Polyphenylene dendrimers with pentafluorophenyl units:: Synthesis and self-assembly

A series of polyphenylene dendrimers (PDs) incorporating additional pentafluorophenyl units have been synthesized. A key building block thereby is the tetrakis(pentafluorophenyl)cyclopentadienone, which serves as the end-capper for making the outer shells of the dendrimers. The variation of the peripheral pentafluorophenyl content was varied using desymmetrized tetraphenylmethane cores for the divergent construction of the dendrimers. The self-assembled nanostructures, prepared by drop-casting solutions of the second-generation species on highly oriented pyrolytic graphite (HOPG), have been investigated by tapping mode atomic force microscopy (AFM). Besides isotropic globular aggregates and percolated networks of nanometer size anisotropic objects, the herein presented dendrimers self-organize into micrometer long nanofibers. The formation of a certain morphology depends upon the amount of pentafluorophenyl rings at the periphery of the dendrimers. Furthermore, it has been observed that by the progressive blending of two dendrimers with different peripheral functionalities a certain control over the length of the formed nanofibers is possible.