10.1021/acsnano.7b03954.s001 Tobias Meier Tobias Meier Rémy Pawlak Rémy Pawlak Shigeki Kawai Shigeki Kawai Yan Geng Yan Geng Xunshan Liu Xunshan Liu Silvio Decurtins Silvio Decurtins Prokop Hapala Prokop Hapala Alexis Baratoff Alexis Baratoff Shi-Xia Liu Shi-Xia Liu Pavel Jelínek Pavel Jelínek Ernst Meyer Ernst Meyer Thilo Glatzel Thilo Glatzel Donor–Acceptor Properties of a Single-Molecule Altered by On-Surface Complex Formation American Chemical Society 2017 chelate film intramolecular charge transfer tetrathiafulvalene-fused dipyridophenazine molecule donor formation adsorption site scanning tunneling microscopy 2017-07-21 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Donor_Acceptor_Properties_of_a_Single-Molecule_Altered_by_On-Surface_Complex_Formation/5241031 Electron donor–acceptor molecules are of outstanding interest in molecular electronics and organic solar cells for their intramolecular charge transfer controlled <i>via</i> electrical or optical excitation. The preservation of their electronic character in the ground state upon adsorption on a surface is cardinal for their implementation in such single-molecule devices. Here, we investigate by atomic force microscopy and scanning tunneling microscopy a prototypical system consisting of a π-conjugated tetrathiafulvalene-fused dipyridophenazine molecule adsorbed on thin NaCl films on Cu(111). Depending on the adsorption site, the molecule is found either in a nearly undisturbed free state or in a bound state. In the latter case, the molecule adopts a specific adsorption site, leading to the formation of a chelate complex with a single Na<sup>+</sup> alkali cation pulled out from the insulating film. Although expected to be electronically decoupled, the charge distribution of the complex is drastically modified, leading to the loss of the intrinsic donor–acceptor character. The chelate complex formation is reversible with respect to lateral manipulations, enabling tunable donor–acceptor molecular switches activated by on-surface coordination.