Collective In-Plane Molecular Rotator Based on Dibromoiodomesitylene π-Stacks

Dynamics of proton, ion, molecule, and crystal lattice in functional molecular assemblies

Dynamic molecular processes, such as short- or long-range proton (H⁺) and ion (M⁺) motions, and molecular rotations in electrical conducting and magnetic molecular assemblies enable the fabrication of electron-H⁺ (or M⁺) coupling systems, while crystal lattice dynamics and molecular conformation changes in hydrogen-bonded molecular crystals have been utilised in external stimuli responsive reversible gas-induced gate opening and molecular adsorption/desorption behavior. These dynamics of the polar structural units are responsible for the dielectric measurements. The H⁺ dynamics are formed from ferroelectrics and H⁺ conductors, while the dynamic M⁺ motions of Li⁺ and Na⁺ involve ionic conductors and coupling to the conduction electrons. In n-type organic semiconductors, the crystal lattices are modulated by replacing M⁺ cations, with cations such as Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺. The use of polar rotator or inversion structures such as alkyl amides, m-fluoroanilinium cations, and bowl-shaped trithiasumanene π-cores enables the formation of ferroelectric molecular assemblies. The host-guest molecular systems of ESIPT fluorescent chromic molecules showed interesting molecular sensing properties using various bases, where the dynamic transformation of the crystal lattice and the molecular conformational change were coupled to each other.

Room-Temperature Ferroelectricity in an Organic Cocrystal

Ferroelectric materials exhibit switchable remanent polarization due to reversible symmetry breaking under an applied electric field. Previous research has leveraged temperature-induced neutral-ionic transitions in charge-transfer (CT) cocrystals to access ferroelectrics that operate through displacement of molecules under an applied field. However, displacive ferroelectric behavior is rare in organic CT cocrystals and achieving a Curie temperature (T_C ) above ambient has been elusive. Here a cocrystal between acenaphthene and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane is presented that shows switchable remanent polarization at room temperature (T_C =68 °C). Raman spectroscopy, X-ray diffraction, and solid-state NMR spectroscopy indicate the ferroelectric behavior is facilitated by acenaphthene (AN) rotation, deviating from conventional design strategies for CT ferroelectrics. These findings highlight the relevance of non-CT interactions in the design of displacive ferroelectric cocrystals.

Phase transition and molecular assembly structure of ellagic acid ester derivatives

Ellagic acid and its esters were examined in terms of phase transition, electronic structure, dielectric constant, and molecular assembly.

Implanted muon spin spectroscopy on 2-O-adamantane: a model system that mimics the liquid[Formula: see text]glasslike transitions

The transition taking place between two metastable phases in 2-O-adamantane, namely the [Formula: see text] cubic, rotator phase and the lower temperature P2₁/c, Z  =  4 substitutionally disordered crystal is studied by means of muon spin rotation and relaxation techniques. Measurements carried out under zero, weak transverse and longitudinal fields reveal a temperature dependence of the relaxation parameters strikingly similar to those exhibited by structural glass[Formula: see text]liquid transitions (Bermejo et al 2004 Phys. Rev. B 70 214202; Cabrillo et al 2003 Phys. Rev. B 67 184201). The observed behaviour manifests itself as a square root singularity in the relaxation rates pointing towards some critical temperature which for amorphous systems is located some tens of degrees above that shown as the characteristic transition temperature if studied by thermodynamic means. The implications of such findings in the context of current theoretical approaches concerning the canonical liquid-glass transition are discussed.

Role of crystallization water molecules on hydrogen-bonded structures and dielectric phase transitions in amino trimethylene phosphonic acid-based crystals

Amino trimethylene phosphonic acid-based organic salts show crystallization water molecule-triggered dielectric transitions and relaxations.

Diffusion-Controlled Rotation of Triptycene in a Metal-Organic Framework (MOF) Sheds Light on the Viscosity of MOF-Confined Solvent

Artificial molecular machines are expected to operate under conditions of very low Reynolds numbers with inertial forces orders of magnitude smaller than viscous forces. While these conditions are relatively well understood in bulk fluids, opportunities to assess the role of viscous forces in confined crystalline media are rare. Here we report one such example of diffusion-controlled rotation in crystals and its application as a probe for viscosity of MOF-confined solvent. We describe the preparation and characterization of three pillared paddlewheel MOFs, with 9,10-bis(4-pyridylethynyl)triptycene 3 as a pillar and molecular rotator, and three axially substituted dicarboxylate linkers with different lengths and steric bulk. The noncatenated structure with a bulky dicarboxylate linker (UCLA-R3) features a cavity filled by 10 molecules of N,N-dimethylformamide (DMF). Solid-state ²H NMR analysis performed between 293 and 343 K revealed a fast 3-fold rotation of the pillar triptycene group with the temperature dependence consistent with a site exchange process determined by rotator-solvent interactions. The dynamic viscosity of the MOF-confined solvent was estimated to be 13.3 N·s/m² (or Pa·s), which is 4 orders of magnitude greater than that of bulk DMF (8.2 × 10^-4 N·s/m²), and comparable to that of honey.

Conformational Transformations of (C12H25NH3(+))(Pyridinesulfonate) in the Solid State

The phase-transition behaviors, crystal structures, and dielectric properties of four kinds of simple 1:1 organic salts of (C12H25NH3(+))(benzenesulfonate) and (C12 H25NH3(+))(pyridine sulfonates) were examined from the viewpoint of intermolecular hydrogen-bonding interactions and dynamic conformational transformation in molecular assemblies. Crystals of (C12H25NH3(+))(benzenesulfonate) and (C12H25NH3(+))(3-pyridinesulfonate) were isostructural and solid-solid and solid-liquid-crystal smectic A (SmA) phase transitions were observed. These two crystals formed rodlike cation-anion assemblies. However, the two salts, (C12H25NH3(+))(2-pyridinesulfonate) and (C12H25NH3(+))(4-pyridinesulfonate), formed largely bent L-shaped cation-anion conformations. Interesting conformational transformations from rodlike to L-shaped assemblies were observed in (C12H25NH3(+))(2-pyridinesulfonate) and (C12H25NH3(+))(3-pyridinesulfonate).

Alkylamide-substituted tetraphenylethylene: three modes of fluorescence based on a hydrogen-bonded excimer

Three modes of emission, with different intensities and wavelengths, were observed in tetraphenylethylenetetraamide 1 depending on the solvent, concentration and irradiation with light.