Porphyrinphosphonate Fibers on Mica and Molecular Rows on Graphite

Abstract

meso-Tetra(phenyl-p-phosphonate) porphyrin forms rigid and well-separated fibers of monomolecular thickness (2.8 nm) and lengths of several micrometers on mica at pH 13 (octasodium salt). The formation of these fibers could be observed directly by tapping mode scanning force microscopy (SFM) and was induced by capillary forces. Normal height images or images with a topographical inversion were observed depending on the distance of the SFM tip. Amplitude-distance curves indicated that a stable meniscus was formed on hydrophilic surface areas below a tip-sample separation of 20 nm. The meniscus let the original nanorods appear as ditches in the mica surface and enabled rearrangements. A partly protonated form of the same porphyrin (pH 11.5) gave rows of flat-lying porphyrins on graphite, which appear with molecular resolution in SFM images as well as two-dimensional platelets of monomolecular thickness.

Synthesis and Supramolecular Properties of a Novel Octaphosphonate Porphyrin

“…Surface patterning experiments were performed by mixing equimolar solutions (1 × 10 –4 M ) of porphyrin 1 in 0.1 M aqueous NaOH and cyclam 2 in water and then applying them, after ultrafiltration, to a freshly prepared gold surface 7d. An example of the obtained AFM images is shown in Figure 2, which clearly displays wire‐like aggregates.…”

“…Furthermore, the interaction of phosphonates with Zr IV salts has been shown to be a useful strategy to form stable (irreversible) fibrous materials 10. Although many multiporphyrin systems have been reported in the literature, [1–7,10] there are only few examples in which the phosphonate group of the porphyrin of fascinating molecular architectures is self‐assembled on the surface7d,10 or attached to the surface11 for studies of molecular‐based information storage on oxide surfaces. New methodologies to functionalize porphyrins with phosphonate substituents other than normal aromatic groups are of particular interest for the preparation of nanomaterials.…”

Porphyrin Assemblies and Their Scaffolds

“…We now turn to noncovalent porphyrin fibers or "wires" of mono-or bimolecular thickness. They appear on hydrophobic (or lipophilic) highly ordered pyrolytic graphite (HOPG) substrates, 36,37 gold nanoparticles, 38 and hydrophilic silicate spheres. 13,39 A zinc tetraphenylporphyrin with an imidazoyl group on a methine bridge produces 100−300-nm-long molecular tapes on graphite.…”

“…The HOPG surface does not fix the porphyrins but rather allows fast adsorption and slows down crystallization. 37 Anionic silicate surfaces create with the same tetraphosphonate at acidic pH values long fibers of uprightstanding porphyrins and/or monolayers, and at high pH, charge repulsion causes shorter fibers, which tend to a rearrange to disordered monolayers. Zirconium(IV), first envisaged as an optimal cement between the phosphonate groups, precipitates the porphyrins as ill-defined clusters.…”

“…In the H-type aggregates, the porphyrins stack directly over each other, and the slipped packing of J aggregates leads to loose packing and mobility (Figure d). H aggregates are usually poor emitters, whereas J aggregates typically show strong luminescence. − …”