“AIE+ESIPT” bis Schiff-base ligands with multicolor emission and their corresponding Eu(III) complexes: Synthesis and properties research

A series of bis Schiff-base ligands and their corresponding Eu(III) complexes were synthesized easily and characterized by 1H NMR,13C NMR, ESI-MS+, Elemental analysis, Molar conductivity, Thermogravimetric analysis. The AIE characteristics of all ligands (L1−4) were investigated, fluorescence and electrochemical properties of Eu(III) complexes (EuL1−4Cl3·2H2O) were also studied. The results indicate that all ligands not only possess AIE characteristics, but exhibit diverse fluorescence emission from orange to green (the emission peaks are 588 nm, 556 nm, 548 nm and 520 nm, respectively). All complexes show characteristic red fluorescence of Eu (III) ion. The effect of various substituent groups on fluorescence intensity of complexes is ordered: –N(CH2CH3)2>-OCH3>-OH > -Cl and EuL4Cl3·2H2O emits the strongest fluorescence. The results of electrochemical properties demonstrate that electron-donating groups increase the HOMO energy level and LUMO energy level of complexes, but the electron-withdrawing groups behaves contrarily. Based on the above results, all ligands and their corresponding Eu(III) complexes are promising materials in the field of optics. [Display omitted] •A series of bis Schiff-base ligands and their Eu(III) complexes were prepared.•Ligands possess typical AIE characteristics in DMF/H2O solutions.•Ligands show multicolor emission (orange to green) due to different substituents.•Eu(III) complexes emit red fluorescence and show excellent thermal stability.•Electron-donating groups enhance fluorescence intensity and HOMO level ofcomplexes.