Efficient and selective photodimerization of 2-naphthalenecarbonitrile mediated by cucurbit[8]uril in an aqueous solution.

The photodimerization of 2-naphthalenecarbonitrile (2-NpCN) in a cucurbit[8]uril (CB[8]) aqueous solution was investigated. Spectroscopic analysis and product distribution reveal that the use of CB[8] as a host inverted the product selectivity from photodimers 2 and 3 in cyclohexane to photodimer 1 in a CB[8] aqueous solution with a large rate acceleration under ambient temperature and pressure.

Gamma-cyclodextrin-directed enantioselective photocyclodimerization of methyl 3-methoxyl-2-naphthoate.

Irradiation of methyl 3-methoxyl-2-naphthoate (2,3-NA) in methanol solution with light lambda > 280 nm produces anti-head-to-head cubane-like photocyclodimer 1 and [4+4] intermediate 2, which is, to the best of our knowledge, the first incidence of directly obtaining the intermediate in photocyclodimerization of naphthalene analogues. X-ray crystal structural analysis has realized the chirality of 1, and the optically pure enantiomers 1(a) and 1(b) have been achieved by HPLC resolution. To understand the fundamental photocyclodimerization of naphthalene analogues mediated by native gamma-CD, the neutral 2,3-NA was selected as a typical reactant in this work. UV-vis, fluorescence, and (1)H NMR analysis reveal that gamma-CD can encapsulate 2,3-NA to make a stable 2:1 inclusion complex 2,3-NA@gamma-CD both in aqueous solution and in the solid state. Irradiation of 2,3-NA@gamma-CD results in photocyclodimerization with remarkable selectivity and efficiency, whereas no photocyclodimers could be detected in host-free aqueous solution and the neat solids. More importantly, the use of native gamma-CD as a chiral reaction vessel turns out to be an effective and versatile strategy for the enantioselective photocyclodimerization of 2,3-NA. The ee values of 48% in aqueous solution and up to 34% in the solid state for anti-head-to-head photocyclodimer 1 have been achieved upon irradiation of the inclusion complex of 2,3-NA@gamma-CD under ambient temperature and pressure. All of the observations indicate that native gamma-CD with hydrophobic interaction only is capable of regulating the orientation of naphthalene analogue 2,3-NA within the cavity of gamma-CD, and thereby leading to the highest ee value of 48% obtained so far for the photocyclodimerization with native gamma-CD in solution.

Formation of cubane-like photodimers from 2-naphthalenecarbonitrile.

Irradiation of 2-naphthalenecarbonitrile (2-NpCN) in solution with a light lambda > 280 nm results in the formation of three rigid cubane-like photodimers, anti-head-to-head 1, anti-head-to-tail 2, and syn-head-to-tail 3, which are not in line with the previously recognized regioselectivity. These cubane-like photodimers have been well characterized by spectroscopic investigation and/or X-ray crystal structural analysis in this work. Moreover, the separation of the optically pure enantiomers of 1, 2, and 3 has been achieved by HPLC resolution.

Porous fluorine-doped γ-Fe2O3 hollow spheres: synthesis, growth mechanism, and their application in photocatalysis.

Porous fluorine-doped maghemite(γ-Fe2O3) hollow spheres have been prepared by facile route based on solvothermal reaction and sequential calcinations. The composition and morphology of the as-prepared samples were characterized by various techniques. The SEM and TEM results showed that the as-synthesized products exhibited a spherical morphology with porous hollow structures. Ultraviolet-visible (UV-vis) diffuse reflectance spectra display that the optical performance of γ-Fe2O3 products are related to their structure and the fluorine concentrations. The porous hollow structured fluorine-doped γ-Fe2O3 spheres exhibit ferromagnetic properties with relatively high saturation magnetization at room temperature. According to the experimental results, a formation mechanism of the fluorine-doped γ-Fe2O3 hollow spheres has been presented. Under UV light irradiation, the photocatalytic degradation activities of the as-synthesized fluorine-doped γ-Fe2O3 samples for RhB dye were 2-5 times higher than that of the undoped sample. The prepared fluorine-doped γ-Fe2O3 hollow spheres will also aroused great interest for their application in catalysis, separation technology, sensors, nanotechnology, and biomedical fields.

Self-assembled 3D porous flowerlike α-Fe2O3 hierarchical nanostructures: synthesis, growth mechanism, and their application in photocatalysis.

In this work, a facile route using a simple solvothermal reaction to synthesize 3D porous flowerlike hierarchical nanostructures (HNs) of α-Fe(2)O(3) without employing templates or matrices for self-assembly is presented. The morphology and compositional characteristics of the 3D HNs were investigated by various techniques. The 3D HNs composed of 2D nanopetals, were intercrossed with each other and constructed from nanobricks with a length of about 100 nm and a diameter of about 30 nm. Influencing factors such as the reaction time, dosage of reactants and the solvents are systematically investigated. A possible formation mechanism for the 3D HNs is proposed. On the basis of characterization results, the growth of such 3D HNs has been proposed as a self-assembly followed by Ostwald ripening process. The specific surface area of the 3D HNs also was investigated by using nitrogen adsorption and desorption isotherms. The as-prepared α-Fe(2)O(3) HNs have a comparatively large Brunauer-Emmett-Teller (BET) surface area of about 52.51 m(2) g(-1). The photocatalytic properties of the as-obtained α-Fe(2)O(3) 3D HNs are systematically investigated, which was evaluated by the degradation of RhB dye under ultraviolet light irradiation. The result shows that photocatalytic activity is greatly affected by the hierarchical and porous structure.

Self-Assembled 3D Flower-Like Hierarchical beta-Ni(OH)(2) Hollow Architectures and their In Situ Thermal Conversion to NiO.

Three-dimensional (3D) flower-like hierarchical beta-Ni(OH)(2) hollow architectures were synthesized by a facile hydrothermal route. The as-obtained products were well characterized by XRD, SEM, TEM (HRTEM), SAED, and DSC-TGA. It was shown that the 3D flower-like hierarchical beta-Ni(OH)(2) hollow architectures with a diameter of several micrometers are assembled from nanosheets with a thickness of 10-20 nm and a width of 0.5-2.5 mum. A rational mechanism of formation was proposed on the basis of a range of contrasting experiments. 3D flower-like hierarchical NiO hollow architectures with porous structure were obtained after thermal decomposition at appropriate temperatures. UV-Vis spectra reveal that the band gap of the as-synthesized NiO samples was about 3.57 eV, exhibiting obviously red shift compared with the bulk counterpart.

Highly efficient cucurbit[8]uril-templated intramolecular photocycloaddition of 2-naphthalene-labeled poly(ethylene glycol) in aqueous solution.

The photodimerization of water-insoluble 2-naphthalene-labeled poly(ethyl glycol) (N-Pn-N) in cucurbit[8]uril (CB[8]) aqueous solution was investigated. UV-vis, fluorescence, and 1H NMR analysis reveal that CB[8] can encapsulate N-Pn-N to make a stable 1:1 inclusion complex N-Pn-N@CB[8] in aqueous solution. Irradiation of N-Pn-N in the CB[8] aqueous solution results in intramolecular photocycloaddition with remarkable selectivity and efficiency, whereas no photodimer could be detected in host-free solution.