A single molecular sensor for selective and differential colorimetric/ratiometric detection of Cu²⁺ and Pd²⁺ in 100%...

A novel salicylaldehyde bis-Schiff-base probe decorated with imidazolium ionic liquid moieties at both ends (SAS-IMIs) was designed and facilely synthesized as a colorimetric/ratiometric sensor to visually detect Cu²⁺ and Pd²⁺ in pure aqueous media. Due to the positively charged characters of its head and tail, the SAS-IMIs exhibited high water solubility with a potential advantage in minimizing the self-aggregation. More importantly, simply by varying the solution pH, colorimetric/ratiometric sensing detection of individual metal ion (Cu²⁺ or Pd²⁺) was realized without any mutual interference. Subsequently, sensitive, selective, and differential detections for Cu²⁺ (LOD: 0.080 μM) and Pd²⁺ (LOD: 0.076 μM) in 100% aqueous solutions were achieved, which proved to be applicable for real water samples. Results from density functional theory (DFT) calculations unveiled the Cu²⁺/Pd²⁺-binding properties of SAS-IMIs, which were in accordance with the experimental observations. Furthermore, a SAS-IMIs-based solid phase sensor was fabricated, which manifested satisfactory detection abilities for Cu²⁺ and Pd²⁺.