Synthesis and structural analysis of two constitutional isomeric libraries of AB2-based monodendrons and supramolecular dendrimers

Article abstract of DOI:10.1021/ja0037771

The synthesis and structural analysis of two constitutional isomeric libraries of self-assembling AB₂ monodendrons based on 3,4- and 3,5-disubstituted benzyl ether internal repeat units containing four different first generation monodendrons, i

Full text of DOI:10.1021/ja0037771

1302
J. Am. Chem. Soc. 2001, 123, 1302-1315
Synthesis and Structural Analysis of Two Constitutional Isomeric
Libraries of AB2-Based Monodendrons and Supramolecular
Dendrimers
Virgil Percec,*,† Wook-Dong Cho,† Goran Ungar,‡ and Duncan J. P. Yeardley‡
Contribution from the Roy & Diana Vagelos Laboratories, Department of Chemistry, UniVersity of
PennsylVania, Philadelphia, PennsylVania 19104-6323, and Department of Engineering Materials and
Center for Molecular Materials, UniVersity of Sheffield, Sheffield S1 3JD, U.K.
ReceiVed October 24, 2000
Abstract: The synthesis and structural analysis of two constitutional isomeric libraries of self-assembling
AB2 monodendrons based on 3,4- and 3,5-disubstituted benzyl ether internal repeat units containing four different
first generation monodendrons, i.e., 3,4,5-tris(n-dodecan-1-yloxy)benzyl ether, 3,4-bis(n-dodecan-1-yloxy)-
benzyl ether, 3,4,5-tris[p-(n-dodecan-1-yloxy)benzyloxy]benzyl ether, and 3,4-bis[p-(n-dodecan-1-yloxy)-
benzyloxy]benzyl ether, on their periphery are described. Regardless of the repeat unit on their periphery, the
first three or four generations of the 3,4-disubstituted series of monodendrons self-assemble into spherical
supramolecular dendrimers that self-organize into a Pm3hn 3-D cubic lattice while the same generations of the
3,5-disubstituted series of monodendrons self-assemble into cylindrical supramolecular dendrimers that self-
organize into a p6mm hexagonal columnar 2-D lattice. The internal repeat unit of the monodendrons determines
the shape of the supramolecular dendrimers. However, for a particular internal repeat unit, the architecture
from its periphery determines the size of the monodendron, the number of monodendrons that self-assemble
into a supramolecular dendrimer, the solid angle of the monodendron, and the dependence of the size of the
supramolecular dendrimer on generation number. Since ultimately all monodendrons must reach the shape of
a single sphere, the diameter of cylindrical and spherical supramolecular dendrimers constructed from these
building blocks is limited to less than 100 Å. The library of 3,5-disubstituted monodendrons also provided the
first five examples of supramolecular dendrimers that undergo reversible shape changes induced by temperature
and functionality at their focal point. In addition, a spherical supramolecular dendrimer based on a
3,5-disubstituted repeat unit that self-assembles in an Im3hm 3-D cubic lattice was discovered in the same
library. The structural information generated by these two AB2 and the previously reported AB3 libraries of
quasi-equiValent monodendrons provides building blocks that enable the construction of externally regulated
functional supramolecular, macromolecular, and single-molecule-based nanosystems self-organizable in
predictable lattices.
Introduction
controlled microenvironment,2a-c,h site isolation,2a-f antenna
effect,2d,g-i carriers for drugs, genes,1j and contrast agents in
medicine and diagnostics,1r etc., have been developed with the
aid of dendritic building blocks.
We are involved in the elaboration of strategies for the
synthesis of monodendritic building blocks that self-assemble
in bulk into supramolecular dendrimers with well-defined shapes
that subsequently self-organize and co-organize in lattices and
superlattices. Three-dimensional (3-D) Pm3hn and Im3hm cubic
lattices3,4 self-organized from spherical supramolecular den-
drimers, two-dimensional (2-D) p6mm hexagonal columnar
lattices5 self-organized from cylindrical supramolecular den-
drimers, and hexagonal columnar superlattices6 co-organized
from mixtures of three-cylindrical bundle supramolecular mini-
In the past decade, dendrimers1a,c and monodendrons1b,c
provided some of the most powerful entries to building blocks
employed in the synthesis of complex functional nanostructures.1
New methodologies to access strategies for the design of
† University of Pennsylvania.
‡ University of Sheffield.
(1) For selected recent reviews on dendrimers and monodendrons, see:
(a) Tomalia, D. A. AdV. Mater. 1994, 6, 529. (b) Fre´chet, J. M. J. Science
1994, 263, 1710. (c) Newkome, G. R.; Moorefield, C. N.; Vo¨gtle, F.
Dendritic Molecules. Concepts, Synthesis, PerspectiVes; VCH: Weinheim,
1996. (d) Moore, J. S. Acc. Chem. Res. 1997, 30, 402. (e) Zeng, F.;
Zimmerman, S. C. Chem. ReV. 1997, 97, 1681. (f) Smith, D. K.; Diederich,
F. Chem. Eur. J. 1998, 4, 1353. (g) Frey, H. Angew. Chem., Int. Ed. Engl.
1998, 37, 2193. (h) Vo¨gtle, F., Ed.; Dendrimers; Topics in Current
Chemistry 197; Springer: Berlin, 1998. (i) Mathews, O. A.; Shipway, A.
N.; Stoddart, J. F. Prog. Polym. Sci. 1998, 23, 1. (j) Fischer, M.; Vo¨gtle, F.
Angew. Chem., Int. Ed. 1999, 38, 884. (k) Bosman, A. W.; Janssen, H. M.;
Meijer, E. W. Chem. ReV. 1999, 99, 1665. (l) Berresheim, A. J.; Mu¨ller,
M.; Mu¨llen, K. Chem. ReV. 1999, 99, 1747. (m) Moore, J. S. Curr. Opin.
Colloid Interface Sci. 1999, 4, 108. (n) Roovers, J.; Comanita, B. AdV.
Polym. Sci. 1999, 142, 179. (o) Schlu¨ter, A. D.; Rabe, J. P. Angew. Chem.,
Int. Ed. 2000, 39, 864. (p) Hawker, C. J. Curr. Opin. Colloid Interface Sci.
1999, 4, 117. (q) Emrick, T.; Fre´chet, J. M. J. Curr. Opin. Colloid Interface
Sci. 1999, 4, 15. (r) Krause, W.; Hackmann-Schlichter, N.; Maier, F. K.;
Mu¨ller, R. Top. Curr. Chem. 2000, 210, 261. (s) Smith, D. K.; Diederich,
F. Top. Curr. Chem. 2000, 210, 183.
(2) (a) Hawker, C. J.; Wooley, K. L.; Fre´chet, J. M. J. J. Am. Chem.
Soc. 1993, 115, 4375. (b) Devadoss, C.; Bharathi, P.; Moore, J. S. Angew.
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R.; Hawker, C. J.; Fre´chet, J. M. J. J. Am. Chem. Soc. 1999, 121, 9471. (d)
Jiang, D.-L.; Aida, T. Nature 1997, 388, 454. (e) Jansen, J. F. G. A.; de
Brabander-van den Berg, E. M. M.; Meijer, E. W. Science 1994, 266, 1226.
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10.1021/ja0037771 CCC: $20.00 © 2001 American Chemical Society
Published on Web 01/26/2001

AB2-Based Monodendrons and Supramolecular Dendrimers
J. Am. Chem. Soc., Vol. 123, No. 7, 2001 1303
dendrimers (i.e., first-generation dendrimers) with cylindrical
supramolecular minidendrimers were reported. The structural
analysis required for the design of these building blocks involves
the identification of the bulk phase in which the supramolecular
dendrimers are self-organized by a combination of differential
scanning calorimetry (DSC) and thermal optical polarized
microscopy (TOPM) followed by the selection of the lattice
symmetry by X-ray diffraction experiments (XRD) performed
on single crystal or single crystal liquid crystal specimens.3-5
The decision on the shape of the supramolecular dendrimer that
generates the lattice is made by a combination of electron density
calculations, transmission electron microscopy (TEM), and
electron diffraction experiments.3 Various modes of self-
assembly of the monodendritic building blocks into supramo-
lecular objects of different shapes are screened and eliminated
during this process. Finally, the retrostructural analysis of the
lattices generated from supramolecular dendrimers of known
shapes by using the lattice dimensions and density data provides
access to the shape, size, and number of monodendritic building
blocks that create the supramolecular dendrimer.
To date we have investigated a library containing from three
to five generations of self-assembling 3,4,5-trisubstituted benzyl
ether monodendrons containing four different minidendritic
architectural motifs on their periphery3a,7 and five generations
of a 3,5-disubstituted benzyl ether monodendron.8 Structural
analysis of these monodendrons allowed the discovery of
building blocks displaying the following shapes: tapered, twin-
tapered, half-disk, disklike, conical, half-sphere, and spherical.
These experiments have confirmed and quantified7a,8 the predic-
tion that the shape of a monodendron or dendrimer should
change by increasing the generation number9 both in solution
and in bulk. In addition, they demonstrated that the shape of
the monodendrons and dendrimers is determined both by the
structure of the repeat unit attached to their periphery7,10 and
by the core multiplicity.11,12 Most recently we have discovered
that the solid angle of a monodendron determines the depen-
dence between the size and shape of a supramolecular dendrimer
and its generation number.7c,13 Simultaneously we have learned
that the first-generation AB3 minimonodendron functionalized
with a suitable group in its core self-assembles in cylindrical
objects that at high temperatures13 undergo a reversible shape
change to spherical objects. However, both the Im3hm lattice4
and the hexagonal columnar superlattice6 were obtained so far
only with the first-generation supramolecular dendrimers (i.e.,
minidendrimers).
This diversity of tertiary and quaternary structural control
accomplished by the modification of the primary structure of
monodendrons is extremely rewarding since it produced libraries
of quasi-equiValent11 building blocks that have been used to
generate new concepts in organic and polymerization reactions
in restricted geometries14 and also opened strategies for the
synthesis of single-molecule functional nanosystems.15 Never-
theless, the transplant of the discoveries made with minimono-
dendrons4,6,13 to larger generations of monodendrons is most
efficiently pursued at this time by investigating libraries of self-
assembling monodendrons.
Toward this goal we are reporting here the synthesis and the
structural analysis of three to four generations from the two
constitutional isomeric libraries of AB2 3,4- and, respectively,
3,5-disubstituted benzyl ether self-assembling monodendrons
containing four minimonodendrons with different architectural
motifs on their periphery. This series of experiments will provide
access to the discovery of novel architectural and structural
concepts and will clarify some of the structural limitations of
these classes of self-assembling monodendrons.
Results and Discussion
Synthesis of Constitutional Isomeric Libraries of AB2
Monodendrons. Two constitutional isomeric libraries of AB2
monodendrons based on 3,4- and 3,5-disubstituted benzyl ether
repeat units functionalized on their periphery with 3,4,5-tris(n-
dodecan-1-yloxy)benzyl ether, 3,4-bis(n-dodecan-1-yloxy)benzyl
ether, 3,4,5-tris[p-(n-dodecan-1-yloxy)benzyloxy]benzyl ether,
and 3,4-bis[p-(n-dodecan-1-yloxy)benzyloxy]benzyl ether first-
generation monodendrons (minidendrons) were synthesized. The
short nomenclature used for these monodendrons is identical
to that employed in previous publications for AB3 3,4,5-
trisubstituted benzyl ether monodendrons.3a,7,15a Scheme 1
outlines their synthesis and reports the yields of the pure
compounds and their theoretical molecular masses. On the top
of this scheme are shown the structures of (3,4,5-3,4)12G2-X
(X ) CO2CH3), (A-X),15a (3,4,5-3,5)12G2-X (X ) CO2CH3),
(B-X),15a (3,4)212G2-X (X ) CO2CH3), (C-X),15a (4-3,4,5)-
12G1-X (X ) CO2CH3,16 CH2OH7a), (D-X), and (4-3,4)-
12G1-X (X ) CO2CH3,15a CH2OH7c), (E-X) that were reported
previously from our laboratory. The second line from Scheme
1 shows the convergent synthesis1b of 3,4-disubstituted series
of monodendrons together with reaction conditions and yields.
The synthetic method used involves the quantitative reduction
(3) (a) Balagurusamy, V. S. K.; Ungar, G.; Percec, V.; Johansson, G. J.
Am. Chem. Soc. 1997, 119, 1539. (b) Hudson, S. D.; Jung, H.-T.; Percec,
V.; Cho, W.-D.; Johansson, G.; Ungar, G.; Balagurusamy, V. S. K. Science
1997, 278, 449.
(4) Yeardley, D. J. P.; Ungar, G.; Percec, V.; Holerca, M. N.; Johansson,
G. J. Am. Chem. Soc. 2000, 122, 1684.
(5) (a) Percec, V.; Johansson, G.; Heck, J.; Ungar, G.; Batty, S. V. J.
Chem. Soc., Perkin Trans. 1 1993, 1411. (b) Percec, V.; Heck, J. A.;
Tomazos, D.; Ungar, G. J. Chem. Soc., Perkin Trans. 2 1993, 2381. (c)
Percec, V.; Heck, J.; Tomazos, D.; Falkenberg, F.; Blackwell, H.; Ungar,
G. J. Chem. Soc., Perkin Trans. 1 1993, 2799. (d) Percec, V.; Tomazos,
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31. (e) Johansson, G.; Percec, V.; Ungar, G.; Abramic, D. J. Chem. Soc.,
Perkin Trans. 1 1994, 447. (f) Tomazos, D.; Out, G.; Heck, J. A.; Johansson,
G.; Percec, V.; Mo¨ller, M. Liq. Cryst. 1994, 16, 509. (g) Percec, V.;
Johansson, G.; Ungar, G.; Zhou, J. J. Am. Chem. Soc. 1996, 118, 9855.
(6) Percec, V.; Ahn, C.-H.; Bera, T. K.; Ungar, G.; Yeardley, D. J. P.
Chem. Eur. J. 1999, 5, 1070.
(7) (a) Percec, V.; Cho, W.-D.; Mosier, P. E.; Ungar, G.; Yeardley, D.
J. P. J. Am. Chem. Soc. 1998, 120, 11061. (b) Percec, V.; Cho, W.-D.;
Mo¨ller, M.; Prokhorova, S. A.; Ungar, G.; Yeardley, D. J. P. J. Am. Chem.
Soc. 2000, 122, 4249. (c) Percec, V.; Cho, W.-D.; Ungar, G. J. Am. Chem.
Soc. 2000, 122, 10273.
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2000, 112, 1661.; Angew. Chem., Int. Ed. 2000, 39, 1597.
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Am. Chem. Soc. 1989, 111, 2339.
(10) Percec, V.; Chu, P.; Ungar, G.; Zhou, J. J. Am. Chem. Soc. 1995,
117, 11441.
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Sheiko, S. S. Nature 1998, 391, 161.
(12) Yin, R.; Zhu, Y.; Tomalia, D. A.; Ibuki, H. J. Am. Chem. Soc. 1998,
120, 2678.
(13) Ungar, G.; Percec, V.; Holerca, M. N.; Johansson, G.; Heck. J. Chem.
Eur. J. 2000, 6, 1258.
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12978.
(15) (a) Percec, V.; Ahn, C.-H.; Cho, W.-D.; Jamieson, A. M.; Kim, J.;
Leman, T.; Schmidt, M.; Gerle, M.; Mo¨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.; Schlueter, D.; Ungar, G.; Cheng,
S. Z. D.; Zhang, A. Macromolecules 1998, 31, 1745. (c) Prokhorova, S.
A.; Sheiko, S. S.; Mo¨ller, M.; Ahn, C.-H.; Percec, V. Macromol. Rapid
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1989, 5, 123.

1304 J. Am. Chem. Soc., Vol. 123, No. 7, 2001
Percec et al.
Scheme 1. Synthesis of Libraries of Constitutional Isomeric 3,4- and 3,5-Disubstituted Benzyl Ether-Based Monodendrons
(followed by TLC, NMR) of the first- or second-generation
methyl benzoate monodendron with LiAlH4 in THF at 20 °C
followed by the quantitative chlorination of the resulted benzyl
alcohol into the corresponding benzyl chloride with SOCl2 in
CH2Cl2 in the presence of 2,6-di-tert-butyl-4-methylpyridine
(DTBMP)17 proton trap. The quantitative chlorination and the
absence of decomposition during the chlorination process were
determined by a combination of NMR, TLC, and HPLC. The
reaction solvent was distilled in a rotary evaporator and the
benzyl chloride derivative was used immediately in the etheri-
fication step. The etherification of methyl 3,4-dihydroxybenzoate
with the monodendritic benzyl chloride was performed in
various mixtures of DMF and THF in the presence of K2CO3
at 70 °C. The quantitative etherification was established by a
combination of NMR, TLC, and HPLC analyses. It is essential
that SOCl2 and CH2Cl2 are of the highest commercial purities
and are used from freshly opened containers. Additional
experimental details of this synthetic procedure are available
in the previous publications from our laboratory.7,15a
preparation of 3,4-disubstituted benzyl ether, the presently
described monodendrons were synthesized by replacing the
Williamson etherification with the Mitsunobu etherification.8,18
Eight out of the 19 monodendrons containing a methyl benzoate
group in their focal point, prepared according to the methods
outlined in Scheme 1, were hydrolyzed with KOH in a mixture
of EtOH and THF at reflux and after the neutralization of the
reaction mixture with dilute CH3COOH yielded the correspond-
ing monodendrons containing a carboxylic acid at their focal
point (Scheme 2).
The increase in the size of these two series of constitutional
isomeric monodendrons could be monitored by their HPLC and
GPC traces since the chromatograms are well separated (Figure
1). The difference between the theoretical and experimental
molecular weights (relative to polystyrene standards) is due to
the difference between the hydrodynamic volume of polystyrene
and of the monodendrons and agrees with previous results from
our laboratory.3
The synthesis of the series of 3,5-disubstituted benzyl ethers
is shown on the last line of Scheme 1. Although they can be
synthesized by the same method as the one used for the
(17) Anderson, A. G.; Stang, P. J. J. Org. Chem. 1976, 41, 3034.
(18) (a) Mitsunobu, O. Synthesis 1981, 1. (b) Hughes, D. L. Org. React.
1992, 42, 335. (c) Ho¨ger, S. Synthesis 1997, 20.

AB2-Based Monodendrons and Supramolecular Dendrimers
J. Am. Chem. Soc., Vol. 123, No. 7, 2001 1305
Scheme 2. Synthesis of 3,4- and 3,5-Disubstituted Benzyl Ether-Based Monodendrons Containing Carboxylic Acid in Their
Focal Point
Scheme 3. Schematic Representation of (a) the
Self-Assembly of Building Blocks Based on Flat Tapered
and Disc-Shaped Monodendrons into Supramolecular
Cylindrical Dendrimers and Their Subsequent
Self-Organization in a p6mm Hexagonal Columnar (Φh)
Lattice and (b) the Self-Assembly of the Conical
Monodendrons into Supramolecular Spherical Dendrimers
and Their Subsequent Self-Organization in Pm3hn and Im3hm
Cubic (Cub) Lattices
Figure 1. GPC traces with Mn and Mw/Mn values determined by GPC
with polystyrene standards for (3,4,5-(3,4)n-1)12Gn-CO2CH3 with n )
1-4.
Structural and Retrostructural Analysis of Supramolecu-
lar Dendrimers. The structural analysis of supramolecular
dendrimers self-assembled in bulk from these two libraries of
monodendrons was carried out by a combination of DSC,
TOPM, and XRD experiments according to standard methods
elaborated in our laboratory for the 2-D hexagonal columnar
p6mm5h and 3-D cubic Pm3hn3a and Im3hm4 lattices. The
retrostructural analysis of these lattices was performed by using
the values of the lattice dimensions and of the densities (F20)
of the supramolecular dendrimers. This procedure is outlined
in Scheme 3 and is described in more detail in previous

1306 J. Am. Chem. Soc., Vol. 123, No. 7, 2001
Percec et al.
Table 1. Theoretical and Experimental Molecular Weights Determined by GPC and Thermal Transitions of 3,4-Disubstituted Monodendrons
thermal transitions (°C) and corresponding enthalpy changes (kcal/mol)a
Mn
Mw/Mn
monodendron
MWt
(GPC) (GPC)
heating
cooling
(3,4,5)12G1-CO2CH3
689.1
910
1839
3108
5085
1.04
1.04
1.05
1.07
kb 44 (23.2) ic
k 23 (15.9) i
i 4 (15.5) k
(3,4,5-3,4)12G2-CO2CH3
(3,4,5-(3,4)2)12G3-CO2CH3
(3,4,5-(3,4)3)12G4-CO2CH3
1454.3
2984.8
6045.6
k 40 (15.34) k 48 (5.03) i
i 33 (1.77) Cubd-13 (2.62)f k
i 57 (0.41)f Cub -23 (4.85) k
i 73 (0.48) Cub -23 (12.15) k
k -5 (1.86) Tge 9 Cub 40 (1.63) i
k 40 (25.94) Cub 69 (0.54) i
k -22 (10.00) Tg 21 Cub 69 (0.57)f i
k -2 (21.36)f k 56 (33.03) Cub 94 (0.56) i
k -18 (19.45) Tg 34 Cub 94 (0.72) i
(3,4)12G1-CH2OH
(3,4)212G2-COOH
476.8
830
1.02
1.05
k 12 (4.23) k 53 (16.06) i
i 27 (10.91) k
k 37 (0.53) -k 39 (2.32) k 52 (14.26) i
k 2 (0.31) k 88 (0.54) -k 97 (3.34)
k 108 (17.58) Cub 119 (0.47) i
1071.7
1567
i 114 (0.40) Cub 67 (17.04) k
-k 86 (4.63) k 108 (22.68) Cub 118 (0.54) i
(3,4)312G3-COOH
(3,4)412G4-COOH
2233.4
4557.0
2767
4563
1.05
1.07
k 70 (11.56) Cub 178 (2.94) i
i 153 (2.33) Cub -15 (4.84) k
i 165 (0.91) Cub -17 (6.92) k
k -10 (2.27) Tg 39 Cub 155 (2.17) i
k -14 (16.61) Tg 41 Cub 194 (2.50) i
k -11 (2.33) Tg 36 Cub 168 (0.97) i
(4-3,4,5)12G1-COOH
993.5
1498
1.02
k 47 (17.05)f -k 58 (1.31) k 70 (11.82)
Φh 145 (3.97) i
i 136 (3.77) Φhg 36 (15.43) k
k 43 (15.10)f Φh 140 (3.71) i
k -9 (2.41) k 51 (23.21) Cub 119 (6.51) i
k -27 (13.05) Cub 119 (4.96)i
k 1 (5.85)f k 39 (2.56) k 78 (8.55)
Cub 178 (4.74) i
(4-3,4,5-3,4)12G2-CO2CH3
(4-3,4,5-3,4)12G2-COOH
2091.1
2077.1
2852
2868
1.05
1.05
i 114 (4.83) Cub -26 (13.11) k
i 167 (0.11) Cub 51 (1.22) Tgg 22
-22 (3.11) k
k -18 (3.73) Tg 31 k 62 (2.51) k 113 (0.08)
Cub 178 (0.37) i
k -24 (13.92) -k 14 (14.24) k 24 (1.36)
k 64 (2.12) Cub 153 (1.46) i
k -25 (28.57) Cub 152 (1.08) i
(4-3,4,5-(3,4)2)12G3-CO2CH3 4258.3
4879
1.07
i 143 (0.84) Cub 22 (0.17)
k -28 (7.01) k
(4-3,4)12G1-CO2CH3
(4-3,4)12G1-COOH
717.0
703.0
930
967
1.04
1.05
1.05
1.07
k 4 (1.96) k 60 (12.57) k 99 (4.87) i
k 7 (1.64) k 55 (3.22) Φh 60 (2.03) i
k -9 (9.89) Φh 125 (18.17) i
k -9 (1.19) Φh 125 (19.22) i
k 55 (14.39) Cub 162 (7.46) i
k -17 (2.25) Cub 158 (6.04) i
k -2 (23.17) k 61 (1.53) Cub 211 (11.83)
Cub 221 (11.35) i
i 54 (1.92) Φh 2 (2.51) k
i 114 (1.00) Φh 110 (15.37)
Φh -15 (0.75) k
i 153 (6.89) Cub -18 (3.12) k
(4-(3,4)2)12G2-CO2CH3
(4-(3,4)3)12G3-CO2CH3
1510.2
3096.5
2068
3872
i 211 (6.61) Cub -22 (6.75) k
k -20 (14.83) Cub 205 (20.13)f i
a Data from the first heating and cooling scans are on the first line, and data from the second heating are on the second line. b k ) crystalline.
c i ) isotropic. d Cub ) Pm3hn cubic lattice. e Tg ) glass transition temperature. f Sum of enthalpies from overlapped peaks. g Φh ) p6mm hexagonal
columnar lattice.
publications.3a,4,5h The DSC traces of all monodendrons are
available in Figures 1-3 of the Supporting Information. The
experimental transition temperatures and the corresponding
enthalpy changes for the series of 3,4-disubstituted monoden-
drons are reported in Table 1, while the corresponding data for
the 3,5-disubstituted monodendrons are listed in Table 2. On
the optical polarized microscope, hexagonal columnar phases
exhibit a focal conic texture (Figure 2), and therefore, this phase
can be qualitatively discriminated from cubic phases that are
optically isotropic. The analysis of the XRD results was carried
out only for the p6mm,5h Pm3hn,3a and Im3hm4 lattices that where
previously understood from structural and model of self-
assembly points of view. Selected examples of diffractograms
that are characteristic of these three lattices are shown in Figure
3, together with their recording temperature. The d-spacings of
the hexagonal columnar (Φh) and cubic (Cub) lattices of both
libraries of compounds are collected in Table 3. The lattice
dimensions (a), the experimental densities (F20), the experimental
diameter of the columnar or spherical supramolecular dendrimer
(D), the number of monodendrons per unit cell (µ′) for the Pm3hn
lattice, and the number of monodendrons per spherical den-
drimer (µ) for the Pm3hn lattice or per 4.7 Å19 column stratum
of the p6mm lattice are reported in Table 4 for the series of
3,4-disubstituted monodendrons and in Table 5 for the series
of 3,5-disubstituted monodendrons. An additional and important
parameter reported in Tables 4 and 5 is the planar angle (R′)
that represents the projection of the solid angle, R (where R )
4π/µ), of the conical and tapered monodendrons (where R′ )
R/2 ) 2π/µ).7c The results from Tables 4 and 5 were used to
generate the mechanisms of self-assembly illustrated in Scheme
4 for the series of 3,4-disubstituted monodendrons and in
Scheme 5 for the 3,5-disubstituted monodendrons. For com-
parison purposes, Scheme 6 compiles the structural analysis of
the complete library of 3,4,5-trisubstituted benzyl ether mono-
dendrons that was previously reported from our laboratory.3a,7a-c
In addition, the values of R′ that were previously reported only
for one monodendron7c are now included for all of them in
Scheme 6.
Let us discuss first the series of 3,4-disubstituted monoden-
drons summarized in Scheme 4. The largest generation mono-
dendron is shown on top of each column of this scheme. The
fragment corresponding to the structure of the first, second, third,
and fourth generation of the monodendrons is marked with a
dotted line on the structure of the largest generation. The dotted
line is made with a color that corresponds to the generation
number (i.e., n ) 1 (blue), n ) 2 (red), n ) 3 (green), etc). In
(19) Ungar, G.; Abramic, D.; Percec, V.; Heck, J. A. Liq. Cryst. 1996,
21, 73.

AB2-Based Monodendrons and Supramolecular Dendrimers
J. Am. Chem. Soc., Vol. 123, No. 7, 2001 1307
Table 2. Theoretical and Experimental Molecular Weights Determined by GPC and Thermal Transitions of 3,5-Disubstituted Monodendrons
thermal transitions (°C) and corresponding enthalpy changes (kcal/mol)a
Mn
(GPC)
Mw/Mn
(GPC)
monodendron
MWt
heating
cooling
i 33 (14.1) k
(3,4,5)12G1-COOH
675.1
934
1.06
k 60b (14.90) ic
k 59 (14.30) i
(3,4,5-3,5)12G2-COOH
1440.3
2193
1.04
k -8 (2.60) k 65 (19.68)d i
i 19 (8.86)d k
k 15 (1.91)d -k 25 (1.96) k 39 (5.28)
-k 47 (0.72) -k 58 (1.20) i
(3,4,5-(3,5)2)12G3-COOH
2970.7
4078
1.08
k -8 (2.60) k 55 (37.26) Cube 92 (0.98) i
k -5 (12.29) Cub 93 (0.99) i
i 87 (0.98) Cub -11 (14.69) k
(3,4)12G1-CH2OH
476.8
1057.7
1071.7
2247.5
830
1663
1673
3216
1.02
1.04
1.04
1.07
k 12 (4.23) k 53 (16.06) i
k 37 (0.53) -k 39 (2.32) k 52 (14.26) i
k 65 (18.54) -k 69 (0.37) k 76 (5.47) i
k 61 (12.91) i
i 27 (10.91) k
(3,4-3,5)12G2-CH2OH
(3,4-3,5)12G2-COOH
(3,4-(3,5)2)12G3-CO2CH3
i 49 (1.24) Φhf 37 (8.72) k
i 63 (4.00) Φh 5 (2.45) k
i 39 (2.55) Φh 27 (2.06) k
k 69 (21.82) i
k 14 (3.02) Φh 68 (3.94) i
k -5 (3.55) k 39 (12.56)
k 45 (2.33) k 50 (0.86) i
k -4 (4.01) Φh 45 (5.22) i
k 15 (72.96)d k 42 (4.38) Φh 66 (1.09) i
k -12 (18.92) Φh 66 (1.06) i
(3,4-(3,5)3)12G4-CO2CH3
(4-3,4,5)12G1-COOH
4571.0
993.5
5998
1498
1.09
1.02
i 58 (0.86) Φh -18 (14.95) k
i 136 (3.77) Φh 36 (15.43) k
k 47 (17.05)d -k 58 (1.31) k 70 (11.82)
Φh 145 (3.97) i
k 43 (15.10)d Φh 140 (3.71) i
k 54 (36.82) -k 66 (9.23) k 82 (0.22) i
k -19 (7.95) Φh 71 (2.13) i
(4-3,4,5-3,5)12G2-CO2CH3
(4-3,4,5-(3,5)2)12G3-CO2CH3
2091.1
4258.3
3104
5876
1.05
1.08
i 66 (2.15) Φh -23 (7.62) k
i 103 (3.72) Φh -22 (21.79) k
k -12 (39.64) k 60 (8.35) Φh 109 (3.63) i
k -17 (44.15) Φh 108 (3.37) i
(4-3,4)12G1-CO2CH3
(4-3,4)12G1-COOH
717.0
703.0
930
967
1.04
1.05
1.04
k 4 (1.96) k 60 (12.57) k 99 (4.87) i
k 7 (1.64) k 55 (3.22) Φh 60 (2.03) i
k -9 (9.89) Φh 125 (18.17) i
i 54 (1.92) Φh 2 (2.51) k
i 114 (1.00) Φh 110 (15.37)
Φh -15 (0.75) k
i 91 (6.90) Φh 9 (4.43) k
k -9 (1.19) Φh 125 (19.22) i
(4-3,4-3,5)12G2-CO2CH3
1510.2
2325
-k -15 (4.89) k 52 (1.31) k 77 (6.27)d
Φh 103 (8.24) i
k 14 (4.60) Φh 104 (8.05) i
k 0 (3.57) k 73 (8.52) Φh 133 (3.28) i
k -12 (6.75) k 85 (0.23) k 94 (1.63)
Φh 133 (3.16) i
(4-3,4-3,5)12G2-CH2OH
1482.2
2356
1.04
i 128 (3.09) Φh 36 (0.13)
k -19 (2.52) k
(4-3,4-3,5)12G2-COOH
(4-3,4-(3,5)2)12G3-CO2CH3
(4-3,4-(3,5)2)12G3-COOH
1496.2
3096.5
3082.4
2320
4506
4518
1.05
1.07
1.07
k -5 (4.75) k 58 (0.53) Φh 159 (2.70) i
k -10 (9.92) k 84 (0.30) Φh 150 (1.81) i
k -6 (15.96) Φh 130 (4.73) i
i 146 (2.68) Φh -15 (5.95) k
i 126 (4.72) Φh -15 (6.48) k
k -11 (9.76) Φh 130 (4.95) i
k -4 (29.16) k 151 (0.39) Φh 189 (2.91) ig
a Data from the first heating and cooling scans are on the first line, and data from the second heating are on the second line. b k ) crystalline.
c i ) isotropic. d Sum of enthalpies from overlapped peaks. e Cub ) Pm3hn cubic lattice. f Φh ) p6mm hexagonal columnar lattice. g Decompostion
after first heating.
each column, next to the generation number (n) is shown the
shape of the supramolecular dendrimer self-assembled from the
monodendron with the corresponding n. Under the shape of each
supramolecular dendrimer, the following data are provided: the
functionality X from the focal point of the monodendron for
which the structural analysis was reported, the temperature of
the XRD experiment in °C (data in parentheses), the lattice
dimension (a in Å), the diameter of the supramolecular
cylindrical or spherical supramolecular dendrimer (D in Å), the
number of monodendrons (µ) that self-assemble into a spherical
supramolecular dendrimer or in a 4.7 Å cross section of the
cylindrical supramolecular dendrimer, and the projection of the
solid angle (planar angle, R′ in degrees) of the monodendron.
Methyl 3,4,5-tris(n-dodecan-1-yloxy)benzoate [(3,4,5)12G1-
CO2CH3], methyl 3,4-bis(n-dodecan-1-yloxy)benzoate [(3,4)-
12G1-CO2CH3], and their corresponding carboxylic acids form
crystal structures that were not yet elucidated, and therefore,
they are not shown in Schemes 4 and 5. (3,4,5-(3,4)n-1)12Gn-
X and (3,4)n12Gn-X with n ) 2-4 self-assemble into spherical
supramolecular dendrimers that self-organize in a Pm3hn lattice.
By increasing the generation number, n, and therefore the size,
the number of monodendrons, µ, that self-assemble in a sphere
decreases and the diameter, D, of the supramolecular dendrimer
increases. However, the increase of the diameter does not
correspond to the theoretical increase in the length of the
monodendron expected for two extended conformations of the
benzyl ether repeat unit i.e., 6.0 Å × 2 ) 12.0 Å. This
dependence is determined by the increase of the planar projec-
tion of the solid angle (R′) of the monodendron with the increase
of the generation number (n).7c,13 For the case of (3,4,5-(3,4)n-1)-
12Gn-X with n ) 2-4, the diameter increases from 52.8 to
54.2 Å and to 55.0 Å, while R′ increases from 11.6 to 22.5°
and to 45.0°. This doubling of R′ at each higher generation is
generated by the simultaneous reduction in half of the number
of monodendrons (µ) that self-assemble in a supramolecular
sphere. A much larger increase in diameter is observed for the
series (3,4)n12Gn-X with n ) 2-4, i.e., starting from 51.8-
59.6 Å to 69.4 or 64.3 Å (the last two values are dependent on
the temperature at which the XRD experiment was carried out).
This trend is due to a lower increase in R′ (from 8.6-12.0° to
15.7° or 19.0° depending on temperature) that is generated by
a higher number of monodendrons that self-assemble in a sphere
(µ) and subsequently a lower decrease of µ by increasing the
generation number. Therefore, according to these two series of
monodendrons, for the same internal repeat unit, it is the unit
from the periphery of the monodendron that determines the size

1308 J. Am. Chem. Soc., Vol. 123, No. 7, 2001
Percec et al.
Figure 2. Representative optical polarized texture exhibited by the hexagonal columnar (Φh) mesophase of (a) (4-3,4)12G1-CO2CH3 obtained
upon cooling from 99 to 61.3 °C at 1 °C/min, (b) (4-3,4-(3,5)2)12G3-CO2CH3 obtained upon cooling from 133 to 130.3 °C at 10 °C/min, (c)
(4-3,4,5-3,5)12G2-CH2OH obtained upon cooling from 101 to 85.3 °C at 1 °C/min, and (d) (4-3,4,5-(3,5)2)12G3-CO2CH3 obtained upon cooling
from 109 to 108.2 °C at 1 °C/min.
of the supramolecular dendrimer and of its monodendrons as
well as the dependence of µ, R′, and D on generation number.
From the analysis of these two series of monodendrons, we can
conclude that the attachment of a 3,4-bis(n-dodecan-1-yloxy)-
benzyl ether unit on the periphery provides a series of mono-
dendrons that have a lower solid angle and a larger increase of
their diameter as a function of n than the similar series
containing the 3,4,5-tris(n-dodecan-1-yloxy)benzyl ether unit on
the periphery.
supramolecular dendrimers. The trend observed for the case of
tapered monodendrons and cylindrical supramolecular dendrim-
ers is continued at higher generations for conical monodendrons
and spherical supramolecular dendrimers; i.e., (4-(3,4)n)12Gn-X
with n ) 2 and 3 exhibit lower R′ and higher diameter than the
series (4-3,4,5-(3,4)n-1)12Gn-X with n ) 2 and 3.
Scheme 6 summarizes the structural data of the library of
AB3 monodendrons functionalized on their periphery with the
same units as the AB2 library described in Scheme 4. At first
sight, these two libraries seem to represent a mirror image of
each other. A more detailed analysis reveals two major
differences. In the case of (4-3,4,5-(3,4)n-1)12Gn-X from the
AB2 library, the change in shape occurs at the transition from
generation 1 to 2, while for the case of the AB3 library for (4-
(3,4,5)n)12Gn-X, an identical change in shape takes place at
the transition from generation 2 to 3. All monodendrons of the
AB3 library (Scheme 6) have larger R′ values and consequently
their supramolecular dendrimers have lower diameters than the
supramolecular dendrimers of the AB2 library (Scheme 4).
Let us now compare the two constitutional isomeric libraries
based on 3,4- and 3,5-disubstituted AB2 internal repeat units
shown in Schemes 4 and 5. At first sight, the shapes of these
supramolecular dendrimers are completely different. This is
expected since we are comparing the physical properties of two
libraries of constitutional isomeric compounds. Since physical
properties of chemical compounds are determined by their
conformation, shape, and crystal structure, we have expected
differences between these two constitutional isomeric libraries.
However, we could not predict the dramatic difference observed
here. In Scheme 5, we see a single spherical supramolecular
dendrimer, i.e., corresponding to (3,4,5-(3,5)n-1)12Gn-X. The
series (3,4-(3,5)n-1)12Gn-X was reported previously8 and is
shown here for comparison. Both (3,4-(3,5)n-1)12Gn-X and (4-
3,4,5-(3,5)n-1)12Gn-X series follow a similar trend; i.e., by
The replacement of 3,4,5-tris(n-dodecan-1-yloxy)benzyl
ether and 3,4-bis(n-dodecan-1-yloxy)benzyl ether from the
periphery of (3,4,5-(3,4)n-1)12Gn-X and (3,4)n12Gn-X mono-
dendrons with 3,4,5-tris[p-(n-dodecan-1-yloxy)benzyloxy]benzyl
etherand, respectively, 3,4-bis[p-(n-dodecan-1-yloxy)benzyloxy]-
benzyl ether groups provides the (4-3,4,5-(3,4)n-1)12Gn-X and
(4-(3,4)n)12Gn-X series of monodendrons that are illustrated
in the last two columns of Table 4. By contrast to the two series
shown in the first two columns of Scheme 4 the first-generation
monodendrons of the last two series self-assemble into cylindri-
cal supramolecular dendrimers. The planar projection of the solid
angle of (4-3,4)12G1-X (R′) is lower than that of (4-3,4,5)-
12G1-X. Simultaneously, the diameter of the supramolecular
dendrimers generated from (4-3,4)12G1-X is larger than that
of the supramolecular dendrimer generated from (4-3,4,5)12G1-
X. At the transition from generation 1 to 2, both supramolecular
dendrimers change their shape from cylindrical to spherical, and
subsequently, their corresponding monodendrons change their
shape from tapered to conic. This shape change is in agreement
with theoretical predictions9 and with previous results from our
laboratory.7a,8 Therefore, we can conclude that the molecular
architecture of the unit from the periphery of the monodendron
determines the dependence of the solid angle of the monoden-
dron and the diameter of supramolecular dendrimer on genera-
tion number for the case of both cylindrical and spherical

AB2-Based Monodendrons and Supramolecular Dendrimers
J. Am. Chem. Soc., Vol. 123, No. 7, 2001 1309
exhibited by the monodendrons and supramolecular dendrimers
marked in the boxes in Scheme 5. They will be discussed in
the next subchapter.
Supramolecular Dendrimers Exhibiting Reversible Shape
Changes. (3,4,5-(3,5)n-1)12Gn-X with n ) 2 and 4 self-
assemble into supramolecular dendrimers with unknown shapes
and subsequently self-organize in lattices that were not yet
elucidated.
(3,4-(3,5)3)12G4-CO2CH3 (n ) 4 in second column of
Scheme 5) has a disklike shape that self-assembles in supramo-
lecular cylinders. The corresponding monodendron containing
a carboxylic acid in its focal point; i.e., (3,4-(3,5)3)12G4-COOH
exhibits a conical shape that self-assembles into a spherical
supramolecular dendrimer (Scheme 7a). Therefore, the cleavage
of the methyl ester group from the focal point of this mono-
dendron induces a change in monodendron shape from discotic
to conical and a supramolecular dendrimer shape change from
cylindrical to spherical (Scheme 7a). Simultaneously, a change
in lattice from the 2-D p6mm to the 3-D Pm3hn occurs. A similar
shape change is observed for (4-3,4,5-(3,5)2)12G3-CO2CH3 and
(4-3,4,5-(3,5)2)12G3-COOH (Scheme 7b). This demonstrates
that discotic monodendrons containing a carboxylic acid rather
than an ester in their focal point have the ability to change the
shape from disk to cone. The cleavage of an ester to a carboxylic
acid can be triggered via various mechanisms, and therefore,
the concept elaborated here can provide strategies to design
externally regulated supramolecular objects.
The most unexpected result is exhibited by (4-3,4,5-3,5)12G2-
CO2CH3 and (4-3,4,5-3,5)12G2-COOH (Scheme 7c). The
former monodendron exhibits a tapered shape that is the
equivalent of a third of a disk. Its carboxylic acid homologue
has a conelike shape. However, although the conical monoden-
dron self-assembles in a spherical supramolecular dendrimer,
its lattice does not have a Pm3hn symmetry as all previous cases
of (4-3,4,5-(3,5)2)12G3-COOH and (3,4-(3,5)3)12G4-COOH
exhibit, but it has an Im3hm symmetry. The possibility of a
bicontinuous structure for the Im3hm lattice was eliminated in a
previous publication.4 In the meantime, TEM and electron
density calculations have definitively confirmed that the Im3hm
lattice is generated from spherical objects. This work will be
published in due time.
Figure 3. X-ray diffractograms of (a) the p6mm 2-D lattice exhibited
by (4-3,4,5-(3,5)2)12G3-CO2CH3 at 87 °C, (b) the Pm3hn 3-D lattice
exhibited by (4-3,4,5-(3,4)2)12G3-CO2CH3 at 132 °C, and (c) the Im3hm
3-D lattice exhibited by (4-3,4,5-3,5)12G2-COOH at 80 °C.
Scheme 8 shows the two examples discovered so far of
supramolecular dendrimers that exhibit thermally induced shape
changes. The first is (4-3,4,5-3,5)12G2-CH2OH (Scheme 8a),
and the second is (4-3,4,5-(3,5)2)12G3-COOH (Scheme 8b). The
first one is based on a monodendron that changes its shape from
a third of a disk to a cone above 87 °C, and during this process,
the supramolecular dendrimer changes its shape from cylindrical
to spherical while the corresponding lattice transforms from a
p6mm to a Pm3hn symmetry. The second example of thermally
induced shape change is shown in Scheme 8b. It is based on a
disklike monodendron that at a higher temperature than 151 °C
(Tables 6-8) becomes conical. The lattice symmetries of these
two examples are identical, i.e., p6mm for the cylindrical supra-
molecular dendrimer and Pm3hn for the spherical supramolecular
dendrimer. Other functionalities at the focal point of these two
monodendrons do not provide molecules and supramolecules
that undergo thermal reversible shape changes. Another interest-
ing feature of the thermally induced phase and shape transition
is that the low-temperature p6mm lattice is 2-D while the high-
temperature Pm3hn phase is 3-D. According to thermodynamic
principles, this is an example of re-entrant phase transition, since
usually the phase at higher temperature should have a lower
symmetry.
increasing the generation number, the monodendrons change
their shape from a quarter of a disk to a third of a disk and
subsequently exhibit the shape of a disklike molecule. In both
series, there is a very small increase in the diameter of the
supramolecular cylindrical dendrimer followed by a decrease
when the supramolecular cylinder is generated from monoden-
dritic disks. The last series of monodendrons from this library,
i.e., (4-3,4-(3,5)n-1)12Gn-X, increases the number of mono-
dendrons forming a 4.7 Å cross section of a cylinder from µ )
12 (at n ) 1) to µ ) 5 (at n ) 2) and to µ ) 3 (at n ) 3).
However, even if the values of R′ increase with the increase in
the generation number, the diameter of the supramolecular
cylindrical dendrimers changes very little. This is partially
because the X-ray experiments were performed at higher
temperatures for higher generations. At higher temperatures, the
diameter of the supramolecular dendrimer shrinks.13 However,
this low increase in diameter is due to a combination of higher
temperature and small increase in size with n. In addition to
the striking and unpredictable structural differences between
these two constitutional isomeric libraries of AB2 monoden-
drons, there are several additional rewarding events that are

1310 J. Am. Chem. Soc., Vol. 123, No. 7, 2001
Percec et al.
Table 3. Measured d-Spacings of the p6mm Hexagonal Columnar and Pm3hn Cubic Lattices Generated by Selected Examples of 3,4- and
3,5-Disubstituted Monodendrons
T
d100
d110
(Å)
d200
(Å)
d210
(Å)
d211
(Å)
d220
(Å)
d310
(Å)
d222
(Å)
d320
(Å)
d321
(Å)
d400
(Å)
d420
(Å)
d421
(Å)
monodendron
(°C) lattice (Å)
(3,4,5-3,4) 12G2-CO2CH3
(3,4,5-(3,4)2)12G3-CO2CH3
(3,4,5-(3,4)2)12G3-CO2CH3
(3,4,5-(3,5)2)12G3-COOH
32 Pm3hn
58 Pm3hn
70 Pm3hn
89 Pm3hn
42.6 38.0 34.5
22.8 21.3
62.3 43.7 38.7 35.3 31.0 27.7 25.3 24.3 23.3 21.8 19.5 19.0
62.7 44.6 39.7 36.0 31.0 28.1 25.7 24.7 23.8 22.3 19.8 19.3
37.0 33.1 30.3 26.2 23.5 21.3 20.5 19.8 18.5
(3,4)212G2-COOH
(3,4)312G3-COOH
(3,4)412G4-COOH
112 Pm3hn
145 Pm3hn
95 Pm3hn
160 Pm3hn
42.4 37.7 34.2 29.6 26.7
48.3 42.9 39.0 33.9 30.5
55.8 50.1 45.6
22.6 21.1 18.8 18.3
25.7 24.0 21.4 20.9
29.9 28.0
52.0 46.3 42.1
32.7
27.8 26.0
(3,4-3,5)12G2-CH2OH
(3,4-3,5)12G2-COOH
(3,4-(3,5)2)12G3-CO2CH3
(3,4-(3,5)3)12G4-CO2CH3
49 p6mm 36.9 21.5 18.3
66 p6mm 38.0 21.5 18.6
36 p6mm 45.7 26.6 23.1
51 p6mm 39.4 22.8 19.8
(4-3,4,5)12G1-COOH
87 p6mm 35.4
112 Pm3hn
17.7
(4-3,4,5-3,4)12G2-CO2CH3
(4-3,4,5-3,4)12G2-COOH
49.1 43.8 40.1 34.8 31.2 28.5 27.4 26.5 24.9 22.2 21.7
45.8 40.9 37.6 32.5 29.1 26.6 25.7 24.8 23.2 20.6 20.2
73.3 51.6 46.3 42.2 36.5 32.6 29.8 28.6 27.5 25.8 23.0 22.5
71.6 50.7 45.4 41.5 35.8 32.1 29.2 28.1 27.0 25.3 22.6 22.1
70.7 49.8 44.7 40.8 35.2 31.4 28.7 27.6 26.6 24.9 22.2 21.6
20.4
140 Pm3hn
(4-3,4,5-(3,4)2)12G3-CO2CH3 117 Pm3hn
132 Pm3hn
142 Pm3hn
60 p6mm 40.5
70 p6mm 40.0
87 p6mm 40.0 23.0 19.9
97 p6mm 39.2 22.7 19.6
(4-3,4,5-3,5)12G2-CO2CH3
(4-3,4,5-(3,5)2)12G3-CO2CH3
20.0
(4-3,4)12G1-CO2CH3
(4-3,4)12G1-COOH
57 p6mm 49.7 28.9 24.9
77 p6mm 46.6
(4-(3,4)2)12G2-CO2CH3
(4-(3,4)3)12G3-CO2CH3
(4-3,4-3,5)12G2-CO2CH3
(4-3,4-3,5)12G2-CH2OH
(4-3,4-3,5)12G2-COOH
(4-3,4-(3,5)2)12G3-CO2CH3
(4-3,4-(3,5)2)12G3-COOH
89 Pm3hn
58.5 52.5 47.9 41.6 37.1 33.9 32.5 31.3 29.3
60.4 54.1 49.4 42.7 38.2 34.9 33.5 32.3 30.2
176 Pm3hn
100 p6mm 49.0 28.4 24.6 18.5
80 p6mm 46.0
100 p6mm 45.6 26.3 22.9
100 p6mm 49.8 29.0 25.1
147 p6mm 45.2 26.2 22.8 17.2
23.0
Table 4. Structural Characterization of Supramolecular Dendrimers Self-Assembled from Selected Examples of 3,4-Disubstituted
Monodendrons
monodendron
T (°C)
lattice
d100 a (Å)
a (Å)
F20c (g/cm3)
D (Å)
µ′ f
µ
R′ i (deg)
(3,4,5-3,4) 12G2-CO2CH3
(3,4,5-(3,4)2)12G3-CO2CH3
(3,4,5-(3,4)3)12G4-CO2CH3
32
58
70
Pm3hn
Pm3hn
Pm3hn
85.1b
87.3b
88.7b
0.98
0.96
0.97
52.8d
54.2d
55.0d
250
129
67
31g
16g
8g
11.6
22.5
45.0
(3,4)212G2-COOH
(3,4)312G3-COOH
(3,4)412G4-COOH
112
145
95
Pm3hn
Pm3hn
Pm3hn
Pm3hn
83.5b
96.0b
1.02
1.01
1.01
1.01
51.8d
59.6d
69.4d
64.3d
334
241
187
149
42g
30g
23g
19g
8.6
12.0
15.7
19.0
111.8b
103.7b
160
(4-3,4,5)12G1-COOH
87
112
140
117
132
142
p6mm
Pm3hn
Pm3hn
Pm3hn
Pm3hn
Pm3hn
35.4
40.9a
98.7b
1.02
1.03
1.03
1.00
1.00
1.00
40.9e
61.2d
57.2d
64.0d
62.8d
61.8d
4h
36g
29g
19g
18g
18g
90.0
10.0
12.4
19.0
20.0
20.0
(4-3,4,5-3,4)12G2-CO2CH3
(4-3,4,5-3,4)12G2-COOH
(4-3,4,5-(3,4)2)12G3-CO2CH3
285
234
155
147
140
92.2b
103.2b
101.3b
99.6b
(4-3,4)12G1-CO2CH3
(4-3,4)12G1-COOH
57
77
89
p6mm
p6mm
Pm3hn
Pm3hn
49.9
46.6
57.6a
53.8a
1.05
1.04
0.99
1.05
57.6e
53.8e
72.8d
75.0d
12h
11h
80g
45g
30.0
32.7
4.5
(4-(3,4)2)12G2-CO2CH3
(4-(3,4)3)12G3-CO2CH3
117.3b
120.9b
637
361
176
8.0
a p6mm hexagonal columnar lattice parameter a ) 2 d100 /31/2; d100 ) (d110 + 31/2d110 + 41/2d200 + 71/2d200)/4. b Pm3hn cubic lattice parameter
a ) (21/2d110 + 41/2d200 + 51/2d210 + 61/2d211 + 81/2d220 + 101/2d310 + 121/2d222 + 131/2d320 + 141/2d321 + 16d400 + 201/2d420 + 211/2d421)/12.
3
3
c
d
F20 ) experimental density at 20 °C. Experimental spherical diameter D ) 2 3a /32π. e Experimental column diameter D ) 2 d100 /31/2
.
x
f Number of monodendrons per unit cell µ′ ) (a3NAF)/M. g Number of monodendrons per Pm3hn spherical dendrimer µ ) µ′/8. h Number
of monodendrons per 4.7 Å column stratum µ ) (31/2NAD2tF)/2M (Avogadro’s number NA ) 6.022 045 × 1023 mol-1, the average height of
the column stratum t ) 4.7 Å, and M ) molecular weight of monodendron). i Projection of the solid angle for tapered and conical monodendron
R′ ) 360/µ (deg).
The monodendrons and supramolecular dendrimers that
undergo shape changes either via the change of the functionality
of their focal point or by temperature are expected to generate
novel technological applications. At the same time, they provide
an elegant demonstration of the quasi-equiValence11 of these
dendritic building blocks.
At present we do not understand the design principles for
the synthesis of additional monodendrons that undergo reversible
shape changes. Nevertheless, several structural particularities
that favor shape changes can be obtained by the inspection of
Schemes 5, 7, and 8. These schemes indicate that the mono-
dendrons that undergo shape changes by chemical modification

AB2-Based Monodendrons and Supramolecular Dendrimers
J. Am. Chem. Soc., Vol. 123, No. 7, 2001 1311
Table 5. Structural Characterization of Supramolecular Dendrimers Self-Assembled from Selected Examples of 3,5-Disubstituted
Monodendrons
monodendron
T (°C)
lattice
d100 a (Å)
a (Å)
F20c (g/cm3)
D (Å)
µ′ f
µ
R′ i (deg)
(3,4,5-(3,5)2)12G3-COOH
(3,4-3,5)12G2-CH2OH
(3,4-3,5)12G2-COOH
89
49
66
36
51
Pm3hn
p6mm
p6mm
p6mm
p6mm
74.1b
42.6a
43.3a
53.1a
45.6a
0.97
0.99
1.02
1.01
0.99
46.0d
42.6e
43.3e
53.1e
45.6e
80
10g
36.0
90.0
90.0
120.0
360.0
36.9
37.5
46.0
39.5
4h
4h
(3,4-(3,5)2)12G3-CO2CH3
(3,4-(3,5)3)12G4-CO2CH3
3h
1h
(4-3,4,5)12G1-COOH
(4-3,4,5-3,5)12G2-CO2CH3
87
60
70
87
97
p6mm
p6mm
p6mm
p6mm
p6mm
35.4
40.7
39.9
39.9
39.2
40.9a
47.0a
46.1a
46.1a
45.3a
1.02
1.02
1.02
1.02
1.02
40.9e
47.0e
46.1e
46.1e
45.3e
4h
3h
3h
1h
1h
90.0
120.0
120.0
360.0
360.0
(4-3,4,5-(3,5)2)12G3-CO2CH3
(4-3,4)12G1-CO2CH3
(4-3,4)12G1-COOH
57
77
100
90
100
100
147
p6mm
p6mm
p6mm
p6mm
p6mm
p6mm
p6mm
49.9
46.6
49.1
46.0
45.7
50.1
45.4
57.6a
53.8a
56.7a
53.1a
52.8a
57.9a
52.4a
1.05
1.04
1.00
1.06
1.03
1.04
1.04
57.6e
53.8e
56.7e
53.1e
52.8e
57.9e
52.4e
12h
11h
5h
30.0
32.7
72.0
72.0
72.0
(4-3,4-3,5)12G2-CO2CH3
(4-3,4-3,5)12G2-CH2OH
(4-3,4-3,5)12G2-COOH
(4-3,4-(3,5)2)12G3-CO2CH3
(4-3,4-(3,5)2)12G3-COOH
5h
5h
3h
120.0
180.0
2h
a p6mm hexagonal columnar lattice parameter a ) 2 d100 /31/2; d100 ) (d110 + 31/2d110 + 41/2d200 + 71/2d200)/4. b Pm3hn cubic lattice parameter
a ) (21/2d110 + 41/2d200 + 51/2d210 + 61/2d211 + 81/2d220 + 101/2d310 + 121/2d222 + 131/2d320 + 141/2d321 + 161/2d400 + 201/2d420 + 211/2d421)/12.
3
3
c
d
F20 ) experimental density at 20 °C. Experimental spherical diameter D ) 2 3a /32π. e Experimental column diameter D ) 2 d100 /31/2
.
x
f Number of monodendrons per unit cell µ′ ) (a3NAF)/M. g Number of monodendrons per Pm3hn spherical dendrimer µ ) µ′/8. h Number
of monodendrons per 4.7 Å column stratum µ ) (31/2NAD2tF)/2M (Avogadro’s number NA ) 6.022 045 × 1023 mol-1, the average height of
the column stratum t ) 4.7 Å, and M ) molecular weight of monodendron). i Projection of the solid angle for tapered and conical monodendron
R′ ) 360/µ (deg).
Scheme 4. Retrostructural Analysis of Supramolecular Dendrimers Self-Assembled from AB2 3,4-Disubstituted Monodendrons
at their focal point or by temperature are based on molecules
that display either a disklike shape or a tapered shape that is
the equivalence of a third of a disk. The functionality that favors
a disklike monodendron and a cylindrical supramolecular
dendrimer is noninteracting, i.e., ester, while the functionality
that stabilizes a conical monodendron and a spherical supramo-

1312 J. Am. Chem. Soc., Vol. 123, No. 7, 2001
Percec et al.
Scheme 5. Retrostructural Analysis of Supramolecular Dendrimers Self-Assembled from AB2 3,5-Disubstituted Monodendron
Table 6. Theoretical and Experimental Molecular Weights Determined by GPC and Thermal Transitions of the Monodendrons that
Self-Assemble into Supramolecular Dendrimers Which Exhibit Reversible Shape Changes
thermal transitions (°C) and corresponding enthalpy changes (kcal/mol)a
Mn Mw/Mn
monodendron
MWt (GPC) (GPC)
heating
cooling
(3,4-(3,5)3)12G4-CO2CH3
4571.0 5998
1.09 kb 15 (72.96) k 42 (4.38) Φhc 66 (1.09) id
k -12 (18.92) Φh 66 (1.06) i
i 58 (0.86) Φh -18 (14.95) k
(3,4-(3,5)3)12G4-COOH
4557.0 5778
1.09 k -10 (11.52) k 39 (38.97) Cube 109 (1.48) i i 104 (1.39) Cub -14 (11.87) k
k -9 (10.58) Cub 109 (1.25) i
(4-3,4,5-3,5)12G2-CO2CH3
(4-3,4,5-3,5)12G2-CH2OH
2091.1 3104
2063.1 3155
1.05 k 54 (36.82) -k 66 (9.23) k 82 (0.22) i
k -19 (7.95) Φh 71 (2.13) i
i 66 (2.15) Φh -23 (7.62) k
1.05 k -18 (0.22) k 57 (13.72)f Φh 87 (0.50)
Cub 101 (0.22) if
i 90 (0.05) Cub 74 (0.68) Φh -24 (3.73) k
k -18 (4.14) Tgg 28 Φh 87 (0.59)
Cub 101 (0.18) i
(4-3,4,5-3,5)12G2-COOH
2077.1 3134
1.05 k 35 (168.4)f Cubh 196 (0.64) i
k -19 (21.02) k 75 (3.34) Cubh 165 (0.86)
Cubh 195 (0.50) i
i 181 (0.17) Cub 64 (1.30) k -22 (8.28) k
i 103 (3.72) Φh -22 (21.79) k
(4-3,4,5-(3,5)2)12G3-CO2CH3 4258.3 5876
(4-3,4,5-(3,5)2)12G3-COOH 4244.2 5737
1.08 k -12 (39.64) k 60 (8.35) Φh 109 (3.63) i
k -17 (44.15) Φh 108 (3.37) i
1.08 k -12 (31.89) k 51 (3.54) Φh 151 (0.21)
Cub 164 (0.44) i
i 152 (0.29) Cub 119 (0.33) Φh 88 (0.32)
Tg 40 -24 (16.37) k
k -21 (23.35) Φh 151 (2.03) Cub 164 (3.05) i
a Data from the first heating and cooling scans are on the first line, and data from the second heating are on the second line. b k ) crystalline.
c Φh ) p6mm hexagonal columnar lattice. d i ) isotropic. e Cub ) Pm3hn cubic lattice. f Sum of enthalpies from overlapped peaks. g Tg ) glassy
transition temperature. h Cub ) Im3hm cubic lattice. The Im3hm to Im3hm transition from the second heating scan of (4-3,4,5-3,5)12G2-COOH represents
a discontinuous change in the XRD intensity of the same symmetry.
lecular dendrimer requires interactions by H-bonding. In addi-
tion, the molecules that undergo shape changes as a function
of temperature always have an H-bonding functionality in their
focal point. Although extensive modeling experiments are in
progress in various laboratories,20,21 we currently do not
understand why the present supramolecular dendrimers self-
organize mostly in a Pm3hn lattice. Examples of small polyphilic
molecules that exhibit transitions between columnar and various
cubic phases are available in the literature.23 However, in this
case,23 the authors claim that the type of the mesophase is
(20) Cagin, T.; Wang, G.; Martin, R.; Goddard, W. A., III, in preparation.
(21) Ziherl, P.; Kamien, R. D. Phys. ReV. Lett. 2000, 85, 3528.

AB2-Based Monodendrons and Supramolecular Dendrimers
J. Am. Chem. Soc., Vol. 123, No. 7, 2001 1313
Scheme 6. Retrostructural Analysis of Supramolecular Dendrimers Self-Assembled from AB3 3,4,5-Trisubstituted Monodendron
Table 7. Measured d-Spacings of the p6mm Hexagonal Columnar, Pm3hn, and Im3hm Cubic Lattices Generated by the Monodendrons that
Self-Assemble into Supramolecular Dendrimers Which Exhibit Reversible Shape Changes
T
d100
d110
(Å)
d200
(Å)
d210
(Å)
d211
(Å)
d220
(Å)
d310
(Å)
d222
(Å)
d320
(Å)
d321
(Å)
d400
(Å)
d420
(Å)
d421
(Å)
monodendron
(°C) lattice (Å)
(3,4-(3,5)3)12G4-CO2CH3
(3,4-(3,5)3)12G4-COOH
51 p6mm 39.4 22.8 19.8
97 Pm3hn 39.4 62.5 44.6 40.0 36.6 31.7 28.4 25.8 24.8 24.0 22.4
(4-3,4,5-3,5)12G2-CO2CH3
(4-3,4,5-3,5)12G2-CH2OH
(4-3,4,5-3,5)12G2-COOH
(4-3,4,5-(3,5)2)12G3-CO2CH3
(4-3,4,5-(3,5)2)12G3-COOH
60 p6mm 40.5
70 p6mm 40.0
67 p6mm 40.4 23.3 20.2
92 Pm3hn
80 Im3hm
120 Im3hm
87 p6mm 40.0 23.0 19.9
97 p6mm 39.2 22.7 19.6
137 p6mm 39.7
20.4
20.0
43.6 39.0 35.7 31.0 27.6 25.2 24.2 23.3 21.8 19.5 19.0
38.5 27.2
36.3 25.7
22.1 19.1
20.9 18.1
155 Pm3hn
43.9 39.3 35.9 31.0 27.8
determined by the principles of classic lyotropic liquid crystals.
In our case, the dendritic architectural effect provides a more
complex and unique phase behavior.
The structural and retrostructural analysis of their corresponding
supramolecular dendrimers have demonstrated that the shapes
of the supramolecular dendrimers and of their monodendritic
building blocks are completely different; i.e., while the supra-
molecular dendrimers derived from 3,4-dibenzyl ether mono-
dendrons are spherical, most the supramolecular dendrimers
derived from 3,5-dibenzyl ether monodendrons are cylindrical.
As a consequence, the monodendritic building blocks of the
3,4-disubstituted series have a conelike shape while those of
3,5-disubstituted series have a shape that corresponds to a
fragment of a disk or a disklike shape. In addition, the 3,4-
dibenzyl ether-based library resembles the 3,4,5-tribenzyl ether
library reported previously from our laboratory.3a,7 The major
Conclusions
Two constitutional isomeric libraries of AB2-based self-
assembling monodendrons containing 3,4-dibenzyl ether and
3,5-dibenzyl ether internal repeat units and four different
minidendritic repeat units on their periphery were synthesized.
(22) (a) Percec, V.; Kawasumi, M. Macromolecules 1992, 25, 3843. (b)
Percec, V.; Chu, P.; Kawasumi, M. Macromolecules 1994, 27, 4441.
(23) Borisch, K.; Diele, S.; Go¨ring, P.; Kresse, H.; Tschierske, C. J.
Mater. Chem. 1998, 8, 529.

1314 J. Am. Chem. Soc., Vol. 123, No. 7, 2001
Percec et al.
Scheme 7. Reversible Shape Changes of Supramolecular Dendrimers via Molecular Recognition and Chemical Reactions
Scheme 8. Temperature-Induced Reversible Shape Change between Cylindrical and Spherical Supramolecular Dendrimers
Self-Organized in a Lattice
difference between the 3,4-disubstituted and 3,4,5-trisubstituted
constitutional isomeric libraries is the number of monodendritic
building blocks that self-assemble in a supramolecular den-
drimer. The 3,4,5-trisubstituted library has fewer monodendrons
self-assembling in a supramolecular dendrimer than the 3,4-
disubstituted-based library.
In all three libraries, the structure of the internal repeat unit
determines the shape of the monodendron and of the supramo-

AB2-Based Monodendrons and Supramolecular Dendrimers
J. Am. Chem. Soc., Vol. 123, No. 7, 2001 1315
Table 8. Structural Characterization of Monodendrons that Self-Assemble into Supramolecular Dendrimers Which Exhibit Reversible Shape
Changes
monodendron
T (°C)
lattice
d100 a (Å)
a (Å)
F20d (g/cm3)
D (Å)
µ′ h
µ
R′ l (deg)
(3,4-(3,5)3)12G4-CO2CH3
(3,4-(3,5)3)12G4- COOH
51
97
p6mm
Pm3hn
39.5
45.6a
89.5b
0.99
1.00
45.6e
55.5f
1i
360.0
30.0
95
12j
(4-3,4,5-3,5)12G2-CO2CH3
(4-3,4,5-3,5)12G2-CH2OH
(4-3,4,5-3,5)12G2-COOH
(4-3,4,5-(3,5)2)12G3-CO2CH3
(4-3,4,5-(3,5)2)12G3-COOH
60
70
67
92
80
120
87
97
137
155
p6mm
p6mm
p6mm
Pm3hn
Im3hm
Im3hm
p6mm
p6mm
p6mm
Pm3hn
40.7
39.9
40.4
47.0a
46.1a
46.7a
87.3b
54.2c
51.3c
46.1a
45.3a
45.8a
87.8b
1.02
1.02
1.01
1.01
1.03
1.03
1.02
1.02
1.04
1.04
47.0e
46.1e
46.7e
54.2f
53.4g
50.5g
46.1e
45.3e
45.8e
54.5f
3i
3i
120.0
120.0
120.0
14.4
15.0
18.0
360.0
360.0
360.0
27.7
3i
196
48
40
25j
24k
20k
1i
39.9
39.2
39.7
1i
1i
100
13j
a p6mm hexagonal columnar lattice parameter a ) 2 d100 /31/2; d100 ) (d110 + 31/2d110 + 41/2d200 + 71/2d200)/4. b Pm3hn cubic lattice parameter
a ) (21/2d110 + 41/2d200 + 51/2d210 + 61/2d211 + 81/2d220 + 101/2d310 + 121/2d222 + 131/2d320 + 141/2d321 + 161/2d400 + 201/2d420 + 211/2d421)/12.
d
c Im3hm cubic lattice parameter a ) (21/2d110 + 41/2d200 + 61/2d211 + 81/2d220)/4. F20 ) experimental density at 20 °C. e Experimental column diameter
3
3
3
3
f
g
D ) 2 d100 /31/2
.
Experimental Pm3hn spherical diameter D ) 2 3a /32π. Experimental Im3hm spherical diameter D ) 2 3a /8π. h Number
x
x
of monodendrons per unit cell µ′ ) (a3NAF)/M. i Number of monodendrons per 4.7 Å column stratum µ ) (31/2NAD2tF)/2M (Avogadro’s number
NA ) 6.022 045 × 1023 mol-1, the average height of the column stratum t ) 4.7 Å, and M ) molecular weight of monodendron). j Number
of monodendrons per Pm3hn spherical dendrimer µ ) µ′/8. k Number of monodendrons per Im3hm spherical dendrimer µ ) µ′/2. l Projection of
the solid angle for tapered and conical monodendron R′ ) 360/µ (deg).
lecular dendrimer. However, for the same internal repeat unit,
the size of the monodendron and of the supramolecular
dendrimer is determined by the structure of the repeat unit on
their periphery. This result is in agreement with the first
examples of monodendrons and hyperbranched polymers that
self-organize in a lattice reported from our laboratory10,22 and
with related experiments reported from other laboratories.24 The
number of monodendrons that self-assemble in a supramolecular
dendrimer determines the solid angle of the monodendron. The
solid angle of the monodendron determines the shape of the
monodendron and of the supramolecular dendrimer and ulti-
mately the diameter of the supramolecular dendrimer. Regardless
of the shape of the monodendron and of the supramolecular
dendrimer, the solid angle of the monodendron increases
with the increase of the generation number. Subsequently, the
shape of the monodendron changes from a fragment of a disk
to a disk, to a cone, to a half of a sphere, and ultimately to a
sphere. As a consequence, the diameter of the supramolecular
dendrimers self-assembled from AB2 or AB3 benzyl ether
monodendrons with identical internal repeat units in each
generation and different repeat units on their periphery seem to
be limited to maximum 80 Å. This is because prior to the
transition from a monodendritic fragment of a sphere to a
monodendritic sphere,7b the increase in solid angle is very large
and as a consequence the increase in diameter is very small.
The library based on 3,5-disubstituted benzyl ethers provides
the first example of quasi-equiValent monodendrons and supra-
molecular dendrimers that are able to change their shape in a
reversible way both by the change of the functionality available
at their focal point and by temperature. In addition, the same
library provided the first example of a spherical supramolecular
dendrimer that self-organizes in an Im3hm lattice and several
examples of monodendrons that self-assemble and subsequently
self-organize into new lattices. The three libraries of self-
assembling monodendrons discussed here provide building
blocks required for the construction of functional supramolecular
and single-molecule-based nanosystems. However, alternative
design principles should be elaborated for the construction
of monodendrons and supramolecular dendrimers of larger
dimensions.
Experimental Section
The synthetic methods and techniques are similar to those used
conventionally in our laboratory.3a,7,8 They are presented in the
Supporting Information.
Acknowledgment. Financial support by the National Science
Foundation (DMR-99-96288), MURI-ARO, the Engineering and
Physical Science Research Council, UK, and the Synchrotron
Radiation Source at Daresbury, UK, are gratefully acknowl-
edged. We are also grateful to Professor S. Z. D. Cheng of the
University of Akron for density measurements.
Supporting Information Available: Experimental proce-
dures with characterization results and figures (PDF). This
material is available free of charge via the Internet at
http://pubs.acs.org.
(24) Baars, M. W. P. L.; So¨ntjens, S. H. M.; Fischer, H. M.; Peerlings,
H. W. I.; Meijer, E. W. Chem. Eur. J. 1998, 4, 2456 and references therein.
JA0037771