An Efficient Fluorescence "Turn-On" Chemosensor Comprising of Coumarin and Rhodamine Moieties for Al 3+ and Hg 2 .

A potent fluorescence 'turn-on' receptor (HL) based on rhodamine and coumarin moieties for the detection of Hg ²⁺ and Al ³⁺ is synthesized by condensation of rhodamine 6G hydrazide and 4-hydroxy-3-acetylcoumarin. In presence of Al ³⁺ and/or Hg ²⁺ the receptor (HL) exhibits deep pink colouration and a sharp band at 528 nm is appeared in UV-vis titration. Upon gradual addition of Al ³⁺ and/or Hg ²⁺ to the solution of HL significant enhancement of fluorescence intensity is observed at 564 nm in MeCN:H ₂ O (1:5, v/v) medium. The receptor is strongly bound to Al ³⁺ and/or Hg ²⁺ and the association constants (K _a ) are found to be 1.74 × 10 ⁴ and 1.04 × 10 ⁴ M ^- 1 for Al ³⁺ and Hg ²⁺ respectively. Graphical Abstract A potent fluorescence 'turn-on' receptor (HL) based on rhodamine and coumarin moieties for the detection of Hg ²⁺ and Al ³⁺ is synthesized and characterized. In presence of Al ³⁺ and/or Hg ²⁺ the receptor (HL) exhibits deep pink colouration and significant enhancement of fluorescence intensity is observed at 564 nm in MeCN:H ₂ O (1:5, v/v) medium. The receptor is strongly bound to Al ³⁺ and/or Hg ²⁺ and the association constants (K _a ) are found to be 1.74 × 10 ⁴ and 1.04 × 10 ⁴ M ^- 1 for Al ³⁺ and Hg ²⁺ respectively.