A research team from the University of Osaka has developed a porous crystal that forms a spring-like helical structure. The crystal can change its shape as solvent molecules move in and out of its internal spaces. Their findings, published in the journal Angewandte Chemie International Edition, could lead to new materials with unique properties. Helical or twisted crystals are known in some organic materials, but in porous materials, they have typically been very small or grouped together, making it hard to study how their internal structure relates to their overall shape. The team used an organic molecule based on pyrene, a compound known for its strong fluorescence and stability. By adjusting the crystallization conditions, they observed different crystal forms. At 60°C, the material formed straight, needle-like crystals. However, when the temperature was increased to 120°C and the solvent evaporated more quickly, the crystals formed a helical, spring-like shape. X-ray analysis showed that both forms of the crystal had nearly identical internal structures, suggesting that the change in shape was not due to a change in the internal arrangement of molecules. The researchers suggest that during rapid crystal growth, small irregularities in the molecular arrangement might get trapped, leading to uneven growth and the formation of a helical shape. However, this is still a hypothesis. Direct observation during the growth process is needed, and other factors, such as solvent effects and convection in the solution, could also play a role. The helical crystals have a high surface area of 1,185 square meters per gram, indicating their high porosity. They also retain their structure when heated above 300°C, making them thermally stable. When solvent molecules are removed from the pores, the helices loosen and extend, and when the solvent is reintroduced, they contract slightly. This ability to change shape in response to chemical stimuli could inspire new materials that move or organize molecules in specific ways. The study was led by Ichiro Hisaki, who noted that the discovery came from careful observation by graduate student Yuzuki Murata and challenged the assumption that crystals are rigid and straight.