SYNTHESIS, CHARACTERIZATION, AND LUMINESCENT PROPERTIES OF EUROPIUM(III) COMPLEXES WITH SALEN-TYPE LIGANDS CONTAINING 1,2,4-TRIAZOLE MOIETIES

• Date: 2024
• Main Authors: Halushchenko, Valeriia, Korovin, Oleksandr, Smola, Serhii, Bibik, Yurii, Khomenko, Dmytro, Doroshchuk, Roman, Lampeka, Rostyslav, Rusakova, Natalya
• Format: Article
• Language: English
• Published: V.I.Vernadsky Institute of General and Inorganic Chemistry 2024
• Online Access: https://ucj.org.ua/index.php/journal/article/view/647
• Journal Title: Ukrainian Chemistry Journal

The study presents the synthesis, characterization, and photophysical investigation of novel Ln(III)complexes with 1,2,4-triazole-based Salen-type ligands, focusing on europium-centered optical pro­perties. An optimized synthetic method for Ln(III) complex formation was developed with the use of various salts, solvents, and deprotonating agents, with methanol, triethylamine, and triethylorthoformate yielding the best results. This approach produced light-yellow crystalline products with a 65–70% yield. Structural characterization through IR spectroscopy and mass spectrometry confirmed coordination by nitrogen and oxygen atoms, as evidenced by shifts in vibrational bands indicative of Eu–N bonds and alterationsin phenolic OH and CO stretching modes. UV-Vis absorption spectra revealed bathochromic shifts, indicating changes in electron density and increased conjugation resulting from complex formation. Upon excitation, the complexes exhibited fluorescence in the 400–500 nm range and phosphorescence in the 450–550 nm range, demonstrating effective energy transfer within the system. The CIE chromaticity coordinates for EuL1 (x=0,631, y=0,368) and EuL2 (x=0,603, y=0,396) denote a deep red emission with color purity and correlated color temperature (CCT) values of 2017,94 K and 1720,92 K, respectively, indicating their potential for high-purity red emissions in optoelectronic applications. Lifetime measurements (0,544 ms at 298 K and 0,706 ms at 77 K) indicate non-radiative relaxation processes that may be modulated by local symmetry, as suggested by the distinctive emission splitting in Eu(III) transitions. Emission spectra revealed prominent transitions typical of Eu(III) ions, with extensive splitting indicative of a low-symmetry environment, likely within C₂ᵥ or Cs point groups. Structural analysis supports a coordination number of 8, suggesting polyhedral arrangements like a bicapped trigonal prism. This synthetic route effectively produces Ln(III) complexes with tunable luminescent properties, revealing key structure-property relationships and enabling tailored red emissions, making these complexes promising precursors for display and lighting technologies.