Scattering of electrons by localized spins is the ultimate process enabling electrical detection and control of the magnetic state of a spin-doped material. At the molecular scale, this scattering is mediated by the electronic orbitals hosting the spin. Here we report the selective excitation of a molecular spin by electrons tunneling through different molecular orbitals. Spatially-resolved tunneling spectra on iron porphyrins on Au(111) reveal that the inelastic spin excitation extends beyond the iron site. The inelastic features also change shape and symmetry along the molecule.Combining DFT simulations with a phenomenological scattering model, we show that the extension and lineshape variations of the inelastic signal are due to excitation pathways assisted by different frontier orbitals, each of them with a different degree of hybridization with the surface. By selecting the intramolecular site for electron injection, the relative weight of iron and pyrrole orbitals in the tunneling process is modified. In this way, the spin excitation mechanism, reflected by its spectral lineshape, changes depending on the degree of localization and energy alignment of the chosen molecular orbital. arXiv:1708.01268v2 [cond-mat.mes-hall]

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Functionalized naphthalene diimides (NDIs) are attractive candidates as small molecule acceptors for various molecular electronic applications due to their reversible two-step one-electron reductions at relatively low potentials. Here, we utilize low-temperature scanning tunneling microscopy (STM) to study the spatial extent and the electronic structure of 2,7-dibenzyl 1,4,5,8-naphthalenetetracarboxylic diimide (BNTCDI) adsorbed on the Pt(111) surface. We succeeded to map in real space the electronic structure of this three-dimensional (3D) molecule with orbital resolution, and thus were able to image an in-plane π-nodal plane located at the benzyl side arms. Furthermore, on the basis of the comparison of voltage dependent STM images and ab initio density functional theory simulations, we are able to explain the STM features of BNTCDI in terms of a convolution between its 3D shape and electronic structure. Importantly, for this weakly coupled molecule on the Pt(111) substrate, the intramolecular N•••H−C hydrogen bonds (i) stabilize the protruding π-systems of the benzyl groups perpendicular to the flat NDI core and (ii) open an effective transport path around Fermi energy.

Naphthalene diimide (NDI) derivatives are extensively studied in the field of supramolecular and materials chemistry due to their versatility in coordination, electron deficiency, and planar aromatic core. Here, we report on the self-assembly behavior and the electronic properties of 2,7dibenzyl-1,4,5,8-naphthalenetetracarboxylic diimide (BNTCDI) studied by low-temperature scanning tunneling microscopy. BNTCDI adsorbed on Au(111) is highly mobile and reveals a tendency to form chain structures on the step edges at low coverages. The chains are kept together by intermolecular hydrogen bonds between neighboring NDI backbones. Within the chain structures, the orbital appearance of single molecules was clearly identified. Additionally, supramolecular structures consisting of ordered double layers were observed on terraces for higher surface coverages. The molecule−substrate interaction is investigated in detail via scanning tunneling spectroscopy for different molecular arrangements. The results reveal distinct insights into the subtle balance between intermolecular and interface interactions determining the self-assembly behavior of BNTCDI resulting in chain structures at step edges and ordered double layers on Au(111) terraces.

The donor–acceptor character of a donor–bridge–acceptor molecule is traced along the complexation with a Pt adatom and adsorption on a Pt(111) substrate. The non-planarity enables the partial preservation of the donor–acceptor character.