Poster
Hot-carrier induced intramolecular H-atom transfer reaction studied by scanning tunneling microscopy
1Department of Physical Chemistry, Fritz-Haber-Institute of the Max-Planck Society, Faradayweg 4-6, 14195 Berlin, Germany
2Department of Physical Chemistry, University of Graz, Heinrichstrasse 28, 8010 Graz, Austria
3Insitute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, Warsaw 01-224, Poland
Intramolecular H-atom transfer reaction, i.e. tautomerization, is an important molecular process in chemistry and biology. Recent study using low-temperature scanning tunneling microscopy (LT-STM) has opened a unique opportunity to examine tautomerization within a single molecule on surfaces [1-3].
We will present a hot-carrier induced tautomerization within a single porphycene molecule (a structural isomer of porphine) on a Cu(111) surface using LT-STM. The porphycene molecule adsorb on the surface as a monomer (Fig. 1a) in a trans tautomer (Fig. 1c,d). It was found that the trans tautomer is the thermodynamically stable species, while a voltage pulse of the STM can induce the unidirectional conversion from the trans to metastable cis configuration (see Fig. 1e,f). The trans→cis tautomerization is induced through vibrational excitation via the inelastic electron tunneling process. Additionally, as shown in Fig. 1b, the tautomerization occurs in nonlocal fashion, with a spatial range of up to ~100 nm from the STM tip position. The metastable cis molecules can be switched back to the trans tautomer by heating the surface. From detailed analyses of the nonlocal tautomerization behavior, we conclude that the process is induced by hot-carriers generated in the surface. These results provide a microscopic insight into local carrier dynamics, and their role in the adsorbate reactions.
Figure 1: a) and b) STM images of porphycene molecules on Cu(111) at 5 K (It = 50 pA; Vsample = 50 mV). a) The porphycene molecules show the thermodynamically stable trans state. b) Same area after a voltage pulse of -2 V for 10 ms was applied at the center of the image (indicated by the white cross). Some of the molecules are converted to the cis configuration as indicated by the dashed circles. c) and e) Enlarged STM images of a single porphycene molecule in the trans d) and cis f) tautomer, respectively.
[1] P. Liljeroth et al., Science 317, 1203 (2007)
[2] W. Auwärter et al., Nature Nanotech. 7, 41 (2011)
[3] T. Kumagai et al., Nature Chem. 6, 41 (2014)