Anti-cooperative supramolecular polymerization: a new K2-K model applied to the self-assembly of perylene bisimide dye proceeding via well-defined hydrogen-bonded dimers

Supramolecular Self-Assembly of Perylene Bisimide Derivatives Assisted by Various Groups

Anthra[2,1,9-def:6,5,10-d'e'f']diisoquinoline-1,3,8,10(2H,9H)-tetraone, namely, perylene bisimides (PBIs), belong to n-type organic semiconductors and possess potential applications in optoelectronic devices. The properties/performance of fabricated nanostructures/devices could be greatly influenced by both molecular structures of PBI building blocks and corresponding arrangement in assembled nanostructures. Many efforts have been made to modify the PBI core and then investigate the nanostructures and properties. However, it is still a great challenge to comprehensively understand the influence of molecular structures on the intermolecular interactions, the self-assembled structures, and the resulting performance. In the present contribution, we mainly summarize recent research aspects on supramolecular assembly behaviors of PBI derivatives assisted by various functional groups. First, a short introduction is given about basic molecular structure, properties, and self-assembly of PBI derivatives. Then, we mainly discuss the modulation of self-assembly of PBIs via introducing various functional groups (flexible or nonflexible chains, and biomolecules especially amino-acid-based groups). After that, the assembly of PBI derivatives from out-of-equilibrium states is described. Finally, a perspective is provided on the design of novel PBI derivatives and the fabrication of unique nanostructures with superior properties.

Coupled Cooperative Supramolecular Polymerization: A New Model Applied to the Competing Aggregation Pathways of an Amphiphilic aza-BODIPY Dye into Spherical and Rod-Like Aggregates

Based on our studies on biphasic self-assembly behavior of an amphiphilic BF₂ -azadipyrromethene (aza-BODIPY) dye 1, a new analytical model to quantitatively describe the thermodynamic properties of the aggregation involving two competing supramolecular polymerization processes is proposed. In this model, the formation of the metastable as well as the thermodynamically stable aggregates was considered to follow a nucleated polymerization mechanism. The numerical calculation based on the new model gives insight into the formation of different species in such complicate aggregate systems. Moreover, the aggregation of the biphasic self-assembly processes for dye 1 was investigated by concentration-dependent UV/Vis spectroscopy. The experimental data were analyzed by using the new model to evaluate the thermodynamic parameters including aggregation constants, the size of nuclei, and the cooperativity the two types of aggregates.

Discrete π-Stacks of Perylene Bisimide Dyes within Folda-Dimers: Insight into Long- and Short-Range Exciton Coupling

Four well-defined π-stacks of perylene bisimide (PBI) dyes were obtained in solution by covalent linkage of two chromophores with spacer units of different length and sterical demand. Structural elucidation of the folda-dimers by in-depth nuclear magnetic resonance studies and geometry optimization at the level of density functional theory suggest different, but highly defined molecular arrangements of the two chromophores in the folded state enforced by the various spacer moieties. Remarkably, the dye stacks exhibit considerably different optical properties as investigated by UV/vis absorption and fluorescence spectroscopy, despite only slightly different chromophore arrangements. The distinct absorption properties can be rationalized by an interplay of long- and short-range exciton coupling resulting in optical signatures ranging from conventional H-type to monomer like absorption features with low and appreciably high fluorescence quantum yields, respectively. To the best of our knowledge, we present the first experimental proof of a PBI-based "null-aggregate", in which long- and short-range exciton coupling fully compensate each other, giving rise to monomer-like absorption features for a stack of two PBI chromophores. Hence, our insights pinpoint the importance of charge-transfer mediated short-range coupling that can significantly influence the optical properties of PBI π-stacks.

Fluorescence quantum yields of dye aggregates: a showcase example based on self-assembled perylene bisimide dimers

Two measurement approaches for the precise quantum yield determination of supramolecular aggregates in highly concentrated solutions are presented and experimentally tested for an emissive perylene bisimide H-type aggregate with a quantum yield of 28%.

H-Aggregated π-Systems Based on Disulfide-Linked Dimers of Dipyrrolyldiketone Boron Complexes

Dipyrrolyldiketone boron complexes linked by a disulfide bond were synthesized, forming H-aggregated dimers assisted by intramolecular π-π and hydrogen-bonding interactions. The conformations of the dimers, with small C-S-S-C dihedral angles, were examined by UV-vis absorption and ¹H NMR spectra as well as single-crystal X-ray analysis and theoretical studies.

Supramolecular Copolymers: Structure and Composition Revealed by Theoretical Modeling

Supramolecular copolymers, non-covalent analogues of synthetic copolymers, constitute a new and promising class of polymers. In contrast to their covalent counterparts, the details of their mechanism of formation, as well as the factors determining their composition and length, are still poorly understood. Here, the supramolecular copolymerization between two slightly structurally different benzene-1,3,5-tricarboxamide (BTA) monomers functionalized with either oligodimethylsiloxane (oDMSi) or alkyl side chains is unraveled by combining experimental and theoretical approaches. By applying the "sergeant-and-soldiers" approach using circular dichroism (CD) experiments, we are able to obtain detailed insights into the structure and composition of these supramolecular copolymers. Moreover, we observe an unexpected chiral induction upon mixing two independently CD-silent solutions of the achiral (soldier) and chiral (sergeant) monomers. We find that the subtle differences in the chemical structure of the two monomers impact their homopolymerization mechanism: whereas alkyl-BTAs cooperatively self-assemble, oDMSi-BTAs self-assemble in an isodesmic manner. The effect of these mechanistic differences in the supramolecular copolymerization process is investigated as a function of the composition of the two monomers and explicitly rationalized by mathematical modeling. The results show that, at low fractions of oDMSi-BTA sergeants (<10 mol%), the polymerization process is cooperative and the supramolecular helicity is biased toward the helical preference of the sergeant. However, at higher fractions of oDMSi-BTA sergeant (>25 mol%), the isodesmic assembly of the increasing amounts of sergeant becomes more dominant, and different species start to coexist in the copolymerization process. The analysis of the experimental data with a newly developed theoretical model allows us to quantify the thermodynamic parameters, the distribution of different species, and the compositions and stack lengths of the formed supramolecular copolymers existing at various feed ratios of the two monomers.

Transformable nanostructures of cholesteryl-containing rhomboidal metallacycles through hierarchical self-assembly

Various interesting nanostructures such as flowers and tadpole shaped structures were successfully obtained from well-defined cholesteryl-containing rhomboidal metallacycles prepared by coordination-driven self-assembly.