The objectives of this work are to demonstrate facile routes to 3-D star materials with octa-and hexadecafunctionality to provide new nanoconstruction tools for the synthesis of new types of stars, dendrimers, and hyperbranched molecules or for the assembly of novel nanocomposites. A further objective is to identify novel properties inherent in the resulting new compounds. Octavinylsilsesquioxane (OVS, [VinylSiO 1.5 ] 8 ) with perfect 3-D or cubic symmetry is elaborated through metathesis with substituted styrenes to produce a series of RStyrenylOS compounds. The p-BrStyrenylOS compound is then further reacted with other sets of p-substituted styrenes via Heck coupling to produce a set of R′VinylStilbeneOS compounds. The R′ ) NH 2 compound is then reacted with 3,5-dibromo or dinitrobenzoyl chloride to produce hexadecafunctional 3-D stars. These synthetic methods provide perfect single core and then core-shell 3-D stars including in the third generation branch points such that these molecules can be used for the synthesis of new dendrimers or hyperbranched molecules. Further, the first sets of materials are fully conjugated. Investigation of the UV-vis absorption, photoluminescence, and two-photon absorption properties of the R′VinylStilbeneOS compounds, especially where R′ ) NH 2 , reveals exceptional red-shifts (120 nm), charge-transfer behavior, and excellent two-photon absorption properties that may suggest that the silica core serves the role of electron acceptor in the system and interacts equally with all eight organic moieties. This observation may imply 3-D conjugation through the core.

A set of stilbene-substituted octasilicates [p-RStil(x)Ph(8-x)SiO(1.5)](8) (R = H, Me, MeO, Cl, NMe(2) and x = 5.3-8) and [o-MeStilSiO(1.5)](8) were prepared. Model compounds were also prepared including the corner and half cages: [p-MeStilSi(OEt)(3)], [p-Me(2)NStilSi(OSiMe(3))(3)], and [p-Me(2)NStilSi(O)(OSiMe)](4). These compounds were characterized by MALDI-TOF, TGA, FTIR, and (1)H NMR techniques. Their photophysical properties were characterized by UV-vis, two-photon absorption, and cathodoluminescence spectroscopy (on solid powders), including studies on the effects of solvent polarity and changes in concentration. These molecules are typically soluble, easily purified, and robust, showing T(d(5%)) > 400 degrees C in air. The full and partial cages all show UV-vis absorption spectra (in THF) identical to the spectrum of trans-stilbene, except for [o-MeStilSiO(1.5)](8), which exhibits an absorption spectrum blue-shifted from trans-stilbene. However, the partial cages show emissions that are red-shifted by approximately 20 nm, as found for stilbene-siloxane macrocycles, suggesting some interaction of the silicon center(s) with the stilbene pi* orbital in both the corner and half cages. In contrast, the emission spectra of the full cages show red-shifts of 60-100 nm. These large red-shifts are supported by density functional theoretical calculations and proposed to result from interactions of the stilbene pi* orbitals with a LUMO centered within the cage that has 4A(1) symmetry and involves contributions from all Si and oxygen atoms and the organic substituents. Given that this LUMO has 3-D symmetry, it appears that all of the stilbene units interact in the excited state, consistent with theoretical results, which show an increased red-shift with an increase in the functionalization of a single corner to functionalization of all eight corners with stilbene. In the case of the Me(2)N- derivatives, this interaction is primarily a charge-transfer interaction, as witnessed by the influence of solvent polarity on the emission behavior. More importantly, the two-photon absorption behavior is 2-3 times greater on a per p-Me(2)Nstilbene basis for the full cage than for the corner or half cages. Similar observations were made for p-NH(2)stilbenevinyl(8)OS cages, where the greater conjugation lengths led to even greater red-shifts (120 nm) and two-photon absorption cross sections. Cathodoluminescence studies done on [p-MeStilSiO(1.5)](8) or [p-MeStilOS](8) powders exhibit essentially the same emissions as seen in solution at high dilution. Given that only the emissions are greatly red-shifted in these molecules, whereas the ground-state UV-vis absorptions are not changed from trans-stilbene, except for the ortho derivative, which is blue-shifted 10 nm. It appears that the interactions are only in the excited state. Theoretical results show that the HOMO and LUMO states are always the pi and pi* states on the stilbene, which show very weak shifts with increasing degrees of functionalization, consistent with the small chan...

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The stability of soddyite under electron irradiation has been studied over the temperature range of 25-300 °C. At room temperature, soddyite undergoes a crystalline-to-amorphous transformation (amorphization) at a total dose of 6.38 × 10(8) Gy. The electron beam irradiation results suggest that the soddyite structure is susceptible to radiation-induced nanocrystallization of UO(2). The temperature dependence of amorphization dose increases linearly up to 300 °C. A thermogravimetric and calorimetric analysis (TGA-DSC) combined with X-ray diffraction (XRD) indicates that soddyite retains its water groups up to 400 °C, followed by the collapse of the structure. Based on thermal analysis of uranophane, the removal of some water groups at relatively low temperatures provokes the collapse of the uranophane structure. This structural change appears to be the reason for the increase of amorphization dose at 140 °C. According to the results obtained, radiation field of a nuclear waste repository, rather than temperature effects, may cause changes in the crystallinity of soddyite and affect its stability during long-term storage.