Angewandte Chemie International Edition
Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
For full article and contact information, see Angew. Chem. Int. Ed. 2003, 42 (28), 3247 - 3250
Highly ordered dye aggregates
through stepwise organization
Plants and a whole series of bacteria can trap energy from sunlight. To harvest the light as effectively as possible and to convert it into chemical energy these species have highly developed photosynthesis systems. Hundreds of dye molecules aggregate together in highly ordered nanostructures. Naturally, scientists would love to be able to construct copies of such systems and thus generate novel materials for future opto-electronic components and effective solar cells. However, such highly organized architectures of dye molecules are difficult to create.
Frank Würthner and Sheng Yao from the University of Würzburg and Uwe Beginn from the RWTH Aachen have made a breakthrough. The researchers selected a so-called bis-merocyanin dye as the starting material for their structure. The dye molecule is made up of a central aromatic carbon ring which has three hydrocarbon "tails" and two merocyanin "arms". As the concentration of the dye increases a stepwise self-organization occurs. First, the arms of different molecules pair-up so that a long, disordered, polymer chain is formed. These chains then organize themselves into helical strands. Then, six of these helices twist around each other to form long cylinders. In this structure all the hydrocarbon tails point outwards. If the concentration is increased further the tails force their way into the neighboring cylinders, which organizes the cylinders into tight bundles with hexagonal packing. The result is a gel with liquid-crystal characteristics.
"The construction by self organization and the cylinder-like structure of this surprisingly well-defined dye aggregate is reminiscent of the natural chlorophyll rod aggregates in photosynthetic bacteria. However, the performance of the artificial dyes is still not comparable with that of their natural counterparts," explains Würthner. "By means of structural modifications we hope to be able to make the step to functional complexity in the next few years."