A research team from Tianjin Normal University has developed a new approach to the precise chemical synthesis of carbon nanotubes, which could pave the way for their on-demand customization.

Known for their exceptional mechanical, electrical and optical properties, carbon nanotubes are considered a core component of next-generation technologies, with potential applications ranging from humanoid robots and targeted drug delivery to foldable transparent displays. But their wider use has long been limited by conventional manufacturing methods, which struggle to precisely control nanotube diameter, length and structure, leading to inconsistent performance.

To overcome that challenge, a team led by professor Li Chunju from the university's chemistry college, working with domestic and international partners, developed a novel molecular manufacturing strategy based on cycloparaphenylenes (CPPs) — ring-shaped molecules that serve as building blocks for carbon nanotubes.

"If a carbon nanotube is a train, a CPP is a standard carriage of that train," Li said. "By using it as a template for extended growth, we can theoretically produce carbon nanotubes with precise structures and uniform performance."

However, the synthesis of CPPs is no easy feat. Due to the high ring strain in their cyclic structure, traditional methods amount to directly weaving an extremely taut micro-scale rope loop with high precision. Preparation processes are often cumbersome and reliant on expensive metal catalysts.

To tackle that issue, the research team jumped out of the mindset of directly weaving a taut ring. Instead, they first constructed a macrocyclic molecule with a relatively relaxed structure, then tightened it through an efficient intramolecular reaction before ultimately shrinking it into the target nanoring.

"This is far easier and more flexible than making a taut nanoring molecule directly," Li said.

The process is highly efficient and holds strong potential for on-demand customization. When constructing the relaxed macrocycle in the first step, researchers can flexibly replace different molecular units and thereby produce nanorings of different sizes and properties.

Based on this simple and broadly applicable synthetic strategy, the research team has successfully constructed 20 structurally diverse CPP derivatives, enabling precise control over key physical properties such as light absorption and fluorescence emission.

"This research provides a new tool for the controlled synthesis of complex strained carbon architectures, which means we can eventually customize carbon nanotubes just like tailoring garments," Li said.

Wang Xiaojing contributed to this story.