A R T I C L E S
Oesterling and Mu¨llen
Scheme 1. Variation of the Chromophore Location in the AB2
Branching Agent: (A) Side Chains and (B) Backbone
Figure 1. Chemical structures of unsubstituted peryleneimide chro-
mophores: perylene-3,4-dicarboximide (PMI) and perylene-3,4,9,10-tetra-
carboxdiimide (PDI).
concomitant decrease in fluorescence intensity.11 Hence, the
chromophore interactions within these dendrimers are rather
complex, and their study is further inhibited by the often low
photostability and fluorescence quantum yields of the chosen
chromophores.12
coefficients, and a fluorescence quantum yield of ∼1.18 These
properties render them attractive candidates for single-molecule
spectroscopy.
The insertion of fluorescent dyes into the scaffold of a rigid
dendrimer can lead to a variety of new and desirable proper-
ties: (i) the number of dyes within the nanoemitter is not
restricted to the number of the possible surface functions; (ii)
the distance between individual dyes in the same or different
generations is defined by the design of the branching units; and
(iii) as the number of chromophores increases within the
dendrimer generations, the intensity of the overall absorption
or emission increases, as does the sensitivity of molecular probes
and biological labels as well. Accordingly, a large number of
chromophores within a confined, well-defined volume is desir-
able.
Herein, we report two different methods of inserting peryle-
neimide dyes into the scaffolding of polyphenylene dendrimers.
In each route, functionalization of the tetraphenylcyclopenta-
dienone branching reagent with peryleneimides is the key step,
resulting in a dendritic branching unit carrying two perylene-
imides and two triisopropylsilyl (TIPS)-protected terminal
alkynes for further dendritic growth. In the first case (route A,
Scheme 1), a chromophore was attached to the phenylene rings
at the R-position of the cyclopentadienone. In the second case
(route B, Scheme 1), the dyes were inserted between the
phenylene rings at the â-position and the alkyne. The dye units
thereby act as stiff spacers between the diene and the dienophile,
maintaining the rigid nature of the resulting dendrimer. The
spacer extends the diameter of the resulting dendrimers com-
pared to the parent polyphenylene dendrimer by approximately
a pentaphenyl moiety per generation. This approach has been
successfully carried out with a p-terphenyl spacer up to the fifth
generation to yield a diameter above 20 nm (see Figure 2).19
Using PDI as a spacer, the buildup of even larger nanoparticles
with an even higher number of generations should be possible.
Furthermore, the insertion of the PDI as a “functional” spacer
permits the material to be used in a number of applications not
accessible to the dendrimer containing the p-terphenyl spacer,
We have recently shown that the use of shape-persistent
polyphenylene dendrimers as rigid dendritic scaffolds ensures
the spatial separation of chromophores. Thus, after loading a
polyphenylene dendrimer with perylenedicarboxmonoimide
(PMI, see Figure 1), the chromophores on the surface do not
show detectable intramolecular aggregation.13 Furthermore, the
interchromophore distances are well defined, which makes them
perfect candidates for investigating excitation energy transfer,
especially at the single-molecule level.14,15
Polyphenylene dendrimers are made by repetitive Diels-
Alder reactions using an ethynyl-functionalized core and a
tetraphenylcyclopentadienone derivative as the branching agent,
leading to pentaphenylbenzene repeating units. The benzene
rings are twisted out-of-plane, and the polyphenylene dendrimers
show high thermal and photochemical stabilities as well as shape
persistence.16
Besides the surface functionalization of polyphenylene den-
drimers with PMI, a variety of polyphenylene dendrimers have
been synthesized carrying perylenetetracarboxdiimide (PDI, see
Figure 1) as the core.17 These dendronized dyes have excellent
thermal, chemical, and photochemical stabilities, high extinction
(11) Stewart, G. M.; Fox, M. A. J. Am. Chem. Soc. 1996, 118, 4354-4360.
(12) Neuwahl, F. V. R.; Righini, R.; Adronov, A.; Malenfant, P. R. L.; Fre´chet,
J. M. J. J. Phys. Chem. B 2001, 105, 1307-1312.
(13) (a) De Belder, G.; Jordens, S.; Lor, M.; Schweitzer, G.; De, R.; Weil, T.;
Herrmann, A.; Wiesler, U. K.; Mu¨llen, K.; De Schryver, F. C. J. Photochem.
Photobiol. A: Chem. 2001, 145, 61-70. (b) Weil, T. Ph.D. thesis, Johannes
Gutenberg-University of Mainz, 2002.
(14) (a) Liu, D. J.; De Feyter, S.; Cotlet, M.; Stefan, A.; Wiesler, U. M.;
Herrmann, A.; Grebel-Koehler, D.; Qu, J. Q.; Mu¨llen, K.; De Schryver, F.
C. Macromolecules 2003, 36, 5918-5925. (b) Masuo, S.; Vosch, T.; Cotlet,
M.; Tinnefeld, P.; Habuchi, S.; Bell, T. D. M.; Oesterling, I.; Beljonne,
D.; Champagne, B.; Mu¨llen, K.; Sauer, M.; Hofkens, J.; De Schryver, F.
C. J. Phys. Chem. B 2004, 108, 16686-16696. (c) Christ, T.; Kulzer, F.;
Weil, T.; Mu¨llen, K.; Basche´, T. Chem. Phys. Lett. 2003, 372, 878-885.
(15) Jordens, S.; De Belder, G.; Lor, M.; Schweitzer, G.; Van der Auweraer,
M.; Weil, T.; Herrmann, A.; Wiesler, U. M.; Mu¨llen, K.; De Schryver, F.
C. Photochem. Photobiol. Sci. 2003, 2, 1118-1124.
(16) Zhang, H.; Grim, P. C. M.; Foubert, P.; Vosch, T.; Vanoppen, P.; Wiesler,
U. M.; Berresheim, A. J.; Mu¨llen, K.; De Schryver, F. C. Langmuir 2000,
16, 9009-9014.
(17) (a) Herrmann, A.; Weil, T.; Sinigersky, V.; Wiesler, U. M.; Vosch, T.;
Hofkens, J.; De Schryver, F. C.; Mu¨llen, K. Chem. Eur. J. 2001, 7, 4844-
4853. (b) Qu, J. Q.; Pschirer, N. G.; Liu, D. J.; Stefan, A.; De Schryver, F.
C.; Mu¨llen, K. Chem. Eur. J. 2004, 10, 528-537.
(18) (a) Graser, F.; Ha¨dicke, E. Liebigs Ann. Chem. 1980, 1994-2011. (b)
Rademacher, A.; Markle, S.; Langhals, H. Chem. Ber. 1982, 115, 2927-
2934. (c) Nagao, Y.; Misono, T. Dyes Pigm. 1984, 5, 171-188.
(19) Andreitchenko, E. V.; Clark, C. G.; Bauer, R. E.; Lieser, G.; Mu¨llen, K.
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4596 J. AM. CHEM. SOC. VOL. 129, NO. 15, 2007