Tetraphenylporphyrin

Tetraphenylporphyrin, abbreviated TPP or H2TPP, is a synthetic heterocyclic compound that resembles naturally occurring porphyrins.

The study of naturally occurring porphyrins is complicated by their low symmetry and the presence of polar substituents.

Tetraphenylporphyrin was first synthesized in 1935 by Rothemund, who caused benzaldehyde and pyrrole to react in a sealed bomb at 150 °C for 24 h.[1] Adler and Longo modified the Rothemund method by allowing benzaldehyde and pyrrole to react for 30 min in refluxing propionic acid (141 °C) open to the air:[2] Despite its modest yields, the synthesis of H2TPP is a common experiment in university teaching labs.

[3][4] Highly efficient routes to H2TPP and many analogues involve the air-free condensation of the pyrrole and aldehyde to give the porphyrinogen.

[citation needed] Unlike natural porphyrins, H2TPP is substituted at the oxidatively sensitive "meso" carbon positions, and hence the compound is sometimes called meso-tetraphenylporphyrin.

Lewis structure for meso-tetraphenylporphyrin
Ball-and-stick model of the tetraphenylporphyrin molecule
Optical properties of tetraphenylporphyrin in toluene
Hydrogen can be removed from individual H 2 TPP molecules by applying excess voltage to the tip of a scanning tunneling microscope (a); this removal alters the I-V curves of TPP from diode like (red curve in b) to resistor like (green curve). Image (c) shows a row of TPP, H 2 TPP and TPP molecules. While scanning image (d), excess voltage was applied to H 2 TPP at the black dot, which instantly removed hydrogen, as shown in the bottom part of (d) and in the re-scan image (e). [ 12 ]