Highly photostable luminescent poly(ε-caprolactone)siloxane biohybrids doped with europium complexes

In this paper, we propose for the first time that the combination of a sol-gel derived diurethane cross-linked siloxane-based biohybrid host including short poly(epsilon-caprolactone) segments (PCL(530)) and lanthanide aquocomplexes incorporating beta-diketonate ligands yields an effective protecting cage that efficiently encapsulates the emitting centers and reduces luminescence quenching. The results obtained using the Eu(tta)(3)(H2O)(2) (where tta(-) is 2-thenoyltrifluoracetonate) complex demonstrate that 1 (2) carbonyl oxygen atoms of the host matrix enter the Eu3+ coordination shell, thus replacing the labile water molecule(s). The significant increase in the quantum efficiency q of the doped hybrid with respect to that of Eu(tta)(3)(H2O)(2) (44.2 versus 29.0%, respectively) reveals that complex anchoring to the PCL(530)-based host structure contributes to enhancement of the D-5(0) quantum efficiency. However, when a complex that contains only strong chelating ligands, such as Eu(tta)(3)phen (where phen is 1,10-phenantroline), is incorporated into the same host medium, the effect is lost and the D-5(0) nonradiative paths in the doped hybrid are higher than those existing in the complex itself. Under UVA exposure, the emission intensity of PCL(530)/siloxane/Eu(tta)(3)(H2O)(2) decreased 10% in 11 h, whereas that of PCL(530)/siloxane/Eu(tta)(3)phen decreased 25% in the same period of time.