Visible-Light Excitable Europium(III) Complexes with 2,7-Positional Substituted Carbazole Group-Containing Ligands

Two novel carbazole-based β-diketones with 2- or 2,7-substituted groups in the carbazole ring, 2-(4′4′4′-trifluoro-1′3′-dioxobutyl)-carbazole (2-TFDBC) and 2,7-bis(4′4′4′-trifluoro-1′’3′-dioxobutyl)-carbazole (2,7-BTFDBC), and their europium(III) ternary complexes Eu(2-TFDBC)3phen and Eu2(2,7-BTFDBC)3(phen)2 were synthesized via a dexterously designed routine, where phen is 1,10-phenanthroline. The Eu(III) complexes were characterized by elementary analysis, IR and UV−visible absorption spectroscopy, thermogravimetric analysis (TGA), and photoluminescence (PL) measurements. TGA shows that the decomposition temperatures of the complexes are 361.4 and 367.3 °C, respectively. PL measurement results indicated that suitably expanded π-conjugation in the complex molecules makes the excitation band redshift to the visible region, and both the Eu(III) complexes exhibit intense red emission under blue-light excitation. The triplet state energy levels of 2-TFDBC and 2,7-BTFDBC in the complexes are higher than that of the lowest excited level of Eu3+ ion, 5 D 0, so the photoluminescence mechanism of the Eu(III) complexes was proposed as a ligand-sensitized luminescence process. All of the results indicate that Eu(2-TFDBC)3phen and Eu2(2,7-BTFDBC)3(phen)2 are promising candidates as visible-light excitable red phosphor for luminescence applications.