The latest nanotech device: Venetian blinds

时间:2019-03-02 07:04:07166网络整理admin

By Kurt Kleiner A molecule that flips its arms like the slats on a Venetian blind might in future find uses in computer displays, computer memory, or even windows that become tinted at the flick of a switch. Molecules whose shapes or movements can be easily controlled are important for nanotechnology. One kind that promises to be useful are those shaped in a helix that can be made to reverse its direction. When that happens the molecule is said to reverse its chirality. Researchers at North Carolina State University in Raleigh and Vanderbilt University in Nashville, Tennessee, were working with a helical polymer called polyguanidine. Polyguanidine actually switched chirality so easily that it was difficult to control. To try to make the helices more stable, the researchers stuck side chains of anthracene along the helical backbone. One characteristic of chiral molecules is that they are optically active – when polarised light passes through them in solution, its plane is rotated one way or another, depending on the chirality of the molecules. The researchers found the new molecule rotated light, as expected, but that the direction of rotation switched depending on the solvent used. Raising or lowering the temperature of the solution above or below 38.5°C also caused a switch. At first the researchers thought the chirality of the molecules was changing. But now they have discovered that the helices are staying put. Instead it is the anthracene side chains that are moving back and forth in unison, like shutters being opened and closed, or Venetian blinds being flipped up and down. The flipping occurs because the molecule has two different states – one high-energy and one low-energy – and these are stable at different temperatures and in solvents with different polarities. Prasad Polavarapu, a chemist at Vanderbilt and part of the research team, says the shutter action might some day make the molecule useful as a nanoscale engine, part of a computer display screen, or as a component in a computer memory. The molecule might also be attached to a glass substrate and used to instantly tint a window. Journal reference: Angewandte Chemie International Edition (vol 44,