Gold Nanoparticles Functionalized with Fully Conjugated Fullerene C60 Derivatives as a Material with Exceptional Capability of Absorbing Electrons

We report a highly electron-absorbing material (electron-sponge) obtained by coupling gold nanoparticles (AuNPs, 8 nm in diameter) with fullerene C-60 spheres by fully conjugated linker molecules. This goal has been achieved through synthesis of a new class of conducting thionoester-substituted and thioketone-substituted azahomo-[60]-fullerenes. The obtained C-60 derivatives have been found to possess the capability of binding covalently to the surface of gold. Thus, for the first time, we show that thioketone and thionoester moieties can be successfully employed as new anchoring groups for conjugated fullerene derivatives. High-resolution X-ray photoelectron spectroscopy studies have revealed that the ligands are attached to the gold surface of AuNPs through strong Au-S bonding. One of the synthesized C-60 derivatives, O-butyl 4-(azahomo(C-60-I-h)fullerene)benzothioate (C-60-BCT-OBu), has been investigated in detail. The C-60-BCT-OBu-coated AuNPs form a highly insoluble precipitate, which can be easily dissolved in toluene into individual AuNPs using cationic surfactants. The precipitate has been found to exhibit an extraordinary capability of absorbing electrons. A single AuNP can absorb on average about 4500 electrons in an experimental condition in which tetrahydrofuran suspension of the precipitate of the C-60-BCT-OBu-coated AuNPs is charged in a lithium naphthalide-mediated process. The electrical properties of the AuNPs are successfully explained by a model in which the C-60-BCT-OBu-coated AuNP is represented by an equipotential heterostructure composed of C-60 spheres connected with the gold AuNP core by conducting linkers.