Supramolecular architectures of C3-symmetrical and asymmetrical discotics

Article abstract of DOI:10.1080/714965604

Chiral (3b) and achiral (3a) C₃-symmetrical nitrogen centered amide disks were investigated with optical polarizing microscopy, differential scanning calorimetry and UV-Vis/circular dichroism spectroscopy. Similar to the carbonyl centered amide

Full text of DOI:10.1080/714965604

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Supramolecular Architectures
of C 3 -Symmetrical and
Asymmetrical Discotics
J. J. Van Gorp a , J. A. J. M. Vekemans a & E. W.
Meijer a
a Laboratory of Macromolecular and Organic
Chemistry, Eindhoven University of Technology, P. O.
Box 513, Eindhoven, 5600, MB, The Netherlands
Published online: 18 Oct 2010.
To cite this article: J. J. Van Gorp , J. A. J. M. Vekemans & E. W. Meijer (2003)
Supramolecular Architectures of C 3 -Symmetrical and Asymmetrical Discotics,
Molecular Crystals and Liquid Crystals, 397:1, 191-205, DOI: 10.1080/714965604
To link to this article: http://dx.doi.org/10.1080/714965604
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Mol. Cryst. Liq. Cryst., Vol. 397, pp. 191/[491]–205/[505], 2003
Copyright # Taylor & Francis Inc.
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421400390214103
SUPRAMOLECULAR ARCHITECTURES OF
C3-SYMMETRICAL AND ASYMMETRICAL
DISCOTICS
J. J. van Gorp, J. A. J. M. Vekemans, and E. W. Meijer
Laboratory of Macromolecular and Organic Chemistry,
Eindhoven University of Technology, P. O. Box 513, 5600 MB,
Eindhoven, The Netherlands
Chiral (3b) and achiral (3a) C3-symmetrical nitrogen centered amide disks
were investigated with optical polarizing microscopy, differential scanning
calorimetry and UV-Vis/circular dichroism spectroscopy. Similar to the car-
bonyl centered amide disks 1a/b, only achiral compound 3a shows order in the
liquid crystalline phase. Using the same techniques, two asymmetrical mono
amide bisurea disks were investigated, one containing 6 ‘‘chiral urea’’ groups
(4) and the other containing 3 ‘‘chiral amide’’ centers (5). These compounds do
show supramolecular aggregation in dilute apolar solutions, featuring hys-
teresis in experiments investigating thermoreversibility; similar to C3-symme-
trical trisurea compounds 2a/b.
Keywords: discotics; supramolecular architectures; CD-spectroscopy
INTRODUCTION
Self-assembled structures may find their application in either biology or
materials science, since supramolecular architectures are well defined
though reversible in nature [1,2,3]. Discotic molecules were found suitable
building blocks for cylindrical architectures [4], and several examples of
columnarliquidcrystallinephasesareknown[5,6]. However, specialdemands
on the directionality and strength of secondary interactions between disks
have to be met to maintain these supramolecular columns in organogels
[7,8], or even in dilute solution [9]. Next to the possibility to create cho-
lesteric and ferroelectric liquid crystals, chirality was recognized as a new
tool to study the self-assembly of the disks in diluted systems [10,11].
We reported on C3-symmetrical discotics that form helical columnar
structures in the solid state [12], in the gel phase [13], as well as in dilute
solution [14]. In case of discotics based on gallic acid derivatives (Scheme
1), a large difference was found between the amide disks 1a/b and the urea
191/[491]

192/[492]
J. J. van Gorp et al.
SCHEME 1 Chemical structures of carbonyl centered trisamides 1a/b (left), and
trisureas 2a/b (right).
disks 2a/b, illustrating that a minor structural variation can have a drastic
effect on the delicate balance between intermolecular interactions needed
for supramolecular aggregation [15]. ‘‘Gallic’’ carbonyl centered trisamides
1a/b were not capable of retaining their columnar structure in apolar
solution. Ordering was only found in the liquid crystalline phases of 1a/b,
and in the case of chiral disk 1b only in a very small temperature window.
On the other hand, the ‘‘gallic’’ trisurea 2a/b did form rigid rod-like
structures at concentrations as low as 10ꢀ5 M.
Urea hydrogen bonding is stronger than amide bonding, because ureas
may display two hydrogen bonds, while amides have only one. Probably,
this causes the difference in supramolecular aggregation between trisamide
and trisurea molecules 1 and 2. However, it could be argued that the
connection of the hydrogen bonding groups to the central benzene ring
rationalizes the difference. The hydrogen bonding groups of amide 1 are
connected to the central core via the carbonyl group, while those of urea 2
are connected via the nitrogen atom. To rule out any influences caused by
this difference in connectivity, nitrogen centered trisamides 3a/b were
synthesized and investigated (Scheme 2).
To better understand why trisamide disks 1 do not form columnar
aggregates in dilute apolar solution and why trisurea disks 2 do, two
asymmetrical ‘‘gallic’’ structures were investigated, each containing one
amide and two urea groups. Mono amide bisurea disk 4 contains 6 chiral
centers, which are connected to the central benzene ring via the urea
groups, while mono amide bisurea disk 5 is equipped with 3 ‘chiral amide’
functionalities. This enables us to investigate separately the aggregation of
the amide or the urea groups of these asymmetrical disks with circular
dichroism spectroscopy. From these data, information concerning the
conformation of the asymmetrical disks in the supramolecular aggregate
can be obtained.

Architectures of Asymmetrical Disks
193/[493]
SCHEME 2 Chemical structures of nitrogen centered trisamides 3a/b (left), and
mono amide bisureas 4 and 5 (right). R-groups of 3a/b are similar to those of 1a/b
(see Scheme 1).
EXPERIMENTAL
General
All starting materials were obtained from commercial suppliers and used
as received. The syntheses of the following compounds have been
described previously: 1a/b [15], 2a/b [15], 3,4,5-tridodecyloxybenzoyl
chloride/3,4,5-tris((S)-3,7-dimethyloctyloxy)benzoyl chloride [12], and 3,
4,5-tridodecyloxybenzene isocyanate/3,4,5-tris((S)-3,7-dimethyloctyloxy)
benzene isocyanate [16]. All moisture sensitive reactions were performed
under an atmosphere of dry argon. Dry and ethanol-free dichloromethane
was obtained by distillation from P2O5; dry tetrahydrofuran was obtained
by distillation from Na/K/benzophenone; toluene was dried on Merck
˚
molsieves (4 A); and triethylamine was dried over potassium hydroxide.
Analytical thin layer chromatography was performed on Kieselgel F-254
precoated silica plates. Visualization was accomplished with UV light.
Column chromatography was carried out on Merck silica gel 60 (70–230
mesh or 230–400 mesh ASTM). 1H-NMR and 13C-NMR spectra were
1
recorded on a Varian Mercury, 400 MHz for H-NMR and 100 MHz for 13C-
1
NMR or on a Varian Gemini, 300 MHz for H-NMR and 75 MHz for 13C-
NMR. Proton chemical shifts are reported in ppm downfield from tetra-
methylsilane (TMS) and carbon chemical shifts in ppm downfield from
TMS using the resonance of the deuterated solvent as internal standard.
Elemental analyses were carried out using a Perkin Elmer 2400. Matrix
assisted laser desorption/ionization mass spectra were obtained using a-
cyano-4-hydroxycinnamic acid as the matrix on a PerSeptive Biosystems
Voyager-DE PRO spectrometer. IR spectra were measured on a Perkin
Elmer 1600 FT-IR. Optical properties and melting points were determined

194/[494]
J. J. van Gorp et al.
using a Jenaval polarization microscope with crossed polarizers equipped
with a Linkham THMS 600 heating device. DSC spectra were obtained on
a Perkin Elmer Pyris 1 DSC. UV/Vis spectra were recorded on a Perkin
Elmer Lambda 40 UV/Vis spectrometer. CD spectra were recorded on a
Jasco J-600 spectropolarimeter equipped with a Jasco PTC-348WI Peltier
type temperature control system.
1,3,5-Tris-(3,4,5-tridodecyloxybenzoylamino)benzene (3a)
A solution of 3,4,5-tridodecyloxybenzoyl chloride (0.49 g, 0.81 mmol) in
dichloromethane (10 ml) was added dropwise to a solution of di-amine 7a
(0.30 g, 0.38 mmol) and triethylamine (0.13 ml, 0.92 mmol) in dichloro-
methane (5 ml). After stirring overnight and evaporation of the dichloro-
methane, the crude product was purified using column chromatography
(flash silica, gradient: chloroform/dichloromethaneþ0–0.5% v/v methanol,
1
Rf ¼ 0–0.3). Finally, white sticky solid 3a (0.67 g, 83%) was obtained: H-
NMR (CDCl3) d 8.24 (NH, s, 3H), 8.10 (H-ortho, s, 3H), 7.05 (H0-ortho, s,
6H), 3.98 (OCH2, m, 18H), 1.80 (OCH2CH2, m, 18H), 1.46 (OCH2CH2CH2,
m, 18H), 1.26 ((CH2)8, m, 144H), 0.88 (CH3, m, 27H); 13C-NMR (CDCl3) d
165.9, 153.3, 141.6, 139.2, 129.1, 107.1, 105.5, 73.5, 69.3, 31.9, 30.4,
29.8, 29.7, 29.7, 29.7, 29.6, 29.5, 29.4, 26.1, 26.1, 22.7, 14.1; IR (ATR): 3278,
2921, 2852, 1645, 1615, 1581, 1536, 1499, 1455, 1385, 1332, 1220, 1112,
1003, 859, 760, 721, 677 cmꢀ1; MALDI-TOF MS: calc.: 2093.81, found:
2116.63 (Na adduct); Analysis: calc.: C135H237N3O12 (2094.41): C, 77.42; H,
11.41; N, 2.01; found: C, 77.44; H, 10.66; N, 2.00.
1,3,5-Tris-[3,4,5-tris((S)-3,7-dimethyloctyloxy)benzoylamino]-
benzene (3b)
Analogous to the previous procedure 3,4,5-tris-((S)-3,7-dimethyloctyloxy)
benzoyl chloride (1.0 g, 1.7 mmol) and di-amine 7b (0.56 g, 0.81 mmol),
1
gave 3b as a white sticky solid (1.18 g, 80%): H-NMR (CDCl3) d 8.05 (H-
ortho, s, 3H), 8.01 (NH, s, 3H), 7.08 (H0-ortho, s, 6H), 4.07 (OCH2, m,
18H), 1.88-0.86 (alkyl H, m, 171H); 13C-NMR (CDCl3) d 165.8, 153.4, 141.7,
139.2, 129.2, 106.7, 105.5, 71.8, 67.7, 39.4, 39.3, 37.5, 37.4, 37.3, 36.4, 29.8,
29.7, 28.0, 24.7, 22.7, 22.6, 22.6, 19.6, 19.6; IR (ATR): 3284, 2954, 2925,
2870, 1650, 1616, 1583, 1551, 1501, 1464, 1429, 1384, 1329, 1216, 1110,
1045, 994, 956, 859, 753, 735, 687 cmꢀ1; MALDI-TOF MS: calc.: 1841.52,
found: 1864.59 (Na adduct); Analysis: calc.: C117H201N3O12 (1841.92): C,
76.30; H, 11.00; N, 2.28; found: C, 76.29; H, 10.46;
N, 2.31.

Architectures of Asymmetrical Disks
195/[495]
N-(3,5-Bis-{3-[3,4,5-tris-((S)-3,7-dimethyloctyloxy)-phenyl]-
ureido}-phenyl)-3,4,5-tridodecyloxy-benzamide (4)
A solution of 3,4,5-tris-((S)-3,7-dimethyloctyloxy)benzoyl azide (0.59 g,
0.96 mmol) in dry toluene (9 ml) was refluxed for 2 h. The mixture was
cooled to 80ꢁC, after which a solution of di-amine 7a (0.30 g, 0.38 mmol) in
dry toluene (7 ml) was added dropwise. After stirring overnight the toluene
was evaporated and the product dissolved in dichloromethane (15 ml). The
solution was cooled with ice. This gave a precipitate that yielded white
sticky solid 4 (0.70 g, 93%) after filtration: 1H-NMR (CDCl3/CH3OH) d 8.97
(amide NH, s, 1H), 8.14 (urea NH, s, 2H), 7.75 (urea NH, s, 2H), 7.54 (H-
ortho, d, 2H), 7.27 (H-ortho, bs, 1H), 7.08 (H0-ortho, s, 2H), 6.64 (H00-ortho,
s, 4H), 3.98 (OCH2, m, 18H), 1.86–0.83 (alkyl H, m, 183 H); 13C-NMR
(CDCl3/CH3OH) d 166.7, 153.6, 153.1, 153.0, 141.2, 140.0, 138.9, 134.2,
133.9, 129.3, 105.7, 105.3, 98.6, 73.5, 71.7, 69.2, 67.2, 39.3, 39.2, 37.5, 37.3,
37.2, 36.4, 31.8, 30.3, 29.7, 29.7, 29.6, 29.6, 29.6, 29.5, 29.4, 29.3, 29.3, 27.9,
26.0, 26.0, 24.7, 24.6, 22.6, 22.5, 22.5, 19.5, 19.3, 14.0; IR (ATR): 3319,
2954, 2923, 2854, 1638, 1603, 1555, 1504, 1457, 1427, 1383, 1329, 1224,
1117, 1003, 824, 754, 719 cmꢀ1; MALDI-TOF MS: calc.: 1955.64, found:
1978.22 (Na adduct); Analysis: calc.: C123H215N5O12 (1956.11): C, 75.53; H,
11.08; N, 3.58; found: C, 74.52; H, 10.39; N, 3.52.
N-{3,5-Bis-[3-(3,4,5-tridodecyloxyphenyl)-ureido]-phenyl}-3,4,5-
tris-((S)-3,7-dimethyloctyloxy)-benzamide (5)
Analogous to the previous procedure 3,4,5-tridodecyloxybenzoyl azide
(1.0 g, 1.4 mmol) and di-amine 7b (0.47 g, 0.68 mmol) in combination with
additional column chromatography (flash silica, dichloromethaneþ0–0.5%
v/v methanol, Rf ¼ 0–0.1) gave white/brown sticky solid 5 (1.2 g, 87%): 1H-
NMR (THF-d8) d 9.27 (amide NH, s, 1H), 7.89 (urea NH, s, 2H), 7.56
(H-ortho, bs, 2H), 7.48 (urea NH, s, 2H), 7.34 (H-ortho, bs, 1H), 7.06 (H0-
ortho, s, 2H), 6.56 (H00-ortho, s, 4H), 3.85 (OCH2, m, 6H), 3.67 (OCH2, m,
12H), 1.69-0.64 (alkyl H, m, 195 H); 13C-NMR (THF-d8) d 167.0, 155.0,
154.9, 154.5, 143.2, 142.6, 142.3, 137.4, 135.7, 132.2, 108.3, 105.7, 99.7,
74.6, 72.9, 70.6, 69.1, 41.4, 71.3, 39.6, 39.5, 38.6, 33.9, 32.5, 31.9, 31.8, 31.8,
31.8, 31.7, 31.6, 31.6, 31.4, 30.0, 28.3, 28.2, 26.8, 26.8, 24.6, 24.2, 24.1, 21.2,
21.0, 15.5; IR (ATR): 3288, 2954, 2922, 2853, 1644, 1604, 1557, 1503, 1467,
1425, 1384, 1333, 1225, 1117, 1004, 826, 757, 719 cmꢀ1; MALDI-TOF MS:
calc.: 2039.73, found: 2039.85; Analysis: calc.: C129H227N5O12 (2040.27): C,
75.94; H, 11.21; N, 3.43; found: C, 74.69; H, 10.39; N, 3.38.
3,4,5-Tridodecyloxy-N-(3,5-dinitrophenyl)-benzamide (6a)
A solution of 3,4,5-tridodecyloxybenzoyl chloride (11.4 g, 16.4 mmol) in
dry THF (150 ml) was added to 3,5-dinitroaniline (3.0 g, 16.4 mmol) and

196/[496]
J. J. van Gorp et al.
triethylamine (2.8 ml, 19.7 mmol) in dry THF (150 ml). After stirring
overnight at 75ꢁC the solvent was evaporated and the product purified with
column chromatography (silica, hexane/ethyl acetate 8/2, Rf ¼ 0.3) in
combination with recrystallisation from hexane/ethyl acetate 9/1 to remove
minor impurities or washing with methanol to remove 3,5-dinitroaniline.
Finally, yellow solid 6a (11.2 g, 81%) was obtained: 1H-NMR (CDCl3) d 8.94
(H-2, d, 2H), 8.78 (H-4, t, 1H), 8.46 (NHCO, s, 1H), 7.02 (H-20, s, 2H), 4.01
(OCH2, m, 6H), 1.79-1.72 (OCH2CH2, m, 6H), 1.44 (OCH2CH2CH2, m, 6H),
1.26 ((CH2)8, m, 48H), 0.88 (CH3, m, 9H); 13C-NMR (CDCl3) d 166.0, 153.3,
148.8, 142.2, 140.5, 127.8, 119.6, 113.6, 105.8, 73.7, 69.5, 31.9, 30.3, 29.7,
29.6, 29.5, 29.4, 29.4, 29.3, 29.3, 26.1, 26.0, 22.7, 14.1; Elemental analysis:
calculated: C49H81N3O8 (840.19): C, 70.05; H, 9.72; N, 5.00; found: C, 70.45;
H, 9.79; N, 4.86; IR (ATR): 3418, 2916, 2848, 1676, 1585, 1541, 1498, 1467,
1429, 1347, 1336, 1202, 1120, 989, 894, 750, 726 cmꢀ1; Analysis: calc.:
C49H81N3O8 (840.19): C, 70.05; H, 9.72; N, 5.00; found: C, 70.45; H, 9.79;
N, 4.86.
3,4,5-Tris-((S)-3,7-dimethyloctyloxy)-N-(3,5-dinitrophenyl)-
benzamide (6b)
Analogous to the previous procedure 3,4,5-tris-((S)-3,7-dimethyloctyloxy)
1
benzoyl chloride (8.8 g, 14.4 mmol) gave yellow solid 6b (9.5 g, 87%): H-
NMR (CDCl3) d 8.94 (H-2, d, 2H), 8.77 (H-4, t, 1H), 8.43 (NHCO, s, 1H),
7.07 (H-20, s, 2H), 4.05 (OCH2, m, 6H), 1.89-0.86 (alkyl H, m, 57H); 13C-
NMR (CDCl3) d 166.0, 153.4, 148.8, 142.3, 140.5, 127.8, 119.6, 113.6, 105.8,
72.0, 67.8, 39.3, 39.2, 37.5, 37.3, 37.3, 36.3, 29.8, 29.7, 28.0, 24.7, 22.7, 22.6,
22.6, 22.6, 19.5; IR (ATR): 3282, 3105, 2954, 2927, 2870, 1662, 1582, 1546,
1499, 1466, 1429, 1383, 1341, 1212, 1116, 1074, 997, 902, 727 cmꢀ1 Ana-
lysis: calc.: C43H69N3O8 (756.04): C, 68.31; H, 9.20; N, 5.56; found: C, 68.41;
H, 8.77; N, 5.54.
N-(3,5-Diamino-phenyl)-3,4,5-tridodecyloxy-benzamide (7a)
The di-nitro 6a (0.84 g, 1.0 mmol) was shaken for 512 h under hydrogen gas
(150 ml, 6 mmol, 3 atm.) together with a 10% w/w palladium on carbon
catalyst (50 mg, 0.050 mmol), ethanol (3 ml) and THF (22 ml). The reaction
mixture was filtered over 3 paper filters to remove the catalyst. After
column chromatography (flash silica, CH2Cl2þ1% Et3Nþ2% MeOH,
1
Rf ¼ 0.3) 7a was obtained as a sticky white/green solid (0.66 g, 85%): H-
NMR (CDCl3) d 7.54 (NHCO, s, 1H), 7.00 (H-20, s, 2H), 6.46 (H-2, d, 2H),
5.83 (H-4, t, 1H), 4.01 (OCH2, m, 6H), 3.62 (NH2, s, 4H), 1.80 (OCH2CH2,
m, 6H), 1.46 (OCH2CH2CH2, m, 6H), 1.26 ((CH2)8, m, 48H), 0.88 (CH3, m,
9H); 13C-NMR (CDCl3) d 165.7, 152.9, 148.0, 141.0, 139.8, 130.0, 105.7,

Architectures of Asymmetrical Disks
197/[497]
98.2, 98.0, 73.4, 69.2, 31.8, 30.3, 29.7, 29.7, 29.6, 29.5, 29.4, 29.3, 26.0, 26.0,
22.6, 14.0; IR (ATR): 3343, 2921, 2852, 1615, 1582, 1544, 1497, 1453, 1335,
1223, 1113, 1002, 829 cmꢀ1; Analysis: calc.: C49H85N3O4 (780.23): C, 75.43;
H, 10.98; N, 5.39; found: C, 75.44; H, 10.57; N, 5.78.
N-(3,5-Diamino-phenyl)-3,4,5-tris-((S)-3,7-dimethyloctyloxy)-
benzamide (7b)
Analogous to the previous procedure di-nitro 6b (2.0 g, 2.7 mmol) gave 7b
as a sticky white/brown solid (0.69 g, 92%): 1H-NMR (CDCl3) d 7.51
(NHCO, s, 1H), 7.01 (H-20, s, 2H), 6.46 (H-2, s, 2H), 5.83 (H-4, s, 1H), 4.05
(OCH2, m, 6H), 3.62 (NH2, s, 4H), 1.88-0.86 (alkyl H, m, 57H); 13C-NMR
(CDCl3) d 165.6, 153.2, 148.0, 141.3, 139.8, 130.2, 105.7, 98.3, 97.9, 71.7,
67.7, 39.3, 39.2, 37.5, 37.3, 37.3, 36.3, 30.3, 29.8, 29.6, 27.9, 25.6, 24.7, 24.7,
22.7, 22.6, 19.5; IR (ATR): 3346, 2954, 2926, 2870, 1616, 1582, 1546, 1497,
1453, 1383, 1334, 1226, 1113, 996, 833, 757, 684 cmꢀ1; MALDI-TOF MS:
calc.: 695.56, found: 696.55.
RESULTS
Synthesis
The synthesis of structures combining amide and urea functions requires
introduction of asymmetry in the benzene-1,3,5-trisamine core. Therefore,
3,5-dinitroaniline was selected as starting compound. First the amine group
was converted to an amide functionality using an acid chloride provided
with solubilizing groups, derived from gallic acid [12], in the presence of
triethylamine (Scheme 3). Achiral compound 6a contains dodecyloxy
SCHEME 3 Synthesis of building blocks 6a/b and 7a/b based on 3,5-dinitroaniline.

198/[498]
J. J. van Gorp et al.
SCHEME 4 Synthesis of nitrogen centered trisamide disks 3a/b.
SCHEME 5 Synthesis of mono amide bisurea disks 4 and 5.
chains, while in chiral compound 6b (S)-3,7-dimethyloctyloxy chains are
present. The nitro groups of di-nitro building block 6a/b could be cataly-
tically reduced with palladium on carbon, to give di-amine building block
1
7a/b quantitatively. All compounds were characterized by H-NMR, 13C-
NMR, and IR spectroscopy, elemental analysis, and mass spectrometry (see
Experimental).
Di-amine building blocks 7a/b could be converted into discotics upon
‘end capping’ with acid chlorides (in case of 3a/b) or isocyanates (in case of
4 and 5). Both achiral (3a) and chiral (3b) nitrogen centered trisamide
disks were synthesized in good yield by treating di-amine 7a/b with 2
equivalents 3,4,5-trialkoxybenzoyl chloride (Scheme 4). Similarly, mono
amide bisurea disks 4 and 5 were obtained using 3,4,5-trialkoxybenzene
isocyanate [16] (Scheme 5). Compounds 4 and 5 both contain one amide
and two urea groups, but where 4 contains 6 chiral centers, which are
connected to the core via the urea groups, 5 is equipped with 3 ‘chiral
amide’ functionalities.

Architectures of Asymmetrical Disks
199/[499]
FIGURE 1 Typical structure found in the liquid crystalline phase of nitrogen
centered achiral amide disk 3a (left) and crystals of chiral amide disk 3b (right).
(See Color Plates XVII & XVIII).
Optical Polarizing Microscopy and Differential Scanning
Calorimetry
Nitrogen centered C3-symmetrical amide disk 3a shows liquid crystallinity
(K: 28ꢀC, 107 kJ/mol : M: 154ꢀC, 53 kJ/mol : I), shown by the typical focal
conic structures (Fig. 1). Chiral amide 3b displays no liquid crystallinity
and only one transition between the crystalline and isotropic phase was
found (K: 87ꢀC, 29 kJ/mol : I). Asymmetric disks 4 and 5 can be smeared
and show birefringence from room temperature up to high temperatures,
but no textures can be grown, as degradation occurs below the iso-
tropization temperature (190ꢀC).
Infrared Spectroscopy
The compounds were studied with IR spectroscopy by following the car-
bonyl stretch vibration in the solid state, and in 10À4 M heptane and
chloroform solutions (Table 1). Carbonyl centered trisamide 1a is not
(completely) aggregated in dilute apolar solution, while trisurea 2a is
aggregated, as shown by similar carbonyl stretch vibrations in the solid
state and in 10À4 M heptane solution. For nitrogen centered trisamide 3a a
value is found in heptane, intermediate between that of the aggregated
(solid) state and the molecularly dissolved one (chloroform). When mono
amide bisurea disk 4 was brought in heptane at a concentration of 10À2 M, a
gel was formed. Unfortunately, no differentiation between the amide and
urea signal was possible. Similar to trisamide 3a, the wavenumbers of mono
amide bisurea 4, are not conclusive, at first glance.
However, in 10À2–10À5 M tetrachloromethane solutions, infrared vibra-
tions of 4 are similar to those in the solid state (1644 cmÀ1), indicating
supramolecular architectures. In chloroform and toluene the molecules are
only partly hydrogen bonded at higher concentrations (10À2 and 10À3 M).

200/[500]
J. J. van Gorp et al.
TABLE 1 Wavenumbers s [cmꢀ1] of the Carbonyl Stretch Vibrations of Carbonyl
Centered Trisamide 1a, Trisurea 2a, Nitrogen Centered Trisamide 3a, and Mono
Amide Bisureas 4 and 5 in the Solid State and in 10ꢀ4 M Heptane or Chloroform
Solutions
Compound
1aa
2aa
3a
4
s solid state
1682
1664
1670
1650
1676
1641
1645
1638
s 10ꢀ4 M heptane
1641
1656
1672
1650
1681
s 10ꢀ4 M chloroform
1644
(1711)
aSee reference 15.
The (partial) aggregation in chloroform-d1 was confirmed by 1H-NMR
spectroscopy, where broad signals were observed, unlike the sharp signals
obtained in chloroform-d1/methanol-d4 mixtures and in tetrahydrofuran-
d8 (see Experimental). As the NMR results of disk 5 were comparable, the
aggregation behavior in solution of 4 and 5 was judged similar at these
concentrations.
CD Studies
C3-symmetrical urea disks 2 form supramolecular aggregates in dilute
apolar solutions, while C3-symmetrical carbonyl centered amide disks 1 are
not able to do so. Therefore, aggregate formation of the nitrogen centered
C3-symmetrical amide 3 and the asymmetrical mono amide bisurea disks 4
(‘‘chiral urea’’) and 5 (‘‘chiral amide’’), was investigated with CD spectro-
scopy (Table 2).
Amide 3b shows no Cotton effect in 10ꢀ4 M or 10ꢀ5 M heptane solutions.
However, disks 4 and 5 do show remarkable effects (Fig. 2), resembling the
signal of the C3-symmetrical urea disk 2 in shape and intensity.
Temperature-dependent measurements with the C3-symmetrical urea
disk 2 revealed that the compound was highly thermally resistant (135ꢁC)
and that upon cooling 2 days were required for the original signal to
restore. The Cotton effect of mono amide bisurea 4 in a 10ꢀ5 M heptane
solution has disappeared completely at 55ꢁC, and here also a large amount
of hysteresis was observed (approximately 2 days). The Cotton effect of
mono amide bisurea 5 in a 10ꢀ4 M heptane solution was only stable up to
30ꢁC. Furthermore, upon cooling not only kinetic effects were observed but
also some irreversibility.

Architectures of Asymmetrical Disks
201/[501]
TABLE 2 UV and CD Data of Carbonyl Centered Trisamide 1b, Trisurea 2b,
Nitrogen Centered Trisamide 3b, and Mono Amide Bisureas 4 and 5; lmax
[nm] ¼ the Absorption Band Most Towards the Red, and e/De [l/molꢀcm] ¼ the
Intensity of the Signala
UV-Vis
CD
No.
lmax
"
lmax
D"
1bb
2bb
3b
4
308
259
286
261
268
2.16104
5.16104
4.86104
4.06104
5.66104
–
275
–
–
ꢁ51.5
–
265
259
ꢁ45.9
5
ꢁ45.1
a1b, 3b, 4, and UV of 5 measured at ꢂ10ꢁ5 M and CD of 5 at ꢂ10ꢁ4 M in heptane;
2b measured at ꢂ10ꢁ5 M in dodecane.
bSee reference 15.
FIGURE 2 CD spectra and temperature-dependent data of mono amide bisurea
disks 4 and 5.

202/[502]
J. J. van Gorp et al.
DISCUSSION
The absence of a liquid crystalline phase shown by nitrogen centered chiral
amide 3b, corresponds to the small liquid crystalline window shown by
carbonyl centered chiral amide 1b [15]. Achiral disks 1a and 3a both do
form columnar liquid crystalline phases, but IR and CD measurements
indicate that the (helical) columnar structure of disks 1 and 3 is not
retained in apolar solution. The similar behavior of the carbonyl centered
trisamides 1 and the nitrogen centered trisamides 3 indicates that the
difference in supramolecular aggregation between trisamides 1 and tri-
sureas 2 is not caused by the difference in connectivity of the hydrogen
bonding groups to the central benzene ring (via the carbonyl group or
the nitrogen atom, respectively). Clearly, in comparison to trisamide 1, the
stronger hydrogen bonding of the urea groups in trisurea 2 increases the
tendency to form helical, columnar architectures.
Disk 4, with two ‘‘chiral urea’’ groups and disk 5, with one ‘‘chiral amide’’
group, both show Cotton effects in CD spectroscopy and their absorptions
are similar in shape and maxima. This means that the urea, as well as the
amide part, are capable of transferring chirality to the ensemble of chro-
´
mophores present in the molecule, implying that urea and amide groups are
hydrogen bonded. The binding of all three groups is confirmed by the fact
that the Cotton effects of mono amide bisureas 4 and 5 resemble the effect
displayed by trisurea 2b judged from shape, maxima, intensity and hys-
teresis (Table 2). As the intensity of the Cotton effect of 4 (6 chiral cen-
ters) is similar to that of 2b (9 chiral centers), one might speak of a
‘sergeants and soldiers’ effect [17]. Presumably, 4 and 5 adopt conforma-
tions in which the amide and urea groups are tilted with respect to the
central benzene ring in a propellor-like way, just like the symmetrical urea
disks 2 (Fig. 3).
From the presented CD data it does not become obvious whether the
mono amide bisurea disks 4 and 5 are stacked urea by urea and amide by
amide, or that also hydrogen bonds between amide and urea groups can
occur. From mixing experiments between trisamides 1 and trisureas 2 it
was deduced that chiral amide disks 1b (that do not form aggregates by
themselves) cannot induce chirality when they are mixed with achiral urea
disks 2a [15]. Assuming that this finding also applies to the asymmetrical
disks 4 and 5, this implies that only urea-urea and amide-amide hydrogen
bonds occur. Presumably, aggregation is induced by the stronger urea
interactions, and when in two superimposed disks two urea groups adopt a
‘‘bent’’ conformation, the amide groups of the two disks are interacting, and
a third hydrogen bond is formed, inducing the thermodynamically most
favorable state. In conclusion, in asymmetrical ‘‘gallic’’ compounds 4 and 5

Architectures of Asymmetrical Disks
203/[503]
FIGURE 3 Schemetical representation of the supposed conformations of mono
amide bisureas 4 and 5 (left) and bisurea 8 (right) in a supramolecular stack. R-
groups of 8 are similar to those of 1b (see Scheme 1). (See Color Plate XIX).
amide-amide hydrogen bonds can be formed, whereas in symmetrical
‘‘gallic’’ compounds 1 and 3, this is not possible.
Although the Cotton effects of mono amide bisurea disks 4 and 5 are
very similar, expression takes place at 10ꢀ5 M for ‘‘chiral urea’’ 4, while for
‘‘chiral amide’’ 5 10ꢀ4 M is needed. This could be rationalized by taking into
account that 4 has 6 chiral centers and 5 has only 3, which renders transfer
of chirality less efficient. However, when the UV maxima in 10ꢀ5 M solu-
tions are examined (Table 2), it is clear that the maximum and the intensity
of 4 (lmax ¼ 261 nm, e ¼ 4.06104 l/molꢁcm) are significantly lower than
those of 5 (lmax ¼ 268 nm, e ¼ 5.66104 l/molꢁcm), meaning that 4 is
aggregated stronger than 5 [18]. This confirms that the stacking of the
amides is induced by the stacking of the ureas. Supposedly, a strong stack
(a low UV maximum) is only obtained when a ‘‘propellor’’ is formed by
rotation of both ureas and the amide in the same direction (either left or
right). One can image that this is easier to reach when 2 ‘‘chiral ureas’’ leave
only 1 choice (left or right) for 1 ‘‘achiral amide’’, than when 1 ‘‘chiral
amide’’ has to overrule the stronger interactions of 2 ‘‘achiral ureas’’.
The concepts postulated above, correspond to the behavior shown by
bisurea 8 [15] (Fig. 3). The bisurea aggregate produces a Cotton effect of a
completely different shape and of much less intensity (lmax ¼ 264 nm,
De ¼ þ15 l/molꢁcm). Furthermore, after the Cotton effect of bisurea 8 has
disappeared at 80ꢂC, no hysteresis occurs upon cooling. This contrasts with
the time-dependent behavior of trisurea 2b, and mono amide bisureas 4
and 5. It is supposed that another Cotton effect implies another supra-

204/[504]
J. J. van Gorp et al.
molecular architecture. Probably, the urea groups of bisurea 8 adopt a
‘linear’ conformation, unlike the ‘bent’ position of the urea groups in 2b, 4,
and 5 (Fig. 3). This needs to be investigated further by for example AFM or
SANS measurements.
CONCLUSIONS
The library of discotics is expanded with nitrogen centered trisamides 3a/b
and mono amide bisureas 4 and 5. Carbonyl centered trisamides 1a/b and
nitrogen centered trisamides 3a/b show the same aggregation behavior.
Only achiral compounds 1/3a form columnar liquid crystalline phases in a
reasonable temperature window, and no aggregation takes place in solu-
tion. This shows that connectivity of the hydrogen bonding groups does not
greatly alter the aggregation behavior, implying that the stronger urea
hydrogen bonding causes the trisureas 2 to form rigid rod-like aggregates,
while the weaker amide hydrogen bonding prevents the trisamides 1 to
aggregate in dilute apolar solution.
Asymmetrical mono amide bisurea disks 4 and 5 do show supramole-
cular aggregates in dilute apolar solution. The Cotton effects themselves
and their time-dependent thermoreversible nature correspond to the
behavior of trisurea 2, and do not coincide with that of bisurea 8. Fur-
thermore, aggregates of disks 4, containing 6 chiral centers connected via
the urea groups, are formed easier than aggregates of disks 5, containing
only 3 chiral centers connected via the amide group. It is supposed that
formation of helical supramolecular aggregates by asymmetrical disks 4 and
5 is induced by urea-urea hydrogen bonding, followed by amide-amide
intermolecular hydrogen bonding.
The applied synthetic method enables us to form asymmetrical disks 4
and 5 provided with two different hydrogen bonding groups. In the future
also discotics containing different peripheral groups (e.g. hydrophobic and
hydrophilic [16,19]) can be synthesized by this method, or discotics con-
taining a ‘‘single tertiary handle’’ [19] or polymerizable groups. The concept
of selective amide-amide and urea-urea stacking might prove useful in
ordering these handles or functionalities.
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