Size compatibility and concentration dependent supramolecular host–guest interactions at interfaces

The quantification of supramolecular host–guest interactions is important for finely modulating supramolecular systems. Previously, most host–guest interactions quantified using force spectroscopic techniques have been reported in force units. However, accurately evaluating the adhesion energies of host–guest pairs remains challenging. Herein, using a surface forces apparatus, we directly quantify the interaction energies between cyclodextrin (CD)-modified surfaces and ditopic adamantane (DAd) molecules in water as a function of the DAd concentration and the CD cavity size. The adhesion energy of the β-CD–DAd complex drastically increased with increasing DAd concentration and reached saturation. Moreover, the molecular adhesion energy of a single host–guest inclusion complex was evaluated to be ~9.51 kBT. This approach has potential for quantifying fundamental information toward furthering the understanding of supramolecular chemistry and its applications, such as molecular actuators, underwater adhesives, and biosensors, which require precise tuning of specific host–guest interactions.

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

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

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

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

Robust thermoelastic microactuator based on an organic molecular crystal

Mechanically responsive molecular crystals that reversibly change shape triggered by external stimuli are invaluable for the design of actuators for soft robotics, artificial muscles and microfluidic devices. However, their strong deformations usually lead to their destruction. We report a fluorenone derivative (4-DBpFO) showing a strong shear deformation upon heating due to a structural phase transition which is reproducible after more than hundred heating/cooling cycles. Molecular dynamic simulations show that the transition occurs through a nucleation-and-growth mechanism, triggered by thermally induced rotations of the phenyl rings, leading to a rearrangement of the molecular configuration. The applicability as actuator is demonstrated by displacing a micron-sized glass bead over a large distance, delivering a kinetic energy of more than 65 pJ, corresponding to a work density of 270 J kg−1. This material can serve as a prototype structure to direct the development of new types of robust molecular actuators.