Shape-Persistent Macrocycles with Intraannular Polar Groups: Synthesis, Liquid Crystallinity, and 2D Organization

Article abstract of DOI:10.1021/ja038484x

The synthesis of macrocycles with intraannular polar ester groups and extraannular oligo-alkyl groups is described. The compounds exhibit stable liquid crystalline phases showing fan-shaped textures under the polarizing microscope, typical for a columnar

Full text of DOI:10.1021/ja038484x

Published on Web 12/09/2003
Shape-Persistent Macrocycles with Intraannular Polar
Groups: Synthesis, Liquid Crystallinity, and 2D Organization
Matthias Fischer,† Gu¨nter Lieser,*,† Almut Rapp,† Ingo Schnell,*,† Wael Mamdouh,‡
Steven De Feyter,*,‡ Frans C. De Schryver,‡ and Sigurd Ho¨ger*,†,§
Contribution from the Max Planck Institute for Polymer Research, Ackermannweg 10,
D-55128 Mainz, Germany, and Katholieke UniVersiteit LeuVen (K.U.LeuVen),
Department of Chemistry, Celestijnenlaan 200 F, B-3001 LeuVen, Belgium
Received September 12, 2003; E-mail: hoeger@chemie.uni-karlsruhe.de
Abstract: The synthesis of macrocycles with intraannular polar ester groups and extraannular oligo-alkyl
groups is described. The compounds exhibit stable liquid crystalline phases showing fan-shaped textures
under the polarizing microscope, typical for a columnar order of the molecules. X-ray powder diffraction
data of the LC phase indicate that the unit cell contains two symmetry-related units, a feature pointing
most probably to a restricted rotation of the macrocycles within a stack. The X-ray data were further
supported by solid-state NMR experiments, showing that the rigid core of the compounds does not rotate
with kHz or higher frequencies within the column in the LC phase. Apart from the organization of the
molecules in the LC phase, the 2D organization of the macrocycles at the solvent-highly oriented pyrolytic
graphite (HOPG) interface was investigated and showed that these compounds are capable of nanofunc-
tionalizing the HOPG surface in the multinanometer regime.
phase.5 Subsequent investigations in this area led recently to
the fabrication of highly efficient photovoltaic elements.6
Introduction
The investigation of shape-persistent macrocycles has become
a topic of growing interest during the past decade. Apart from
the synthesis, special emphasis is given to the supramolecular
aspects of these compounds. These include, among others, the
binding of appropriate guest molecules, the pattern formation
at interfaces, and the organization of the molecules in the
crystalline and in the liquid crystalline state.1 Liquid crystalline
materials based on disklike mesogens (discotic liquid crystals)
were first described by Chandrasekhar more than 25 years ago.2
They are, in general, composed of a disklike or macrocyclic
core and flexible side groups pointing to the outside.3 Apart
from their possible applications in display technology,4 they have
attracted much attention since Adam et al. found that discotic
liquid crystals based on a polycyclic aromatic core exhibit high
mobilities for photoinduced charge carriers in the columnar
If the mesogenic unit of the liquid crystal is a macrocycle,
the arrangement of the mesogens in an axial stack might form
a hollow column leading to a tubular superstructure.7
A
necessary prerequisite for the formation of a supramolecular
hollow columnar structure is to prevent the macrocycles from
collapsing. In flexible ring systems, this can be accomplished
by the formation of host-guest complexes.8 However, the
formation of tubular superstructures from shape-persistent
macrocycles seems to be more attractive because these mesogens
are, per se, noncollapsed.9 Therefore, functional groups inside
the rings (intraannular substituents) are not blocked by the
interaction with guest molecules but remain rather free, leading
to the formation of intraannular functionalized nanotubes.10,11
As an additional feature unavailable in discotic liquid crystals
based on disklike molecules, shape-persistent macrocycles allow
† Max Planck Institute for Polymer Research.
(5) Adam, D.; Schuhmacher, P.; Simmerer, J.; Ha¨ussling, L.; Siemensmeyer,
K.; Etzbach, K. H.; Ringsdorf, H.; Haarer, D. Nature 1994, 371, 141-
143.
(6) (a) Ito, S.; Wehmeier, M.; Brand, J. D.; Ku¨bel, C.; Epsch, R.; Rabe, J. P.;
Mu¨llen, K. Chem.-Eur. J. 2000, 6, 4327-4342. (b) Schmidt-Mende, L.;
Fechtenko¨tter, A.; Mu¨llen, K.; Moons, E.; Friend, R. H.; MacKenzie, J. D.
Science 2001, 293, 1119-1122.
(7) Behr, J.-P.; Lehn, J.-M.; Dock, A.-C.; Moras, D. Nature 1982, 295, 526-
527.
(8) (a) Lehn, J. M.; Maltheˆte, J.; Levelut, A. M. J. Chem. Soc., Chem. Commun.
1985, 1794-1796. (b) Lattermann, G. Mol. Cryst. Liq. Cryst. 1990, 182B,
299-311. (c) Liebmann, A.; Mertesdorf, C.; Plesnivy, T.; Ringsdorf, H.;
Wendorff, J. H.; Angew. Chem. 1991, 103, 1358-1361; Angew. Chem.,
Int. Ed. Engl. 1991, 30, 1375-1377.
(9) (a) Mindyuk, O. Y.; Stetzer, M. R.; Heiney, P. A.; Nelson, J. C.; Moore,
J. S. AdV. Mater. 1998, 10, 1363-1366. (b) Zhang, J.; Moore, J. S. J. Am.
Chem. Soc. 1994, 116, 2655-2656.
(10) For the concept of intraannular functional groups, see for example: (a)
Vo¨gtle, F.; Neumann, P. Tetrahedron 1970, 26, 5299-5318. (b) Weber,
E.; Vo¨gtle, F. Chem. Ber. 1976, 109, 1803-1831.
‡ Katholieke Universiteit Leuven (K. U. Leuven).
§ New address: Polymer Institute, Universita¨t Karlsruhe, Engesserstr.
18, D-76131 Karlsruhe, Germany.
(1) For recent reviews on shape-persistent macrocycles, see for example: (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.
(2) (a) Chandrasekhar, S.; Sadashiva, B. K.; Suresh, K. A. Pramana 1977, 7,
471-480. (b) Chandrasekhar, S. In Handbook of Liquid Crystals; Demus,
D., Goodby, J., Gray, G. W., Spiess, H.-W., Vill, V., Eds.; Wiley-VCH:
Weinheim, Germany, 1998; Vol. 2B, pp 749-780. (c) Bushby, R. J.;
Lozman, O. R. Curr. Opin. Colloid Interface Sci. 2002, 7, 343-354.
(3) For an exception of this rule, see: Ho¨ger, S.; Enkelmann, V.; Bonrad, K.;
Tschierske, C. Angew. Chem. 2000, 112, 2356-2358; Angew. Chem., Int.
Ed. 2000, 39, 2268-2270.
(4) Kumar, S.; Varshney, S. K. Angew. Chem. 2000, 112, 3270-3272; Angew.
Chem., Int. Ed. 2000, 39, 3140-3142.
9
214
J. AM. CHEM. SOC. 2004, 126, 214-222
10.1021/ja038484x CCC: $27.50 © 2004 American Chemical Society

Macrocycles with Intraannular Polar Groups
A R T I C L E S
Chart 1
Chart 2
problem could be solved by attaching polystyrene substituents
to the macrocyclic backbone, as in the macrocycles 2 (Chart
2).15
These compounds dissolve even in cyclohexane and form
supramolecular tubes in solution, depending on the size of the
attached polystyrene, as has been investigated by scattering as
well as imaging methods. However, none of these coil-ring-
coil block copolymers exhibit a thermotropic columnar meso-
phase. These observations lead us to the assumption that the
large internal void inside the noncollapsible macrocycles
prevents the system from forming a stable thermotropic meso-
phase due to the frustration between the molecular anisotropy
and the empty space inside the rings: It can be assumed that
the empty space inside the rings is not filled by backfolding of
the extraannular substituents attached to the periphery of 1 or
2. Hence, the alkyl (oligo-styryl) groups of adjacent rings have
to point inside the macrocycles, and the competition between
orientational correlation of the rigid parts of the molecule and
the necessity of the side groups to fill the interior of adjacent
rings prevent the formation of a stable LC phase. This hypothesis
is further supported by the observation that isomers of 1a with
a filled cavity do exhibit a stable mesophase.3 However, an
alternative explanation for the absence of a stable thermotropic
mesophase in 1 and 2 could be the incorrect balance between
the core dimension and the size of the flexible periphery.16
To get a deeper insight into the molecular requirements for
the formation of a stable LC phase in these macrocycles, we
intended to investigate derivatives of 1 in which the interior of
the mesogenic unit is filled by intraannular polar groups. If the
balance between rigid and flexible parts of the molecule is
correct, the filling of the interior should allow the formation of
a stable LC phase. Additionally, the intermolecular interaction
of the polar intraannular groups should prevent the molecules
from sliding relative to each other and, in this way, stabilize a
columnar packing motive in the mesophase.
the investigation of the influence of intraannular substituents
(e.g., size, polarity, etc.) on the thermal behavior of the materials,
while other molecular parameters (e.g., core dimension, grafting
positions, length of the aliphatic tails, etc.) can be kept
constant.12
Recently, we described shape-persistent macrocycles 1a-c
with alkyl and oligo-alkyl substituents of defined size (Chart
1).13 At first glance, these compounds match the design principle
of discotic liquid crystals, namely, a stiff core unit surrounded
by a flexible periphery. However, none of the compounds
exhibits a stable thermotropic LC phase. In addition, the
formation of a tubular superstructure by the aggregation of the
macrocycles in solution could also not be observed. An
aggregation of the macrocycles in CH2Cl2 could be induced by
the addition of hexane, which is a nonsolvent for the rigid
macrocyclic core, but restricted compound solubility prevents
the observation of high aggregation constants.14 The solubility
(11) For shape-persistent macrocycles containing intraannular functional groups,
see for example: (a) Anderson, H. L.; Sanders, J. K. M. J. Chem. Soc.,
Chem. Commun. 1992, 946-947. (b) Anderson, S.; Neidlein, U.; Gramlich,
V.; Diederich, F. Angew. Chem. 1995, 107, 1722-1726; Angew. Chem.,
Int. Ed. Engl. 1995, 34, 1596-1600. (c) Morrison, D. L.; Ho¨ger, S. J. Chem.
Soc., Chem. Commun. 1996, 2313-2314. (d) Tobe, Y.; Utsumi, N.;
Kawabata, K.; Nagano, A.; Naemura, K. Angew. Chem. 1998, 110, 1347-
1349; Angew. Chem., Int. Ed. 1998, 37, 1285-1287. (e) Ho¨ger, S.;
Meckenstock, A.-D. Chem.-Eur. J. 1999, 5, 1686-1691. (f) Lehman, U.;
Schlu¨ter, A. D. Eur. J. Org. Chem. 2000, 3483-3487. (g) Hosokawa, Y.;
Kawase, T.; Oda, M. J. Chem. Soc., Chem. Commun. 2001, 1948-1949.
(h) Ho¨ger, S.; Morrison, D. L.; Enkelmann, V. J. Am. Chem. Soc. 2002,
124, 6734-6736. (i) Fischer, M.; Ho¨ger, S. Eur. J. Org. Chem. 2003, 441-
446. (j) Grave, C.; Lentz, D.; Scha¨fer, A.; Samori, P.; Rabe, J. P.; Franke,
P.; Schlu¨ter, A. D. J. Am. Chem. Soc. 2003, 125, 6907-6918. (k) Fischer,
M.; Ho¨ger, S. Tetrahedron 2003, 59, 9441-9446.
(12) Heinrich, B.; Praefke, K.; Guillon, D. J. Mater. Chem. 1997, 7, 1363-
1372.
(13) Ho¨ger, S.; Bonrad, K.; Mourran, A.; Beginn, U.; Mo¨ller, M. J. Am. Chem.
Soc. 2001, 123, 5651-5659.
(14) For the aggregation of large macrocycles, see, for example: (a) Zhang, J.;
Moore, J. S. J. Am. Chem. Soc. 1992, 114, 9701-9702. (b) Shetty, A. S.;
Zhang, J.; Moore, J. S. J. Am. Chem. Soc. 1996, 118, 1019. (c) Tobe, Y.;
Nagano, A.; Kawabata, K.; Sonoda, M.; Naemura, K. Org. Lett. 2000, 2,
3265-3268. (d) Nakamura, K.; Okubo, H.; Yamaguchi, M. Org. Lett. 2000,
2, 3265. (e) Tobe, Y.; Utsumi, N.; Kawabata, K.; Nagano, A.; Adachi, K.;
Araki, S.; Sonoda, M.; Hirose, K.; Nakamura, K. J. Am. Chem. Soc. 2002,
124, 5350-5364. (f) Zhao, D.; Moore, J. S. J. Org. Chem. 2002, 67, 3548-
3554. (g) Saiki, Y.; Sugiura, H.; Nakamura, K.; Yamaguchi, M.; Hoshi,
T.; Anzai, J. J. Am. Chem. Soc. 2003, 125, 9268-9269.
(15) (a) Rosselli, S.; Ramminger, A.-D.; Wagner, T.; Silier, B.; Wiegand, S.;
Ha¨uâler, W.; Lieser, G.; Scheumann, V.; Ho¨ger, S. Angew. Chem. 2001,
113, 3234-3237; Angew. Chem., Int. Ed. 2001, 40, 3138-3141. (b) Ho¨ger,
S.; Bonrad, K.; Rosselli, S.; Meckenstock, A.-D.; Wagner, T.; Silier, B.;
Wiegand, S.; Ha¨uâler, W.; Lieser, G.; Scheumann, V. Macromol. Symp.
2002, 177, 185-191. (c) Rosselli, S.; Ramminger, A.-D.; Wagner, T.;
Lieser, G.; Ho¨ger, S. Chem.-Eur. J. 2003, 9, 3481-3491.
(16) Kohne, B.; Praefcke, K. Chem.-Ztg. 1985, 109, 121-127.
9
J. AM. CHEM. SOC. VOL. 126, NO. 1, 2004 215

A R T I C L E S
Fischer et al.
Scheme 1 a
a (a) 4-Bromotrimethylorthobutyrate, K2CO3, DMF (73%). (b) PdCl2(PPh3)2, CuI, NEt3 (87%). (c) Bu4NF, THF/H2O (74%). (d) PdCl2(PPh3)2, CuI, NEt3/
THF (81%). (e) TMS-acetylene, PdCl2(PPh3)2, CuI, piperidine (86%). (f) K2CO3, MeOH/THF (89%). (g) CuCl, CuCl2, pyridine, 29%. (h) p-TsOH, MeOH,
CHCl3, 68%. (i) tris(alkoxy)benzyl chloride, K2CO3, DMF, 30-48%.
Apart from the formation of 1D superstructures, shape-
persistent macrocycles can be the basis for regular 2D structures.
In the case of extraannular functionalized macrocycles, it has
been shown that the interaction of the polar groups in the solid
state can lead to the formation of (quasi) 2D structures.17
However, in that case, the functional groups are essential for
the superstructure stabilization and do not remain free for the
recognition of additional objects. Pattern formation at interfaces
is an attractive alternative because it does not rely on the specific
functional group interaction. Therefore, those remain free and
might be used for the creation of supramolecular 3D structures,
using the 2D structure as a template. Previous experiments have
shown that 1c forms regular 2D structures at the surface of
highly oriented pyrolytic graphite (HOPG). In that case, the
driving force for the pattern formation is purely dissipative.13
Therefore, similar pattern formation of intraannular function-
alized macrocycles should offer additional features since it leads
not only to a nanopatterned surface but also to a functionalized
nanopatterned surface using the intraannular anchor groups for
the epitaxially induced 3D superstructure formation.18
Results and Discussion
Synthesis and Characterization. Target structures of our
investigations are the macrocycles 3a and 3b, which can be
viewed as intraannular functionalized analogues of the previ-
ously described compound 1. The synthesis of the macrocycles
is outlined in Scheme 1.
2,6-Diiodo-4-methylphenol (4) was alkylated by treatment
with 4-bromo-trimethylorthobutyrate to yield the ester 5 in 73%
(18) For a recent report of the functionalization of an Au(111) surface see: Pan,
G.-B.; Liu, J.-M.; Zhang, H.-M.; Wan, L.-J.; Zheng, Q.-Y.; Bai, C.-L.
Angew. Chem. 2003, 115, 2853-2857; Angew. Chem., Int. Ed. 2003, 42,
2747-2751.
(17) Venkataramen, D.; Lee, S.; Zhang, J.; Moore, J. S. Nature 1994, 371, 591-
593.
9
216 J. AM. CHEM. SOC. VOL. 126, NO. 1, 2004

Macrocycles with Intraannular Polar Groups
A R T I C L E S
Figure 1. Texture of 3a (left, 150 °C) and 3b (right, 110 °C) between
crossed polarizers.
yield.19 Palladium-catalyzed Hagihara-Sonogashira coupling
with the monoprotected bisacetylene 6 and subsequent desilyl-
ation by treating 7 (87%) with Bu4NF gave the bisacetylene 8
(74%). As described previously, the basicity of the fluoride was
reduced by adding about 5% of water to the THF.11e Reaction
of 8 with a 7-fold excess of the THP-protected diiodophenol 9
gave the diiodo compound 10 in 81% yield. The excess of 9
was nearly quantitatively recovered and could be used for
subsequent coupling reactions. Coupling of 10 with trimethyl-
silyl (TMS)-acetylene yielded 11 (86%), which was desilylated
with K2CO3 to give 12 (89%). The statistical intermolecular
oxidative dimerization of 12 was performed by slow addition
of a solution of 12 in pyridine to a suspension of CuCl and
CuCl2 in the same solvent at 60 °C, a compromise between
increased coupling rate and decreased product stability at
elevated temperatures.20 The crude cyclization product (dimer
content ca. 60% (GPC)) was purified by radial chromatography
to give pure 13 in 29% isolated yield. Acid-catalyzed depro-
tection of the THP groups gave the tetraphenol 14 (68%).
Alkylation of 14 with the benzyl chlorides 15a and 15b gave
the oligo-alkyl-substituted macrocycles 3a and 3b, respec-
tively.21 3a and 3b were characterized by elemental analysis,
NMR spectroscopy, gel permeation chromatography (GPC), and
matrix-assisted laser desorption ionization time-of-flight
(MALDI TOF) spectroscopy. In solution, the 1H NMR spectra
of the compounds show molecules with a high degree of
symmetry, as expected from the molecular structure (Supporting
Information). Additionally, the results of the GPC analysis
indicate that the compounds do not contain incompletely
alkylated impurities. The assigned structure based on the NMR
and GPC data was verified by the results of the mass
spectroscopic analysis. The MALDI TOF spectra of 3a and 3b
show the masses of single peaks corresponding to the masses
of the macrocyclic Ag+ adducts (Supporting Information).
Thermal Behavior. Of special interest was the investigation
of the thermotropic behavior of the oligo-alkyl-substituted
macrocycles 3a and 3b, which was performed by optical
polarization microscopy (OPM) and differential scanning cal-
orimetry (DSC). Both compounds exhibit stable mesophases and
show, in the LC phase, beautiful fan-shaped textures under the
polarizing microscope, which are typical for a columnar order
of the molecules (Figure 1). 3a melts at 93 °C (∆Ht ) 176 kJ
mol-1; second heating) to form a LC phase that becomes
isotropic at 195 °C. As expected, the melting point of 3b is
lower (82 °C; ∆Ht ) 151 kJ mol-1; second heating), and also,
Figure 2. X-ray powder diffractogram of 3a at 120 °C.
the temperature range of the LC phase that is formed is smaller,
showing a clearing temperature of 145 °C.22
The observation of a stable LC phase in 3a, that cannot be
observed in 1c, shows that the balance between the core
dimension and the flexible periphery in these molecules were
correct, but the large internal void in 1c destabilizes a thermo-
tropic mesophase. It is also interesting to note that the melting
point of 3a is about 30 °C below the melting point of 1c,
although the former contains additional (intraannular) polar ester
groups. This is another indication for our previously reported
hypothesis that the large empty interior in these shape-persistent
macrocycles can act as a physical cross-link.3
X-ray and Electron Diffraction. To obtain a better insight
into the supramolecular organization of the macrocycles in the
liquid crystalline and, for comparison, in the solid state, a
combined X-ray and electron diffraction study was performed.
In X-ray powder diffraction diagrams of 3a and 3b (measured
in transmission), several reflections are seen in the LC phase
in the range up to a scattering angle of 12° (Figure 2; Table 1).
Because stacking of the macrocycles can be suggested with
a distance between the rings of only a few Å, the d values of
the reflections in the measured range are too high to be indexed
with l * 0.15c All the data match an oblique net with the basal
periodicities a ) 67.6 and b ) 42.5 Å and an angle between
the main directions γ ) 109.6° for 3a and a ) 72.6, b ) 45.6
Å, and γ ) 98.5° for 3b. In both compounds, two stacks of the
macrocycles run through one mesh of this oblique net (Z ) 2).
Keeping in mind that this basal net belongs to a liquid crystal,
the fact that a possible unit cell contains two symmetry-related
units is rather surprising and requires that both stacks be
discriminated from each other also in the liquid crystalline state
(Figure 3).9a,23,24 This feature points most probably to a restricted
rotation of the macrocycles within the stacks.
(19) Attempts to obtain 5 by the alkylation of 4 with ethyl 4-bromobutyrate
failed and gave only unidentified dark products.
(20) Ho¨ger, S.; Bonrad, K.; Karcher, L.; Meckenstock, A.-D. J. Org. Chem.
2000, 65, 1588-1589.
(22) Although different heating and cooling rates were employed, we were not
able to observe the LC-isotropic transition in the DSC.
(21) Balagurusamy, V. S. K.; Ungar, G.; Percec, V.; Johansson, G. J. Am. Chem.
Soc. 1997, 119, 1539-1555.
(23) Frank, F. C.; Chandrasekhar, S. J. Phys. (Paris) 1980, 41, 1285-1288.
(24) Levelut, A. M. J. Chim. Phys. 1983, 80, 149-161.
9
J. AM. CHEM. SOC. VOL. 126, NO. 1, 2004 217

A R T I C L E S
Fischer et al.
Table 1. Reflections of 3a (at 120 °C) and 3b (at 110 °C) in the
Liquid Crystalline State
Table 2. Reflections of 3a and 3b in the Solid State at Room
Temperature
3aa
3bb
3aa
3bb
2ϑobsd
2ϑcalcd
indexing
d
calcd
2ϑobsd
2ϑcalcd
indexing
d
calcd
2ϑobsd
2ϑcalcd
dobsd
indexing
d
calcd
2ϑobsd
2ϑcalcd
indexing
d
calcd
[deg]
[deg]
hk
[Å]
[deg]
[deg]
hk
[Å]
[deg]
[deg]
[Å]
hkl
[Å]
[deg]
[deg]
hkl
[Å]
1.39
2.19
1.386
2.175
2.204
2.772
2.906
4.154
4.158
4.350
4.408
4.944
5.545
10
1h1
01
20
2h1
1h2
30
2h2
02
3h2
40
63.7
40.6
40.1
31.8
30.4
21.3
21.2
20.3
20.0
17.9
15.9
1.18
1.92
2.16
2.52
1.229
1.958
2.153
2.459
2.462
2.908
3.917
4.919
4.925
5.878
6.700
10
01
1h1
20
11
2h1
02
40
22
03
23
71.8
45.1
41.0
35.9
35.9
30.4
22.6
17.9
17.9
15.0
13.2
1.56 1.609
100
54.9 1.52 1.414
1.76 1.845
46.9 2.12 2.162
39.1 2.48 2.476
2.82 2.827
33.0 3.66 3.690
3.82 3.762
27.4 4.24 4.242
4.38 4.324
23.4 4.98 4.953
5.44 5.494
20.3 5.78 5.690
6.52 6.487
100
010
1h10
110
200
020
1h20
300
2h20
220
030
400
3h30
62.5
47.9
40.9
35.7
31.2
23.9
23.5
20.8
20.4
17.8
16.1
15.5
13.6
56.6
48.2
010
1h10
2.92
4.20
4.40
2.34 2.258
2.72 2.679
3.30 3.219
3.79 3.768
4.22 4.343
4.51 4.518
39.1
33.2
27.3
23.3
20.3
18.7
2.92
3.94
4.81
110
200
020
120
2h20
4.80
5.47
5.89
6.80
a
Lattice base a ) 67.6 Å, b ) 42.5 Å, γ ) 109.6°, Z ) 2 (some
b
19.4
reflections superimpose without visible separation). Lattice base a ) 72.6
Å, b ) 45.6 Å, γ ) 98.5°, Z ) 2 (some reflections superimpose without
visible separation).
4.80 4.829
5.27 5.359
300
220
18.2
16.5
16.2
5.53 5.653
030
15.6
15.4
13.7
12.7
11.7
10.3
9.3
400
4h20
040
240
600
440
13.7
12.8
11.7
10.2
9.1
8.1
8.2
a
Monoclinic lattice with the parameters a ) 55.7 Å, b ) 47.6 Å, c )
4.8 Å, γ ) 99.8°, Z ) 2 (c is inferred from electron diffraction). The data
result in a density of F ) 1.17 g cm-3. (For this listing, two sets of data
were used: diffractometer measurements are given by scattering angles of
b
the reflections, and flatfilm Kiessig data are given by d values.)
Figure 3. Two-dimensional lattice symmetry in 3a and 3b, projection along
the stack axes.
Monoclinic lattice with the parameters a ) 62.7 Å, b ) 48.7 Å, c ) 4.8 Å,
γ ) 97.8°, Z ) 2 (c is inferred from electron diffraction). The data result
in a crystalline density of F ) 1.16 g cm-3
.
In the X-ray diffraction diagram of a powder, even in an
extended angular range, no trace of any feature has been found
that could be attributed to a periodicity along the suggested
stacks. The hope to orient the sample to see something similar
to a fiber diagram when the sample was cooled slowly in the
mark capillary was in vain. Also, for the solids we disposed of
powder data only. They are compiled in Table 2.
Under the assumption of a monoclinic lattice (see below),
the X-ray reflections of the solids can be explained by a lattice
with the parameters a ) 55.7 Å, b ) 47.6 Å, c ) 4.8 Å, γ )
99.8° (Z ) 2), and F ) 1.17 g cm-3 for 3a and a ) 62.7 Å, b
) 48.7 Å, c ) 4.8 Å, γ ) 97.8° (Z ) 2), and F ) 1.16 g cm-3
for 3b (also for the solid state, the parameter c could not be
determined by X-ray data. Electron diffraction patterns (see
below) display continuous layer lines that would not show up
in X-ray powder diagrams as distinct reflections). During the
phase transition from the liquid crystalline to the crystalline state,
the a-parameter is shortened and the b-parameter is extended.
The angle γ has only changed significantly for 3a.
Additional information on the solid-state structure of 3a and
3b was obtained by electron diffraction. In contrast to the X-ray
experiments, in the electron diffraction studies the specimen
scale allowed for observation of a fiberlike diagram in restricted
areas. Recording of an electron diffractogram at ambient
temperature is only possible in exceptional cases because of
the high irradiation damage of the specimen by 120 keV
electrons. Most of the electron diffraction work was therefore
performed at -130 °C. An example of such an electron
diffraction diagram is displayed in Figure 4.
Figure 4. Electron diffraction pattern of a thin film of 3a, recorded at
-130 °C.
The electron diffraction pattern shows a fiberlike texture
present in limited areas of a thin film. This observation supports
not only the lattice symmetry for 3a and 3b as obtained from
the X-ray data but also gives additional information on the
packing behavior of the macrocycles within the crystal lattice.
The continuous intensity along the layer lines, implying that
adjacent stacks of macrocycles are not in register, is the
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218 J. AM. CHEM. SOC. VOL. 126, NO. 1, 2004

Macrocycles with Intraannular Polar Groups
A R T I C L E S
predominant feature of the electron diffraction pattern. In 3a,
more distinctly than in 3b, some off-meridional sampling and
even evident reflections on the layer lines are seen. This feature
indicates that a herringbone structure is the most probable
packing scheme in the solid. From this observation it can be
inferred that the axis of the stacks is perpendicular to the plane
of the basal oblique net, and this orientation is also suggested
for the liquid crystalline state. The packing of the solid is then
treated in terms of a monoclinic unit cell. In case of a
herringbone structure, the normals to the planes of the macro-
cycles are oriented obliquely to the stack axis. The meridional
distance corresponds for both 3a and 3b to a repeating period
of 4.8 Å between two macrocycles along the stack axis. Some
diffractograms of 3b show a ring corresponding to a d value of
4.1 Å (Supporting Information). It originates certainly from the
hexadecyl residues attached to the macrocycles, demonstrating
that the aliphatic side chains are able to form crystallites as a
function of crystallization kinetics. The side-chain crystallites
are not oriented in-plane with the macrocycles; their function
is more a space-filling one. This additional ring was never
observed as a crystalline reflection for 3a. In that case,
sometimes a broad halo can be seen in the corresponding angular
region. This observation is in agreement with the findings for
a series of alkyl-substituted hairy rod polymers where separate
alkyl crystallization is also a function of alkyl chain length for
equal distances of attachment sites along the main chain.25
(reduced) dipolar coupling to the immobile case, a dynamic
order parameter S can be determined for individual segments,
where S ) 1 represents a perfectly immobile segment and
S f 0 isotropic motion.
The dynamical properties of three different types of phenyl
rings and several methyl groups in the macrocycle 3b were
investigated in the LC phase at 85 °C. The results are
schematically summarized in Figure 5. Considering first the
aromatic CH group (marked blue in Figure 5), a dipolar coupling
of DCH ) (21.0 ( 0.5) kHz is extracted from the respective
spinning sideband pattern (depicted in blue in Figure 5), which
obviously agrees with the value of an immobile group. Hence,
the phenyl ring is perfectly immobile on time scales below the
millisecond range. In particular, there is no rotation of the
macrocycles with frequencies above the kHz range in the
columnar LC phase. Similar dynamics, i.e., overall molecular
reorientations occurring at slower than kHz frequencies, were
observed in the mesophases of phthalocyanines.31
Turning to the aromatic CH groups depicted in green in Figure
5, a reduced dipolar coupling of DCH ) (16.4 ( 0.5) kHz was
measured, corresponding to a dynamic order parameter of S ≈
0.80. This parameter indicates a small-angle motion of the
phenyl ring with a mean excursion of (15°,32 as indicated in
Figure 5. A full rotation or a flip of the phenyl ring can be
excluded, because it would lead to dipolar couplings signifi-
cantly lower than the one observed. The dynamics of the OCH2
group attached to the phenyl ring (marked red, together with
the sideband pattern, in Figure 5) result in a residual coupling
of DCH ) (12.0 ( 0.5) kHz, corresponding to S ≈ 0.55.
Assuming that the phenyl and OCH2 motions are coupled but
occur independently from each other, they can be separated by
dividing the order parameters. Then, the OCH2R segment
exhibits an individual order parameter of S ≈ 0.70. This
segmental dynamics can be rationalized and illustrated in terms
of a cone with an opening angle of (20°, which encompasses
the core volume filled by the moving OCH2R group.
Solid-State NMR. Although a lattice symmetry with two
symmetry-related units in a unit cell was discussed soon after
the discovery of discotic liquid crystals, the restricted rotation
of the molecules in the liquid crystalline state has only been
rarely investigated.20,26 The lower melting point of 3b prompted
us to perform advanced solid-state 1H-13C NMR investigations
to gain further insight into the molecular dynamics of this
macrocycle in the liquid crystalline phase. Fast magic-angle
spinning (MAS) was applied,27 together with standard dipolar
decoupling28 and recoupling29 techniques, to ensure sufficient
1
resolution of the 13C resonance lines and to measure H-13C
Considering the oligo-alkyl substituents, a large mobility
gradient was observed, starting with S ) 1 at the immobile
macrocyclic core and decreasing to S < 0.1 at the -CH2CH3
terminus of the alkyl chains (depicted in yellow in Figure 5).
For the aromatic CH group within the substituent (marked purple
in Figure 5) a residual dipolar coupling of DCH ) (8.7 kHz (
0.5) kHz is determined. The corresponding dynamic order
parameter, S ≈ 0.40, can directly be related to a motion of the
substituent as a whole, which occurs within a cone-shaped
volume with an opening angle of (30°.
Thus, for different segments in the macrocycle 3b, individual
degrees of mobility could be determined by solid-state NMR,
showing that the macrocyclic core is rather rigid in the liquid
crystalline phase and does not rotate with kHz or higher
frequencies within the column. The substituents, in contrast,
show significant mobility above the kHz range, and their moving
alkyl chains fill the space around the core. This combination of
rigid and flexible parts within a macrocycle is essential for the
formation of a thermotropic liquid crystalline phase. Moreover,
the immobility of the rigid phenylethynyl core in the LC phase,
dipole-dipole couplings. On the basis of this spectral resolution,
the segmental dynamics of individual CHn groups can be
determined from 1H-13C dipole-dipole couplings that are subject
to motional averaging effects. In 2D MAS NMR experiments,
dipolar recoupling pulse sequences reintroduce 1H-13C dipole-
dipole couplings for certain periods and generate characteristic
spinning sideband patterns for all distinguishable CHn groups.28
These sideband patterns are a sensitive measure for individual
1H-13C dipole-dipole couplings, which are then compared to
coupling values of immobile segments, such as CH, CH2, CH3,
1
or a phenyl ring, calculated from known H-13C bond lengths.
Typically, an immobile C-H segment is characterized by a
coupling of DCH ) 21 kHz, which is reduced when molecular
motions occur on time scales below ∼10 µs, corresponding to
a frequency range of >100 kHz.30 By relating the measured
(25) (a) Stern, R.; Ballauff, M.; Lieser, G.; Wegner, G. Polymer 1991, 32, 2096-
2105. (b) Cervinka, L.; Ballauff, M. Colloid Polym. Sci. 1992, 270, 859-
872.
(26) Zamir, S.; Poupko, R.; Luv, Z.; Hu¨ser, B.; Boeffel, C.; Zimmermann, H.
J. Am. Chem. Soc. 1994, 116, 1973-1980.
(27) Schnell, I.; Spiess, H. W. J. Magn. Reson. 2001, 151, 153-227.
(28) Bennett, A. E.; Rienstra, C. M.; Auger, M.; Lakshmi, K. V.; Griffin, R. G.
J. Chem. Phys. 1995, 103, 6951.
(29) Saalwa¨chter, K.; Schnell, I. Solid State Nucl. Magn. Reson. 2002, 22, 154-
(31) Ford, W. T.; Sumner, L.; Zhu, W.; Chang, Y. H.; Um, P.-J.; Choi, K. H.;
Heiney, P. A.; Maliszewskyj, N. C. New J. Chem. 1994, 18, 495-505.
(32) Hentschel, R.; Sillescu, H.; Spiess, H. W. Polymer 1981, 22, 1516-1521.
187.
(30) Brown, S. P.; Spiess, H. W. Chem. ReV. 2001, 101, 4125.
9
J. AM. CHEM. SOC. VOL. 126, NO. 1, 2004 219

A R T I C L E S
Fischer et al.
Figure 5. Schematic representation of the segmental dynamics (faster than kHz frequencies) in 3b. On the left, the degree of mobility for individual
segments is given by the respective dynamic order parameter, S, while on the right the corresponding motions are depicted. At the bottom, three examples
of spinning sideband patterns are given, from which the residual 1H-13C dipolar couplings and the corresponding segmental dynamics are extracted (left and
middle: HDOR patterns, right: REREDOR pattern; the experiments are described in detail in ref 29). The black and colored lines represent experimental
and fitted data, respectively.
as determined from the NMR experiments, is consistent with
the observation that the unit cell of the basal net contains two
symmetry-related units, as determined by the X-ray experiments.
Adsorption. As indicated before, there is a considerable
interest in the investigation of the 2D ordering of the macro-
cycles because nanopatterns and functionalized nanopatterns
may provide a tool for the formation of supramolecular 3D
structures by epitaxial growth.33 One common technique for the
investigation of 2D ordering of these macrocycles at the liquid-
solid interface is scanning tunneling microscopy (STM).34 For
this purpose, the macrocycles were dissolved in phenyloctane,
and a drop of the solution was brought onto a freshly cleaved
HOPG surface. The STM investigations were then performed
at the liquid-solid interface.11j,13,35
Figure 6 is a set of STM pictures of 3a and 3b at the liquid
(1-phenyloctane)-solid (graphite) interface. The brightness
refers to the level of the detected tunneling current. Aromatic
and conjugated parts of molecules are known to show a higher
tunneling efficiency than the aliphatic alkyl parts.36 Therefore,
the bright parts can be attributed to the shape-persistent
(33) (a) Zeng, C.; Wang, B.; Li, B.; Wang, H.; Hou, J. G. Appl. Phys. Lett.
2001, 79, 1685-1688. (b) Abdel-Mottaleb, M. M. S.; Schuurmans, N.; De
Feyter, S.; van Esch, J.; Feringa, B. L.; De Schryver, F. C. Chem. Commun.
2002, 1894-1895. (c) Hoeppener, S.; Wonnemann, J.; Chi, L.; Erker, G.;
Fuchs, H. ChemPhysChem 2003, 4, 490-494. (d) Hoeppener, S.; Chi, L.;
Fuchs, H. ChemPhysChem 2003, 4, 494-498.
Figure 6. STM images of 3a (a, b) and 3b (c, d) at the liquid
(1-phenyloctane)-solid (graphite) interface. (a) 17.7 × 17.7 nm2, I ) 0.65
nA; V ) -0.714 V. (b) 12.7 × 12.7 nm2, I ) 0.8 nA; V ) -0.784 V. (c)
25.9 × 25.9 nm2, I ) 0.35 nA; V ) -0.926 V. (d) 18 × 18 nm2, I ) 0.35
nA; V ) -1.208 V.
(34) Rabe J.; Buchholz, S. Science 1991, 253, 424-427.
(35) Kro¨mer, J.; Rios Carreras, I.; Fuhrmann, G.; Musch, C.; Wunderlin, M.;
Debaerdemaeker, T.; Mena-Osteritz, E.; Ba¨uerle, P. Angew. Chem. 2000,
112, 3623-3628; Angew. Chem., Int. Ed. 2000, 39, 3481-3486.
(36) De Feyter, S.; Gesquie`re, A.; Abdel-Mottaleb, M. M. S.; Grim, P. C. M.;
Meiners, C.; Sieffert, M.; Valiyaveettil, S.; Mu¨llen, K.; De Schryver, F. C.
Acc. Chem. Res. 2000, 33, 520-531.
backbone of the compounds. The molecular dimensions ob-
served here correspond well with those obtained by single-
crystal X-ray analysis of similar macrocycles. In addition, the
9
220 J. AM. CHEM. SOC. VOL. 126, NO. 1, 2004

Macrocycles with Intraannular Polar Groups
A R T I C L E S
Summary
contrast within a macrocycle correlates with the density of the
highest occupied molecular orbital (HOMO) of the macrocycle,
as we have described before.13 Moreover, the presence of the
four exo phenyl rings carrying the alkyl chains stresses the long
axis of the molecules and allows the determination of the
orientation of the macrocycles on the graphite support in a
straightforward fashion. The dark areas between the macrocycles
are occupied by alkyl chains. In a few cases, their orientation
could be determined. As is often the case, they are oriented
along one of the main symmetry axes of graphite. The interior
of the macrocycles remains dark, and no details of the
intraannular groups can be observed.
In summary, we have presented the synthesis of the shape-
persistent macrocycles 3a and 3b with extraannular oligo-alkyl
substituents and intraannular polar groups which can be viewed
as intraannular filled analogues of the previously reported
macrocycles 1. The macrocycles 1 do not exhibit a stable liquid
crystalline phase and several arguments indicate that the large
internal void of the macrocycles 1 is responsible for that.
However, the incorrect balance between the dimensions of the
core and the flexible periphery might have been an alternative
explanation. The investigation of the thermal behavior of 3a
and 3b has shown that both compounds exhibit stable columnar
mesophases (as revealed by optical microscopy, X-ray and
electron diffraction studies, and solid-state NMR), showing that
the balance between the rigid and the flexible parts in 1 and 3
was correct. This finding is another support for our hypothesis
that the large internal void in nanometer-size shape-persistent
macrocycles destabilizes a thermotropic mesophase. Apart from
their thermotropic behavior, the adsorption of 3a and 3b on
HOPG has been investigated. The compounds form monolayers
on the graphite, and their 2D ordering was investigated by STM,
indicating that the macrocycles allow not only the formation of
nanostructured surfaces but also the creation of functionalized
nanostructured surfaces.
In contrast to the data published on 1c,13 3a and 3b do not
tend to form extended well-defined 2D arrays. Although local
ordering is found to a certain degree, the rings do not form a
2D crystal. However, the extent of ordering depends on the
solvent used for the investigations. When physisorbed from a
1,2,4-trichlorobenzene solution, the degree of ordering is often
more pronounced (although far from ideal) compared to images
obtained for monolayers physisorbed from 1-phenyloctane,
although the image resolution is worse (see Supporting Informa-
tion). Several factors can contribute to this lack of long-range
ordering. Imaging occurs at rather high set point values (see
figure captions), which leads to an increased interaction with
the macrocycles. However, repeated scanning does not affect
the relative orientation of the macrocycles. In our opinion, the
main reason for the lack of long-range order is the balance or
competition between kinetically and thermodynamically con-
trolled monolayer formation. The interplay between the solute-
solvent interaction and the solute-substrate interaction will play
an important factor. Both molecules contain 12 long alkyl chains,
which will lead to a considerable interaction with the graphite
substrate upon adsorption (in addition to the interaction between
the aromatic cores and the substrate). Even if the molecule is
not packed in an ideal fashion, the molecules-substrate inter-
action will be large enough to immobilize the molecules to a
certain degree on the substrate, and as such, they can be
kinetically trapped. Given that 1,2,4-trichlorobenzene is a better
solvent for the macrocycles than 1-phenyloctane, the extent of
kinetic trapping will be less in 1,2,4-trichlorobenzene, leading,
on the time scale of the experiment, to more long-range ordered
systems. Further investigations will therefore also deal with
optimization of the physisorption protocol, which includes,
among other parameters, a variation of the solvent, temperature,
and concentration. Nevertheless, for 3a the lattice constants of
a 2D unit cell of oblique symmetry were extrapolated to be in
the order of A ) 3.4 nm, B ) 5.2 nm, and Γ ) 87°. Although
these parameters cannot be obtained with accuracy, they show
a similar molecular size of 1c and 3a on the graphite. In
comparison to the basal net a and b of the 3D structure of 3a,
the distinctive feature between the two piles of macrocycles is
lost by the induced parallelism of rings and substrate. Therefore,
the lattice parameter recognizable on the STM pattern of the
surface is considerable smaller.
Experimental Section
Synthesis. Compounds 6 and 9 were prepared according to literature
procedures.13 For synthetic procedures and analytical data for all other
compounds, please see the Supporting Information.
X-ray Scattering and Electron Diffraction. Temperature-dependent
X-ray scattering was mainly performed on a homemade 2-circle
diffractometer (Huber) in transmission mode. The diffractometer was
equipped with a germanium monochromator enabling the separation
of the copper KR dublett, using for the measurement CuKR1 with λ )
1.5406 Å. For data recording, a position-sensitive 120° Inel detector
was used. Electron diffraction of the solid compound was performed
in a LEO 912 transmission electron microscope with an integrated
electron energy loss spectrometer at a high voltage of 120 kV. Thin
films were prepared from solution and transferred to carbon-coated
supporting grids prior to being molten and subsequently recrystallized
on the carbon film (electron diffraction on films in the liquid crystalline
state was not possible because of the very high irradiation damage at
elevated temperatures).
Solid-State NMR. Data were collected on a Bruker DRX spec-
trometer with a 16.4 T magnet (700 and 176 MHz for H and 13C,
1
respectively). A double resonance MAS (magic-angle spinning) probe
was used, allowing MAS frequencies of 30 kHz. The samples (∼15
mg) were packed into rotors of 2.5-mm outer diameter. The spectra
are referenced to adamantane (1.63 ppm for 1H, and 38.5 ppm for 13CH).
STM Investigation. Experiments were performed using a Discoverer
scanning tunneling microscope (Topometrix Inc. Santa Barbara, CA)
with a typical frame acquisition time of 7 s, along with an external
pulse/function generator (model HP 8111 A), with negative sample
bias. Tips were etched electrochemically from Pt/Ir wire (80%/20%,
diameter 0.2 mm) in a 2 N KOH/6 N NaCN solution in water. Prior to
imaging, the compound under investigation was dissolved in 1-phenyl-
octane or 1,2,4-trichlorobenzene (Aldrich), and a drop of this solution
(0.1 wt %) was applied on a freshly cleaved surface of HOPG. The
STM investigations were then performed at the liquid-solid interface.
The presented STM images were acquired in the variable current mode
(constant height) under ambient conditions. In the STM images, white
corresponds to the highest and black to the lowest measured tunneling
current. The experiments were repeated in several sessions using
Macrocyclic esters 3a and 3b are examples of the extension
of the concept of nanopatterning toward nanofunctionalization
of the HOPG surface in the multinanometer regime. The use of
these surfaces for the formation of supramolecular 3D structures
is in progress.
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J. AM. CHEM. SOC. VOL. 126, NO. 1, 2004 221

A R T I C L E S
Fischer et al.
different tips to check the reproducibility and to avoid artifacts. After
registration of an STM image of the monolayer structure, the underlying
graphite lattice was recorded at the same position by decreasing the
bias voltage, serving as an in situ calibration. All STM images contain
raw data and are not subjected to any manipulation or image processing.
Materials and Miniaturized Devices Center (BMBF 03N 6500)
is gratefully acknowledged. S.D.F. thanks the F.W.O.-Flanders
(Belgium) for a postdoctoral fellowship.
Supporting Information Available: Synthetic procedures and
analytical data for the compounds prepared (PDF). This material
is available free of charge via the Internet at http://pubs.acs.org.
Acknowledgment. Dedicated to Professor Erhard W. Fischer
on the occasion of his 75th birthday. Financial support by the
Deutsche Forschungsgemeinschaft and the Multifunctional
JA038484X
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222 J. AM. CHEM. SOC. VOL. 126, NO. 1, 2004