Lightly Switched Gel

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Science  29 Jul 2005:
Vol. 309, Issue 5735, pp. 671
DOI: 10.1126/science.309.5735.671a

The formation of supramolecular assemblies can be controlled through light-induced structural movements, such as cis-trans isomerization, that alter the interactions between weakly bonding molecules. Yagai et al. have characterized disc-shaped hydrogen-bonded hexamers (rosettes) formed from two molecules: one a melamine bearing two long side chains containing azo groups and the other a much smaller cyanurate. In cyclohexane solution, the rosettes formed from the trans-azobenzene isomer can stack through aromatic interactions and bunch into columns that eventually intertwine and gel. Irradiation of the gel with ultraviolet light disrupts the stacking and initially reduces the aggregate size from 52 to 28 nm; further irradiation recovers the isolated rosettes (8-nm aggregates). The dissociation is reversible, and exposure to visible light and subsequent storage in the dark yields the gel with total conversion of the cis isomers back to trans-azobenzenes. — PDS

J. Am. Chem. Soc. 10.1021/ja052645a (2005).

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