Directing the Self‐Assembly Behaviour of Porphyrin‐Based Supramolecular Systems

Abstract

The self-assembly behaviour of a library of tetra-amidated porphyrin molecules decorated with a variety of solubilizing wedges is investigated as dilute solutions in methylcyclohexane. Small changes in the solubilising wedge of the porphyrins resulted in different aggregated states, as evidenced by CD and UV/Vis absorption spectroscopy. The porphyrins form co-facially stacked H-aggregates, slip-stacked J-aggregates or a mixture of both. Detailed thermodynamic and kinetic analysis showed that in all cases the formation of J-aggregates proceeds via an isodesmic mechanism whereas H-aggregates are formed via a cooperative mechanism. It is shown that these aggregates assemble in a parallel pathway, in which both compete for the monomer, compared to a sequential pathway, in which one of the aggregates interconverts into the other. Interestingly, kinetic analysis of porphyrins that only form H-aggregates in thermodynamic equilibrium revealed that the competing pathway towards J-aggregates is operational in these systems as well. Our findings show that the balance between H- and J-aggregates depends on remarkably small changes in the architecture of the solubilising wedges.

Tunable Energy Landscapes to Control Pathway Complexity in Self‐Assembled N‐Heterotriangulenes: Living and Seeded Supramolecular Polymerization

“…For all the solvent mixtures and concentrations utilized, the EQ model did not fit properly. The deviation of the fit could be indicative of the operation of a more complex supramolecular polymerization mechanism . In fact, a first proof of this complex mechanism is obtained by the strong thermal hysteresis observed when the disassembly process (heating curves) is monitored in comparison to the self‐assembly process taking place during the cooling curves (Figure S5, Supporting Information).…”

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

“…Upon increasing the volume fraction CHCl 3 , the absorbance and CD intensity at 392 nm decrease, with a concomitant gradual emergence of a broad, CD-silent absorption band at 425 nm, indicative of the formation of a weakly coupled J-type aggregate or otherwise less ordered aggregate (from here on referred to as J-type aggregates). 22 , 23 Approaching the critical solvent composition, the CD intensity at 392 nm rapidly decreases and the absorption at 425 nm rises sharply, indicating the destruction of cooperatively formed co-facially stacked H-aggregates ( Figure 2 ). At volume percentages above 5–7.5 vol% CHCl 3 , the CD signal has disappeared due to the destabilization of the H-aggregates, and a further increase in the CHCl 3 volume fraction results in a gradual increase in intensity and sharpening of the absorption peak.…”

“…Moreover, the asymptotic behavior of the minimal concentration required to form H-aggregates renders the system insensitive to changes in concentration in the limit of high concentration. As the various porphyrin morphologies, whose aggregation behaviors can be engineered through chemical synthesis, 22 are known to exhibit different material properties, 17 we envision that the combination of solvent composition and temperature control can be used to synthesize a plethora of functional supramolecular materials from only a very limited number of starting materials in a very easy and controllable manner.…”

“…As a result, formation of the cooperative polymers is very sensitive to solvent composition and temperature, and the system becomes insensitive to changes in concentration. Through the delicate interplay of pathway complexity with the molecular structure of the monomer, 22 the presence of competing polymerization pathways in supramolecular polymerizations can be employed to tailor the stability of supramolecular materials in a controllable fashion.…”

Porphyrins Through the Looking Glass: Spectroscopic and Mechanistic Insights in Supramolecular Chirogenesis of New Self-Assembled Porphyrin Derivatives

“…Addressed protocols pursued for the formation of such a species usually rely on the use of either chiral or achiral platforms (Monti, 2014;Liu et al, 2015;Magna et al, 2019). In the former case, the stereochemical course of the self-assembling process is governed by the presence of chiral groups linked on the porphyrin peripheral frame (Oliveira-González et al, 2015;van der Weegen et al, 2017). In the latter issue, final chiral suprastructures are obtained by interaction of achiral substrates with external physical effectors, such as hydrodynamic directional forces (Sorrenti et al, 2012;Arteaga et al, 2016); magnetic fields (Micali et al, 2012); LB and LS techniques (Chen et al, 2011), or chiral molecular templates, such as surfactants (El-Hachemi et al, 2008), chiral polymeric matrices (D'Urso et al, 2012), chiral ligands (Borovkov and Inoue, 2006;Berova et al, 2007) or carboxylic acids (Castriciano et al, 2011).…”