Topology Effects in Molecular Organic Electronic Materials: Pyrene and Azupyrene**

Pyrene derivatives play a prominent role in organic electronic devices, including field effect transistors, light emitting diodes, and solar cells. The flexibility in the desired properties has previously been achieved by variation of substituents at the periphery of the pyrene backbone. In contrast, the influence of the topology of the central π-electron system on the relevant properties such as the band gap or the fluorescence behavior has not yet been addressed. In this work, pyrene is compared with its structural isomer azupyrene, which has a π-electron system with non-alternant topology. Using photoelectron spectroscopy, near edge X-ray absorption fine structure spectroscopy, and other methods, it is shown that the electronic band gap of azupyrene is by 0.72 eV smaller than that of pyrene. The difference of the optical band gaps is even larger with 1.09 eV, as determined by ultraviolet–visible absorption spectroscopy. The non-alternant nature of azupyrene is also associated with a more localized charge distribution. Further insight is provided by density functional theory (DFT) calculations of the molecular properties and ab initio coupled cluster calculations of the optical transitions. The concept of aromaticity is used to interpret the major topology-related differences.     

Formation of a cationic alkylidene complex via formal hydride abstraction: synthesis and structural characterization of [W(PMe3)4(η2-CHPMe2)H]X (X = Br, I)

W(PMe(3))(4)(η(2)-CH(2)PMe(2))H reacts with aryl halides to give the alkylidene complex, [W(PMe(3))(4)(η(2)-CHPMe(2))H](+), which reacts with LiAlD(4) to give selectively W(PMe(3))(4)(η(2)-CHDPMe(2))H, in which the deuterium resides in the methylene group; subsequent migration of deuterium from the methylene group provides a means to measure the rate constant for the formation of the 16-electron species [W(PMe(3))(5)] from W(PMe(3))(4)(η(2)-CH(2)PMe(2))H.     

Next‐Generation Heteronuclear Decoupling for High‐Field Biomolecular NMR Spectroscopy

Ultra‐high‐field NMR spectroscopy requires an increased bandwidth for heteronuclear decoupling, especially in biomolecular NMR applications. Composite pulse decoupling cannot provide sufficient bandwidth at practical power levels, and adiabatic pulse decoupling with sufficient bandwidth is compromised by sideband artifacts. A novel low‐power, broadband heteronuclear decoupling pulse is presented that generates minimal, ultra‐low sidebands. The pulse was derived using optimal control theory and represents a new generation of decoupling pulses free from the constraints of periodic and cyclic sequences. In comparison to currently available state‐of‐the‐art methods this novel pulse provides greatly improved decoupling performance that satisfies the demands of high‐field biomolecular NMR spectroscopy.     

Supermolecular liquid crystal dendrimers based on the octasilsesquioxane core

Liquid crystalline dendrimers are proving to be a fascinating class of materials that possess unusual physical properties. The self-assembling process involved in the formation of the mesomorphic state apparently deforms the spherical disposition of the supermolecular dendrimers to give rod-like entities that pack together to yield disordered Smectic A and smectic C mesophases.     

Carbon nanocones: A variety of non-crystalline graphite

Previously known graphitic structures of conical shape – whiskers and helical cones – consist of a single wrapped graphene sheet, which gives a rather amorphous tip structure. Carbon nanocones, on the other hand, are nearly perfect sheets, curved by 1–5 pentagonal rings in the otherwise hexagonal network of carbon atoms. However, the resulting loss of periodicity implies electronic properties quite different from those of graphite and nanotubes. Experimental results have so far been limited by restricted access to sample material, but the cones have shown a unique capability of storing hydrogen gas reversibly at normal temperatures. The cones are characterized by large electrostatic dipole moments which will influence future experiments and technological applications. In this paper we study the interplay between topology, geometry and electronic properties, and investigate the magnitude of the dipole moments as a function of size and apex angle of the cones.     

Submillimeter-wave emission assignments for 1,1-difluoroethylene

Many of the known submillimeter wave emissions of 1,1-difluoroethylene are assigned by using new data from infrared diode laser heterodyne spectroscopy. Six new submillimeter lines are also reported and assigned.