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Metal-free photochemical silylations and transfer hydrogenations of benzenoid hydrocarbons and graphene.

ABSTRACT: The first hydrogenation step of benzene, which is endergonic in the electronic ground state (S₀), becomes exergonic in the first triplet state (T₁). This is in line with Baird's rule, which tells that benzene is antiaromatic and destabilized in its T₁ state and also in its first singlet excited state (S₁), opposite to S₀, where it is aromatic and remarkably unreactive. Here we utilized this feature to show that benzene and several polycyclic aromatic hydrocarbons (PAHs) to various extents undergo metal-free photochemical (hydro)silylations and transfer-hydrogenations at mild conditions, with the highest yield for naphthalene (photosilylation: 21%). Quantum chemical computations reveal that T₁-state benzene is excellent at H-atom abstraction, while cyclooctatetraene, aromatic in the T₁ and S₁ states according to Baird's rule, is unreactive. Remarkably, also CVD-graphene on SiO₂ is efficiently transfer-photohydrogenated using formic acid/water mixtures together with white light or solar irradiation under metal-free conditions.

SUBMITTER: Papadakis R

PROVIDER: S-EPMC5059713 | biostudies-literature | 2016 Oct

REPOSITORIES: biostudies-literature

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Metal-free photochemical silylations and transfer hydrogenations of benzenoid hydrocarbons and graphene.

Papadakis Raffaello R Li Hu H Bergman Joakim J Lundstedt Anna A Jorner Kjell K Ayub Rabia R Haldar Soumyajyoti S Jahn Burkhard O BO Denisova Aleksandra A Zietz Burkhard B Lindh Roland R Sanyal Biplab B Grennberg Helena H Leifer Klaus K Ottosson Henrik H

Nature communications 20161006

The first hydrogenation step of benzene, which is endergonic in the electronic ground state (S0), becomes exergonic in the first triplet state (T1). This is in line with Baird's rule, which tells that benzene is antiaromatic and destabilized in its T1 state and also in its first singlet excited state (S1), opposite to S0, where it is aromatic and remarkably unreactive. Here we utilized this feature to show that benzene and several polycyclic ...[more]

PMID: 27708336

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Project description:During the past decades micro-electromechanical microphones have largely taken over the market for portable devices, being produced in volumes of billions yearly. Because performance of current devices is near the physical limits, further miniaturization and improvement of microphones for mobile devices poses a major challenge that requires breakthrough device concepts, geometries, and materials. Graphene is an attractive material for enabling these breakthroughs due to its flexibility, strength, nanometer thinness, and high electrical conductivity. Here, we demonstrate that transfer-free 7 nm thick multilayer graphene (MLGr) membranes with diameters ranging from 85-155 to 300 μm can be used to detect sound and show a mechanical compliance up to 92 nm Pa-1, thus outperforming commercially available MEMS microphones of 950 μm with compliances around 3 nm Pa-1. The feasibility of realizing larger membranes with diameters of 300 μm and even higher compliances is shown, although these have lower yields. We present a process for locally growing graphene on a silicon wafer and realizing suspended membranes of patterned graphene across through-silicon holes by bulk micromachining and sacrificial layer etching, such that no transfer is required. This transfer-free method results in a 100% yield for membranes with diameters up to 155 μm on 132 fabricated drums. The device-to-device variations in the mechanical compliance in the audible range (20-20000 Hz) are significantly smaller than those in transferred membranes. With this work, we demonstrate a transfer-free method for realizing wafer-scale multilayer graphene membranes that is compatible with high-volume manufacturing. Thus, limitations of transfer-based methods for graphene microphone fabrication such as polymer contamination, crack formation, wrinkling, folding, delamination, and low-tension reproducibility are largely circumvented, setting a significant step on the route toward high-volume production of graphene microphones.

Dataset Information

Metal-free photochemical silylations and transfer hydrogenations of benzenoid hydrocarbons and graphene.

Publications

Metal-free photochemical silylations and transfer hydrogenations of benzenoid hydrocarbons and graphene.

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