Molecular Resonance Imaging and Manipulation of Hexabenzocoronene on NaCl(001) and KBr(001) on Ag(111)

The adsorption of hexa-<i>peri</i>-hexabenzocoronene (HBC) on NaCl and KBr bilayers deposited on Ag(111) is studied by scanning tunneling microscopy (STM) and spectroscopy at low temperature (5 K). HBC tends to move under the influence of the STM tip on NaCl/Ag(111), even in the mildest imaging conditions, preventing the imaging of its molecular electronic resonances (MERs). It is more stable on KBr, due to a higher diffusion barrier, as confirmed by a force-field based calculation of its adsorption on both surfaces. The MER associated with the lowest unoccupied molecular orbital (LUMO) of HBC is imaged and analyzed in detail on KBr/Ag(111). Assemblies of two to four HBC could be built on NaCl by lateral manipulations with the STM tip. These objects present a higher stability than single molecules making them more amenable to MER imaging in a large bias voltage range. While the constituting molecules are too far apart to interact chemically, their electronic clouds overlap, producing in some cases complex images of the MERs that are difficult to disentangle to extract the single molecule contributions. This problem is examined by comparing the images of a two HBC assembly to those of a single molecule on KBr. A combination rule is proposed that could be extended to extract single molecule contributions from larger assemblies

Scanning Tunneling Microscope Tip-Induced Formation of a Supramolecular Network of Terarylene Molecules on Cu(111)

Bottom-up approaches allow for molecular-level control of engineering new nanostructures. For next-generation molecular circuits, machines, and phase-change materials, supramolecular structure formation and interactions must be investigated on a two-dimensional solid substrate. Scanning tunneling microscopy (STM) provides a method not only to address such supramolecular structures at the molecular level on a solid surface but also to locally control and manipulate such structures. In this article, we show that a terarylene molecule, a subfamily of photoswitching diarylethenes that promise a lot of applications from molecular switches to photoelectronics, assembles upon application of a bias voltage pulse from an STM tip. We show that molecules organize themselves in order to align their dipole moment to follow those of the electric field induced in the tunneling junction. The 2D assembly is stabilized by π–π stacking interactions and van der Waals interactions. This expands the repertoire of currently available bottom-up techniques for fabrication of supramolecular nanostructures

UHV-STM Investigations and Numerical Calculations of a Ruthenium β-Diketonato Complex with Protected Ethynyl Ligand: [Ru(dbm)₂(acac-TIPSA)]

The quest of molecular electronic devices necessitates addressing model molecular systems as starting points. Among the targeted functions, electron transfer between specific moieties inside a molecule is expected to play a fundamental role for ultimate logical gates. Here we propose a coordination complex exhibiting two inorganic centers (Ru and Si) that constitutes a step toward a more complex architecture. Starting from the complex <b>1</b> [Ru­(dbm)₂(acac-I)] (dbm = dibenzoylmethanate ion, acac-<i>I</i> = 3-iodo-2,4-pentanedionate ion), the complex <b>2</b> [Ru­(dbm)₂(acac-TIPSA)] (acac-TIPSA = 3-(triisopropylsilyl)­acetylene-2,4-pentanedionate ion) was obtained through Sonogashira cross coupling reaction under classical conditions. This complex <b>2</b> was characterized by elemental analysis, IR, ¹H NMR, ¹³C NMR, UV–vis, cyclic voltammetry, mass spectroscopy as well as X-ray single-crystal diffraction. It crystallized with empirical formula of C₄₆H₄₉O₆Ru₁Si₁ in a monoclinic crystal system and space group <i>P</i>2₁/<i>c</i> with <i>a</i> = 21.077(3) Å, <i>b</i> = 9.5130(7) Å, <i>c</i> = 21.8790(12) Å, β = 94.125(7)°, <i>V</i> = 4375.5(7) ų and <i>Z</i> = 4. Additionally, scanning tunneling microscopy measurements at liquid He temperature and in an ultrahigh vacuum (UHV-STM) were conducted on complex <b>2</b> on a Ag(111) surface. The STM images, supported by adsorption and STM image calculations, demonstrate that the molecules exist in two stable forms when adsorbed on the metallic surface