Scientists have created the longest single-atom copper chains ever made, using extreme pressure to transform copper phthalocyanine (CuPc) into atomic-scale wires. CuPc is a compound commonly used to produce the blue pigment known as phthalo blue. Under immense pressure—over 21 gigapascals, which is about 200,000 times the pressure of Earth’s atmosphere—the researchers converted CuPc crystals into copper atomic chains that stretched for micrometers. These chains were encased in a carbon sheath, forming structures that resembled household power cords at the atomic level. The resulting wires, known as single-metal-atom chains (sSMACs), have three distinct layers and exhibit strong anisotropy, meaning electricity flows easily along the wire but not easily sideways across it. Each of these atomic wires contains over 4,000 copper atoms, making them two to three orders of magnitude longer than any previously made single-atom chains. The previous record for such chains was only 28 atoms. These one-dimensional metal wires are the thinnest possible and are of great interest due to their unique electronic, magnetic, and catalytic properties. Scientists are also using them to explore how matter behaves at the smallest scales. While single-atom chains have been made before, creating longer ones has been difficult due to the limitations of traditional synthesis methods. Traditionally, SMACs are grown in liquid solutions with ligands—molecular structures that help stabilize the metal atoms. However, as chains grow longer, these ligands can become insoluble in the liquid, halting the synthesis process and resulting in wires shorter than 10 atoms. The researchers bypassed this problem by using a high-pressure solid-state reaction. Starting with copper phthalocyanine, whose flat, ring-like molecules naturally stack like coins, they placed the crystals into a diamond anvil cell—a device that applies extreme pressure. This caused the copper atoms to be pushed very close together, while the outer carbon rings of the molecules fused to form a tough, diamond-like carbon tube around the copper core. The resulting nanowires have three concentric layers: a core of copper atoms, a conductive ring made of carbon and nitrogen atoms, and an outer carbon sheath that protects the wire. These wires are stable in air and can withstand harsh conditions like highly acidic solutions and ultrasonic vibrations. Electrical current flows more than 10 times faster along the wire than sideways, and computer models suggest that a perfect, defect-free wire could conduct electricity 1,000 times faster. The copper atoms themselves do not conduct the electricity; instead, the overlapping carbon and nitrogen atoms in the ring framework facilitate the current. These findings highlight the potential of high-pressure synthesis for creating ultralong atomic copper wires, despite the challenge of achieving the extreme pressures required for such production.