Effect of chirality in the supramolecular polymerization of N-annulated perylenediimides: Cancelling pathway complexity.

Herein, the synthesis of two chiral NPBIs, (S)-1 and (R)-1, is reported and their self-assembling features investigated. The reported NPBIs form chiral supramolecular polymers with a rich dichroic pattern by the π-stacking of the aromatic backbones and the formation of an array of H-bonds between the amide functional groups. Furthermore, the peripheral 3,4,5-trialkoxy benzamide groups can form seven-membered pseudocycles by the intramolecular H-bonding interaction between the NH of the peripheral amides and one of the carbonyls of the imide units thus yielding a kinetically controlled self-assembly process. Unlike achiral NPBI 1, that has been reported to form up to four supramolecular polymorphs, the reported chiral NPBIs form only a J-type aggregated species. The results presented herein reveal how subtle changes exert an enormous influence on the supramolecular polymerization outcome.

Unveiling the Role of Hydrogen Bonds in Luminescent N-Annulated Perylene Liquid Crystals.

We report the liquid-crystalline (LC) and luminescent properties of a series of N-annulated perylenes (1-4) in whose molecular structures amide and ester groups alternate. We found that the LC properties of these compounds not only depend on the number of hydrogen-bonding units, but also on the relative position of the amide linkers in the molecule. The absence of amide groups in compound 1 leads to no LC properties, whereas four amide groups induce the formation of a wide temperature range columnar hexagonal phase in compound 4. Remarkably, compound 3, with two amide groups in the inner part of the structure, stabilizes the columnar LC phases better than its structural isomer 2, with the amide groups in the outer part of the molecule. Similarly, we found that only compounds 1 and 2, which have no hydrogen bonding units in the inner part of the molecule, exhibit luminescence vapochromism upon exposure to organic solvent vapors.

Globular Aggregates Stemming from the Self-Assembly of an Amphiphilic N-Annulated Perylene Bisimide in Aqueous Media.

Herein, we describe the synthesis of highly emissive amphiphilic N-annulated PBI 1 decorated with oligo ethylene glycol (OEG) side chains. These polar side chains allow the straightforward solubility of 1 in solvents of different polarity such as water, iPrOH, dioxane, or chloroform. Compound 1 self-assembles in aqueous media by π-stacking of the aromatic units and van der Waals interactions, favored by the hydrophobic effect. The hypo- and hypsochromic effect observed in the UV-Vis spectra of 1 in water in comparison to chloroform is diagnostic of H-type aggregation. Solvent denaturation experiments allow deriving the free Gibbs energy for the self-assembly process in aqueous media and the factor m that is indicative of the influence exerted by a good solvent in the stability of the final aggregates. The ability of compound 1 to self-assemble in water yields globular aggregates that have been visualized by TEM imaging.

N-Annulated Perylene Bisimides to Bias the Differentiation of Metastable Supramolecular Assemblies into J- and H-Aggregates.

The unique self-assembling features of N-annulated perylene bisimides (PBIs) 1 and 2 are reported. The stability of the aggregates of diester 1, in which no H-bonding interactions are operative, corroborates the significance of long-range van der Waals and dipole-dipole electrostatic interactions in the construction of stable supramolecular assemblies. The incorporation of amide functional groups within the N-annulated PBI in 2 stimulates pathway differentiation to achieve up to three J-type aggregates and a fourth H-type aggregate depending on the experimental conditions. The results presented demonstrate unprecedented levels of control over synthetic supramolecular self-assembly and the rich differentiation that N-annulated PBIs exhibit, opening the door to new, complex, functional supramolecular materials.

Disclosing chirality in consecutive supramolecular polymerizations: chiral induction by light in N-annulated perylenetetracarboxamides.

A multichiroptical characterization of the different aggregates formed by the consecutive supramolecular polymerization of chiral N-annulated perylenetetracarboxamides is reported. They form one-handed helical aggregates, which emit circularly polarized light with remarkable |glum| values. In addition, the chiral induction by circularly polarized light in the supramolecular polymerization of the achiral counterpart is demonstrated.

Consecutive Supramolecular Polymerization of a Rylene-Based Twistacene.

The synthesis and self-assembling features of twistacene 1 are reported. The supramolecular polymerization of 1 displays a consecutive pathway to afford slipped (AggI) and rotationally displaced (AggII) aggregates conditioned by the formation of intramolecularly H-bonded pseudocycles. In methylcyclohexane, both AggI and AggII are highly stable and the interconversion of the kinetically controlled AggI into the thermodynamically controlled AggII takes several weeks to occur. The utilization of toluene as solvent changes the energetic level for both aggregates and favors a faster conversion of AggI into AggII within a period of minutes. This conversion can be accelerated by the addition of seeds. Furthermore, concentration dependent kinetic studies demonstrate the consecutive character of the supramolecular polymerization of 1.

Decoding the Consequences of Increasing the Size of Self-Assembling Tricarboxamides on Chiral Amplification.

A complete series of experimental and theoretical investigations on the supramolecular polymerization of chiral (1 and 2) and achiral (3) oligo(phenylene ethynylene) tricarboxamides (OPE-TAs) is reported. The performance of seargents-and-soldiers (SaS) and majority rules (MR) experiments has allowed deriving a full set of thermodynamic parameters, including the helix reversal penalty (HRP) and the mismatch penalty (MMP). The results described illustrate the influence exerted by the number of stereogenic centers per monomeric unit and the temperature on the chiral amplification phenomenon. While the HRP decreases upon decreasing the number of chiral side chains, the MMP follows an opposite trend. The experimental trend observed in MR experiments contrasts with that reported for benzenetricarboxamides (BTAs), for which the chiral amplification ability increases by lowering the number of stereogenic centers or increasing the temperature. Theoretical calculations predict that the rotational angle between adjacent monomeric units in the stack (ca. 18°) gradually decreases when decreasing the number of branched chiral side chains and leads to higher MMP values, in good accord with the experimental trend. The reduction of the rotational angle gives rise to less efficient H-bonding interactions between the peripheral amide functional groups and is suggested to provoke a decrease of the HRP as experimentally observed. In BTAs, increasing the number of stereogenic centers per monomeric unit results in a negligible change of the rotation angle between adjacent units (ca. 65°), and, consequently, the steric bulk increases with the number of chiral side chains, leading to higher MMP values. The data presented herein contribute to shed light on the parameters controlling the transfer and amplification of chirality processes in supramolecular polymers, highlighting the enormous influence exerted by the size of the self-assembling unit on the final helical outcome.

Hierarchy of Asymmetry in Chiral Supramolecular Polymers: Toward Functional, Helical Supramolecular Structures.

The formation of helical structures through the supramolecular polymerization of a variety of self-assembling units is reviewed. These scaffolds are usually obtained by efficient transfer or amplification of chirality phenomena, in which the starting self-assembling molecules possess different elements of asymmetry, such as point or axial chirality. Relevant examples of helical supramolecular structures investigated under thermodynamic control are reviewed, and the helical outcome of remarkable examples of chiral entities obtained through kinetic control are also highlighted. Finally, selected examples of flexible macroscopic chirality and catalysis are described to illustrate the applicability of helical aggregates.

Pathway Complexity Versus Hierarchical Self-Assembly in N-Annulated Perylenes: Structural Effects in Seeded Supramolecular Polymerization.

Studies were carried out on the hierarchical self-assembly versus pathway complexity of N-annulated perylenes 1-3, which differ only in the nature of the linking groups connecting the perylene core and the side alkoxy chains. Despite the structural similarity, compounds 1 and 2 exhibit noticeable differences in their self-assembly. Whereas 1 forms an off-pathway aggregate I that converts over time (or by addition of seeds) into the thermodynamic, on-pathway product, 2 undergoes a hierarchical process in which the kinetically trapped monomer species does not lead to a kinetically controlled supramolecular growth. Finally, compound 3, which lacks the amide groups, is unable to self-assemble under identical experimental conditions and highlights the key relevance of the amide groups and their position to govern the self-assembly pathways.

Seeded Supramolecular Polymerization in a Three-Domain Self-Assembly of an N-Annulated Perylenetetracarboxamide.

The three-domain cooperative supramolecular polymerization of 1, together with the lag time in which the monomeric species remains inactive, allows seeded supramolecular polymerization to be performed. The kinetic experiments demonstrate that only seeds based on the intermediate aggregate are able to propagate the supramolecular polymerization of 1 from their active sites. The results presented herein constitute a new example of kinetically controlled supramolecular systems and contribute to expanding knowledge about the structural requirements of a self-assembling molecule to experience seeded supramolecular polymerization.

Influence of Axial and Point Chirality in the Chiral Self-Assembly of Twin N-Annulated Perylenecarboxamides.

The synthesis of three bis(N-annulated perylenecarboxamides) endowed with achiral or chiral side chains is reported. The restricted rotation of the perylene moieties yields atropisomers that can be separated by chiral HPLC. The CD spectra of the six stereoisomers show a dichroic pattern in a good solvent that changes drastically upon adding a poor solvent that favors the aggregation. The cooperative character of the supramolecular polymerization mechanism of 1-3 has been determined by denaturation experiments, which reveal that the formation of homochiral aggregates is favored over the formation of heterochiral aggregates. A complete set of amplification of chirality experiments have been carried out, revealing the preponderance of axial chirality over point chirality. The results presented herein shed relevant light on the structural conditions exhibited by molecular units endowed with different elements of asymmetry to generate chiral supramolecular structures and the supremacy of axial chirality over point chirality in the origin of homochirality.