Directed assembly of optoelectronically active alkyl–π-conjugated molecules by adding n-alkanes or π-conjugated species

A compound eye-like morphology formed through hexagonal array of hemispherical microparticles where an alkyl-fullerene derivative self-assembled at atmosphere-sealed air/water interface

Self-assembly processes are widely used in nature to form hierarchically organized structures, prompting us to investigate such processes at the macroscopic scale. We report an unprecedented approach toward the self-assembly of alkyl-fullerene (C60) derivatives into a hexagonal array of hemispherical microparticles akin to the morphology of a compound eye. The method includes casting solvated alkyl-C60compound on an air/water interface followed by controlled evaporation of the solvent under atmosphere-sealed conditions. This leads to the formation of a thin film floating on water with a diameter of up to 1.3 centimeters and exhibiting a hexagonally-packed hemispherical structure with a diameter of approximately 38µm. Various measurements of the formed film reveal that amorphousness is necessary for suppressing uncontrollable crystallization, which affects the microparticle size and film formation mechanism. We tested the feasibility of this approach for the self-assembly of a relatively common C60derivative, [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM), resulting in the formation of a film with a similar pattern of hexagonally-packed larger microparticles approximately 152µm in size of diameter.

Alkyl-π Functional Molecular Gels: Control of Elastic Modulus and Improvement of Electret Performance

The development of optoelectronically-active soft materials is drawing attention to the application of soft electronics. A room-temperature solvent-free liquid obtained by modifying a π-conjugated moiety with flexible yet bulky alkyl chains is a promising functional soft material. Tuning the elastic modulus (G') is essential for employing optoelectronically-active alkyl-π liquids in deformable devices. However, the range of G' achieved through the molecular design of alkyl-π liquids is limited. We report herein a method for controlling G' of alkyl-π liquids by gelation. Adding 1 wt % low-molecular-weight gelator formed the alkyl-π functional molecular gel (FMG) and increased G' of alkyl-π liquids by up to seven orders of magnitude while retaining the optical properties. Because alkyl-π FMGs have functional π-moieties in the gel medium, this new class of gels has a much higher content of π-moieties of up to 59 wt % compared to conventional π-gels of only a few wt %. More importantly, the gel state has a 23 % higher charge-retention capacity than the liquid, providing better performance in deformable mechanoelectric generator-electret devices. The strategy used in this study is a novel approach for developing next-generation optoelectronically-active FMG materials.

Perforin-Mimicking Molecular Drillings Enable Macroporous Hollow Lignin Spheres for Performance-Configurable Materials

Despite the first observations that the perforin can punch holes in target cells for live/dead cycles in the human immune system over 110 years ago, emulating this behavior in materials science remains challenging. Here, a perforin-mimicking molecular drilling strategy is employed to engineer macroporous hollow lignin spheres as performance-configurable catalysts, adhesives, and gels. Using a toolbox of over 20 molecular compounds, the local curvature of amphiphilic lignin is modulated to generate macroporous spheres with hole sizes ranging from 0 to 100 nm. Multiscale control is precisely achieved through noncovalent assembly directing catalysis, synthesis, and polymerization. Exceptional performance mutations correlate with the changes in hole size, including an increase in catalytic efficiency from 50% to 100%, transition from nonstick synthetics to ultrastrong adhesives (adhesion ≈18.3 MPa, exceeding that of classic epoxies), and transformation of viscous sols to tough nanogels. Thus, this study provides a robust and versatile noncovalent route for mimicking perforin-induced structural variations in cells, representing a significant stride toward the exquisite orchestration of assemblies over multiple length scales.

Impact of Ring-Closing on the Photophysical Properties of One-Dimensional π-Conjugated Molecular Aggregate

The self-assembled state of molecules plays a pivotal role in determining how inherent molecular properties transform and give rise to supramolecular functionalities and has long attracted attention. However, understanding the influence of morphologies spanning the nano- to mesoscopic scales of supramolecular assemblies derived from identical intermolecular interactions has been notoriously challenging due to dynamic structural change and monomer exchange of assemblies in solution. In this study, we demonstrate that curved one-dimensional molecular assemblies (supramolecular polymers) of lengths of around 70-200 nm, originating from the same luminescent molecule, exhibit distinct photoluminescent properties when they form closed circular structures (toroids) versus when they possess chain termini in solution (random coils). By exploiting the difference in kinetic stability between the toroids and random coils, we developed a dialysis protocol to selectively purify the former. It was revealed that these terminus-free closed structures manifest higher energy and more efficient luminescence compared with their mixed state with random coils. Time-resolved fluorescence measurements unveiled that random coils, due to their dynamic structural fluctuation in solution, generate local defects throughout the main chain, leading to luminescence from lower energy levels. In mixtures of the two assemblies, luminescence was exclusively observed from such a lower energy level of random coils, a result attributed to energy transfer between the assemblies. This work emphasizes that for identical supramolecular assemblies, only averaged properties have traditionally been considered, but their structures at the nano- to mesoscopic scale are important especially if they have a certain degree of shape persistency even in solution.

Alkyl-C60 liquid electrets as deformable mechanoelectric generators

Special attention is being paid to the potential applicability of various soft electronics in deformable/wearable devices. These devices must be constantly connected to energy sources to ensure their uninterrupted operation. Electrets, which are capable of retaining quasi-permanent electric charges inside or on the surface of materials, are expected to be a battery-less power source. Here, we present a strategy for harvesting the charges in alkyl-C60 liquids. Suitable substitution of bulky yet flexible branched long-alkyl chains generated C60-mono-adducts and regioisomeric bis-adducts as room-temperature solvent-free liquids. These alkyl-C60 liquids were negatively poled by the corona-discharging and soaked in nylon fabric. The liquid of the C60 bis-adduct exhibited better charge retention in comparison to the liquid of the C60 mono-adduct. This suggests that the bulky long-alkyl chains provided proper insulation for the C60 core and charge trapping in the liquid. This charge-trapping behaviour and the inherent fluidity of the alkyl-C60 liquids enabled their fabrication into deformable mechanoelectric generator (MEG) devices. The MEG exhibited applicability as a deformable micropower source or vibration sensor by generating output voltage pulses even under folded/twisted/rolled conditions. The alkylated-liquid-based MEGs worked at frequencies similar to human body motion, showing promising potential for body motion sensors and healthcare applications.

Application and Research Prospect of Functional Polymer Gels in Oil and Gas Drilling and Development Engineering

Polymer gel materials are formed by physically crosslinking and chemically crosslinking to form a gel network system with high mechanical properties and reversible performance. Due to their excellent mechanical properties and intelligence, polymer gel materials are widely used in biomedical, tissue engineering, artificial intelligence, firefighting and other fields. Given the current research status of polymer gels at home and abroad and the current application status of oilfield drilling, this paper reviews the mechanism of polymer gels formed by physically crosslinking and chemically crosslinking, summarizes the performance characteristics and the mechanism of action of polymer gels formed by non-covalent bonding, such as hydrophobic bonding, hydrogen bonding, electrostatic and Van der Waals interactions interactions, and covalent bonding such as imine bonding, acylhydrazone bonding and Diels-Alder reaction. The current status and outlook of the application of polymer gels in drilling fluids, fracturing fluids and enhanced oil recovery are also introduced. We expand the application fields of polymer gel materials and promote the development of polymer gel materials in a more intelligent direction.

Liquid Structures and Diffusion Dynamics of Alkyl-Pyrene Liquids Studied by Molecular Dynamics Simulations

Functional molecular liquids (FMLs) based on alkylated π-conjugated molecules have attracted attention as solvent-free and nonvolatile liquid materials with prominent optoelectronic features. Recently, novel FML compounds containing pyrene as the functional core were synthesized, and their rheological and photochemical properties were investigated. Although the molecules differ only in the number of alkyl chain substituents and their substitution positions, their viscosity coefficients are largely different beyond the Stokes-Einstein relation on the assumption of identical microscopic friction, indicating that local microscopic molecular interactions are crucial for the macroscopic rheological properties. Here, we report a theoretical study on the rheological properties of the alkyl-pyrene liquids by means of atomistic molecular dynamics (MD) simulations. We performed long-time MD simulations for tens of microseconds to obtain ample statistical samples of the alkyl-pyrene liquids and analyzed their liquid structures and diffusion dynamics based on spatiotemporal correlation functions. We found the formation of characteristic local liquid structures of π-π stacking of the pyrene moieties and locally anisotropic and anomalous diffusion dynamics, which remarkably vary depending on the alkyl substituent patterns. The present results provide an atomistic insight into the macroscopic rheological properties of alkyl-π FMLs and molecular design strategy for them.

Self-assembly of fullerene C60-based amphiphiles in solutions

Fullerene C₆₀ is an all-carbon cage molecule with rich physicochemical properties. It is highly symmetric and hydrophobic, which can be used as a building block for the preparation of amphiphiles that self-assemble into diverse supramolecular structures in aqueous solutions. Meanwhile, C₆₀ is also lipophobic, which is different from the alkyl chains in traditional surfactants. By attaching alkyl chains to the C₆₀ sphere, a new type of lipophobic-lipophilic amphiphiles can be constructed which undergo self-assembly in n-alkanes. When inorganic clusters such as polyoxometalate are linked to the C₆₀ sphere, organic-inorganic hybrids will be obtained which can self-assemble in polar organic solvents. Pristine C₆₀ has also been modified by polar groups such as hydroxy and carboxy, which are linked to hydrophobic moieties and form a new class of amphiphiles. In this review, the self-assembly of C₆₀-based amphiphiles in aqueous and nonaqueous solutions will be summarized. The characteristics exhibited by C₆₀-based amphiphiles during the self-assembly will be discussed with close comparison to traditional surfactants, and the influences of the aggregate formation on the physicochemical properties of the C₆₀ sphere will be described. Finally, a brief summary will be given together with a promising perspective in near future.

Self-assembled organic and hybrid materials derived from oligo-(p-phenyleneethynylenes)

Oligo-(p-Phenyleneethynylenes) (OPEs) have garnered widespread interest over the past three decades due to their excellent opto-electronic properties. However, the chief focus has been on the use of mainly small molecules or polymeric systems for the study of their structural diversity in opto-electronic applications. Recently, researchers have started delving deeper into their utility in material applications. Purely organic materials such as supramolecular polymers, self-assembled nanostructures, nanostructured organogels and single-crystalline materials derived from OPEs have already been developed and researched. Chirality has also been introduced into these systems. Additionally, these have shown physical properties such as polymorphism, liquid crystallinity, melt formation, mechanochromism, etc. All these materials have also shown excellent luminescence properties with high quantum yield and some have even shown energy harvesting properties. There have also been sporadic reports on OPE linker based hybrid systems such as metallogels and metal-organic framework (MOF) structures where structural analysis reveals the origin of tunable emission in these materials. Furthermore, by innovative structural design, unexplored properties of OPEs such as water repellency, bioimaging, drug delivery, photocatalysis, energy transfer, nanomorphology control, photoconductivity, and colour tunability could be achieved. This feature article will, therefore, encompass a detailed discussion on the development of this field as well as the analysis of the properties realized in OPE derived self-assembled supramolecular materials. The main focus will be on the following classes of materials: soft supramolecular materials, crystalline supramolecular π-systems, nanoscale metal-organic frameworks (NMOFs) and bulk metal-organic frameworks (MOFs) and how their application horizon has been expanded by integrating OPEs into their structures.

Molecular nanoribbon gels

Herein, we show that twisted molecular nanoribbons with as many as 322 atoms in the aromatic core are efficient gelators capable of self-assembling into ordered π-gels with morphologies and sol–gel transitions that vary with the length of the nanoribbon. In addition, the nanoribbon gels show a red fluorescence and also pseudoconductivity values in the same range as current state-of-the-art π-gels.

Herein, we show that twisted molecular nanoribbons with as many as 322 atoms in the aromatic core are efficient gelators capable of self-assembling into ordered π-gels with morphologies and sol–gel transitions that vary with the length of the nanoribbon.

3,4-Ethylenedioxythiophene (EDOT) End-Group Functionalized Poly-ε-caprolactone (PCL): Self-Assembly in Organic Solvents and Its Coincidentally Observed Peculiar Behavior in Thin Film and Protonated Media

End-group functionalization of homopolymers is a valuable way to produce high-fidelity nanostructured and functional soft materials when the structures obtained have the capacity for self-assembly (SA) encoded in their structural details. Herein, an end-functionalized PCL with a π-conjugated EDOT moiety, (EDOT-PCL), designed exclusively from hydrophobic domains, as a functional "hydrophobic amphiphile", was synthesized in the bulk ROP of ε-caprolactone. The experimental results obtained by spectroscopic methods, including NMR, UV-vis, and fluorescence, using DLS and by AFM, confirm that in solvents with extremely different polarities (chloroform and acetonitrile), EDOT-PCL presents an interaction- and structure-based bias, which is strong and selective enough to exert control over supramolecular packing, both in dispersions and in the film state. This leads to the diversity of SA structures, including spheroidal, straight, and helical rods, as well as orthorhombic single crystals, with solvent-dependent shapes and sizes, confirming that EDOT-PCL behaves as a "block-molecule". According to the results from AFM imaging, an unexpected transformation of micelle-type nanostructures into single 2D lamellar crystals, through breakout crystallization, took place by simple acetonitrile evaporation during the formation of the film on the mica support at room temperature. Moreover, EDOT-PCL's propensity for spontaneous oxidant-free oligomerization in acidic media was proposed as a presumptive answer for the unexpected appearance of blue color during its dissolution in CDCl3 at a high concentration. FT-IR, UV-vis, and fluorescence techniques were used to support this claim. Besides being intriguing and unforeseen, the experimental findings concerning EDOT-PCL have raised new and interesting questions that deserve to be addressed in future research.

Glassy Porphyrin/C60 Composites: Morphological Engineering of C60 Fullerene with Liquefied Porphyrins

Morphological control of C₆₀ fullerene using liquefied porphyrins (1 and 2) as the host matrices was explored. Slow evaporation of the solvent of the equimolar mixture of porphyrin and C₆₀ in toluene afforded the porphyrin/C₆₀ composite with a 3:1 molar ratio. The stoichiometric binding behaviors suggest that specific porphyrin-C₆₀ interactions operate the formation of the porphyrin/C₆₀ composites, as corroborated by spectroscopic and thermal properties, and glazing-incidence wide-angle X-ray diffraction. Under the bulk conditions, the conventional thermodynamic advantage of multiple binding cooperativity for molecular recognition is unlikely to explain the stoichiometric binding behaviors. Instead, we propose a size-matching effect on the porphyrin-C₆₀ interaction in the bulk porphyrin matrices, i.e., "supramolecular solvation". The glassy nature of the porphyrin matrices was transmitted to C₆₀ through the specific interaction, and the porphyrin/C₆₀ composites adopted glassy states at room temperature.

Macroscopic quantum electrodynamics and density functional theory approaches to dispersion interactions between fullerenes

The processing and material properties of commercial organic semiconductors, for e.g. fullerenes is largely controlled by their precise arrangements, specially intermolecular symmetries, distances and orientations, more specifically, molecular polarisabilities. These supramolecular parameters heavily influence their electronic structure, thereby determining molecular photophysics and therefore dictating their usability as n-type semiconductors. In this article we evaluate van der Waals potentials of a fullerene dimer model system using two approaches: (a) Density Functional Theory and, (b) Macroscopic Quantum Electrodynamics, which is particularly suited for describing long-range van der Waals interactions. Essentially, we determine and explain the model symmetry, distance and rotational dependencies on binding energies and spectral changes. The resultant spectral tuning is compared using both methods showing correspondence within the constraints placed by the different model assumptions. We envision that the application of macroscopic methods and structure/property relationships laid forward in this article will find use in fundamental supramolecular electronics.

Opportunities for Cryogenic Electron Microscopy in Materials Science and Nanoscience

Cryogenic electron microscopy (cryo-EM) was the basis for the 2017 Nobel Prize in Chemistry for its profound impact on the field of structural biology by freezing and stabilizing fragile biomolecules for near atomic-resolution imaging in their native states. Beyond life science, the development of cryo-EM for the physical sciences may offer access to previously inaccessible length scales for materials characterization in systems that would otherwise be too sensitive for high-resolution electron microscopy and spectroscopy. Weakly bonded and reactive materials that typically degrade under electron irradiation and environmental exposure can potentially be stabilized by cryo-EM, opening up exciting opportunities to address many central questions in materials science. New discoveries and fundamental breakthroughs in understanding are likely to follow. In this Perspective, we identify six major areas in materials science that may benefit from the interdisciplinary application of cryo-EM: (1) batteries, (2) soft polymers, (3) metal-organic frameworks, (4) perovskite solar cells, (5) electrocatalysts, and (6) quantum materials. We highlight long-standing questions in each of these areas that cryo-EM can potentially address, which would firmly establish the powerful tool's broad scope and utility beyond biology.

Different agglomeration properties of PC61BM and PC71BM in photovoltaic inks – a spin-echo SANS study

Fullerene derivatives are used in a wide range of applications including as electron acceptors in solution-processable organic photovoltaics.

Visible-to-UV Photon Upconversion in Nanostructured Chromophoric Ionic Liquids

Visible-to-ultraviolet (vis-to-UV) triplet-triplet annihilation based photon upconversion (TTA-UC) is achieved in a non-volatile chromophoric ionic liquid (IL) for the first time. A novel IL is synthesized by combining UV-emitting anion 4-(2-phenyloxazol-5-yl)benzenesulfonate (PPOS) and trihexyltetradecylphosphonium cation (P66614). The nanostructured organization of chromophoric anions is demonstrated by synchrotron X-ray and optical measurements. When the IL is doped with a triplet sensitizer tris(2-phenylpyridinato)iridium(III) (Ir(ppy)3), the visible-to-UV TTA-UC with a relatively low threshold excitation intensity of 61 mW cm-2 is achieved. This is due to a large triplet diffusion coefficient in the IL (1.4×10-7 cm2 s-1) as well as a high absorption coefficient 15 cm-1 and a long PPOS triplet lifetime of 1.55 ms, all implemented in the condensed IL system. This work demonstrates the unique potential of ILs to control chromophore arrangements for desired functions.

Dynamic covalent chemistry steers synchronizing nanoparticle self-assembly with interfacial polymerization

Precise organization of matter across multiple length scales is of particular interest because of its great potential with advanced functions and properties. Here we demonstrate a simple yet versatile strategy that enables the organization of hydrophobic nanoparticles within the covalent organic framework (COF) in an emulsion droplet. The interfacial polymerization takes place upon the addition of Lewis acid in the aqueous phase, which allows the formation of COF after a crystallization process. Meanwhile, the interaction between nanoparticles and COF is realized by the use of amine-aldehyde reactions in the nearest loci of the nanoparticles. Importantly, the competition between the nanoparticle self-assembly and interfacial polymerization allows control over the spatial distribution of nanoparticles within COF. As a general strategy, a wide variety of COF-wrapped nanoparticle assemblies can be synthesized and these hybridized nanomaterials could find applications in optoelectronics, heterogeneous catalysis and energy chemistry.

Molecular Model for the Self-Assembly of the Cyclic Lipodepsipeptide Pseudodesmin A

Self-assembly of peptides into supramolecular structures represents an active field of research with potential applications ranging from material science to medicine. Their study typically involves the application of a large toolbox of spectroscopic and imaging techniques. However, quite often, the structural aspects remain underexposed. Besides, molecular modeling of the self-assembly process is usually difficult to handle, since a vast conformational space has to be sampled. Here, we have used an approach that combines short molecular dynamics simulations for peptide dimerization and NMR restraints to build a model of the supramolecular structure from the dimeric units. Experimental NMR data notably provide crucial information about the conformation of the monomeric units, the supramolecular assembly dimensions, and the orientation of the individual peptides within the assembly. This in silico/in vitro mixed approach enables us to define accurate atomistic models of supramolecular structures of the bacterial cyclic lipodepsipeptide pseudodesmin A.

Self-Assembled and Nonassembled Alkylated-Fullerene Materials

Fullerene (C₆₀), a π-conjugated cage molecule consisting of 60 sp²-hybridized carbon atoms that are arranged into perfect icosahedral symmetry, is one of the most extensively studied nanocarbon materials by virtue of its characteristic spherical structure, fascinating optoelectronic properties, and widespread applications in material science. To implement practical applications, C₆₀ is generally used as a building motif to assemble into various ordered superstructures. Unlike the controllable face-to-face π-π interactions of planar π-conjugated molecules, the π-π interactions between the three-dimensional spherical C₆₀ units are random and directionless, which generally lead to complicated aggregated structures and unpredictable properties. The primary target of our research is to produce a robust design strategy for functional C₆₀ materials, by which the single C₆₀ molecules can be engineered into desirable self-organized architectures with optimized functions. To this end, we focused on alkylated fullerene (alk-C₆₀) derivatives, a simple molecular system whose two components, alkyl chains and C₆₀, exhibit both hydrophobicity yet different affinities to organic solvents. As a result, the alk-C₆₀ derivatives present an unusual "hydrophobic amphiphile" system. Through systematic tuning of the substitution pattern of a series of alkyl side chains (number, length, branching, and substitution position) and external experimental conditions, the factors influencing alk-C₆₀ self-assembly behaviors were determined. In addition, the feasibility of forming hybrid coassemblies with alk-C₆₀ and other nanocarbon materials was demonstrated. By taking full advantage of the hydrophobic nature and active optoelectronic properties of these self- or hybrid-assemblies, various superhydrophobic materials and/or optoelectronic devices were developed. However, supported only by weak noncovalent interactions, these ordered superstructures are intrinsically fragile under various external stimuli. To improve the structural stability and achieve consistent optoelectronic performance of these novel materials, we strengthened the ordered structures via metallization and plasticization. Both approaches gave rise to robust and endurable materials with functions inherited from the pristine assemblies but at the cost of their former softness and facile processability. Thereafter, we focused on amorphous materials in view of their consistent and predictable optoelectronic properties that are independent of their geometry and physical environment. Unexpectedly, the amorphous materials obtained were liquids at room temperature, whose excellent deformability might enable applications in flexible/wearable optoelectronic devices. However, the lack of sufficient molecular order impaired their optoelectronic performance. To address this, we devised a straightforward strategy toward the directed ordered self-assembly of the alk-C₆₀ liquids by adding molecular cofactors (n-alkanes or C₆₀) into the liquids. Using this strategy, the balance between intermolecular order and material softness can be readily adjusted to meet different application requirements. Through iterative refinements to our novel alk-C₆₀ system, we have demonstrated its power in generating numerous self-assembled, hybrid-assembled, and nonassembled materials toward versatile applications. We believe such a comprehensive description of these alk-C₆₀-based functional materials provides deep insights into these still-evolving materials, which will underpin more advanced applications in near future.

Added-Value Surfactants

Surfactants are ubiquitous in cellular membranes, detergents or as emulsification agents. Due to their amphiphilic properties, they cannot only mediate between two domains of very different solvent compatibility like water and organic but also show fascinating self-assembly features resulting in micelles, vesicles, or lyotropic liquid crystals. The current review article highlights some approaches towards the next generation surfactants, for example, those with catalytically active heads. Furthermore, it is shown that amphiphilic properties can be obtained beyond the classical hydrophobic-hydrophilic interplay, for instance with surfactants containing one molecular block with a special shape. Whereas, classical surfactants are static, researchers have become more interested in species that are able to change their properties depending on external triggers. The article discusses examples for surfactants sensitive to chemical (e.g., pH value) or physical triggers (temperature, electric and magnetic fields).

Effect of Fullerene Volume Fraction on Two-Dimensional Crystal-Constructed Supramolecular Liquid Crystals

The volume fraction plays an important role in phase segregated soft matters. We demonstrate here that at high fullerene volume fraction in soft chain-tethered-fullerene dyads, different two-dimensional (2D) crystal-constructed smectic-like lamella liquid crystalline (LC) phases can be formed with triple-layer (S_T phase) or quadruple-layer (S_Q phase) stacking of fullerenes in 2D crystals. The combination of 2D crystal and LC properties in one system affords these fullerene dyads controlled electron mobility in the range of 10^-5 -10^-3  cm²  V^-1  s^-1 at room temperature (S_T phase), by regulating the insulated soft layer thickness between 2D crystals via the manipulation of fullerene volume fraction.

Supercooling of functional alkyl-π molecular liquids

Metastable states of soft matters are extensively used in designing stimuli-responsive materials. However, the non-steady properties may obstruct consistent performance. Here we report an approach to eradicate the indistinguishable metastable supercooled state of functional molecular liquids (FMLs), which remains as a liquid for weeks or months before crystallizing, via rational molecular design. The phases (solid, kinetically stable liquid, and supercooled liquid) of a model FML, branched alkyl chain-substituted 9,10-diphenylanthracene (DPA), are found to be governed by subtle alterations of the molecular structure (alkyl-DPA ratio and bulkiness of the DPA unit). We thus outline molecular design principles to avoid supercooled FML formation. Moreover, we demonstrate a practical technique to rapidly discriminate supercooled FMLs (within 5 h) by accelerating their crystallization in differential scanning calorimetry heating via pre-annealing or relatively slow scanning.

Solvent Control over Supramolecular Gel Formation and Fluorescence for a Highly Crystalline π-Conjugated Polymer

In π-conjugated polymers (πCPs), crystallinity and fluorescence typically exhibit a trade-off relationship. Here, we have synthesized a highly crystalline and fluorescent π-conjugated polymer with a simple alternating structure of 1,2,4,5-tetrafluorophenylene and 3,3'-dihexyl-2,2'-bithiophene units. In film, the polymer exhibited efficient red-colored fluorescence, an improved quantum yield (Φsol =13 %→Φfilm =23 %) and a crystalline structure. Interestingly, supramolecular gel formation occurred in appropriate solvents, and the macrostructure and fluorescence properties of the gel could be directly controlled by the choice of the solvent. The polymer self-assembled into a spherical form that exhibited red fluorescence in non-aromatic solvent (1,2-dichloroethane) and into a fibrous form that exhibited yellow fluorescence in aromatic solvent (mesitylene).

Transforming a C 3-Symmetrical Liquid Crystal to a π-Gelator by Alkoxy Chain Variation

Rational understanding of the structural features involving different noncovalent interactions is necessary to design a liquid crystal (LC) or an organogelator. Herein, we report the effect of the number and positions of alkoxy chains on the self-assembly induced physical properties of a few π-conjugated molecules. For this purpose, we designed and synthesized three C ₃-symmetrical molecules based on oligo(p-phenylenevinylene), C ₃ OPV1-3. The self-assembly properties of these molecules are studied in the solid and solution states. All of the three molecules follow the isodesmic self-assembly pathway. Upon cooling from isotropic melt, C ₃ OPV1 having nine alkoxy chains (-OC₁₂H₂₅) formed a columnar phase with two-dimensional rectangular lattice and retained the LC phase even at room temperature. Interestingly, when one of the -OC₁₂H₂₅ groups from each of the end benzene rings is knocked out, the resultant molecule, C ₃ OPV2 lost the LC property, however, transformed as a gelator in toluene and n-decane. Surprisingly, when the -OC₁₂H₂₅ group from the middle position is removed, the resultant molecule C ₃ OPV3 failed to form either the LC or the gel phases.

Fluorescent-Cavity Host: An Efficient Probe to Study Supramolecular Recognition Mechanisms

Using fluorometry to study the interactions between guests and host cavities is often challenging, especially for hosts with small cavities because the fluorophore may not be close to the binding site. Therefore, it is critical to overcome this hurdle to broaden the applicability of fluorometry in supramolecular chemistry. Herein, we designed a fluorescent-cavity host (H1) by conjugating the binding site of a pillar[5]arene cavity and studied its host-guest recognition mechanism in the cavity. Distinct fluorescent responses of H1 were observed for cyano homologues: the fluorescence was enhanced for succinonitrile but quenched for malononitrile. Such an unusual phenomenon with such subtle difference in guest structure was attributed to the different host-guest interactions induced by the subtle difference of guest locations within the H1 cavity. Our results indicate that developing fluorescent-cavity hosts as probes will provide a powerful and insightful way to explore the exquisite detail of host-guest recognition, self-assembly, and molecular machinery.

Self-assembly of highly conductive self-n-doped fullerene ammonium halides and their application in the in situ solution-processable fabrication of working electrodes for alcohol electrooxidation

Stable and highly conductive self-n-doped fullerene ammonium halides are promising optoelectronic materials. It is necessary to thoroughly understand their structure-function relationship and to develop their applications. Here, the assembly behaviors of the self-n-doped fullerene ammonium halides, as well as the functional areas in the well-developed 2D-3D lamellar structures in their ordered aggregates are systematically characterized using comprehensive methods. In the self-assembly, the solvation effect of DMSO promotes the flexibility of side-chains and drives the formation of fullerene ammonium halides into ordered bilayer structures. The conductivity-active area, which contains tightly packed halide anions sandwiched between fullerenes, provides good electron transfer property. Remarkably, residual DMSO in the side-chain area can induce aqueous Pd precursor into the highly conductive framework. After reduction, Pd nanoparticles are immobilized in the confined spaces within the conductive support. The resulting electrode can be used to electrooxidize ethanol. This study provides a facile solution strategy for the in situ fabrication of electrocatalysts on working electrodes, which can be applied in direct alcohol fuel cells.

The aggregation of an alkyl-C60 derivative as a function of concentration, temperature and solvent type

Contrast-variation small-angle neutron scattering (CV-SANS), small-angle X-ray scattering (SAXS), nuclear magnetic resonance (NMR) measurements of diffusion and isothermal titration calorimetry (ITC) are used to gain insight into the aggregation of an alkyl-C₆₀ derivative, molecule 1, in n-hexane, n-decane and toluene as a function of concentration and temperature. Results point to an associative mechanism of aggregation similar to other commonly associating molecules, including non-ionic surfactants or asphaltenes in non-aqueous solvents. Little aggregation is detected in toluene, but small micelle-like structures form in n-alkane solvents, which have a C₆₀-rich core and alkyl-rich shell. The greatest aggregation extent is found in n-hexane, and at 0.1 M the micelles of 1 comprise around 6 molecules at 25 °C. These micelles become smaller when the concentration is lowered, or if the solvent is changed to n-decane. The solution structure is also affected by temperature, with a slightly larger aggregation extent at 10 °C than at 25 °C. At higher concentrations, for example in solutions of 1 above 0.3 M in n-decane, a bicontinuous network becomes apparent. Overall, these findings aid our understanding of the factors driving the assembly of alkyl-π-conjugated hydrophobic amphiphiles such as 1 in solution and thereby represent a step towards the ultimate goal of exploiting this phenomenon to form materials with well-defined order.

The effect of regioisomerism on the photophysical properties of alkylated-naphthalene liquids

Novel alkylated naphthalene liquids with a correlation among the 1- and 2-regioisomeric chemical structures and their photophysical, calorimetric and rheological properties are presented.

Fabrication of diverse nano-architectures through the self-assembly of a naphthalene diimide derivative bearing four carbamates

We found that naphthalene diimide (W2) bearing four carbamates bonds can organise various well-defined self-assembled nanostructures driven by π–π interaction and carbamate H-bonding.

A Guide to Design Functional Molecular Liquids with Tailorable Properties using Pyrene-Fluorescence as a Probe

Solvent-free, nonvolatile, room-temperature alkylated-π functional molecular liquids (FMLs) are rapidly emerging as a new generation of fluid matter. However, precision design to tune their physicochemical properties remains a serious challenge because the properties are governed by subtle π-π interactions among functional π-units, which are very hard to control and characterize. Herein, we address the issue by probing π-π interactions with highly sensitive pyrene-fluorescence. A series of alkylated pyrene FMLs were synthesized. The photophysical properties were artfully engineered with rational modulation of the number, length, and substituent motif of alkyl chains attached to the pyrene unit. The different emission from the excimer to uncommon intermediate to the monomer scaled the pyrene-pyrene interactions in a clear trend, from stronger to weaker to negligible. Synchronously, the physical nature of these FMLs was regulated from inhomogeneous to isotropic. The inhomogeneity, unexplored before, was thoroughly investigated by ultrafast time-resolved spectroscopy techniques. The result provides a clearer image of liquid matter. Our methodology demonstrates a potential to unambiguously determine local molecular organizations of amorphous materials, which cannot be achieved by conventional structural analysis. Therefore this study provides a guide to design alkylated-π FMLs with tailorable physicochemical properties.

Reversible Polymorphism, Liquid Crystallinity, and Stimuli-Responsive Luminescence in a Bola-amphiphilic π-System: Structure-Property Correlations Through Nanoindentation and DFT Calculations

We report the design, synthesis, detailed characterization, and analysis of a new multifunctional π-conjugated bola-amphiphilic chromophore: oligo-(p-phenyleneethynylene)dicarboxylic acid with dialkoxyoctadecyl side chains (OPE-C₁₈-1). OPE-C₁₈-1 shows two polymorphs at 123 K (OPE-C₁₈-1') and 373 K (OPE-C₁₈-1″), whose crystal structures were characterized via single crystal X-ray diffraction. OPE-C₁₈-1 also exhibits thermotropic liquid crystalline property revealing a columnar phase. The inherent π-conjugation of OPE-C₁₈-1 imparts luminescence to the system. Photoluminescence measurements on the mesophase also reveal similar luminescence as in the crystalline state. Additionally, OPE-C₁₈-1 shows mechano-hypsochromic luminescence behavior. Density functional theory (DFT)-based calculations unravel the origins behind the simultaneous existence of all these properties. Nanoindentation experiments on the single crystal reveal its mechanical strength and accurately correlate the molecular arrangement with the liquid crystalline and mechanochromic luminescence behavior.

A nanomesh scaffold for supramolecular nanowire optoelectronic devices

Supramolecular organic nanowires are ideal nanostructures for optoelectronics because they exhibit both efficient exciton generation as a result of their high absorption coefficient and remarkable light sensitivity due to the low number of grain boundaries and high surface-to-volume ratio. To harvest photocurrent directly from supramolecular nanowires it is necessary to wire them up with nanoelectrodes that possess different work functions. However, devising strategies that can connect multiple nanowires at the same time has been challenging. Here, we report a general approach to simultaneously integrate hundreds of supramolecular nanowires of N,N'-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) in a hexagonal nanomesh scaffold with asymmetric nanoelectrodes. Optimized PTCDI-C8 nanowire photovoltaic devices exhibit a signal-to-noise ratio approaching 10⁷, a photoresponse time as fast as 10 ns and an external quantum efficiency >55%. This nanomesh scaffold can also be used to investigate the fundamental mechanism of photoelectrical conversion in other low-dimensional semiconducting nanostructures.

Supramolecular Differentiation for Construction of Anisotropic Fullerene Nanostructures by Time-Programmed Control of Interfacial Growth

Supramolecular assembly can be used to construct a wide variety of ordered structures by exploiting the cumulative effects of multiple noncovalent interactions. However, the construction of anisotropic nanostructures remains subject to some limitations. Here, we demonstrate the preparation of anisotropic fullerene-based nanostructures by supramolecular differentiation, which is the programmed control of multiple assembly strategies. We have carefully combined interfacial assembly and local phase separation phenomena. Two fullerene derivatives, PhH and C12H, were together formed into self-assembled anisotropic nanostructures by using this approach. This technique is applicable for the construction of anisotropic nanostructures without requiring complex molecular design or complicated methodology.

A π-gel scaffold for assembling fullerene to photoconducting supramolecular rods

Nonequilibrium self-assembly of molecules holds a huge prospect as a tool for obtaining new-generation materials for future applications. Crystallization of neutral molecules within a supramolecular gel matrix is one example in which two nonequilibrium processes occur orthogonal to each other. On the other hand, electronically interacting donor-acceptor two-component systems are expected to form phase-miscible hybrid systems. Contrary to the expectation, we report the behavior of a π-gel, derived from oligo(p-phenylenevinylene), OPVA, as a scaffold for the phase separation and crystallization of fullerene (C₆₀) to supramolecular rods with increased transient photoconductivity (φƩμ_max = 2.4 × 10^-4 cm² V^-1 s^-1). The C₆₀ supramolecular rods in the π-gel medium exhibited high photocurrent in comparison to C₆₀ loaded in a non-π-gel medium. This finding provides an opportunity for large-scale preparation of micrometer-sized photoconducting rods of fullerenes for device application.

Supramolecular Assemblies of Ferrocene-Hinged Naphthalenediimides: Multiple Conformational Changes in Film States

We design a new naphthalenediimide (NDI) π-system, NDI-Fc-NDI, having a ferrocene linker as a hinge unit and long alkyl chains as supramolecular assembling units. The NDI units are "directionally flexible" in concert with the pivoting motion of the ferrocene unit with a small rotational barrier. The NDI units rotate around the ferrocene unit faster than the NMR time scale in solution at room temperature. UV-vis absorption, synchrotron X-ray diffraction, and atomic force microscope studies reveal that NDI-Fc-NDI forms a fibrous supramolecular assembly in solution (methylcyclohexane and highly concentrated chloroform) and film states, wherein the NDI units are in the slipped-stack conformation. The NDI-Fc-NDI supramolecular assembly in the film state exhibits multiple phase transitions associated with conformational changes at different temperatures, which are confirmed by differential scanning calorimetry, polarized optical microscopy, and temperature-dependent X-ray diffraction. Such thermal transitions of NDI-Fc-NDI films also induce changes in the optical and electronic properties as revealed by UV-vis absorption and photoelectron yield spectroscopies, respectively. The thermal behaviors of NDI-Fc-NDI, realized by the unique molecular design, are considerably different from the reference compounds such as an NDI dimer connected with a flexible 1,4-butylene linker. These results provide us with a plausible strategy to propagate the molecular dynamics of the π-system into macroscopic properties in film states; the key factors are (i) the supramolecular alignment of molecular switching units and (ii) the directional motion of the switching units perpendicular to the supramolecular axis.

Facile Method toward Hierarchical Fullerene Architectures with Enhanced Hydrophobicity and Photoluminescence

A two-step self-assembly strategy has been developed for the preparation of fullerene hierarchical architectures. Typically, the precipitation method is utilized to synthesize the initial fullerene microstructures, and subsequently a drop-drying process is employed to facilitate the fullerene microstructures to self-assemble into the final hierarchical structures. Overall, this methodology is quite simple and feasible, which can be applied to prepare fullerene hierarchical structures with different morphological features, simply by choosing proper solvent. Moreover, the as-obtained C70 hierarchical structures have many superior properties over the original C70 microrods such as superhydrophobicity and unique photoluminescence behaviors, promising their applications as waterproof optoelectronics.

A slippery molecular assembly allows water as a self-erasable security marker

Protection of currency and valuable documents from counterfeit continues to be a challenge. While there are many embedded security features available for document safety, they are not immune to forgery. Fluorescence is a sensitive property, which responds to external stimuli such as solvent polarity, temperature or mechanical stress, however practical use in security applications is hampered due to several reasons. Therefore, a simple and specific stimuli responsive security feature that is difficult to duplicate is of great demand. Herein we report the design of a fluorescent molecular assembly on which water behaves as a self-erasable security marker for checking the authenticity of documents at point of care. The underlying principle involves the disciplined self-assembly of a tailor-made fluorescent molecule, which initially form a weak blue fluorescence (λ_em = 425 nm, Φ_f = 0.13) and changes to cyan emission (λ_em = 488 nm,Φ_f = 0.18) in contact with water due to a reversible molecular slipping motion. This simple chemical tool, based on the principles of molecular self-assembly and fluorescence modulation, allows creation of security labels and optically masked barcodes for multiple documents authentication.