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

Abstract

Two novel coumarin-based Schiff-base chemosensors are presented. Courtesy to an extended conjugation between the coumarin ring and the attached π-containing groups, both chemosensors display noteworthy photo-physical properties including emission maxima at > 550 nm. Both chemosensors function as the selective sensors for the 'turn-off' detection of copper ion with the significant nanomolar detection limits. The sensing event was investigated through proton NMR and mass spectroscopy; pH studies; life-time and quantum yield measurements and DFT studies. The solution-generated [chemosensor-Cu] species illustrated remarkably selective secondary 'turn-on' detection of the citrate ion. The sequential detection of the copper and citrate ions have been utilized for the construction of logic gates as well as several low-cost detection methods.

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

“…It is important to note that, for both species, the isotopic distribution patterns nicely matched that of the simulated patterns. The mass spectra further asserted a 1:1 metal binding stoichiometry to L1 [ 58 ]. The said binding stoichiometry was further confirmed by Job’s plot for both Al 3+ and Ga 3+ ions ( Figure S24 ) [ 59 ].…”

“…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.…”

“…Such L1 coated test strips were dipped into an aqueous solution of Al 3+ and Ga 3+ ions as well as Asp (2.5 equiv.). These paper test strips were then investigated under the UV lamp (λ ex = 365 nm) [ 58 , 59 ].…”