Mechanically Flexible Organic Crystals Achieved by Introducing Weak Interactions in Structure: Supramolecular Shape Synthons

Controlling mechanical properties of ordered organic materials remains a formidable challenge, despite their great potential for high performance mechanical actuators, transistors, solar cells, photonics, and bioelectronics. Here we demonstrate a crystal engineering approach to design mechanically reconfigurable, plastically flexible single crystals (of about 10) of three unrelated types of compounds by introducing active slip planes in structures via different noninterfering supramolecular weak interactions, namely van der Waals (vdW), π-stacking, and hydrogen bonding groups. Spherical hydrophobic groups, which assemble via shape complementarity (shape synthons), reliably form low energy slip planes, thus facilitating an impressive mechanical flexibility, which allowed molding the crystals into alphabetical characters to spell out "o r g a n i c c r y s t a l". The study, which reports the preparation of a series of exotic plastic crystals by design for the first time, demonstrates the potential of soft interactions for tuning the mechanical behavior of ordered molecular materials, including those from π-conjugated systems.