chemosensors have the ability to selectively detect Cu 2+ ion from a contaminated pool of other metal ions without any significant interference (vide infra). Selectivity of both L1 and L2 towards the Cu(II) ion can be rationalized by the fact that both chemosensors offer hard donors, O‐ and N‐atoms, which prefer to bind a hard Cu(II) ion in addition to the formation of a stable six‐membered chelate ring between a chemosensor and a Cu(II) ion [40,57] …”

“…Selectivity of both L1 and L2 towards the Cu(II) ion can be rationalized by the fact that both chemosensors offer hard donors, O-and N-atoms, which prefer to bind a hard Cu(II) ion in addition to the formation of a stable six-membered chelate ring between a chemosensor and a Cu(II) ion. [40,57]…”

“…In fact, our research group has recently developed a coumarin‐benzothiazole‐based fluorescent probe for the multi‐channel reversible “turn‐on” detection of Mg 2+ and Zn 2+ ions with large Stokes shifts [39] . Similarly, two coumarin‐pyrene‐based chemosensors have illustrated notable detection switch between the Cu 2+ and Zn 2+ ions as a result of a methylene spacer that separated the two rings [40] . Inspired by the outstanding features of assorted coumarin‐based chemosensors (Table S1), in this work, we report two novel coumarin‐based chemosensors functionalized with Schiff‐base‐based biphenyl methyl ester ( L1 ) or methyl(phenyl)acrylate ( L2 ) offering noteworthy photo‐physical characteristics.…”

“…[39] Similarly, two coumarin-pyrene-based chemosensors have illustrated notable detection switch between the Cu 2 + and Zn 2 + ions as a result of a methylene spacer that separated the two rings. [40] Inspired by the outstanding features of assorted coumarin-based chemosensors (Table S1), in this work, we report two novel coumarin-based chemosensors functionalized with Schiff-base-based biphenyl methyl ester (L1) or methyl(phenyl)acrylate (L2) offering noteworthy photo-physical characteristics. Both chemosensors have been utilized for the selective nanomolar 'turn-off' detection of copper ion and secondary 'turn-on' detection of citrate ion.…”

Discriminative ‘Turn-on’ Detection of Al3+ and Ga3+ Ions as Well as Aspartic Acid by Two Fluorescent Chemosensors

“…The relative fluorescence quantum yields (Φ F ) of L1 , L1 at f w = 70% L1 –Al, L1 –Ga, L1 –Asp, L2 , and L2 –Ga were calculated using Equation (3) [ 57 , 58 , 59 ]: Φ F = Φ st × S u /S st × A st /A u × n 2 D u /n 2 D st where Φ F is the fluorescence quantum yield of the samples. Here in the equation, the subscripts u and st refer to the unknown and standard samples, respectively.…”