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

Herein, a series of molecular actuators based on thecrystals 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 uniquebending behavior under UV irradiation. The 1D crystals of BOAF4 and BTAF4 bent towards light, whereas those of BOAF24 and BTAF24 bent away from light. Although the chemical structures of these compounds are similar, we found that the F⋯H–C interaction played a key role in their 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 photomechanical property, we achieved the potential application in pushing objects, as well as enriching and removing pollutants. Hence, the molecular actuators with different bending behavior could be fabricated via introducing different number of F atom, which may open a novel gate for crystal engineering.