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2022

• Inhalt ausklappen Inhalt einklappen Adv. Mater. Interfaces, "On the Role of Collective Electrostatic Effects in Electronic Level Pinning and Work Function Changes by Molecular Adlayers: The Case of Partially Fluorinated DNTTs Adsorbed Flat-Lying on Various Metals and Hetero-Structures"Adv. Mater. Interfaces, "On the Role of Collective Electrostatic Effects in Electronic Level Pinning and Work Function Changes by Molecular Adlayers: The Case of Partially Fluorinated DNTTs Adsorbed Flat-Lying on Various Metals and Hetero-Structures"

  

  Maximilian Dreher, David Cornil, Matthias W. Tripp, Ulrich Koert, Jérôme Cornil and
  Gregor Witte
  Adv. Mater. Interfaces, 2200361 (2022), • Doi:
  10.1002/admi.202200361
  
  Modifying the work function of metal electrodes by monolayers of molecules with
  specifically tailored electronic properties is a versatile tool, but such chemical
  modifications often also affect the adsorption geometry and packing density,
  making microscopic modeling difficult. Using scanning tunneling microscopy, it
  is shown that the recently synthesized partially fluorinated dinaphthothienothiophenes
  (DNTTs) adopt the same interface structure on different metal substrates
  independent of the degree of fluorination. Combining Kelvin probe measurements
  and density functional theory (DFT) calculations, a highest occupied molecular
  orbital (HOMO) pinning effect for such FxDNTTs on Au(111) and Ag(111)
  induced by collective electrostatic interactions in the monolayer is observed.
  Since the adsorption of weakly interacting molecules such as the FxDNTTs is not
  restricted to specific surfaces as is the case with SAMs, this concept is extended
  to metal substrates with quite different work function values. For a low work
  function surface such as Cs(110), a lowest unoccupied molecular orbital (LUMO)
  pinning effect is predicted at the theoretical level. Since such alkali metal surfaces
  are not experimentally accessible, a well-defined Cs monolayer on Cu(100) as a
  low work function substrate is used instead. For this substrate, however, a variation
  is observed in the LUMO energies and the work function as a function of the
  degree of fluorination. This is attributed to the formation of a second interface
  dipole at the buried Cs/Cu interface, which is modulated with the degree of
  fluorination and competes with the dipole at the outer molecule/Cs interface.
  Such a second internal interface dipole, which can be modified by the top layer,
  has to be considered when going to more complex heterointerfaces.

• Inhalt ausklappen Inhalt einklappen CHEM. EUR. J., "Regioselective Fluorination of Acenes: Tailoring of Molecular Electronic Levels and Solid State Properties"CHEM. EUR. J., "Regioselective Fluorination of Acenes: Tailoring of Molecular Electronic Levels and Solid State Properties"

  

  Daniel Bischof, Matthias W. Tripp, Philipp E. Hofmann, Chun-Ho Ip, Sergei I. Ivlev, Marina Gerhard, Ulrich Koert and Gregor Witte
  CHEM. EUR. J., 28, e202103653 (2022), • Doi: 10.1002/chem.202103653
  
  Optoelectronic properties of molecular solids are important for organic electronic devices and are largely determined by the adopted molecular packing motifs. In this study we analyzed such structure-property relationships for the partially regioselective fluorinated tetracenes 1,2,12-trifluorotetracene, 1,2,10,12-tetra­fluoro­tetracene and 1,2,9,10,11-penta­fluoro­­tetracene that were further compared with tetracene and perfluoro-tetracene. Quantum chemical DFT calculations in combination with optical absorption spectroscopy data show that the frontier orbital energies are lowered with the degree of fluorination, while their optical gap is barely affected. However, the crystal structure changes from a herringbone packing motif of tetracene towards a planar stacking motif of the fluorinated tetracene derivatives, which is accompanied by the formation of excimers and leads to strongly red-shifted photolumin with larger lifetimes.