Mimicking Chlorophyll Assembly

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Science  08 Aug 2003:
Vol. 301, Issue 5634, pp. 735
DOI: 10.1126/science.301.5634.735a

Natural photosynthesis relies on precisely organized groups of dye molecules for the absorption of light energy and its conversion into charge separation. It would be desirable to be able to use these kinds of assemblies in electronic devices built on organic molecules, but it has been difficult to fabricate the sort of complex structures seen in nature.

Würthner et al. describe a structure based on highly polarizable merocyanine dyes. By attaching nonpolar substituents to the dyes, the authors increased the solubility of the dyes in low-polarity solvents; in these solvents, electrostatic interactions between the dye portions of the molecules are favored, leading to dimer formation. Joining two dye moieties with one bridging substituent leads to the formation of stable polymeric aggregates. As the dye concentration is increased further, a complex hierarchical assembly ensues. First, the supramolecular polymer adopts a helical shape. Second, these polymers aggregate into a rod-like bundle of six helical strands. Finally, at high concentrations, these rods or columns form a hexagonal arrangement, which resembles that of chlorophyll dye molecules in some bacteria. — JFU

Angew. Chem. Int. Ed. 42, 3247 (2003).

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