Magazine article Science News

Optical Excitations, Molecule by Molecule

Magazine article Science News

Optical Excitations, Molecule by Molecule

Article excerpt

In a feat of spectroscopic magic, two researchers have used a finely tuned laser to transform the optical properties of individual molecules, making them "disappear" and, possibly, rendering them useful for storing information.

Last year, physicist W.E. Moerner and his colleagues at the IBM Almaden Research Center in San Jose, Calif., demonstrated that they could monitor the light given off by single molecules lodged in a crystal (SN: 1/19/91, p.37). Now, Moerner and IBM physical chemist Thomas Basche have discovered that single-molecule spectroscopy works with materials widely dispersed in amorphous solids, revealing interesting quantum-mechanical properties about embedded molecules. They describe their new findings in the Jan. 23 NATURE.

For their experiment, Moerner and Basche made a clear, 10-micron-thick, polyethylene film that contained the organic compound perylene. They cooled the film to 1.5 kelvins and trained a tunable laser on it. Perylene molecules resonate and fluoresce when excited by laser light of a particular wavelength. The pressure exerted by the surrounding polyethylene alters this property, so that different perylene molecules resonate at slightly different frequencies.

Using a very efficient detector to monitor perylene's fluorescence spectrum, the IBM team discovered that an excited perylene molecule puts pressure on adjacent polymers, thereby changing its local environment. That change, in turn, slightly shifts the perylene's energy levels so that it no longer responds to the same wavelength laser. …

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