Helical structures such as double helical DNA and the α-helical proteins found in biological systems are among the most beautiful natural structures. Chiral nanoarchitectonics, which is used here to describe the hierarchical formation and fabrication of chiral nanoarchitectures that can be observed by atomic force microscopy (AFM), scanning tunneling microscopy (STM), scanning electron microscopy (SEM), or transmission electron microscopy (TEM), is one of the most effective ways to mimic those natural chiral nanostructures. This article focuses on the formation, structure, and function of the most common chiral nanoarchitectures: nanoscale chiral twists and helices. The types of molecules that can be designed and how they can form hierarchical chiral nanoarchitectures are explored. In addition, new and unique functions such as amplified chiral sensing, chiral separation, biological effects, and circularly polarized luminescence associated with the chiral nanoarchitectures are discussed.

One-dimensional (1D) solid-state supramolecular structures based on porphyrin chromophores arouse numerous expectations from the interdisciplinary scientific communities of supramolecular chemistry and advanced soft materials science. This stems from the intrinsic assembly capability of porphyrins to form various well-defined 1D assemblies, which have broad opportunities in the fields of advanced soft matter. A brief review on 1D porphyrin micro-/nanoassemblies constructed via surfactant-assisted self-assembly is presented here, in terms of addressing new ideas recently developed for controlled assembly, hierarchical organization, and new-type functional surfactants etc. The functionalization of the as-assembled 1D structures with regard to supramolecular photocatalysis, non-linear optics, nanoelectronic gas sensors, photoelectrochemical solar cells, etc. is highlighted.

A new class of L-glutamic gelators, LG₁₂(CH₂)_nCOOH, containing different lengths of methylene spacer were synthesized. It was found that the gelation ability of these compounds themselves was very weak. However, when another compound, p-xylylenediamine (XEA), was introduced, the gelation ability was improved greatly. In particular, LG₁₂(CH₂)₁₀COOH showed super-gelation ability in the presence of XEA, which could immobilize almost all of the solvents except methanol. Moreover, the formed supramolecular gels even could be molded. Interestingly, some supramolecular gels of LG₁₂(CH₂)_nCOOH and XEA could respond to multiple stimuli, such as heating, shaking, sonication, and acid/base. The studies of CD spectra suggested that the supramolecular chirality induced by self-assembled chiral gelator molecules in gels could be tuned by the length of methylene spacer. In addition, the supramolecular chirality could be regulated as on/off by heating–cooling or external NH₃/HCl. This would facilitate the development of dual chiroptical switches by temperature and acid/base.

An intelligent molecular hydrogel with a volume phase transition was constructed to regulate the chiral packing of a well-known cyanine dye on a dynamically self-assembled chiral nanofiber by using a pH trigger. During the shrinkage of the gel, the chiral nanofiber hierarchically assembled into a superhelix and simultaneously drove the dye molecules to stack, from a predominantly monomer form, in an unexpected helical H-aggregation manner. Through such a transformation, the supramolecular chirality of the system was significantly enhanced and a new property of visual discrimination for chiral amines emerged.

Supramolecular chirality, which arises from the nonsymmetric spatial arrangement of components in the self-assembly systems, has gained great attention owing to its relation to the natural biological structures and the possible new functions in advanced materials. During the self-assembling process, both chiral and achiral components are possible to form chiral nanostructures. Therefore, it becomes an important issue how to fabricate these molecular components into chiral nanostructures. Furthermore, once the chiral nanostructure is obtained, will it show new functions that simple component molecule could not? In this research news, we report our recent development in the regulation of chiral nanostructures in soft gels or vesicle materials. We have further developed several new functions pertaining to the soft gel materials, which single chiral molecules could not perform, such as the chiroptical switch, chiral recognition and the asymmetry catalysis.

Graphene-based ultrathin films with tunable performances, controlled thickness, and high stability are crucial for their uses. The currently existing protocols, however, could hardly simultaneously meet these requirements. Using amino-substituted π-conjugated compounds, including 1,4-diaminobenzene (DABNH2), benzidine (BZDNH2), and 5,10,15,20-tetrakis (4-aminophenyl)-21H,23H-porphine (TPPNH2), as cross-linkages, a new protocol through which graphene oxide (GO) nanosheets can be anchored on solid supports with a high stability and controlled thickness via a layer-by-layer method is presented. A thermal annealing leads to the reduction of the films, and the qualities of the samples can be inherited by the as-produced reduced GO films (RGO). When RGO films are integrated as source/drain electrodes in OFETs, tunable performances can be realized. The devices based on the BZDNH2-crosslinked RGO electrodes exhibit similar electrical behaviors as those based on the non-π-conjugated compound crosslinked electrodes, while improved performances can be gained when those crosslinked by DABNH2 are used. The performances can be further improved when RGO films crosslinked by TPPNH2 are employed. This work likely paves a new avenue for graphene-based films of tunable performances, controlled thickness, and high stability.

A C₃-symmetric benzene-1,3,5-tricarboxamide substituted with ethyl cinnamate was found to self-assemble into supramolecular gels with macroscopic chirality in a DMF/H₂O mixture. The achiral compound simultaneously formed left- and right-handed twists in an unequal number, thus resulting in the macroscopic chirality of the gels without any chiral additives. Furthermore, ester–amide exchange reactions with chiral amines enabled the control of both the handedness of the twists and the macroscopic chirality of the gels, depending on the structures of the chiral amines. These results provide new prospects for understanding and regulating symmetry breaking in assemblies of supramolecular gels formed from achiral molecular building blocks.

A series of new π-conjugated gelators that contain various aromatic rings (phenyl, naphthyl, 9-anthryl) and amphiphilic L-glutamide was designed, and their gel formation in organic solvents and self-assembled nanostructures was investigated. The gelators showed good gelation ability in various organic solvents that ranged from polar to nonpolar. Those gelator molecules with small rings such as phenyl and naphthyl self-assembled into nanotube structures in most organic solvents and showed strong blue emission. However, the 9-anthryl derivative formed only a nanofiber structure in any organic solvent, probably owing to the larger steric hindrance. All of these gels showed enhanced fluorescence in organogels. Furthermore, during the gel formation, the chirality at the L-glutamide moiety was transferred to the nanostructures, thus leading to the formation of chiral nanotubes. One of the nanotubes showed chiral recognition toward the chiral amines.

A shrinkable supramolecular metallo-hydrogel based on the L-glutamic acid dendron and magnesium showed reversible volume-phase transition depending on pH changes. The hydrogel further showed selective shrinkage upon addition of positively charged species, while it remained in the gel state when negatively charged species were incorporated. Based on this property, the gel could be used as the matrix to efficiently separate ionic dye mixtures, in which the cationic dye was incorporated predominantly in the shrunken gel, while the negatively charged dye was released into the aqueous solution. More interestingly, the shrinkable gel can be used as a model drug-delivery vehicle for the stepwise release of a two-component drug system, in which the negatively charged drug is released first and then the second component is released with a pH trigger.

Although solvent is the major component of the gel, it still remains unclear how the solvent molecules take part in the formation of the gel nanostructures in many gels. In this study it was observed that the vicinal effect on gel formation as well as their nanostructures, that is, the vicinal solvent molecules to the gelator, determine the molecular packing and their subsequent structures and properties. A naphthylacryl-conjugated L-glutamide gelator was found to form organogels in various solvents and nanofiber structures. While the nanofibers from other solvents could not show any further reaction, the gel from the alcohol could undergo topochemical [2+2] cycloaddition under photoirradiation and resulted in toruloid nanostructures. Various pure alcohol solvents from methanol to pentanol were found to show a similar property. Interestingly, switching from a single alcohol solvent to mixed solvents of alcohol with miscible or immiscible non-alcohol solvents could still cause the same change, showing the vicinal effect of alcohol on controlling the molecular packing as well as the structural transformation. More interestingly, when nanofiber xerogel, obtained from non-alcohol solvents, was exposed to alcohol vapor, the nanofiber was transferred into nanotoruloid. These results provide a new insight into the gelator–solvent interaction in soft gels.

Highly stable graphene oxide (GO)-based multilayered ultrathin films can be covalently immobilized on solid supports through a covalent-based method. It is demonstrated that when (3-aminopropyl) trimethoxysilane (APTMS), which works as a covalent cross-linking agent, and GO nanosheets are assembled in an layer-by-layer (LBL) manner, GO nanosheets can be covalently grafted on the solid substrate successfully to produce uniform multilayered (APTMS/GO)N films over large-area surfaces. Compared with conventional noncovalent LBL films constructed by electrostatic interactions, those assembled using this covalent-based method display much higher stability and reproducibility. Upon thermal annealing-induced reduction of the covalent (APTMS/GO)N films, the obtained reduced GO (RGO) films, (APTMS/RGO)N, preserve their basic structural characteristics. It is also shown that the as-prepared covalent (APTMS/RGO)N multilayer films can be used as highly stable source/drain electrodes in organic field-effect transistors (OFETs). When the number of bilayers of the (APTMS/RGO)N film exceeds 2 (ca. 2.7 nm), the OFETs based on (APTMS/RGO)N electrodes display much better electrical performance than devices based on 40 nm Au electrodes. The covalent protocol proposed may open up new opportunities for the construction of graphene-based ultrathin films with excellent stability and reproducibility, which are desired for practical applications that require withstanding of multistep post-production processes.

The self-assembly of a low-molecular-weight organogelator into various hierarchical structures has been achieved for a pyridylpyrazole linked L-glutamide amphiphile in different solvents. Upon gel formation, supramolecular chirality was observed, which exhibited an obvious dependence on the polarity of the solvent. Positive supramolecular chirality was obtained in nonpolar solvents, whereas it was inverted into negative supramolecular chirality in polar solvents. Moreover, the gelator molecules self-assembled into a diverse array of nanostructures over a wide scale range, from nanofibers to nanotubes and microtubes, depending on the solvent polarity. Such morphological changes could even occur for the xerogels in the solvent vapors. We found that the interactions between the pyridylpyrazole headgroups and the solvents could subtly change the stacking of the molecules and, hence, their self-assembled nanostructures. This work exemplifies that organic solvents can significantly involve the gelation, as well as tune the structure and properties, of a gel.

A dual-functional metallogel, which was based on the copper(II) complex of quinolinol-substituted L-glutamide, showed both redox-responsive and enantioselective properties; moreover, the metallogels collapsed into a sol after reduction and could be revived upon subsequent oxidation. The supramolecular chirality and morphology also reversible changed with the gel–sol transition. Furthermore, the metallogels showed new enantioselective recognition towards chiral aromatic amino acids. A new emission band in the blue-light region at around 393 nm appeared when the metallogels encountered L-aromatic amino acids, whereas no new emission band was observed for the corresponding D-aromatic amino acids. Such enantioselectivity only occurred in the gel state. No similar phenomenon could be observed in solution. This result suggested that, during the gel formation, the gelator molecules self-assembled into ordered, chiral supramolecular structures and enhanced the enantiorecognition of the L-aromatic amino acids.

Novel amphiphilic molecules composed of naphthylacryl and L-glutamide moieties (1-NA and 2-NA) have been designed and their organogel formation in various organic solvents as well as their self-assembled nanostructures have been investigated. Both compounds formed organogels in many organic solvents, ranging from nonpolar to polar, and self-assembled into essentially nanofiber structures, although some twist or belt structures could be observed in certain solvents. A gel of compound 2-NA in ethanol initially self-assembled into nanofibers and then these were transformed into a family of coaxial hollow toruloid-like (CHTL) nanostructures under irradiation, in which various toroids and disks of different sizes were stacked coaxially. We have established that a topochemical [2+2] cycloaddition in the organogel triggers this transformation. When the gel was fabricated into xerogels in which no ethanol remained, such morphological changes could not happen. This might be the first report of an organogel, in which both organized nanofibers and solvent coexist, controlling a topochemical reaction as well as the self-assembled nanostructures formed. Due to the formation of the toruloid-like nanostructures, the gel collapsed to a precipitate. However, upon heating this precipitate with ethanol, it redissolved and then formed a gel and self-assembled into nanofibers once more. Thus, a reversible morphological transformation between nanofibers and an unprecedented series of toruloid-like nanostructures can be induced by alternately heating and irradiating the gel.

Supramolecular polymers from the bolaamphiphilic L-histidine (BolaHis) and benzene dicarboxylic acids (o-phthalic acid, OPA; isophthalic acid, IPA and terephthalic acid, TPA) were found to form hydrogels although neither of the single components could gel water. It was suggested that the hydrogen bond and ionic interactions among different imidazole and carboxylic acid groups are responsible for the formation of the supramolecular polymer as well as the hydrogel formation. Depending on the structures of the dicarboxylic acids, different behaviors of the gels were observed. The hydrogels from OPA/BolaHis and IPA/BolaHis showed thixotropic properties, that is, the hydrogel was destroyed by hand shaking and then slowly gelated again at room temperature. However, the hydrogels of TPA/BolaHis could not. Interestingly, when Eu^III was doped into IPA/BolaHis supramolecular polymers, very strong luminescence enhancement was observed. FT-IR spectroscopies and XRD analysis revealed that the strong luminescence enhancement could be attributed to the matched supramolecular nanostructures, which render the correct binding and a good dispersion of Eu^III ions. The work offers a new approach for fabricating functional hydrogels through the supramolecular polymers.

New amphiphilic gelators that contained both Schiff base and L-glutamide moieties, abbreviated as o-SLG and p-SLG, were synthesized and their self-assembly in various organic solvents in the absence and presence of metal ions was investigated. Gelation test revealed that o-SLG formed a thermotropic gel in many organic solvents, whilst p-SLG did not. When metal ions, such as Cu²⁺, Zn²⁺, Mg²⁺, Ni²⁺, were added, different behaviors were observed. The addition of Cu²⁺ induced p-SLG to from an organogel. In the case of o-SLG, the addition of Cu²⁺ and Mg²⁺ ions maintained the gelating ability of the compound, whilst Zn²⁺ and Ni²⁺ ions destroyed the gel. In addition, the introduction of Cu²⁺ ions caused the nanofiber gel to perform a chiral twist, whilst the Mg²⁺ ions enhanced the fluorescence of the gel. More interestingly, the Mg²⁺-ion-mediated organogel showed differences in the fluorescence quenching by D- and L-tartaric acid, thus showing a chiral recognition ability.

A series of amphiphilic L-glutamic acid derivatives with various saturated alkyl chains has been designed and their co-assembly with 4,4′-bipyridine in aqueous media has been investigated. While the individual amphiphiles formed hydrogels with water and self-assembled into fine fiber networks, the addition of 4,4′-bipyridine caused significant changes in the co-assembled nanostructures such that twisted chiral ribbons were formed. In these supramolecular systems, either fine structural changes or adjustment of the stoichiometric ratio of the two components had crucial effects on the formation of the chiral twists. Based on detailed investigations by SEM and XRD analyses, FTIR, CD, and UV/Vis spectroscopies, and molecular simulation, it is considered that a delicate synergistic balance between π–π stacking, hydrophobic, and chiral interactions is responsible for the formation of the chiral twists. An interesting sandwich structure, in which an excess of 4,4′-bipyridine is inserted into the space of primary cages constructed from the amphiphile and 4,4′-bipyridine, is proposed. Remarkably, the handedness of these chiral twists is related not only to the chiral center of the glutamic unit, but also the chain length of the alkyl tails. This work provides a deeper understanding of the formation mechanism of chiral twists, and exemplifies a feasible shortcut to the rational design of chiral structures from basic molecular structures to supramolecular systems.

An amphiphilic dendron containing three dendrite L-glutamic acid units and a long alkyl chain was synthesized by a convergent method. It was found that the dendron could form hydrogels over a wide pH range from 2 to 13. Moreover, accompanying the pH change, the compounds self-assembled into various chiral structures: from helical nanotube, helical nanotube with a string of beads, and coiled superhelix to dendrite nanostructures, such as pine, feather, etc. A series of characterizations based on TEM observations, X-ray diffraction and FTIR spectroscopic measurements revealed that the dendron formed a bilayer first and then hierarchically self-assembled into various chiral nanostructures. The four carboxylic acid groups and three amide groups played an important role in the self-assembly. The interaction between the multiamide groups stabilized the bilayer structures, whereas the ionization degree of the carboxylic acids was responsible for the formation of various chiral structures. The work presented a hydrogel system with wide pH adaptability and showed the regulation on chiral structures by simple pH variations.

A new method is described through which the macroscopic chirality of interfacial molecular assemblies of an achiral porphyrin can be mechanically controlled using an original yet efficient Langmuir–Blodgett (LB) technique. By using the unilateral compression geometry, we find that the assemblies deposited from the mirror regions of the LB trough display mirror macroscopic chirality. It is indicated that vortex-like flows could be generated during compression, and that it is the direction of this compression-generated vortex-like flow that determine the macroscopic chirality of the formed assemblies. Moreover, the standard sample-fabrication method with bilateral compression geometry is reformed, and we find that the samples formulated around the left-hand- and right-hand-side Langmuir barriers display opposite macroscopic chiralities. The results suggest that mechanically controlled supramolecular chirogenesis could be efficiently realized through such an LB technique. The investigation establishes a new forum for further investigation of the mechanically induced preferred supramolecular chirality in terms of interfacial organization, and provides the old LB technique with new opportunities for controlling the macroscopic chirality of a supramolecular system that is wholly composed of achiral units.

Enantiomeric L- or D-glutamic acid based lipids were designed and their self-assembly was investigated. It was found that at a certain concentration, either L- or D-enantiomeric derivatives could self-assemble in absolute alcohol to form a white organogel, which was composed of ultralong nanotubes with an aspect ratio higher than 1000. Further investigations revealed that these nanotubes were in chiral forms. The chirality of the nanotubes was determined by that of the enantiomers employed. In addition, when D and L enantiomers were mixed in different ratios, the nanotube could be tuned consecutively from nanotubes with a helical seam to nanotwists, the chirality of which being determined by the excess enantiomer in the mixed systems. In the case of an equimolar mixture of the enantiomers, flat nanoplates instead of helical nanotubes or nanotwists were obtained. The FTIR vibrational data and XRD layer-distance values showed a consecutive change as a function of the enantiomeric excess. It was further revealed that the slightly stronger interaction between D–L enantiomeric pairs than that between D–D or L–L pairs was responsible for the formation of the diverse self-assembled nanostructures.

Molecular assemblies of metalloporphyrins trans-dichloro(5,10,15,20-tetra-p-tolylporphyrinato)tin(IV) (SnCl2TPPMe) and trans-dihydroxo(5,10,15,20-tetra-p-tolylporphyrinato)tin(IV) (Sn(OH)2TPPMe), which have two trans axial ligands, as well 5,10,15,20-tetrakis(4-methoxyphenyl)-21H,23H-porphine iron(III) chloride (FeClTPPOMe) and 5,10,15,20-tetraphenyl-21H,23H-porphine manganese(III) chloride (MnClTPP), which have one axial ligand, are interfacially organized by Langmuir and Langmuir–Blodgett (LB) techniques. SnCl2TPPMe and Sn(OH)2TPPMe form nanofibrous structures which can display distinct supramolecular chirality, although the molecular units themselves are achiral, while FeClTPPOMe and MnClTPP form irregular nanoparticles that display negligible supramolecular chirality. An interpretation in terms of the effects of the axial ligands is proposed for this interesting phenomenon. Moreover, compared with assemblies of the diprotonated free-base porphyrins, which are fabricated by interfacial (air/2.4 M HCl) organization of free-base porphyrin, those of SnCl2TPPMe and Sn(OH)2TPPMe display higher stability in terms of supramolecular chirality. These results indicate that the assembly properties of metalloporphyrins can essentially be affected by the axial ligands that are attached to their chromophores, and that stable chiral porphyrin supramolecular associations can be easily produced by using achiral metalloporphyrins bearing two trans axial ligands.

Chirality plays an important role in biological and material sciences. By introducing chiral elements into functional materials, new properties are created and an increase in information density can be achieved. Chiral properties of functional materials do not only rely on molecular structure, but also on supramolecular interaction between the building blocks. In contrast to the generally accepted opinion that chiral systems should include chiral molecules, this Research News introduces the role of achiral molecules in realizing chiral properties in films and gel-like materials. Even a system that is entirely composed of achiral molecules can exhibit interesting chiroptical properties in supramolecular ultrathin films. This article demonstrates how achiral molecules can be assembled into supramolecular chiral films and organogels. It further shows how the incorporated achiral molecules can be used to switch the chiral properties of these supramolecular films and organogels.