1,10-Phenanthroline decorated with substituent groups forming europium(III) complexes: synthesis, crystal structure, photoluminescence properties and their bioimaging in living cells.

With 2-thenoyltrifluoroacetone (tta) as the first ligand and phenanthroline derivatives as the second ligand, two europium(III) complexes, Eu(tta)3L1 (L1 = 11-nitrodipyrido[3,2-a:2',3'-c]phenazine) (1) and Eu(tta)3L2 (L2 = 11-methoxydipyrido[3,2-a:2',3'-c]phenazine) (2), have been synthesized and their structures were characterized by NMR and single-crystal X-ray crystallography. The two complexes exhibited red emissions that belonged to 5D0→7Fj (j = 0-4) transitions of Eu in different solutions and solid state. Complex 2 with the electron-donating group showed preferable luminous properties to that of complex 1 with the electron-withdrawing group. Moreover, complex 2 displayed much longer lifetimes, higher quantum yields and better CIE color coordinates corresponding to pure red in color (x = 0.67, y = 0.33). In addition, the two complexes had strong intracellular luminescence, which indicated that they could be employed in luminescence imaging of living cells. [ABSTRACT FROM AUTHOR]