Various conventional reactions in polymer chemistry have been translated to the supramolecular domain, yet it has remained challenging to devise living supramolecular polymerization. To achieve this, ...self-organization occurring far from thermodynamic equilibrium--ubiquitously observed in nature--must take place. Prion infection is one example that can be observed in biological systems. Here, we present an 'artificial infection' process in which porphyrin-based monomers assemble into nanoparticles, and are then converted into nanofibres in the presence of an aliquot of the nanofibre, which acts as a 'pathogen'. We have investigated the assembly phenomenon using isodesmic and cooperative models and found that it occurs through a delicate interplay of these two aggregation pathways. Using this understanding of the mechanism taking place, we have designed a living supramolecular polymerization of the porphyrin-based monomers. Despite the fact that the polymerization is non-covalent, the reaction kinetics are analogous to that of conventional chain growth polymerization, and the supramolecular polymers were synthesized with controlled length and narrow polydispersity.
Amino acid based diamides are widely used as a substructure in supramolecular polymers and are also key components of polypeptides that help to understand protein folding. The interplay of folding ...and aggregation of a diamide was used to achieve seed‐initiated supramolecular polymerization. For that purpose, a pyrene‐substituted diamide was synthesized in which pyrene is used as a tracer to monitor the supramolecular polymerization. Thermodynamics and time‐dependent studies revealed that the folding of the diamide moiety, via the formation of intramolecular hydrogen bonds, effectively prevents a spontaneous nucleation that leads to supramolecular polymerization. Under such out‐of‐equilibrium conditions, the addition of seeds successfully initiates the supramolecular polymerization. These results demonstrate the utility of such amino acid based diamides in programmable supramolecular polymerizations.
Seeded polymerization: The hydrogen‐bond‐directed folding of a diamide group effectively prevents the spontaneous nucleation in the supramolecular polymerization of extended diamides. The seeded polymerization of pyrene, as an example of luminescent π‐conjugated systems, was accomplished under out‐of‐equilibrium conditions in these coupled equilibria.
Whilst bacteriochlorophyll
,
, and
dyes self-assemble into the most efficient light harvesting J-aggregate systems found in nature, their supramolecular packing arrangements are still a matter of ...debate and a significant number of models have been suggested for their local and long-range ordering. Here we reveal for a synthetic model system based on a zinc chlorin (ZnChl) dye an intriguing interplay of two competing aggregation pathways by kinetic and thermodynamic studies in MeOH/water solvent mixtures: the formation of kinetically controlled off-pathway nanoparticles consisting of excitonically coupled J-dimers
the formation of thermodynamically more stable one-dimensional helical fibers consisting of J-coupled extended aggregates. The higher order of the latter is evidenced by atomic force microscopy and a more narrow absorption spectrum of the J-aggregates. Based on a recently developed thermodynamic model that combines the cooperative
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growth model with a competing dimerization model, an energy landscape could be derived that describes the pathway complexity of this biomimetic system. Our studies reveal that the kinetic stability of the off-pathway nanoparticles increases with increasing concentration of ZnChl or water content in a MeOH/water solvent mixture. For a water content >90% deeply trapped off-pathway nanoparticle products are formed that do not transform anymore to the more ordered thermodynamic product within reasonable time scales. Based on these observations, we hypothesize that out-of-equilibrium aggregate structures of natural BChl dyes may also exist in the natural chlorosomes of green bacteria.
A new amphiphilic BF2‐azadipyrromethene (aza‐BODIPY) dye 1 has been synthesized using a CuI‐catalyzed “click” reaction. For this dye, two self‐assembly pathways that lead to different type of ...J‐aggregates with distinct near‐infrared optical properties have been discovered. The metastable off‐pathway product displays a broad, structureless absorption band while the thermodynamically stable on‐pathway aggregate exhibits the characteristic spectral features of a J‐aggregate, that is, red‐shifted intense absorption band with significantly narrowed linewidth. The morphology and structure of the aggregates were studied by atomic force microscopy, transmission and scanning electron microscopy. The aggregation processes of 1 were investigated by temperature‐ and concentration‐dependent UV/Vis spectroscopy and evaluated by models for cooperative self‐assembly.
Chlorophyll analog: An amphiphilic BF2‐azadipyrromethene (aza‐BODIPY) dye 1 forms two types of aggregates with distinct optical properties and nanoscale morphologies through competing cooperative self‐assembly pathways. The observed rod‐like morphology and exciton characteristics for the aza‐BODIPY‐based J‐aggregates are comparable to those of natural chlorophyll dye assemblies.
Far‐from‐equilibrium thermodynamic systems that are established as a consequence of coupled equilibria are the origin of the complex behavior of biological systems. Therefore, research in ...supramolecular chemistry has recently been shifting emphasis from a thermodynamic standpoint to a kinetic one; however, control over the complex kinetic processes is still in its infancy. Herein, we report our attempt to control the time evolution of supramolecular assembly in a process in which the supramolecular assembly transforms from a J‐aggregate to an H‐aggregate over time. The transformation proceeds through a delicate interplay of these two aggregation pathways. We have succeeded in modulating the energy landscape of the respective aggregates by a rational molecular design. On the basis of this understanding of the energy landscape, programming of the time evolution was achieved through adjusting the balance between the coupled equilibria.
Finding the right balance: The energy landscape of a supramolecular polymerization in which the supramolecular assembly transforms from a J‐aggregate to an H‐aggregate over time has been modulated by a rational molecular design. Based on this, kinetic control over pathway complexity was achieved through adjusting the balance between the coupled equilibria.
The self‐assembly of an amide‐functionalized dithienyldiketopyrrolopyrrole (DPP) dye in aqueous media was achieved through seed‐initiated supramolecular polymerization. Temperature‐ and ...time‐dependent studies showed that the spontaneous polymerization of the DPP derivative was temporally delayed upon cooling the monomer solution in a methanol/water mixture. Theoretical calculations revealed that an amide‐functionalized DPP derivative adopts an energetically favorable folded conformation in the presence of water molecules due to hydration. This conformational change is most likely responsible for the trapping of monomers in the initial stage of the cooperative supramolecular polymerization in aqueous media. However, the monomeric species can selectively interact with externally added fragmented aggregates as seeds through concerted π‐stacking and hydrogen‐bonding interactions. Consequently, the time course of the supramolecular polymerization and the morphology of the aggregated state can be controlled, and one‐dimensional fibers that exhibit a J‐aggregate‐like bathochromically shifted absorption band can be obtained.
Seeded polymerization in aqueous media: A seeding approach afforded control over the time course of the supramolecular polymerization and aggregate structure of an amide‐functionalized diketopyrrolopyrrole (DPP) dye in aqueous media. The effect of water on the conformation of the monomer and the initial step of the self‐assembly were elucidated by detailed experimental analyses and theoretical calculations.
We report the thermodynamic and kinetic aqueous self-assembly of a series of amide-functionalized dithienyldiketopyrrolopyrroles (TDPPs) that bear various hydrophilic oligoethylene glycol (OEG) and ...hydrophobic alkyl chains. Spectroscopic and microscopic studies showed that the TDPP-based amphiphiles with an octyl group form sheet-like aggregates with J-type exciton coupling. The effect of the alkyl chains on the aggregated structure and the internal molecular orientation was examined via computational studies combining MD simulations and TD-DFT calculations. Furthermore, solvent and thermal denaturation experiments provided a state diagram that indicates the formation of unexpected nanoparticles during the self-assembly into nanosheets when longer OEG side chains are introduced. A kinetic analysis revealed that the nanoparticles were obtained selectively as an on-pathway intermediate state toward the formation of thermodynamically controlled nanosheets. The metastable aggregates were used for seed-initiated supramolecular assembly, which allowed establishing control over the assembly kinetics and the aggregate size. The sheet-like aggregates prepared using the seeding method exhibited coherent vibration in the excited state, indicating a well-ordered orientation of the TDPP units. These results underline the significance of fine tuning of the hydrophobic/hydrophilic balance in the molecular design to kinetically control the assembly of amphiphilic π-conjugated molecules into two-dimensional nanostructures in aqueous media.
For the creation of next‐generation organic electronic materials, the integration of π‐systems has recently become a central theme. Such functional materials can be assembled by supramolecular ...polymerization when aromatic π‐systems are used as monomers, and the properties of the resulting supramolecular polymer strongly depend on the electronic structure of the monomers. Here, we demonstrate the construction of a supramolecular polymer consisting of an antiaromatic π‐system as the monomer. An amide‐functionalized NiII norcorrole derivative formed a one‐dimensional supramolecular polymer through π‐π stacking and hydrogen‐bonding interactions, ensuring the persistency of the conducting pathway against thermal perturbation, which results in higher charge mobility along the tightly bound linear aggregates than that of the aromatic analogue composed of ZnII porphyrins.
A supramolecular polymer that consists of an antiaromatic π‐system as the monomer has been created. An amide‐functionalized NiII norcorrole derivative forms a one‐dimensional supramolecular polymer through π‐π stacking and hydrogen‐bonding interactions. The formation of a long‐range π‐π‐stacking array ensures the persistency of the conducting pathway against thermal perturbation and achieves high charge‐carrier mobility along the tightly‐bound linear aggregates.
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