Design of Flexible Lewis Acidic Sites in Porous Coordination Polymers by using the Viologen Moiety

Charged up: A novel porous coordination polymer with a charged organic surface (COS) comprising a zwitterionic organic linker, viologen, has been synthesized. The COS shows strong Lewis acidity accompanied with flexibility, and the isosteric heat of H(2) adsorption is 9.5?kJ?mol(-1) , which is comparable to that of open metal sites (OMSs).     

Fluorescence detection of single guest molecules in ultrasmall droplets of nonpolar solvent

We have investigated emissive behaviours of individual perylenebisimide derivatives, N,N'-dipropyl-1,6,7,12-tetrakis(4-tert-butylphenoxy)-3,4,9,10-perylenetetra-carboxydiimide (BP-PDI), in single ultrasmall droplets of n-octane at room temperature by using confocal and wide-field microscopic techniques. Single BP-PDIs in the small droplets show no distinguishable blinking in the time courses of fluorescence intensity. This is attributed to small probabilities of the formation of the long-lived ionized state leading to the off-state of the fluorescence. Temporal change in the degree of polarization of fluorescence and wide-field fluorescence images indicated short-time adsorption of the fluorescent molecules at the interfaces between n-octane and watery environments. Fluorescence correlation spectroscopy revealed that the adsorption/desorption processes took place at least in two different time scales, probably due to the difference in the adsorption geometry and/or in the interaction, such as van der Waals interaction and hydrogen bonding, between the dye and the interface.     

Effect of hetero-interfaces on in situ wafer curvature behavior in InGaAs/GaAsP strain-balanced MQWs

Using high-accuracy in situ curvature measurement during growth of InGaAs/GaAsP strain-compensated multiple quantum wells (MQWs) by metal organic vapor phase epitaxy (MOVPE), we have successfully clarified the effect of hetero-interfaces on strain control in InGaAs/GaAsP strain-balanced MQWs. By analyzing curvature transients and X-ray diffraction (XRD) fringe patterns, we found that an inadequate gas-switching sequence induces unintended atomic content at the interfaces between InGaAs and GaAsP and then influences the average strain of the structure. Through considering the atomic characteristics and measuring the reflectance anisotropy transient during growth, it has been revealed that the optimized stabilization time for arsenic and phosphorus mixture before GaAsP barrier growth should be longer than 3 s at 610 °C.     

Highly ordered aluminium-planted mesoporous silica as active catalyst for Biginelli reaction and formyl C-H insertion reaction with diazoester

Al-planted MCM-41s (Al-M41s) with regular mesoporous structure and Si/Al ratio of 23-32 were successfully prepared by the template-ion exchange method in which the template/Si molar ratio and Si/Al ratio were adjusted at 1.44 and 5-15, and showed much higher catalytic activity for the titled reactions than the other types of Al-M41s prepared by post-synthesis or sol-gel methods.     

N 1s photoelectron angular distributions from fixed-in-space NO2 molecules: stereodynamics and symmetry considerations

Angular distributions of N 1s photoelectrons from fixed-in-space NO(2) molecules have been measured over the energy region of shape resonance and above. A multiple-coincidence velocity-map imaging technique for observation of molecular frame photoelectron angular distributions (MF-PADs) has been extended to nonlinear molecular targets. Density functional theory calculations have also been conducted to elucidate the photoionization dynamics and shape resonance in the N 1s photoionization of NO(2). Results show that the N 1s MF-PADs exhibit strong shape variation as a function of both photoelectron kinetic energy and symmetries of final states, whereas asymmetry parameters of laboratory frame PADs show a local minimum around the shape resonance region and increase monotonically as the photon energy increases. Over the shape resonance, the spatial shape of the photoelectron wave function with b(2)-symmetry closely resembles that of 5b(2)(?) unoccupied molecular orbital of NO(2), although the MF-PAD pattern for b(2)-symmetry does not correspond directly to the 5b(2)(?) orbital shape. At higher kinetic energy of 90 eV, MF-PADs become less structured, but still show a significant dependence on the symmetry of final states.     

Order-disorder transition on Si(001)

A phase transition between c(4x2) and 2x1 structures on the Si(001) surface has been observed at 200 K by low-energy electron diffraction. This transition is a second order order-disorder transition of the asymmetric dimer configuration. The streak pattern remains up to well above the transition temperature. The temperature dependence of the width and the length of the streak can be described in terms of the effects of a strong anisotropic coupling between adjacent asymmetric dimers.     

Collision-energy-resolved Penning ionization electron spectroscopy of thiazole and benzothiazole: study of ionic states and anisotropic interactions between a metastable He(23S) atom and hetero cyclic compounds

Anisotropic interactions between a metastable He(2(3)S) atom and aromatic heterocyclic compounds (thiazole and benzothiazole) as well as their electronic structures were studied by means of collision-energy/electron-energy resolved two-dimensional Penning ionization electron spectroscopy combined with ab initio molecular orbital calculations. Different collision-energy dependence of partial ionization cross sections (CEDPICS) were clearly observed for different ionic states depending on anisotropic extents of molecular orbitals from which an electron is removed. It was found that thiazole and benzothiazole most strongly attract a He(2(3)S) atom around the region where the nitrogen lone pair orbital extends. For another heteroatom, sulfur, it is relatively weak, but a certain attractive interaction was found for the directions perpendicular to the molecular plane. Benzothiazole was shown to widely attract a He(2(3)S) atom in the out-of-plane directions, since the benzene moiety showed a deeper potential well than the five-membered ring. Assignments of the ionic states including shake-up states were also discussed from observed CEDPICS and ab initio molecular orbital calculations. In particular, for the satellite bands, a negative collision energy dependence of the band intensity was well supported by a configuration-interaction calculation that assigns the satellite bands to be the ionization from pi orbitals accompanying pi-pi or n-pi excitations.     

Host-guest complexation affected by pH and length of spacer for hydroxyazobenzene-modified cyclodextrins

Three modified beta-cyclodextrins appended with a hydroxyazobenzene as a dye unit, 1, 2, and 3, each incorporating a different length spacer between the beta-CD and the dye unit with a bis(propyl(oxyethylene)), butylene, and amide bond spacer, respectively, were synthesized in order to investigate their spectroscopic changes induced by pH and host-guest complexation as well as to investigate their conformations and guest-binding properties by means of absorption and induced circular dichroism spectroscopies in aqueous solutions. All hosts accommodated the dye unit in their own CD cavities with an orientation parallel to the CD axis, forming intramolecular complexes. When the pH of the solution changed, the structure changed in response to pH without conformational changes. Existing as the phenol form under acidic condition, they were converted to the yellow phenolate form by dissociation of a proton of the hydroxyl group in the dye unit with increasing pH (pK(a1); 7.62 for 1, 7.44 for 2, 8.00 for 3). Further increase in pH led to the dissociation of the ammonium proton in the secondary amine group in the spacer of 1 and 2 (pK(a2); 8.76 for 1, 8.67 for 2). Upon addition of 1-adamantanol (AN) as a guest, all hosts accommodated AN in their CD cavities, forming 1:1 host-guest inclusion complexes. The complexation phenomena were accompanied with changes in the conformation of the hosts, in which the dye units of 1 and 2 are excluded to outside of the cavity, but not for 3. The dye unit of 3 remained in the cavity, where the guest was also included partly. Therefore, the guest-binding abilities of 1 and 2 were larger than that of 3, which has poor binding ability. The binding constants of 1, 2, and 3 for AN are estimated to be 7400, 1940, and 140 M(-1) at pH 3.2, respectively. However, the guest-binding abilities of 1 and 2 were dependent on the pH of the solution. The ability of 1 under weak alkaline condition was stronger than under acidic or alkaline conditions, while that of 2 increased with increasing pH. Under the condition from neutral to weak alkaline media, 1 and 2 demonstrated color changes from colorless to yellow upon formation of inclusion complexes. When 1-adamantanecarboxylic acid (AC) was used as the charged guest, 1 and 2 bound to AC with a larger binding constant than AN. On the other hand, 1 and 2 bound to 1-adamantineamine (AA) with a smaller binding constant than AN. All these results demonstrate that the complexation phenomena depend on the pH of the solution as well as the length of the spacer of the hosts and that the electrostatic interaction between the host and the guest is also important for forming a stable complex.     

Photochromism of a diarylethene charge-transfer complex: photochemical control of intermolecular charge-transfer interaction

A diarylethene derivative bearing a phenylenediamine group formed radical ions with an electron acceptor molecule in solution, and the concentration of the radical ions was modulated by the photochromic reaction of the diarylethene, reflecting the difference in the electron-donating character between the open- and closed-ring isomers.