The subsequent step were the experiments under high vacuum and at very low temperature (5 K, which means five degree above the absolute zero). A single porphycene molecule laying on the copper substrate was observed with a scanning tunnelling microscope. The instrument allowed for recording changes in electron density of the molecule, and thus for monitoring changes of its shape. The images obtained with this technique allowed to determine current positions of both protons. Therefore the researchers were able to observe the movement of atoms inside the molecule in the course of a chemical reaction.
"We were pretty much surprised to find that after depositing on the copper substrate, hydrogen ions in porphycene molecule formed a configuration that was never observed so far, in spite of many, many years of research on this compound. Instead of being located in opposite corners of the tetragon formed by nitrogen atoms, both protons took positions next to each other. Quite surprisingly we found a new porphycene tautomer!", comments Prof. Waluk.
Using a tip of the scanning tunnelling microscope, in subsequent attempts a single copper atom was moved closer to the porphycene molecule, from different sides. It turned out that depending on the position of the copper atom, both protons in porphycene, moving between the nitrogen atoms, were located once on one side, and then on the other side of the molecule. Thus, the porphycene molecule acted as a binary switch, controlled with a single copper atom only. A change in position of the copper atom by less than a ten-billionth of a meter was sufficient to initiate the transition between the states.
The research carrie
|Contact: Jacek Waluk|
Institute of Physical Chemistry of the Polish Academy of Sciences