Proton dynamics in one-dimensional hydrogen-bonding system in molecular co-crystals TMP-D2ca and DMP-H2ca

The proton dynamics in one-dimensional hydrogen-bonding system in molecular co-crystals of tetramethylpyrazine (TMP) with chloranilic acid (H₂ca), as well as 2,6-dimethylpyrazine (DMP) with H₂ca is studied by ³⁵Cl NQR and ²H NMR spin-lattice relaxation measurements. No transfer motion of proton between the acid and base molecules is observed in DMP-H₂ca, while the motion of the acid proton is excited in TMP-H₂ca and the activation energy for the motion increases from 35 kJ mol^???1 to 50 kJ mol^???1 by the deuteration.     

Optical properties of organic-inorganic hybrid films prepared by the two-step growth process

Thin films of microcrystalline (C₈H₁₇NH₃)₂PbBr₄ have been prepared by the two-step growth process as follows: (1) precipitation of nanometer-sized PbBr₂ particles on substrates by vapor deposition and then (2) growth of (C₈H₁₇NH₃)₂PbBr₄ films by exposing PbBr₂ particles to C₈H₁₇NH₃Br vapor. Atomic force microscope observations reveal that the substrate is fully covered with nanometer-sized rodlike precipitates. X-ray diffraction studies suggest that (C₈H₁₇NH₃)₂PbBr₄ films are found to be microcrystalline form, single phase and highly oriented with the c-axis perpendicular to the substrate surface. (C₈H₁₇NH₃)₂PbBr₄ films show a clear exciton absorption and free-exciton emission even at room temperature. At low temperatures below 40 K, the emission band separates into three bands at 3.07 (A-band), 3.14 (B-band) and 3.20 (C-band) eV, respectively. Both A- and C-bands correspond to the free-exciton emission with large binding energies. On the contrary, time-resolved PL spectra indicate that the B-band is attributed to phosphorescence formed by the intersystem crossing.     

Water‐ and Temperature‐Triggered Reversible Structural Transformation of Tetranuclear Cobalt(II) Cores Sandwiched by Polyoxometalates

Although stimuli‐responsive structural transformations of inorganic materials have attracted considerable attention because of their potential use as functional switchable materials, multinuclear metal cores frequently suffer from unexpected dissociation of metal cations and/or irreversible transformations into infinite structures. In this study, we describe the successful demonstration of the water‐ and temperature‐triggered reversible structural transformation between cubane‐ and planar‐type tetranuclear Co^II cores sandwiched by polyoxometalates. The arrangements and coordination geometries of the Co^II cations were interconverted by simple hydration and dehydration, resulting in the manipulation of the magnetic and optical properties of these compounds. Moreover, this system showed unique thermochromism through temperature‐dependent reversible structural interconversion.     

Fullerene sensors based on calix[5]arene

A new class of fullerene sensors based on calix[5]arenes has produced the highly sensitive detection of C60 and C70.     

Discontinuous pressure effect upon enantiodifferentiating photosensitized isomerization of cyclooctene

A hydrostatic pressure of up to 750 MPa induced discontinuous changes in the enantiomeric excess of the (E)-isomer obtained in the enantio-differentiating photoisomerization of (Z)-cyclooctene and (Z,Z)-cycloocta-1,5-diene, sensitized by chiral benzene-1,2,4,5-tetracarboxylates; indicating a switching of the enantio-differentiation mechanism, which is attributable to dramatic conformational changes of chiral alkoxycarbonyl auxiliaries at a specific pressure.     

Complexation and chiral recognition thermodynamics of 6-amino-6-deoxy-beta-cyclodextrin with anionic, cationic, and neutral chiral guests: counterbalance between van der Waals and coulombic interactions

The stability constant (K), standard free energy (Delta G degrees), enthalpy (Delta H degrees), and entropy changes (T Delta S degrees) for the complexation of 6-amino-6-deoxy-beta-cyclodextrin with more than 50 negatively or positively charged as well as neutral guests, including 22 enantiomer pairs, have been determined in aqueous phosphate buffer (pH 6.9) at 298.15 K by titration microcalorimetry. The thermodynamic parameters obtained in this study and the relevant data for native beta-cyclodextrin indicate that the complexation and chiral discrimination behavior of the cationic host with charged guests are governed by the critical counterbalance between the electrostatic interactions of the charged groups in host and guest and the conventional intracavity interactions of the hydrophobic moiety of guest, such as hydrophobic, van der Waals, solvation/desolvation, and hydrogen-bonding interactions.     

Memory effect on the glass transition in vulcanized rubber

The memory effect upon glassification is studied in the glass-to-rubber transition of vulcanized rubber with the strain as a controlling parameter. A phenomenological model is proposed, taking the history of the temperature and the strain into account, by which the experimental results are interpreted. The data and the model demonstrate that the glassy state memorizes the time course of strain upon glassification, not as a single parameter but as the history itself. The data also show that the effect of irreversible deformation in the glassy state is beyond the scope of the present model.     

Stereoselective photocycloaddition of alkenes to naphthalene rings assisted by hydrogen bonding

Introduction of a hydrogen-bonding substituent to 1-cyanonaphthalene and alkene resulted in the selective formations of endo-photocycloadducs. Furthermore, the yield and selectivity were improved as the reaction temperature was lowered.