Study of the luminescence properties of praseodymium complexes with 1,10-phenanthroline-N-amino acid

Four Pr-phen-acyl amino acid ternary complexes (Pr [CH 3 (CH 2 ) n CONHCH(CH 3 )COO] 3 ·phenanthroline, n = 4,6,8,10) were synthesized by a method used for optical materials that is based on solution chemical reactions. The molecular structure of the praseodymium complexes was determined using CHN elemental analysis, 13 C-Nuclear Magnetic Resonance ( 13 C NMR) spectroscopy, and Fourier Transform-Infrared (FT-IR) spectroscopy. X-ray diffraction and polarized light microscopy showed that Pr(hex‑ala) 3 ·phen, Pr(oct‑ala) 3 ·phen, and Pr(dec‑ala) 3 ·phen have good crystallinity and exhibit excellent optical anisotropy in the molten state. Ultraviolet-Visible (UV–Vis) spectroscopy revealed that the light absorption of the praseodymium complexes is in the range of 200 nm - 500 nm after the introduction of phenanthroline (phen). Fluorescence spectral analyses in the visible region, at an excitation wavelength of 417 nm, indicated that Pr(hex‑ala) 3 ·phen emits green light. In contrast, the other three praseodymium complexes with long carbon chains emit red light. Furthermore, phen significantly enhances the fluorescence intensity of the complexes and remarkably prolongs their fluorescence lifetimes. Variable-temperature fluorescence spectroscopy revealed that the praseodymium complexes maintained a high luminescence intensity throughout the heating process, ranging from 25 °C to 200 °C, which is attributed to their conjugated functionalities.