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

Two novel carbazole-based beta-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)(3)phen and Eu-2(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 degrees C, respectively. PL measurement results indicated that suitably expanded pi-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, D-5(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)(3)phen and Eu-2(2,7-BTFDBC)(3)(phen)(2) are promising candidates as visible-light excitable red phosphor for luminescence applications.