Investigation of the Supramolecular Assembly of Luminescent Lanthanide Nanoparticles Surface Functionalized by p-Sulfonato-Calix[4]arenes with Charged Aromatic Compounds

The surface coordination of p-sulfonato- (C[4]), p-sulfonatothia- (SC[4]) and p-sulfonato-sulfoxocalix[4]arene (SO2C[4]) on La0.9Tb0.1F3 nanoparticles (TbNP) was investigated by UV-Vis absorption and luminescence spectroscopies. SO2C[4] displayed the strongest affinity towards the NPs and a significant antenna effect leading to observation of the characteristic Tb emission bands upon calixarene excitation. NPs decorated by a shell of SO2C[4] were prepared and the interaction with rhodamine 6G (R6G) was studied. The progressive addition of R6G resulted in a strong Tb to R6G energy transfer process, as revealed by a long lived emission of R6G upon SO2C[4] excitation. The FRET efficiency was almost quantitative (87-90 %), pointing to an average distance of 28 to 32 angstrom between the R6G and the Tb emitting centres of the NP. An association of one R6G per SO2C[4] was deduced with a very strong apparent affinity (K=2.5x10(7) M-1) in water. Similar interactions were observed with paraquat, resulting in TbNP luminescence quenching. In both cases, an unexpected increase of the association constant of the cation with SO2C[4] was observed when SO2C[4] is anchored at the surface of the NP.