Syntheses And Luminesecence Properties Study Of Eu(â…¢) Complexes Based On Phenanthroline Derivatives Carboxylate Ligands

In this paper, we have synthesized 16 new phenanthroline derivatives carboxylate ligands, 14 ligands contain imidazole moiety and two others contain pyrazine moiety, their chemical structures were shown as follows:The series of Br-substituted ligands R=o-Br,L01;m-Br,L02; p-Br, L03 The series of OCH3-substituted ligands R=o-OCH3, L04; m-OCH3, L05; p-OCH3, L06 The series of NO2-substituted ligands R=o-NO2, L07; m- NO2, L08; p- NO2, L09 The series of COOH-substituted ligands R=o-COOH, L10; m- COOH, L11; p-COOH, L12 R=p-CF3, L13; p-CHO, L14 ligandsThe ligands and the corresponding Eu(III) complexes have been characterized by 1HNMR, elemental analysis, Vis-UV and IR spectra. The formula of these complexes was confirmed to be [Eu2(Lx)3]·6H2O. We have got The single state and triple state energy levels of the ligands were obtain by measured the UV-Vis spectra and phosphorescent spectra of the corresponding Gd(III) complexes at 77 K. Theluminescent properties of the Eu(III) complexes were thoroughly investigated. The results showed that:1. All the ligands show strong absorption bands in the range of 280~300nm, which can be ascribed to Ï€-Ï€* transitions of the ligands. The moderate shoulder bands within a range 325-375 nm can be assign to n-Ï€* transitions of the ligands. Eu(III) complexes show strong UV absorptions, compared with the most ligands, The UV-Vis spectra of Eu(III) complexes show red-shifted to certain extent owing to metal ions perturbed electron configuration changes 2. All the Eu(III) complexes containing imidazole moiety exhibit excellent photo-luminescent properties with good luminescence quantum yields of 22-39% apart from the series of NO2-substituted Eu(III) complexes, which have very poor luminescent efficiencies. The luminescence properties of Eu(III) complexes containing pyrazine moiety are better than that of Eu(III) complexes containing imidazole moiety with the quantum yield and lifetime of about 46.4% and 2.81 ms respectively. Through determining the UV-vis spectra and the phosphorescence spectra of the corresponding Gd(III) complexes under 77 K, we find that Eu3+ ion can be well sensitized by most ligands, and the of energy transfer efficiencies from the ligands to Eu3+ ion are very high. The the domination of the 5D0â†'7F2 transition reveals that the Eu3+ ions are not located in the inversion center of the compounds and the complexes have good monochromaticity. Furthermore the singlet of the 5D0â†'7F0 transition indicates the presence of a single coordination environment of Eu3+ ion in all the complexes. 3. We have summarized the effects of different substituents of benzene ring on the luminescence properties of Eu(III) complexes, and find that in the same series electron-donating group on benzene ring can increase the luminescence efficiency of Eu(III) complex while electron-withdrawing decrease it. In the Eu(III) complexes containing imidazole moiety, electron-withdrawing group such as –COOH,-CHO,-CF3 and-NO2 lower the luminescent efficiency in different degrees.-NO2 groups with strong conjugated electron-withdrawing effects decrease the luminescent efficiencies greatly, and as a result, the complexes containing nitro groups have external quantum yields of only 0.8%~4.2%. The observed lifetimes of most complexes are verylong( about 2ms), indicating that the Eu3+ ions are located in the inner rigid N2O2 coordination sphere and are well shielded from the non-radiative deactivations of solvent molecules. 4. The comparison between the solution and the solid-state luminescent efficiencies of the Eu(III) complexes show that the strong Ï€-Ï€ stacking interactions between the large conjugate planes of the ligands can result in apparently luminescence quenching, and the solid-state quantum yield of the Eu(III) complexes are greatly reduced consequently.