Photo- and Stress-Induced Bending of (E)-1,2-Bis(pyridinium-4-yl)ethene Dinitrate Crystals

We report on the elastic and photodynamic properties of (E)-1,2-bis(pyridinium-4-yl)ethene dinitrate [H2Ebpe](NO3)2, whose needle-like crystals can be reversibly deformed by applying external mechanical stress. The macro-scale mechanical properties of [H2Ebpe](NO3)2 crystals were quantified by a three-point bending test, which gave a stress-strain curve with an elastic modulus of 1.18 GPa, and its values are lower than those of other flexible elastic organic crystals. It can also be reversibly bent through the [2+2] cycloaddition reaction of the olefin moiety, depending on the direction of UV irradiation.

Crystal structure of trans-1,2-bis(pyridinium-4-yl) ethylene bis(2-carboxy-4-bromobenzoate) – water (1/4), C14H14BrNO6

C14H14BrNO6, triclinic, P 1 ‾ $\overline{1}$ (no. 2), a = 6.9693(3) Å, b = 8.6514(5) Å, c = 13.6726(8) Å, α = 72.774(5)°, β = 81.547(4)°, γ = 74.370(4)°, V = 756.26(7) Å3, Z = 2, R gt (F) = 0.0341, wR ref (F 2) = 0.0689, T = 290.7(3) K.

Electron transfer photochromism of solid-state supramolecules constructed by cucurbit[n]uril (n = 5–8) and 1-(4-carboxybenzyl)-4-[2-(4-pyridyl)-vinyl]-pyridinium chloride

Solid-state supramolecular complexes of a bispyridinium ethylene derivative with cucurbit[n = 5–8]uril exhibit fast responsive photochromic properties, which are caused by the electron transfer from the host to the guest.

Solid-State Photoinitiated Cycloaddition Reaction of 4,4′-(Ethene-1,2-diyl)bis(pyridinium) Dinitrate: Charge-Density Perspective on Initial Stage of the Reaction

Solid-state photoinitiated [2 + 2] cycloaddition reaction 2(H2bpe)(NO3)2 → (H4tpcb)(NO3)4 (bpe = 1,2-bis(pyrid-4-yl)ethylene; tpcb = 1,2,3,4-tetrakis(pyrid-4-yl)cyclobutane) was carried out in a single-crystal-to-single-crystal manner. The reaction product was characterized by means of X-ray diffraction and 1H NMR spectroscopy. Only the rctt-isomer of tpcb was found as the reaction product. Intermolecular interactions in a single crystal of (H2bpe)(NO3)2 were studied within the QTAIM approach. Although sum energy of strong and weak hydrogen bonds dominates in total packing energy, contribution of π…π stacking interactions to the packing energy is also prominent. At solid (H2bpe)(NO3)2, stacking of photoreactive H2bpe2+ cations is realized via N…C, C…C and C–H…C bonding, although no four-membered cycles formed by these bond paths was found in molecular graph representation. Reduced density gradient (RDG) surfaces and molecular Voronoi surfaces clearly demonstrate accumulation of charge density between olefin groups prone to take part in photoinitiated cycloaddition reactions. Good correlation between description of hydrogen bonding in terms of QTAIM and Voronoi approaches was demonstrated. The Voronoi approach confirmed that during the photoreaction the system of hydrogen bonds remained almost unchanged.

Thermally induced 1D to 2D polymer conversion accompanied by major packing changes in single-crystal-to-single-crystal transformation

The molecular packing in crystals is highly sensitive to temperature and pressure. We report a thermally-induced H-bonded 1D → 2D polymer formation via SCSCT.

Structural Tuning of Anion-Templated Motifs with External Stimuli through Crystal-to-Crystal Transformation

Protonation of trans-1,2-bis(4-pyridyl)ethylene (4,4'-bpe) with dilute sulfuric acid (33 %) afforded a protonated adduct [{4,4'-bpe⋅2 H⁺ }₂ {HSO₄ }^-2 {SO₄ }^-2 {H₂ O}₂ ] (1). The neighboring olefinic bond in 1 is in a suitable range (3.931-4.064 Å) to undergo a photochemical [2+2] cycloaddition reaction. Upon irradiation with UV light (365 nm), 1 undergoes a molecular sliding involving the 4,4'-bpe⋅2 H⁺ units, affording 2, stabilized through O_SO4 ⋅⋅⋅π interactions. Heating 1 to 50° C leads to a 3D hydrogen-bonded organic framework (HOF) (3). This process occurs through thermal dissociation of the bisulfate anion. Diffusion of iodine through the crystal lattice of 1 and 3 enables the reduction of sulfate to bisulfate, affording a 1D hydrogen-bonded chain (4). Solid-state ¹³ C CPMAS NMR, IR, DSC, and powder XRD studies further support stimuli-responsive structural tuning through crystal-to-crystal transformation. All these conversions occur with significant translational and rotational movements along with a series of bond-breaking and bond-forming processes.

Crystal structure of trans-1,2-bis(pyridinium-4-yl)ethylene–2-carboxy-4-methylbenzoate (1/2), C30H26N2O8

C30H26N2O8, monoclinic, C2/c (no. 15), a = 17.567(2) Å, b = 13.1375(17) Å, c = 13.4212(17) Å, β = 124.08(1)°, V = 2565.3(6) Å3, Z = 4, R gt (F) = 0.0379, wR ref (F 2 ) = 0.0839, T = 296 K.

A dual-stimuli responsive small molecule organic material with tunable multi-state response showing turn-on luminescence and photocoloration

A multiple responsive organic small molecular material has been developed, which exhibits dual pathway photoreactions and gives turn-on luminescence and photocoloration under different light sources.

Structurally Flexible C₃-Symmetric Receptors for Molecular Recognition and Their Self-Assembly Properties

The bioinspired design and synthesis of building blocks and their assemblies by the supramolecular approach has ever fascinated scientists to utilize such artificial systems for numerous purposes. Flexibility is a basic feature of natural systems. However, in artificial systems this is difficult to control, especially if there is no preorganization of the component(s) of a system. We have designed and synthesized a series of C3 -symmetric N-bridged flexible receptors and successfully utilized them to selectively entrap the notorious and toxic nitrate anion in aqueous medium. This was the first report of highest binding affinity for the nitrate anion in aqueous medium. An impressive self-sorting phenomenon of reversibly formed hydrogen-bonded capsules, which self-assembled from flexible tripodal receptors having branches of similar size and bearing the same amide functionality, has been disclosed. Encapsulated nitrate anion has been further utilized for the photochemical [2+2] cycloaddition reaction for the synthesis of strained four-membered ring structures through dynamic self-assembly. In this Personal Account, we summarize these results showing the utility of naturally inspired flexibility in artificial systems.

Artificial receptors for nitrate: a comprehensive overview

In this feature article, we describe the current status and recent development of synthetic anion receptors for the recognition of nitrate.