Narrowing band gap chemically and physically: conductive dense hydrocarbon

Enhancing intermolecular interactions can reduce the band gap energy of organic molecules. Consequently, certain polycyclic aromatic hydrocarbons – typically wide-band-gap insulators – may undergo insulator-to-metal transitions under simple compression. This pressure-induced electronic transition could enable the transformation of non-metallic organic materials into states exhibiting intriguing electronic properties, including high-temperature superconductivity. Here we investigate a pressure-induced transition in dicoronylene (C48H20), an insulator at ambient conditions, to a semiconducting state with a resistivity drop of three-orders-of-magnitude at 23.0 GPa. Through the complementary integration of transport property measurements with in situ UV-Visible absorption, Raman spectroscopy and synchrotron X-ray diffraction experiments, as well as first-principles studies, we propose a possible mechanism for the pressure-driven electronic structure evolution of C48H20. The discovery of an intriguing electronic transition at pressures well below the megabar observed marks a promising step towards realizing a single-component purely hydrocarbon molecular metal. Polycyclic aromatic hydrocarbons, typically wide-band-gap insulators, may transform into metals under compression, offering potential for interesting electronic properties. Here, a pressure-induced insulator-to-semiconductor transition in dicoronylene was demonstrated, achieving a resistivity drop at 23.0 GPa, and a mechanism was proposed for this transition, paving the way for hydrocarbon-based molecular metals.