Dendrimers polyphenylene

Wiesler U-M, Weil T, Mullen K (2001) Nanosized Polyphenylene Dendrimers. 212 1-40 Williams RM, Stocking EM, Sanz-Cervera JF (2000) Biosynthesis of Prenylated Alkaloids Derived from Tryptophan. 209 97-173 Wirth T (2000) Introduction and General Aspects. 208 1-5 Wirth T (2003) Introduction and General Aspects. 224 1-4... 

Bauer RE, Grimsdale AC, Mullen K (2005) Functionalised Polyphenylene Dendrimers and Their Applications. 245 253-286 Beaulac R, see Bussito G (2004) 241 97-118... 

Wessjohann LA, Ruijter E (2005) Strategies for Total and Diversity-Oriented Synthesis of Natural Product(-Like) Macrocycles. 243 137-184 Wiesler U-M,Weil T, Mullen K (2001) Nanosized Polyphenylene Dendrimers.212 1-40 Williams P, see Chhabra SR (2005) 240 279-315... 

Wiesler U-M, Weil T, Mullen K (2001) Nanosized Polyphenylene Dendrimers. 212 1 -40... 

Dendrimers with a polyphenyl core around a central biphenyl unit decorated at the rim with peryleneimide chromophores have been investigated both in bulk and at the single-molecule level in order to understand their time and space-resolved behavior [28]. The results obtained have shown that the conformational distribution plays an important role in the dynamics of the photophysical processes. Energy transfer in a series of shape-persistent polyphenylene dendrimers substituted with peryleneimide and terryleneimide chro-mophoric units (4-7) has been investigated in toluene solution [29]. 

F. Morgenroth, E. Reuther K Mullen, Polyphenylene Dendrimers From Three-Dimensional to Two-Dimensional Structures , Angew. Chem. 1997, 109, 647-649 Angew. Chem. Int. Ed Engl 1997,36,631-634. 

In order to obtain isolated molecules on a surface, fourth generation polyphenylene dendrimers with-... 

Scheme 20. Polyphenylene dendrimers in the 1st 68 and in the 2nd generation 70 which are decorated with fluorescent perylene imide chromophores on the surface. Perylenedicarboxi-mide derivative 69 serves as a model compound for spectroscopic investigations.

Embedding of pinacyanol in a three-dimensional polyphenylene dendrimer results in a red-shift of absorption (from 600 to 620 nm) and emission (from 625 to 648 nm) maxima and in an increase of the quantum yield from 9 x KT4 for free dye in water to 1.4 x 10 2 after insertion in the dendrimeric architecture [71]. This dendrimer was used to develop two FRET systems utilizing cyanine dyes as the donor (DTCI) and the acceptor (pinacyanol and 26a) molecules [72], The FRET system allows the time-resolved detection, where energy transfer can be observed at the single-molecule level. 

Scheme 1. Second generation of polyphenylene dendrimers based on palladium catalyzed coupling (1) and Diels-Alder cycloaddition (2)...

To the best of our knowledge, apart from the above-mentioned systems of Miller and Neenan and the dendrimers presented by our group, no further work on large, highly branched polyphenylene dendrimers has been reported. This chapter will start therefore with the different ways of synthesizing these dendrimers, followed by their functionalization, characterization, and some applications. Finally, we present an outlook describing future work. 

Scheme 3. Divergent synthesis of the polyphenylene dendrimers based on the Diels-Alder cycloaddition... 

The first report of all-phenylene dendrimers was presented in 1990 by Miller and Neenan [10], Via a convergent approach, they coupled arylboronic acids to arylbromides under Suzuki-type conditions to synthesize the first two generations of polyphenylene dendrimers based on 1,3,5-triphenylene building units (Scheme 1). 

Scheme 6. Palladium catalyzed synthesis of polyphenylene dendrimers...

The fourfold cycloaddition of an excess of cyclopentadienone dendron 27 to the tetraethynyltetraphenylmethane 4 in diphenylether at 200°C affords dendri-mer 2 in 85% isolated yield, respectively (see Scheme 7). Dendrimer 2 corresponds to the second-generation polyphenylene dendrimer made by the divergent method [30]. It should be mentioned that while the addition of dendron 27 to the biphenyl core 9 takes two days the addition to the tetraphenylcore 4 takes one week. This can be explained by the higher mobiUty of the biphenylic core compared to the stiff tetrahedral core, which allows the proper orientation of the ethynyl functions for reactions with the bulky dendrons. 

The characterization of our polyphenylene dendrimers via mass spectrometry is particularly valuable because it allows the detection of potential growth imperfections during the [2+4] cycloaddition, even at the higher generations with molecular masses above 20,000 g/mol. In this way, incompletely reacted products give signals at lower molecular masses with characteristic mass differences in comparison to a perfectly reacted dendrimer. 

Beside mass spectrometry, NMR spectroscopy is a useful and widely applied tool to characterize the structure of dendrimers and estimate their purity [37]. In the case of polyphenylene dendrimers NMR spectroscopy is of only limited value for determining structure and purity. This is due to the large number of... 

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