Soluble Two-dimensional Supramolecular Organic Frameworks (SOFs): An Emerging Class of 2D Supramolecular Polymers with Internal Long-range Orders

Cucurbituril-based supramolecular host-guest complexes: single-crystal structures and dual-state fluorescence enhancement

Two supramolecular complexes were prepared using cucurbiturils [CBs] as mediators and a four-armed p-xylene derivative (M1) as a guest molecule. The single crystals of these two complexes were obtained and successfully analyzed by single-crystal X-ray diffraction (SCXRD). An unexpected and intriguing 1 : 2 self-assembly arrangement between M1 and CB[8] was notably uncovered, marking its first observation. These host-guest complexes exhibit distinctive photophysical properties, especially emission behaviors. Invaluable insights can be derived from these single-crystal structures. The precious single-crystal structures provide both precise structural information regarding the supramolecular complexes and a deeper understanding of the intricate mechanisms governing their photophysical properties.

Single-crystal structures of cucurbituril-based supramolecular host-guest complexes for bioimaging

Two single-crystal structures of cucurbit[n]uril mediated supramolecular complexes were obtained in which [1+3] and [2+3] self-assembly modes are adopted due to the different sizes of cucurbit[7]uril and cucurbit[8]uril. An obvious red-shift in absorption and emission was observed compared to the guest molecule itself which makes them good biolabels.

Supramolecular Chiral 2D Materials and Emerging Functions

Chiral materials are widely applied in various fields such as enantiomeric separation, asymmetric catalysis, and chiroptical effects, providing stereospecific conditions and environments. Supramolecular concepts to create the chiral materials can provide an insight for emerging chiro-optical properties due to their well-defined scaffolds and the precise functionalization of the surfaces or skeletons. Among the various supramolecular chiral structures, 2D chiral sheet structures are particularly interesting materials because of their extremely high surface area coupled with many unique chemical and physical properties, thereby offering potential for the next generation of functional materials for optically active systems and optoelectronic devices. Nevertheless, relatively limited examples for 2D chiral materials exhibiting specific functionality have been reported because incorporation of molecular chirality into 2D architectures is difficult at the present stage. Here, a brief overview of the recent advances is provided on the construction of chiral supramolecular 2D materials and their functions. The design principles toward 2D chirality and their potential applications are also discussed.

Stimuli-Responsive Two-Dimensional Supramolecular Polymers Based on Trinuclear Platinum(II) Scaffolds: Reversible Modulation of Photoluminescence, Cavity Size, and Water Permeability

Here we report the first two-dimensional (2D) supramolecular polymer, which has varying structure and function arising from the perturbation of noncovalent metal···metal interactions in response to acid-base stimuli. This 2D assembly possesses a positively charged, honeycomb-like nanostructure consisting of trinuclear alkynylplatinum(II) terpyridine complexes appended with acid-sensitive dimethylamino groups. Upon addition of acids and bases, reversible switching mediated by protonation and deprotonation of dimethylamino and dimethylammonium moieties intrinsically alters the positive charge density of the constituent cationic units, which causes interior cavities to adaptively adjust their size, accompanied by drastic photoluminescence changes. When water molecules pass through the membranes obtained from 2D supramolecular polymers, the permeating flux can also be tuned by the pH values of the buffer media. This work paves the way toward supramolecularly engineered 2D smart materials with stimuli-responsive properties.

Ultrathin Supramolecular Architectures Self-Assembled from a C3-Symmetric Synthon for Selective Metal Binding

Ultrathin supramolecular nanoarchitectures are an emerging class of two-dimensional (2D) materials with dynamic features that facilitate their on-demand functions. However, facile and efficient synthesis for multiple 2D topologies by taking advantage of spontaneous self-assembly is limited. In this work, we report the synthesis of ultrathin supramolecular nanoarchitectures from the self-assembly of a π-conjugated C₃-symmetric synthon (tribenzyloxybenzoic acid, TBBA), with the benzene-1,3,5-tricarboxamide core terminated by three carboxylic acids. Supported by the carboxylic acid-amide hydrogen-bonding and π-π/CH-π interactions, TBBA self-assembles into freestanding microsheets with the thickness of around 2 nm, demonstrating considerable integrity in different solvent systems or in the presence of carboxylic acid binders such as bipyridines. The deprotonation of the carboxylic acids endows TBBA with amphiphilicity, allowing for the formation of mixed micelles that are sensitive to transition-metal ions. Selectively, TBBA^3- shows relatively strong coordination to Cu(II), giving rise to long and thin organometallic ribbons (about 3 nm thickness) with a pronounced aging process. Kinetically insufficient coordination was probed by various characterization techniques and molecular dynamics simulation, which played a vital role in directing the formation of thin ribbons. This work provides a proof-of-concept study for a feasible and versatile construction of both flexible and rigid 2D supramolecular nanostructures with promising applications.

A water-soluble two-dimensional supramolecular organic framework with aggregation-induced emission for DNA affinity and live-cell imaging

A water-soluble two-dimensional supramolecular organic framework (2D SOF) was prepared via self-assembly of cucurbit[8]uril (CB[8]) and a three-arm flat linker molecule, which contains a benzene ring as the core and three Brooker's merocyanine (BM) analogs as arms. The strong host-guest interactions between BM and CB[8] and the directional head-to-tail stacking modes between the BM arms synergistically led to the formation of a 2D SOF. The structure of the 2D SOF was verified by ¹H NMR, 2D ¹H NMR NOESY, and DLS characterizations, while the monolayer structure was characterized by Cryo-TEM and AFM measurements. The 2D SOF exhibited an obvious AIE enhancement effect in H₂O. In addition, DNA induced photoluminescence enhancement was observed for the monomer. As a result, this AIEgen-based 2D SOF could feature not only as a cell visualizer but also as a tracker for the nucleus in biological imaging due to the dynamic assembly process.

A pore-expanded supramolecular organic framework and its enrichment of photosensitizers and catalysts for visible-light-induced hydrogen production

A 3.6 nm-pore SOF is constructed, which adsorbs both photosensitizers and polyoxometallates for visible light-induced proton reduction to produce H₂.

A ureido-pyrimidone based aspartic acid derivative: synthesis and pH-responsive self-assembly in water

The pH-responsive UPy-aspartic acid aggregates can act as templates for the controlled synthesis of silver nanostructures.