The syntheses of three new ligands (L 1 – 3 ), which are based upon a DO3A core and appended with additional receptor sites for metal cations, are described, together with their corresponding Eu(III) complexes (Eu–L 1 – 3 ). The complexes are visibly luminescent in aqueous solution, following sensitization via the pyridine chromophore, showing characteristic narrow line-like emission from Eu(III). The luminescence properties show that water is effectively excluded from the inner coordination sphere of europium (q=0). Each of the complexes showed perturbed luminescence properties upon addition of a variety of d-block metal ions. For example, emission quenching was observed for each complex following addition of Cr(III) and Cu(II). Selectivity towards Hg(II) (over Cd(II), Cu(II) and Zn(II)) was demonstrated with Eu–L 3 , which possesses a receptor site incorporating a softer thiophene moiety. More specifically, Hg(II) binding resulted in changes in the form of the steady state emission spectrum, together with a corresponding reduction of the luminescence lifetime in water, which can be attributed to an increase in inner sphere hydration (q=2) and thus enhanced non-radiative deactivation of the 5 D 0 state by proximate O–H oscillators.