Photoresponsive Supramolecular Polymers Capable of Intrachain Folding and Interchain Aggregation

The competition between polymer chain folding and aggregation is a critical structuring process that determines the physical properties of synthetic and biopolymers. However, supramolecular polymer systems that exhibit both processes have not yet been reported. We herein introduce a system in which folded supramolecular polymers spontaneously undergo interchain aggregation due to a rearrangement in internal molecular order, converting them into crystalline aggregates. These folded supramolecular polymers slowly crystallize over the course of half a day, due to their characteristic higher-order structures. However, the photoisomerization of the trans-azobenzene incorporated into the monomer to the cis isomer leads to unfolding of the polymer, accelerating the intrachain and interchain molecular ordering to a few hours. The intermediate structures visualized by AFM demonstrate that the unfolding is coupled with interchain aggregation.

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.

A Coformer Approach for Supramolecular Polymerization at High Concentrations

Insolubility of functional molecules caused by polymorphism sometimes poses limitations for their solution-based processing. Such a situation can also occur in the preparation processes of supramolecular polymers formed in a solution. An effective strategy to address this issue is to prepare amorphous solid states by introducing a "coformer" molecule capable of inhibiting the formation of an insoluble polymorph through co-aggregation. Herein, inspired by the coformer approach, we demonstrated a solubility enhancement of a barbiturate π-conjugated compound that can supramolecularly polymerize through six-membered hydrogen-bonded rosettes. Our newly synthesized supramolecular coformer molecule features a sterically demanding methyl group in the π-conjugated unit of the parent molecule. Although the parent molecule exhibits low solubility in nonpolar solvents due to the formation of a crystalline polymorph comprising a tape-like hydrogen-bonded array prior to the supramolecular polymerization, mixing with the coformer compound enhanced the solubility by inhibiting mesoscopic organization of the tapes. The two monomers were then co-polymerized into desired helicoidal supramolecular polymers through the formation of heteromeric rosettes.

Stereoelectronically-induced allosteric binding: shape complementarity promotes positive cooperativity in fullerene/buckybowl complexes

A novel 2 : 1 host-guest complex forms between 8-tert-butyl-6b²-azapenta-benzo[bc,ef,hi,kl,no]corannulene (1) and C₆₀ with positive cooperativity (α = 2.56) and high affinity (K₁ × K₂ = 2.8 × 10⁶ M^-2) at 25 °C. The C₆₀ undergoes increasing shape complementarity toward 1 throughout the binding process.

Room-Temperature Pentacene Fluids: Oligoethylene Glycol Substituent-Controlled Morphologies and Singlet Fission

We report the first synthesis of solvent-free pentacene fluids at room temperature together with observation of singlet fission (SF). Three pentacenes with different number of ethylene glycol (EG) side chains (n) were employed (denoted as (EG)_n-Pc-(EG)_n: n = 2, 3, and 4). The morphologies of these pentacenes largely depend on the lengths of EG chains (n). (EG)₃-Pc-(EG)₃ and (EG)₄-Pc-(EG)₄ indicate fluid compounds at room temperature, whereas (EG)₂-Pc-(EG)₂ is a solid compound. Microscopic clustering with short-range interactions between pentacene chromophores was confirmed in X-ray diffraction profiles of solvent-free fluids. Such a structural trend is an important origin of SF and consistent with the steady-state spectroscopic results. To one's surprise, femtosecond transient absorption spectroscopy demonstrated that SF occurred in thin films prepared from solvent-free fluids of (EG)₃-Pc-(EG)₃ and (EG)₄-Pc-(EG)₄ in spite of such excessive EG chains.

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.

Nanoscale Crystalline Sheets and Vesicles Assembled from Nonplanar Cyclic π-Conjugated Molecules

A fundamental challenge in chemistry and materials science is to create new carbon nanomaterials by assembling structurally unique carbon building blocks, such as nonplanar π-conjugated cyclic molecules. However, self-assembly of such cyclic π-molecules to form organized nanostructures has been rarely explored despite intensive studies on their chemical synthesis. Here we synthesized a family of new cycloparaphenylenes and found that these fully hydrophobic and nonplanar cyclic π-molecules could self-assemble into structurally distinct two-dimensional crystalline multilayer nanosheets. Moreover, these crystalline multilayer nanosheets could overcome inherent rigidity to curve into closed crystalline vesicles in solution. These supramolecular assemblies show that the cyclic molecular scaffolds are homogeneously arranged on the surface of nanosheets and vesicles with their molecular isotropic x-y plane standing obliquely on the surface. These supramolecular architectures that combined exact crystalline order, orientation-specific arrangement of π-conjugated cycles, controllable morphology, uniform molecular pore, superior florescence quench ability, and photoluminescence are expected to give rise to a new class of functional materials displaying unique photonic, electronic, and biological functions.

Recent Advances of Hierarchical and Sequential Growth of Macromolecular Organic Structures on Surface

The fabrication of macromolecular organic structures on surfaces is one major concern in materials science. Nanoribbons, linear polymers, and porous nanostructures have gained a lot of interest due to their possible applications ranging from nanotemplates, catalysis, optoelectronics, sensors, or data storage. During decades, supramolecular chemistry has constituted an unavoidable approach for the design of well-organized structures on surfaces displaying a long-range order. Following these initial works, an important milestone has been established with the formation of covalent bonds between molecules. Resulting from this unprecedented approach, various nanostructures of improved thermal and chemical stability compared to those obtained by supramolecular chemistry and displaying unique and unprecedented properties have been developed. However, a major challenge exists: the growth control is very delicate and a thorough understanding of the complex mechanisms governing the on-surface chemistry is still needed. Recently, a new approach consisting in elaborating macromolecular structures by combining consecutive steps has been identified as a promising strategy to elaborate organic structures on surface. By designing precursors with a preprogrammed sequence of reactivity, a hierarchical or a sequential growth of 1D and 2D structures can be realized. In this review, the different reaction combinations used for the design of 1D and 2D structures are reported. To date, eight different sequences of reactions have been examined since 2008, evidencing the intense research activity existing in this field.

Understanding the affinity of bis-exTTF macrocyclic receptors towards fullerene recognition

Embracing [60]fullerene: Quantification of the C₆₀ affinity with a new series of exTTF macrocycles allows understanding the driving forces governing the supramolecular recognition upon increasing the alkyl ether chain size. Counterintuitively, an outside-ring complexation is found as the preferred arrangement over the expected inside-ring disposition.

Programmed Hierarchical Hybrid Nanostructures from Fullerene-Dendrons and Pyrene-Dendrons

The construction of fullerene (C₆₀ ) hierarchical nanostructures with the help of amphiphilic molecules remains a challenging task in nanoscience and nanotechnology. Utilizing the host-guest complex concept, sub-10 nm layered superstructures are constructed from a monofunctionalized C₆₀ dendron (C₆₀ D, guest) and tweezer-like pyrene dendron (PD, host). Since C₆₀ D and PD are asymmetric shape amphiphiles having liquid crystal (LC) dendrons, both C₆₀ D and PD construct head-to-head bilayer superstructures by themselves. From fluorescence titration experiments, it is realized that the host-guest complex shows 1:1 stoichiometric binding with a binding constant (K_sv = 2.45 × 10⁵ m^-1 ). Based on the morphological observations and scattering analyses, it is found that buckle-like asymmetric building blocks (C₆₀ D·PD) are self-assembled by the host-guest complex and construct multilayer hybrid nanostructures. The hierarchical hybrid nanostructures consist of the self-assembled C₆₀ D·PD bilayer with a 2D C₆₀ ·P nanoarray sandwiched between LC dendrons. This advanced strategy is expected to be a practicable and rational guideline for the fabrication of programmed hierarchical hybrid nanostructures.

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.

SMART Design of a Bulk-Capped Supramolecular Segment for the Assembly into Organic Interdigital Lipid Bilayer-Like (ILB) Nanosheets

Rational molecular design for the organic nanocrystal morphology still remains a challenge due to the structural diversity and complicated weak intermolecular interactions. In this work, a typical attractor-repulsor molecule N,N-diphenyl-4-(9-phenyl-fluoren-9-yl) phenylamine (TPA-PF) is designed to explore a general assembly strategy for 2D nanocrystals. Via an interdigital lipid bilayer-like (ILB) molecular packing mode, large-sized lamellar 2D nanosheets are obtained with a length:width:thickness ratio as ≈2500:1000:1. The d-spacing of the largest (001) plane is 1.32 nm, which equals to the thickness of a single interdigital stacking layer. The synergetic effect of the attractive supramolecular segment (TPA) and the repulsive bulky group (PF) is supposed to be the critical factor for the ILB packing that leads to the 2D structures. The attractor-repulsor molecule design is expected to be an effective strategy for the growth of 2D nanocrystals based on small organic molecules.

Tetraalkoxyphenanthrene-Fused Thiadiazoloquinoxalines: Synthesis, Electronic, Optical, and Electrochemical Properties, and Self-Assembly

π-Extended thiadiazoloquinoxaline (TQ) derivatives 1a,b-3a,b, in which a tetraalkoxyphenanthrene moiety is annulated with the TQ core and benzene rings are incorporated via the ethynylene spacer, were synthesized. They display absorption bands reaching into 750 nm and possess the electron-affinity comparable to [60]fullerene. The CF₃- and OMe-substituents on the benzene rings have moderate effects on modulation of the HOMO and LUMO levels. Tetraalkoxyphenanthrene-fused TQs 1a,b-3a,b aggregate in the solid state and assemble in solution through π-π stacking interactions. The self-assembly of 1a,b-3a,b into 1D superstructures was confirmed, and the difference in the alkoxy groups and the solvents for self-assembly proved to change their morphology. Comparison of the properties of 1a and those of reference compounds 4 and 5 clarified the effects of both the fusion of the phenanthrene moiety and the introduction of ethynylene spacers on the properties.

Frontiers of solvent-free functional molecular liquids

The breakthrough of functional molecular liquids (FMLs) in cutting-edge research and their fundamental liquid features on the basis of molecular architectures are highlighted in this Feature Article.

Cooperative supramolecular polymerization of a perylene diimide derivative and its impact on electron-transporting properties

H-bonding-promoted supramolecular polymerization of a perylene diimide (PDI) building block and its impact on charge carrier mobility.

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.

Reversible morphology transitions of supramolecular polymer self-assemblies for switch-controlled drug release

A novel method for switch-controlled drug release was developed through the reversible morphology transitions of supramolecular branched copolymer self-assemblies. The reversible transitions from vesicles to nanoparticles were successfully achieved by alternating UV and visible light irradiation to obtain morphology-controlled drug release in a switch mode.

H-bonding directed programmed supramolecular assembly of naphthalene-diimide (NDI) derivatives

In this review we have collated various supramolecular designs, all surrounding H-bonding among well-known functional groups (peptides, nucleic acids, amides, ureas, carboxylic acids, pyridine-hydroxyls, urethanes, imides and others), to dictate self-assembly of naphthalenediimide (NDI) π-systems (both small molecules and polymeric building blocks) that exhibit several exciting features including strong propensity for π-π interactions, π-acidity, excellent n-type semiconductivity, CT-complexation, ion-π interactions, ring-substitution dependent redox properties and photophysical properties. This article reveals that H-bonding can indeed serve as a very powerful and versatile tool to programmed self-assembly of a single or multiple dye system producing a wide range of tailored soft materials, including fibrillar gels, chromonic mesophases, foldamers, nanotubes, vesicles, reverse micelles and polymersomes, both in water and organic medium with distinct photophysical properties, charge transport properties, conductivity properties and functional group displays that are highly relevant in the fields of biology and organic electronics.

Bis-naphthalimides bridged by electron acceptors: optical and self-assembly characteristics

The self-assembly of small organic molecules into molecular stacks plays a vital role in the construction of stable supramolecular structures.

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.

J-aggregation, its impact on excited state dynamics and unique solvent effects on macroscopic assembly of a core-substituted naphthalenediimide

Herein we reveal a straightforward supramolecular design for the H-bonding driven J-aggregation of an amine-substituted cNDI in aliphatic hydrocarbons. Transient absorption spectroscopy reveals sub-ps intramolecular electron transfer in isolated NDI molecules in a THF solution followed by a fast recombination process, while a remarkable extension of the excited state lifetime by more than one order of magnitude occurred in methylcyclohexane likely owing to an increased charge-separation as a result of better delocalization of the charge-separated states in J-aggregates. We also describe unique solvent-effects on the macroscopic structure and morphology. While J-aggregation with similar photophysical characteristics was noticed in all the tested aliphatic hydrocarbons, the morphology strongly depends on the "structure" of the solvents. In linear hydrocarbons (n-hexane, n-octane, n-decane or n-dodecane), formation of an entangled fibrillar network leads to macroscopic gelation while in cyclic hydrocarbons (methylcyclohexane or cyclohexane) although having a similar polarity, the cNDI exhibits nanoscale spherical particles. These unprecedented solvent effects were rationalized by establishing structure-dependent specific interactions of the solvent molecules with the cNDI which may serve as a general guideline for solvent-induced morphology-control of structurally related self-assembled materials.

Alkyl-π engineering in state control toward versatile optoelectronic soft materials

Organic π-conjugated molecules with extremely rich and tailorable electronic and optical properties are frequently utilized for the fabrication of optoelectronic devices. To achieve high solubility for facile solution processing and desirable softness for flexible device fabrication, the rigid π units were in most cases attached by alkyl chains through chemical modification. Considerable numbers of alkylated-π molecular systems with versatile applications have been reported. However, a profound understanding of the molecular state control through proper alkyl chain substitution is still highly demanded because effective applications of these molecules are closely related to their physical states. To explore the underlying rule, we review a large number of alkylated-π molecules with emphasis on the interplay of van der Waals interactions (vdW) of the alkyl chains and π-π interactions of the π moieties. Based on our comprehensive investigations of the two interactions' impacts on the physical states of the molecules, a clear guidance for state control by alkyl-π engineering is proposed. Specifically, either with proper alkyl chain substitution or favorable additives, the vdW and π-π interactions can be adjusted, resulting in modulation of the physical states and optoelectronic properties of the molecules. We believe the strategy summarized here will significantly benefit the alkyl-π chemistry toward wide-spread applications in optoelectronic devices.

Fulleropeptide esters as potential self-assembled antioxidants

The potential use of amphiphilic fullerene derivatives as a bionanomaterial was investigated by cyclic voltammetry (CV), scanning electron microscopy (SEM), and the ferrous ion oxidation-xylenol orange (FOX) method. Despite the disrupted delocalization of the π-electronic system over the C60 sphere, its antioxidant capacity remained high for all twelve derivatives. The compounds expressed up to two-fold and 5-12-fold better peroxide quenching capacity as compared to pristine C60 and standard antioxidant vitamin C, respectively. During precipitation and slow evaporation of the solvent, all compounds underwent spontaneous self-assembly giving ordered structures. The size and morphology of the resulting particles depend primarily on the sample concentration, and somewhat on the side chain structure.

Fulleropyrrolidines derived from dioxa- and trioxaalkyl-tethered diglycines

The synthesis, characterization, morphological, electrochemical and antioxidant properties of fulleropyrrolidines bridged by polyoxaalkyl chains are described.

Synthesis and sub-10 nm supramolecular self-assembly of a nanohybrid with a polynorbornene main chain and side-chain POSS moieties

A polynorbornene-based mesogen-jacketed liquid crystalline polymer containing side-chain crystalline POSS moieties was synthesized through ROMP. It self-assembles into an organic–inorganic hybrid inclusion complex on the sub-10 nm scale.

π–π interactions in carbon nanostructures

A concise tutorial review on the basic concepts of π–π interactions involving fullerenes, carbon nanotubes, and graphene.

Fulleropyrrolidine molecular dumbbells act as multi-electron-acceptor triads. Spectroscopic, electrochemical, computational and morphological characterizations

Three novel fulleropyrrolidine dumbbells consisting three electron acceptor moieties joined by alkyl linker displaying tunable electrical and morphological properties were synthesized and characterized.

Extended supramolecular organization of π-systems using yet unexplored simultaneous intra- and inter-molecular H-bonding motifs of 1,3-dihydroxy derivatives

Simultaneous intra- and inter-molecular H-bonding among 1,3-dihydroxyl derivatives with acceptor chromophores leads to fibrillar gelation facilitating π-stacking and specific donor intercalation.