A lanthanide complex for selective sensing of Fe(III) ions

The lanthanide complex [Eu(Tpy-NH₂)₂Cl₂]Cl (1), where Tpy-NH₂ is 4-(paminophenyl)-2,2:6,2"-terpyridine, was synthesized. Its photophysical properties, e.g., Fourier Transform Infrared (FTIR) spectra, UV-visible absorption spectra, and luminescence properties, in the presence of various metal ions were studied. Tpy-NH₂ acts as chromophore, or light-harvesting photo sensitizing antenna moiety, for Eu³⁺ luminescence. The bright luminescence in 1 suggests that favourable photo-induced energy transfer occurs from the Tpy-NH₂ antenna to the Eu³⁺ to fill the long-lived emissive excited states of Eu³⁺ f-f transitions. The luminescence spectral profile of complex 1 showed a characteristic sharp emission band maximum for ⁵D₀ →⁷F₂ f-f transitions at 614 nm originating from Eu³⁺ ions. The luminescence studies revealed that this material possesses a highly selective fluorescence quenching response to Fe³⁺ ions in liquid suspension. The dose-dependent fluorescent quenching showed good linearity, and a Fe³⁺ detection limit of 0.655 μM was calculated for complex 1. This material can potentially be used as a fluorosensor for sensing Fe³⁺ ions; its luminescence quenching response can be explained in terms of a competitive absorption mechanism.