Organic-inorganic azafullerene-gold C(59)N-Au nanohybrid: synthesis, characterization, and properties.

Azafullerene (C59 N) was functionalized using a Mannich-type reaction and then subsequently condensed with lipoic acid to yield dithiolane-modified C59 N. In the following step, the extended dithiolane moiety from the C59 N 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 C59 N to produce the C59 N/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 C59 N/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 C59 N/DT⋅Au nanohybrid. Excited-state interactions in C59 N/DT⋅Au were probed by photoluminescence assays. It was found that the weak emission of C59 N at 819 nm was blueshifted by 14 nm in C59 N/DT⋅Au, but was stronger in intensity, thus suggesting energy transfer to C59 N, within the organic-inorganic C59 N/DT⋅Au nanohybrid. Finally, with the aid of pump-probe measurements and transient absorption spectroscopy, the formation of the singlet excited state of C59 N was identified.