Nanopatterned Superlattices in Self‐Assembled C2‐Symmetric Oligodimethylsiloxane‐Based Benzene‐1,3,5‐Tricarboxamides

The synthesis of C₃‐ and C₂‐symmetric benzene‐1,3,5‐tricarboxamides (BTAs) containing well‐defined oligodimethylsiloxane (oDMS) and/or alkyl side chains has been carried out. The influence of the bulkiness of the oDMS chains in the aggregation behavior of dilute solutions of the oDMS‐BTAs in methylcyclohexane was studied by temperature‐dependent UV spectroscopy. The formation of hierarchically self‐assembled aggregates was observed at different BTA concentrations, the tendency of aggregation increases by shortening or removing oDMS chains. Chiral BTAs were investigated with circular dichroism (CD) spectroscopy, showing a stronger tendency to aggregate than the achiral ones. Majority rules experiments show a linear behavior consistent with the existence of a high mismatch penalty energy. The most efficient oDMS‐BTAs organogelators have the ability to form stable organogels at 5 mg mL^?1 (0.75 wt %) in hexane. Solid‐state characterization techniques indicate the formation of an intermolecular threefold hydrogen bonding between adjacent molecules forming thermotropic liquid crystals, exhibiting a hexagonal columnar organization from room temperature to above 150 °C. A decrease of the clearing temperatures was observed when increasing the number and length of the oligodimethylsiloxane chains. In addition to the three‐fold hydrogen bonding that leads to columnar liquid crystalline phase, segregation between the oDMS and aliphatic chains takes place in the BTA functionalized with two alkyl and one oDMS chain leading to a superlattice within the hexagonal structure with potential applications in lithography.     

Monosaccharides as Versatile Units for Water‐Soluble Supramolecular Polymers

We introduce monosaccharides as versatile water‐soluble units to compatibilise supramolecular polymers based on the benzene‐1,3,5‐tricarboxamide (BTA) moiety with water. A library of monosaccharide‐based BTAs is evaluated, varying the length of the alkyl chain (hexyl, octyl, decyl and dodecyl) separating the BTA and saccharide units, as well as the saccharide units (α‐glucose, β‐glucose, α‐mannose and α‐galactose). In all cases, the monosaccharides impart excellent water compatibility. The length of the alkyl chain is the determining factor to obtain either long, one‐dimensional supramolecular polymers (dodecyl spacer), small aggregates (decyl spacer) or molecularly dissolved (octyl and hexyl) BTAs in water. For the BTAs comprising a dodecyl spacer, our results suggest that a cooperative self‐assembly process is operative and that the introduction of different monosaccharides does not significantly change the self‐ assembly behaviour. Finally, we investigate the potential of post‐assembly functionalisation of the formed supramolecular polymers by taking advantage of dynamic covalent bond formation between the monosaccharides and benzoxaboroles. We observe that the supramolecular polymers readily react with a fluorescent benzoxaborole derivative permitting imaging of these dynamic complexes by confocal fluorescence microscopy.     

Control of H‐ and J‐Type π Stacking by Peripheral Alkyl Chains and Self‐Sorting Phenomena in Perylene Bisimide Homo‐ and Heteroaggregates

The synthesis, self‐assembly, and gelation ability of a series of organogelators based on perylene bisimide (PBI) dyes containing amide groups at imide positions are reported. The synergetic effect of intermolecular hydrogen bonding among the amide functionalities and π–π stacking between the PBI units directs the formation of the self‐assembled structure in solution, which beyond a certain concentration results in gelation. Effects of different peripheral alkyl substituents on the self‐assembly were studied by solvent‐ and temperature‐dependent UV‐visible and circular dichroism (CD) spectroscopy. PBI derivatives containing linear alkyl side chains in the periphery formed H‐type π stacks and red gels, whereas by introducing branched alkyl chains the formation of J‐type π stacks and green gels could be achieved. Sterically demanding substituents, in particular, the 2‐ethylhexyl group completely suppressed the π stacking. Coaggregation studies with H‐ and J‐aggregating chromophores revealed the formation of solely H‐type π stacks containing both precursor molecules at a lower mole fraction of J‐aggregating chromophore. Beyond a critical composition of the two chromophores, mixed H‐aggregate and J‐aggregate were formed simultaneously, which points to a self‐sorting process. The versatility of the gelators is strongly dependent on the length and nature of the peripheral alkyl substituents. CD spectroscopic studies revealed a preferential helicity of the aggregates of PBI building blocks bearing chiral side chains. Even for achiral PBI derivatives, the utilization of chiral solvents such as (R)‐ or (S)‐limonene was effective in preferential population of one‐handed helical fibers. AFM studies revealed the formation of helical fibers from all the present PBI gelators, irrespective of the presence of chiral or achiral side chains. Furthermore, vortex flow was found to be effective in macroscopic orientation of the aggregates as evidenced from the origin of CD signals from aggregates of achiral PBI molecules.     

Chiral Perylene Diimides: Building Blocks for Ionic Self‐Assembly

A chiral perylene diimide building block has been prepared based on an amine derivative of the amino acid L ‐phenylalanine. Detailed studies were carried out into the self‐assembly behaviour of the material in solution and the solid state using UV/Vis, circular dichroism (CD) and fluorescence spectroscopy. For the charged building block BTPPP, the molecular chirality of the side chains is translated into the chiral supramolecular structure in the form of right‐handed helical aggregates in aqueous solution. Temperature‐dependent UV/Vis studies of BTPPP in aqueous solution showed that the self‐assembly behaviour of this dye can be well described by an isodesmic model in which aggregation occurs to generate short stacks in a reversible manner. Wide‐angle X‐ray diffraction studies (WXRD) revealed that this material self‐organises into aggregates with π–π stacking distances typical for π‐conjugated materials. TEM investigations revealed the formation of self‐assembled structures of low order and with no expression of chirality evident. Differential scanning calorimetry (DSC) and polarised optical microscopy (POM) were used to investigate the mesophase properties. Optical textures representative of columnar liquid–crystalline phases were observed for solvent‐annealed samples of BTPPP. The high solubility, tunable self‐assembly and chiral ordering of these materials demonstrate their potential as new molecular building blocks for use in the construction of chiro‐optical structures and devices.     

Supramolecular Polymerization of C3‐Symmetric Organogelators: Cooperativity,Solvent, and Gelation Relationship

A systematic study of the influence of solvent and the size of C₃‐symmetric discotics on their supramolecular polymerization mechanism is presented. The cooperativity of the self‐assembly of the reported compounds is directly related to their gelation ability. The two series of C₃‐symmetric discotics investigated herein are based on benzene‐1,3,5‐tricarboxamides (BTAs) and oligo(phenylene ethynylene)‐based tricarboxamides (OPE? TAs) that are peripherally decorated with achiral ( 1 a and 2 a ) or chiral N‐(2‐aminoethyl)‐3,4,5‐trialkoxybenzamide units ( 1 b and 2 b ). The supramolecular polymerization of compounds 1 a , b and 2 a , b has been exhaustively investigated in a number of solvents and by using various techniques: variable‐temperature circular dichroism (VT‐CD) spectroscopy, concentration‐dependent ¹H NMR spectroscopy, and isothermal titration calorimetry (ITC). The supramolecular polymerization mechanism of compounds 2 is highly cooperative in solvents such as methylcyclohexane and toluene and is isodesmic in CHCl₃. Unexpectedly, chiral compound 1 b is practically CD‐silent, in contrast with previously reported BTAs. ITC measurements in CHCl₃ demonstrated that the supramolecular polymerization of BTA 1 a is isodesmic. These results confirm the strong influence of the π‐surface of the central aromatic core of the studied discotic and the branched nature of the peripheral side chains on the supramolecular polymerization. The gelation ability of these organogelators is negated in CHCl₃, in which the supramolecular polymerization mechanism is isodesmic.     

Interplay between H‐Bonding and Alkyl‐Chain Ordering in Self‐Assembly of Monodendritic L‐Alanine Derivatives

This paper reports on the synthesis and self‐organizing properties of monodendrons consisting of L ‐alanine at the focal point and alkyl chains with different length at the periphery. The structures of thin films and monolayers are studied by temperature‐resolved grazing‐incidence X‐ray diffraction and scanning force microscopy. The interplay between H‐bonding and ordering of the alkyl chains results in a rich temperature‐dependent phase behavior. The monodendrons form H‐bonded stabilized clusters with the number of molecules depending on the length of the aliphatic chains and temperature. The clusters play the role of constitutive units in the subsequent self‐assembly. Short alkyl chains allow the material to form thermodynamically stable crystalline phases. The molecules with longer side groups exhibit additional transitions from the crystalline phase to thermotropic columnar hexagonal or columnar rectangular liquid‐crystalline phases. In monolayers deposited on highly ordered pyrolytic graphite, the materials show ordering similar to thin films. However, for the compound bearing hexadecyl chains the affinity of the alkyl groups to graphite dominates the self‐assembly and thereby allows epitaxial growth of a 2D lattice with flat‐on oriented molecules.     

Self‐Assembly of Coronene Bisimides: Mechanistic Insight and Chiral Amplification

The study of the organization of small π‐conjugated molecules is imperative to understanding and controlling its properties for various applications. Coronene bisimides (CBIs) are potential candidates for novel liquid‐crystalline materials and active n‐type semiconductor molecules in organic electronics. To understand the self‐assembly of this seldom‐studied chromophore, we have designed two derivatives of CBIs bearing chiral and achiral 3,4,5‐trialkoxyphenyl groups at the imide position, named as CBI‐GCH and CBI‐GACH , respectively. CBI‐GCH self‐assembles mainly through π‐stacking and van der Waals interactions in nonpolar methylcyclohexane to result in long 1D fibrillar stacks. The mechanism of supramolecular polymerization was probed by using chiroptical studies, which showed an isodesmic pathway for CBI‐GCH . The thermodynamic parameters that govern the self‐assembly are detailed. CBI‐GACH also shows similar self‐assembly behavior as its chiral counterpart. X‐ray diffraction studies of both molecules reveals a 2D hexagonal columnar arrangement. The coassembly of CBI‐GCH and CBI‐GACH shows chiral amplification (sergeant and soldiers experiment) with saturation at 30–50 % of the chiral derivative, which was further used to study the dynamics of the assembly. Thus, this study presents a rare report of chiral amplification in an isodesmic system.     

Phase Behavior and Mesophase Structures of 1,3,5‐Benzene‐ and 1,3,5‐Cyclohexanetricarboxamides: Towards an Understanding of the Losing Order at the Transition into the Isotropic Phase

One of the simplest and most‐versatile motifs in supramolecular chemistry is based on 1,3,5‐benzenetricarboxamides. Variation of the core structure and subtle changes in the structures of the lateral substituents govern the self‐assembly and determine the phase behavior. Herein, we provide a comprehensive comparison between the phase behavior and mesophase structure of a series of 1,3,5‐benzene‐ and 1,3,5‐cyclohexanetricarboxamides that contain linear and branched alkyl substituents. Depending on the substituent, different crystalline, plastic crystalline, and liquid crystalline phases were formed. The relatively rare columnar nematic (N_C) phase was only observed in cyclohexane‐based trisamides that contained linear alkyl substituents. Of fundamental interest in liquid crystalline supramolecular systems is the transition from the mesomorphic state into the isotropic state and, in particular, the question of how the order decreases. Temperature‐dependent IR spectroscopy and XRD measurements revealed that columnar H‐bonded aggregates were still present in the isotropic phase. At the clearing transition, mainly the lateral order was lost, whilst shorter columnar aggregates still remained. A thorough understanding of the phase behavior and the mesophase structure is relevant for selecting processing conditions that use supramolecular structures in devices or as fibrillar nanomaterials.     

Control over the Self‐Assembly Modes of PtII Complexes by Alkyl Chain Variation: From Slipped to Parallel π‐Stacks

We report the self‐assembly of a new family of hydrophobic, bis(pyridyl) Pt^II complexes featuring an extended oligophenyleneethynylene‐derived π‐surface appended with six long (dodecyloxy ( 2 )) or short (methoxy ( 3 )) side groups. Complex 2 , containing dodecyloxy chains, forms fibrous assemblies with a slipped arrangement of the monomer units (d_Pt???Pt≈14 Å) in both nonpolar solvents and the solid state. Dispersion‐corrected PM6 calculations suggest that this organization is driven by cooperative π–π, C?H???Cl and π–Pt interactions, which is supported by EXAFS and 2D NMR spectroscopic analysis. In contrast, nearly parallel π‐stacks (d_Pt???Pt≈4.4 Å) stabilized by multiple π–π and C?H???Cl contacts are obtained in the crystalline state for 3 lacking long side chains, as shown by X‐ray analysis and PM6 calculations. Our results reveal not only the key role of alkyl chain length in controlling self‐assembly modes but also show the relevance of Pt‐bound chlorine ligands as new supramolecular synthons.     

Thioamides: Versatile Bonds To Induce Directional and Cooperative Hydrogen Bonding in Supramolecular Polymers

The amide bond is a versatile functional group and its directional hydrogen‐bonding capabilities are widely applied in, for example, supramolecular chemistry. The potential of the thioamide bond, in contrast, is virtually unexplored as a structuring moiety in hydrogen‐bonding‐based self‐assembling systems. We report herein the synthesis and characterisation of a new self‐assembling motif comprising thioamides to induce directional hydrogen bonding. N,N′,N′′‐Trialkylbenzene‐1,3,5‐tris(carbothioamide)s (thioBTAs) with either achiral or chiral side‐chains have been readily obtained by treating their amide‐based precursors with P₂S₅. The thioBTAs showed thermotropic liquid crystalline behaviour and a columnar mesophase was assigned. IR spectroscopy revealed that strong, three‐fold, intermolecular hydrogen‐bonding interactions stabilise the columnar structures. In apolar alkane solutions, thioBTAs self‐assemble into one‐dimensional, helical supramolecular polymers stabilised by three‐fold hydrogen bonding. Concentration‐ and temperature‐dependent self‐assembly studies performed by using a combination of UV and CD spectroscopy demonstrated a cooperative supramolecular polymerisation mechanism and a strong amplification of supramolecular chirality. The high dipole moment of the thioamide bond in combination with the anisotropic shape of the resulting cylindrical aggregate gives rise to sufficiently strong depolarised light scattering to enable depolarised dynamic light scattering (DDLS) experiments in dilute alkane solution. The rotational and translational diffusion coefficients, D_trans and D_rot, were obtained from the DDLS measurements, and the average length, L, and diameter, d, of the thioBTA aggregates were derived (L=490 nm and d=3.6 nm). These measured values are in good agreement with the value L_w=755 nm obtained from fitting the temperature‐dependent CD data by using a recently developed equilibrium model. This experimental verification validates our common practice for determining the length of BTA‐based supramolecular polymers from model fits to experimental CD data. The ability of thioamides to induce cooperative supramolecular polymerisation makes them effective and broadly applicable in supramolecular chemistry.     

Highly Fluorescent Non‐Conventional Boron‐Difluoride‐Based π Organogel with Gelation‐Assisted Piezochromism

Triphenylamine‐functionalized boron 2‐(2′‐pyridyl)imidazole complex bearing no alkyl chains or H‐bond unit was found to be able to gelate a series of solvents, and the balanced intermolecular π–π interactions play an important role in its supramolecular self‐assembly. The gelator molecule is piezochromic, and the dried gel responded to pressure more sensitively than regular crystalline powder.     

Supramolecular Copolymerization as a Strategy to Control the Stability of Self‐Assembled Nanofibers

A major challenge in supramolecular polymerization is controlling the stability of the polymers formed, that is, controlling the rate of monomer exchange in the equilibrium between monomer and polymer. The exchange dynamics of supramolecular polymers based on benzene‐1,3,5‐tricarboxamide (BTA) can be regulated by copolymerizing molecules with dendronized (dBTA) and linear (nBTA) ethylene glycol‐based water‐soluble side chains. Whereas nBTAs form long nanofibers in water, dBTAs do not polymerize, forming instead small spherical aggregates. The copolymerization of the two BTAs results in long nanofibers. The exchange dynamics of both the BTA monomers in the copolymer are significantly slowed down in the mixed systems, leading to a more stable copolymer, while the morphology and spectroscopic signature of the copolymers are identical to that of nBTA homopolymer. This copolymerization is the supramolecular counterpart of styrene/ maleic anhydride copolymerization.     

Hierarchical Self‐Assembly of Supramolecular Helical Fibres from Amphiphilic C3‐Symmetrical Functional Tris(tetrathiafulvalenes)

The preparation and self‐assembly of the enantiomers of a series of C₃‐symmetric compounds incorporating three tetrathiafulvalene (TTF) residues is reported. The chiral citronellyl and dihydrocitronellyl alkyl chains lead to helical one dimensional stacks in solution. Molecular mechanics and dynamics simulations combined with experimental and theoretical circular dichroism support the observed helicity in solution. These stacks self‐assemble to give fibres that have morphologies that depend on the nature of the chiral alkyl group and the medium in which the compounds aggregate. An inversion of macroscopic helical morphology of the citronellyl compound is observed when compared to analogous 2‐methylbutyl chains, which is presumably a result of the stereogenic centre being further away from the core of the molecule. This composition still allows both morphologies to be observed, whereas an achiral compound shows no helicity. The morphology of the fibres also depends on the flexibility at the chain ends of the amphiphilic components, as there is not such an apparently persistent helical morphology for the dihydrocitronellyl derivative as for that prepared from citronellyl chains.     

In Situ Controlled Construction of a Hierarchical Supramolecular Chiral Liquid‐Crystalline Polymer Assembly

Hierarchical supramolecular chiral liquid‐crystalline (LC) polymer assemblies are challenging to construct in situ in a controlled manner. Now, polymerization‐induced chiral self‐assembly (PICSA) is reported. Hierarchical supramolecular chiral azobenzene‐containing block copolymer (Azo‐BCP) assemblies were constructed with π–π stacking interactions occurring in the layered structure of Azo smectic phases. The evolution of chirality from terminal alkyl chain to Azo mesogen building blocks and further induction of supramolecular chirality in LC BCP assemblies during PICSA is achieved. Morphologies such as spheres, worms, helical fibers, lamellae, and vesicles were observed. The morphological transition had a crucial effect on the chiral expression of Azo‐BCP assemblies. The supramolecular chirality of Azo‐BCP assemblies destroyed by 365 nm UV irradiation can be recovered by heating–cooling treatment; this dynamic reversible achiral–chiral switching can be repeated at least five times.     

Synthesis and Supramolecular Self‐Assembly of Coil‐Rod‐Coil Molecules: The Relationship between Self‐Assembled Nanostructures and Molecular Structures

Herein, the relationship between the supramolecularly self‐assembled nanostructures and the chemical structures of coil‐rod‐coil molecules is discussed. A series of nonamphiphilic coil‐rod‐coil molecules with different alkyl chains, central mesogenic groups, and chemical linkers were designed and synthesized. The solvent‐mediated supramolecular self‐assembling of these coil‐rod‐coil molecules resulted in rolled‐up nanotubes, nanofibers, submicron sized belts, needle‐like microcrystals, and amorphous structures. The self‐assembling behaviors of these coil‐rod‐coil molecules have been systematically investigated to reveal the relationship between the supramolecularly self‐assembled nanostructures and their chemical structures. With respect to the formation of rolled‐up nanotubes by self‐assembly of coil‐rod‐coil molecules, we have systematically investigated the following three influencing structural factors: 1) the alkyl chain length; 2) the central mesogenic group; (3) the linker type. These studies disclosed the key structural features of coil‐rod‐coil molecules for the formation of rolled‐up nanotubes.     

Supramolecular [60]Fullerene Liquid Crystals Formed By Self‐Organized Two‐Dimensional Crystals

Fullerene‐based liquid crystalline materials have both the excellent optical and electrical properties of fullerene and the self‐organization and external‐field‐responsive properties of liquid crystals (LCs). Herein, we demonstrate a new family of thermotropic [60]fullerene supramolecular LCs with hierarchical structures. The [60]fullerene dyads undergo self‐organization driven by π–π interactions to form triple‐layer two‐dimensional (2D) fullerene crystals sandwiched between layers of alkyl chains. The lamellar packing of 2D crystals gives rise to the formation of supramolecular LCs. This design strategy should be applicable to other molecules and lead to an enlarged family of 2D crystals and supramolecular liquid crystals.     

Self‐Assembly in Helical Columnar Mesophases and Luminescence of Chiral 1H‐Pyrazoles

Chiral polycatenar 1H‐pyrazoles self‐assemble to form columnar mesophases that are stable at room temperature. X‐ray diffraction and CD studies in the mesophase indicate a supramolecular helical organization consisting of stacked H‐bonded dimers. The liquid‐crystalline compounds reported are 3,5‐bis(dialkoxyphenyl)‐1H‐pyrazoles that incorporate two or four dihydrocitronellyl chiral tails. It can be observed that the grafting of these branched chiral substituents onto the 3,5‐diphenyl‐1H‐pyrazole core has a beneficial role in inducing mesomorphism, because isomeric linear‐chain compounds are not liquid crystalline; this is not the usual scheme of behavior. Furthermore, the molecular chirality is transferred to the columnar mesophase, because preferential helical arrangements are observed. Films of the compounds are luminescent at room temperature and constitute an example of the self‐organization of nondiscoid units into columnar liquid‐crystalline assemblies in which the functional molecular unit transfers its properties to a hierarchically built superstructure.     

Halogen‐Bond‐Mediated Assembly of a Single‐Component Supramolecular Triangle and an Enantiomeric Pair of Double Helices from 2‐(Iodoethynyl)pyridine Derivatives

Construction of single‐component supramolecular triangle and unprecedented spontaneous resolution of pairs of intertwined supramolecular 3₁‐ and 3₂‐double helices by the self‐assembly of achiral 2‐(iodoethynyl)pyridine and its derivatives have been achieved through intermolecular ethynyl C?I????N halogen bonds in the crystalline state. Fine‐tuning of the molecular structure of the achiral monomer and choice of solvents for crystallization have a dominant effect on the resultant supramolecular architectures.     

Water‐Binding‐Mediated Gelation/Crystallization and Thermosensitive Superchirality

Determination of molecular structural parameters of hydrophobic cholesterol–naphthalimide conjugates for water binding capabilities as well as their moisture‐sensitive supramolecular self‐assembly were revealed. Water binding was a key factor in leading trace water‐induced crystallization against gelation in apolar solvent. Ordered water molecules entrapped in self‐assembly arrays revealed by crystal structures behave as hydrogen‐bonding linkers to facilitate three‐dimensional growth into crystals rather than one‐dimensional gel nanofibers. Water binding was also reflected on the supramolecular chirality inversion of vesicle self‐assembly in aqueous media via heating‐induced dehydration. Structural parameters that favor water binding were evaluated in detail, which could help rationally design organic building units for advancing soft materials, crystal engineering, and chiral recognition.     

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.