Hierarchical organization of self-assembled structures into superstructures is omnipresent in Nature but has been rarely achieved in synthetic molecular assembly due to the absence of clear structural rules.W eh erein report on the selfassembly of scissor-shaped azobenzene dyads which form discrete nanotoroids that further organizei nto 2D porous networks.T he steric demand of the peripheral aliphatic units diminishes the trend of the azobenzene dyad to constitute stackable nanotoroids in solution, thus affording isolated (unstackable) nanotoroids upon cooling. Upon drying, these nanotoroids organizea tg raphite surface to form well-defined 2D porous networks.The photoirradiation with UV and visible light enabled reversible dissociation and reconstruction of nanotoroids through the efficient trans$cis isomerization of azobenzene moieties in solution.

Recent advances in the research field of supramolecularly engineered dye aggregates have enabled the design of simple one-dimensional stacks such as fibers and of closed structures such as nanotoroids (nanorings). More...

Unique relationships between hierarchically organized biological nanostructures and functions have motivated chemists to construct sophisticated artificial nanostructured systems from small and simple synthetic molecules through self-assembly. As one of such sophisticated systems, we have investigated scissor-shaped photochromic dyads that can hierarchically selfassemble into discrete nanostructures showing photoresponsive properties. We synthesized various azobenzene dyads and found that these dyads adopt intramolecularly folded conformation like a closed scissor, and then self-assemble into toroidal nanostructures by generating curvature. The toroids further organize into nanotubes and further into helical supramolecular fibers depending on the nature of alkyl substituents. All of these nanostructures can be dissociated and reorganized through the photoisomerization of azobenzene units. On the other hand, the introduction of stilbene chromophores instead of azobenzenes leads to onedimensional supramolecular polymerization, which upon the intramolecular photocyclization of stilbene chromophores shifts to curved self-assembly leading to helicoidal fibers with distinct supramolecular chirality.

Hierarchical organization of self-assembled structures into superstructures is omnipresent in Nature but has been rarely achieved in synthetic molecular assembly due to the absence of clear structural rules.W eh erein report on the selfassembly of scissor-shaped azobenzene dyads which form discrete nanotoroids that further organizei nto 2D porous networks.T he steric demand of the peripheral aliphatic units diminishes the trend of the azobenzene dyad to constitute stackable nanotoroids in solution, thus affording isolated (unstackable) nanotoroids upon cooling. Upon drying, these nanotoroids organizea tg raphite surface to form well-defined 2D porous networks.The photoirradiation with UV and visible light enabled reversible dissociation and reconstruction of nanotoroids through the efficient trans$cis isomerization of azobenzene moieties in solution.

The crystal structure of barium oxalate hydrate, BaC 2 0 4 3.5H20. was solved using synchrotron X-ray powder diffraction data, neutron powder diffraction data of BaC20-+ 3 SD20, and synchrotron X-ray single crystal diffraction data, measured on a microcrystal. The compound is monoclinic, g = 13.489(1), Q = 7.663(1). f = 15.085(1) A, B.= 113.569(5) 0• from the neutron data, space group ~2/f, No. 15, Z = 4. The precision of the structure arrived at with the syncJu·otron X-ray single crystal data is higher than that obtained with the neutron powder diffraction data. The barium atoms are bonded to the oxalate ions and to the water molecules with ten bmium oxygen bonds in the range 2.704(3) to 2.974(3) A. The structure has hydrogen bonds in the range 2.732 (4) Applications of anomalous dispersion in mate1ials science crystallography is a rapidly developing field, which has benefitted tremendously from the increasing availability and quality of X-ray synchrotron sources in the past decade. At the European Synchrotron Radiation Facility (ESRF). we have at the Mate1ials Science Bemnline recorded powder diffractograms of the zeolitic ionic conductor, tin mordenite, at 47 incident photon energies in the range from 29.008 keY to 29.708 keY, bracketing the Sn K-absorption edge at 29.2 ke V. The purpose of this study is to dete1mine the Sn atomic positions and the Sn-Sn interatomic distances which cannot be revealed by traditional crystallographic techniques clue to a disorder over several sites of the tin ions. (Knudsen. N .. Krogh-Andersen, E., K.roghAndersen, I. G., Norby, P., Skou. E. Solid St. Ionics. 61, (1993), 1 53). The sample also contains grains of tinoxide, Sn02. which complicates the analysis, and eliminates a nom1al EXAFS analysis as a possibility to determine interatomic distances. In order to solve the problem we use the newly developed diffraction anomalous fine structure (DAFS) technique. (Pickeiing, I. J., Sansone, M .• Mm·sch, J .. George, G. N. J. Am. Chem. Soc. 115, (1993), 6302. Stragier. H., Cross, J. 0., Rehr, J. J., Sorensen, L. B., Bouldin, C. E., Woicik, J. C. Phys. Rev. Lett. 69, (1992), 3064). This method in principle allows extraction of site-specific absorption spectra, so that despite crystallographic disorder and multiple phases, interatomic distances and valence states of the probe atoms can be cleteimined reliably. We will present the first results of this work.PS01.05.12 APPLICATIONS OF E:N""ERGY DISPERSIVE DIFFRACTION WITH SYNCHROTRON RADIATION. P. Suortti, V. Honkimaki, European Synchrotron Radiation Facility, B. P. 220, F-38043 Grenoble Cedex. FranceThe spectral b1ightness of a high-field wiggler at the ESRF bas been determined by using energy dispersive diffraction (EDD) from well-characteiized powder specimens. The results m·e in a close agreement with the brightness calculated from the emittm1ce of the elect:ron beam and the measured magnetic field of the wiggler. The precisely known brightness of the synclu·ot.ron beam can be used in many different studies with EDD. In the case of...

A scissor-shaped foldable diphenylanthracene dyad has been synthesized and found to self-assemble in a nonpolar solvent into elongated thin nanofibers, showing intense blue emission. At a millimolar concentration, efficient gelation was observed while the emission property of the building block was retained in the gel state.