Desymmetrization of 3,3′-bis(acylamino)-2,2′-bipyridine-based discotics: The high fidelity of their self-assembly behavior in the liquid-crystalline state and in solution

Article abstract of DOI:10.1002/chem.200902416

Two novel nonsymmetrical disc-shaped molecules 1 and 2 based on 3,3′-bis(acylamino)-2,2′-bipyridine units were synthesized by means of a statistical approach. Discotic 1 possesses six chiral dihydrocitronellyl tails and one peripheral phenyl group, whereas discotic 2 possesses six linear dodecyloxy tails and one peripheral pyridyl group. Preorganization by strong intramolecular hydrogen bonding and subsequent aromatic interactions induce self-assembly of the discotics. Liquid crystallinity of 1 and 2 was determined with the aid of polarized optical microscopy, differential scanning calorimetry and X-ray diffraction. Two columnar rectangular mesophases (Col_r) have been identified, whereas for C₃-symmetrical derivatives only one Col_r mesophase has been found.^[1] In solution, the molecularly dissolved state in chloroform was studied with ¹H NMR spectroscopy, whereas the self-assembled state in apolar solution was examined with optical spectroscopy. Remarkably, these desymmetrized discotics, which lack one aliphatic wedge, behave similar to the symmetric parent compound. To prove that the stacking behavior of discotics 1 and 2 is similar to that of reported C₃-symmetrical derivatives, a mixing experiment of chiral 1 with C₃-symmetrical 13 has been undertaken; it has shown that they indeed belong to one type of self-assembly. This helical J-type self-assembly was further confirmed with UV/Vis and photoluminescence (PL) spectroscopy. Eventually, disc 2, functionalized with a hydrogen-bonding acceptor moiety, might perform secondary interactions with molecules such as acids.

Full text of DOI:10.1002/chem.200902416

DOI: 10.1002/chem.200902416
Desymmetrization of 3,3’-Bis(acylamino)-2,2’-bipyridine-Based Discotics:
The High Fidelity of Their Self-Assembly Behavior in the
Liquid-Crystalline State and in Solution
Michel H. C. J. van Houtem,[a] Rafael Martꢀn-Rapffln,[a, b] Jef A. J. M. Vekemans,[a] and
E. W. Meijer*[a]
Abstract: Two novel nonsymmetrical
disc-shaped molecules 1 and 2 based
on 3,3’-bis(acylamino)-2,2’-bipyridine
units were synthesized by means of a
statistical approach. Discotic 1 possess-
es six chiral dihydrocitronellyl tails and
one peripheral phenyl group, whereas
discotic 2 possesses six linear dodecy-
loxy tails and one peripheral pyridyl
group. Preorganization by strong intra-
molecular hydrogen bonding and sub-
sequent aromatic interactions induce
self-assembly of the discotics. Liquid
crystallinity of 1 and 2 was determined
with the aid of polarized optical mi-
croscopy, differential scanning calorim-
etry, and X-ray diffraction. Two colum-
nar rectangular mesophases (Colr) have
been identified, whereas for C3-sym-
metrical derivatives only one Colr mes-
ophase has been found.[1] In solution,
the molecularly dissolved state in
ics, which lack one aliphatic wedge,
behave similar to the symmetric parent
compound. To prove that the stacking
behavior of discotics 1 and 2 is similar
to that of reported C3-symmetrical de-
rivatives, a mixing experiment of chiral
1 with C3-symmetrical 13 has been un-
dertaken; it has shown that they
indeed belong to one type of self-as-
sembly. This helical J-type self-assem-
bly was further confirmed with UV/Vis
and photoluminescence (PL) spectros-
copy. Eventually, disc 2, functionalized
1
chloroform was studied with H NMR
spectroscopy, whereas the self-assem-
bled state in apolar solution was exam-
ined with optical spectroscopy. Re-
markably, these desymmetrized discot-
Keywords: chirality · desymmetri-
zation · discotics · liquid crystals ·
self-assembly
with
a
hydrogen-bonding acceptor
moiety, might perform secondary inter-
actions with molecules such as acids.
Introduction
greatly enhances their possible application as functional ma-
terials in, for example, one-dimensional conductors or pho-
tovoltaic cells.[3,4] Self-assembly into nematic mesophases is
important for the application in liquid-crystal displays.[5]
Apart from p–p stacking,[6] self-assembly driven by hydro-
gen bonding[7] or coordination[8,9] may give rise to discotic
mesophases.[10] In solution, discotics may self-assemble to
give fiberlike structures.[11] Often stacks of discotics are heli-
cal and, since the helix is an intrinsically chiral object, chir-
ality present in the individual molecule may be transferred
to the complete stack at the supramolecular level.[12] Hydro-
gen bonding may be a major driving force for columnar, hel-
ical stacking as is the case for small N,N’,N“-trialkyl ben-
zene-1,3,5-tricarboxamide (BTA) discs in which the amide
functionality is involved in a threefold helical array of inter-
molecular hydrogen bonding.[13,14] More than a decade ago,
we described a specific kind of discotic mesogens based on
the BTA core, A (Figure 1a), which possesses a large central
core resulting from amidation of 1,3,5-benzenetricarbonyl
trichloride with three monoacylated 2,2’-bipyridine-3,3’-di-
Discotics have attracted widespread attention due to their
self-organization capabilities in the solid state and in solu-
tion. In the solid state they often display columnar liquid
crystallinity in which the rigid core of the discotic is organ-
ized in one-dimensional columns, whereas the more flexible
disordered periphery remains less organized.[2] This behavior
[a] M. H. C. J. van Houtem, Dr. R. Martꢀn-Rapffln,
Dr. J. A. J. M. Vekemans, Prof. Dr. E. W. Meijer
Laboratory of Macromolecular and Organic Chemistry
Eindhoven University of Technology
P.O. Box 513, 5600 MB Eindhoven (The Netherlands)
Fax : (+31)40-245-1036
E-mail: E.W.Meijer@tue.nl
[b] Dr. R. Martꢀn-Rapffln
Current address: Institute of Chemical Research of Catalonia
Av. Països Catalans, 1643007 Tarragona (Spain)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200902416.
2258
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FULL PAPER
eral alkoxy tails induce phase separation and solubility and
they determine the polarity of the compounds. In the solid
state, columnar liquid crystallinity is present over a very
broad temperature window (>300 K) provided long periph-
eral tails are present. In solution, these tails ensure solubility
and allow the introduction of chirality into the system.[17] Bi-
pyridine-based discotics equipped with polar oligo(ethylene
oxide) tails have also been described as displaying solubility
and expressing chirality in aqueous media as well as meso-
phase formation.[18,19] Both apolar and polar bipyridine-
based discotic systems obey in dilute solution the ”sergeant
and soldiers“ principle,[17,20,21] and the apolar discotics also
obey the ”majority rules“,[22] both proposed by Mark Green
et al. for covalent polymers.
Possible applications for these discotics are emerging.[19,23]
Our aim is to widen the applicability of these star-shaped
3,3’-bis(acylamino)-2,2’-bipyridine discotics in supramolec-
ular systems by replacing one of the trialkoxyphenyl moiet-
ies with a functional unit. Such a unit would allow interac-
tion with other compounds with the goal of influencing
liquid-crystalline behavior to introduce chirality by secon-
dary interactions and performing covalent or supramolec-
ular fixation of the discotic assembly. Numerous nonsym-
metric discotics have been described with the aim of altering
mesophase properties and transitions,[14,24] thereby allowing
interactions and functionality in the mesophase[25] or pro-
ducing discotic mesogens with special optical properties.[26]
In solution, desymmetrized, amphiphilic hexabenzocoro-
nenes, which are designed to self-assemble into chiral, heli-
cal tapes and nanotubes are well known,[27] as are nanofiber-
forming amphiphilic, ionic hexabenzocoronenes.[28] Some de-
symmetrized discotics are prone to covalent[29,30] or even
supramolecular[31] fixation.
In this paper, the synthesis and the characterization in the
mesophase and in solution of two nonsymmetric discotics 1
and 2 (Figure 1c) are described. The main question is wheth-
er these desymmetrized molecules adopt similar discotic
structures and self-assemblies in the mesophase and in solu-
tion as previously reported C3-symmetrical analogues. If so,
in the case of disc 2, introduction of functionality into these
discotic systems will be possible. In both discotics 1 and 2,
one trialkoxyphenyl wedge has been replaced by the smaller
phenyl and 4-pyridyl moieties, respectively. Discotic 1,
equipped with chiral dihydrocitronellyl tails, is relevant
since its chirality allows its stacking properties to be studied
with chiral-optical techniques like CD spectroscopy. Discotic
2 incorporates a basic pyridyl group that affords functionali-
ty to the discotic system, thereby allowing interactions with
other compounds and supramolecular fixation of the self-as-
sembled stacks.
Figure 1. a) C3-symmetrical discotics A with a benzene core and equipped
with three 3,3’-bis(acylamino)-2,2’-bipyridine moieties and nine nonpolar
[16]
[18]
ꢀ
ꢀ
(R=O alkyl)
or polar (R=O oligo(ethylene oxide))
alkoxy pe-
drawing.
ripheral tails. b) Their helical self-assembly depicted as
a
c) Chiral, nonsymmetric benzene discotic 1 and achiral, nonsymmetric
pyridine discotic 2. Intramolecular hydrogen bonding is represented with
dashed lines.
amine moieties.[15] Strong intramolecular hydrogen bonding
ꢀ
between amide N H groups and bipyridine N atoms preor-
ganizes the molecule into a C3-symmetrical conformation
that is, on average, planar.[16] Stacking due to mainly aromat-
ic interactions occurs in the solid state and in dilute solution.
In these self-assemblies the discotics adopt a propeller-like
conformation to afford helicity (Figure 1b). The nine periph-
Results and Discussion
Synthesis of chiral benzene discotic 1: The synthesis of non-
symmetric discotic
1 was performed as depicted in
Scheme 1. This statistical synthesis relies on two different ar-
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2259

E. W. Meijer et al.
group and the phenyl group.
Also, stacking of the different
components when present in
concentrated solution during
chromatographic
purification
hampers their efficient separa-
tion. Analytical GPC[33] did not
show a difference in retention
time between the different
components. Eventually, the pu-
rification was performed in two
steps. Precipitation in a polar
solvent in which desired prod-
uct 6 does not dissolve allowed
the removal of unreacted
mono-protected amine 5 and
N,N-diisopropylethylamine
(DIPEA) salts by simple filtra-
tion. Then the crude product
was further chromatographical-
ly purified with a chloroform/
pyridine mixture as the eluting
solvent to minimize stacking.
However,
according
to
1H NMR spectroscopy and
MALDI-TOF mass spectrome-
try, some impurities remained.
The Boc groups of intermediate
Scheme 1. a) Synthesis of monoacylated compounds 4 and 5: i) benzoyl chloride (1.1 equiv), TEA, CH2Cl2,
08C!RT, 28 h; ii) di-tert-butyl dicarbonate (1.2 equiv), ethanol, 358C, 5.5 h. b) One-pot reaction towards non-
symmetric compound 6 followed by deprotection of the Boc groups and subsequent acylation with chiral,
mesogenic acid chloride 9: i) DIPEA, CH2Cl2, 108C!RT, 3 h; ii) DIPEA, CH2Cl2, 108C!RT, 17 h; iii) TFA,
CH2Cl2, 08C!RT, 5 h; iv) TEA, acetone, 10 min; v) SOCl2, DMF, CH2Cl2, RT, 17 h; vi) DIPEA, N-methyl-2-
pyrrolidone, 17 h.
product
6 were removed by
TFA in dichloromethane fol-
lowed by neutralization with
triethylamine (TEA). Surpris-
ingly, the TFA salt is soluble in
dichloromethane and acetone,
omatic amines 4 and 5 that consecutively were reacted with
trimesyl chloride to afford nonsymmetrical precursor 6 in
one step (Scheme 1b). Aromatic amines 4 and 5 were ob-
tained by reacting 2,2’-bipyridine-3,3’-diamine (3) with one
molar equivalent of an acid chloride or anhydride (Sche-
me 1a).[15] The synthesis of tert-butoxycarbonyl (Boc)-pro-
tected 5 was slightly adjusted due to the low reactivity of
poorly nucleophilic 3 towards di-tert-butyl dicarbonate.[32]
Deactivation of the second amino functionality of 3 due to
intramolecular hydrogen bonding and concomitant planari-
zation ensured highly selective monoacylation.[16] In the first
reaction step of the one-pot reaction, one molar equivalent
of aromatic amine 4 was added slowly to trimesyl chloride
to obtain, on average, monoacylation (Scheme 1b) subse-
quently followed by addition of an excess of Boc-protected
aromatic amine 5 to ensure complete amidation of the re-
maining acid chloride functionalities. The Boc groups of
compound 6 allow incorporation of any alkylated wedge
after deprotection with trifluoroacetic acid (TFA). The one-
pot synthesis of 6 was relatively easy to carry out, but had
the disadvantage that the purification of the statistical mix-
ture to afford pure 6 was quite tedious due to comparable
polarities and hydrodynamic volumes of the tertiary butyl
whereas the neutralized product 7 is not (Scheme 1b). The
limited solubility of this neutralized product 7 required
polar N-methyl-2-pyrrolidone as solvent in the final reaction
step in which it was reacted with chiral acid chloride 9. The
latter acid chloride was obtained from the corresponding
carboxylic acid 8 according to a slightly modified literature
procedure,[16,30,34] whereas carboxylic acid 8 was obtained ac-
cording to established procedures.[16] Precipitation of the re-
action mixture in polar solvent and column chromatography
gave pure, nonsymmetric discotic 1. Based on amino precur-
sor 4, the overall yield amounted to 14%.
Synthesis of achiral pyridyl discotic 2: The synthesis of non-
symmetric, functionalized discotic 2 has been performed
with an adjusted statistical method in which the alkylated
wedges were directly incorporated, thereby allowing the
final separation step to be based on hydrodynamic volumes
(Scheme 2). Recycling gel permeation chromatography
(GPC) proved to be an effective method to purify discotics
equipped with bulky alkylated wedges; the side products
either lack or have an excess of three long alkoxy tails or
even a complete 3’-(3,4,5-trisalkoxybenzoylamino)-2,2’-bi-
pyridyl-3-amine wedge. The synthesis of 4-pyridyl-function-
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Desymmetrization of Discotics
FULL PAPER
DSC and polarizing optical mi-
croscopy: For compounds 1 and
2 in both DSC and POM, a
transition to the isotropic melt
at about 3258C was observed
that allowed the growth of
liquid-crystalline textures under
the microscope by slow cooling
to confirm the mesogenic prop-
erties of the compounds. The
enthalpy values associated with
the clearing point are on the
same order of magnitude as
that of similar C3-symmetrical
discotics.[16] Depicted in Fig-
ures 2 and 3 are the pseudo-
focal-conic textures, typical of
columnar mesophases, exhibit-
ed by discs 1 and 2 in the meso-
phase below the isotropization
temperature.[36] The straight
lines present in the textures are
indicative of an ordered colum-
Scheme 2. a) Synthesis of 4-pyridyl-functionalized aromatic amine 11 starting with isonicotinic acid: i) thionyl
chloride, 768C, 5 h; ii) DIPEA, CH2Cl2, 08C!RT, 5 h. b) One-pot reaction to obtain nonsymmetric, achiral
discotic 2 in only two steps from their aromatic amine precursors 11 and 12: i) DIPEA, CH2Cl2, 108C, 10 min;
ii) DIPEA, CH2Cl2, 108C!RT, 3 h.
Table 1. DSC data for the phase transitions of discotics 1 and 2.[a]
alized aromatic amine precursor 11 is shown in Scheme 2a.
Pyridine-4-carbonyl chloride HCl salt (10) was synthesized
by reacting isonicotinic acid in hot thionyl chloride.[35] The
obtained acid chloride was subsequently reacted with 3 by
slow addition of 10 to 3 to prevent diacylation and maximize
product formation.[15] The synthesis of hydrophobic aromatic
amine precursor 12 has been reported previously.[16] In a
one-pot reaction, amines 11 and 12 were added successively
to a solution of trimesyl chloride to afford disc 2 together
with its statistically determined analogues. Chromatographic
purification as described above yielded pure disc 2 in a yield
of 12% based on amino precursor 11.
[b]
[b]
First cooling run (108Cminꢀ1
)
Second heating run (108Cminꢀ1
)
Compd Tonset DH
Phase
Compd Tonset DH
Phase
[8C]
A
]
transition[c]
[8C]
A
]
transition[c]
1
2
329
201
336
206 10
ꢀ3 38
6
9
6
I–LC
LC–LC
I–LC
LC–LC
LC–Cr
1
2
328
6
LC–I
LC–LC
LC–I
LC–LC
Cr–LC
203 10
335
215 11
42
7
3
[a] Measurements were conducted between ꢀ50 and 3508C. The onset was
taken for the transition temperatures. [b] Heating and cooling runs at a rate
of 10 Kminꢀ1 are given in Figures S2 and S3 of the Supporting Information.
[c] Type of phase transition according to POM. Exact mesophase was deter-
mined with XRD. LC=liquid crystalline; Cr=crystalline.
Liquid-crystalline behavior of discotics 1 and 2: Both non-
symmetric discs 1 and 2 are sticky solids at room tempera-
ture, as are the majority of C3-symmetrical analogues that
display a very broad liquid-crystalline window of more than
300 K.[16] The mesogenic properties of both discotics 1 and 2
were determined using differential scanning calorimetry
(DSC), polarizing optical microscopy (POM), and X-ray dif-
fraction (XRD). The influence of the adaptation, in which a
bulky, alkylated group is replaced by a small, rigid group on
the liquid-crystalline properties of discotics 1 and 2 is of es-
pecial interest. Thermal gravimetric analysis (TGA) (see
Figure S1 in the Supporting Information) was used to deter-
mine the thermal stability of discotic 1. Compound 1 dis-
plays no degradation below 3508C under a nitrogen atmos-
phere. However, severe decomposition starting from 3008C
was observed when TGA was performed under an oxygen-
rich atmosphere. Therefore, DSC and POM were conducted
under a nitrogen atmosphere to ensure reliable results. The
DSC measurements of discotics 1 and 2 are shown in
Table 1.
nar mesophase.[37] Interestingly, a transition to a lower tem-
perature mesophase was detected by DSC for both 1 and 2
at approximately 2008C. This transition is not present in
their symmetrical analogues.[16] Apparently, it does not
matter whether a phenyl or pyridyl group replaces the trial-
koxyphenyl wedge in 1 and 2 for the appearance and ther-
mal position of the transition between the two mesophases.
Also, this transition temperature between two mesophases is
not influenced by a branching of the aliphatic tails. The en-
thalpy values associated with this transition are relatively
small, which means that there is no large structural differ-
ence between the two mesophases of 2 and 3. The transition
between the two mesophases can actually consist of a two-
step transition, as is supported by the presence of two peaks
in the DSC run of disc 1 (see the Supporting Information,
Figure S2).[38] This transition was observed by POM for discs
1 and 2 as a rapid change of the texture around 2108C,[39]
while the compound remained fluidic under pressure (Figur-
es 2b and Figure 3b). The discotics display a very broad
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E. W. Meijer et al.
due to the presence of branched side tails in compound 1
that will lower the melting point.[40] The isotropic transitions
of both discs 2 and 3 are lower than that of related nonpolar
discotics A (Figure 1a), which is in agreement with other re-
ported desymmetrized systems.[41] All discussed phases in
discotics 1 and 2 are enantiotropic and little hysteresis was
observed for the LC–LC transitions at approximately 2008C
for both 1 and 2 and for the Cr–LC transition of discotic 2
(see Figures S2 and S3 of the Supporting Information for
the DSC plots).
X-ray diffraction: The two discotics 1 and 2 were investigat-
ed by small- (SAXD) and wide-angle (WAXD) X-ray dif-
fraction with the aim of verifying the type of mesophase and
to determine the structural parameters. As seen in the DSC
traces, the structures of the mesophases at room tempera-
ture (RT) and above are equivalent for both compounds.
Below RT an additional phase was detected for discotic 2,
and for that reason the results for discotic 2 will be dis-
cussed in particular. All SAXD and WAXD data for both
discotics 1 and 2 are gathered in Table 2.
Figure 2. Polarized optical micrographs of discotic
b) 1758C (same area, rotated).
1 at a) 295 and
The WAXD profile of discotic 2 at RT (Figure 4a) exhib-
its two features in the large-angle region. One peak corre-
sponds to a distance of 3.3 Š, which is in the range of the
stacking distance between aromatic rings in the liquid-crys-
talline state. This confirms the ordered columnar structure
of the phase. The other feature is a diffuse halo that corre-
sponds to a distance of about 4.5 Š, the typical distance be-
tween molten alkyl chains in a mesophase.[42] These features
remained present up to the maximum temperature limit of
2008C of the WAXD setup. Upon cooling from RT to
ꢀ218C, the alkyl chains freeze in a more ordered or crystal-
line phase, and the diffuse halo turned into a peak that cor-
responded to 4.2 Š.
SAXD patterns of discotic 2 at ꢀ218C and RT are analo-
gous and display a set of maxima with an additional peak at
the lower temperature (Figure 4b). The ratio between the
spacings that correspond to the peaks is not a reciprocal
ratio indicative of square or hexagonal two-dimensional lat-
tices. However, they can be indexed according to a rectan-
gular symmetry P2gg based on the extinction rules. The lat-
tice parameters of the rectangular arrangement are given in
Table 2. The phase at ꢀ218C has the same structure as the
liquid-crystalline phase at RT, except for the peripheral
alkyl chains, which are crystallized in the columnar rectan-
gular mesophase Colr1. Upon an increase in temperature, a
third phase Colr3 appeared. The SAXD profile at 2408C is
simpler than the profiles at lower temperatures. Only three
peaks are present in the small-angle region, which can be in-
dexed according to a rectangular symmetry too. Neverthe-
less, the unit cell for this Colr3 phase is much smaller than
for the lower temperature phases (Table 2). As commented
above, WAXD data unfortunately were not available for
this phase. In a columnar rectangular phase, there are typi-
cally two columns per unit cell, one of which is in the
center, and the other is in the corner of the unit cell. This is
the case for the Colr3 phase, which exhibits similar lattice pa-
Figure 3. Polarized optical micrographs of discotic
b) 1608C (same area).
2 at a) 315 and
liquid-crystalline window (>300 K) and are liquid crystalline
at room temperature, which is important for future applica-
tions.[3] Apparently, the removal of one trialkoxy group com-
pared to their C3-symmetrical analogues does not decrease
the ability of discotics 1 and 2 to form mesophases. Below
room temperature, discotic 2 exhibits a liquid-crystalline to
crystallization (LC–Cr) transition. Although the observed
texture undergoes only very subtle changes, we assign the
transition as crystallization as it is accompanied by a large
enthalpic change relative to the transitions at approximately
2008C and 3258C. For compound 1 no melting transition
was observed. The absence of a melting point is probably
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Desymmetrization of Discotics
FULL PAPER
Table 2. X-ray results for the mesophases of nonsymmetrical discotics 1
and 2.
Compound T
[8C]
Phase h k l dobsd
dcalcd
[Š]
Lattice
constants
[Š]
1calcd
[gcmꢀ3
]
[b]
[Š][a]
U
discotic 1 RT Colr2 2 0 0 50.3
P2gg 1 1 0 34.5
4 0 0 25.4
50.3
34.5
25.1
16.6
15.7
14.8
13.4
–
a=100.5 0.91
b=36.8
c=38.0[c]
h=3.3
0 2 1 16.6
2 2 1 15.8
4 2 1 14.4
7 1 0 13.3
alkyl 4.5 (br)
p–p 3.3
Z=4[d]
–
230[e] Colr3 2 0 0 34.7
C2mm 1 1 0 29.8
0 2 0 16.5
34.7
29.8
16.5
53.3
38.0
32.3
a=69.4 0.93
b=33.0[c]
Z=2[d]
[f]
discotic 2 ꢀ21 Colr1 2 0 0 53.3
a=106.6 0.98
b=40.6
P2gg 1 1 0 38.0
2 1 0 32.5
c=36.5[c]
3 1
0, 4
0 0
0 2 0 20.8
0 2 1 17.7
6 0 1 16.1
alkyl 4.2
26.4
26.6, 26.7 h=3.3
20.3
17.8
16.0
–
Z=4[d]
p–p
3.3
–
RT Colr2 2 0 0 53.8
53.8
37.0
a=107.6 1.00
b=39.4
P2gg 1 1 0 37.0
3 1
0, 4
0 0
26.9
26.5, 26.9 c=36.5[c]
4 1 1 19.0
2 2 1 16.5
4 2 1 14.4
1 3 0 13.3
alkyl 4.5 (br)
19.0
16.5
14.6
13.0
–
h=3.3
Z=4[d]
p–p
3.3
–
240[e] Colr3 2 0 0 33.4
C2mm 1 1 0 31.7
4 0 0 18.1
33.6
31.7
18.0
a=67.2 0.88
b=34.8[c]
Z=2[d]
[a] br=broad maximum.[b] Calculated density for two columns per unit
cell in the case of Colr3 and 4 columns per unit cell in the cases of Colr1
and Colr2. 1calcd =(10”Z”Mr)/(a”b”h”6.02), in which Mr is the molecular
weight and h is assumed to equal 3.3 Š for Colr3. [c] c corresponds to the
periodicity of the helix. [d] Z is the number of discotics per slice of the
unit cell. [e] No WAXD measurement is available above 2008C. [f] Crys-
talline phase.
rameters to those of the Colr phase of the symmetrical
parent compound when one takes into account the differen-
ces in the structure of the discotics and in the temperature
of the measurements.[1] However, in Colr1 and Colr2 phases
an unusual value of Z=4 was calculated based on density
considerations (Table 2).[43] When comparing the lattice pa-
rameters, b is similar for all phases for both discotic 1 and
discotic 2, but a in Colr1 and Colr2 is nearly twice a in the
Colr3. It is assumed that at lower temperatures the symmetry
decreases, and as a result two unit cells of Colr3 combined to
give rise to the new unit cell of the Colr2 and Colr1 phases
(Figure 4c). The loss of symmetry in the supramolecular or-
ganization when lowering the temperature might arise from
different orientation in the plane of the nonsymmetric mole-
cules or from a vertical shift of neighboring columns, which
Figure 4. a) WAXD profiles for discotic 2 at ꢀ218C (g), RT (b),
and 2008C (c). b) SAXD profiles for discotic 2 at ꢀ218C (c), RT
(c), 2008C (b), and 2408C (g). c) Proposed structures of Colr2
and Colr3 phases for discotic 2. The unit cell is filled with diagonal lines.
X-ray profiles of discotic 1 are given in Figure S4 of the Supporting Infor-
mation.
are inherently helical, at least in solution as will be discussed
below. X-ray diffraction studies on aligned samples can be
used to elucidate the structure of the helix in the liquid-crys-
talline phase.[9,42,44] SAXD and WAXD patterns of an
aligned sample of discotic 2 at RT (Colr2) are shown in
Figure 5. The meridional position of the peak due to the p–
Chem. Eur. J. 2010, 16, 2258 – 2271
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2263

E. W. Meijer et al.
ꢀ
hydrogen bonding between amide N H and neighboring
pyridine N atoms.[16] This hydrogen bonding was observed
with 1H NMR spectroscopy in CDCl3 in which the amide
protons were shifted downfield to approximately d=15 ppm
together with a downfield shift of several aromatic core pro-
tons, which is indicative of an on average almost flat shape
of the discotic. This C3-symmetrical preorganization allows
the molecules to form long stacks primarily by p–p stacking,
which leads to a propeller shape of the aggregated discotics
inducing helicity, as is confirmed by X-ray diffraction (Fig-
ure 1b).[1] Since the helix is an intrinsically chiral object,
chirality in the aliphatic periphery of the discotic is trans-
ferred to the helical stack. This process can be observed
with circular dichroism (CD) spectroscopy by the appear-
ance of a Cotton effect that corresponds to an electronic
transition in UV/Vis absorption spectroscopy. First of all,
1H NMR and CD spectroscopy of discotic 1 is discussed to
prove that the conformation of discotic 1 in a good solvent
(CDCl3) and the self-assembly of discotic 1 in a nonsolvent
(alkanes) are similar to that of C3-symmetrical discotics in
these solvents.[17] Secondly, the behavior of achiral discotic 2
has been probed with spectroscopic techniques to show that
its behavior in solution is similar to that of discotic 1 and
C3-symmetrical analogues.
Figure 5. a) WAXD and b) SAXD patterns of an aligned sample of dis-
cotic 2 at RT. The capillary axis is vertical.
p stacking, in addition to the three most intense peaks in
the small-angle region being on the equator, confirms that
the phase is columnarly ordered with the central benzene
ring of disc 2 being perpendicular to the axis of the columns
(Figure 5a). In the helical organization, the molecules adopt
a propeller shape in which the bipyridine units are tilted
with respect to the central benzene unit (Figure 1b).[1]
Therefore, an additional meridional maximum at a slightly
lower diffraction angle than the p–p stacking maximum that
corresponds to 3.7 Š is ascribed to the perpendicular dis-
tance between the bipyridine units of consecutive discs.[1]
The less intense maxima in the small-angle region are split
into a four-spot pattern (Figure 5b). This feature was as-
cribed to helical intracolumnar order and to the existence of
three-dimensional order in the mesophase. From split
maxima a periodicity of 36.5–38.0 Š can be measured along
the axis of the columns. This value is only slightly larger
than the periodicity in helices of the symmetrical analogue
A,[1] although a value three times larger would be expected
in this case due to the absence of C3 symmetry. We have
two hypotheses to explain this observation. Firstly, there is
no correlation between the position of the pyridine moieties
in consecutive discotics disordered along the column, so that
the overall symmetry is the same as with C3-symmetrical de-
rivatives A.[1] Secondly, electron density is similar for the al-
kylated and nonalkylated wedges so that they are not distin-
guished by X-ray diffraction. In the structure we propose,
the relative rotation between consecutive discotics in a
column of discotic 2 is about 118 and around 33 discotics are
needed for a complete rotation of 3608. A shift of the phase
of neighboring columns/helices with a large correlation dis-
tance in the plane perpendicular to the columns could be
the cause of the large size of the unit cell in the Colr1 and
Colr2 phases. Upon an increase in the temperature, in Colr3
disorder increases and the correlation between the phases of
neighboring columns is lost, thus resulting in an increase of
the symmetry of the rectangular lattice.
1
NMR spectroscopy: When an H NMR spectrum of dis-
cotic 1 was taken in CDCl3, protons characteristic of a pre-
organized structure were observed (Figure 6a). In chloro-
form, discotics 1 and 2 are mainly molecularly dissolved,
thereby resulting in sharp peaks that allow for a structural
investigation of the compounds. In a nonpolar solvent like
heptane or methyl cyclohexane, molecules 1 and 2 are pri-
marily stacked, which results in very broad NMR spectro-
scopic peaks. Peak assignment of discotics 1 and 2 in CDCl3
1
was confirmed with gCOSY H–1H 2D NMR spectroscopy
(see Figures S5 and S6 in the Supporting Information).
Almost all aromatic and amide protons were observed in a
2:1 integration ratio that corresponds to the trialkoxyphen-
yl/phenyl wedge ratio of 2:1 (Figure 6). The secondary
amide protons 7 are located between d=16 and 14 ppm, in-
dicative of very strong intramolecular hydrogen bonding
with the nitrogen atoms of the bipyridine system. The aro-
matic protons 4 are located between d=9.6 and 9.4 ppm
due to strong anisotropic deshielding by the adjacent amide
carbonyl. At d=9.25 ppm, a singlet that belongs to central
benzene core protons 10 and 11 is located. It is remarkable
that protons 6’ and [6]’ of the outer pyridine rings are shifted
d=0.6 ppm downfield compared to protons 6 and [6] of the
inner pyridine rings. This may reflect deshielding of protons
6’ and [6]’ by the neighboring amide carbonyls, which is a
strong indication of an on average rather planar conforma-
tion of discotic 1.[16] This means that the aromatic amide
core of disc 1 is C3 symmetrical as is drawn in Figure 6. Fi-
nally, between d=8.1 and 7.2 ppm, less deshielded aromatic
protons can be observed; their complete assignment is given
in the Experimental Section. With an increase in the con-
centration of discotic 1 in CDCl3, peak broadening and up-
field shifts can be observed that are indicative of aggrega-
Self-assembly and induction of chirality in solution: Besides
the formation of columnar aggregates in the liquid-crystal-
line state, discotics 1 and 2 also self-assemble in nonpolar
solution. Previous studies on C3-symmetrical discotics based
on the 3,3’-bis(acylamino)-2,2’-bipyridine units have re-
vealed that they are preorganized by strong intramolecular
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Desymmetrization of Discotics
FULL PAPER
Figure 7. 1H NMR spectra of discotic 2 in CDCl3 at 3 mm. Only the hy-
drogen bonding and aromatic regions are shown. The full spectrum is
given in Figure S8 of the Supporting Information (R=OC12H25).
group influences the self-assembly behavior of these discot-
ics in nonpolar, dilute solution. To compare the aggregation
behavior of discotic 1 with parent C3-symmetrical com-
pounds, a mixing experiment in which chiral discotic 1 was
added to achiral, symmetric discotic 13 was performed
(Figure 8).[17] C3-symmetrical discotic 13 is known to self-as-
semble into well-defined supramolecular, helical columns in
alkanes like heptane due to phase separation, p–p stacking,
and preorganization by intramolecular hydrogen bonding. A
chiral analogue of discotic 13 equipped with dihydro-citro-
nellyl side chains (discotic 14, Figure 8, right) is able to shift
the equilibrium between right-handed (P) and left-handed
(M) helices to one of them, thereby creating an overall
chiral, supramolecular structure.[17] From mixing experi-
ments in alkanes, it is known that a small amount of chiral
discotic 14 is able to bias the helicity of columns of achiral
discotic 13. This is known as the “sergeant and soldiers” ex-
periment in which chiral 14 acts as a sergeant directing a
platoon of achiral discotic 13 soldiers.[20,45] If nonsymmetri-
cal, chiral discotic 1 is able to bias the helicity of achiral dis-
cotic 13 in a similar fashion, and we may assume discotic 1
and achiral analogue 2 to display the same aggregation be-
havior as C3-symmetrical discotic 13 and its analogues. The
latter is a prerequisite to transfer the knowledge gained
from symmetrical systems to the design of a nonsymmetrical
discotic equipped with the desired functional group for
supramolecular interactions. Thus, dilute solutions of discot-
ic 1 in heptane were added to dilute solutions of discotic 13
of the same concentration in heptane (Figure 8). For every
measuring point in Figure 8, a fresh mixture was prepared
from the two stock solutions of discotics 1 and 13, respec-
tively.
Figure 6. 1H NMR spectra of discotic 1 in CDCl3 at a) 0.5, b) 6, and
c) 14 mm at 258C (R=OC10H21*). Only the aromatic and hydrogen-
bonded proton region is shown. Full spectra are given in Figure S7 of the
Supporting Information.
tion (Figure 6b and c). In particular, the central phenyl pro-
tons 10 and 11 broaden and they also display the largest up-
field shift (d=9.25 to 8.8 ppm). However, no ordered, heli-
cal aggregates are formed in chloroform according to CD
and UV/Vis spectroscopy. The observed 1H NMR spectro-
scopic data of discotic 1 confirm that the conformation of
disc 1 in chloroform is similar to that of its C3-symmetrical
derivatives. Thus, the removal of one alkylated group does
not affect the overall conformation of discotic 1.
The 1H NMR spectrum of discotic 2 is depicted in
Figure 7. It strongly resembles the spectrum of discotic 1
shown in Figure 6, which suggests that compounds 1 and 2
adopt a comparable conformation in solution. Also for dis-
ꢀ
cotic 2 separate aromatic and amide N H peaks can be ob-
served for the alkylated wedge and the nonalkylated wedge
in an integration ratio of 2:1.
Optical spectroscopy: The self-assembly of discotic 1 was
further investigated using CD spectroscopy with the goal of
establishing how the removal of one alkylated, solubilizing
Chem. Eur. J. 2010, 16, 2258 – 2271
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2265

E. W. Meijer et al.
Figure 9. a) Temperature-dependent UV/Vis absorption spectra of discot-
ic 2 in dodecane;[49] c=17 mm, cooling rate=1 Kminꢀ1. The spectrum in
chloroform was taken at RT, c=19 mm (full temperature ranges are given
in Figure S10 of the Supporting Information). b) Temperature-dependent
fluorescence spectra of discotic 2 in dodecane; c=1 mm, cooling rate=
1 Kminꢀ1. Excitation performed at 365 nm.
Figure 8. a) “Sergeant-and-soldiers” measurement with discotics 1 and
13; the g values were measured at 387 nm for mixtures of discotics 1 and
13 in heptane at RT. Concentration=27 mm. The magnitude of the
Cotton effect is stable after mixing. Full CD and UV/Vis spectra are
given in Figure S9 of the Supporting Information. b) C3-symmetrical dis-
cotics achiral 13 and chiral 14.
ane displayed a bathochromic and hypsochromic shift be-
tween 100 and 708C, and a bathochromic and hypsochromic
shift between 70 and 108C (Figure 9a). The bathochromic
shift of the absorption maximum belonging to the gallic
moieties amounts to 2 nm (292–294 nm), and the bathochro-
mic shift of the absorption maximum belonging to the bipyr-
idine moiety amounted to 4 nm (360–364 nm). In the region
of the p–p* transition of the bipyridine system around
362 nm, the fine structure was observed in a more pro-
nounced fashion. This fine structure, with absorption
maxima at 364 and 383 nm and a shoulder at 351 nm, is indi-
cative of the formation of well-ordered, helical stacks in so-
lution. The shape of the spectrum at 1008C is similar to a
spectrum of discotic 2 in chloroform (Figure 8), in which the
discotics are molecularly dissolved. The latter spectrum
shows a hypsochromic shift of about 12 nm compared to the
spectrum of discotic 2 in dodecane. In the fluorescence spec-
trum (Figure 9b), a large, gradual increase of the fluores-
cence intensity can be observed upon cooling. This increase
is, together with the redshift in UV/Vis, indicative of the for-
mation of J-aggregates in dilute solutions in dodecane, a
phenomenon also observed for discotics that contain oxadia-
zole moieties.[47] This formation of J-aggregates coincides
with our molecular picture of a helical stack of discotic 2 in
In Figure 8a, the Cotton effect, given as the anisotropic g
factor, is plotted against the amount of chiral disc 1 added;
a strong nonlinear dependence is clearly visible. After the
addition of just 5 mol% chiral disc 1, the same amplitude of
the Cotton effect as with 100 mol% chiral 1 was observed.
This indicates a strong bias of the helical sense of assemblies
of achiral 13 by chiral 1, thus strongly suggesting the pres-
ence of mixed assemblies of discotic 1 with 13. The Cotton
effect emerged immediately after mixing and was stable
with time, thereby indicating that the dynamic system imme-
diately adopts its thermodynamically most favorable state.
The maximum in CD intensity was observed around
25 mol% disc 1, which might be rationalized by more effi-
cient packing of achiral disc 13, which lacks methyl branch-
es, relative to chiral disc 1. A dependence of the aggregation
on the branched character of the aliphatic periphery has
been observed for hexabenzocoronene discotics.[46]
For achiral discotic 2, temperature-dependent self-assem-
bly in nonpolar solution has been examined with UV/Vis
and fluorescence spectroscopy to study its aggregation be-
havior in diluted nonpolar solution (Figure 9). Upon cool-
ing, the UV/Vis absorption spectrum of discotic 2 in dodec-
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Desymmetrization of Discotics
FULL PAPER
quartz cuvette was used for the measurements, wavelengths are given in
which the 3,3’-bis(acylamino)-2,2’-bipyridine chromophores
are placed on top of each other in a slipped and tilted ship-
screw-like manner (Figure 1b).[1,17] When a dilute solution of
discotic 2 in dodecane was heated to 1008C, the fluores-
cence was largely quenched as in a solution of 2 in chloro-
form at room temperature in which the molecularly dis-
solved state of 2 is present. The fluorescence maximum is lo-
cated at 513 nm, thus reflecting a large Stokes shift of about
148 nm, presumably due to intramolecular double-proton
transfer within the diamino bipyridine moieties in the excit-
ed state.[48]
nm, and absorptions in Lmolꢀ1 cmꢀ1
. Thermal gravimetric analysis
(TGA) was carried out on a Perkin–Elmer Pyris 6 Thermogravimetric
Analyzer. Heating was performed from 30 to 6008C with a slope of
108Cminꢀ1 under a nitrogen atmosphere. Polarized optical microscope
images were made using a Carl Zeiss Jenaval polarization microscope
equipped with a Linkam THMS 600 heating device and a Polaroid digital
camera model PDMC-2. Measurements were performed under a nitrogen
atmosphere to prevent thermal degradation. DSC analysis was performed
using a Perkin–Elmer Pyris 1 or Thermal Analysis Q2000 instrument
under a nitrogen atmosphere. For all SAXD and WAXD measurements,
the crude product was filled in a Lindemann glass capillary (0.9 mm di-
ameter). Aligned samples were obtained by shearing inside the capillary
at the temperature of the mesophase, typically at 1608C. The studies on
the aligned sample were carried out at University of Zaragoza with a pin-
hole camera (Anton Paar) operating with a point-focused Ni-filtered
CuKa beam. The capillary axis was perpendicular to the X-ray beam, and
the pattern was collected on a flat photographic film perpendicular to the
beam. Spacings were obtained by means of Braggꢂs law. In this setup, the
whole beam path was under vacuum for RT measurements. SAXD meas-
urements were made using a homemade setup with a rotating anode X-
ray generator (Rigaku RU-H300, 18 kW) equipped with two parabolic
multilayer mirrors (Bruker, Karlsruhe, Germany), thereby giving a highly
parallel beam (divergence about 0.0258) of monochromatic CuKa radia-
tion, (l=1.54 Š). The SAXD intensity was collected with a two-dimen-
sional gas-filled wire detector (Bruker Hi-Star). To change the tempera-
ture, an adapted Linkam THMS 600 hot stage was used. Powder WAXD
measurements were performed using a home-built system at Philips
(Eindhoven) consisting of a sealed X-ray tube (CuKa radiation), a primary
graphite monochromator, a pinhole collimator, a sample stage, and a Sie-
mens Hi-Star area detector. Samples were prepared in a 0.9 mm diameter
Lindemann capillary tube and mounted in a home-built furnace based on
a TMS94 Linkam hot stage. WAXD patterns were recorded with a
sample-to-detector distance of 8.1 cm.
Conclusion
Nonsymmetrical discotics 1 and 2 based on 2,2’-bipyridine-
3,3’-diamine units linked to a trimesic core have been suc-
cessfully synthesized and characterized. These mesogens dis-
play columnar liquid crystallinity over a very broad temper-
ature window (>300 K) in which two different rectangular
columnar mesophases are observed. The columns in the
mesophase possess a helical structure with a small relative
rotation of about 118 between superimposed molecules, sim-
ilar to their C3-symmetrical analogues. In solution, NMR
spectroscopic measurements on discotics 1 and 2 revealed
an on average rather flat conformation when they are in the
molecular dissolved state. The aromatic amide core of the
discs is C3 symmetrical in this conformation. Optical spec-
troscopy showed well-ordered helical stacking in nonsol-
vents like alkanes together with expression and amplifica-
tion of chirality as is observed for disc 1 with a “sergeant
and soldiers” mixing experiment. Excitingly, the replace-
ment of one of the trialkoxyphenyl disordered wedges by a
aromatic, rigid wedge does not prevent the formation of col-
umnar liquid-crystalline phases and highly ordered helical
stacking in solution. They even mix at the molecular level
with their C3-symmetrical parent compounds. This might
enable functionalization of molecules like 2 with the goal of
introducing catalytic sites or functionality by secondary in-
teractions.
Please see the Supporting Information for further Experimental details.
3’-Benzoylamino-2,2’-bipyridine-3-amine (4):[15] Under argon, a solution
of benzoyl chloride (0.88 mL, 10.2 mmol) in dry diethyl ether (110 mL)
was added dropwise to an ice-cold well-stirred dark yellow suspension of
3[50] (1.744 g, 9.37 mmol) and triethylamine (1.65 mL, 11.9 mmol) in dis-
tilled diethyl ether (95 mL). After 15 min, a white-yellow precipitate
formed and the solution turned brownish. The reaction mixture was al-
lowed to reach RT and stirred for 28 h under argon. Subsequently, the
brown-yellow suspension was washed with ice-cold water (2”100 mL),
the aqueous layers were combined and extracted with dichloromethane
(2”50 mL). The organic layers were combined, after which a clear brown
solution was obtained. This organic layer was washed with brine (2”
100 mL), dried with MgSO4, and filtered. Concentration of the filtrate in
vacuo gave a brownish residue that was purified by column chromatogra-
phy (silica gel, 3 vol% CH3CN in CHCl3 to elute the bisamide side prod-
uct and 10 vol% CH3CN in CHCl3 to elute the target product), which
gave amine 4 as a yellow powder. Finally, recrystallization from boiling
CH3CN (30 mL) gave pure title product 4 (2.35 g, 85%) as a crystalline,
yellow compound. Rf =0.29 (silica gel, 3 vol% CH3CN in CHCl3); GC–
MS: tR =8.26 min; m/z: calcd: 290.12; found: 290 (radical cation); m.p.
168.0–168.58C (lit. 167.5–168.58C); 1H NMR (400 MHz, CDCl3, 258C):
Experimental Section
General: 1H and 13C NMR spectra were recorded using a Varian Mercury
Vx 400 MHz (100 for 13C), a Varian Gemini 300 MHz (75 MHz for 13C),
or a Varian Mercury Plus 200 MHz (50 MHz for 13C) NMR spectrometer.
1H chemical shifts were determined with tetramethylsilane as internal
standard (d=0 ppm). 13C chemical shifts were determined from the deu-
terated solvent CDCl3 (d=77.36 ppm) or tetramethylsilane (d=0 ppm)
as internal standard. gCOSY 2D experiments were performed in CDCl3
using a Varian Mercury 400 MHz spectrometer with standard Varian pa-
rameters for CDCl3. CD spectra were recorded using a Jasco J-600 spec-
tropolarimeter equipped with a Jasco PTC-348WI Peltier-type tempera-
ture control system, UV/Vis spectra were recorded using a Perkin–Elmer
Lambda 40 UV/Vis spectrometer equipped with a Perkin–Elmer PTP-1
Peltier temperature control system, and fluorescence spectra were mea-
sured using a Perkin–Elmer LS50B luminescence spectrometer equipped
with a Perkin–Elmer PTP-1 Peltier temperature control system. A 1 cm
d=14.70 (s, 1H; [7]’), 9.29 (d, 3J
3J(H,H)=4.43 Hz, 1H; [6]’), 8.07 (d, 3J
(m, 1H; [6]), 7.56–7.49 (3H; [11]’+[12]’), 7.30 (dd, 3J
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
4.43 Hz, 1H; [5]’), 7.13–7.08 (2H; [4]+[5]), 6.60 ppm (s, 2H; [7]);
13C NMR (100 MHz, CDCl3, 258C, APT): d=166.6, 145.3, 143.7, 140.9,
138.6, 136.4, 135.8, 134.9, 131.8, 128.7, 128.6, 127.6, 125.4, 124.2,
ꢀ
122.8 ppm; FTIR (ATR): n˜ =3427 (NH2), 3285 (NH2), 3028, 2754 (C H
ꢀ
aryl), 1649 (amide C=O), 1601, 1569 (amide N H), 1558, 1520, 1492,
ꢀ
1471, 1453, 1429, 1397, 1323, 1309 (amide C N), 1272, 1250, 1208, 1198,
1162, 1066, 1028, 1001, 979, 967, 930, 906, 865, 795, 733, 720, 701,
672 ppm; elemental analysis calcd (%) for C17H14N4O: C 70.33, H 4.86, N
19.30; found: C 70.04, H 4.76, N 19.17.
Chem. Eur. J. 2010, 16, 2258 – 2271
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2267

E. W. Meijer et al.
3’-tert-Butoxycarbonylamino-2,2’-bipyridine-3-amine (5): Under argon,
2,2’-bipyridine-3,3’-diamine (3) (3.310 g, 17.78 mmol) and di-tert-butyl di-
carbonate (4.646 g, 21.29 mmol) were dissolved in ethanol (32 mL) at RT
while being stirred. The stirred solution was heated at 358C for 5.5 h, al-
lowed to reach RT, and then diethyl ether (100 mL) was added. The ob-
tained orange solution was washed with dilute brine (3”50 mL), dried
with MgSO4, and filtered. Concentration of the filtrate in vacuo gave an
orange, sticky residue that was purified by column chromatography
(silica gel, 20 vol% ethyl acetate in heptane to elute the di-Boc-protected
side product and 40 vol% ethyl acetate in heptane to elute the desired
compound) to give 5 as a yellow, thick syrup that solidified after thor-
ough drying (3.378 g, 73%). Rf =0.39 (silica gel, 40 vol% ethyl acetate in
CHCl3); GC–MS: tR =6.51 min; m/z: calcd: 286.34; found: 286 (radical
cation); m.p. 83.0–84.58C; 1H NMR (400 MHz, CDCl3, 258C): d=12.46
1581, 1496, 1466, 1428, 1383, 1366, 1324, 1235, 1185, 1140, 1115, 1028,
984, 918, 852, 762, 736, 693, 665 cmꢀ1
.
N,N’-Bis{3
ACHTUNGTRENNUNG
pyridyl]}-N’’-{3AHCTUNGTRENNUNG
amide (1): Under argon, a mixture of TFA and dichloromethane (10 mL,
1:1 v/v) was added dropwise to an ice-cold stirred solution of 6 (0.806 g,
0.791 mmol) in distilled dichloromethane (20 mL). The yellow reaction
mixture was stirred at RT for 5 h, concentrated in vacuo without heat-
ing,[51] and dried under vacuum to yield a dark yellow shining residue,
which was subsequently dissolved in acetone (30 mL). Triethylamine
(5 mL) dissolved in acetone (25 mL) was added dropwise to this stirred
solution of the TFA salt, after which the obtained beige suspension was
stirred for another 10 min and filtered over a Büchner funnel. The resi-
due was washed with acetone (2”10 mL) and ethanol (2”50 mL) to
yield yellowish product 7 (0.5274 g, 81%) that was used as such.
3
3
(s, 1H; 7’), 8.75 (d, J
ACHTUNGTRENNUNG(H,H)=8.43 Hz, 1H; 4’), 8.21 (d, JCAHTUNGTRENNUNG
1H; 6’), 7.99 (d, 3J(H,H)=3.66 Hz, 1H; 6), 7.21 (dd, 3J
G
ACHTUNGTRENNUNG
Under argon, diamine 7 (0.333 g, 0.406 mmol), gallic acid chloride 9
(0.550 g, 0.903 mmol), and diisopropylethylamine (0.3 mL, 1.72 mmol)
were mixed in distilled N-methyl-2-pyrrolidone (5 mL) at RT and stirred
overnight. The obtained thick, yellow suspension was concentrated in
vacuo, dissolved in hot CHCl3 (5 mL), and subsequently suspended in
ice-cold methanol (150 mL). The beige suspension was filtered using a
Büchner funnel yielding a beige residue (0.703 g), which was washed with
methanol (2”25 mL). The beige residue was purified by column chroma-
tography (flash silica, 4 vol% ethyl acetate in chloroform to elute a less-
polar side product, 5 vol% ethyl acetate in chloroform to elute the de-
sired product) to yield the desired title compound 1 (0.173 g, 22%) as a
beige, sticky compound. Rf =0.32 (silica gel, 4 vol% ethyl acetate in
CHCl3); tR =12.2 min (analytical GPC, CHCl3, 2”PL gel 3 mm 100 Š
column, one peak); 1H NMR (400 MHz, CDCl3, 258C, 6 mm): d=15.40
(s, 1H; [7]), 15.35 (s, 2H; 7), 14.65 (s, 1H; [7]’), 14.34 (s, 2H; 7’), 9.45–
9.41 (3H; 4+[4]), 9.36–9.32 (3H; 4’+[4]’), 9.00–8.96 (4H; 6’+[6]’+10),
4.40 Hz, 1H; 5’), 7.06–7.04 (2H; 4+5), 6.36 (s, 2H; 7), 1.53 ppm (s, 9H;
11’); 13C NMR (75 MHz, CDCl3, 258C, APT): d=153.5, 144.6, 143.1,
139.6, 138.8, 136.3, 135.3, 127.2, 124.8, 123.8, 122.6, 80.0, 28.4 ppm; FTIR
ꢀ
(ATR): n˜ =3429 (NH2), 3291 (NH2), 3055, 2980, 2928 (C H aryl and
ꢀ
alkyl), 1700 (urethane C=O), 1604, 1578 (urethane N H), 1504, 1475,
1454, 1438, 1402, 1391, 1366, 1330, 1308, 1297, 1273, 1247, 1212, 1196,
1157, 1124, 1079, 1067, 1050, 1025, 972, 932, 906, 866, 835, 790, 775, 748,
731, 701 cmꢀ1; elemental analysis calcd (%) for C15H18N4O2: C 62.92, H
6.34, N 19.57; found: C 62.77, H 6.28, N 19.54.
N-{3
nylamino)-2,2’-bipyridyl]}benzene-1,3,5-tricarboxamide (6): Under argon,
diisopropylethylamine (0.70 mL, 4.0 mmol) and aromatic amine
ACHTUNGTRENNUNG[3’-(Benzoylamino)-2,2’-bipyridyl]}-N’,N’’-bis{3ACHTUNGTRENN[UGN 3’-(tert-butoxycarbo-
4
(0.984 g, 3.39 mmol) dissolved in distilled dichloromethane (60 mL) were
added dropwise to a well-stirred, chilled (108C) solution of trimesyl chlo-
ride (0.90 g, 3.39 mmol) in distilled dichloromethane (60 mL). After 3 h
of being stirred while the reaction temperature was allowed to reach RT,
diisopropylethylamine (1.4 mL, 2.092 g) and aromatic amine 5 (2.092 g,
7.306 mmol) dissolved in distilled dichloromethane (55 mL) were added
dropwise to the well-stirred, chilled (108C) white suspension. The yellow,
clear solution was stirred under argon overnight after which a dark
orange reaction mixture containing a white precipitate was obtained that
was concentrated in vacuo. The residue was dissolved in a minimal
amount of hot chloroform (12 mL) and precipitated in chilled methanol
(160 mL). Filtration over a Büchner funnel yielded a beige residue which
was washed with methanol (2”20 mL), redissolved in chloroform
(150 mL) and filtered over celite. Concentration of the filtrate in vacuo
yielded a beige residue that was purified by column chromatography
(silica, 3 vol% pyridine in chloroform) to give discotic 6 as a beige, sticky
solid (2.140 g, 62%) that was used as such. Rf =0.32 (silica gel, 4 vol%
pyridine in CHCl3); tR =14.48 min (analytical GPC, CHCl3, 2”PL gel
3 mm 100 Š column, one peak); decomposes; 1H NMR (400 MHz,
CDCl3, 258C): d=14.41 (s, 1H; [7]), 14.38 (s, 2H; 7), 14.27 (s, 1H; [7]’),
8.94 (s, 2H; 11), 8.25 (d, 3J
3.07 Hz, 1H; [6]), 7.93 (d, 3J
1H; [12]’), 7.44–7.40 (5H; 5’+[5]’+[11]’), 7.32 (dd, 3J
4.40 Hz, 2H; 5), 7.27 (dd, 3J
(H,H)=8.36, 4.40 Hz, 1H; [5]), 7.21 (s, 4H;
A
ACHTUNGTRENNUNG(H,H)=
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
10’), 4.11–4.03 (12H; 13’+14’), 1.95–1.86 (m, 6H; 15’), 1.76–1.74 (m,
12H; 16’), 1.69–1.53 (18H; 15’+17’+20’), 1.34–1.16 (30H; 17’+18’+
19’), 1.00–0.94 (m, 18H; 22’), 0.90 ppm (d, 3J
ACTHNUTRGNE(UNG H,H)=6.60 Hz, 36H; 21’);
13C NMR (400 MHz, CDCl3 with 8 vol% hexafluoroisopropanol (HFIP)
258C, 6 mm): d=167.5, 167.4, 164.0, 163.9, 153.3, 142.1, 142.0, 141.7,
141.5, 141.4, 140.4, 137.4, 137.2, 136.9, 136.8, 136.7, 135.7, 135.6, 134.6,
134.5, 132.5, 130.0, 129.9, 129.4, 128.9, 127.3, 124.7, 124.2, 106.4, 72.6,
68.1, 39.5, 39.4, 37.6, 37.5, 37.3, 36.5, 30.0, 29.9, 28.1, 24.9, 24.8, 22.8, 22.7,
ꢀ
ꢀ
22.6, 19.6, 19.5 ppm; FTIR (ATR): n˜ =2953 (C H alkyl), 2925 (C H
ꢀ
ꢀ
alkyl), 2869 (C H alkyl), 1670 (amide C=O), 1567 (amide N H), 1509
(aromatic), 1492 (aromatic), 1468, 1445, 1427, 1369, 1328, 1296 (amide
ꢀ
C N), 1239, 1201, 1115, 1074, 1045, 1029, 997, 945, 913, 865, 798, 746,
730, 716, 700 cmꢀ1; UV/Vis (heptane, 27 mm, 258C): lmax (e)=209 (63.3”
103), 291 (40.8”103), 351 (shoulder, 14.6”103), 364 (18.2”103), 383 nm
(13.8”103 mꢀ1 cmꢀ1); UV/Vis (chloroform, 36 mm, 258C): lmax (e)=292
(83.0”103), 341 (shoulder, 47.7”103), 352 (51.1”103), 368 nm (shoulder,
32.6”103 mꢀ1 cmꢀ1); MALDI-TOF MS: m/z: calcd: 1964.25; found:
1965.26 [M+H+], 1987.23 [M+Na+], 2003.24 [M+K+], 2028.18 [M+Cu+];
elemental analysis calcd (%) for C120H162N12O12: C 73.36, H 8.31, N 8.56;
found: C 73.47, H 8.56, N 8.45.
12.65 (s, 2H; 7’), 8.81 (d, 3J
7.43 Hz, 1H; [4]’), 8.44–8.42 (m, 4H; 4+4’), 8.36 (d, 3J
1H; [6]’), 8.33 (d, 3J
(H,H)=2.74, 1H; 6’), 7.84 (s, 1H; 10), 7.73 (s, 2H;
11), 7.63 (d, 3J(H,H)=6.64 Hz, 2H; [10]’), 7.50 (d, 3J
(H,H)=2.74 Hz,
2H; 6), 7.37 (t, 3J
(H,H)=6.64 Hz, 1H; [12]’), 7.32–7.26 (m, 3H; [6] and
[11]’), 6.88 (dd, 3J(H,H)=7.82, 3.52 Hz, 2H; 5), 6.81 (dd, 3J
(H,H)=7.82,
3.52 Hz, 1H; [5]), 6.46 (dd, 3J
(H,H)=7.42, 3.52 Hz, 2H; 5’), 6.41 (dd,
3J
(H,H)=7.42, 3.52 Hz, 1H; [5]’), 1.49 ppm (s, 18H; 11’); FTIR (ATR):
A
ACHTUNGTRNE(NUNG H,H)=
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
Pyridine-4-carbonyl chloride·HCl (10): Under argon, isonicotinic acid
(2.059 g, 16.7 mmol) was added slowly to stirred thionyl chloride (80 mL)
heated at reflux. The reaction mixture was heated at reflux for 5 h and
subsequently concentrated in vacuo, thus yielding a beige solid. High
vacuum was used to remove traces of volatile compounds. The residue
was used without further purification. 1H NMR (200 MHz, [D6]acetone,
258C): d=9.43 (d, 2H; [10]’), 8.84 ppm (d, 2H; [11]’); FTIR (ATR): n˜ =
3070, 2965, 2714, 2563, 2097, 2016, 1892, 1814, 1750, 1732, 1637, 1607,
1506, 1497, 1394, 1336, 1275, 1236, 1195, 1129, 1064, 1044, 1003, 898, 823,
ꢀ
ꢀ
ꢀ
n˜ =2953 (C H alkyl), 2925 (C H alkyl), 2869 (C H alkyl), 1670 (amide
ꢀ
C=O), 1567 (amide N H), 1509 (aromatic), 1492 (aromatic), 1468, 1445,
ꢀ
1427, 1369, 1328, 1296 (amide C N), 1239, 1201, 1115, 1074, 1045, 1029,
997, 945, 913, 865, 798, 746, 730, 716, 700 cmꢀ1; MALDI-TOF MS: m/z:
calcd: 1018.39; found: 1019.27 [M+H+], 1041.27 [M+Na+], 1057.27
[M+K+].
3,4,5-Tris-((S)-3,7-dimethyloctyloxy)benzoyl chloride (9): Under argon,
thionyl chloride (3.5 mL, 29.4 mmol) and DMF (2 drops) were added at
RT to a stirred solution of benzoic acid 8 (0.534 g, 0.903 mmol) in dis-
tilled dichloromethane (20 mL). The reaction mixture was stirred over-
night at RT, concentrated in vacuo, and placed under high vacuum to
remove all traces of volatile compounds to yield a beige, thick oil that
was used as such. FTIR (ATR): n˜ =3433, 2954, 2926, 2870, 1752 (C=O),
757, 729, 684 cmꢀ1
.
3’-(4-Pyridylcarbonylamino)-2,2’-bipyridine-3-amine (11): Under argon,
HCl salt 10 (2.97 g, 16.7 mmol) dissolved in distilled dichloromethane
(110 mL) and DIPEA (4 mL) was added dropwise to a well-stirred, ice-
2268
www.chemeurj.org
ꢁ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 2258 – 2271

Desymmetrization of Discotics
FULL PAPER
ly concentrated in vacuo. The obtained
dark gray residue was dissolved in hot
chloroform (20 mL) and precipitated
dropwise in acetone (250 mL) while
stirring. Then the suspension was fil-
tered using
a Büchner funnel. The
gray residue was dissolved in hot
chloroform (50 mL) and mixed with
acetone (100 mL) to obtain a gray sus-
pension that was heated at reflux for
0.5 h and filtered on a Büchner funnel
to yield
a gray residue that was
washed with a mixture of acetone and
chloroform (10 vol% chloroform in
acetone, 2”20 mL). Repetitive column
chromatography (silica gel, 2 vol%
ethyl acetate in chloroform; silica gel,
2.5 vol% methanol in chloroform;
and flash silica gel, 5–10 vol% triethyl
amine in chloroform) gave after evap-
oration of the product fractions
a
crude, brown-beige product (0.886 g,
16%). Finally, 0.290 g crude product
cold solution of 3 (2.590 g, 13.9 mmol) and DIPEA (3 mL) in distilled di-
chloromethane (110 mL). The stirred, brownish, clear reaction mixture
was allowed to reach RT and stirred for an additional 5 h, after which the
reaction mixture was washed with aqueous Na2CO3 solution (saturated,
2”50 mL). The aqueous layers were combined and extracted with di-
chloromethane (1”50 mL). The combined organic layers were washed
with brine (2”25 mL) and dried with MgSO4. Filtration gave a clear,
brown solution that was concentrated in vacuo. Column chromatography
(silica, 5 vol% pyridine in chloroform) of the residue yielded a yellow
was purified using preparative recycling GPC (chloroform, 2”Jai-Gel
column) to yield desired discotic 2 (0.224 g, 77%) as a beige-white sticky
solid. Rf =0.34 (silica gel, 5 vol% triethyl amine in CHCl3), tR =12.1 min
(GPC, CHCl3, 2”PL gel 3 mm 100 Š column, one peak); 1H NMR
(400 MHz, CDCl3, 258C, 3.3 mm): d=15.39 (s, 2H; 7), 15.36 (s, 1H; [7]),
14.96 (s, 1H; [7]’), 14.29 (s, 2H; 7’), 9.50–9.46 (3H; 4+[4]), 9.33–9.30
(3H; 4’+[4]’), 9.03 (d, 3J
11+6’), 8.78 (d, 3J
(H,H)=6.04 Hz, 2H; [11]’), 8.27–8.24 (3H; 6+[6]),
7.75 (d, 3J
(H,H)=5.64 Hz, 2H; [10]’), 7.46–7.39 (3H; 5’+[5]’), 7.38–7.33
ACHTUNGTRENUN(NG H,H)=6.28 Hz, 1H; [6]’), 8.97–8.96 (5H; 10+
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
compound that was crystallized from
a mixture of boiling ethanol
(3H; 5+[5]), 7.18 (s, 4H; 10’), 4.05–4.00 (12H; 13’+14’), 1.89–1.75
(12H; 15’), 1.53–1.48 (12H; 16’), 1.39–1.29 (96H; 17’), 0.92–0.87 ppm
(18H; 18’); 13C NMR (400 MHz, CDCl3 with 8 vol% HFIP, 258C,
28 mm): d=168.5, 165.3, 165.2, 165.1, 153.5, 149.4, 144.2, 143.0, 142.8,
142.3, 142.3, 141.6, 141.5, 141.1, 137.3, 137.0, 136.8, 136.5, 136.4, 131.1,
131.0, 130.8, 130.7, 130.5, 130.1, 125.2, 125.1, 125.0, 124.8, 122.4, 106.4,
75.0, 70.0, 32.2, 32.2, 30.2, 30.0, 29.9, 29.9, 29.9, 29.9, 29.8, 29.7, 29.6, 29.5,
(200 mL) and ethyl acetate (5 mL) to yield product 11 as yellow needles
(2.02 g, 50%). Rf =0.33 (silica gel, 5 vol% pyridine in CHCl3); GC–MS:
tR =9.15 min; m/z: calcd: 291.11; found: 291 (radical cation); m.p. 199.5–
200.08C; 1H NMR (400 MHz, CDCl3, 258C): d=15.10 (s, 1H; [7]’), 9.25
(d, 3J
8.36 (d, J
7.89 (d, 3J
ACHTUNGTRENNUNG ACHTUNGTRENN(UGN H,H)=4.57 Hz, 2H; [11]’),
(H,H)=8.30 Hz, 1H; [4]’), 8.84 (d, 3J
3
3
N
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
ꢀ
26.3, 26.1, 22.9, 22.9, 14.2, 14.2 ppm; FTIR (ATR): n˜ =2921 (C H alkyl),
1H; [5]’), 7.18–7.12 (2H; [4]+[5]), 6.70 ppm (s, 2H; [7]); 13C NMR
(50 MHz, CDCl3, 258C, APT): d=164.1, 150.7, 145.4, 143.6, 142.8, 141.3,
138.0, 135.7, 134.6, 128.5, 125.5, 124.4, 122.6, 121.2 ppm; FTIR (ATR):
ꢀ
ꢀ
2852 (C H alkyl), 1671 (amide C=O), 1567 (amide N H), 1510 (aro-
ꢀ
matic), 1493 (aromatic), 1467, 1445, 1428, 1370, 1330, 1296 (amide C N),
1239, 1201, 1118, 1074, 1029, 1005, 945, 913, 863, 799, 745, 729, 717,
696 cmꢀ1; UV/Vis (dodecane, 17 mm, 258C): lmax (e)=209 (94.9”103),
294 (62.3”103), 353 (shoulder, 31.5”103), 364 (36.1”103), 383 nm (25.2”
103 mꢀ1 cmꢀ1); UV/Vis (chloroform, 19 mm, 258C): lmax (e)=293 (83.2”
103), 341 (shoulder, 48.6”103), 352 (51.9”103), 366 nm (shoulder, 34.2”
ꢀ
n˜ =3357 (NH2), 3241 (NH2), 3026, 2821 (C H aryl), 1946, 1664 (amide
ꢀ
C=O), 1605, 1572 (amide N H), 1554, 1512, 1493, 1473, 1454, 1439, 1408,
ꢀ
1400, 1346, 1327, 1312, (amide C N), 1276, 1259, 1216, 1200, 1152, 1132,
1099, 1060, 999, 972, 959, 910, 875, 847, 819, 797, 750, 732, 721, 696,
674 cmꢀ1; elemental analysis calcd (%)
for C16H13N5O: C 65.97, H 4.50,
24.04; found: C 65.57, H 4.22, N 23.70.
N-{3[3’-(4-Pyridyl-carbonylamino)-
2,2’-bipyridyl]}-N’,N’’-bis{3[3’-(3,4,5-
N
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
tris(dodecyloxy)benzoylamino)-2,2’-bi-
pyridyl]}benzene-1,3,5-tricarboxamide
(2): Under argon, a mixture of aromat-
ic monoamine 11 (0.759 g, 2.60 mmol)
and DIPEA (0.9 mL) mixed in dis-
tilled dichloromethane (65 mL) was
added to a chilled, well-stirred solu-
tion of trimesyl chloride (0.693 g,
2.61 mmol) in distilled dichlorome-
thane (65 mL). After 10 min, a solu-
tion of nonpolar monoamine 12
(4.600 g, 5.45 mmol) and DIPEA
(1.2 mL) in distilled dichloromethane
(5 mL) was added slowly to the
brownish, turbid, well-stirred reaction
mixture. The reaction mixture was
stirred for another 3 h and subsequent-
Chem. Eur. J. 2010, 16, 2258 – 2271
ꢁ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
2269

E. W. Meijer et al.
103 mꢀ1 cmꢀ1); MALDI-TOF MS: m/z: calcd: 2133.43; found: 2134.26
[M+H+], 2156.48 [M+Na+], 2172.47 [M+K+], 2197.29 [M+Cu+]; ele-
mental analysis calcd (%) for C131H185N13O12: C 73.73, H 8.74, N 8.53;
found: C 73.65, H 8.63, N 8.51.
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Acknowledgements
We thank Dr. Xianwen Lou for the MALDI-TOF MS measurements,
Henk Eding for performing elemental analysis, Chunxia Sun for perform-
ing TGA measurements, and Ralf Bovee for helping with the (recycling)
GPC measurements. Jolanda Spiering is acknowledged for the synthesis
of 3,4,5-tris[(S)-3,7-dimethyloctyloxy]benzoic acid, and Martijn Veld for
the artwork in Figure 1. We thank Professors J. Barberµ and W. de Jeu
for providing us access to their X-ray diffraction equipment at, respec-
tively, the University of Zaragoza (ES) and the FOM institute (NL); and
Dr. D. Byelov for his assistance with the latter one. R.M.R. acknowledges
support from an EU Marie Curie Intra-European Fellowship (project
MEIF-CT-2006-042044) within the EC Sixth Framework Programme.
This work was financially supported by the NRSC-Catalysis Institute.
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Received: October 30, 2009
Published online: December 22, 2009
Chem. Eur. J. 2010, 16, 2258 – 2271
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