A Light Scattering Study of the Self-Assembly of Dendron Rod-Coil Molecules

Dendron rod-coil molecules are a novel supramolecular building block, comprising a dendritic unit, a rodlike unit, and a coil unit (J. Am. Chem. Soc. 2001, 123, 4105). It was proposed that in solution these molecules assemble into ribbonlike aggregates of high aspect ratio. We report here on the self-assembly of DRC-molecules in 2-propanol and ethyl acetate as studied with static and dynamic light scattering. In 2-propanol, aggregation occurs on a time scale of minutes. In ethyl acetate, aggregation proceeds more slowly until an equilibrium is reached. Static light scattering on 2-propanol-based samples reveals the presence of rodlike aggregates that grow with time. The static light scattering data of the ethyl acetate samples could be fitted to Kholodenko’s expression for the form factor of a wormlike chain (Macromolecules 1993, 26, 4179), yielding a persistence length of 45 nm. Dynamic light scattering on ethyl acetate-based samples shows three modes. The dominant mode corresponds to translation of aggregates. Interactions between aggregates are shown to be negligible. The relaxation time spectrum was converted into a mass distribution, showing that only a fraction of the dendron rod-coil molecules aggregate to form the one-dimensional objects. This accounts for the observed low absolute scattering intensity of the solutions studied.