Helical DNA Origami Tubular Structures with Various Sizes and Arrangements

We developed a novel method to design various helical tubular structures using the DNA origami method. The size‐controlled tubular structures which have 192, 256, and 320 base pairs for one turn of the tube were designed and prepared. We observed the formation of the expected short tubes and unexpected long ones. Detailed analyses of the surface patterns of the tubes showed that the short tubes had mainly a left‐handed helical structure. The long tubes mainly formed a right‐handed helical structure and extended to the directions of the double helical axes as structural isomers of the short tubes. The folding pathways of the tubes were estimated by analyzing the proportions of short and long tubes obtained at different annealing conditions. Depending on the number of base pairs involved in one turn of the tube, the population of left‐/right‐handed and short/long tubes changed. The bending stress caused by the stiffness of the bundled double helices and the non‐natural helical pitch determine the structural variety of the tubes.     

Helical Mesoporous Tantalum Oxide Nanotubes: Formation,Optical Activity,and Applications

Nanomaterials with helical morphologies have attracted much attention owing to their potential applications as nanosprings, chirality sensors and in chiral optics. Single‐handed helical Ta₂O₅ nanotubes prepared through a supramolecular templating approach are described. The handedness is controlled by that of the organic self‐assemblies of chiral low‐molecular‐weight gelators (LMWGs). The chiral LMWGs self‐assemble into single‐handed twisted nanoribbons through H‐bonding, hydrophobic association, and π‐π stacking. The Ta₂O₅ nanotubes are formed by the adsorption and polycondensation of Ta₂O₅ oligomers on the surfaces and edges of the twisted organic nanoribbons followed by removal of the template. The optical activity of the nanotubes is proposed to originate from the chiral defects on the inner surfaces of the tubular structures. Single‐handed twisted LiTaO₃ nanotubes can also be prepared using Ta₂O₅ nanotubes.     

Peculiar Triarylamine‐Based Co‐assembled Supramolecular Polymers That Exhibit Two Transition Temperatures in the Formation of a Coiled Helical Bundle

This paper describes the peculiar co‐assembly supramolecular polymerization behavior of triphenylamine trisamide derivatives with d ‐alanine ( T‐ala ) or glycine ( T‐gly ) moieties. Concentration and temperature‐dependent circular dichroism (CD) spectroscopy revealed that the heating curves of co‐assemblies obtained at various molar ratios of T‐ala to T‐gly exhibited two distinct transition temperatures. The first transition was due to the transformation from coiled helical bundles to single helical fibers without handedness. The second was due to a change from typical elongation to nucleation. These phenomena were confirmed by solvent‐dependent decoiling of coiled helical structures and concentration‐dependent morphological analysis. The two transitioning temperatures were dependent on the concentration of T‐ala in the co‐assemblies, suggesting that T‐ala concentration plays an important role in the formation of coiled helical bundles. Our study demonstrated the first observation of two distinct transition temperatures in supramolecular polymers.     

Herringbone and Helical Self‐Assembly of π‐Conjugated Molecules in the Solid State through CH/π Hydrogen Bonds

Self‐organization of organic molecules through weak noncovalent forces such as CH/π interactions and creation of large hierarchical supramolecular structures in the solid state are at the very early stage of research. The present study reports direct evidence for CH/π interaction driven hierarchical self‐assembly in π‐conjugated molecules based on custom‐designed oligophenylenevinylenes (OPVs) whose structures differ only in the number of carbon atoms in the tails. Single‐crystal X‐ray structures were resolved for these OPV synthons and the existence of long‐range multiple‐arm CH/π interactions was revealed in the crystal lattices. Alignment of these π‐conjugated OPVs in the solid state was found to be crucial in producing either right‐handed herringbone packing in the crystal or left‐handed helices in the liquid‐crystalline mesophase. Pitch‐ and roll‐angle displacements of OPV chromophores were determined to trace the effect of the molecular inclination on the ordering of hierarchical structures. Furthermore, circular dichroism studies on the OPVs were carried out in the aligned helical structures to prove the existence of molecular self‐assembly. Thus, the present strategy opens up new approaches in supramolecular chemistry based on weak CH/π hydrogen bonding, more specifically in π‐conjugated materials.     

Inversion of Supramolecular Helicity in Oligo‐p‐phenylene‐Based Supramolecular Polymers: Influence of Molecular Atropisomerism

The helical organization of oligo‐p‐phenylene‐based organogelators has been investigated by atomic force microscopy, circular and vibrational circular dichroism, and Raman techniques. Whilst OPPs with more than two phenyl rings in the core self‐assemble into left‐handed helices, that with a biphenyl core shows an inversion of the supramolecular helicity depending on the formation conditions through the atropisomerism of the biphenyl central unit. The results presented herein outline a new example of kinetically controlled modulation of supramolecular helicity.     

Solvent‐Induced Helical Assembly and Reversible Chiroptical Switching of Chiral Cyclic‐Dipeptide‐Functionalized Naphthalenediimides

Understanding the roles of various parameters in orchestrating the preferential chiral molecular organization in supramolecular self‐assembly processes is of great significance in designing novel molecular functional systems. Cyclic dipeptide (CDP) chiral auxiliary‐functionalized naphthalenediimides (NCDPs 1 – 6 ) have been prepared and their chiral self‐assembly properties have been investigated. Detailed photophysical and circular dichroism (CD) studies have unveiled the crucial role of the solvent in the chiral aggregation of these NCDPs. NCDPs 1 – 3 form supramolecular helical assemblies and exhibit remarkable chiroptical switching behaviour (M‐ to P‐type) depending on the solvent composition of HFIP and DMSO. The strong influence of solvent composition on the supramolecular chirality of NCDPs has been further corroborated by concentration and solid‐state thin‐film CD studies. The chiroptical switching between supramolecular aggregates of opposite helicity (M and P) has been found to be reversible, and can be achieved through cycles of solvent removal and redissolution in solvent mixtures of specific composition. The control molecular systems (NCDPs 4 – 6 ), with an achiral or D ‐isomer second amino acid in the CDP auxiliary, did not show chiral aggregation properties. The substantial roles of hydrogen bonding and π–π interactions in the assembly of the NCDPs have been validated through nuclear magnetic resonance (NMR), photophysical, and computational studies. Quantum chemical calculations at the ab initio, semiempirical, and density functional theory levels have been performed on model systems to understand the stabilities of the right (P‐) and left (M‐) handed helical supramolecular assemblies and the nature of the intermolecular interactions. This study emphasizes the role of CDP chiral auxiliaries on the solvent‐induced helical assembly and reversible chiroptical switching of naphthalenediimides.     

Crystallization‐Driven Asymmetric Helical Assembly of Conjugated Block Copolymers and the Aggregation Induced White‐light Emission and Circularly Polarized Luminescence

Controlling the self‐assembly morphology of π‐conjugated block copolymer is of great interesting. Herein, amphiphilic poly(3‐hexylthiophene)‐block‐poly(phenyl isocyanide)s (P3HT‐b‐PPI) copolymers composed of π‐conjugated P3HT and optically active helical PPI segments were readily prepared. Taking advantage of the crystallizable nature of P3HT and the chirality of the helical PPI segment, crystallization‐driven asymmetric self‐assembly (CDASA) of the block copolymers lead to the formation of single‐handed helical nanofibers with controlled length, narrow dispersity, and well‐defined helicity. During the self‐assembly process, the chirality of helical PPI was transferred to the supramolecular assemblies, giving the helical assemblies large optical activity. The single‐handed helical assemblies of the block copolymers exhibited interesting white‐light emission and circularly polarized luminescence (CPL). The handedness and dissymmetric factor of the induced CPL can be finely tuned through the variation on the helicity and length of the helical nanofibers.     

Helical Carbon and Graphite Films Prepared from Helical Poly(3,4‐ethylenedioxythiophene) Films Synthesized by Electrochemical Polymerization in Chiral Nematic Liquid Crystals

Helical carbon and graphite films from helical poly(3,4‐ethylenedioxythiophene) (H‐PEDOT) films synthesized through electrochemical polymerization in a chiral nematic liquid‐crystal (N*‐LC) field are prepared. The microscope investigations showed that the H‐PEDOT film synthesized in the N*‐LC has large domains of one‐handed spiral morphology consisting of fibril bundles. The H‐PEDOT films exhibited distinct Cotton effects in circular dichroism spectra. The highly twisted N*‐LC with a helical pitch of smaller than 1 μm produced the H‐PEDOT film with a highly ordered morphology. The spiral morphologies with left‐ and right‐handed screws were observed for the carbon films prepared from the H‐PEDOT films at 800 °C and were well correlated with the textures and helical pitches of the N*‐LCs. The spiral morphologies of the precursors were also retained even in the graphite films prepared from the helical carbon films at 2600 °C.     

A Heterobimetallic AuIII‐PtII Photocatalyst for Water Reduction to Hydrogen

A supramolecular complex, [Au(C^N^C)(C≡CC₆H₄C≡C)Pt(terpy)]⁺, has been synthesized as a photocatalyst for water reduction. This compound consists of a cyclometalated alkyne‐gold(III) photosensitizer and a platinum(II) terpyridine complex bridged through a central phenylethynyl group.     

Synthesis and Self‐Assembled Helical Supramolecular Polymer of Ethyl 7,8‐dihydro‐3‐hydroxy‐9‐methyl‐7‐(4′‐nitrophenyl)‐6H‐dibenzo[c]‐ pyran‐6‐one‐8‐carboxylate

A structurally novel compound was isolated as the main product of tandem Pechmann–dehydration between diethyl 4‐hydroxy‐4‐methyl‐2‐(4′‐nitrophenyl)‐6‐oxocyclohexane‐1,3‐dicarboxylate ( 1 ) and resorcinol in the presence of trifluoroacetic acid. The structure of the product was determined as a racemate of (7R,8R)‐ and (7S,8S)‐ethyl 7,8‐dihydro‐3‐hydroxy‐9‐methyl‐7‐(4′‐nitrophenyl)‐6H‐dibenzo[c]‐pyran‐6‐one‐8‐carboxylate ( 3a ) enantiomers by single crystal X‐ray diffraction analysis. The X‐ray crystal structure revealed that 3a possesses an extended and more stable conjugated aromatic system as a consequence of the stereoselectivity of intramolecular dehydration behavior of Pechmann condensation product 2 . In the crystal superstructure, the (7R,8R)‐ and (7S,8S)‐isomers of 3a respectively self‐assembled into left‐ and right‐handed supramolecular helical chains with a channel size of 3.70 Å × 10.20 Å in virtue of intermolecular hydrogen bonding together with dramatic twisting between carboxylate group at C8 and tricyclic ring framework of 3a , which are then arranged alternatively along the b‐axis direction with a pitch length of 7.894 Å.     

Trismaleimide Dendrimers: Helix‐to‐Superhelix Supramolecular Transition Accompanied by White‐Light Emission

Reported here are unprecedented fluorescent superhelices composed of primary, supramolecular polymers of the opposite helical twist. A new class of functional dendrimers was synthesized by amino‐ene click reactions, and they demonstrate an alternating OFF/ON fluorescence with generation growth. A peripherally alkyl‐modified dendrimer displays helix‐sense‐selective supramolecular polymerization, which predominantly forms right‐handed (or left‐handed) helical supramolecular polymers in the solution containing chiral solvents. With increasing the concentration, these primary helical supramolecular polymers spontaneously twist around themselves in the opposite direction to form superhelical structures. Atomic force microscopy and circular dichroism measurements were used to directly observe the helix‐to‐superhelix transition occurring with a reversal in the helical direction. Exceptional white‐light emission was observed during superhelix formation.     

The Helix to Super‐Helix Transition in the Self‐Assembly of π‐Systems: Superseding of Molecular Chirality at Hierarchical Level

Higher‐order super‐helical structures derived from biological molecules are known to evolve through opposite coiling of the initial helical fibers, as seen in collagen protein. A similar phenomenon is observed in a π‐system self‐assembly of chiral oligo(phenyleneethylene) derivatives (S )‐ 1 and (R )‐ 1 that explains the unequal formation of both left‐ and right‐handed helices from molecule having a specific chiral center. Concentration‐ and temperature‐dependent circular dichroism (CD) and UV/Vis spectroscopic studies revealed that the initial formation of helical aggregates is in accordance with the molecular chirality. At the next level of hierarchical self‐assembly, coiling of the fibers occurs with opposite handedness, thereby superseding the command of the molecular chirality. This was confirmed by solvent‐dependent decoiling of super‐helical structures and concentration‐dependent morphological analysis.     

Effects of the Auxiliary Ligands on the Structures of Diphenate Complexes: From 1D Helical Chain to 2D Network

Two coordination polymers, [Cd(dpa)(L1)] ( 1 ) and [Cd(dpa)(L2)]·CH₃CH₂OH₃ ( 2 ) (L1 = 2,6‐bis(1H‐benzimidazol‐2yl)‐pyridine, L2 = 2,2′‐(1,4‐butanediyl) bis (1H‐ benzimidazole) (L2), both of which contain helical chain subunits, were synthesized by the reaction of Cd^II salts and diphenic acid (H₂dpa) with rigid, chelating and flexible, bridging auxiliary ligands, respectively. Compound 1 has a 1D helical chain structure, in which dpa^2– as bridging ligand is responsible for the formation of the main framework and L1 as chelating ligand grafts on one side of the helical chain. This structure is further extended into a 3D supramolecular framework through two kinds of strong hydrogen bonding interactions. Compound 2 has a 2D structure, in which dpa^2– bridges the Cd^II atoms into helical chains and L2 bridges the left‐ and right‐handed chains into a racemic layer with a [4,4] topology.     

Enantioselective Assembly of a Ruthenium(II) Polypyridyl Complex into a Double Helix

Evolution can increase the complexity of matter by self‐organization into helical architectures, the best example being the DNA double helix. One common aspect, apparently shared by most of these architectures, is the presence of covalent bonds within the helix backbone. Here, we report the unprecedented crystal structures of a metal complex that self‐organizes into a continuous double helical structure, assembled by non‐covalent building blocks. Built up solely by weak stacking interactions, this alternating tread stairs‐like double helical assembly mimics the DNA double helix structure. Starting from a racemic mixture in aqueous solution, the ruthenium(II) polypyridyl complex forms two polymorphic structures of a left‐handed double helical assembly of only the Λ‐enantiomer. The stacking of the helices is different in both polymorphs: a crossed woodpile structure versus a parallel columnar stacking.     

Light‐Directed Dynamic Chirality Inversion in Functional Self‐Organized Helical Superstructures

Helical superstructures are widely observed in nature, in synthetic polymers, and in supramolecular assemblies. Controlling the chirality (the handedness) of dynamic helical superstructures of molecular and macromolecular systems by external stimuli is a challenging task, but is of great fundamental significance with appealing morphology‐dependent applications. Light‐driven chirality inversion in self‐organized helical superstructures (i.e. cholesteric, chiral nematic liquid crystals) is currently in the limelight because inversion of the handedness alters the chirality of the circularly polarized light that they selectively reflect, which has wide potential for application. Here we discuss the recent developments toward inversion of the handedness of cholesteric liquid crystals enabled by photoisomerizable chiral molecular switches or motors. Different classes of chiral photoresponsive dopants (guests) capable of conferring light‐driven reversible chirality inversion of helical superstructures fabricated from different nematic hosts are discussed. Rational molecular designs of chiral molecular switches toward endowing handedness inversion to the induced helical superstructures of cholesteric liquid crystals are highlighted. This Review is concluded by throwing light on the challenges and opportunities in this emerging frontier, and it is expected to provide useful guidelines toward the development of self‐organized soft materials with stimuli‐directed chirality inversion capability and multifunctional host–guest systems.     

Helical Graphitic Carbon Nitrides with Photocatalytic and Optical Activities

Graphitic carbon nitride can be imprinted with a twisted hexagonal rod‐like morphology by a nanocasting technique using chiral silicon dioxides as templates. The helical nanoarchitectures promote charge separation and mass transfer of carbon nitride semiconductors, enabling it to act as a more efficient photocatalyst for water splitting and CO₂ reduction than the pristine carbon nitride polymer. This is to our knowledge a unique example of chiral graphitic carbon nitride that features both left‐ and right‐handed helical nanostructures and exhibits unique optical activity to circularly polarized light at the semiconductor absorption edge as well as photoredox activity for solar‐to‐chemical conversion. Such helical nanostructured polymeric semiconductors are envisaged to hold great promise for a range of applications that rely on such semiconductor properties as well as chirality for photocatalysis, asymmetric catalysis, chiral recognition, nanotechnology, and chemical sensing.     

Novel 1D Copper(II) Helical Chain Formed by Weak Coordination‐driven Self‐assembly: Synthesis,Structure, and Magnetic Property

A novel 1D copper(II) helical chain is constructed through the connection of tetranuclear copper(II) units [Cu₄(L)(Py)₄] (H₈L=N,N′‐(BINOL‐3,3′‐dicarboxyl)‐disalicylhydrazide, where BINOL is 1,1′‐binaphthalenyl‐2,2′‐diol, py=pyridine) by weak coordination‐driven self‐assembly, and characterized by IR, single crystal X‐ray diffraction, thermogravimetric analysis, and X‐ray power diffraction analysis. Interestingly, the helical chains are packed in an alternating left‐(M) and right‐handed (P) chirality, the orientation of the helices was determined by the axial chirality of the ligand. The complex shows antiferromagnetic interactions between the copper centers.     

Non‐covalent Versus Covalent Control of Self‐Assembly and Chirality of Nile Red‐modified Nucleoside and DNA

A DNA‐based covalent versus a non‐covalent approach is demonstrated to control the optical, chirooptical and higher order structures of Nile red ( Nr ) aggregation. Dynamic light scattering and TEM studies revealed that in aqueous media Nr ‐modified 2′‐deoxyuridine aggregates through the co‐operative effect of various non‐covalent interactions including the hydrogen bonding ability of the nucleoside and sugar moieties and the π‐stacking tendency of the highly hydrophobic dye. This results in the formation of optically active nanovesicles. A left‐handed helically twisted H‐type packing of the dye is observed in the bilayer of the vesicle as evidenced from the optical and chirooptical studies. On the other hand, a left‐handed helically twisted J‐type packing in vesicles was obtained from a non‐polar solvent (toluene). Even though the primary stacking interaction of the dye aggregates transformed from H→J while going from aqueous to non‐polar media, the induced supramolecular chirality of the aggregates remained the same (left‐handed). Circular dichroism studies of DNA that contained several synthetically incorporated and covalently attached Nr ‐modified nucleosides revealed the formation of helically stacked H‐aggregates of Nr but—in comparison to the noncovalent aggregates—an inversed chirality (right‐handed). This self‐assembly propensity difference can, in principle, be applied to other hydrophobic dyes and chromophores and thus open a DNA‐based approach to modulate the primary stacking interactions and supramolecular chirality of dye aggregates.     

Orthogonal Halogen‐Bonding‐Driven 3D Supramolecular Assembly of Right‐Handed Synthetic Helical Peptides

Peptide‐mediated self‐assembly is a prevalent method for creating highly ordered supramolecular architectures. Herein, we report the first example of orthogonal C?X???X?C/C?X???π halogen bonding and hydrogen bonding driven crystalline architectures based on synthetic helical peptides bearing hybrids of l ‐sulfono‐γ‐AApeptides and natural amino acids. The combination of halogen bonding, intra‐/intermolecular hydrogen bonding, and intermolecular hydrophobic interactions enabled novel 3D supramolecular assembly. The orthogonal halogen bonding in the supramolecular architecture exerts a novel mechanism for the self‐assembly of synthetic peptide foldamers and gives new insights into molecular recognition, supramolecular design, and rational design of biomimetic structures.     

Self‐Assembly through Coordination and π‐Stacking: Controlled Switching of Circularly Polarized Luminescence

Multiple noncovalent interactions can drive self‐assembly through different pathways. Here, by coordination‐assisted changes in π‐stacking modes between chromophores in pyrene‐conjugated histidine (PyHis), a self‐assembly system with reversible and inversed switching of supramolecular chirality, as well as circularly polarized luminescence (CPL) is described. It was found that l ‐PyHis self‐assembled into nanofibers showing P‐chirality and right‐handed CPL. Upon Zn^II coordination, the nanofibers changed into nanospheres with M‐chirality, as well as left‐handed CPL. The process is reversible and the M‐chirality can change to P‐chirality by removing the Zn^II ions. Experimental and theoretical models unequivocally revealed that the cooperation of metal coordination and π‐stacking modes are responsible the reversible switching of supramolecular chirality. This work not only provides insight into how multiple noncovalent interactions regulate self‐assembly pathways.