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Abstract Chemical reactions conducted in the solid phase (specifically, crystalline) are much less numerous than solution reactions, primarily due to reduced motion, flexibility, and reactivity. The main advantage of crystalline‐state transformations is that reactant molecules can be designed to self‐assemble into specific spatial arrangements, often leading to high control over product regiochemistry and/or stereochemistry. In crystalline‐phase transformations, typically only one type of reaction occurs, and a sacrificial template molecule is frequently used to facilitate self‐assembly, similar to a catalyst or enzyme. Here, we demonstrate the first system designed to undergo two chemically unique and orthogonal cycloaddition reactions simultaneously within a single crystalline solid. Well‐controlled supramolecular self‐assembly of two molecules containing different reactive moieties affords orthogonal reactivity without use of a sacrificial template. Using only UV light, the simultaneous [2+2] and [4+4] cycloadditions are achieved regiospecifically, stereospecifically, and products are obtained in high yield, whereas a simultaneous solution‐state reaction affords a mixture of isomers in low yield. Application of dually‐reactive systems toward (supra)molecular solar thermal storage materials is also discussed. This work demonstrates fundamental chemical approaches for orthogonal reactivity in the crystalline state and highlights the complexity and reversibility that can be achieved with supramolecular design. 

Small differences in molecular or solid-state structure can afford significant differences in properties. Here, a diene derivative, 1,3-bis((E)-2-bromostyryl)benzene (2Brm), is synthesized and crystallized into two unique solid-state forms, each exhibiting a different π–π stacking geometry, which imparts distinct reactivity and photoresponsivity. Upon exposure of the two solids to UV–Vis light, a [2 + 2] photocycloaddition occurs to afford regioisomeric products due to the difference in the stacking geometries of the dienes. From a single molecular precursor, we further demonstrate that under different wavelengths of light, the chemical functionality can be programmed into discrete and distinct products containing one, two, or three cyclobutane rings as well as oligomeric/polymeric products. Moreover, the two initial solid forms exhibit wavelength-dependent photomechanical behaviors (i.e., photosalience). This work demonstrates a rare, template-free, self-assembly-based strategy that enables access to a suite of discrete and oligomeric/polymeric products via regiocontrolled solid-state photocycloadditions and further presents potential routes toward the design of photoactuating materials. 

The thermal and thermomechanical behavior of multi-component organic solids is tuned at the molecular levelviapreparation of mixed cocrystals. 

Thermosalience in an anthracene-thiocarboxamide occurs due to strong anisotropic thermal expansion, and the solid responds uniquely to different external stimuli. 

The thermal expansion behavior of a series of halogen-bonded cocrystals containing 1,4-diiodoperchlorobenzene as the donor is described. Two of the solids are polymorphs and contain 4-stilbazole as the acceptor, while the third solid contains 4-(phenylethynyl)pyridine as the acceptor, and this solid is isostructural with one of the polymorphs. All solids are sustained by I···N halogen bonds, and the least thermal expansion occurs along this direction in all solids. The polymorphs exhibit significant differences in π stacking, and we show that electronically similar face-to-face stacked rings undergo more expansion compared to electronically different stacked rings. Moreover, in the two polymorphs, the directions of moderate expansion and most expansion are reversed, demonstrating how cocrystal polymorphism can affect material properties. 

Designing materials to have three unique but predictable thermal expansion axes represents a major challenge. Inorganic materials and hybrid frameworks tend to crystallize in high-symmetry space groups, which necessarily limits this by affording isotropic behavior. On the other hand, molecular organic materials tend to crystallize in lower-symmetry space groups, offering significant opportunity to achieve anisotropic properties. The challenge arises in self-assembling the organic components into a predictable arrangement to afford predictable thermal expansion properties. Here, we demonstrate a design strategy for engineering organic solid-state materials that exhibit anisotropic thermomechanical behaviors. Presented are a series of multicomponent solids wherein one component features a BODPIY core strategically decorated with orthogonal hydrogen- and halogen-bond donor groups. A series of size-matched halogen-bond acceptors are used as the second component in each solid. By matching the molecular dimensions with the interaction strength, we obtained good control over the anisotropic thermal expansion of the molecular materials. Moreover, using shape-size mimicry and propensity for molecular motion, a rare ternary molecular system that is isostructural to the two binary solids was successfully achieved. The diiodo-functionalized BODIPY core in this study has been previously used in photocatalysts, and halogen bonding was hypothesized as a driving force; here, we provide corroborating solution and solid-state evidence of intermolecular halogen bonding in multicomponent solids featuring a 2,6-diiodo BODIPY.