Intervalence Charge Transfer Mediated by Silicon Nanoparticles

Stable silicon nanoparticles (SiNPs) were synthesized by using a wet chemical method with (3-aminopropyl)triethoxysilane as the silicon source and ethynylferrocene as the capping ligands by taking advantage of the unique chemical reactivity of acetylene moieties with silicon hydride on the nanoparticle surface, forming Si−CH=CH− interfacial bonds under UV photoirradiation. Transmission electron microscopic measurements showed good dispersion of the nanoparticles with an average core diameter of 2.96±0.46 nm. From UV/Vis absorption measurements, the nanoparticle bandgap was estimated to be 2.6 eV. XPS measurements confirmed the successful attachment of ethynylferrocene ligands onto the nanoparticle surface, with a footprint consistent with that of ferrocene. Electrochemically, the nanoparticles exhibited only one pair of voltammetric waves in the dark, suggesting a lack of effective electronic communication between the particle-bound ferrocenyl moieties, because of the low conductivity of the nanoparticle cores; whereas, under UV photoirradiation (365 nm), two pairs of voltammetric peaks were observed, with a potential spacing of 125 mV, suggesting that the nanoparticles behaved analogously to a Class II compound. This was ascribed to photo-enhanced electronic conductivity of the nanoparticle cores that facilitated intervalence charge transfer of the particle-bound ferrocene moieties.