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Tetracoordinated carbon therein surprisingly employs orbitals that are more similar to sp2 than to sp3 hybrids in sigma bonds with adjacent ring atoms. Both leaving groups and nucleo- or electrophiles may donate electrons to the π-system depending on the availability of p-type orbitals to fulfill Hückel (4N+2) or Möbius (4N) rules of aromaticity in analogy to conjugated transition-metal metallacycles.© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.Substituent Effect on Triplet State Aromaticity of Benzene.Density functional theory calculations have been performed to explore the substituent effect on benzene's structure and aromaticity upon excitation to the first triplet excited state (T1).
Discussion is based on spin density analysis, HOMA (harmonic oscillator model of aromaticity), NICS (nucleus-independent chemical shift), ACID (anisotropy of the induced current density), and monohydrogenation free energies and shows that a large span of aromatic properties, from highly antiaromatic to strongly aromatic, could be achieved by varying the substituent. This opens up a possibility of controlling benzene's physicochemical behavior in its excited state, while molecular motion, predicted for several derivatives, could be of interest for the development of Hückel Molecular Orbital Analysis for Stability and Instability of Stacked Aromatic and Stacked Antiaromatic Systems.University, Nishi-ku, Fukuoka 819-0395, Japan.Face-to-face stacking of aromatic compounds leads to stacked antiaromaticity, while that of antiaromatic compounds leads to stacked aromaticity. This is a prediction with a long history; in the late 2000s, the prediction was confirmed by high-precision quantum chemical calculations, and finally, in 2016, a π-conjugated system with stacked aromaticity was synthesized. Several variations have since been reported, but essentially, they are all the same molecule. To realize stacked aromaticity in a completely new and different molecular system and to trigger an extension of the concept of stacked aromaticity, it is important to understand the origin of stacked aromaticity.
The Hückel method, which has been successful in giving qualitatively correct results for π-conjugated systems despite its bold assumptions, is well suited for the analysis of stacked aromaticity. We use this method to model the face-to-face stacking systems of benzene and cyclobutadiene molecules and discuss their stacked antiaromaticity and stacked aromaticity on the basis of their π-electron energies. By further developing the discussion, we search for clues to realize stacked aromaticity in synthesizable molecular systems.Cofabrication: a strategy for building multicomponent microsystems.Street, Cambridge, Massachusetts 02138, USA.This Account describes a strategy for fabricating multicomponent microsystems in which the structures of essentially all of the components are formed in a single step of micromolding. This strategy, which we call "cofabrication", is an alternative to multilayer microfabrication, in which multiple layers of components are sequentially aligned ("registered") and deposited on a substrate by photolithography.
Cofabrication has several characteristics that make it an especially useful approach for building multicomponent microsystems. It rapidly and inexpensively generates correctly aligned components (for example, wires, heaters, magnetic field generators, optical waveguides, and microfluidic channels) over very large surface areas. By avoiding registration, the technique does not impose on substrates the size limitations of common registrations tools, such as steppers and contact aligners. We have demonstrated principle, device size is only limited by the requirements of generating the original master. In Seebio UV-Activated Acid Generator , cofabrication can serve as a low-cost strategy for building microsystems. The technique is amenable to a variety of laboratory settings and uses fabrication tools that are less expensive than those used for multistep microfabrication. Moreover, the process requires only small amounts of solvent and photoresist, a costly chemical required for photolithography; in cofabrication, photoresist is applied and developed only once to produce a master, which is then used to produce multiple copies of molds containing the microfluidic channels.
From a broad perspective, cofabrication represents a new processing paradigm in which the exterior (or shell) of the desired structures are produced before the interior (or core). This approach, generating the insulation or packaging structure first and injecting materials that provide function in channels in liquid phase, makes it possible to design and build microsystems with component materials that cannot be easily manipulated conventionally (such as solid materials with low melting points, liquid metals, liquid crystals, fused salts, foams, emulsions, gases, polymers, biomaterials, and fragile organics). Moreover, materials can be altered, removed, or replaced after the manufacturing stage. For example, cofabrication allows one to build devices in which a liquid flows through the device during use, or is replaced after use. Metal wires can be melted and reset by heating (in principle, repairing a break).
