Impact of Positional Isomerism on Pathway Complexity in Aqueous Media

Abstract

Pathway complexity has become an important topic in recent years due to its relevance in the optimization of molecular assembly processes, which typically require precise sample preparation protocols. Alternatively, competing aggregation pathways can be controlled by molecular design, which primarily rely on geometrical changes of the building blocks. However, understanding how to control pathway complexity by molecular design remains elusive and new approaches are needed. Herein, we exploit positional isomerism as a new molecular design strategy for pathway control in aqueous self‐assembly. We compare the self‐assembly of two carboxyl‐functionalized amphiphilic BODIPY dyes that solely differ in the relative position of functional groups. Placement of the carboxyl group at the 2‐position enables efficient pairwise H‐bonding interactions into a single thermodynamic species, whereas meso‐substitution induces pathway complexity due to competing hydrophobic and hydrogen bonding interactions. Our results show the importance of positional engineering for pathway control in aqueous self‐assembly.

Anti‐cooperative Self‐Assembly with Maintained Emission Regulated by Conformational and Steric Effects

“…Additionally, a broadening of the main absorption band is observed, suggesting the formation of an aggregated species ( Agg1 ) in MCH. This atypical aggregate absorption spectrum, almost unaltered in comparison to the monomer, suggests the presence of weak aromatic interactions between the BODIPY dyes [11, 15] …”

“… [6, 7] This limitation can be commonly overcome in two different ways: i) introducing sterically bulky substituents in the molecular design, typically at the chromophore's core, [8, 9–11] or ii) including chromophores with various freely‐rotating groups that undergo restriction in intramolecular rotation (RIR) upon aggregation (Scheme 1). [12, 13] While the former strategy often induces a J‐type aggregation process with red‐shifted absorption and emission, [11, 14, 15] the latter approach leads to a turn‐on or a dramatic amplification of the emission compared to the monomer species via aggregation‐induced emission (AIE) [12, 16] . Thus, self‐assembly of π‐conjugated building blocks generally results in significant changes in the original photophysical properties of the system.…”

“…For this purpose, we selected a conformationally flexible monomer unit with a central 1,3‐substituted (diphenyl)urea hydrogen bonding synthon that is tethered to two BODIPY dyes featuring sterically bulky trialkoxybenzene substituents at the meso ‐position (see compound 1 in Scheme 1; for synthesis and characterization, see the Supporting Information). This molecular design enables an appropriate balance of attractive forces (hydrogen bonding and aromatic interactions) and destabilizing effects (steric effects and multiple possible monomer conformations due to a high conformational freedom) that are required to suppress an elongated growth [9–11, 15] . As a result, we were able to increase the dye‐dye distances, thereby attenuating the aggregation at the stage of short oligomers and leading to maintained emission compared to the monomer state.…”

A novel pathway and seeded polymerizations of aggregates at the thermodynamic state for an amido-anthraquinone compound

“…Supramolecular pathways have been found to be rationally tuned by a variety of methods such as temperature-, 3 solution-, 4 time- 5 and thermal-annealing. 6 Furthermore, supramolecular self-assembly pathways could also be controlled by the molecular design of the building blocks based on the conformational changes of monomers.…”

Exploring the tubular self-assembly landscape of dinucleobase amphiphiles in water

“…In the same way, aqueous synthetic assemblies are increasingly using more elaborate monomers in which such directional interactions are embedded in molecular structure, but shielded from water by strategically positioned lipophilic pockets. [9][10][11][12][13][14][15][16][17][18][19] This allows to attain higher levels of structural sophistication and, potentially, novel and complex functions in the designed self-assembled systems. Employing this strategy, we recently managed to confer a tubular shape to micelle assemblies by protecting directional Watson-Crick interactions between complementary nucleobases from the otherwise competing water medium.…”