Dynamic supramolecular snub cubes.

Mimicking the superstructures and properties of spherical biological encapsulants such as viral capsids and ferritin offers viable pathways to understand their chiral assemblies and functional roles in living systems. However, stereospecific assembly of artificial polyhedra with mechanical properties and guest-binding attributes akin to biological encapsulants remains a formidable challenge. Here we report the stereospecific assembly of dynamic supramolecular snub cubes from 12 helical macrocycles, which are held together by 144 weak C-H hydrogen bonds.

Charge-transfer mediated J-aggregation in red emitting ultra-small-single-benzenic -fluorophore crystals.

Red emission in crystals has been observed with an ultra-small-single-benzenic -fluorophore () with a molecular weight (MW) of only 197 Da, bettering the literature report of fluorophores with the lowest MW = 252 Da. Supramolecular extensive hydrogen-bonding and J-aggregate type centrosymmetric discrete-dimers or a 1D chain of s led to red emission ( = 610-636 nm) in crystals. Unlike in the solution phase showing one absorption band, in thin films and in crystals the transition from the S state to both the S state and S state becomes feasible.

Metal-Assisted Carbohydrate Assembly.

The sequence-controlled assembly of nucleic acids and amino acids into well-defined superstructures constitutes one of the most revolutionary technologies in modern science. The elaboration of such superstructures from carbohydrates, however, remains elusive and largely unexplored on account of their intrinsic constitutional and configurational complexity, not to mention their inherent conformational flexibility. Here, we report the bottom-up assembly of two classes of hierarchical superstructures that are formed from a highly flexible cyclo-oligosaccharide─namely, cyclofructan-6 (CF-6).

Autonomous self-healing organic crystals for nonlinear optics.

Non-centrosymmetric molecular crystals have a plethora of applications, such as piezoelectric transducers, energy storage and nonlinear optical materials owing to their unique structural order which is absent in other synthetic materials. As most crystals are brittle, their efficiency declines upon prolonged usage due to fatigue or catastrophic failure, limiting their utilities. Some natural substances, like bone, enamel, leaf and skin, function efficiently, last a life-time, thanks to their inherent self-healing nature.

Photosalience and Thermal Phase Transitions of Azobenzene- and Crown Ether-Based Complexes in Polymorphic Crystals.

Stimuli-responsive molecular crystals have attracted considerable attention as promising smart materials with applications in various fields such as sensing, actuation, and optoelectronics. Understanding the structure-mechanical property relationships, however, remains largely unexplored when it comes to functionalizing these organic crystals. Here, we report three polymorphic crystals (, , and ) formed by the non-threaded complexation of a dibenzo[18]crown-6 (DB18C6) ether ring and an azobenzene-based ammonium cation, each exhibiting distinct thermal phase transitions, photoinduced deformations, and mechanical behavior.

Dual Nanomechanics in Anisotropic Porous Covalent Organic Framework Janus-Type Thin Films.

Empowered by crystalline ordered structures and homogeneous fabrication techniques, covalent organic frameworks (COFs) have been realized with uniform morphologies and isotropic properties. However, such homogeneity often hinders various surface-dependent properties observed in asymmetric nanostructures. The challenge remains to induce heterogeneity in COFs by creating an asymmetric superstructure such as a Janus thin film.

Autonomous self-repair in piezoelectric molecular crystals.

Living tissue uses stress-accumulated electrical charge to close wounds. Self-repairing synthetic materials, which are typically soft and amorphous, usually require external stimuli, prolonged physical contact, and long healing times. We overcome many of these limitations in piezoelectric bipyrazole organic crystals, which recombine following mechanical fracture without any external direction, autonomously self-healing in milliseconds with crystallographic precision.

Self-Assembly-Driven Nanomechanics in Porous Covalent Organic Framework Thin Films.

Nanomechanics signifies a key tool to interpret the macroscopic mechanical properties of a porous solid in the context of molecular-level structure. However, establishing such a correlation has proved to be significantly challenging in porous covalent organic frameworks (COFs). Structural defects or packing faults within the porous matrix, poor understanding of the crystalline assembly, and surface roughness are critical factors that contribute to this difficulty.

Mechanical-Bending-Induced Fluorescence Enhancement in Plastically Flexible Crystals of a GFP Chromophore Analogue.

Single crystals of optoelectronic materials that respond to external stimuli, such as mechanical, light, or heat, are immensely attractive for next generation smart materials. Here we report single crystals of a green fluorescent protein (GFP) chromophore analogue with irreversible mechanical bending and associated unusual enhancement of the fluorescence, which is attributed to the strained molecular packing in the perturbed region. Soft crystalline materials with such fluorescence intensity modulations occurring in response to mechanical stimuli under ambient pressure conditions will have potential implications for the design of technologically relevant tunable fluorescent materials.

Mechanophotonics: Flexible Single-Crystal Organic Waveguides and Circuits.

We present the one-dimensional optical-waveguiding crystal dithieno[3,2-a:2',3'-c]phenazine with a high aspect ratio, high mechanical flexibility, and selective self-absorbance of the blue part of its fluorescence (FL). While macrocrystals exhibit elasticity, microcrystals deposited at a glass surface behave more like plastic crystals due to significant surface adherence, making them suitable for constructing photonic circuits via micromechanical operation with an atomic-force-microscopy cantilever tip. The flexible crystalline waveguides display optical-path-dependent FL signals at the output termini in both straight and bent configurations, making them appropriate for wavelength-division multiplexing technologies.

Metal-like Ductility in Organic Plastic Crystals: Role of Molecular Shape and Dihydrogen Bonding Interactions in Aminoboranes.

Ductility is a common phenomenon in many metals but is difficult to achieve in molecular crystals. Organic crystals bend plastically on one or two face-specific directions but fracture when stressed in any other arbitrary directions. An exceptional metal-like ductility and malleability in the isomorphous crystals of two globular molecules, BH NMe and BF NMe , is reported, with characteristic tensile stretching, compression, twisting, and thinning.

Mechanically interlocked architecture aids an ultra-stiff and ultra-hard elastically bendable cocrystal.

Molecular crystals are not known to be as stiff as metals, composites and ceramics. Here we report an exceptional mechanical stiffness and high hardness in a known elastically bendable organic cocrystal [caffeine (CAF), 4-chloro-3-nitrobenzoic acid (CNB) and methanol (1:1:1)] which is comparable to certain low-density metals. Spatially resolved atomic level studies reveal that the mechanically interlocked weak hydrogen bond networks which are separated by dispersive interactions give rise to these mechanical properties.