Three-Dimensional Crystalline Organic Framework Stabilized by Molecular Mortise-and-Tenon Jointing.

Three-dimensional (3D) crystalline organic frameworks with complex topologies, high surface area, and low densities afford a variety of application prospects. However, the design and construction of these frameworks have been largely limited to systems containing polyhedron-shaped building blocks or those relying on component interpenetration. Here, we report the synthesis of a 3D crystalline organic framework based on molecular mortise-and-tenon jointing. This new material takes advantage of tetra(4-pyridylphenyl)ethylene and chlorinated bis(benzodioxaborole)benzene as building blocks and is driven by dative B-N bonds. A single-crystal X-ray diffraction analysis of the framework reveals the presence of two-dimensional (2D) layers with helical channels that are formed presumably during the boron-nitrogen coordination process. The protrusion of dichlorobenzene units from the upper and lower surfaces of the 2D layers facilitates the key mortise-and-tenon connections. These connections enable the interlocking of adjacent layers and the stabilization of an overall 3D framework. The resulting framework is endowed with high porosity and attractive mechanical properties, rendering it potentially suitable for the removal of impurities from acetylene.

Adaptive and Robust Vitrimers Fabricated by Synergy of Traditional and Supramolecular Polymers.

Vitrimers offer a unique combination of mechanical performance, reprocessability, and recyclability that makes them highly promising for a wide range of applications. However, achieving dynamic behavior in vitrimeric materials at their intended usage temperatures, thus combining reprocessability with adaptivity through associative dynamic covalent bonds, represents an attractive but formidable objective. Herein, we couple boron-nitrogen (B-N) dative bonds and B-O covalent bonds to generate a new class of vitrimers, boron-nitrogen vitrimers (BNVs), to endow them with dynamic features at usage temperatures. Compared with boron-ester vitrimers (BEVs) without B-N dative bonds, the BNVs with B-N dative bonds showcase enhanced mechanical performance. The excellent mechanical properties come from the synergistic effect of the dative B-N supramolecular polymer and covalent boron-ester networks. Moreover, benefiting from the associative exchange of B-O dynamic covalent bonds above their topological freezing temperature (Tv), the resultant BNVs also possess the processability. This study leveraged the structural characteristics of a boron-based vitrimer to achieve material reinforcement and toughness enhancement, simultaneously providing novel design concepts for the construction of new vitrimeric materials.

Adaptisorption of Nonporous Polymer Crystals.

Although our knowledge and understanding of adsorptions in natural and artificial systems has increased dramatically during the past century, adsorption associated with nonporous polymers remains something of a mystery, hampering applications. Here we demonstrate a model system for adaptisorption of nonporous polymers, wherein dative B-N bonds and host-guest binding units act as the kinetic and thermodynamic components, respectively. The coupling of these two components enables nonporous polymer crystals to adsorb molecules from solution and undergo recrystallization as thermodynamically favored crystals. Adaptisorption of nonporous polymer crystals not only extends the types of adsorption in which the sorbate molecules are integrated in a precise and orderly manner in the sorbent systems, but also provides a facile and accurate approach to the construction of polymeric materials with precise architectures and integrated functions.

Formation of polyrotaxane crystals driven by dative boron-nitrogen bonds.

The integration of mechanically interlocked molecules (MIMs) into purely organic crystalline materials is expected to produce materials with properties that are not accessible using more classic approaches. To date, this integration has proved elusive. We present a dative boron-nitrogen bond-driven self-assembly strategy that allows for the preparation of polyrotaxane crystals. The polyrotaxane nature of the crystalline material was confirmed by both single-crystal x-ray diffraction analysis and cryogenic high-resolution low-dose transmission electron microscopy. Enhanced softness and greater elasticity are seen for the polyrotaxane crystals than for nonrotaxane polymer controls. This finding is rationalized in terms of the synergetic microscopic motion of the rotaxane subunits. The present work thus highlights the benefits of integrating MIMs into crystalline materials.

Modulus watch: In situ determination of the gel modulus by timing the fluorescence color change.

The gel modulus, a key parameter for gel materials, is traditionally determined by cumbersome rheometer. Recently, probe technologies occur to meet the requirements of in situ determination. Till now, in situ and quantitatively testing of gel materials with unabridged structure informations still remains a challenge. Here, we provide a facile, in situ approach to determine the gel modulus, by timing the aggregation of a doped fluorescence probe. The probe shows green emission during aggregation and shifts to blue once it forms aggregates. The higher modulus of the gel, the longer probe's aggregation time. Furthermore, a quantitative correlation of gel modulus with the aggregation time is established. The in situ method not only facilitates the scientific researches in the field of gels, but also provides a new approach for spatiotemporal materials.

Contradiction or Unity? Thermally Stable Fluorescent Probe for In Situ Fast Identification of Self-sort or Co-assembly of Multicomponent Gelators with Sensitive Properties.

Analyzing the assembly patterns of multicomponent gelators is important for understanding their assembly rules and precisely manipulating their molecular structure to form a tailored multifunctional supramolecular gel. But the fast in situ recognition technology to infer whether the assembly pattern is a self-sorting or co-assembled system is lacking. For developing a widely applicable stable and sensitive fluorescent probe to infer assembly patterns, we design and synthesize the multiple peripheral functional group tetraphenylethene (TPE) modified well-defined cubic core polyhedral oligomeric silsesquioxane (POSS) three-dimensional (3D) dendrimer. POSS-TPE can form a thermally stable self-assembly structure after being incubated in a wide temperature range, and the resultant special thermally stable photoluminescence (PL) intensity provides a novel possibility of fluorescent probe. Then, POSS-TPE sensitively catches the mechanical stress changes of the confined space provided by the gel networks and infers the assembly patterns by comparing the mechanical stress change laws of a self-sorting or co-assembled system. So, the application of fluorescent probe in assembly fields is enlarged in this research. In the future, this widely applicable fluorescent probe will be helpful to develop supramolecular assembly materials consisting of multicomponent gels.

The Special "Morse Code" between Solvent Polarity and Morphology Flexibility in a POSS-Dendrimer Supramolecular System.

An amazing phenomenon of the relative magnitude of modulus of two liquid-crystal (LC) gels is found inverted under/above their phase transition temperature TLC-iso , which is further proved to be caused by their diverse morphology flexibility. By testing the polarity of two LCs, gelator POSS-G1-Boc (POSS=polyhedral oligomeric silsesquioxane) was discovered to self-assemble into more flexible structures in a relatively low polar LC, whereas more rigid ones are formed in higher polar LC. Hence, a fitting function to connect morphology flexibility with solvent polarity was established, which can even be generalized to a number of common solvents. Experimental observations and coarse-grained molecular dynamics simulations revealed that solvent polarity mirrors a "Morse code", with each "code" corresponding to a specific morphology flexibility.