Chemical Functionalization Meets Enhanced Electrical Conductivity in Iron Oxide Nanoparticles

Abstract

An excellent combination of either oxides or metallic nanoparticles (NPs) and functional π-electron rich conjugated molecules can originate a variety of intriguing phenomena convenient for technological applications. Functional π-conjugated aromatic molecules can hold the potential to control the size, shape, morphology, and optoelectronic properties of nanoparticles through the formation of covalent interfaces. Interfacial charge transfer at the nanoparticles−molecules interfaces plays vital roles in modulating photophysical and electrical conductivity properties, which found enormous applications in catalysis, electrical, and magnetism. This work illustrates iron oxide nanoparticles (Fe₃O₄ NPs) capped with in situ generated aryl radicals for tuning electrical properties. Organic molecules with different functional groups are covalently attached to the surface of Fe₃O₄ NPs through radical formation. An electrical insulating pristine Fe₃O₄ NPs turns into semiconductor behavior upon aryl radical functionalization, which is due to the synergistic and efficient intermolecular charge transfer between Fe₃O₄ NPs of mixed valence metal ions (Fe²⁺, a d⁶ electronic system, and Fe³⁺, a d⁵ electronic system) and π-electron rich aromatic molecules (donor–acceptor interactions). A theoretical framework strongly supports the experimental findings. These findings on tuning the electrical conductivity of nanoparticles using a small molecule can provide a promising avenue for a wide range of electronic applications.