Organic–Inorganic Azafullerene-Gold C59N-Au Nanohybrid: Synthesis, Characterization, and Properties

Azafullerene (C59N) was functionalized using a Mannich-type reaction and then subsequently condensed with lipoic acid to yield dithiolane-modified C59N. In the following step, the extended dithiolane moiety from the C59N core was utilized to decorate the azafullerene sphere with gold nanoparticles (Au NPs). The latter were initially stabilized with dodecanothiol (DT⋅Au) and then integrated on azafullerene through a ligand exchange reaction with the dithiolane-functionalized C59N to produce the C59N/DT⋅Au nanohybrid. The nanohybrid was fully characterized by spectroscopy and microscopy, revealing the formation of spherical nanoparticles with a diameter in the range of 2–5 nm, as imaged by HR-TEM. In the electronic absorption spectrum of C59N/DT⋅Au nanohybrid, the characteristic surface plasmon band (SPB) of Au NPs was observed, however, it was redshifted compared with that of DT⋅Au. The redshift of the SPB is indicative of closer interparticle proximity of Au NPs, in accordance with the formation of aggregated NPs as observed by TEM, in C59N/DT⋅Au nanohybrid. Excited-state interactions in C59N/DT⋅Au were probed by photoluminescence assays. It was found that the weak emission of C59N at 819 nm was blueshifted by 14 nm in C59N/DT⋅Au, but was stronger in intensity, thus suggesting energy transfer to C59N, within the organic–inorganic C59N/DT⋅Au nanohybrid. Finally, with the aid of pump–probe measurements and transient absorption spectroscopy, the formation of the singlet excited state of C59N was identified.