Single-Component Upconverting Polymeric Nanoparticles.

Low-power light upconversion is a highly desirable feature for a broad range of applications and new materials enabling this process are sought in both bulk and particulate form. Here, the preparation of upconverting nanoparticles is reported from a methacrylic terpolymer bearing diphenylanthracene and meso-phenoxytris(heptyl)porphyrin pendant groups by a microemulsion technique. The use of a terpolymer in which the upconvering dye molecules are covalently attached mitigates some of the drawbacks of triplet-triplet annihilation upconverting nanoparticles made by other techniques, in particular dye leakage from the nanoparticles, and limited control of the sensitizer and emitter concentration within each nanoparticle. Size and morphology of the new upconverting nanoparticles are investigated by dynamic light scattering and transmission electron microscopy and elucidated their upconverting properties by luminescence spectroscopy.

Template-assisted synthesis of Janus silica nanobowls.

The preparation of anisotropic nanoparticles has drawn much attention in the literature, with most of the efforts being dedicated to convex particles. In this work, instead, we present a reliable method to synthesis silica nanobowls with one well-defined opening, covering a broad range of sizes. The nanobowls have been obtained from asymmetrically functionalized silica-polymer Janus nanodumbbells, used as templates, by removing of the polymer. Polystyrene seeds having different sizes as well as surface chemistry have been used as starting material in a two-step seeded emulsion polymerization, which leads to polymer nanodumbbells. These dumbbells are also asymmetrically functionalized due to the presence of silane groups on only one of their two hemispheres. This allows us to selectively coat the silane-bearing hemisphere of the dumbbells with a silica layer by means of a Stoeber process. The silica nanobowls are eventually obtained after either calcination or dissolution of the polymeric template. Depending on the route followed to remove the polymer, nanobowls made of pure silica (from calcination) or hybrid Janus nanobowls with a silica outer shell and a covalently bound hydrophobic polymer layer inside the cavity (from dissolution) could be prepared. The difference between the two types of nanobowls has been proved by electrostatically binding oppositely charged silica nanoparticles, which adhere selectively only on the outer silica part of the nanobowls prepared by polymer dissolution, while they attach both inside and outside of nanobowls prepared by calcination. We also show that selective functionalization of the outer surface of the Janus nanobowls from dissolution is possible. This work is one of the first examples of concave objects bearing different functionalities in the inner and outer parts of their surface.

Mechanism of the aerobic oxidation of alpha-pinene.

A combined experimental and theoretical approach is used to study the thermal autoxidation of alpha-pinene. Four different types of peroxyl radicals are generated; the verbenyl peroxyl radical being the most abundant one. The peroxyl radicals propagate a long radical chain, implying that chain termination does not play an important role in the production of the products. Two distinct types of propagation steps are active in parallel: the abstraction of allylic H atoms and the addition to the unsaturated C=C bond. The efficiency for both pathways appears to depend on the structure of the peroxyl radical. The latter step yields the corresponding epoxide product, as well as alkoxyl radicals. Under the investigated reaction conditions the alkoxyl radicals seem to produce both the alcohol and ketone products, the ketone presumably being formed upon the abstraction of the weakly bonded alphaH atom by O2. This mechanism explains the predominantly primary nature of all quantified products. At higher conversion, co-oxidation of the hydroperoxide products constitutes an additional, albeit small, source of alcohol and ketone products.