C O M M U N I C A T I O N S
extended aggregates (as it is observed for 1). However, the ion-
triggered aggregation process induces a conformational locking of
the macrocycles in the boat conformation that self-blocks the top
and bottom of the dimer, hindering a further aggregation after the
dimerization. As far as we know, this behavior has not been
described before for shape-persistent macrocycles.
In summary, we have shown by detailed DLS and X-ray
scattering experiments that nanometer-size dicationic shape-
persistent macrocycles in nonpolar solvents do not form infinite
tubular aggregates, as might be expected from their chemical
structure, but dimerize to defined supermolecules. The exclusive
dimerization is not programmed by synthetic efforts but is a result
of the ability of the macrocycles to adopt during the aggregation a
self-complementary shape that blocks the top and bottom of the
supermolecule, thus preventing a further aggregation. It has to be
marked that dimerization occurs even at the lowest investigated
concentration. Currently, we are investigating the concentration and
counterion dependence of the aggregation process further as well
as the behavior of this and other charged macrocycles in different
environments.
Figure 1. (a) CONTIN fit of DLS-derived distribution of 1 in cyclohexane
(1.5 wt %, dashed gray line) and of 2 in cyclohexane (1.4 wt %, solid
line). (b) Experimental scattering intensity of 2 in cyclohexane (O) compared
to theoretical scattering of different models: (dashed black line) tube due
to the packing of 20 macrocycles; (dashed gray line) tube due to the packing
of 100 macrocycles; (gray line) sphere (2.2 nm) (for a scattering vector q
< 1.0 nm-1 the curve superimposes with the scattering curve of the disk);
(black line) disk with a diameter of 4.5 nm and a height of 2.35 nm.
Acknowledgment. Financial support by the Deutsche Fors-
chungsgemeinschaft is gratefully acknowledged. We gratefully
acknowledge beamtime and local support by the ESRF, 6 rue Jules
Horowitz, BP 220, F-38043 Grenoble Cedex, France.
Figure 2. Proposed structure of the supramolecular dimer (only the rigid
backbone of the rings is displayed): the extraannular p-(tert-butyl)phenyl
groups block the top and bottom of the dimer and prevent an aggregation
of the supermolecules.
Supporting Information Available: Synthesis and characterization
of all new compounds as well as information about the X-ray scattering
experiments. This material is available free of charge via the Internet
served scattering data (O) can be clearly distinguished from spheres
and tubular objects of different length. The observed data correspond
well to the calculated scattering profile of a disk with a diameter
of 4.5 nm and a height of 2.35 nm. By assuming a compound
density of 1.14 g/cm3,12 the molecular weight of the scattering object
is calculated to be 10 000 g/mol.
References
(1) For recent reviews on shape-persistent macrocycles, mainly phenylene
ethynylene-based, see: (a) Moore, J. S. Acc. Chem. Res. 1997, 30, 402-
413. (b) Ho¨ger, S. J. Polym. Sci. Part A: Polym. Chem. 1999, 37, 2685-
2698. (c) Haley, M. M.; Pak, J. J.; Brand, S. C. Top. Curr. Chem. 1999,
201, 81-130. (d) Grave, C.; Schlu¨ter, A. D. Eur. J. Org. Chem. 2002,
3075-3098. (e) Zhao, D.; Moore, J. S. Chem. Commun. 2003, 807-818.
(f) Yamaguchi, Y.; Yoshida, Z. Chem.sEur. J. 2003, 9, 5430-5440. (g)
Ho¨ger, S. Chem.sEur. J. 2004, 10, 1320-1329.
(2) (a) Moore, J. S. Curr. Opin. Colloid Interface Sci. 1999, 4, 108-116. (b)
Schmittel, M.; Kalsani, V. Top. Curr. Chem. 2005, 245, 1-53.
(3) Ghadiri, M. R.; Kobayashi, K.; Granja, J. R.; Chadha, R. K.; McRee, D.
E. Angew. Chem., Int. Ed. Engl. 1995, 34, 93-95.
(4) Nakamura, K.; Okubo, H.; Yamaguchi, M. Org. Lett. 2001, 3, 1097-1099.
(5) A dimeric sandwich-like structure has been proposed for the complexes
between Cs+-induced tubular self-assembly of Schiff-base macrocycles
but not investigated in detail: Gallant, A. J.; MacLachlan, M. J. Angew.
Chem., Int. Ed. 2003, 42, 5307-5310.
(6) Kalsani, V.; Ammon, H.; Ja¨ckel, F.; Rabe, J. P.; Schmittel, M. Chem.s
Eur. J. 2004, 10, 5481-5492.
(7) Ho¨ger, S.; Bonrad, K.; Mourran, A.; Beginn, U.; Mo¨ller, M. J. Am. Chem.
Soc. 2001, 123, 5651-5659.
(8) (a) Rosselli, S.; Ramminger, A.-D.; Wagner, T.; Silier, B.; Wiegand, S.;
Ha¨ussler, W.; Lieser, G.; Scheumann, V.; Ho¨ger, S. Angew. Chem., Int.
Ed. 2001, 40, 3138-3141. (b) Rosselli, S.; Ramminger, A.-D.; Wagner,
T.; Lieser, G.; Ho¨ger, S. Chem.sEur. J. 2003, 9, 3481-3491.
(9) Ho¨ger, S.; Rosselli, S.; Ramminger, A.-D.; Enkelmann, V. Org. Lett. 2002,
4, 4269-4272.
(10) Provencer, S. W. Makromol. Chem. 1979, 180, 201-209.
(11) For some pyridyl macrocycles see ref 1f and additionally, see: (a) Tobe,
Y.; Nagano, A.; Kawabata, K.; Sonoda, M.; Naemura, K. Org. Lett. 2000,
2, 3265-3268. (b) Campbell, K.; McDonald, R.; Branda, N. R.;
Tykwinski, R. R. Org. Lett. 2001, 3, 1045-1048. However, we are not
aware of any reports about quarternized structures.
(12) Data from ref 8b and: Fischer, M.; Lieser, G.; Rapp, A.; Schnell, I.;
Mamdouh, W.; De Feyter, S.; De Schryver, F. C.; Ho¨ger, S. J. Am. Chem.
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(13) MM calculations have shown that the boat and chair conformations of
shape-persistent phenylene ethynylene macrocycles of this type are
energetically slightly favored over the planar conformation (ref 7). A
computational analysis explaining at a molecular level the preference of
2 for dimerization over oligomerization is in progress.
(14) (a) Cram, D. J.; Cram, J. M. Container Molecules and Their Guests; Royal
Society of Chemistry: Cambridge, 1994. (b) Ungaro, R.; Pochini, A.;
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197-201.
The results of the X-ray scattering experiments and DLS
experiments undoubtedly show that the quarternization of the
slightly aggregating macrocycles 1 does not lead to the formation
of extended tubular structures in the nonpolar solvent, as it is was
expected. Rather, the DLS and X-ray scattering experiments indicate
the presence of well-defined dimers of the amphiphile 2 in the
cyclohexane solution. This is also confirmed by the size of the disk
described above. A simple computer model of 2 (stiff cycle, random
walk side chains) gives an idea of the size of one macrocycle: Its
scattering can be described by a disk with a diameter of 4.3 nm
and a thickness of 1.1 nm, that is, half the disk thickness that was
extracted from the experimental scattering data. It should be noted
that within the investigated concentration regime (0.005-1.4 wt
%) no large aggregates could be detected, but dimerization occurs
completely even at the lowest concentration.
Although on first glance an infinite aggregation should be
preferred to shield the charged parts of the macrocycle from the
nonpolar cyclohexane environment, the exclusive dimer formation
can be explained with a boat conformation of the macrocycles in
which the pyridinium groups point into the dimer center that
accommodates the four bromide ions (Figure 2).13
The proposed structure resembles sandwich-type complexes of
crown ethers or inclusion complexes of calixarenes.14 As pointed
out before, well-defined aggregates of shape-persistent macrocycles
are only scarcely observed.3-5 In the cases reported before, the
structure and functionality of the single macrocycle determines the
preference of dimerization over infinite aggregation. In the example
described here, the macrocycle is in principle capable of forming
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