An effective colorimetric sensor for detecting Cu²⁺ based on benzothiazole moiety

An effective colorimetric chemosensor, 2,4-dichloro-6-((E)-(((Z)-3-methylbenzo[d]thiazol-2(3H)-ylidene)hydrazono)methyl)phenol (HMD), was synthesised for Cu²⁺ detection. HMD with benzothiazole moiety showed a large bathochromic shift (153 nm) and a definite colour change for Cu²⁺. HMD could detect Cu²⁺ down to 0.47 μmol/L in the solution phase and could clearly distinguish it from other metal ions, even in the test strip. The binding mode between HMD and Cu²⁺ was determined to be 1:1 using Job plot and electrospray ionisation mass spectrometry. The sensing mechanism of HMD for Cu²⁺ was illustrated as the combination of metal-to-ligand charge transfer and intramolecular charge transfer via theoretical calculation.