Review of 2H-tetraphenylporphyrins metalation in ultra-high vacuum on metal surfaces (original) (raw)
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Chemistry - A European Journal, 2011
Organic monolayers on metal surfaces allow the realization of new compounds of low-dimensional metal-organic architectures and patterned surfaces, which cannot be achieved by conventional methods. Among organic compounds, porphyrins represent one of the most studied molecules due to the presence of the unsaturated macrocycle, which has alternating single and double bonds inside the ring, making the porphyrins chemically very stable. Moreover, this creates great versatility for these chemical systems, mainly because there are several positions in which different functional groups can be substituted (meso substituents), which influence and introduce new and useful properties. [1] In addition, the macrocycle can host a wide range of metals at the center of the ring, forming metalloporphyrins. [2] In metalloporphyrin monolayers, the interaction of the metal at the center of the molecule with the substrate atoms may play a fundamental role in the adsorption behavior, as well as in the electronic and chemical properties of the systems. The presence of these central metals, the flexibility of the porphyrin core and the rotational degrees of freedom of the meso substituents, permit conformational adaptation of the molecule to its local environment and render these molecules one of the building blocks for metal-organic networks in solid-state chemistry and in molecular engineering. [1][2] Herein, we study the formation on AgA C H T U N G T R E N N U N G (111) of one monolayer of metal-free 2H-tetraphenylporphyrins (2H-TPP). These molecules are of notable importance because they form novel architectures and patterned surfaces, with which an array of catalytic, magnetic, optoelectronic, and sensing materials can be produced simply by evaporating the central metal atom in ultra-high vacuum (UHV). In fact, individual atoms are difficult to arrange in regular patterns. Taking advantage of the highly selective porphyrin complexation kinetics and thermodynamics for different metals and considering that lateral coordination with the molecular ligands yields unsaturated yet stable coordination bonds, 2H-TPP can be used to fabricate two-dimensional arrays of metallic centers with nanometric spacing. Understanding and controlling the properties of such arrays at the interface with metal or semiconductor substrates, constitutes a basic step toward the exploitation of heterogeneous molecularbased devices.
The Journal of Physical Chemistry C, 2011
In-situ metalation of porphyrin molecules in ultrahigh vacuum (UHV) is of great interest for the characterization of pure species in a controlled environment. Here, we report the characterization of the electronic states and the molecules' geometrical adaptation during the formation of pure 2H-5,10,15,20-tetraphenylporphyrin (2H-TPP) and Fe-tetraphenylporphyrin (Fe-TPP) layers on Ag(111) single crystal. Core level absorption spectra indicate the flat conformation of the monolayer suggesting an adatom hopping instead of a surface mediated dopant diffusion for the metalation process. Photoemission points out that the interaction between Fe d z -states and Ag bands increases the monolayer metallic character already induced by the charge transfer from the substrate.
Surface Science, 2006
Monolayers of protoporphyrin-IX molecules are prepared on a Pt(1 1 1) surface by a self-assembly process in order to manufacture organic devices with controlled electronic properties. Scanning tunnelling microscopy (STM) and two-colour sum-frequency generation (2C-SFG) are performed ex situ in ambient air, in order to characterize their molecular conformation and electronic properties at the monolayer level, respectively. STM measurements performed with functionalized gold tips reveal a high covering rate of the metal surface. 2C-SFG measurements highlight CH stretching modes of vinyl substituted groups (RACH@CH 2 ) in the 2800-3200 cm À1 infrared spectral range and particular electronic features in the visible spectral range, i.e. a Soret band red shift and band separation compared to the liquid phase. Moreover, similar measurements are performed on Zn(II)Protoporphyrin-IX and 5-[p-(6-mercaptohexoxy)-phenyl]-10,15,20-triphenylporphin films for comparison. These results suggest a film conformation with the molecules having different tilt angles with respect to the substrate normal, depending on the ion metal presence or the chain length bonded to the porphyrin moiety.
Following the Metalation Process of Protoporphyrin IX with Metal Substrate Atoms at Room Temperature
The Journal of Physical Chemistry C, 2011
The interaction of planar metal complexes, such as porphyrins, phthalocyanines, or corroles (tetrapyrrole molecules), with surfaces is especially interesting for designing novel catalysts, sensors, and other devices. Because of their photophysical properties they are good candidates for the construction of photonic devices, such as solar cells and organic light diodes. 1,2 Depending on the required applications, the properties of these macrocycles can be tailored, for example, by changing the functional groups around the central core or the metal in the center of the core. On the other hand, the chemical reactivity of the metal core may affect the performance of the application devices, for example, by rapid oxidation of the metal, which makes it necessary to work with passivated molecules, or by loss of the metal by interaction with the surfaces. 3 An alternative procedure for handling with these metalomolecules is to start with nonmetalated molecules (free molecules) and metalate them directly on a surface. The incorporation of selected metal atoms into porphyrins and phthalocyanines on the surface, 4À14 also called metalation process, represents an advantage against the direct sublimation of metalomolecules. 4À14 The routes reported in the literature for surface-mediated metalation in ultrahigh vacuum (UHV) conditions involve evaporation of the metal atoms by vapor deposition in the appropriate stoichiometry before or after the molecular deposition, usually followed by annealing of the system formed by the substrateÀmoleculeÀ metal atoms. 4À14 Interestingly, in none of the reported cases was the formation of complexes with the substrate metal atoms detected, although such a mechanism would simplify the surface synthesis of metalloporphyrins and could likely improve some of their properties. Moreover, since the metal core and the substrate atoms are of the same nature, the moleculeÀsubstrate contact can be enhanced. Metalation with the substrate has been suggested but it has never been proven so far. In this work we demonstrate that surface metalation takes place when the protoporphyrin IX (H2PPIX) molecule is deposited on Cu substrates.
Chemistry (Weinheim an der Bergstrasse, Germany), 2014
We explore a photochemical approach to achieve an ordered polymeric structure at the sub-monolayer level on a metal substrate. In particular, a tetraphenylporphyrin derivative carrying para-amino-phenyl functional groups is used to obtain extended and highly ordered molecular wires on Ag(110). Scanning tunneling microscopy and density functional theory calculations reveal that porphyrin building blocks are joined through azo bridges, mainly as cis isomers. The observed highly stereoselective growth is the result of adsorbate/surface interactions, as indicated by X-ray photoelectron spectroscopy. At variance with previous studies, we tailor the formation of long-range ordered structures by the separate control of the surface molecular diffusion through sample heating, and of the reaction initiation through light absorption. This previously unreported approach shows that the photo-induced covalent stabilization of self-assembled molecular monolayers to obtain highly ordered surface co...
Journal of the American …, 2001
Thin films of vapor-deposited Ni(II) octaethylporphyrin (NiOEP) were studied supported on gold. Thin films thermally deposited onto flame-annealed Au (111) were analyzed by ultraviolet photoelectron spectroscopy (UPS) using He I radiation and by X-ray photoelectron spectroscopy (XPS) using Mg KR radiation. Reflectance absorption infrared spectroscopy (RAIRS) was used to study NiOEP films on polycrystalline gold. Scanning tunneling microscopy (STM) and orbital-mediated tunneling spectroscopy (STM-OMTS) were performed on submonolayer films of NiOEP supported on Au(111). The highest occupied π molecular orbitals of the porphyrin ring were seen in both STM-OMTS and in UPS at about 6.4 and 6.8 eV below the vacuum level. The lowest unoccupied π* molecular orbital of the porphyrin ring also was observed by STM-OMTS to be located near 3.4 eV below the vacuum level.
The Journal of Physical Chemistry C, 2014
We present a systematic X-ray standing wave (XSW) study of the πconjugated organic compound 2H-tetraphenylporphyrin (2HTPP) and copper(II)tetraphenylporphyrin (CuTPP) on Cu(111) at room and low temperatures. We exploit the feature of thermally activated self-metalation of 2HTPP to CuTPP to study the influence of the central metal atom on the bonding distance of the molecule to the substrate surface. Comparison between the average adsorption distances of the carbon and nitrogen atoms of 2HTPP reveals a distorted molecule with the nitrogen atoms being closer to the surface than the carbon ones on average. Additionally, the measured positions of the two chemically inequivalent types of nitrogen atoms (iminic and aminic) of 2HTPP indicate a distorted porphyrin ring. After the chemical reaction from 2HTPP to CuTPP at 500 K, no change of the adsorption distance of the carbon skeleton is seen, but the entire molecule becomes flattened. Despite the changes upon metalation, adsorption distances for both molecules show a strong interaction with the substrate in comparison to similar π-conjugated molecules.