Efficient Bromination of Naphthalene Dianhydride and Microwave-Assisted Synthesis of Core-Brominated Naphthalene Diimides

This article presents an efficient method for the synthesis of core-brominated naphthalene diimides (NDI) from naphthalene dianhydride (NDA). A procedure for monitoring the NDA bromination reaction by ¹H NMR spectroscopy is described, allowing for optimization and greater consistency of this reaction. Furthermore, the subsequent bis-imidization reaction of the brominated NDA product has been significantly enhanced using microwave-assisted conditions, with recovery of pure product via simple filtration in excess of 90% of theoretical yield. This chemistry offers greatly improved methodology for obtaining core-substituted NDI compounds with high efficiency and good yields.     

Polymer brushes on graphene

A critical bottleneck for the widespread use of single layer graphene is the absence of a facile method of chemical modification which does not diminish the outstanding properties of the two-dimensional sp(2) network. Here, we report on the direct chemical modification of graphene by photopolymerization with styrene. We demonstrate that photopolymerization occurs at existing defect sites and that there is no detectable disruption of the basal plane conjugation of graphene. This method thus offers a route to define graphene functionality without degrading its electronic properties. Furthermore, we show that photopolymerization with styrene results in self-organized intercalative growth and delamination of few layer graphene. Under these reaction conditions, we find that a range of other vinyl monomers exhibits no reactivity with graphene. However, we demonstrate an alternative route by which the surface reactivity can be precisely tuned, and these monomers can be locally grafted via electron-beam-induced carbon deposition on the graphene surface.     

Two calorimetric glass transitions do not necessarily indicate immiscibility: The case of PEO/PMMA

Differential scanning calorimetry has been used to examine blends of a poly(ethylene oxide) (PEO), M_n = 300 g/mol, and a poly(methylmethacrylate) (PMMA), M_n = 10,000 g/mol, across the complete composition range. The relatively low molar mass of the PEO minimizes interference from crystallization. In the midrange of composition, ～25–70% PEO, two broad, but distinct, glass transitions are resolved. These are interpreted as distinct glass transitions of the two components, as anticipated by the self‐concentration model of Lodge and McLeish. The composition dependence of the observed transitions is well described by the self‐concentration approach, using lengthscales of approximately two‐thirds of the Kuhn length. The results are compared with previous measurements on PEO/PMMA blends and other miscible systems. The principal, general conclusion is that one should actually expect two glass transitions in a miscible polymer blend or polymer solution; the rule of thumb that two transitions indicate immiscibility is incorrect. Furthermore, attempts to rationalize two transitions on the basis of incomplete segmental mixing, or other unspecified “nanoheterogeneity,” may not be justified in many cases. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 756–763, 2006     

Synthesis of cis- and trans-2,4-dibenzylidine-1,3-ditelluretan from sodium phenyl acetylide and tellurium metal; a reinvestigation and structure proof

Reaction of sodium phenyl acetylide with tellurium metal and subsequent protonation yields the title compounds, rather than a 1,3-ditellurole as recently reported.     

Population models with partial migration

Populations exhibiting partial migration consist of two groups of individuals: Those that migrate between habitats, and those that remain fixed in a single habitat. We propose several discrete-time population models to investigate the coexistence of migrants and residents. The first class of models is linear, and we distinguish two scenarios. In the first, there is a single egg pool to which both populations contribute. A fraction of the eggs is destined to become migrants, and the remainder become residents. In a second model, there are two distinct egg pools to which the two types contribute, one corresponding to residents and another to migrants. The asymptotic growth or decline in these models can be phrased in terms of the value of the basic reproduction number being larger or less than one respectively. A second class of models incorporates density dependence effects. It is assumed that increased densities in the various life history stages adversely affect the success of transitioning of individuals to subsequent stages. Here too we consider models with one or two egg pools. Although these are nonlinear models, their asymptotic dynamics can still be classified in terms of the value of a locally defined basic reproduction number: If it is less than one, then the entire population goes extinct, whereas it settles at a unique fixed point consisting of a mixture of residents and migrants, when it is larger than one. Thus, the value of the basic reproduction number can be used to predict the stable coexistence or collapse of populations exhibiting partial migration.     

Anion-directed self-assembly of a 2,6-bis(2-anilinoethynyl)pyridine bis(amide) scaffold

Bis(sulfonamide) receptors based on the 2,6-bis(2-anilinoethynyl)pyridine scaffold form persistent dimers with water and halides in solution and in the solid-state. The structurally related bis(amide) receptor derived from 3,5-dinitrobenzoyl chloride is a dimer in the solid-state with two HCl molecules directing the self-assembly. The 2+2 dimer, with a twisted ‘S’-shaped backbone, is held together by six hydrogen bonds. Dissolution of the (H2⁺√Cl ^? )₂ adduct in CHCl₃ results, however, in a monomeric structure. DOSY and ¹H NMR experiments were used to identify the dominance of monomer in solution for both 2 and H2⁺√Cl ^? . The ‘OFF–ON’ fluorescence response of 2,6-bis(2-anilinoethynyl)pyridine is retained with amide arms.     

Carbon networks based on benzocyclynes. 6. synthesis of graphyne substructures via directed alkyne metathesis

Intramolecular ring closing alkyne metathesis afforded the graphyne biscyclyne (3) in high macrocyclization yield and good overall yield. This methodology also furnished the tris[12]cyclyne 4, which contains the longest linear diphenylacetylene conjugation pathway for any graphyne substructure based on the tribenzo[12]cyclyne core.