Mechanically Tunable Quantum Transport in Graphene Nanoribbons with Antiaromatic Motifs

Abstract

Nonbenzenoid graphene nanoribbons provide a versatile platform for tailoring electronic structures beyond conventional benzenoid π-conjugated systems, yet the impact of their topology on quantum transport remains largely unexplored. Here, we investigate electrical conductance through suspended ladder phenylene nanoribbons containing antiaromatic four-membered rings using scanning tunneling microscope lifting spectroscopy. As the nanoribbon is progressively detached from the substrate, differential conductance measurements reveal successive charge-state transitions accompanied by alternating Kondo resonances, demonstrating the dynamic generation of localized spins in an intrinsically closed-shell nanoribbon. Density functional theory calculations show that the antiaromatic topology reduces the HOMO–LUMO gap and induces a pronounced length dependence of the occupied frontier orbitals, which shift progressively toward and eventually across the electrode Fermi level with increasing suspended length, driving successive charge-state transitions. The transport behavior is quantitatively described within a double-barrier tunneling framework incorporating charge quantization and many-body interactions. These results suggest an antiaromaticity-driven mechanism for charge-state evolution and propose antiaromaticity as a molecular design principle for controlling charge and spin states in nonbenzenoid carbon nanostructures.