Partially π-exposed 3D carbohelicene for mechanical tuning of conductance and thermopower in single-molecule junctions

Helicenes, composed of ortho-fused benzene rings, possess a spring-like π-backbone, enabling electron delocalization through both bonds and space. Theoretical predictions suggest that mechanical stretching or compression of molecular junctions in higher-order diazahelicenes could increase conductance and thermopower. However, this theory has not been experimentally verified, likely due to the difficulty of forming robust higher-order helicene molecular junctions using existing heteroatom anchors and the high electrical resistance of metal–heteroatom bonds. Thus, constructing mechanically stable single-molecule junctions through multipoint metal–π interactions would be ideal. Here we verify this theory using a 3D carbohelicene with a shielded π-face bearing bulky tert-butyl groups and an exposed π-face lacking tert-butyl groups. This partially π-exposed 3D carbohelicene forms a robust monolayer on the Au(111) substrate at room temperature through multipoint metal–π interactions. Using the break-junction technique, we demonstrate a compression-induced increase in both peak conductance (10–3–10–2 G0) and thermopower (−44 μV/K). A theory has suggested that mechanical deformation in helicenes with spring-like backbones could effectively modulate both conductance and thermopower in molecule electronics. Fujii et al. verify this using a three-dimensional carbohelicene-based break-junction, demonstrating a thermopower of −44 μV/K.