Monodisperse polyphenylene dendrimers up to the fourth generation were synthesized using a divergent growth protocol. By varying the core, dendrimers with dumbbell-, tetrahedral- and propeller-like structures were synthesized. Because of the high-density packing of benzene rings within their branches, these dendrimers are stiff and thus shape persistent. To obtain these dendrimers with a globular shape, a 4-fold (A4B) dendrimer building unit was introduced. In this case, monodisperse dendrimers are obtained only up to the second generation due to the significantly increased density of benzene rings within the structure. For structure elucidation methods, like MALDI−TOF mass spectrometry, NMR spectroscopy, GPC, VPO, TGA, and DSC were used. Dendrimers of the third and fourth generations were visualized by transmission electron microscopy.

A new synthetic approach leading to asymmetrically substituted polyphenylene dendrimers is presented. Following this method, polyphenylene dendrimers decorated with an increasing number of chromophores at the periphery have been obtained up to the second generation. Especially the synthesis of a polyphenylene dendrimer bearing three donor chromophores and one acceptor chromophore has been realized. Intramolecular energy transfer within this molecule is demonstrated by applying absorption and fluorescence measurements.

Individual polyphenylene dendrimer 1 and their self-assembled nanostructures, prepared by spincoating and solvent casting on various substrates such as mica, silanized mica, and highly oriented pyrolytic graphite (HOPG), have been investigated by noncontact atomic force microscopy. Besides globular clusters and monolayers, polyphenylene dendrimer 1 self-organizes into micrometer long nanofibers on a HOPG surface. Fibrillar nanostructures have also been visualized on a silanized mica surface, while on a mica surface the dendrimers only aggregate into globular clusters. Two possibilities for the development of dendrimer nanofibers are proposed.

Well-separated, individual polyphenylene dendrimer molecules have been prepared by spin coating on a mica surface, and subsequently imaged by noncontact atomic force microscopy (NCAFM). The observed height is in good agreement with the size of a single dendrimer molecule, as calculated by molecular dynamics simulation. By using pulsed force mode (PFM) AFM, stiffness and adhesion properties of individual polyphenylene dendrimers have been studied. They could be related to the molecular structure and the chemical nature of the outer surface of the dendrimers and the thin film of water adsorbed on mica when imaged under ambient conditions. Finally, by changing the concentration of the spin-coating solution, two different kinds of aggregates have been characterized.

The fluorescence of polyphenylene dendrimers and the intramolecular energy transfer in polyphenylene dendrimers containing a perylenediimide core have been investigated in this paper. Polyphenylene dendrimers composed of tens or hundreds of out-of-plane twisted phenyl units exhibit strong fluorescence, with quantum yields ranging from 0.2 to 0.5 depending on the dendrimer generation and its degree of functionality. The fluorescence of polyphenylene dendrimers can be efficiently quenched by the incorporated perylenediimide core, and consequently, a predominant emission from the core has been observed, indicating a very efficient intramolecular energy transfer.

No abstract

No abstract

We report on a single-molecule study of a host-guest system that consists of a second-generation polyphenylene dendrimer and the cyanine dye Pinacyanol. The use of single-molecule spectroscopy enables us to obtain more detailed information on the properties of the host-guest system and can be used to confirm solution data. At low dye to dendrimer ratios the system is present as a one-to-one complex, while for higher ratios an ion-pair system is formed. Changes in the spectral properties of the single molecules are explained by differences in local polarisability. The difference of the triplet lifetimes of single free dye molecules and of associated ones is interpreted as deriving from a larger free volume for the dye molecules in the dendritic host relative to the rigid polymer matrix.