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

Abstract

A water-soluble and emissive Eu-complex (EuL1) 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). EuL1 binds to Cu²⁺ ions selectively (K_B = 1.2 × 10⁵ M⁻¹) inducing 17-fold luminescence quenching and forming a 1 : 1 stoichiometric complex (EuL1–Cu²⁺), which responds to H₂S selectively with restoration of the original Eu emission of EuL1 followed by a further 40-fold luminescence enhancement, forming a 1 : 1 stoichiometric complex (EuL1–Na₂S, K_B = 1.5 × 10⁴ M⁻¹). Without Cu²⁺ ions, EuL1 showed non-specific binding towards H₂S with only a 5-fold luminescence enhancement.