Functionalized Fullerene Nanomaterials: Evaluating Heteroatom Identity for Enhanced Charge-Transfer and Reactivity

This study explored the electronic and structural tunability of fullerene (C60) derivatives via functionalization with heteroatoms (O, S, Se) in mono-, di-, and tri-bridged configurations, including covalently modeled dimers. Calculations were performed using density functional theory (DFT) at the B3LYP/6-31G(d,p) level. Electronic descriptors such as total dipole moments (TDMs), HOMO–LUMO energy gaps (ΔE), global reactivity descriptors, total density of states (TDOS), molecular electrostatic potential (MESP) and non-covalent interactions (NCIs) were analyzed to elucidate how functionalization alters reactivity and stability. Key findings indicate that TDM increases and ΔE decreases in all functionalized C60; for example, the TDM increased from 0 Debye for C60 to 2.156 Debye for C60–O–S–Se, and ΔE decreased from 2.762 eV (C60) to 2.532 eV (C60–Se), indicating enhanced reactivity. This aligns with global reactivity descriptors such as reduced ionization energy and hardness. Mapped MESP surfaces showed activation around heteroatom sites. Quantum theory of atoms in molecules (QTAIM) and NCI analyses revealed that while mono-bridged structures retain covalent linkages, dimeric systems such as C60–O–C60 and C60–S–C60 relax into weak, van der Waals-type interactions. OPDOS (overlap population density of states) highlighted antibonding character between the fragments in the conduction region. These results demonstrate that heteroatom functionalization enhances the electronic properties of C60, making it a promising candidate for optoelectronic, organic photovoltaic, and sensor applications.