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.