Cyclic Phosphazenes for the Surface Modification of Lanthanide Phosphate-based Nanoparticles

Cyclic phosphazenes with positively charged substituents were investigated as surface modifiers for lanthanide phosphate nanoparticles. Cyclotriphosphazenes bearing aromatic (1, 2) and aliphatic (3‐6) substituents with terminal tertiary amino functions have been synthesized and subsequently quaternized by treatment with methyl iodide. In subsequent tests, their influence as surface modifiers for the lanthanide phosphate‐based nanoparticles was analysed with respect to the resulting particle solubility and the degree of surface interaction. While an interaction of the completely quaternized cyclic phosphazenes 2 and 4 with the nanoparticles leads to an agglomeration, stable nanocrystal‐linker complexes in methanol could be formed with the compounds 5 and 6. Aromatic functions were not suitable due to interference with the UV absorbance of the nanocrystals, while aliphatic side chains allowed a good fluorescence detection of the nanocrystals with UV excitation without any loss of intensity as compared to the untreated particles.