Luminescent Möbius Strip of a Flexible Halogen-Bonded Cocrystal Evolved from Ring and Helix

Elastic circular organic microcrystals prepared by photoinduced delamination

Circular organic crystals are essential as optically transducive components in flexible organic optoelectronics, yet this crystal habit is not easily obtained through traditional crystallization approaches. Here, we present a photoresponsive organic crystalline material that when exposed to ultraviolet or visible light, initially undergoes photoinduced bending, followed by photosalient effect and accompanied by delamination to elastic quasicircular microcrystals. Curvature analysis under different conditions confirms the controllability of this process. Light at 365 nm, 405 nm, and 445 nm generates microcrystals with high curvatures (11-12 mm-1), while 470 nm light produces lower curvature (5 mm-1), aligning with the absorption profile. Increasing the excitation power from 15 mW to 150 mW results in increase of the yield of microcrystals with high curvatures (10-20 mm-1) from 20% to 94%. This light-driven fabrication method provides a controlled and reproducible means of realizing rare crystal morphologies, highlighting the potential for exploring quantitative relationships between such morphologies and their unconventional optical properties.

Assembly Orientation Engineering of Organic Microcrystal Laser for Modulating Cavity Dimension

The modulation of cavity dimension is crucial for the realization of versatile micro-/nanolasers, yet the fabrication of molecular crystals is derived from the high-orientation assembly mode of molecules, limiting the optical cavity to a low-dimensional anisotropic topography with sharp corners and high thresholds. Here, we propose an innovative strategy to achieve the assembly orientation engineering of organic microcrystals for flexibly modulating cavity dimension. The isotropic and anisotropic assembly orientations generate different-dimensional microcavity structures (one-dimensional microbelts and three-dimensional (3D) microspheres) with distinct lasing actions. The 3D microspheres with perfect spherical morphology and strong light confinement capability function as low-threshold whispering gallery-mode microlasers. Moreover, the single-crystalline microbelts with smooth lateral sides act as Fabry-Pérot-mode lateral-cavity microlasers, which are formed between two lateral faces of the microbelts. The results offer useful insights into exploiting multidimensional micro-/nanolasers for integrated photonic circuits.

Emergent chiral and topological nanoarchitectonics in self-assembled supramolecular systems

The fabrication of structures with designated topologies at the nanoscale is an intriguing issue, attributed to the possibility of both imparting unique properties to functional materials and unravelling the codes that lie in many natural systems. As a significant bottom-up approach, the self-assembly strategy is potent in formulating various exquisite structures. While the building of common types of miniaturized structures such as tubes, twists and spheres has been investigated in depth to gain insight into the intrinsic principles that dictate their formation and functions, the preparation of peculiar topological nanostructures is still scattered and unsystematic. In parallel, chirality is among the most ubiquitous phenomena of fundamental significance in nature and is in close relationship with the origin of life. Essentially, chirality represents a type of orderliness and thus may interplay with peculiar topologies in an orchestrated and serendipitous way. In this review, we describe the development of constructing emergent chiral and topological nanoarchitectures via the self-assembly method, mainly focusing on structures including toroids, catenanes, Möbius strips, spirals and fractals. In addition, other types involving toruloids/kebabs, trumpets and bamboos, screws, dendritic and lamellar twists are also exemplified. The design of building blocks and various self-assembling strategies towards these target architectures are highlighted in this review, in an effort to provide an overview of the feasible approaches that facilitate the tailored construction of mesoscopic structures.

Flexible Organic Crystalline Fibers and Loops with Strong Second Harmonic Generation

Flexible organic crystals represent a novel class of smart materials that open many opportunities for optical applications. While it has been established that elastic or plastic deformation of slender molecular crystals can be commonly induced by external intervention, crystals that grow in bent or curled shapes naturally are rarely reported. This study introduces an extraordinarily flexible organic crystalline fibrous material, (Z)-3-(2,3-dichloropyridin-4-yl)-2-(3,5-dimethylphenyl)acrylonitrile (DPA), that crystallizes both as straight and curled crystals. Crystals of DPA are easily obtained from solution either as long fibers or as crystals that are curled to various extent, and sometimes even closed into a loop. The straight crystalline fibers can be bent mechanically by applying force or photochemically by exposure to ultraviolet light. The straight and curled crystals are both polar and capable of highly efficient second harmonic generation (SHG) with respective intensities of 2.03 ± 0.15 and 1.52 ± 0.12 times (equivalent strain ≈ 1%) that of urea. Curling during crystal growth provides direct access to curved SHG-active flexible organic optical waveguiding elements, such as crystalline optical ring resonators, thereby circumventing the necessity for manual crystal bending, which is usually not readily scalable. This work highlights the unconventional properties and capabilities that fibrous molecular crystalline materials bring to the global materials space and their potential applications as shape-conforming, nonlinear organic materials.

Macroscopic Gold Cluster Helical Tendrils

Handedness-controllable macroscopic helices are needed for understanding the chirality transfer through scales and design of high-performance devices. Bottom-up self-assembly rarely affords macroscopic helical superstructures because of accumulating disorder that is difficult to avoid during hierarchical self-assembly. Here, we demonstrate that tetragold Au4 clusters can assemble into macroscopic helices at the centimeter scale. Halogen-bond induces hierarchical self-assembly from nanotubes to aslant stacked nanotubes and finally to macrohelices. Sacrificial template synthesis via solvent-corrosion sufficiently removes the embedded 1,3,5-trifluoro-2,4,6-triiodobenzene to produce helical skeletons. Homochiral macroscopic tendrils are controllably synthesized by chiral halogen bonding donors, allowing high-fidelity chiral amplification. This work contributes to the development of macroscopic helical superstructures by hierarchical assembly.

Biomimetic light-harvesting antennas via the self-assembly of chemically programmed chlorophylls

The photosynthetic pigment "chlorophyll" possesses attractive photophysical properties, including efficient sunlight absorption, photoexcited energy transfer, and charge separation, which are advantageous for applications for photo- and electro-functional materials such as artificial photosynthesis and solar cells. However, these functions cannot be realized by individual chlorophyll molecules alone; rather, they are achieved by the formation of sophisticated supramolecules through the self-assembly of the pigments. Here, we present strategies for constructing and developing artificial light-harvesting systems by mimicking photosynthetic antenna complexes through the highly ordered supramolecular self-assembly of synthetic dyes, particularly chlorophyll derivatives.

Symmetry-Breaking and Symmetry-Retaining Morphological Evolution of the Single Crystals of Cyclodextrin Metal-Organic Frameworks

The morphological symmetry-retaining and symmetry-breaking of single crystals of the γ-cyclodextrin metal-organic framework have been achieved via introducing lower symmetric β-cyclodextrins and α-cyclodextrins, respectively. β-cyclodextrins led to a morphological evolution with retained symmetry from cubic to rhombic dodecahedra, while α-cyclodextrins resulted in the original cubic crystal missing a vertex angle presenting symmetry-breaking behavior. The crystal structures of rhombic dodecahedra and angle-deficient crystals were confirmed through X-ray crystallography, and the mechanisms underlying the morphological transformation evolution were further analyzed. Our work not only provides a rare case realizing two different paths of morphological evolution in one system, but also encourages future efforts towards the evolution of artificial crystal systems in a natural way.

Dimension Evolution of Self-Assembled Organic Microcrystal for Laser and Polarization-Rotation Function

Multidimensional integrated micro/nanostructures are vitally important for the implementation of versatile photonic functionalities, whereas current material structures still suffer undesired surface defects and contaminations in either multistep micro/nanofabrications or extreme synthetic conditions. Herein, the dimension evolution of organic self-assembled structures 2D microrings and 3D microhelixes for multidimensional photonic devices is realized via a protic/aprotic solvent-directed molecular assembly method based on a multiaxial confined-assisted growth mechanism. The 2D microrings with consummate circle boundaries and molecular-smooth surfaces function as high-quality whispering-gallery-mode microcavities for dual-wavelength energy-influence-dependent switchable lasing. Moreover, the 3D microhelixes with smooth surfaces and natural twistable characteristics act as active photon-transport materials and polarization rotators. These results will broaden the horizon of constructing multidimensional microstructures for integrated photonic circuits.

Directional Crystal Jumping Controlled by Chirality

Jumping crystals of racemic mixtures of asparagine monohydrate have been presented in this contribution to emphasize the key role of molecular chirality in governing the direction of macroscopic motions. When heated at the specific faces of the single crystals, a pair of enantiomorphs jump in opposite directions, which are further utilized for chiral resolution. The hydrogen-bonded networks between asparagine molecules in a specific direction provide oriented channels for the escape of water molecules during the dehydration, serving as a foundation for the directional crystal jumping. Our findings not only lay the foundation for the future creation of directed actuation systems based on dynamic crystals but shall also guide the efforts to reveal the correlation between chirality and motion across diverse realms of knowledge.