Temperature Directs the Majority-Rules Principle in Supramolecular Copolymers Driven by Triazine–Benzene Interactions

Supramolecular copolymers have typically been studied in the extreme cases, such as self-sorting or highly mixed copolymer systems, while the intermediate systems have been less understood. We have reported the temperature-dependent microstructure in copolymers of triazine- and benzene-derivatives based on charge-transfer interactions with a highly alternating microstructure at low temperatures. Here, we investigate the temperature-dependent copolymerization further and increase the complexity by combining triazine- and benzene-derivatives with opposite preferred helicities. In this case, intercalation of the benzene-derivative into the triazine-derivative assemblies causes a helical inversion. The inversion of the net helicity was rationalized by comparing the mismatch penalties of the individual monomers, which indicated that the benzene-derivative dictates the helical screw-sense of the supramolecular copolymers. Surprisingly, this was not reflected in further investigations of slightly modified triazine- and benzene-derivatives, thus highlighting that the outcome is a subtle balance between structural features, where small differences can be amplified due to the competitive nature of the interactions. Overall, these findings suggest that the temperature-dependent microstructure of triazine- and benzene-based supramolecular copolymers determines the copolymer helicity of the presented system in a similar way as the mixed majority-rules phenomenon.</p

Controlling Helical Asymmetry in Supramolecular Copolymers by In Situ Chemical Modification

Amplification of asymmetry in complex molecular systems results from a delicate interplay of chiral supramolecular structures and their chemical reactivity. In this work, we show how the helicity of supramolecular assemblies can be controlled by performing a non-stereoselective methylation reaction on comonomers. By methylating chiral glutamic acid side chains in benzene-1,3,5-tricarboxamide (BTA) derivatives to form methyl esters, the assembly properties are modulated. As reacted comonomers, the methyl ester-BTAs induce a stronger bias in the screw-sense of helical fibers predominantly composed of stacked achiral alkyl-BTA monomers. Hence, applying the in situ methylation in a system with the glutamic acid-BTA comonomer induces asymmetry amplification. Moreover, mixing small quantities of enantiomers of glutamic acid-BTA and glutamate methyl ester-BTA in the presence of the achiral alkyl-BTAs leads to deracemization and inversion of the helical structures in solution via the in situ reaction toward a thermodynamic equilibrium. Theoretical modeling suggests that the observed effects are caused by enhanced comonomer interactions after the chemical modification. Our presented methodology enables on-demand control over asymmetry in ordered functional supramolecular materials.</p

Simulating Assembly Landscapes for Comprehensive Understanding of Supramolecular Polymer-Solvent Systems

Complexity in supramolecular polymer systems arises from interactions between different components, including solvent molecules. By varying their concentration or temperature in such multicomponent systems, complex phenomena can occur such as thermally bisignate and dilution-induced assembly of supramolecular polymers. Herein, we demonstrate that both these phenomena emerge from the same underlying interaction mechanism between the components. As a model system, amide-decorated supramolecular polymers of porphyrins were investigated in combination with aliphatic alcohols as hydrogen-bond scavengers, and thermodynamic mass-balance models were applied to map the three-dimensional assembly landscapes. These studies unveiled that the interaction between hydrogen-bond scavengers and monomers is temperature-dependent and becomes dominant at high monomer concentrations. With these insights, we could exploit competitive monomer-alcohol interactions to prompt the dilution-induced assembly of various common monomers as well as bisignate assembly events. Moreover, kinetic insights were obtained by navigating through the assembly landscape. Similar to phase diagrams of covalent polymers, these assembly landscapes provide a comprehensive picture of supramolecular polymerizations, which helps to precisely regulate the system properties. The generality of this approach using assembly landscapes makes it relevant for any supramolecular system, and this enhanced control will open the door to build complex and functional supramolecular polymer systems.</p

Chirality and Supramolecular Copolymerizations – The Elusive Role of Subtle Solvation Effects

Recent investigations of supramolecular polymers based on chiral triphenylene-2,6,10-tricarboxamides (TTAs) showed how temperature-induced changes in solvation can greatly influence the preferred helical conformation of the supramolecular polymers formed. Here, we combine chiral TTA with achiral copolymerization partners to further investigate temperature-dependent solvation effects. Systematic variation of the system's composition shows clear impacts on the temperature window where the conformational change occurs. Further, simple chain length variations in the achiral comonomer greatly affect the ability to influence the conformational change in the copolymer, while the differences in the properties of the individual homopolymers are rather small. We herein highlight how subtle changes in the monomers can impact the observed copolymer properties drastically; an effect arising from the emerging complexity of multicomponent interactions in supramolecular copolymers with solvent-solute interactions being more important than typically thought

Supramolecular polymorphism in aggregates of a boron-difluoride complex of Peri-naphthoindigo via solvent- and pathway-dependent self-assembly

Supramolecular polymorphism in dye aggregates and examples of N,O-bidentate boron difluoride complexes are very uncommon in chemistry. Both rarities have been addressed by synthesising a new N,O-bidentate boron difluoride complex PNIBF2, which shows polymorphic aggregation. Depending upon the nature of the solvent and preparation methods, PNIBF2 produced three different aggregates. In a non-polar environment, the dye produced emissive linear nanoaggregates Agg1. In contrast, in a polar solvent (76 : 24 v/v water-THF mixture), the dye produced two different types of cyclic aggregates, nanoellipsoids Agg2 and nanospheres Agg3. Kinetically controlled Agg2 were produced at room temperature, while Agg3 were generated at elevated temperatures. Supramolecular assemblies Agg2 could be readily converted into Agg3 by heating and subsequent slow cooling. Our results highlight the relevance of peri-naphthoindigo as a new molecular building block for the creation of functional supramolecular systems

Supramolecular Polymerization as a Tool to Reveal the Magnetic Transition Dipole Moment of Heptazines

Heptazine derivatives have attracted significant interest due to their small S1-T1 gap, which contributes to their unique electronic and optical properties. However, the nature of the lowest excited state remains ambiguous. In the present study, we characterize the lowest optical transition of heptazine by its magnetic transition dipole moment. To measure the magnetic transition dipole moment, the flat heptazine must be chiroptically active, which is difficult to achieve for single heptazine molecules. Therefore, we used supramolecular polymerization as an approach to make homochiral stacks of heptazine derivatives. Upon formation of the supramolecular polymers, the preferred helical stacking of heptazine introduces circular polarization of absorption and fluorescence. The magnetic transition dipole moments for the S1 ← S0 and S1 → S0 are determined to be 0.35 and 0.36 Bohr magneton, respectively.</p

Unraveling the Complexity of Supramolecular Copolymerization Dictated by Triazine-Benzene Interactions

Supramolecular copolymers formed by the noncovalent synthesis of multiple components expand the complexity of functional molecular systems. However, varying the composition and microstructure of copolymers through tuning the interactions between building blocks remains a challenge. Here, we report a remarkable discovery of the temperature-dependent supramolecular copolymerization of the two chiral monomers 4,4′,4″-(1,3,5-triazine-2,4,6-triyl)tribenzamide (S-T) and 4,4′,4″-(benzene-1,3,5-triyl)tribenzamide (S-B). We first demonstrate in the homopolymerization of the two individual monomers that a subtle change from the central triazine to benzene in the chemical structure of the monomers significantly affects the properties of the resulting homopolymers in solution. Homopolymers formed by S-T exhibit enhanced stability in comparison to S-B. More importantly, through a combination of spectroscopic analysis and theoretical simulation, we reveal the complex process of copolymerization: S-T aggregates into homopolymers at elevated temperature, and upon slow cooling S-B gradually intercalates into the copolymers, to finally give copolymers with almost 80% alternating bonds at 10 °C. The formation of the predominantly alternating copolymers is plausibly contributed by preferred heterointeractions between triazine and benzene cores in S-T and S-B, respectively, at lower temperatures. Overall, this work unravels the complexity of a supramolecular copolymerization process where an intermediate heterointeraction (higher than one homointeraction and lower than the other homointeraction) presents and proposes a general method to elucidate the microstructures of copolymers responsive to temperature changes