The first example of a smart crystalline material, the 2:1 cocrystal of probenecid and 4,4'-azopyridine, which responds reversibly to multiple external stimuli (heat, UV light, and mechanical pressure) by twisting, bending, and elastic deformation without fracture is reported. This material is also able to self-heal on heating and cooling, thereby overcoming the main setbacks of molecular crystals for future applications as crystal actuators. The photo- and thermomechanical effects and self-healing capabilities of the material are rooted in reversible trans-cis isomerization of the azopyridine unit and crystal-to-crystal phase transition. Fairly isotropic intermolecular interactions and interlocked crisscrossed molecular packing secure high elasticity of the crystals.

Thermally Twistable, Photobendable, Elastically Deformable, and Self-Healable Soft Crystals.

The recent progress of charge-transfer complexes (CTCs) for application in many fields, such as charge transport, light emission, nonlinear optics, photoelectric conversion, and external stimuli response, makes them promising candidates for practical utility in pharmaceuticals, electronics, photonics, luminescence, sensors, molecular electronics and so on. Multicomponent CTCs have been gradually designed and prepared as novel organic active semiconductors with ideal performance and stability compared to single components. In this review, we mainly focus on the recently reported development of various charge-transfer complexes and their performance in field-effect transistors, light-emitting devices, lasers, sensors, and stimuli-responsive behaviors.

Multifunctional Features of Organic Charge-Transfer Complexes: Advances and Perspectives.

Elastically flexible crystals form an emerging class of materials that exhibit a range of notable properties. The mechanism of thermal expansion in flexible crystals of bis(acetylacetonato)copper(II) is compared with the mechanism of molecular motion induced by bending and it is demonstrated that the two mechanisms are distinct. Upon bending, individual molecules within the crystal structure reversibly rotate, while thermal expansion results predominantly in an increase in intermolecular separations with only minor changes to molecular orientation through rotation.

https://www.onlinelibrary.wiley.com/doi/epdf/10.1002/anie.201901968

Elastically Flexible Crystals have Disparate Mechanisms of Molecular Movement Induced by Strain and Heat.

The advancement of our understanding of stimuli-responsive molecular crystals has led to the realization that they hold great yet unexplored potential as adaptive materials. Although molecular crystals that exhibit a single mechanical response to a single input stimulus are now abundant, crystals that are capable of response to multiple stimuli are rather scarce. Here we report two photoswitchable acylhydrazone derivatives, Ac-1 and Ac-2, which respond to light as well as to mechanical force. Upon application of localized mechanical stress, the anhydrous (Ac-1a) and monohydrate (Ac-1h) crystals of Ac-1 undergo plastic shearing deformation and bending, whereas monohydrate crystals of Ac-2 undergo elastic deformation. When they are exposed to UV light, crystals of Ac-1h and Ac-2 undergo photoinduced bending; on the other hand, crystals of Ac-1a and thicker crystals of Ac-2 exhibit photosalient effect (light-induced leaping). It is demonstrated that the synergistic action of multiple stimuli (UV light and fo...

Crystalline Acylhydrazone Photoswitches with Multiple Mechanical Responses

Lactate serves as a biomarker for a plethora of microbial contamination in cow milk. In this context, a novel nickel-metal organic framework (Ni-MOF) modified platinum electrode was fabricated for the effective and reliable detection of lactate in cow milk samples. The Ni-MOF of mean size 12 μm in length and 0.7 nm in width was synthesized by an inexpensive mild solution method. The Ni-MOF modified platinum, platinum wire and Ag/AgCl were employed as the working, counter and reference electrodes to design a potentiostatic three-electrode configuration device. The developed Ni-MOF modified platinum electrode exhibits good sensitivities (106.617 and 29.533 μA mM−1) towards lactate over the wide linear ranges of 0.01–0.9 and 1–4 mM with a correlation coefficient of R2 = 0.99, a detection limit of 5 μM, a repeatability of 0.57% RSD and a stability of 95.3% for 20 days. The nano-flower like morphology of Ni-MOF provides accessible sites for the electro-oxidation of lactate and thereby high sensitivity to lactate. Furthermore, the developed electrode remained free from potential interfering species and thus provides a promising tool for rapid detection of lactate in cow milk samples.

Mousumi Hazarika

Papers

Plastically bendable crystals of probenecid and its cocrystal with 4,4′-Bipyridine