A smart “off–on” gate for the in situ detection of hydrogen sulphide with Cu(<scp>ii</scp>)-assisted europium emission

Abstract

A water-soluble and emissive Eu-complex (<b>EuL1</b>) bearing a DO3A(Eu³⁺)-pyridine-aza-crown motif has been prepared and its Cu²⁺ complex has been demonstrated to be a smart luminescence "off-on" gate for H₂S detection in water with a nano-molar detection limit (60 nM). <b>EuL1</b> binds to Cu²⁺ ions selectively (<i>K</i>_B = 1.2 × 10⁵ M^-1) inducing 17-fold luminescence quenching and forming a 1 : 1 stoichiometric complex (<b>EuL1</b>-Cu²⁺), which responds to H₂S selectively with restoration of the original Eu emission of <b>EuL1</b> followed by a further 40-fold luminescence enhancement, forming a 1 : 1 stoichiometric complex (<b>EuL1</b>-Na₂S, <i>K</i>_B = 1.5 × 10⁴ M^-1). Without Cu²⁺ ions, <b>EuL1</b> showed non-specific binding towards H₂S with only a 5-fold luminescence enhancement.