10.1021/acs.jpcc.7b10564.s001
Jens Kügel
Jens
Kügel
Lucas Klein
Lucas
Klein
Markus Leisegang
Markus
Leisegang
Matthias Bode
Matthias
Bode
Analyzing and Tuning the Energetic Landscape of H<sub>2</sub>Pc Tautomerization
American Chemical Society
2017
H 2 Pc Tautomerization
step-like increase
STM
scanning tunneling microscope
tautomerization barrier heights
excitation
deprotonated H 2 Pc
silver atom manipulation
H 2 Pc
analysis
mode
H 2 Pc molecule
2017-11-27 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Analyzing_and_Tuning_the_Energetic_Landscape_of_H_sub_2_sub_Pc_Tautomerization/5682772
We present a detailed
analysis of the energetic landscape of phthalocyanine
(H<sub>2</sub>Pc) tautomerization on Ag(111), i.e., the switching
of protons between different sites in the molecular frame, which is
induced and measured by a low-temperature scanning tunneling microscope
(STM). We demonstrate that tautomerization of this molecule is preferentially
triggered by the excitation of the N–H stretching mode. Interestingly,
a step-like increase of the tautomerization rate is observed at a
bias voltage that corresponds to the second harmonic of this vibrational
mode, which we attribute to the crossover from quantum tunneling through
the tautomerization barrier to an excitation over the barrier. This
hypothesis is supported by the analysis of four modified versions
of H<sub>2</sub>Pc, produced by single silver atom manipulation and/or
deprotonation of the pristine H<sub>2</sub>Pc molecule. Depending
on the particular modification, the step-like increase varies strongly,
spanning the entire range from further enhancement to almost complete
disappearance. We interpret this behavior in terms of different tautomerization
barrier heights which for most molecules lies between the first and
second harmonics of the N–H stretching mode but which is strongly
reduced well below the first harmonic for deprotonated H<sub>2</sub>Pc.