Positive/Negative Phototropism: Controllable Molecular Actuators with Different Bending Behavior

Herein, a series of molecular actuators based on the crystals of (E)‐2‐(4‐fluorostyryl)benzo[d]oxazole (BOAF4),
(E)‐2‐(2,4‐difluorostyryl)benzo[d]oxazole (BOAF24), (E)‐2‐(4‐fluorostyryl)benzo[d]thiazole (BTAF4) and (E)‐2‐
(2,4‐difluorostyryl)benzo[d]thiazole (BTAF24) showed unprecedented different bending behavior under UV
irradiation. BOAF4 and BTAF4 bent towards light, whereas BOAF24 and BTAF24 bent away from light.
Although the chemical structures of these compounds are similar, we found out the F‒H‒C interaction was
the main driving force for the different molecular packing in the crystals, which led to the positive/negative
phototropism of the actuators. Moreover, the theoretical calculation was carried out to reveal the mechanical
properties of the crystals. Taking advantage of the photo responsive property, we achieved the potential
application in pushing objects, as well as enriching and removing pollutants. This system not only achieved a
class of molecular actuators with different bending behavior through introducing different number of F atom,
but also realized pushing and catching behavior within one molecule, which opens a novel gate for crystal
engineering