A Modular and Convergent Synthetic Route to Supramolecular Cyclic Dimers Based on Amidinium-Carboxylate Interactions.

We describe herein the optimized design and modular synthetic approach towards supramolecularly programmed monomers that can form discrete macrocyclic species of controllable size and shape through amidinium-carboxylate interactions in apolar and polar media.

Stacked or Folded? Impact of Chelate Cooperativity on the Self-Assembly Pathway to Helical Nanotubes from Dinucleobase Monomers.

Self-assembled nanotubes exhibit impressive biological functions that have always inspired supramolecular scientists in their efforts to develop strategies to build such structures from small molecules through a bottom-up approach. One of these strategies employs molecules endowed with self-recognizing motifs at the edges, which can undergo either cyclization-stacking or folding-polymerization processes that lead to tubular architectures. Which of these self-assembly pathways is ultimately selected by these molecules is, however, often difficult to predict and even to evaluate experimentally. We show here a unique example of two structurally related molecules substituted with complementary nucleobases at the edges (i.e., G:C and A:U) for which the supramolecular pathway taken is determined by chelate cooperativity, that is, by their propensity to assemble in specific cyclic structures through Watson-Crick pairing. Because of chelate cooperativities that differ in several orders of magnitude, these molecules exhibit distinct supramolecular scenarios prior to their polymerization that generate self-assembled nanotubes with different internal monomer arrangements, either stacked or coiled, which lead at the same time to opposite helicities and chiroptical properties.

Correction: Stereomutation and chiroptical bias in the kinetically controlled supramolecular polymerization of cyano-luminogens.

[This corrects the article DOI: 10.1039/D2SC03449B.].

The Role of Peripheral Amide Groups as Hydrogen-Bonding Directors in the Tubular Self-Assembly of Dinucleobase Monomers.

Nanotubes are a fascinating kind of self-assembled structure which have a wide interest and potential in supramolecular chemistry. We demonstrated that nanotubes of defined dimensions can be produced from dinucleobase monomers through two decoupled hierarchical cooperative processes: cyclotetramerization and supramolecular polymerization. Here we analyze the role of peripheral amide groups, which can form an array of hydrogen bonds along the tube axis, on this self-assembly process. A combination of 1 H NMR and CD spectroscopy techniques allowed us to analyze quantitatively the thermodynamics of each of these two processes separately. We found out that the presence of these amide directors is essential to guide the polymerization event and that their nature and number have a strong influence, not only on the stabilization of the stacks of macrocycles, but also on the supramolecular polymerization mechanism.

Dual-Mode Chiral Self-Assembly of Cone-Shaped Subphthalocyanine Aromatics.

Columnar polymers and liquid crystals obtained from π-conjugated cone-shaped molecules are receiving increasing interest due to the possibility of obtaining unconventional polar organizations that show anisotropic charge transport and unique chiroptical properties. However, and in contrast to the more common planar discotics, the self-assembly of conic or pyramidic molecules in solution remains largely unexplored. Here, we show how a molecular geometry change, from flat to conic, can generate supramolecular landscapes where different self-assembled species, each of them being under thermodynamic equilibrium with the monomer, exist exclusively within distinct regimes. In particular, depending on the solvent nature-aromatic or aliphatic-cone-shaped C3-symmetric subphthalocyanine 1 can undergo self-assembly either as a tail-to-tail dimer, showing monomer-dimer sigmoidal transitions, or as a head-to-tail noncentrosymmetric columnar polymer, exhibiting a nucleation-elongation polymerization mechanism. Moreover, the experimental and theoretical comparison between racemic and enantiopure samples revealed that the two enantiomers (1M and 1P) tend to narcissistically self-sort in the dimer regime, each enantiomer showing a strong preference to associate with itself, but socially self-sort in the polymer regime, favoring an alternate stacking order along the columns.

Nanostructured Micelle Nanotubes Self-Assembled from Dinucleobase Monomers in Water.

Despite the central importance of aqueous amphiphile assemblies in science and industry, the size and shape of these nano-objects is often difficult to control with accuracy owing to the non-directional nature of the hydrophobic interactions that sustain them. Here, using a bioinspired strategy that consists of programming an amphiphile with shielded directional Watson-Crick hydrogen-bonding functions, its self-assembly in water was guided toward a novel family of chiral micelle nanotubes with partially filled lipophilic pores of about 2 nm in diameter. Moreover, these tailored nanotubes are successfully demonstrated to extract and host molecules that are complementary in size and chemical affinity.

Self-Assembly of Diacetylene-Bridged Phenylenevinylene Oligomers in Water and Organic Solvents.

Rodlike π-conjugated molecules in which two OPV fragments are connected through a diacetylene bond self-assemble in aqueous and organic media. Optical spectroscopy and AFM measurements indicated that, in water, strong hydrophobic interactions between π-cores promote aggregation into robust, uniform micellar structures. In contrast, in apolar solvents, a fibrilar morphology is obtained by coiling of columnar stacks. These stacks are formed in a nucleation-elongation process with degrees of cooperativity of 0.006, that is influenced by the low rotation barriers around the σ-bonds in the diacetylene linker.

Supramolecular control over the structural organization of a second-order NLO-active organogelator.

A study of the structural parameters which govern the supramolecular organization of an organogelator built from the Disperse Red moiety is proposed. In particular, the key balance between intermolecular H-bonding and/or π-π interactions is addressed by comparing the effect of a secondary amide vs. an ester linker within the molecular structure. Solution 1H-NMR studies show the superiority of the former interaction in promoting the nanostructuring process, allowing it to reach a gel state in toluene. The nanostructures obtained from both the amide and the ester derivatives were also studied in the solid state. In particular, the use of second-harmonic generation microscopy demonstrates that an anisotropic organization of the material can even be observed in the case of the ester derivative, which demonstrates the efficiency of the tris(alkoxy)benzene unit in directing the self-assembly process, independently of additional H-bond interactions.

Promoting Spontaneous Second Harmonic Generation through Organogelation.

An organogelator based on the Disperse Red nonlinear optical chromophore was synthesized according to a simple and efficient three-step procedure. The supramolecular gel organization leads to xerogels which display a spontaneous second harmonic generation (SHG) response without any need for preprocessing, and this SHG activity appears to be stable over several months. These findings, based on an intrinsic structural approach, are supported by favorable intermolecular supramolecular interactions, which promote a locally non-centrosymmetric NLO-active organization. This is in sharp contrast with most materials designed for SHG purposes, which generally require the use of expensive or heavy-to-handle external techniques for managing the dipoles' alignment.

Color-Tunable Cyano-Substituted Divinylene Arene Luminogens as Fluorescent π-Gelators.

The synthesis of three cyano-substituted divinylene π-gelators is reported. The modulation of the color is achieved by placing the cyano groups in appropriate position of the conjugated backbone, thus modulating the donor-acceptor interaction. Variable-temperature UV-vis data have been utilized to investigate the self-assembly of the gelators 1-3 that is governed by a cooperative mechanism. A complete set of photophysical parameters (ΦF,τ, kr and knr) demonstrate the role of the molecular aggregation in enhanced emission upon self-assembly.

Synthesis, electronic properties and WOLED devices of planar phosphorus-containing polycyclic aromatic hydrocarbons.

We describe the synthesis and the physical properties of polyaromatic hydrocarbons (PAHs) containing a phosphorus atom at the edge. In particular, the impact of the successive addition of aromatic rings on the electronic properties was investigated by experimental (UV/Vis absorption, fluorescence, cyclic voltammetry) and theoretical studies (DFT). The physical properties recorded in solution and in the solid state showed that the P-containing PAHs exhibit properties expected for an emitter in white organic light-emitting diodes (WOLEDs).

Breaking the odd-even effect in the self-assembly of linear bis(benzamides).

The twisting of supramolecular aggregates formed from simple linear bis(benzamides) has been investigated. The antiparallel arrangement of the amide functional groups controls the generation of twisted supramolecular structures. The results presented herein could contribute to elaborate predictive tools applicable in the generation of chiral supramolecular structures.

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.

Supramolecular polymerization of C3-symmetric organogelators: cooperativity, solvent, and gelation relationship.

A systematic study of the influence of solvent and the size of C(3)-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 C(3)-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 (1a and 2a) or chiral N-(2-aminoethyl)-3,4,5-trialkoxybenzamide units (1b and 2b). The supramolecular polymerization of compounds 1a,b and 2a,b has been exhaustively investigated in a number of solvents and by using various techniques: variable-temperature circular dichroism (VT-CD) spectroscopy, concentration-dependent (1)H 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 CHCl(3). Unexpectedly, chiral compound 1b is practically CD-silent, in contrast with previously reported BTAs. ITC measurements in CHCl(3) demonstrated that the supramolecular polymerization of BTA 1a 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 CHCl(3), in which the supramolecular polymerization mechanism is isodesmic.

Optical waveguides from 4-aryl-4H-1,2,4-triazole-based supramolecular structures.

Ribbon-like supramolecular structures prepared by the organized aggregation of 4-aryl-4H-1,2,4-triazoles act as optical waveguides that propagate photoluminescence.

Cooperative self-assembly of linear organogelators. Amplification of chirality and crystal growth of pharmaceutical ingredients.

Linear organogelators 1 and 2, which self-assemble cooperatively into fibrillar structures, act as efficient crystal growth media for common pharmaceutical ingredients like ASP, CAF, IND and CBZ.

Mirror helices and helicity switch at surfaces based on chiral triangular-shape oligo(phenylene ethynylenes).

The self-assembly of triangular-shaped oligo(phenylene ethynylenes) (OPEs), peripherally decorated with chiral and linear paraffinic chains, is investigated in bulk, onto surfaces and in solution. Whilst the X-ray diffraction data for the chiral studied systems display a broad reflection centered at 2θ ∼20° (λ=Cu(Kα)), the higher crystallinity of OPE 3, endowed with three linear decyl chains, results in a diffractrogram with a number of well-resolved reflections that can be accurately indexed as a columnar packing arranged in 2D oblique cells. Compounds (S)-1 a and (R)-1 b-endowed with (S)- and (R)-3,7-dimethyloctyloxy chains-transfer their chirality to the supramolecular structures formed upon their self-assembly, and give rise to helical nanostructures of opposite handedness. A helicity switch is noticeable for the case of chiral (S)-2 decorated with (S)-2-methylnonyloxy chains which forms right-handed helices despite it possesses the same stereoconfiguration for their stereogenic carbons as (S)-1 a that self-assembles into left-handed helices. The stability and the mechanism of the supramolecular polymerization in solution have been investigated by UV/Vis experiments in methylcyclohexane. These studies demonstrate that the larger the distance between the stereogenic carbon and the aromatic framework is, the more stable the aggregate is. Additionally, the self-assembly mechanism is conditioned by the peripheral substituents: whereas compounds (S)-1 a and (R)-1 b self-assemble in a cooperative manner with a low degree of cooperativity, the aggregation of (S)-2 and 3 is well described by an isodesmic model. Therefore, the interaction between the chiral coil chains conditions the handedness of the helical pitch, the stability of the supramolecular structure and the supramolecular polymerization mechanism of the studied OPEs.

Amplification of chirality in N,N'-1,2-ethanediylbisbenzamides: from planar sheets to twisted ribbons.

A remarkable sergeants-and-soldiers effect is observed in the coassembly of N,N'-1,2-ethanediylbisbenzamides onto surfaces that experience an amplification of chirality able to transform flat lamellae into twisted ribbons.

Helical and flat structures from chiral dendronized rectangular oligo(phenylene ethynylene)s.

The synthesis of two chiral amphiphiles and their self-assembling features in solution and onto surfaces is reported. The different degree of interdigitation of the paraffinic substituents has an enormous influence in the chirality of the aggregates. Thus, while oligo(phenylene ethynylene) 1 shows a bisignated Cotton effect in solution and P-type helices onto surfaces, compound 2 lacks in any dichroic response at room temperature and self-assembles into flat ribbons.