doi:10.1038/nindia.2016.111 Published online 26 August 2016
By modifying three organic compounds, researchers have synthesized single crystals that show remarkable plasticity under mechanical stress, making them potentially useful for fabricating flexible optoelectronic devices1.
Current methods make single crystals that are brittle. To make flexible single crystals, the researchers adopted a crystal-engineering approach. This involved adding weakly interacting groups to the periphery of planar molecules of three organic compounds: naphthalene diimide, benzoic acid and a compound derived from vanillin.
The planar organic molecules self-assembled into single crystals by one molecule stacking on another in layers. This resulted in the weakly interacting groups lying on the crystal surfaces, which caused the layers to stick together loosely, forming slip planes.
When subjected to mechanical stress, the molecular sheets in the crystals slid one over another along the slip planes with minimal friction, causing the crystals to bend. By exploiting such molecular movements, the researcher could mold the crystals into acronyms such as “SEM” and “IIRS” and words such as “organic crystal.”
The crystals retained their structural integrity even when bent at large angles, such as in the letters “S” and “M”. Some of the crystals made from naphthalene diimide could even be bent by 360 degrees, indicating that they have excellent flexibility.
“Since the crystals can respond to external stimuli such as mechanical stress, light and heat, they could be used to make pressure sensors and mechanical actuators,” says lead scientist Chilla Malla Reddy from the Indian Institute of Science Education and Research, Kolkata.