Novel phenanthroline derivatives and their europium(III) and zinc(II) complexes have been prepared in up to 92 %. In contrast to the stable zinc complexes, the europium compounds exhibit a strong luminescence in THF solution and complete dissociation of the complexes back to free ligands in DMSO. 1H NMR studies of the Eu(III)-complexes 5 and 6 also confirmed the existence of different states depending on the solvent used. Moreover, it was found that the compound 5 is stable in EtOH-PBS solutions; here a strong signal in the emission spectra corresponding to the europium ion was detected. These metal complexes can be used as fluorescence markers for the diagnosis of esophageal squamous carcinoma (OE21) cells at low concentrations. Cell images were acquired using the compound 5, 7-9 as luminescent markers. The first images were taken already after 20 min incubation time at a very low concentration range (0.7-1.6 μM). ; PUBLISHED ; This work was supported by funding from the Health Research Board (translational research award 2007 TRA/2007/11), Science Foundation Ireland (SFI P.I. 09/IN.1/B2650) and Fundação da Ciência e Tecnologia.