Functionalization of Mechanochemically Passivated Germanium Nanoparticles via "Click" Chemistry
Germanium nanoparticles (Ge NPs) may be fascinating for their electronic and optoelectronic properties, as the band gap of Ge NPs can be tuned from the infrared into the visible range of solar spectru. Further functionalization of those nanoparticles may potentially lead to numerous applications ranging from surface attachment, bioimaging, drug delivery and nanoparticles based devices. Blue luminescent germanium nanoparticles were synthesized from a novel top-down mechanochemical process using high energy ball milling (HEBM) of bulk germanium. Various reactive organic molecules (such as, alkynes, nitriles, azides) were used in this process to react with fresh surface and passivate the surface through Ge-C or Ge-N bond. Various purification process, such as gel permeation chromatography (GPC), Soxhlet dailysis etc. were introduced to purify nanoparticles from molecular impurities. A size separation technique was developed using GPC. The size separated Ge NPs were characterize by TEM, small angle X-ray scattering (SAXS), UV-vis absorption and photoluminescence (PL) emission spectroscopy to investigate their size selective properties. Germanium nanoparticles with alkyne termini group were prepared by HEBM of germanium with a mixture of n-alkynes and α, ω-diynes. Additional functionalization of those nanoparticles was achieved by copper(I) catalyzed azide-alkyne ""click"" reaction. A variety of organic and organometallic azides including biologically important glucals have been reacted in this manner resulting in nanopartilces adorned with ferrocenyl, trimethylsilyl, and glucal groups. Additional functionalization of those nanoparticles was achieved by reactions with various azides via a Cu(I) catalyzed azide-alkyne ""click"" reaction. Various azides, including PEG derivatives and cylcodextrin moiety, were grafted to the initially formed surface. Globular nanoparticle arrays were formed through interparticle linking via ""click"" chemistry or ""host-guest"" chemistry. Copper(I) catalyzed ""click"" chemistry also can be explored with azido-terminated Ge NPs which were synthesized by azidation of chloro-terminated Ge NPs. Water soluble PEGylated Ge NPs were synthesized by ""click"" reaction for biological application. PEGylated Ge NP clusters were prepared using α, ω-bis alkyno or bis-azido polyethylene glycol (PEG) derivatives by copper catalyzed ""click"" reaction via inter-particle linking. These nanoparticles were further functionalized by azido β-cyclodextrin (β-CD) and azido adamantane via alkyne-azide “click” reactions. Nanoparticle clusters were made from the functionalized Ge NPs by “host-guest” chemistry of β-CD functionalized Ge NPs either with adamantane functionalized Ge NPs or fullerene, C60.