Nanosized polyphenylene dendrimers based upon pentaphenylbenzene units

A facile divergent synthesis of monodisperse polyphenylene dendrimers having diameters of 21-55 Angstrom is presented. These nanoparticles have been prepared via a [2 + 4] cycloaddition-deprotection sequence using an excess of tetraphenylcyclopentadienone 1a as monomer and the tetraethynylbiphenyl 2 as core. Due to the dense packing of 22, 62 or 142 benzene rings in generations G(1), G(2) and G(3), respectively, the conformational freedom of the higher generations G(2) and G(3) is limited. Molecular mechanics calculations as well as molecular dynamics simulations are included in a discussion of the structure and the shape-persistence of G(2). The calculations revealed that selected inner distances of the molecule varied only 5-10% during the molecular dynamics simulations, thus indicating that the overall shape of the molecule essentially did not change throughout the simulation time.