Dual-State Ambipolar Charge Transport in Antiaromatic [4]cyclodibenzopentalene Single-Molecule Nanohoops.

Antiaromatic compounds are of great interest due to their narrow highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gaps, high reactivity, and enhanced charge mobility, yet their role in single-molecule electronics is still not well understood. Using electrochemically controlled scanning tunneling microscopy break junction (ECSTM-BJ) measurements, we compared the energy-alignment-dependent conductance of the aromatic [10]cycloparaphenylene ([10]CPP) and the antiaromatic [4]cyclodibenzopentalene ([4]CDBP). While [10]CPP showed a single conductance state via the HOMO, [4]CDBP exhibited two distinct states involving both the HOMO and LUMO. Our analysis and DFT calculations attribute this dual-state behavior to unique anchoring mode and energy-level realignment within a narrow HOMO-LUMO gap. This property enables electron- and hole-dominated pathways that depend on the anchoring configuration and coexist at a fixed gate potential. This phenomenon, also observed in the [4]CDBP⊃C60 structure, highlights the potential of antiaromatic molecules for advanced molecular electronics.