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Logo 22nd ISBC & 20th ISLS


Excited state dynamics and ultrafast processes

Different emission sensitization pathways in Ln3+ chelates with O8, O6N2 and O8N2 chemical environments

Paula Gawryszewska1, Albano N. C. N.2, E. K.1, Aneta L.1, Justyna N.1, Viktor A. T.3, Lukasz M.1, Agata B.1, Volodymyr M. A.3, Oscar L. M.4, Janina L.1

1Faculty of Chemistry, University of Wroclaw, 14 F. Joliot-Curie Str., 50-383 Wroclaw, Poland, 2Physics Department and CICECO-Aveiro Institute of Materials, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal, 3Department of Chemistry, Kyiv National Taras Shevchenko University, Volodymyrska str. 64, Kyiv 01601, Ukraine, 4Departamento de Química Fundamental, Universidade Federal de Pernambuco, Cidade Universitária, 50740-560 Recife, Brazil

E-mail: paula.gawryszewska-wilczynska@uwr.edu.pl

Lanthanide (Ln3+) compounds are of great interest due to their special luminescence properties and their various applications for technological purposes. Ln3+ luminescence is associated with transitions within the 4f subshell. Due to the small value of the molar absorption coefficient, Ln3+ emission requires sensitization. One way involves the so-called antenna effect, i.e. the use of organic ligands with strong absorption, which transfer excitation energy to the excited levels of Ln3+ via intramolecular non-radiative energy transfer (IET). It is important to know the paths and mechanisms of IET as well as the impact of structural modification on the sensitized emission of the Ln3+ ions. Knowledge of these issues is helpful in designing Ln3+ coordination compounds with specific luminescent properties. We provide insights into the different pathways and mechanisms of IET for two series of Ln3+ coordination compounds with N-phosphorylated sulfonyl- and carboxamides, which were designed as UV to Vis converters. We will show that the pathways and mechanisms of IET are also affected by slight changes in the crystal structure of the chelates in the second coordination sphere, such as counter ions or solvent molecules. We will analyze the influence of the ligand-to-Ln charge transfer state (LMCT), which, by depopulating the ligand singlet state (S1), dramatically reduces the sensitization efficiency of the Eu3+ emission while changing the dominant mechanism of IET. The key role of the 7F5 state of Tb3+ in IET will be proved, as well as the dominance of IET through the S1 state for Tb3+ coordination compounds with 2,2'- bipyridine and 1, 10- phenanthroline as the co-ligand. We will also demonstrate how proper ligand design, combined with stiffening of the crystal structure of the coordination compound by introducing alkali metal cations into the first coordination sphere, affects IET efficiency and the intensity of sensitized emission. The above examples provide new insights into the sensitization processes of Tb3+ and Eu3+ coordination compounds.

Keywords: lanthanide, luminescence, energy transfer, crystal structure, N-phosphorylated amides

Acknowledgments: University of Wroclaw, BPIDUB.4610.207.2022

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