Luminescent sensor for Cd²⁺, Hg²⁺ and Ag⁺ in water based on a sulphur‐containing receptor: quantitative binding–softness relationship

Abstract

A water-soluble, high-output fluorescent sensor, based on a lumazine ligand with a thiophene substituent for Cd(2+), Hg(2+) and Ag(+) metal ions, is reported. The sensor displays fluorescence enhancement upon Cd(2+) binding (log beta = 2.79 +/- 0.08) and fluorescence quenching by chelating with Ag(+) and Hg(2+) (log beta = 4.31 +/- 0.15 and 5.42 +/- 0.1, respectively). The mechanism of quenching is static and occurs by formation of a ground-state non-fluorescent complex followed by rapid intersystem crossing. The value of the Stern-Volmer quenching rate constant (k(q)) by Ag(+) ions is close to 6.71 x 10(12) mol/L/s at 298 K. The thermodynamic parameters (DeltaG, DeltaH and DeltaS) were also evaluated and indicated that the complexation process is spontaneous, exothermic and entropically favourable. The quantitative linear relationship between the softness values of Klopman (sigma(K)) or Ahrland (sigma(A)) and the experimental binding constants (beta) being in the order of Hg(2+) > Ag(+) > Cd(2+) suggests that soft-soft interactions are the key for the observed sensitivity and selectivity in the presence of other metal ions, such as: Pb(2+), Ni(2+), Mn(2+), Cu(2+), Co(2+), Zn(2+) and Mg(2+) ions.

Fluorescence Enhancement/Quenching Based on Metal Orbital Control: Computational Studies of a 6-Thienyllumazine-Based Mercury Sensor

“…20 Intensity enhancement and blue shift of the fluorescence are observed with the addition of Cd 2+ . In contrast, fluorescence quenching (without shift) was observed with the addition of Hg 2+ .…”

Photoluminescent Graphene Oxide Microarray for Multiplex Heavy Metal Ion Analysis

“…In comparison with the Ag + , the rQE of Hg 2+ shows an improved detection limit by 10 000‐fold. Although the reason is not clear at this moment, we assume that the formation of the Hg 2+ ‐aptamer complexes would be more energetically favorable than those of the Ag + ‐aptamer, and the heavy atom effect might be involved in the quenching mechanism 13. From the above results, we could conclude that single‐layered GO displays a unique PL emission signal and such an optical property could be applied for metal‐ion detection through electron transfer between GO and the metal ions.…”

Two‐channel near‐infrared fluorescence Ag+ ion sensing of a new star‐shaped dendrimer

“…Fluorescent chemosensors for Ag + have attracted great attention because of their high sensitivity, lower cost, high detection limits, and essential simplicity . To date, fluorescent chemosensors for Ag + have developed rapidly . Recently, Pei et al .…”