Chemosensing Ensembles of 2-(2-Thiazolylazo)-p-cresol with Metal Ions in Colorimetric Detection of Anions

Abstract

This paper reports that changing metal ions (Co²⁺, Ni²⁺, Cu²⁺, or Cd²⁺) in the 2-(2-thiazolylazo)-p-cresol (TAC)-metal ensemble may generate varied optical responses to anions. The TAC and Ni²⁺ ensemble can detect and quantify CN⁻ in a highly sensitive and selective manner. CN⁻ competes for the Ni²⁺ present in the ensemble during recognition events, which thereby triggers colorimetric and absorption spectral changes. CN⁻ and S²⁻ decomposed TAC-Cu²⁺ ensemble by forming [Cu(CN)_x]ⁿ⁻ species and CuS, respectively; however, the discrimination of CN⁻ and S²⁻ was not achieved. The TAC-Co²⁺ ensemble exhibited discriminated interaction with CN⁻ through the absorption channel, but CN⁻ was not quantitatively determined. Although the TAC-Cd²⁺ ensemble responded to different anions, it did not recognize each anion selectively. These results demonstrated that metal ions can powerfully modulate anion identification to some extent, which can be an effective strategy to achieve selectivity of certain anions by varying the metal ions in the ensemble.