Ordering aspects and intramolecular conformation of tetraphenylporphyrins on Ag(111)

Abstract

A systematic scanning tunnelling microscopy study of the self-assembly, intramolecular conformation and supramolecular ordering of different tetraphenylporphyrins (xTPP) with or without a central metal atom (x = 2H, Fe, Co) on Ag(111) at room temperature is presented. The investigation covers a wide range, i.e. the adsorption behaviour from the low sub-monolayer up to the multilayer regime is described in detail and conclusively discussed in regard to molecule-molecule and molecule-substrate interactions. At monolayer coverage the molecules self-assemble in domains with a square unit cell caused by "T-type" intermolecular interactions, while the orientation of the domains along the symmetry axes is determined by adsorbate-substrate interactions. Interestingly for ordered monolayers domain boundaries always separate domains of different organizational chirality but same orientation of the square unit cell. This demonstrates that in the particular system chirality obviously restricts the long range order of the supramolecular TPP assemblies. In combination with DFT calculations it is also demonstrated that the previously reported intramolecular saddle shape deformation of TPPs upon adsorption is more pronounced for metallo-TPP than for 2HTPP.

Adsorption of cobalt (II) 5,10,15,20-tetrakis(2-aminophenyl)-porphyrin onto copper substrates: Characterization and impedance studies for corrosion inhibition

“…An indication of this multilayer are the bright dots, observed in the AFM images ( Figure 5), attributed initially to the aggregated islands of Co(II)(T(o-NH 2 )PP), which form a square unit cell of a lattice in the multilayer induced by the substrate/adsorbate interactions [40]. The islands and the lattice are formed due to the compression because of a considerable tilt angle of the individual porphyrins in the multilayer, i.e.…”

“…the porphyrin plane is not parallel with the surface. The angle tilt could be caused by specific interactions between the molecules in the top layer or by a rough topography of the first layer, which serves as a substrate for the multilayer [40]. The best way to explain this multilayer formation is to assume an attractive lateral interaction between the different self-assembled layers of the porphyrin complex.…”

“…Two types of attractive interactions of the 8 phenyl rings of the TPPs (tetraphenyl porphyrin) appear to be likely, namely п-п stacking or Tstacking, which also plays a key role in biological recognition. This means the phenyl groups of the individual porphyrins are either parallel (π-π) or perpendicular (T-type) to each other [40].…”

“…The film coverage is calculated by the ratio of the charge transfer resistance of the bare and the modified surface [40]. The coverage (θ) of the film is defined using the following expression:…”

Charge-induced distortion and stabilization of surface transfer doped porphyrin films

“…The completely close-packed structure, detailed in Figure 2(b), is due to an edge-to-face stacking of the phenyl rings rather than a face-to-face π -π stacking. 27 Buchner et al 28 adjacent porphyrin phenyl rings preferably appear to be in the edge-to-face "T-shape" stacking configuration. Even though the unit cell is almost perfectly square with a = b = 1.4 nm and θ = (88 ± 1) • , the intramolecular conformation does not exhibit a perfect "cross-like" geometry, given δ = (34 ± 1) • and γ = (66 ± 1) • (angles of the opposite phenyl rings with respect to the unit cell), where δ + γ = 100 • > 90 • .…”