Synthesis and optical properties of polymeric complexes of europium based on polyvinylpyrrolidone derivatives - potential luminescent markers for bioimaging

Polymeric derivatives of poly-N-vinylpyrrolidone containing different amounts of linker carboxylate ligands (partially hydrolyzed poly-N-vinylpyrrolidone with 5 mol% COOH groups and copolymers of N-vinylpyrrolidone with other monomers) were synthesized. The following copolymers were obtained: N-vinylpyrrolidone/crotonic acid and N-vinylpyrrolidone/N-vinylamidoanthanoic acid (containing 16 and 50 mol% COOH-groups). Metal-polymer complexes (MPC) with varying europium content were prepared through the interaction of the obtained polymers with equimolar amounts of hydroxocomplex Eu(Phen)₂(OH)₃ (Phen = 1,10-phenanthroline). The polymers and MPC were characterized by elemental analysis, IR, UV-vis spectroscopy and photoluminescence; their cytotoxicity toward living cells was estimated. All the obtained MPC exhibited photoluminescence with higher intensity than that of the reference complex Eu(Phen)₂Br₃. The dependence of luminescence intensity on the content of metallocenters in MPC was demonstrated. The relative quantum yield of luminescence was found to decrease with increasing europium content in MPC. It was shown that none of the polymers under investigation exhibited cytotoxicity. Furthermore, the presence of the polymeric anion in MPC contributed to a sharp decrease in the toxicity of metallocenter [Eu(Phen)₂]³⁺_solv. The MPC based on the N-vinylpyrrolidone/N-vinylamidoanthanoic acid copolymer exhibited no cytotoxicity within the entire investigated concentration range.