Stabilizing Porphyrin Stacks

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Science  19 Jan 2007:
Vol. 315, Issue 5810, pp. 303
DOI: 10.1126/science.315.5810.303b

Expanded porphyrins are larger versions of the familiar tetrapyrrole compounds. These extended aromatic frameworks could potentially form discotic, liquid-crystalline phases, but the floppiness of the electron-rich structure disrupts stacking.

StEmbedded Imagepieñ et al. have prepared cyclo[8]pyrrole cations bearing phenylalkyl side chains and a central sulfate counter-ion. They find that electron- acceptor molecules such as trinitrobenzene (TNB) form 1:1 adducts with the expanded porphyrins, which leads to changes in color and can produce columnar stacking and the formation of discotic mesophases. This approach, if successfully applied to related explosives such as TNT (trinitrotoluene), might provide a simple visual method for detection or sensing. — PDS

Angew. Chem. Int. Ed. 10.1002/anie.200603893 (2006).

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