Positional Isomeric Symmetric Dipodal Receptors Dangled with Rotatable Binding Scaffolds: Fluorescent Sensing of Silver Ions and Sequential Detection of l-Histidine and Their Multifarious Applications

Three simple dipodal artificial acyclic symmetric receptors, SDO, SDM, and SDP, driven by positional isomerism based on xylelene scaffolds were designed, synthesized, and characterized by 1H NMR, 13C NMR, and mass spectroscopy techniques. Probes SDO, SDM, and SDPdemonstrated selective detection of Ag+metal ions and amino acid l-histidine in a DMSO–H2O solution (1:1 v/v, HEPES 50 mM, pH = 7.4). The detection of Ag+metal ions occurred in three ways: (i) inhibition of the photoinduced electron-transfer (PET) process, (ii) blueshifted fluorescence enhancement via the intramolecular charge-transfer (ICT) process, and (iii) restricted rotation of the dangling benzylic scaffold following coordination with a Ag+metal ion. Job’s plot analysis and quantum yields confirm the binding of probes to Ag+in 1:1, 1:2, and 1:2 ratios with LODs and LOQs found to be 1.3 μM and 3.19 × 10–7M, 6.40 × 10–7and 2.44 × 10 –6M, and 9.76 × 10–7and 21.01 × 10–7M, respectively. 1H NMR titration, HRMS, ESI-TOF, IR analysis, and theoretical DFT investigations were also used to establish the binding stoichiometry. Furthermore, the probes were utilized for the detection of Ag+ions in water samples, food samples, soil analysis, and bacterial imaging in Escherichia colicells and a molecular logic gate was constructed.