Influence of Chlorine Substitution on the Self-Assembly of Zinc Phthalocyanine

Temperature-dependent phase composition of fluorinated zinc phthalocyanine thin films and their sensing properties towards gaseous NO2

This work presents a temperature-dependent phase composition study of thin films (200 nm) of fluorinated zinc phthalocyanines (4F, 16F) and their chemiresistive response towards NO2 gas.

p-Type and n-type conductometric behaviors of octachloro-metallophthalocyanine-based heterojunctions, the key role of the metal

In the present work, we determined the electrical properties of octachlorinated metallophthalocyanines with Co(II) and Cu(II) ions as metal centers. We engaged them in heterojunctions, with lutetium bisphthalocyanine as a partner. Surprisingly, cobalt and copper complexes show opposite behaviors, the first being an [Formula: see text]-type material whereas the latter is a [Formula: see text]-type material, as deduced from the response of the heterojunctions towards ammonia; showing the unusual key role played by the metal center. While the LuPc[Formula: see text]/Cu(Cl[Formula: see text]Pc) complex exhibits a negative response to ammonia, the LuPc[Formula: see text]/Co(Cl[Formula: see text]Pc) complex exhibits a positive response to ammonia, with a sensitivity of 1.47% ppm[Formula: see text] at concentrations lower than 10 ppm and a limit of detection of 250 ppb. All the devices operate at room temperature and in real atmosphere.

Off-Center Rotation of CuPc Molecular Rotor on a Bi(111) Surface and the Chiral Feature

Molecular rotors with an off-center axis and the chiral feature of achiral CuPc molecules on a semi-metallic Bi(111) surface have been investigated by means of a scanning tunneling microscopy (STM) at liquid nitrogen (LN₂) temperature. The rotation axis of each CuPc molecular rotor is located at the end of a phthalocyanine group. As molecular coverage increases, the CuPc molecules are self-assembled into various nanoclusters and finally into two-dimensional (2D) domains, in which each CuPc molecule exhibits an apparent chiral feature. Such chiral features of the CuPc molecules can be attributed to the combined effect of asymmetric charge transfer between the CuPc and Bi(111) substrate, and the intermolecular van der Waals interactions.

Observation and modeling of conformational molecular structures driving the self-assembly of tri-adamantyl benzene on Ag(111)

A STM image of the hexagonal network of tri-adamantyl benzene molecules on Ag(111).

Extended halogen bonding between fully fluorinated aromatic molecules

Halogen bonding is a noncovalent interaction where an electrophilic cap on a halogen atom, the so-called σ-hole, attracts a nucleophilic site on an adjacent molecule. The polarizability of halogens relates to the strength of the σ-hole, and accordingly the halogen-halogen distance becomes shorter in the order of Cl, Br, and I. Fully fluoro-substituted aromatic molecules, on the contrary, are generally believed not to form halogen bonds due to the absence of a σ-hole. Here, we study atomic-scale in-plane F-F contacts with high-resolution force microscopy. Our ab initio calculations show that the attractive dispersion forces can overcome the electrostatic repulsion between the fluorine atoms, while the anisotropic distribution of the negative electrostatic potential leads the directional bond and even changes the gap. The coexistence of these two competing forces results in the formation of a "windmill" structure, containing three C-F···F bonds among neighboring molecules. While the σ-hole is absent, the scheme of the C-F···F bonding has a high similarity to halogen bonding.

Supramolecular self-assembly of metal-free naphthalocyanine on Au(111)

The self-assembly of metal-free naphthalocyanine (H2Nc) on the Au(111) surface is studied under ultrahigh vacuum conditions at room temperature using a combination of scanning tunnelling microscopy (STM), low-energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS). The STM measurements reveal that the molecules form a well-ordered, defect-free structure with a square-like unit cell at monolayer coverage with their molecular plane parallel to the substrate plane. The molecular lattice direction is aligned along one of the principal directions of the underlying Au(111) substrate while the molecular orientation remains unchanged for different domains. XPS measurements show that there is no significant difference in the electronic structure of H2Nc between monolayer and multilayer coverage. Combining the information obtained from STM, LEED and XPS measurements demonstrates that the self-assembled structure of H2Nc on Au(111) is mainly stabilized by intermolecular interactions while the molecule-substrate interactions are responsible for the rotational alignment of the molecules with respect to the principal Au directions.

Understanding the adsorption of CuPc and ZnPc on noble metal surfaces by combining quantum-mechanical modelling and photoelectron spectroscopy

Phthalocyanines are an important class of organic semiconductors and, thus, their interfaces with metals are both of fundamental and practical relevance. In the present contribution we provide a combined theoretical and experimental study, in which we show that state-of-the-art quantum-mechanical simulations are nowadays capable of treating most properties of such interfaces in a quantitatively reliable manner. This is shown for Cu-phthalocyanine (CuPc) and Zn-phthalocyanine (ZnPc) on Au(111) and Ag(111) surfaces. Using a recently developed approach for efficiently treating van der Waals (vdW) interactions at metal/organic interfaces, we calculate adsorption geometries in excellent agreement with experiments. With these geometries available, we are then able to accurately describe the interfacial electronic structure arising from molecular adsorption. We find that bonding is dominated by vdW forces for all studied interfaces. Concomitantly, charge rearrangements on Au(111) are exclusively due to Pauli pushback. On Ag(111), we additionally observe charge transfer from the metal to one of the spin-channels associated with the lowest unoccupied π-states of the molecules. Comparing the interfacial density of states with our ultraviolet photoelectron spectroscopy (UPS) experiments, we find that the use of a hybrid functionals is necessary to obtain the correct order of the electronic states.

Step-by-step on-surface synthesis: from manganese phthalocyanines to their polymeric form

On-surface reaction of tetracyanobenzene molecules with Mn atoms is presented.

Structures and orientations of cobalt phthalocyanine adsorbed on Sb(111)

The structures and orientations of cobalt phthalocyanine (CoPc) adsorbed on Sb(111) were investigated by low-temperature scanning tunneling microscope. We found that at the initial coverage molecular domains formed both on the terraces and at the vicinity of step edges that were saturated by molecular chains in advance. With the increasing of molecular coverage, the alternately arranged molecular rows of CoPc adsorbed on the bridge sites of Sb(111) and the orientations of them were rotated by 14° ± 2° with respect to the [-101] direction. At the coverage above one monolayer, the molecules of the second layer were assembled along the directions of the underlying molecular rows and showed similar configurations. Consequently, the second-layer CoPc molecules interacted with neighboring molecules via π orbitals, resulting in the observation of overlapped molecular orbitals.

Locking the free-rotation of a prochiral star-shaped guest molecule inside a two-dimensional nanoporous network by introduction of chlorine atoms

Two star-shaped triazatrinaphthylene (TrisK) derivatives form highly-organized nanoporous honeycomb networks when adsorbed at the n-tetradecane/HOPG interface. STM reveals that replacing three H-atoms by three Cl-atoms in the chemical structure of the TrisK skeleton results in locking the free-rotation of the guest molecules inside the pore of the host network as a result of symmetry breaking.

Scanning tunneling microscopy investigation of self-assembled CuPc/F16CuPc binary superstructures on graphite

The self-assembly of the binary molecular system comprising copper(II) phthalocyanine (CuPc) and copper-hexadecafluoro-phthalocyanine (F(16)CuPc) on graphite has been investigated by in situ low-temperature scanning tunneling microscopy (LT-STM). The adsorption of this binary molecular system on graphite results in the formation of a well-ordered chessboardlike nanopattern. The in-plane molecular orientation of the guest CuPc molecules can be tuned by varying the coverage. At low coverage, the sparse CuPc molecules are randomly embedded in the host F(16)CuPc monolayer, possessing two different in-plane orientations; as the CuPc coverage increases, the in-plane molecular orientations of CuPc and F(16)CuPc become unidirectional and a highly ordered chessboardlike pattern forms. Molecular dynamic (MD) simulation results suggest that the selective and directional intermolecular hydrogen bonding determines the in-plane molecular orientation as well as the supramolecular packing arrangement.

Interface dipole formation of different ZnPcCl(8) phases on Ag(111) observed by Kelvin probe force microscopy

Recently, we investigated the adsorption of octachloro zinc phthalocyanine (ZnPcCl(8)) on Ag(111) by scanning tunneling microscopy. Compared to the standard phthalocyanine, halogenated phthalocyanine molecules show a much more complex binding behavior, which results in the formation of three different structural phases. These phases follow from the ordering process with the formation of 8, 4 and 0 intermolecular hydrogen-halogen bonds (Abel et al 2006 ChemPhysChem 7 82). In the present work we investigate these phases by Kelvin probe force microscopy in order to quantitatively deduce the electric interface barrier of the first monolayer. Our measurements reveal that the binding behavior does not only affect the structural ordering but also the interface dipole formation, which leads to different work functions. The fact that we observe interface barriers of opposite signs between ordered and disordered molecular layers underlines the importance of exactly knowing the molecular arrangement at the interface when assembling organic molecule devices.