Self-assembled coronene nanofibers: optical waveguide effect and magnetic alignment

Self-Assembled Molecular Fibers Aligned by Compression in Water

Molecular self-assembly has attracted much attention as a potential approach for fabricating nanostructured functional materials. To date, energy-efficient fabrication of nano-objects such as nanofibers, nanorings, and nanotubes is achieved using well-designed self-assembling molecules. However, the application of molecular self-assembly to industrial manufacturing processes remains challenging because regulating the positions and directions of self-assembled products is difficult. Non-covalent molecular assemblies are also too fragile to allow mechanical handling. The present work demonstrates the macroscopic alignment of self-assembled molecular fibers using compression. Specifically, the macroscopic bundling of self-assembled nanofibers is achieved following dispersion in water. These fiber bundles can also be chemically crosslinked without drastic changes in morphology via trialkoxysilyl groups. Subsequently, vertically oriented porous membranes can be produced rapidly by slicing the bundles. This technique is expected to be applicable to various functional self-assembled fibers and can lead to the development of innovative methods of producing anisotropic nanostructured materials.

Nonclassical Crystal Growth of Supramolecular Polymers in Aqueous Medium

A mechanistic understanding of the principles governing the hierarchical organization of supramolecular polymers offers a paradigm for tailoring synthetic molecular architectures at the nano to micrometric scales. Herein, the unconventional crystal growth mechanism of a supramolecular polymer of superbenzene(coronene)-diphenylalanine conjugate (Cr-FFOEt ) is demonstrated. 3D electron diffraction (3D ED), a technique underexplored in supramolecular chemistry, is effectively utilized to gain a molecular-level understanding of the gradual growth of the initially formed poorly crystalline hairy, fibril-like supramolecular polymers into the ribbon-like crystallites. The further evolution of these nanosized flat ribbons into microcrystals by oriented attachment and lateral fusion is probed by time-resolved microscopy and electron diffraction. The gradual morphological and structural changes reveal the nonclassical crystal growth pathway, where the balance of strong and weak intermolecular interactions led to a structure beyond the nanoscale. The role of distinct π-stacking and H-bonding interactions that drive the nonclassical crystallization process of Cr-FFOEt supramolecular polymers is analyzed in comparison to analogous molecules, Py-FFOEt and Cr-FF forming helical and twisted fibers, respectively. Furthermore, the Cr-FFOEt crystals formed through nonclassical crystallization are found to improve the functional properties.

Magnetically controlled assembly: a new approach to organic integrated photonics

Hierarchical self-assembly of organic molecules or assemblies is of great importance for organic photonics to move from fundamental research to integrated and practical applications. Magnetic fields with the advantages of high controllability, non-contact manipulation, and instantaneous response have emerged as an elegant way to prepare organic hierarchical nanostructures. In this perspective, we outline the development history of organic photonic materials and highlight the importance of organic hierarchical nanostructures for a wide range of applications, including microlasers, optical displays, information encoding, sensing, and beyond. Then, we will discuss recent advances in magnetically controlled assembly for creating organic hierarchical nanostructures, with a particular focus on their potential for enabling the development of integrated photonic devices with unprecedented functionality and performance. Finally, we present several perspectives on the further development of magnetically controlled assembly strategies from the perspective of performance optimization and functional design of organic integrated photonics.

Repeatable Actuations of Organic Single Crystal Fibers Driven by Thermosalient-Phase-Transition-Induced Buckling

Thermosalient crystals are molecular solids that exhibit explosive motions, such as sudden breaks and jumps, due to temperature-induced structural phase transitions between two polymorphs. Therefore, the development of molecular actuators with superior speed and power by deriving mechanical work from explosive motion is a fascinating concept. However, thermosalient transitions often cause crystal disintegration, which hampers repeatable phase transitions between the polymorphs. Here, it is reported that single crystal nano/microfibers of 1, 2, 4, 5-tetrabromobenzene (TBB), whose bulk crystals exhibit thermosalient behavior at ≈40 °C, can repeatedly transform between the low and high temperature polymorphs without disintegration. The structural tolerance against phase transition is attributed to the high flexibility of the nano/microfibers. It is observed that a structure consisting of a TBB fiber with both ends pinned to the substrate repeatedly buckles and straightens when the temperature is varied between 30 and 40 °C. It is demonstrated that buckling can lead to large displacement actuation as compared to a simple length change of the fiber. Moreover, the force generated by the buckling fiber is estimated and it is found that it can generate a force large enough to flick an object ≈10⁴ times heavier than the fiber itself into the air against gravity.

High-Quality All-Inorganic Perovskite CsPbBr3 Microsheet Crystals as Low-Loss Subwavelength Exciton-Polariton Waveguides

Nanostructured all-inorganic metal halide perovskites have attracted considerable attention due to their outstanding photonic and optoelectronic properties. Particularly, they can exhibit room-temperature exciton-polaritons (EPs) capable of confining electromagnetic fields down to the subwavelength scale, enabling efficient light harvesting and guiding. However, a real-space nanoimaging study of the EPs in perovskite crystals is still absent. Additionally, few studies focused on the ambient-pressure and reliable fabrication of large-area CsPbBr₃ microsheets. Here, CsPbBr₃ orthorhombic microsheet single crystals were successfully synthesized under ambient pressure. Their EPs were examined using a real-space nanoimaging technique, which reveal EP waveguide modes spanning the visible to near-infrared spectral region. The EPs exhibit a sufficient long propagation length of over 16 μm and a very low propagation loss of less than 0.072 dB·μm^-1. These results demonstrate the potential applications of CsPbBr₃ microsheets as subwavelength waveguides in integrated optics.

Phase-transition-induced jumping, bending, and wriggling of single crystal nanofibers of coronene

For decades, it has been reported that some organic crystals suddenly crack, break, or jump when they are heated from room temperature. Recently, such crystals have been intensively studied both in fundamental science and for high-speed mechanical device applications. According to these studies, the sudden crystal motions have been attributed to structural phase transitions induced by heating. Stress created by the phase transition is released through the sudden and rapid motion of the crystals. Here we report that single crystal nanofibers of coronene exhibit a new type of ultrafast motion when they are cooled from room temperature and subsequently heated to room temperature. The nanofibers make centimeter-scale jumps accompanied by surprisingly unique behaviors such as sharp bending and wriggling. We found that the motions are caused by a significantly fast structural phase transition between two polymorphs of coronene. A theoretical investigation revealed that the sudden force generated by the phase transition together with the nanoscale dimensions and elastic properties create dynamical instability in the nanofibers that results in the motions. Our finding demonstrates the novel mechanism that leads to ultrafast, large deformation of organic crystals.

Continuum Modelling for Interacting Coronene Molecules with a Carbon Nanotube

The production of single dimensional carbon structures has recently been made easier using carbon nanotubes. We consider here encapsulated coronene molecules, which are flat and circular-shaped polycyclic aromatic hydrocarbons, inside carbon nanotubes. Depending on the radius of the nanotube, certain specific configurations of the coronene molecules can be achieved that give rise to the formation of stacked columns or aid in forming nanoribbons. Due to their symmetrical structure, a coronene molecule may be modelled by three inner circular rings of carbon atoms and one outer circular ring of hydrogen atoms, while the carbon nanotube is modelled as a circular tube. Using the continuous model and the Lennard-Jones potential, we are able to analytically formulate an expression for the potential energy for a coronene dimer and coronene inside a carbon nanotube. Subsequently, stacking of coronene molecules inside a nanotube is investigated. We find that the minimum energy tilt angle of coronenes in a stack differs from that of a single coronene within the same nanotube. More specifically, for both (18, 0) and (19, 0) zigzag carbon nanotube, we find that the minimum energy tilt angles of the single coronene case (≈42° and ≈20° respectively) do not occur in the stack model.

Scale Effect of a Fluorescent Waveguide in Organic Micromaterials: A Case Study Based on Coumarin Microfibers

The classical method for evaluating the waveguide ability only focuses on the optical loss coefficient. However, for the micro- or submicroscale, an organic waveguide is demonstrated by the present study whose scale effect should not be neglected. We found that the optical loss coefficient increased remarkably when decreasing the sectional size of the microfibers. Furthermore, simulations based on Finite-Difference Time-Domain also demonstrated the size-dependent effect of the waveguide. Both the experimental and simulating results showed that the optical loss coefficient converges to a certain value, which means that the scale effect can be neglected as the sectional size is large enough. On the basis of the present study, we suggest that the scale-dependent effect on the sectional size of the waveguide should be investigated by evaluating the waveguide ability by the optical loss coefficient.

Peroxidase activity of the coronene bisimide supramolecular architecture and its applications in colorimetric sensing of H2O2 and glucose

A new water soluble coronene bisimide derivative (CTDI) was designed and synthesized. CTDI self-assembled in an aqueous solution and formed supramolecular nanofibers through π-π stacking and hydrophobic interactions. The nanofibers exhibit distinct peroxidase-like catalytic activity, and can catalyze the redox reaction of 3,3,5,5-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide. Clear assay solution color changes were observed. The peroxidase-like catalytic property was utilized for the sensitive detection of H₂O₂ and glucose. The assay shows excellent sensitivity, and 1 μM of glucose could be easily detected. Glucose detection in dilute human blood samples was also demonstrated, and the results were verified using a commercial glucose meter. Our method is simple, convenient, sensitive and selective, and could facilitate the sensing of glucose in relation to biological and biomedical research applications.

Facet-Selective Growth of Organic Heterostructured Architectures via Sequential Crystallization of Structurally Complementary π-Conjugated Molecules

In contrast to those for their polymeric counterparts, the controlled construction of organic heterostructured architectures derived from π-conjugated organic molecules has been rare and remains a great challenge. Herein, we develop a simple single-step solution strategy for the realization of organic heterostructures comprising coronene and perylene. Under a sequential crystallization process, an efficient doping step for coronene and perylene domains enables their perfect lattice matching, which facilitates facet-selective epitaxial growth of perylene domains on both the tips and the side surfaces of the preformed seed microwires by manipulating the growth pathways of the two pairs of materials. The present synthetic route provides a promising platform to investigate the detailed formation mechanism of complex organic heterostructures with specific topological configurations, further directing the construction of more functional heterostructured materials.

Self-assembled coronene nanofiber arrays: toward integrated organic bioelectronics for efficient isolation, detection, and recovery of cancer cells

Integrated coronene-based nanofiber array devices for circulating tumor cell isolation, detection, and recovery through electrical stimulation.

Alignment and Patterning of Ordered Small-Molecule Organic Semiconductor Micro-/Nanocrystals for Device Applications

Large-area alignment and patterning of small-molecule organic semiconductor micro-/nanocrystals (SMOSNs) at desired locations is a prerequisite for their practical device applications. Recent strategies for alignment and patterning of ordered SMOSNs and their corresponding device applications are highlighted.

Wavelength-tunable waveguides based on polycrystalline organic-inorganic perovskite microwires

Hybrid organic-inorganic perovskites have emerged as new photovoltaic materials with impressively high power conversion efficiency due to their high optical absorption coefficient and long charge carrier diffusion length. In addition to high photoluminescence quantum efficiency and chemical tunability, hybrid organic-inorganic perovskites also show intriguing potential for diverse photonic applications. In this work, we demonstrate that polycrystalline organic-inorganic perovskite microwires can function as active optical waveguides with small propagation loss. The successful production of high quality perovskite microwires with different halogen elements enables the guiding of light with different colours. Furthermore, it is interesting to find that out-coupled light intensity from the microwire can be effectively modulated by an external electric field, which behaves as an electro-optical modulator. This finding suggests the promising applications of perovskite microwires as effective building blocks in micro/nano scale photonic circuits.

Shape-controlled synthesis of platinum octaethylporphyrin crystalline aggregates modulated by versatile ionic liquids

ILs-mediated solution self-assembly was exploited to produce the well-defined single-crystalline PtOEP microwires, which had highly sensitive photo-response and active optical waveguide characteristics.

Photobleaching induced time-dependent light emission from dye-doped polymer nanofibers

Photobleaching induced time-dependent light emission at different positions along dual-dye-doped polymer nanofibers.

Magnetically aligned supramolecular hydrogels

The magnetic-field-induced alignment of the fibrillar structures present in an aqueous solution of a dipeptide gelator, and the subsequent retention of this alignment upon transformation to a hydrogel upon the addition of CaCl2 or upon a reduction in solution pH is reported. Utilising the switchable nature of the magnetic field coupled with the slow diffusion of CaCl2 , it is possible to precisely control the extent of anisotropy across a hydrogel, something that is generally very difficult to do using alternative methods. The approach is readily extended to other compounds that form viscous solutions at high pH. It is expected that this work will greatly expand the utility of such low-molecular-weight gelators (LMWG) in areas where alignment is key.

Uniaxially aligned electrospun cellulose acetate nanofibers for thin layer chromatographic screening of hydroquinone and retinoic acid adulterated in cosmetics

Uniaxially aligned cellulose acetate (CA) nanofibers were successfully fabricated by electrospinning and applied to use as stationary phase for thin layer chromatography. The control of alignment was achieved by using a drum collector rotating at a high speed of 6000 rpm. Spin time of 6h was used to produce the fiber thickness of about 10 μm which was adequate for good separation. Without any chemical modification after the electrospinning process, CA nanofibers could be readily devised for screening hydroquinone (HQ) and retinoic acid (RA) adulterated in cosmetics using the mobile phase consisting of 65:35:2.5 methanol/water/acetic acid. It was found that the separation run on the aligned nanofibers over a distance of 5 cm took less than 15 min which was two to three times faster than that on the non-aligned ones. On the aligned nanofibers, the masses of HQ and RA which could be visualized were 10 and 25 ng, respectively, which were two times lower than those on the non-aligned CA fibers and five times lower than those on conventional silica plates due to the appearance of darker and sharper of spots on the aligned nanofibers. Furthermore, the proposed method efficiently resolved HQ from RA and ingredients commonly found in cosmetic creams. Due to the satisfactory analytical performance, facile and inexpensive production process, uniaxially aligned electrospun CA nanofibers are promising alternative media for planar chromatography.