Hot Carrier-Induced Tautomerization within a Single Porphycene Molecule on Cu(111).

Here, we report the study of tautomerization within a single porphycene molecule adsorbed on a Cu(111) surface using low-temperature scanning tunneling microscopy (STM) at 5 K. While molecules are adsorbed on the surface exclusively in the thermodynamically stable trans tautomer after deposition, a voltage pulse from the STM can induce the unidirectional trans → cis and reversible cis ↔ cis tautomerization. From the voltage and current dependence of the tautomerization yield (rate), it is revealed that the process is induced by vibrational excitation via inelastic electron tunneling. However, the metastable cis molecules are thermally switched back to the trans tautomer by heating the surface up to 30 K. Furthermore, we have found that the unidirectional tautomerization can be remotely controlled at a distance from the STM tip. By analyzing the nonlocal process in dependence on various experimental parameters, a hot carrier-mediated mechanism is identified, in which hot electrons (holes) generated by the ...