Luminescence and cytotoxic study of red emissive europium(III) complex as a cell dye

A novel non-toxic red luminescent Eu(III)-complex, (Na[Eu(Fmpc)(4)(H2O)(4)].3H(2)O), based on a carboxylic acid ligand was synthesized and characterized by several techniques, such as elemental analysis, MALDI TOF spec-trometry, thermogravimetric analyses, UV-vis, FT-IR, and photoluminescence spectroscopies; also its structure was optimized theoretically by the AM1 sparkle model. The Gd(III)-complex, (Na[Gd(Fmpc)(4)(H2O)(3)].4H(2)O), was also synthesized and characterized, to evaluate the Fmpc ligand triplet excited state, revealing that the energy of the ligand is suitable to sensitize the similar Eu(III)-complex, indicating a high sensitization rate of the Fmpc ligand to Eu3+ ion with 98% efficiency. The Na[Eu(Fmpc)(4)(H2O)(4)].3H(2)O luminescent properties were investigated, and its excited state lifetime was also determined as 0.76 ms in acetonitrile solution. The complex relative quantum yield was estimated to be 27.9%, evidencing that the Fmpc ligand is efficient in transferring the absorbed energy to the europium(III) ion emitting level. Furthermore, the cytotoxicity of Na[Eu(Fmpc)(4)(H2O)(4)] .3H(2)O was tested in CHO-k1 cells by the MTT assay, and no cytotoxicity was observed at 24 h of exposure within the concentrations tested (25-200 mu g/mL). Its use for cell imaging was also evaluated by fluorescence and confocal microscopies. Our findings indicated that Na[Eu(Fmpc)(4)(H2O)(4)].3H(2)O complex exhibited great lumi-nescent properties, it is non-toxic, and it has potential for bioimaging application as a luminescent dye.