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We exploited the inherent geometrical isomerism of a PtII complex as a new tool to control supramolecular assembly processes. UV irradiation and careful selection of solvent, temperature, and concentration leads to tunable coordination isomerism, which in turn allows fully reversible switching between two distinct aggregate species (1D fibers↔2D lamellae) with different photoresponsive behavior. Our findings not only broaden the scope of coordination isomerism, but also open up exciting possibilities for the development of novel stimuli-responsive nanomaterials.
Self-assembly of multi-stranded perylene dye J-aggregates in columnar liquid-crystalline phases
(2018)
Many discoid dyes self-assemble into columnar liquid-crystalline (LC) phases with packing arrangements that are undesired for photonic applications due to H-type exciton coupling. Here, we report a series of crystalline and LC perylene bisimides (PBIs) self-assembling into single or multi-stranded (two, three, and four strands) aggregates with predominant J-type exciton coupling. These differences in the supramolecular packing and optical properties are achieved by molecular design variations of tetra-bay phenoxy-dendronized PBIs with two N–H groups at the imide positions. The self-assembly is driven by hydrogen bonding, slipped π–π stacking, nanosegregation, and steric requirements of the peripheral building blocks. We could determine the impact of the packing motifs on the spectroscopic properties and demonstrate different J- and H-type coupling contributions between the chromophores. Our findings on structure–property relationships and strong J-couplings in bulk LC materials open a new avenue in the molecular engineering of PBI J-aggregates with prospective applications in photonics.
Natural light harvesting as well as optoelectronic and photovoltaic devices depend on efficient transport of energy following photoexcitation. Using common spectroscopic methods, however, it is challenging to discriminate one-exciton dynamics from multi-exciton interactions that arise when more than one excitation is present in the system. Here we introduce a coherent two-dimensional spectroscopic method that provides a signal only in case that the presence of one exciton influences the behavior of another one. Exemplarily, we monitor exciton diffusion by annihilation in a perylene bisimide-based J-aggregate. We determine quantitatively the exciton diffusion constant from exciton–exciton-interaction 2D spectra and reconstruct the annihilation-free dynamics for large pump powers. The latter enables for ultrafast spectroscopy at much higher intensities than conventionally possible and thus improves signal-to-noise ratios for multichromophore systems; the former recovers spatio–temporal dynamics for a broad range of phenomena in which exciton interactions are present.
The chirality of the interlocked bay-arylated perylene motif is investigated upon its material prospect and the enhancement of its chiroptical response to the NIR spectral region. A considerable molecular library of inherently chiral perylene bisimides (PBIs) was utilized as acceptors in organic solar cells to provide decent device performances and insights into the structure-property relationship of PBI materials within a polymer blend. For the first time in the family of core-twisted PBIs, the effects of enantiopurity on the device performance was thoroughly investigated. The extraordinary structural sensitivity of CD spectroscopy served as crucial analytical tool to bridge the highly challenging gap between molecular properties and device analytics by proving the excitonic chirality of a helical PBI dimer. The chirality of this perylene motif could be further enhanced on a molecular level by both the expansion and the enhanced twisting of the π-scaffold to achieve a desirable strong chiroptical NIR response introducing a new family of twisted QBI-based nanoribbons. These achievements could be substantially further developed by expanding this molecular concept to a supramolecular level. The geometrically demanding supramolecular arrangement necessary for the efficient excitonic coupling was carefully encoded into the molecular design. Accordingly, the QBIs could form the first J-type aggregate constituting a fourfold-stranded superhelix of a rylene bisimide with strong excitonic chirality. Therefore, this thesis has highlighted the mutual corroboration of experimental and theoretical data from the molecular to the supramolecular level. It has demonstrated that for rylene bisimide dyes, the excitonic contribution to the overall chiroptical response can be designed and rationalized. This can help to pave the way for new organic functional materials to be used for
chiral sensing or chiral organic light-emitting devices.
A series of novel imide‐functionalized C\(_{64}\) nanographenes is investigated as acceptor components in organic solar cells (OSCs) in combination with donor polymer PM6. These electron‐poor molecules either prevail as a monomer or self‐assemble into dimers in the OSC active layer depending on the chosen imide substituents. This allows for the controlled stacking of electron‐poor and electron‐rich π–scaffolds to establish a novel class of non‐fullerene acceptor materials to tailor the bulk‐heterojunction morphology of the OSCs. The best performance is observed for derivatives that are able to self‐assemble into dimers, reaching power conversion efficiencies of up to 7.1%.
Thermoresponsive polymers are frequently involved in the development of materials for various applications. Here, polymers containing poly(2- benzhydryl-2-oxazine) (pBhOzi) repeating units are described for the first time. The homopolymer pBhOzi and an ABA type amphiphile comprising two flanking hydrophilic A blocks of poly(2-methyl-2-oxazoline) (pMeOx) and the hydrophobic aromatic pBhOzi central B block (pMeOx-b-pBhOzi-b-pMeOx) are synthesized and the latter is shown to exhibit inverse thermogelling properties at concentrations of 20 wt.% in water. This behavior stands in contrast to a homologue ABA amphiphile consisting of a central poly(2-benzhydryl-2-oxazoline) block (pMeOx-b-pBhOx-b-pMeOx). No inverse thermogelling is observed with this polymer even at 25 wt.%. For 25 wt.% pMeOx-b-pBhOzi-b-pMeOx, a surprisingly high storage modulus of ≈22 kPa and high values for the yield and flow points of 480 Pa and 1.3 kPa are obtained. Exceeding the yield point, pronounced shear thinning is observed. Interestingly, only little difference between self-assemblies of pMeOx-b-pBhOzi-b-pMeOx and pMeOx-b-pBhOx-b-pMeOx is observed by dynamic light scattering while transmission electron microscopy images suggest that the micelles of pMeOx-b-pBhOzi-b-pMeOx interact through their hydrophilic coronas, which is probably decisive for the gel formation. Overall, this study introduces new building blocks for poly(2-oxazoline) and poly(2-oxazine)-based self-assemblies, but additional studies will be needed to unravel the exact mechanism.
A new perylene bisimide (PBI), with a fluorescence quantum yield up to unity, self‐assembles into two polymorphic supramolecular polymers. This PBI bears four solubilizing acyloxy substituents at the bay positions and is unsubstituted at the imide position, thereby allowing hydrogen‐bond‐directed self‐assembly in nonpolar solvents. The formation of the polymorphs is controlled by the cooling rate of hot monomer solutions. They show distinctive absorption profiles and morphologies and can be isolated in different polymorphic liquid‐crystalline states. The interchromophoric arrangement causing the spectral features was elucidated, revealing the formation of columnar and lamellar phases, which are formed by either homo‐ or heterochiral self‐assembly, respectively, of the atropoenantiomeric PBIs. Kinetic studies reveal a narcissistic self‐sorting process upon fast cooling, and that the transformation into the heterochiral (racemic) sheetlike self‐assemblies proceeds by dissociation via the monomeric state.
In this paper, we bridge the gap between procedural content generation (PCG) and user-generated content (UGC) by proposing and demonstrating an interactive agent-based model of self-assembling ensembles that can be directed though user input. We motivate these efforts by considering the opportunities technology provides to pursue game designs based on according game design frameworks. We present three different use cases of the proposed model that emphasize its potential to (1) self-assemble into predefined 3D graphical assets, (2) define new structures in the context of virtual environments by self-assembling layers on the surfaces of arbitrary 3D objects, and (3) allow novel structures to self-assemble only considering the model’s configuration and no external dependencies. To address the performance restrictions in computer games, we realized the prototypical model implementation by means of an efficient entity component system (ECS). We conclude the paper with an outlook on future steps to further explore novel interactive, dynamic PCG mechanics and to ensure their efficiency.
Besides their widespread use in coordination chemistry, 2,2’‐bipyridines are known for their ability to undergo cis–trans conformational changes in response to metal ions and acids, which has been primarily investigated at the molecular level. However, the exploitation of such conformational switching in self‐assembly has remained unexplored. In this work, the use of 2,2’‐bipyridines as acid‐responsive conformational switches to tune supramolecular polymerization processes has been demonstrated. To achieve this goal, we have designed a bipyridine‐based linear bolaamphiphile, 1, that forms ordered supramolecular polymers in aqueous media through cooperative aromatic and hydrophobic interactions. Interestingly, addition of acid (TFA) induces the monoprotonation of the 2,2’‐bipyridine moiety, leading to a switch in the molecular conformation from a linear (trans) to a V‐shaped (cis) state. This increase in molecular distortion along with electrostatic repulsions of the positively charged bipyridine‐H\(^{+}\) units attenuate the aggregation tendency and induce a transformation from long fibers to shorter thinner fibers. Our findings may contribute to opening up new directions in molecular switches and stimuli‐responsive supramolecular materials.
Depending on the connectivity of solubilizing oligoethylene glycol (OEG) side chains to the π‐cores of amphiphilic naphthalene and perylene bisimide dyes, self‐assembly in water occurs either upon heating or cooling. Herein, we show that this effect originates from differences in the enwrapping capability of the π‐cores by the OEG chains. Rylene bisimides bearing phenyl substituents with three OEG chains attached directly to the hydrophobic π‐cores are strongly sequestered by the OEG chains. These molecules self‐assemble at elevated temperatures in an entropy‐driven process according to temperature‐ and concentration‐dependent UV/Vis spectroscopy and calorimetric dilution studies. In contrast, for rylene bisimides in which phenyl substituents with three OEG chains are attached via a methylene spacer, leading to much weaker sequestration, self‐assembly originates upon cooling in an enthalpy‐driven process. Our explanation for this controversial behavior is that the aggregation in the latter case is dictated by the release of “high energy water” from the hydrophobic π‐surfaces as well as dispersion interactions between the π‐scaffolds which drive the self‐assembly in an enthalpically driven process. In contrast, for the former case we suggest that in addition to the conventional explanation of a dehydration of hydrogen‐bonded water molecules from OEG units it is in particular the increase in conformational entropy of back‐folded OEG side chains upon aggregation that provides the pronounced gain in entropy that drives the aggregation process. Thus, our studies revealed that a subtle change in the attachment of solubilizing substituents can switch the thermodynamic signature for the self‐assembly of amphiphilic dyes in water from enthalpy‐ to entropy‐driven.