Competing Interactions in Hierarchical Porphyrin Self-Assembly Introduce Robustness in Pathway Complexity

Abstract

Pathway complexity in supramolecular polymerization has recently sparked interest as a method to generate complex material behavior. The response of these systems relies on the existence of a metastable, kinetically trapped state. In this work, we show that strong switch-like behavior in supramolecular polymers can also be achieved through the introduction of competing aggregation pathways. This behavior is illustrated with the supramolecular polymerization of a porphyrin-based monomer at various concentrations, solvent compositions, and temperatures. It is found that the monomers aggregate via an isodesmic mechanism in weakly coupled J-type aggregates at intermediate solvent quality and temperature, followed by nucleated H-aggregates at lower solvent qualities and temperatures. At further increased thermodynamic driving forces, such as high concentration and low temperature, the H-aggregates can form hierarchical superhelices. Our mathematical models show that, contrary to a single-pathway polymerization, the existence of the isodesmic aggregation pathway buffers the free monomer pool and renders the nucleation of the H-aggregates insensitive to concentration changes in the limit of high concentrations. We also show that, at a given temperature or solvent quality, the thermodynamically stable aggregate morphology can be selected by controlling the remaining free external parameter. As a result, the judicious application of pathway complexity allows us to synthesize a diverse set of materials from only a single monomer. We envision that the engineering of competing pathways can increase the robustness in a wide variety of supramolecular polymer materials and lead to increasingly versatile applications.

Counterintuitive consequences of competitive pathways in supramolecular polymerizations

“…The thermodynamic values of the elongation phases, which determine the elongation temperatures of the polymers, have been chosen such that the elongation temperature of state A is at 80 °C, and the system is predominantly polymerized below this temperature and monomerically dissolved above the elongation temperature. The stabilities of the elongation phases of states A and B are equal at 20 °C, with state B being more stable below 20 °C, which results in the A‐B transition between the two polymer states at that temperature . Although the elongation and transition temperatures are equal for all simulations, Figure clearly shows that varying the cooperativities of the supramolecular polymerizations has a strong influence on the shape of the A‐B transition at 20 °C.…”

“…Similarly, several systems that show multiple thermodynamically rather than kinetically controlled polymer morphologies at various temperatures or solvent compositions have been experimentally observed and these reports have recently gained more attention . Interestingly, these thermodynamically controlled competitive polymerizations show concentration‐independent polymer–polymer transitions that are solely determined by the relative stabilities of the aggregates, making them very responsive to changes in solvent or temperature . However, in addition to concentration independency, these transitions between supramolecular polymers have been shown to exhibit more intricate features, such as gradual or sharp onsets and asymmetry in the transition [Fig.…”

A Competing Hydrogen Bonding Pattern to Yield a Thermo‐Thickening Supramolecular Polymer

“…Ester-bis-ureas contain both as trong bis-urea sticker that is responsible for the build-up of long rod-like objects by hydrogen bonding and ester groups that can interfere with this main pattern in as ubtle way. [14] An umber of studies describe the possibility of selecting one of these nanostructures by carefully controlling the conditions of aggregation, namely,t ime, [15][16][17][18] concentration, [19] temperature, [20] solvent, [21][22][23][24][25] and diffusion, [26] or by tuning the nature of the monomer. The transition from the low-temperature structure to the next occurs reversibly by heating and is accompanied by an increase in viscosity,arare feature for solutions in hydrocarbons.…”

“…[1][2][3][4] Ther eversible but directional non-covalent interactions responsible for their self-assembly provides tunability and responsiveness [5] to various stimuli. [14] An umber of studies describe the possibility of selecting one of these nanostructures by carefully controlling the conditions of aggregation, namely,t ime, [15][16][17][18] concentration, [19] temperature, [20] solvent, [21][22][23][24][25] and diffusion, [26] or by tuning the nature of the monomer. [14] An umber of studies describe the possibility of selecting one of these nanostructures by carefully controlling the conditions of aggregation, namely,t ime, [15][16][17][18] concentration, [19] temperature, [20] solvent, [21][22][23][24][25] and diffusion, [26] or by tuning the nature of the monomer.…”

“…[30,31] However,achange in the properties of the supramolecular assemblies at the macroscale has been reported for very few cases. [33] In particular,w hen two competing SPs can assemble from the same monomer, [25] the transition between the two structures can result in noticeable macroscopic property changes. [33] In particular,w hen two competing SPs can assemble from the same monomer, [25] the transition between the two structures can result in noticeable macroscopic property changes.…”