Fused-Ring Nanothread Synthesized via High-Pressure Polymerization of Naphthalene

Carbon nanothreads (CNThs) are one-dimensional saturated carbon nanomaterials with exceptional mechanical properties. Polycyclic aromatic hydrocarbons (PAHs) are anticipated to form thicker, multi-ring CNThs with improved mechanical performance under high-pressure. Herein, we systematically investigated the high-pressure polymerization of naphthalene, the simplest PAH, using multiple cutting-edge methods. Naphthalene molecules adopt a herringbone stacking along the a-b direction, and underwent reactions along this stacking direction above 20 GPa, affording one-dimensional unsaturated CNThs with the [4+2] cycloaddition reaction as the dominant reaction path. In contrast to the formation of many reported CNThs, the nucleation of the naphthalene-derived CNThs occurs during compression while their growth proceeds during decompression; this behavior is likely common among aromatics with a herringbone structure. The unit cell of the as-obtained CNTh crystal was determined, and a possible structure of the CNTh product was proposed. Our research reveals the polymerization characteristics of naphthalene under high-pressure, highlighting that the slip-angle and herringbone-angle play an important role in governing the polymerization pathway.