Molecular switch



A molecular switch is a molecular machines.


Photochromic molecular switches

A widely studied class are photochromic compounds which are able to switch between electronic configurations when irradiated by light of a specific wavelength. Each state has a specific absorption maximum which can then be read out by stilbenes, spiropyrans and phenoxynaphthacene quinones.

Chiroptical molecular switches are a specific subgroup with photochemcial switching taking place between an circularly polarized light

Chiroptical molecular switches that show directional motion are considered synthetic molecular motors [2]:

Host-guest molecular switches

In acetonitrile gives back the open form.

In 1980 Yamashita et al. [5] construct a crown ether already incorporating the anthracene units (an anthracenophane) and also study ion uptake vs photochemistry.

Also in 1980 Shinkai throws out the anthracene unit as photoantenna in favor of an alkali metal group). In the dark the reverse isomerization takes place.

Shinkai employs this devices in actual ion transport mimicking the biochemical action of nigericin [7] [8]: in a biphasic system ions are taken up triggered by light in one phase and deposited in the other phase in absence of light.

Mechanically-interlocked molecular switches

Some of the most advanced molecular switches are based on catenane [10] [11]


Photo switchable catenane Vögtle 1993Molecular switch Stoddart 1994


This compound is based on two ring systems: one ring holds the photoswichable azobenzene ring and two NMR spectroscopy shows that in the azo trans-form the polyether ring is free to rotate around its partner ring but then when a light trigger activates the cis azo form this rotation mode is stopped

Stoddart in 1994 modifies his radical ion) and significantly both processes are reversible.

In 2007 molecular shuttles are utilized in an experimental DRAM circuit [13]. The device consists of 400 bottom monolayer of a bistable rotaxane depicted below:

Each bit in the device consists of a silicon and a titanium crossbar with around 100 rotaxane molecules filling in the space between them at perpendicular angles. The hydrophilic chemical half-life of around one hour. The problem of defects is circumvented by adopting a defect-tolerant architecture also found in the Teramac project. In this way a circuit is obtained consisting of 160,000 bits on an area the size of a white blood cell translating into 1011 bits per square centimeter.

References

  1. ^ Molecular Machines & Motors (Structure and Bonding) J.-P. Sauvage Ed. ISBN 3540413822
  2. ^ Chiroptical Molecular Switches Ben L. Feringa, Richard A. van Delden, Nagatoshi Koumura, and Edzard M. Geertsema Chem. Rev.; 2000; 100(5) pp 1789 - 1816; (Review) doi:10.1021/cr9900228
  3. ^ Cation complexing photochromic materials involving bisanthracenes linked by a polyether chain. Preparation of a crown-ether by photocycloisomerization Jean-Pierre Desvergne and Henri Bouas-Laurent J. Chem. Soc., Chem. Commun., 1978, 403 - 404, doi:10.1039/C39780000403
  4. ^ FROM ANTHRACENE PHOTODIMERIZATION TO JAW PHOTOCHROMIC MATERIALS AND PHOTOCROWNS Henri Bouas-Laurent, Alain Castellan and Jean-Pierre Desvergne Pure & Appl. Chem.5 Vol.52, pp.2633—2648. 1980 Link
  5. ^ Synthetic macrocyclic ligands. II. Synthesis of a photochromic crown ether Tetrahedron Letters, Volume 21, Issue 6, 1980, Pages 541-544 Isamu Yamashita, Mieko Fujii, Takahiro Kaneda, Soichi Misumi and Tetsuo Otsubo doi:10.1016/S0040-4039(01)85550-7
  6. ^ Photoresponsive crown ethers. 1. Cis-trans isomerism of azobenzene as a tool to enforce conformational changes of crown ethers and polymers Seiji Shinkai, Takahiro Nakaji, Yoshihiro Nishida, Toshiyuki Ogawa, and Osamu Manabe J. Am. Chem. Soc.; 1980; 102(18) pp 5860 - 5865; doi:10.1021/ja00538a026
  7. ^ Photoresponsive crown ethers. 2. Photocontrol of ion extraction and ion transport by a bis(crown ether) with a butterfly-like motion Seiji Shinkai, Takahiro Nakaji, Toshiyuki Ogawa, Kazuyoshi Shigematsu, and Osamu Manabe J. Am. Chem. Soc.; 1981; 103(1) pp 111 - 115; doi:10.1021/ja00391a021 10.1021/ja00391a021
  8. ^ Switch-functionalized systems in biomimetic chemistry Seiji Shinkai Pure & App!. Chem., Vol. 59, No. 3, pp. 425-430, 1987 Link
  9. ^ A molecular shuttle Pier Lucio Anelli, Neil Spencer, and J. Am. Chem. Soc.; 1991; 113(13) pp 5131 - 5133; doi:10.1021/ja00013a096
  10. ^ Photoswitchable Catenanes Fritz Vögtle, Walter Manfred Müller, Ute Müller, Martin Bauer, Kari Rissanen
  11. ^ Also in 1993: A Light-Induced Molecular Shuttle Based on a [2]Rotaxane-Derived Triad Angewandte Chemie International Edition in English Volume 32, Issue 10, Date: October 1993, Pages: 1459-1461 Andrew C. Benniston, Anthony Harriman doi:10.1002/anie.199314591
  12. ^ A chemically and electrochemically switchable molecular shuttle Richard A Bissell, Emilio Córdova, Angel E. Kaifer, J. Fraser Stoddart Nature 369, 133 - 137 (12 May 1994) Letter doi:10.1038/369133a0
  13. ^ A 160-kilobit molecular electronic memory patterned at 1011 bits per square centimetre Jonathan E. Green, Jang Wook Choi1, Akram Boukai, Yuri Bunimovich, Ezekiel Johnston-Halperin, Erica DeIonno, Yi Luo, Bonnie A. Sheriff, Ke Xu, Young Shik Shin, Hsian-Rong Tseng, J. Fraser Stoddart and James R. Heath Nature 445, 414-417 (25 January 2007) | doi:10.1038/nature05462
 
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