A Kondo resonance has been observed on purely organic molecules in several combinations of charge transfer complexes on a metal surface. It has been regarded as a fingerprint of the transfer of one electron from the donor to the extended π orbital of the acceptor's LUMO. Here, we investigate the stoichiometric checkerboard structure of tetrathiafulvalene (TTF) and tetracyanoethylene (TCNE) on a Au(111) surface using scanning tunneling and atomic force microscopy at 4.8 K. We find a bistable state of the TCNE molecules with distinct structural and electronic properties. The two states represent different conformations of the TCNE within the structure. One of them exhibits a Kondo resonance, whereas the other one does not, despite of both TCNE types being singly charged.
@article{arxiv.1809.09229,
title = {Correlation of Kondo effect and molecular conformation of the acceptor molecule in the TTF-TCNE charge transfer complex},
author = {Paul Stoll and Christian Lotze and Janina N. Ladenthin and Tobias R. Umbach and Isabel Fernandez-Torrente and Katharina J. Franke},
journal= {arXiv preprint arXiv:1809.09229},
year = {2018}
}