PHILIPPE PLAILLY / SCIENCE PHOTO LIBRARY PHILIPPE PLAILLY / SCIENCE PHOTO LIBRARY
Molecular switches. Samples of chemicals which act as molecular switches. The coloured samples at right are the chemicals in their 'on' (electron- conducting) state, and at left are in their 'off' state. Molecular switches are chemicals whose structure is altered by light to allow or block the passage of electrons. Most are switched on by ultraviolet light; this closes a bond between two thiophen (carbon-sulphur) rings and allows electrons to flow across the molecule. Infrared light breaks the extra bond, and prevents electron flow. These chemicals could be used as molecule- sized switches in future optical computers.
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