page_title: Porphyrin
section_title: Supramolecular chemistry
hierarchical_section_title: Porphyrin / Potential applications / Supramolecular chemistry
caption_attribution_description: (a) Overview STM image (350 × 350 nm2) and close-up STM image (50 × 50 nm2) for submonolayer coverage of porphyrin 1 on Au(111) after adding Co atoms. Rosette structures and 1D polymer chains co-exist. (c) and (d) Zoom-in STM images (10 × 10 nm2) showing rosette structures of two different sizes. The rosette in (c) consists of 12 molecules: 4 molecules in the inner core and 8 molecules in the outer ring, while that in (d) is made up of 15 molecules: 5 molecules in the inner core and 10 molecules in the outer ring. The blue and green bars in (c) and (d) indicate the two different conformational isomers A and B, respectively (cf. Figure S5). The STM images were taken at 77 K with U = –1.8 V, I = 20 pA. The set of three arrows in (a) indicates the principal directions of the underlying substrate.
context_page_description: Porphyrins are a group of heterocyclic macrocycle organic compounds, composed of four modified pyrrole subunits interconnected at their α carbon atoms via methine bridges. The parent of porphyrin is porphine, a rare chemical compound of exclusively theoretical interest. Substituted porphines are called porphyrins. With a total of 26 π-electrons, of which 18 π-electrons form a planar, continuous cycle, the porphyrin ring structure is often described as aromatic. One result of the large conjugated system is that porphyrins typically absorb strongly in the visible region of the electromagnetic spectrum, i.e. they are deeply colored. The name "porphyrin" derives from the Greek word πορφύρα, meaning purple.
  Metal complexes derived from porphyrins occur naturally. One of the best-known families of porphyrin complexes is heme, the pigment in red blood cells, a cofactor of the protein hemoglobin.
context_section_description: Porphyrins are often used to construct structures in supramolecular chemistry. These systems take advantage of the Lewis acidity of the metal, typically zinc. An example of a host–guest complex that was constructed from a macrocycle composed of four porphyrins. A guest-free base porphyrin is bound to the center by coordination with its four-pyridine substituents.
caption: On a gold surface porphyrin derivative molecules (a) form chains and clusters (b). Each cluster in (c,d) contains 4 or 5 molecules in the core and 8 or 10 molecules in the outer shells (STM images).[30]
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