Design and structural analysis of the first spherical monodendron self- organizable in a cubic lattice [19]

Full text of DOI:10.1021/ja9943400

J. Am. Chem. Soc. 2000, 122, 4249-4250
4249
Design and Structural Analysis of the First Spherical
Monodendron Self-Organizable in a Cubic Lattice
Scheme 1. Self-assembly of Conical Monodendrons into
Supramolecular Spherical Dendrimers and the Subsequent
Self-Organization of the Supramolecular Dendrimers in a
Pm 3h n Cubic Lattice
,
†
†
‡
Virgil Percec,* Wook-Dong Cho, Martin M o¨ ller,
‡
§
Svetlana A. Prokhorova, Goran Ungar, and
Duncan J. P. Yeardley§
Roy & Diana Vagelos Laboratories
Department of Chemistry, UniVersity of PennsylVania
Philadelphia, PennsylVania 19104-6323
Organische Chemie II, Makromolekulare Chemie
UniVersit a¨ t Ulm, D-89069 Ulm, Germany
Department of Engineering Materials and
Center for Molecular Materials
Scheme 2. Synthesis of (3,4-(3,4,5)n-1)12Gn-X (n ) 1 to 5)
Monodendrons and Determination of Shape and Size by XRD
Analysis of the Pm 3h n Cubic Lattice
UniVersity of Sheffield, Sheffield S1 3JD, U.K.
ReceiVed December 13, 1999
Monodendrons1 synthesized by a convergent method and
1
1,2
dendrimers (prepared by a divergent method or by the covalent
3
or supramolecular assembly of monodendrons to a multiple
1
2
molecular or macromolecular core) are valuable building blocks
used in the construction of object-like nanosystems with novel
functions and properties.1 Recently, we have elaborated a novel
approach to the design, shape, and size analysis of self-assembling
,2,4
monodendrons5 and of self-organizable supramolecular and
-7
macromolecular dendrimers (Scheme 1).2
,5-7
This strategy in-
volves the quantitative analysis by X-ray diffraction (XRD) of
the thermotropic liquid crystalline (LC) 2-D hexagonal columnar
5
6a,b
6c
p6mm and 3-D cubic Pm 3h n and Im 3h m lattices self-organized
from cylindrical and respectively spherical supramolecular den-
drimers. These building blocks are subsequently employed in the
construction of more complex functional architectural motives.2
This contribution reports the design, synthesis, and the structural
analysis by XRD of the first spherical functional monodendron
that self-organizes in a cubic Pm 3h n lattice. The direct visualization
by scanning force microscopy (SFM) of the spherical monoden-
dron both as a single molecule and in disordered monolayers is
also reported. Previous examples of spherical dendritic objects
self-organizable in a cubic lattice were obtained only by the self-
assembly of conical and hemispherical monodendrons.6 Den-
drimers obtained by a divergent synthesis, that have a spherical
shape in solution but lack the shape perfection required for self-
,8
,7
9
organization in a lattice, were also reported. Their spherical shape
9a,b
was estimated, in solution, by SAXS and TEM and on a surface
by AFM or SFM.9
c-f
Scheme 2 and Table 1 summarize the synthesis and the results
of the structural analysis by a combination of differential scanning
calorimetry (DSC), thermal optical polarized microscopy (TOPM),
†
University of Pennsylvania.
‡
Universit a¨ t Ulm.
§
University of Sheffield.
1) (a) Fr e´ chet, J. M. J. Science 1994, 263, 1710. (b) Tomalia. D. A. AdV.
n-1
XRD, and SFM of the first five generations of (3,4-(3,4,5) )-
(
Mater. 1994, 6, 529. (c) Newkome, G. R.; Moorefield, C. N.; V o¨ gtle, F. Den-
dritic Molecules. Concepts, Synthesis, PerspectiVes; VCH: Weinheim, 1996.
12Gn-X (where n is the generation number, n ) 1 to 5)
monodendrons. The difference between the GPC and theoretical
molecular weights of these monodendrons is in agreement with
previously reported data, demonstrating the decrease in hydro-
(
2) Percec, V.; Ahn, C.-H.; Ungar, G.; Yeardley, D. J. P.; M o¨ ller, M.;
Sheiko, S. S. Nature 1998, 391, 161.
3) Zimmerman, S. C.; Zeng, F.; Reichert, D. E. C.; Kolotuchin, S. V.
Science 1996, 271, 1095.
4) (a) Fischer, M.; V o¨ gtle, F. Angew. Chem., Int. Ed. 1999, 38, 884. (b)
Moore, J. S. Acc. Chem. Res. 1997, 30, 402. (c) Jiang, D.-L.; Aida, T. Nature
(
6a
dynamic volume with the increase of Gn. The Pm 3h n cubic lattice
(
dimension (a, in Å), the diameter of the supramolecular or
molecular dendritic sphere (D, in Å), the number of monodendrons
1
997, 388, 454. (d) Bosman, A. W.; Janssen, H. M.; Meijer, E. W. Chem.
ReV. 1999, 99, 1665. (e) Percec, V.; Ahn, C.-H.; Barboiu, B. J. Am. Chem.
(µ) that self-assemble into a sphere, the temperature at which the
Soc. 1997, 119, 12978.
XRD analysis was performed, the functional group X, and the
theoretical molar mass of the monodendron are also shown in
(
5) Percec, V.; Johansson, G.; Ungar, G.; Zhou, J. J. Am. Chem. Soc. 1996,
1
18, 9855.
6) (a) Balagurusamy, V. S. K.; Ungar, G.; Percec, V.; Johansson, G. J.
(
Am. Chem. Soc. 1997, 119, 1539. (b) Percec, V.; Cho, W.-D.; Mosier, P. E.;
Ungar, G.; Yeardley, D. J. P. J. Am. Chem. Soc. 1998, 120, 11061. (c)
Yeardley, D. J. P.; Ungar, G.; Percec, V.; Holerca, H. N.; Johansson, G. J.
Am. Chem. Soc. 2000, 122, 1684.
(9) (a) Jackson, C. L.; Chanzy, H. D.; Booy, F. P.; Drake, B. J.; Tomalia,
D. A.; Bauer, B. J.; Amis, E. J. Macromolecules 1998, 31, 6259. (b) Prosa,
T. J.; Bauer, B. J.; Amis, E. J.; Tomalia, D. A.; Scherrenberg, R. J. Polym.
Sci., Part B: Polym. Phys. 1997, 35, 2913. (c) Sheiko, S. S.; Eckert, G.;
Ignat’eva, G.; Muzafarov, A.; Spickermann, J.; R a¨ der, H. J.; M o¨ ller, M.
Macromol. Rapid Commun. 1996, 17, 283. (d) Hierlemann, A.; Campbell, J.
K.; Baker, L. A.; Crooks, R. M.; Ricco, A. J. J. Am. Chem. Soc. 1998, 120,
5323. (e) Sheiko, S. S. AdV. Polym. Sci. 2000, 151, 61. (f) Huck, W. T. S.;
Veggel, F. C. J. M.; Kropman, B. L.; Blank, D. H. A.; Keim, E. G.; Smithers,
M. M. A.; Reinhoudt, D. N. J. Am. Chem. Soc. 1995, 117, 8293. (g) Percec,
V.; Chu, P.; Ungar, G.; Zhou, J. J. Am. Chem. Soc. 1995, 117, 11441.
(
7) Hudson, S. D.; Jung, H.-T.; Percec, V.; Cho, W.-D.; Johansson, G.;
Ungar, G.; Balagurusamy, V. S. K. Science 1997, 278, 449.
8) (a) Percec, V. Ahn, C.-H.; Cho, W.-D.; Jamieson, A. M.; Kim, J.;
(
Leman, T.; Schmidt, M.; Gerle, M.; M o¨ ller, M.; Prokhorova, S. A.; Sheiko,
S. S.; Cheng, S. Z. D.; Zhang, A.; Ungar, G.; Yeardley, D. J. P. J. Am. Chem.
Soc. 1998, 120, 8619. (b) Percec, V.; Ahn, C.-H.; Bera, T. K.; Ungar, G.;
Yeardley, D. J. P. Chem. Eur. J. 1999, 5, 1070.
1
0.1021/ja9943400 CCC: $19.00 © 2000 American Chemical Society
Published on Web 04/14/2000

4250 J. Am. Chem. Soc., Vol. 122, No. 17, 2000
Communications to the Editor
a
Table 1. Theoretical and Experimental Molecular Weights Determined by GPC, Experimental Densities, and Thermal Transitions of Selected
n-1
Examples of (3,4-(3,4,5) )12Gn-X (X ) CH
2
OH, COOH, and CO
2
CH
thermal transitions (°C) and corresponding enthalpy changes (kcal/mol)b
heating cooling
i 27 (10.91) k
3
) Monodendrons
a
M
n
M
w/
M
n
F
20
3)
monodendron
3,4)12G1-CH OH
MW
t
(GPC) (GPC) (g/cm
(
(
(
2
477
830 1.02
1.00
1.00
0.99
kc12 (4.23) k 53 (16.06) i
k 37 (0.53) -k 39 (2.32) k 52 (14.26) i
k 0 (2.42) k 60 (39.14) Cub 133 (4.45) i
second heating
3,4-3,4,5)12G2-CH
d
2
OH
1532 2069 1.04
4713 5067 1.07
i 128 (4.31) Cub 15 (20.49) k
second heating
k 42 (18.32) Cub 133 (4.30) i
2
3,4-(3,4,5) )12G3-COOH
k -7 (42.87) -k 12 (6.84) k 131 (15.74)
Cub 190 (0.71) ie
3
e
(
(
3,4-(3,4,5) )12G4-COOH
14214 10112 1.06
42731 13450 1.06
0.99
0.98
k -10 (25.72) k 101 (56.90) Cub 200 (4.68) i
k -15 (56.51) k 48 (20.91) Cub 194 (7.34) i
k -9 (231.64) Cub 191 (5.51) i
4
3,4-(3,4,5) )12G5-CO
2
CH
3
i 175 (7.34) Cub -15 (169.41) k
second heating
a
b
Densities were measured at 20 °C. Data from the first DSC heating and cooling scans are on the first line, and data from the DSC second
heating are on the second line. k ) crystalline. Cub ) Cubic Pm 3h n. e Decomposition after first heating.
c
d
Scheme 2. Both their synthesis and structural analysis were carried
out as reported previously for the first four generations of (3,4,5-
n-1
6a
n
(
1
3,4,5) )12Gn-X and the first three generations of (4-(3,4,5) )-
2Gn-X6b monodendrons. (3,4-(3,4,5) )12Gn-X represents the
n-1
third series from a library of self-assembling monodendrons based
6
3
on 3,4,5-trisubstituted AB benzyl ether repeat units. They are
functionalized on the periphery with 3,4-bis(n-dodecan-1-yloxy)-
n-1
benzyl ether groups. (3,4,5-(3,4,5) )12Gn-X series is func-
tionalyzed on the periphery with 3,4,5-tris(n-dodecan-1-yloxy)-
6a
n
benzyl ether, while the series (4-(3,4,5) )12Gn-X contains 3,4,5-
tris[p-(n-dodecan-1-yloxy)benzyloxy]benzyl ether groups on the
periphery.6b
4
2 3
Figure 1. Visualization of spherical (3,4-(3,4,5) )12G5-CO CH mono-
dendrons by SFM on mica. Samples were prepared by dipping mica in
a dodecane solution of the monodendron with c ) 0.01 mg/mL. The
height of monodendrons in disorded monolayer (a) is 50 Å and diameter
is 60 Å. The height and diameter of single monodendrons are 25 and
100 Å, respectively (b).
The rational for the selection of the series of experiments
described in Scheme 2 is as follows. The analysis of (3,4,5-
n-1
6a
n
6b
(3,4,5) )12Gn-X and (4-(3,4,5) )12Gn-X demonstrated that
for the same internal repeat unit the shape and size of the
monodendron is determined by the structure of the first generation
monodendron attached on the periphery. The fourth generation
3
hundred were visualized by SFM on mica (Figure 1). Within
islands, the average diameter of the molecule is 60 Å, and the
average height is 50 Å (Figure 1a). These results are in excellent
agreement with the diameter determined by XRD in a lattice (57
Å). If we consider that the resolution of the SFM is (5 Å, these
data may suggest that on a surface, a monolayer of densely packed
monodendrons could adopt only a slightly oblate spherical shape
monodendron (3,4,5-(3,4,5) )12G4-COOH has a hemispherical
shape and a theoretical molar mass of 19 191.6a Attempts to
synthesize its fifth generation did not succeed due to the low molar
concentration of its X group and the steric hindrance induced by
3
its shape. The third generation of (4-(3,4,5) )12G3-CO
2
CH
3
has
a shape that is equivalent with a sixth of a sphere and a theoretical
6b
molar mass of 9252. Therefore, two additional generations would
have been required to accomplish a spherical monodendron. This
would have produced an even larger molar mass and similar steric
(Figure 1a). The average diameter of the single monodendron is
100 Å, and its height is 25 Å (Figure 1b). The distortion of the
3
shape of the single monodendron on a surface is in agreement
with previous reports.9 However, in these reports the dendrimers
did not assemble into a lattice. Therefore, these authors could
not offer information on the shape of the dendrimers within such
a lattice. This distortion is most probably due to the interaction
of the single monodendron with the surface and/or its soft
structure.9 The most dramatic shape change reported so far is
constrains as (3,4,5-(3,4,5) )12G4-X. Therefore, we have ad-
c-e
vanced the hypothesis that the experiments summarized in Scheme
2
could alleviate some of these problems since this series of
monodendrons would be expected to have shapes, sizes, and molar
masses between those of the two series reported previously.6
The results presented in Scheme 2 can be summarized as
c-e
follows. (3,4)12G1-X (not shown in Scheme 2) is only crystalline.8a
9
g
from spherical in solution to “windscreen wiper” in a lattice.
2
Twenty three (3,4-3,4,5)12G2-CH OH monodendrons and re-
2
Experiments to quantitatively elucidate the similarities and
differences between monodendrons in a lattice, in the disordered
bulk state, in solution, and as single molecules together with the
spectively 10 (3,4-(3,4,5) )12G3-COOH monodendrons self-
assemble into a sphere. Therefore, we hypothesize that each has
3
a conical shape. Only three (3,4-(3,4,5) )12G4-COOH mono-
elaboration of novel single molecule-based functional nanosys-
dendrons of molar mass 14214 are required to self-assemble into
tems1
,4,10
are in progress.
4
a sphere. Finally, a single (3,4-(3,4,5) )12G5-CO
2
CH
3
mono-
dendron forms a sphere. This functional single monodendron-
Acknowledgment. Financial support by the National Science Founda-
tion (DMR-97-08581) is gratefully acknowledged.
single sphere has a single X functionality isolated in its core
(Scheme 2). The most significant difference between a spherical
monodendron and a spherical dendrimer is that the last one does
not have a single functional group in its core.
Supporting Information Available: Reaction schemes, experimental
procedures, analytical data, tables with characterization results, and
references (PDF). This material is available free of charge via the Internet
at http://pubs.acs.org.
According to the results outlined in Scheme 2, a single (3,4-
4
(
3,4,5) )12G5-CO
2
CH
3
monodedron of theoretical molar mass
4
2 731, most probably the largest synthesized so far, exhibits a
JA9943400
spherical shape when the molecule is self-organized in a cubic
Pm 3h n lattice. The most intriguing question is what is the shape
of this molecule in a disordered assembly or as a single molecule?
Does it display the same shape as in its Pm 3h n lattice? Single
molecules and disordered molecules within islands of several
(10) (a) Hawker, C. J.; Wooley, K. L.; Fr e´ chet, J. M. J. J. Am. Chem. Soc.
1
993, 115, 4375. (b) Kawa, M.; Fr e´ chet, J. M. J. Chem. Mater. 1998, 10,
2
86. (c) Piotti, M. E.; Rivera, F., Jr.; Bond, R.; Hawker, C. J.; Fr e´ chet, J. M.
J. J. Am. Chem. Soc. 1999, 121, 9471. (d) Sato, T.; Jiang, D.-L.; Aida, T. J.
Am. Chem. Soc. 1999, 121, 10658.