No abstract

The divergent polyphenylene dendrimer synthesis of the largest chemically monodisperse molecules to date, up to 28 nm at 271.6 kDa for the sixth generation, is presented. Monodispersity, conformational flexibility, and an assembly behavior reminiscent of multimeric proteins for the locally stiff, macroporous dendrimers were evaluated with a combination of molecular and polymer characterization tools, namely size exclusion chromatography, atomic force microscopy, ultrahigh-mass MALDI-TOF mass spectrometry, and dynamic light scattering. Remarkably, the high-precision MegaDalton assembly of shape-adaptable dendrimers occurs in the absence of electrostatic or hydrogen-bonding interactions and is the product of Lilliputian solvophobic interactions, mediated by the dendrimer arm size, shape, and stiffness. This covalent/noncovalent approach offers a general molecular shaping motif that is completely different than what has been previously accessible with conventional self-assembly.

Different generation polyphenylene dendrimers possessing eight diphenylacetylene units in the dendritic scaffold between the layers of the first and second generation have been synthesized by using a new p-phenylene ethynylene-functionalized tetraphenylcyclopentadienone branching unit. The heterogeneous hydrogenation of the embedded triple bonds in the final dendrimers was successfully performed via heterogeneous catalysis. Moreover a "softening" effect of the dendritic structure in consequence of the hydrogenation is observed, allowing for the first time the investigation of this effect upon size, shape, and intramolecular voids in the case of similar dendrimer pairs. Quartz microbalance studies revealed that upon hydrogenation the capacity in host uptake is decreased allowing the incorporation of a lower number of guest molecules compared to the parent materials.