Synthesis and Optical Performance of terbium complexes with octanoyl amino acids

As multifunctional materials, amino acid rare-earth compounds exhibit unique physical and chemical properties. Considering their wide applications, we synthesized a new type of amino acid terbium complexes, which exhibit interesting optical properties. Three novel octanoyl amino acid terbium complexes were synthesized and investigated in this study: terbium octanoyl-alaninate (Tb(oct-ala)(3)center dot H2O), terbium (III) octanoyl-phenylalaninate (Tb(oct-phe)(3)center dot H2O), and terbium (III) octanyl-serinate (Tb(oct-ser)(3)center dot 3H(2)O). The molecular structure and surface morphology of these three complexes were studied using various methods, including H-1 (Nuclear Magnetic Resonance) NMR, Fourier-Transform Infrared Spectroscopy (FT-IR), powder X-Ray Diffraction (XRD), and Scanning Electron Microscope (SEM). The XRD results show that Tb(oct-phe)(3)center dot H2O and Tb(oct-ser)(3)center dot 3H(2)O present long-range disorder and short-range order, while Tb(oct-ala)(3)center dot H2O shows long-range disorder and short-range disorder. SEM results revealed irregular shapes of the samples synthesized. Polarizing Microscopy (PM) observations show that Tb(oct-phe)(3)center dot H2O and Tb(oct-ser)(3)center dot 3H(2)O samples are optically anisotropic at and above the room temperature. Tb(oct-ala)(3)center dot H2O exhibits optical homogeneity over the investigated temperature range. Also, the optical properties of complexes were examined using Ultraviolet-Visible Spectroscopy (UV-Vis), Emission Spectroscopy, Fluorescence Lifetime, and Quantum Yields (QY). The UV-Vis absorption spectra show that the complexes have excellent absorption properties in the UV region, and the absorption range of the complexes (200-400 nm) is larger than that of the ligands (200-270 nm). After irradiation with a 254 nm UV lamp, these three complexes are bright green in both solution and solid form. For the emission spectra, the luminescent intensity of the three complexes increases with an increase in concentration. Comparing the fluorescence spectra of the three powders, we observed that Tb(oct-phe)(3)center dot H2O has stronger luminescent intensity, longer fluorescence lifetime and larger quantum yield than the other two complexes. The structure of these terbium complexes was investigated using Density-Functional Theory (DFT) calculations and combining theory with experiment. (C) 2021 The Author(s). Published by Elsevier B.V.

Automated summary

Rare-earth amino acid complexes synthesized in this study exhibit unique physical and chemical properties, with optical anisotropy observed at and above room temperature in some cases. The complexes show excellent UV absorption properties, with a broader absorption range compared to their corresponding ligands. Among the three complexes studied, one exhibits stronger luminescent intensity, longer fluorescence lifetime, and larger quantum yield than the other two. The molecular structure and optical properties of these terbium complexes were investigated using various analytical techniques, with promising results for potential applications in optical devices.