Preparation, Characterization, and Surface Modification of Trifluoroethyl Ester-Terminated Silicon Nanoparticles

Platinum-catalyzed hydrosilylation of hydrogen-terminated silicon nanoparticles (Si NPs) with 2,2,2-trifluoroethyl 4-pentenoate gave well-defined nanoparticles (NPs) with surface groups that are reactive toward amines. The particles showed a diameter of 1.4 ± 0.2 nm as revealed by transmission electron microscopy (TEM) measurements. Characterization with 1 H, 13 C and heteronuclear NMR techniques revealed that the trifluoroethyl pentenoate group is attached to the Si NP surface via the terminal carbon atom. The trifluoroethyl ester is reactive toward primary amines, allowing for additional surface functionalization. Modification of the Si NPs was performed with benzylamine, 1,2-diaminoethane, and propargylamine. The modification gave a complete substitution of the trifluoroethyl group to amide groups. The modified Si NPs were characterized in detail by a series of one-dimensional (1-D) and two-dimensional (2-D) NMR techniques and by FT-IR. The propargylamide-terminated Si NPs were further functionalized with an azide-terminated fluorescent dye (Azide-Fluor 585 sulphorhodamine) using a copper-catalyzed azide-alkyne cycloaddition reaction (CuAAC). Gel permeation chromatography and time-resolved fluorescence anisotropy spectroscopy of the dye reveal a significant increase in the hydrodynamic radius upon clicking of the dye. Additionally, NMR spectroscopy reveals the presence of a 1,2,3-triazole ring in the product, which confirms that the increase in the hydrodynamic radius is caused by the attachment of the dye to the Si NP surface via the CuAAC reaction.