Interfacial Electron Transfer in Self-Assembled Arylated Gold Nanoparticles-Ferrocenium Organometallics

The incorporation of ferrocenium in aryl gold nanoparticles has been investigated to synthesize a robust assembly of Fc-aryl-AuNPs. The oxidation of ferrocene via interfacial electron transfer in a two-phase redox reaction using a carboxyl-functionalized aryldiazonium gold(III) salt yielded Fc-aryl-AuNPs. SEM-STEM and HR-TEM revealed 15-30 nm nanoparticles comprising Au cores, with XPS established a fully metallic gold(0) core with a slightly positive BE shift due to Fc⁺ -Au interaction and iron(III) species. The reflection electron energy-loss spectroscopy (REELS), ultraviolet photoelectron spectroscopy (UPS), and diffuse reflectance spectroscopy (DRS) investigation confirmed a low-energy band gap (2.4 eV; optical Eg = 2.1 eV), a valence band maximum (VBM) at ∼1.4 eV below the Fermi level, and an ionization potential of 6.7 eV. It was also supported by the self-consistent field (ΔSCF) method, calculated using density functional theory (DFT), with an Fc-aryl-Au₃₈ model. Bader charge and charge density difference (CDD) analysis revealed charge transfer from the Au core via the carboxyl bridge. Fc-aryl-AuNPs shown for one-electron oxidation using two redox models: hemoglobin, with a buried heme-Fe(II) center, showed UV hyperchromicity without oxidation, while K₄[Fe(CN)₆] underwent outer-sphere electron transfer to form Fe(II)/Fe(III) species. This redox behavior makes Fc-aryl-AuNPs promising in catalysis, biosensing, and engineered nanomaterials.