Adaptable Biomolecule-Interactive Dual Colorimetric Chemosensor for Cu²⁺ and Pd²⁺: Insight from Crystal Structure, Photophysical Investigations, Real-Time Sampling, and Molecular Logic Circuits

Considering the crisis of single probes for the simultaneous colorimetric detection of both Cu 2+ and Pd 2+ metal ions, which are toxic to living organisms even in trace amounts, in this communication, we report the facile synthesis and characterization, including single-crystal X-ray diffraction (SCXRD), of a single molecular probe (E)-3-((2-(methylthio)phenyl)diazenyl)-[1,1′-biphenyl]-4-ol ( TABH ). TABH is bioactive and avidly interacts with biomolecules such as BSA protein and CT DNA, as evidenced by spectrofluorometric and photometric tests. The probe is also proficient in the selective and swift colorimetric sensing of Cu 2+ and Pd 2+ ions in ACN/H 2 O (4/1 v/v, pH = 7.2) medium over other metal ions. The sensor’s ability to selectively bind the analytes is demonstrated by a noticeable color shift from yellow to reddish brown for Cu 2+ and violet for Pd 2+, which is clearly visible to the human eye. A detailed investigation of the recognition mechanism using Job’s plot, 1 H nuclear magnetic resonance (NMR), infrared (IR) analysis, electrospray ionization (ESI) mass analysis, and density functional theory (DFT) calculations confirmed a 1:1 binding stoichiometry for both ions. Furthermore, the chemosensor exhibits a strong association affinity (7.61 × 10 4 and 1.42 × 10 5 M –1 for Cu 2+ and Pd 2+, respectively) and a low detection limit (54.8 and 5.32 nM for Cu 2+ and Pd 2+, respectively). Binding data and absorption studies revealed that Pd 2+ had a higher affinity for the probe than Cu 2+ . This makes it simple for Pd 2+ to replace Cu 2+ in the [TAB-Cu 2+ ] complex, increasing Pd 2+ ’s differential selectivity over Cu 2+ . Cu 2+ sensing is reversible with the addition of both ethylenediaminetetraacetic acid (EDTA) and triphenylphosphine (PPh 3 ), whereas Pd 2+ sensing is exclusively reversible with the presence of PPh 3 only. The sensing activities were also investigated with molecular logic operations of AND, OR, and NOT gates. In addition, the chemoprobe proved to be effective in identifying Cu 2+ and Pd 2+ in actual water samples. It was then converted into test strips, creating a portable device for on-site analysis and testing.