AIE and ESIPT Schiff base ligands and corresponding Eu(III) complexes: Multiple-color and fluorescence properties.

[Display omitted] • A series of Schiff-base ligands and corresponding Eu(III) complexes with ligands and auxiliary ligands were prepared • Ligands possessed typical AIE characteristics in DMF/H2O solutions. • Ligands shown multiple-color emission (orange to green) due to different substituents. • Eu(III) complexes emitted red luminescence with excellent thermal stability. • Electron-donating group enhance luminescence intensity and lifetime of complexes. The organic ligands with good coordination ability to Eu(III) ion attracted great attention, but the preparation of multifunctional organic ligands with excellent performance and the potential application was still a challenge in the field of rare earth coordination. In this work, a series of Schiff-base ligands and their corresponding Eu(III) complexes were successfully prepared. The ligands L1−4 exhibited typical AIE properties with various fluorescence emissions and high fluorescence quantum yields in an aggregated state. The luminescence intensity and luminescence lifetime of Eu(III) complexes were investigated by comparing different substituents of ligands. Density functional theory (DFT) calculations suggested that the electronegativity of the ligands L1−4 changed with the change of the substituents on the salicylaldehyde, which led to the phenomenon that the ligands exhibited diverse fluorescence emission from green to orange (maximum emission wavelengths were 525 nm, 546 nm 569 nm and 582 nm, respectively). All target Eu(III) complexes exhibited red luminescence of Eu(III) ions, accompanied by outstanding thermal stability and long luminescence lifetime. The effect of various substituent groups on luminescence intensity and luminescence lifetime of complexes was ordered: EuL3(Phen)(NO 3) 3 > EuL2(Phen)(NO 3) 3 > EuL1(Phen)(NO 3) 3 > EuL4(Phen)(NO 3) 3. Based on the above results, all ligands and corresponding target Eu(III) complexes had good application prospects in the field of optical materials. [ABSTRACT FROM AUTHOR]