Role of PSS-based assemblies in stabilization of Eu and Sm luminescent complexes and their thermoresponsive luminescence.

The present work introduces self-assembled polystyrenesulfonate (PSS) molecules as soft nanocapsules for incorporation of Eu-Sm complexes by the solvent exchange procedure. The high levels of Eu- and Sm-luminescence of the complexes derives from the ligand-to-metal energy transfer, in turn, resulted from the complex formation of Euand Sm ions with the three recently synthesized cyclophanic 1,3-diketones. The structural features of the ligands are optimized for the high thermal sensitivity of Eu- luminescence in DMF solutions. The PSS-nanocapsules (∼100 nm) provide both colloid and chemical stabilization of the ultrasmall (3-5 nm) nanoprecipitates of the complexes, although their luminescence spectra patterns and excited state lifetimes differ from the values measured for the complexes in DMF solutions. The specific concentration ratio of the Eu-Sm complexes in the DMF solutions allows to tune the intensity ratio of the luminescence bands at 612 and 650 nm in the heterometallic Eu-Sm colloids. The thermal sensitivity of the Eu- and Sm-luminescence of the complexes derives from the static quenching both in PSS-colloids and in DMF solutions, while the thermo-induced dynamic quenching of the luminescence is significant only in DMF solutions. The reversibility of thermo-induced luminescence changes of the Eu-Sm colloids is demonstrated by six heating-cooling cycles. The DLS measurements before and after the six cycles reveal the invariance of the PSS-based capsule as the prerequisite for the recyclability of the temperature monitoring through the ratio of Eu-to- Sm luminescence.