Study on the structural and photophysical properties of N-acyl amino acid europium complexes

In this paper, a series of acyl amino acid europium complexes (Eu[CH3(CH2CH2)nCONHCH(CH3)COO]3, n=0∼5) were synthesized using N-acyl amido alanine as ligands, and their structures and photophysical properties were studied.The structural and functional group information of europium complexes was obtained by elemental analysis, as well as infrared and hydrogen nuclear magnetic spectral analysis (1H NMR). The theoretical structure of the complexes was obtained by density functional theory (DFT) calculations; the theoretical structure of the complex was shown to be reliable by the comparison of theoretical and experimental vibrational and 1H NMR spectra. Additionally, the photophysical properties of the solid complexes at room temperature were determined by analysis of Ultraviolet–visible spectroscopy(UV-vis) and luminescence spectra. From the test results, it can be seen that the complex had good light absorption capacity in the range of 200 - 300 nm; By comparison of the luminescence intensities of the complexes and EuCl3 proved that acyl amino acid ligands played a role in sensitizing Eu3+ characteristic luminescence. In addition, the effect of solution concentration on fluorescence performance has been studied. It can be inferred that complexes with longer carbon chains are less prone to aggregation in solution (increasing repulsive forces with increasing hydrophobicity), and the concentration, where fluorescence quenching occurs, is higher. Moreover, the solvent effect on the luminescence performance of the complexes was investigated by testing the luminescence spectrum of the complexes with different carbon chain lengths in a methanol solution(0.01 mol/L). Finally, the variable temperature spectral analysis provided information on the temperature-dependent variation of the luminescence properties of the complexes. The fluorescence performance of complexes with different carbon chain lengths that having different changing trends with temperature, with long carbon chain complexes exhibiting better high-temperature fluorescence stability.