Model-driven optimization of multicomponent self-assembly processes

Abstract

Here, we report an engineering approach toward multicomponent self-assembly processes by developing a methodology to circumvent spurious, metastable assemblies. The formation of metastable aggregates often hampers self-assembly of molecular building blocks into the desired nanostructures. Strategies are explored to master the pathway complexity and avoid off-pathway aggregates by optimizing the rate of assembly along the correct pathway. We study as a model system the coassembly of two monomers, the R-and S-chiral enantiomers of a π-conjugated oligo(p-phenylene vinylene) derivative. Coassembly kinetics are analyzed by developing a kinetic model, which reveals the initial assembly of metastable structures buffering free monomers and thereby slows the formation of thermodynamically stable assemblies. These metastable assemblies exert greater influence on the thermodynamically favored self-assembly pathway if the ratio between both monomers approaches 1:1, in agreement with experimental results. Moreover, competition by metastable assemblies is highly temperature dependent and hampers the assembly of equilibrium nanostructures most effectively at intermediate temperatures. We demonstrate that the rate of the assembly process may be optimized by tuning the cooling rate. Finally, it is shown by simulation that increasing the driving force for assembly stepwise by changing the solvent composition may circumvent metastable pathways and thereby force the assembly process directly into the correct pathway.kinetic modeling | chiral amplification | supramolecular polymers | systems chemistry | pathway selection S elf-assembled nanostructures often are considered to be in fast exchange with their molecular building blocks (1). Although this is true for highly dynamic systems, the assembly of more rigid systems-i.e., systems most often used in applicationshave relatively slow dynamics and are often not in equilibrium (2-5). The long lifetime of the resulting assemblies allows the hierarchical construction of functional nanostructures from selfassembly of multiple components, because aggregates formed in earlier steps will not reequilibrate after addition of subsequent components. Via this approach, 1D multisegment nanorods (6) have been assembled, as have supramolecular electronic structures containing different types of wires (7) and p-n junctions (8). Slow self-assembly dynamics also play a critical role in the processing of organic materials such as bulk heterojunction solar cells. For example, prolonged annealing often is required to obtain optimal morphologies of electron donor and acceptor components (9-11). A drawback of the slow monomer exchange dynamics, however, is that the molecular components may get trapped easily in metastable off-pathway assemblies that hamper assembly along the correct pathway, a phenomenon known as pathway complexity (12). Hence, obtaining the desired supramolecular morphology often is nontrivial, and many variables, including solvent composition, concentration, temperature, and preparation ...

Toward model‐driven engineering of supramolecular copolymers

“…41,42 ROPV 3 is synthesized following a procedure analogous to the synthesis of ROPV 4 , as reported in detail in ref. 40. Methylcyclohexane (SigmaAldrich, spectroscopic grade) is used as received.…”

Controlling supramolecular polymerization through multicomponent self‐assembly

“…33 De HIGHLIGHT Greef, Meijer and coworkers have further elucidated the role of the monomer conformation, aggregate morphology, the role of cosolvents and fragmentation events. [33][34][35][435][436][437] Independently, the groups of W€ urthner, 37,438 and Miyajima and Aida, 38 have reported a methodology that introduces intramolecular noncovalent interactions, which are able to stabilize the monomeric species and thereby introduces a kinetic barrier toward intermolecular supramolecular interactions and polymerization. The W€ urthner lab uses perylene diimide type monomers PDI4 in MCH/toluene mixtures [ Fig.…”

“…21,22 Similar to covalent polymers, mechanistic investigations of supramolecular systems have highlighted the need to differentiate between the thermodynamically controlled cooperative nucleation-elongation mechanism, noncooperative isodesmic self-assembly or ringchain equilibria, 8,[23][24][25][26][27][28][29][30] and kinetically controlled self-assembly pathways. 22,[30][31][32][33][34][35][36][37][38][39][40][41][42] However, despite the large advances in elucidating mechanistic details, strategies to rationally manipulate mechanisms and self-assembly pathways in supramolecular polymerization remain scarce. While it is possible to use the toolbox of supramolecular and physical organic chemistry to tune the affinity of a monomer for itself, via molecular design or via concentration and temperature dependent selfassembly, precise engineering of molecular weight, shape, and size of the produced supramolecular polymer remains challenging.…”

“…These could be reduced by the addition of what the authors call a chain terminator, a monofunctional (N-methyl)imidazolyl Znporphyrin. In the light of recent developments in manipulating the kinetic stabilities and kinetic pathways in selfassembled supramolecular complexes [128][129][130][131][132][133][134][135][136] and supramolecular polymers, 22,[30][31][32][33][34][35][36][37][38][39][40][41][42]130,[137][138][139][140][141][142][143][144][145] it is interesting to note, that the addition of the chain stopper to the polymers did not lead to instantaneous disassembly. 127 The expected depolymerization and shortening of the polymers based on the comonomer feed ratio was only observed when the di-and monofunctional comonomers were premixed in a good FIGURE 3 (a) Chemical structures for the bi-and monofunctional phosphine ligands, P(Phe) 2 C 12 (Phe) 2 P and P(Phe) 2 C 12 , in order to prepare palladium(II)-based coordination polymers.…”

First assembly times and equilibration in stochastic coagulation-fragmentation

“…Moreover, kinetic theories designed to resolve discrepancies in classical nucleation theory often invoke multi-stage mechanisms across different cluster sizes and rely on understanding the formation times of finite-sized critical clusters. 14,[18][19][20][21][22] Another desired result of self-assembly studies is an estimate of the time it takes for a full cluster to first appear, a quantity that can only be determined through a fully stochastic treatment. These estimates may be useful in determining how fast-growing protein aggregates, filaments, or viral capsids form.…”