Anomalous Interfacial Electronic Structure of Solid Films of Non-Planar pi-Conjugated Molecule 6-Cycloparaphenylene

n-Cycloparaphenylene ([n]CPP) is a non-planar pi-conjugated molecule with a macrocyclic, hoop-like molecular structure that allows for control of the electronic structure unlike planar molecules. Thus, [n]CPP has the potential as a novel functional material in organic electronics. In this study, the unique electronic structure of [6]CPP is revealed, which originates from its macrocyclic molecular structure by comparison with p-sexiphenyl, a linear molecule also consisting of six phenylenes. The morphology of the vapor-deposited [6]CPP polycrystalline film is found to be highly dependent on the evaporation rate and the type of substrate. It is also found that a [6]CPP molecular layer is formed at the interface between the film and gold substrate, which has a much smaller energy gap than that of the bulk [6]CPP. This anomalous molecular layer is composed of [6]CPP molecules with a smaller dihedral angle than that in the bulk because of the interaction with a gold substrate. When [6]CPP is used as a semiconducting layer in electronic devices, this layer can play a role in improving the charge injection efficiency from the electrode to the [6]CPP film.