ИСТИНА

Long excited state lifetimes make lanthanide coordination compounds (LCCs) the ideal materials for bioimaging, whereas the involvement of the triplet state of the ligand in the luminescence makes them promising for organic light-emitting diodes (OLEDs). Aromatic carboxylates are particularly important due to high quantum yields and chemical stability, but they usually demonstrate low solubility due to the formation of coordination polymers, and also usually do not have transport properties, which is important for OLEDs [1]. To increase the solubility, as well as the electronic mobility, we chose anions of pyrazolecarboxylates, containing nitrogen heteroatom in the alpha position relative to the carboxy-group, as ligands. It was found that all the obtained LCCs are well-soluble due to isle structure formation. Terbium pyrazolecarboxylates demonstrated high quantum yields up to 100%, and their transport properties depended on the substituent nature: high electron mobility was demonstrated only by aryl-substituted CCs. It made it possible to successfully use them as emission layers of OLEDs. At the same time, the isomerism exerted a large influence on the luminescent properties of europium CCs. Thus, β-methyl-substituted pyrazolecarboxylates had quantum yields up to 16%, whereas α-methyl-substituted isomers had no luminescence at all because of the presence of a quenching ligand-to-metal charge transfer state caused by the presence of a free electron pair in the beta position. Cellular studies have shown that europium pyrazolecarboxylates are non-toxic. Since for luminescent bioimaging not only the quantum yield, but also the absorption of CC is important, europium phenylpyrazolecarboxylate demonstrated the greatest intensity of luminescence in cellulo. The data obtained make it possible to consider pyrazolecarboxylates of lanthanides as promising luminescent materials for various applications. [1] VV Utochnikova, NP Kuzmina. Russ. J. Coord. Chem., 2016, 42, 640-656. Acknowledgements – the authors thank RFBR, grant #16-29-10755 e-mail: szv@org.chem.msu.ru , valentina@inorg.chem.msu.ru