Porphyrins, and phthalocyanines have highly tunable photochemical and electrochemical activity as well as the potential for forming complexes.
Photochromic and photoisomerizable groups have the ability to change their shapes and properties upon exposure to light.
TTF and quinones have more than one stable oxidation state, and therefore can be switched with redox chemistry or electrochemistry. Other units such as benzidine derivatives, viologens groups and fullerenes, have also been utilized in supramolecular electrochemical devices.
Porphyrin
is a heterocyclic macrocycle derived from four pyrroline subunits interconnected via their α carbon atoms via methine bridges . Porphyrins are aromatic and they obey Huckel's rule for aromaticity in that they possess electrons which are delocalized over the macrocycle. The macrocycle, therefore, is a highly-conjugated system, and, as a consequence, is deeply coloured - the name porphyrin comes from a Greek word for purple. The macrocycle has 22 pi electrons.Many porphyrins occur in nature, such as in green leaves and red blood cells, and in bio-inspired synthetic catalysts and devices. The parent porphyrin is porphine, and substituted porphines are called porphyrins.
Benzidine
is the trivial name for 4,4'-diaminobiphenyl, a carcinogenic aromatic amine which has been used as part of a test for cyanide and also in the synthesis of dyes. It has been linked to bladder cancer and pancreatic cancer.
In common with benzidine some other aromatic amines such as 2-aminonaphthalene have been withdrawn from use in almost all industries because they are so carcinogenic.
In the past a common test for blood used benzidine but this has largely been replaced by tests using phenolphthalein / hydrogen peroxide and luminol. An enzyme in blood causes the benzidine to be oxidized to a polymer which is blue coloured. The test for cyanide uses similar chemistry to give the blue colour.