Star-shaped triphenylene discotic liquid crystalline oligomers and their hydrogen-bonded supramolecular complexes with simple acids

Article abstract of DOI:10.1039/c5tc02576a

The synthesis and self-assembly properties of four novel star-shaped oligomers containing triphenylene discotic mesogens are reported. These materials have been synthesized in good yields by the Cu-catalyzed coupling cycloaddition reaction (CuAAC) between

Full text of DOI:10.1039/c5tc02576a

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Star-shaped triphenylene discotic liquid crystalline oligomers and
their hydrogen-bonded supramolecular complexes with simple
acids
Received 00th January 20xx,
Accepted 00th January 20xx
Ke-Qing Zhao,a,*, Xiao-Yan Bai,a Bo Xiao,a Yue Gao,a Ping Hu,a Bi-Qin Wang,a Qing-Dao Zeng,b Chen
DOI: 10.1039/x0xx00000x
Wang,b Benoît Heinrichc and Bertrand Donnioc,d,
*
www.rsc.org/
The synthesis and self-assembly properties of four novel star-shaped oligomers containing triphenylene discotic mesogens
are reported. These materials have been synthesized in good yields by the Cu-catalyzed coupling cycloaddition reaction
(CuAAC) between 1,3,5,-tris(2-trimethylsilylethynyl)benzene and three equivalents of the appropriate discogen bearing a
pending terminated-azide alkyl substituent. The molecular structures of the discotic oligomers, thereof consisting of three
lateral triphenylenes linked together by various soft methylene spacers to a central 1,3,5-tris(triazolyl)benzene, have been
fully characterized by 1H and 13C NMR, and their purity confirmed by elemental analysis. Their thermal and liquid
crystalline supramolecular organization behaviours have been studied by combining polarized optical microscopy,
differential scanning calorimetry and small-angle X-ray scattering. These investigations showed that only the two
oligomers with short spacers display
a hexagonal columnar mesophase, while those with long spacer are not
mesomorphic. Scanning tunneling microscopy revealed that one of the mesomorphic oligomer self-assembles on a
solid/liquid interface into a well ordered two-dimensional architecture that closely resembles to the proposed bulk
mesomorphic supramolecular organization deduced from X-ray measurements. Furthermore, columnar mesophases have
been induced in the corresponding hydrogen-bonded supramolecular complexes obtained by reaction of one of the non-
mesogenic oligomeric derivative with various simple acids, e.g. hexanoic, benzoic, and 4-hexyloxybenzoic acids,
respectively, in molar ratios of 1:2 and 1:3. The optical properties of these D-A dyads have been studied by UV-Vis
absorption and fluorescent emission.
corrected automatically during the self-assembling process,
and whose morphology can be controlled at the molecular
level, i.e. by the shape anisotropy of the mesogens.
Introduction
Liquid crystals are unique examples of soft self-organizations
that combine anisotropy of the physical properties and fluidity
within single components into a wide diversity of long-range
ordered, low-dimensional periodic structures.1,2 Their dynamic
and adaptive nature, and their ability to integrate and amplify
various functions through specific molecular interactions,3 to
tolerate defects and to respond to multiple external stimuli
make liquid crystals extremely relevant for widespread
technological and sensing/detection applications. These
assemblies can furthermore form very uniform and
homogeneous thin membranes where local defects can be
Due to their specific chemical structures, which essentially
consist of a flat, disc-like π-conjugated, polycyclic, aromatic
system to which are connected several diverging flexible alkyl
chains, discotic mesogens spontaneously self-organize into
liquid crystalline columnar mesophases of various two-
dimensional lattices.4 Since the stacking periodicity of the
aromatic cores into columns is rather short (typically hπ
≈ 3-4
Å), the π-overlap between adjacent conjugated aromatic rings
then allows unidirectional electrons and excitons migration
along the columnar axis.5 Therefore, DLCs (discotic liquid
crystals) have been regarded as potentially new types of
organic semiconductors,6,7 and have shown attractive
application prospects in organic photovolatics (OPVs),8,9
organic light-emitting diodes (OLEDs),10 organic field-effect
transistors (OFETs),11 as well as in sensors for gas, biological
molecules and explosives.12
DLCs are classified into small molecules, oligomers, and
polymers.13,14 Monodisperse DLC oligomers usually have
favorable characteristic features compared to corresponding
monomeric homologues and polymers: they possess defined
and modulable chemical compositions, bearing identical or
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different discogens, connected via flexible or rigid spacers, synthesis of predestined biological and functional molecular-
with linear or star-shaped topologies.15 They lead to a wide based materials with a great diversity of structures.42 Click
range of original structures, are a priori easier to isolate and chemistry has successfully been adapted to the fabrication of
purify, show better film-forming ability over large area with liquid crystalline materials with novel molecular structures and
absence of crystallites and grain boundaries between domains physical properties, including propeller-like discogens,43 liquid
due to their intrinsic fluidity and self-healing behavior, lower crystalline dendrimers,44 fullerenes,45 metal complexes,36 gold
phase transition temperatures and wide mesophases’ nanoparticles,46
aggregation-induced
light-emitting
temperature ranges. Triphenylene (TP) derivatives are oligomers,47 and discotic block copolymers and networks.48,49
workhorses of DLCs16 and possess large π-conjugated system Based on these molecular designing considerations, the
and high symmetry, as well as displaying excellent targeted star-shaped discogens have been constructed
photoelectric
containing DLC oligomers are mainly linked via ether,17 triethynylbenzene and the corresponding triphenylene-
ester,18,19 amide,20 siloxane,21-23 or oligo-methylene functional containing alkyl-azides,
. The length of the soft spacer
properties.
Traditionally,
triphenylene- efficiently in one-step by CuAAC click reaction between 1,3,5-
2
groups.24 Recently, click chemistry principles have been connecting the peripheral TP-discogens and the central core
applied to the synthesis of triphenylene-containing DLC was varied to modulate the mesomorphism (Scheme 1).
oligomers via a triazole linkage.25-31 Furthermore, the clicked The synthesis started from 3,6,7,11,12-pentakis(hexyloxy)-
triazoles have been transformed into hydrogen-bonding triphenylene-2-ol, synthesized according to known literature
supramolecules31-35 and metal complexes,36 which permit to methods,14,15 followed by the monoalkylation with various
modulate further their physical properties.
In this study, we have synthesized a new series of oligomeric dibromobutane,
discotic-based compounds by copper-catalyzed azide-alkyne dibromodecane, respectively, to produce compounds 1a
cycloaddition (CuAAC) click reaction: these materials are high yield. The terminal bromides were then almost
α,ω-dibromoalkanes, including 1,3-dibromopropane, 1,4-
1,6-dibromohexane, and 1,10-
in
-d
composed of a benzene ring as the central core, connected to quantitatively converted into azides 2a
three peripheral triphenylene units by 1,2,3-triazoles as with NaN3.28
bridges and soft chains of different lengths (Scheme 1). The
-d by exchange reaction
mesomorphism of the neat oligomers (4a-d) was investigated
and compared to the properties of the supramolecular
assemblies prepared by the reaction with aliphatic or benzoic
acids. Due to the drastic drop of the isotropization
temperatures reported for long aliphatic chains bearing acids,
the present contribution is restricted to the relatively short
hexyl chains, which moreover appear appropriate for efficient
space filling, as suggested from preliminary ChemBio3D
simulation. In contrast to previous reports limited to the 1:3
stoichiometry, the study extends to systems with 1:1 and 1:2
stoichiometries as well. Among the supramolecular complexes
obtained by the reaction with the non-mesomorphous
oligomer 4d, only those with molar ratios 1:2 and 1:3 of
hexanoic, benzoic, 4-hexyloxybenzoic acids were found to be
mesomorphic (5a-f).
Results and Discussion
Methodology, Synthesis and Characterization of the
Oligomers
The synthetic concept of click chemistry has been conceived to
produce in a quick and reliable manner, complex molecules by
joining well-defined, smaller and simpler molecular units
together, in a specific and selective way.38,39 Among various
synthetic processes,40,41 the Cu(I)-catalyzed azide-alkyne 1,3-
dipolar cycloaddition (CuAAC) is the most widely used. This
reaction is i) region-specific and exclusively leads to the
formation of the 1,4-substituted-1,2,3 triazole isomer, ii) highly
modular and versatile, iii) usually proceeds in high yields, iv)
only requires simple and straightforward reaction conditions,
and v) can be performed in a variety of solvents (including
water). This reaction is therefore ideally adapted for the
For the synthesis of 1,3,5-triethynylbenzene, the other key
intermediate compound, Pd/Cu catalyzed Sonogashira
coupling15
trimethylsilylethyne
between
was
1,3,5-tribromobenzene
and
used yielding 1,3,5-tris(2-
trimethylsilylethynyl)benzene, followed by deprotection with
tetrabutylammonium fluoride (TBAF). However, 1,3,5-
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undifferentiated contribution of the molten alkyl chains, spacers
and central part (ca. 2θ ≈ 20°). The small-angle region contains a
triethynylbenzene was found unstable for long storage
periods, and purification by sublimation was needed prior
reacting. In addition, clicking derivatives 2a
triethynylbenzene yielded the wanted star-shaped discogens
4a , but in low yields, i.e. 25-30%. For improving the synthetic
-
d
and strong and sharp diffraction peak around 18 Å (labeled 11) assigned
to the first-order reflection of the hexagonal sub-lattice formed by
triphenylene rings stacked in columns (Figure 3, C).
-d
yield of the click products, TBAF was introduced in the reaction
mixture for the simultaneous in situ deprotection of the
alkynyl-TMS group during the CuAAC coupling.50 Consequently,
the four oligomers 4a-d were produced in yields greater than
70%.
The synthetic intermediates and star-shaped discogens were
fully characterized by 1H NMR (400Hz) and 13C NMR (100Hz)
and IR spectroscopies (Figures S1-S25), and elemental analysis
(EA). The results were in good agreement with the expected
chemical structures.
Mesomorphism of the oligomers
The mesomorphic properties of the oligomeric discogens were
investigated by polarizing optical microscopy (POM), differential
scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS).
These investigations revealed that only 4a and 4b spontaneously
self-organize into columnar mesophases, whereas 4c and 4d did not
show mesomorphism. The previously reported intermediates 1a,
1c, 2a and 2c,26 and the newly synthesized azide-containing
compounds, 1b, 1d, 2b and 2d are all mesomorphic (Table 1). POM
images of 4a and 4b (Figure 1) displayed typical fan-shaped textures
associated to discotic columnar mesophase.
Table 1. Mesophases, transition temperatures and enthalpy changes of star-
shaped oligomers and discotic intermediates (heating and cooling rate of 10
oC·min-1)a
Cpds
Second heating [first cooling] / oC (ΔH, kJ·mol-1)
4a
Colhex 117 (17.7) I [I 109 (16.2) Colhex
]
4b
Colhex 115 (19.9) I [I 107 (18.3) Colhex
]
4cb
4db
2a[26]
2b
Cr 54 (53.5) I
Cr 47 (39.9) I
All new compounds were measured by differential scanning
calorimetry (DSC, Figures
2 and S34-S39), and the transition
Cr 60 (41.2) I [I 51 (1.6) Colhex 47 (38.2) Cr]
Cr 61 (38.9) Colhex 84 (3.4) I [I 82 (3.5) Colhex 48 (40.6) Cr]
Cr 54 (40.3) I [I 49 (1.5) Colhex 44 (38.7) Cr]
Cr 40 (38.5) I [I 21 (38.1) Cr]
temperatures and enthalpy changes are summarized in Table 1. The
star-shaped discogens 4a and 4b have similar DSC curves (Figure 2),
with a single sharp peak in the cooling and second heating runs, and
a quite large transition temperature delay on cooling (109 and 107
°C, compared to 117 and 115 °C on heating). This peak corresponds
to the transition between the isotropic liquid and the mesophase,
which is maintained below room temperature, down to -50 oC or
lower. Therefore, both the oligomers 4a and 4b are room
temperature liquid crystals. On the contrary, the oligomers 4c and
4d with longer spacers, devoid of mesomorphism, are crystalline at
room temperature, on first heating.
2c[26]
2d
Cr 56 (32.1) Colhex 100 (4.8) I [I 99 (4.6) Colhex 28 (32.1)
Cr]
1a[26]
1b
Cr 63 (37.4) Colhex 86 (4.0) I [I 84 (4.0) Colhex 51 (39.6) Cr]
Cr 63 (37.5) Colhex 93 (3.9) I [I 90 (3.7) Colhex 41 (33.8) Cr]
Cr 43 (41.6) I [I 23 (40) Cr]
1c[26]
1d
a
Cr, crystalline phase; Colhex, hexagonal columnar mesophase; I, isotropic
liquid.b For virgin sample from solution, on 1st heating run the phase
transition can be observed, however, no phase transition can be observed on
1st cooling and 2nd heating run at 109oC.
The SAXS patterns of the mesophases of 4a and 4b are shown in
Figure 3 (A and B respectively). Both showed a scattering maximum
at 3.60 Å (ca. 2θ ≈ 25°), hπ, arising from the π stacking of the
triphenylenes, and a broad halo at 4.4 Å, hch+hmes, from the
The insertion of the tris(triazolyl)benzene linkers in the aliphatic
periphery however makes the column shape irregular and explains
that higher orders reflections are nearly extinct.51 The presence of
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an additional weak lower-angle reflection, with a spacing ratio close long-range or short-rang correlation were encountered for other
to √3, moreover confirms that the linkers self-assemble into high systems.52
electronic density stems. The stem distribution then defines the As already reported in hexakis(alkoxy)triphenylene series, the
real hexagonal lattice that involves a single molecular stack and transition between columnar phase and isotropic liquid shifts to
thus one stem and three columns [a = 35.0 Å (4a), 36.6 Å (4b); lower temperature when one tail is replaced by a longer chain.53
indexation and intensity of the reflection sequence: (10) weak, (11) The insertion of additional chain segments then locally increases
very strong, (20)/(30) very weak, Table 2]. It should be mentioned the spacing of triphenylene cores and logically anticipates the
that reflection (10) is also clearly broadened with regard to the disappearance of the regular columnar lattice. In series 1 and 2, the
modified tail is moreover terminated by either a bulky bromine
group or an even more voluminous azide group, what reinforces the
steric disturbance and leads to even earlier vanishing of the
columnar phase. The central core with the short spacers of the
series 4 retains on the contrary the three peripheral triphenylene
groups in line with triazol branches and promotes the columnar
arrangement of the whole entities formed by the four
interconnected cycles. Consistently, the columnar mesophase (and
crystal arrangements) of 4a and 4b maintains to higher
temperature as for reference hexakis(hexyloxy)triphenylene.53
However the effect only holds for short spacers, whose limited
length, compared to space requirements of the further alkyl tails,
forces relatively stretched conformations. With the longer spacers,
the triphenylene groups become free to move and to form
individual columns. The central cores then change role and merely
act as voluminous peripheral groups that disturb the lateral packing
of triphenylene and cause rapid disappearance of the columnar
phase and drop of melting temperatures, as found for 4c and 4d. It
should be noticed that the molecular geometry hampers the
development of the long-range correlated structures whereas the
individual segments stay segregated at the local range. As for other
multisegregated systems,54 the self-association of mesogenic units
and their segregation from molten chains are indeed maintained in
the isotropic liquid state and lead to scattering signals persisting far
beyond the melting temperature (Figure S43).
Table 2. SAXS indexation of the mesophases of the oligomersa
Cpds
2θmeas
dmeas
hk
I
dcalc
2θmeas
10
11
20
hch+hmes
hπ
2.90
5.00
5.85
20.0
24.7
30.4
17.6
15.1
4.4
M (br)
VS (sh)
W (sh)
VS (br)
S (br)
30.4
17.5
15.2
-
2.90
5.04
5.81
-
4a
3.6
-
-
10
11
30
hch+hmes
2.77
4.81
8.38
20.0
24.9
31.9
18.3
10.5
4.4
S (br)
VS (sh)
VW (sh) 10.6
VS (br)
31.7
18.3
2.78
4.82
8.33
-
4b
-
-
3.6
S (br)
-
hπ
a2θmeas, 2θcalc, dmeas and dcalc stand for measured and calculated diffraction
angles and spacings, hk are the Miller indices, I corresponds to the intensity
of the reflections (VS: very strong, S: strong, M: medium, W: weak, VW: very
weak; br and sh stand for broad and sharp); hch+hmes represents the
undifferentiated contribution of the molten alkyl chains, spacers and central
part, and hπ arises from the π stacking of the triphenylenes.
sharp (11) one, proving that the stem arrangement correlates over
intermediate distances, while similar (super-)lattices with either
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2D self-assembly of the oligomers on solid/liquid interface
as compared to that of the aromatic cores.15,55 The analysis of the
Scanning tunneling microscopy is a powerful technique to study the high-resolution STM images of the star-shaped discogen 4b then
self-assembly behavior of DLC oligomers15,55 and important leads to the organizational model shown in Figure 4C, which turns
information can be obtained from comparing the two-dimensional out to be very similar to the organization in the bulk mesophase,
supramolecular structures (STM) and the three-dimensional bulk with in particular a similar lattice parameter (3.6 nm), but with a
mesophase structures (SAXS).
slightly distorted hexagonal symmetry (θ ≈ 110o against γ = 120o).
The self-organizing properties of the star-shaped discogen 4b and
its two-dimensional self-assembling behavior on the liquid/solid UV-Vis absorption and fluorescent emission of the oligomers
interface were observed by scanning tunneling microscopy (STM). As the star-shaped discogens are composed of three electron-
As shown in Figure 4A, 4b form large-area ordered assemblies on
Table 3. Spectroscopic Data of UV-Vis Absorption and Fluorescent Emissiona
HOPG/1-octylbenzene interface. The detailed packing arrangement
Compd. λmax/nm (ε)
λex=240 nm
λem/nm (I)
383 (2.56)
383 (2.26)
λex=280 nm
λem/nm (I)
383 (5.47)
383 (3.86)
of 4b oligomers is shown in Figure 4B. As the triphenylenes form
stacks of high electron density, they appear as bright circles in the
image. The central tris(triazolyl)benzene is imaged as a light yellow
slightly fuzzy contour, as the δ-bonded benzene-triazole is twisted
and rotated, and thus non-coplanar. The rest of the image is filled
by alkyl chains images as dark due to their lower tunneling current
TP
4a
280 (1.18)/308 (0.29)
240 (1.41)
280 (3.77)/308 (0.95)
240 (1.21)
280 (3.36)/308 (0.86)
240 (1.09)
4b
4c
4d
383 (2.45)
383 (2.67)
383 (2.61)
383 (6.23)
383 (8.20)
383 (8.22)
280 (3.21)/308 (0.74)
240 (1.10),
280 (3.13)/308 (0.81)
aε, absorption coefficient (x105 L·mol-1·cm-1); I, Intensity(x105).
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donating TP discogens and one electron-acceptor central unit, it emission intensities. The lower intensity of the first term is
was of interest to investigate the intramolecular electron and presumably due to aggregation-caused quenching (ACQ), while
energy transfer. The UV-Vis absorption and fluorescent emission lengthening of the spacer beyond (CH2)6 has no effect on the
spectra of the targeted compounds in dilute solution (1×10-5 M) of fluorescence.
CH2Cl2 have been measured. All the absorption spectra were similar
to hexakis(hexyloxy)triphenylene (C6OTP), with two peak maxima Supramolecular Liquid Crystals by Complementary Hydrogen
at 280 and 310 nm (Figure 5A, Table 3), assigned to the π-π* and n- Bonding
Supramolecular liquid crystals based on intermolecular hydrogen
bonding possess the ability of being dynamically reversible and to
specifically respond to various external stimuli. The pseudo planar
conformation of the central 1,3,5-tris(triazolyl)benzene core has
been shown to be modulated by intermolecular hydrogen bonding,
resulting in increased π-π interactions and improved columnar
stacking.31-35 Considering the structure-mesomorphism relationship
of the star-shaped discotic oligomers described above, it was
realized that for compounds with the longer spacers, the peripheral
TP discogens could move more freely, which actually seems
π*, respectively, transitions of the triphenylene unit. An additional
absorption band nevertheless appears at 240 nm, arising from the
n-π* transition of the central benzene-triazolyl core moiety.56
For the light-emitting measurement, the compounds were
successively excited at 240 nm and 280 nm; the emission spectra of
all compounds looked similar, with a main peak at 383 nm. The
influence of the excitation wavelength is associated to a change of
the emission intensity, which is below 300,000 in the 350 ~ 450 nm
range with a 240 nm excitation (Figure 5B, Table 3), but grows to
800,000 at 280 nm (Figure 5C). A further enhancement of the
emission follows the variation of the spacer length in the 4a-4d
series. More precisely, 4a shows the lowest emission intensity with
respect to that of the peripheral TP unit, whilst that of 4b is similar
to the reference compound, and 4c and 4d have the highest
deleterious for
a regular arrangement of the columns and
ultimately to induce stable mesomorphic properties as observed in
some rigid conducting polymers bearing TP side-groups.57
Furthermore, the sigma-bonded tris(triazolyl)benzene central core
is not that favorable to mesomorphism, as it is not planar and
excludes the possibility for strong π-π interactions.51,58 This
fragment is however a good hydrogen-bonding acceptor,32 which
can react with carboxylic acids and form flat supramolecular
complexes, since the H-bonds will pull the triazole rings back to the
benzene plane. Hence, additional π-π interactions might appear and
foster columnar mesomorphism.
Based on these speculations, the oligomer 4d devoid of
mesomorphism was selected for the preparation of supramolecular
complexes with various acids, in the expectation that the linker
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modification would induce mesomorphism. In this line, reactions ppm, from CHa of the central benzene unit in 4d, shifts to 8.33 ppm
with hexanoic, benzoic, 4-hexyloxybenzoic,
3,4- in 5d, while the signal at 7.95 ppm from CHb of the triazole shifts
bis(hexyloxy)benzoic, and 3,4,5-tris(hexyloxy)benzoic acid were downfield to 7.99 ppm. These changes result from the carbonyl
systematically performed with the oligomer-to-acid ratios 1:1, 1:2, group bonded with the hydrogen atoms of both the benzene and
and 1:3. In the 15 tests realized, only six supramolecular complexes triazole rings, and demonstrate the formation of the
revealed mesomorphic properties (5a-f, Scheme 2). None of them supramolecular complex. The IR spectra (Figure 6B) confirmed the
with the 1:1 stoichiometry were mesomorphic, likely because the H-bonding interactions through the C=O stretching vibration of
effect on planarity of the three triazole rings is not efficient and benzoic acid shifting from 1687 cm-1 in 4d to 1701 cm-1 in 5d, which
requires at least two acids per oligomer. The polycatenar benzoic is however still lower than that in free carboxylic acids (1733 cm-1).
acids also failed to produce any mesophase too, which is likely due This means that the carbonyl group also interacts with further
to the mismatch between the volume of the polycatenar benzoic hydrogen atoms, which could be the Hb of the triazole rings.
acid and the size of the available cavity.
In all cases, NMR and IR proved the formation of hydrogen bonds Mesomorphism of the supramolecular complexes
(Figures 6 and S25-S33). As shown in Figure 6A, the signal at 8.31 The mesomorphic properties of the supramolecular complexes
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Table 4. Mesophases and phase transition temperatures of the
supramolecular complexes 5 (heating and cooling rate of 5 oC·min-1)a
Mesophases and phase transition
Supramolecular
complex
temperatures (oC)
2nd heating
(1st cooling)
5a (4d/hexanoic acid, 1:2)
5b (4d/hexanoic acid, 1:3)
5c (4d/benzoic acid, 1:2)
5d (4d/benzoic acid, 1:3)
5e (4d/C6H13OPhCO2H, 1:2)
5f (4d/ C6H13OPhCO2H, 1:3)
G 9 Col 64 I [I 53 Col 3 G]
Col 69 I [I 38 Col]
G 17 Colhex 78 I [I 73 Colhex 13 G]
Colhex 83 I [I 66 Colhex
]
G 7 Col 71 I [I 55 Col 3 G]
G 9 Col 77 I [I 57 Col 5 G]
aG, glass state; Col, columnar mesophase; Colhex, hexagonal columnar
mesophase; I, isotropic liquid..
were also investigated by POM, DSC and SAXS (Table 4). The six
mesomorphous supramolecular LCs displayed optical textures with
very small domains, hampering an unambiguous identification of
mesophases.
The DSC curves of the supramolecular systems are shown in Figure
7, while the transition temperatures and enthalpy changes are
summarized in Table 3. The phase transitions from columnar (Col)
mesophase to isotropic liquid have been observed on both heating
and cooling runs. In the 2nd heating runs, clearing points of 5a-f
were detected at 64oC, 69oC, 78oC, 83oC, 71oC, and 77oC,
substantially above the melting temperature of the parent oligomer
and validates our concept of induced mesomorphism by linker
modification. The reverse transitions on cooling runs turned out to
be considerably delayed, due to the slow mesophase formation, as
also noticed by POM: the mesophase appears at respectively 38oC,
66oC and 57oC for 5b, 5d and 5f (complexes with ratio 1:3), while for
5a, 5c, and 5e (complexes with ratio 1:2), it even freezes in a glassy
state without crossing the transition. The mesophases of 5b, 5d
likely also freeze in a glassy state on cooling, since the crystallization
was not observed down to -50°C, but the associated transition
could not be detected in the curves.
Optical properties for supramolecular complexes
The absorption and emission of the supramolecular complexes 5
are shown in Figure 9 and the data summarized in Table 5. The
similarity of the optical spectra (absorption and emission) between
4d and of the various acid complexes 5 is obvious, except that they
have higher light-emission intensity, and suggest that the
introduction of one or two lateral acidic wedges do not affect
dramatically the optical properties of these oligomeric structures.
SAXS patterns of both the benzoic acid complexes 5c (1:2 ratio) and
5d (1:3 ratio) are shown in Figure 8 as representative examples (see
also Figures S40-S42). 5c and 5d as expected show the broad halo at
about 4.5 Å, arising from the molten alkyl chains and the central
core, the characteristic peak at 3.5 Å, due to π-stacked cores into
columns, and the strong small-angle reflection around 18 Å from
the sub-lattice formed by triphenylene columns. Similarly as for the
mesomorphous terms of the neat oligomer series, additional weak
reflections are detectable for 5c and 5d that indicate the lattice
tripling induced by the linker distribution. Surprisingly, 5d shows
markedly reduced intensity for (10) and (11) and no resolved
higher-order reflections but a trailing wide-angle wing adjacent to
(11). This reveals some degrees of disorder in the arrangement of
triphenylene columns inside the lattice, which can be understood
from the perturbation introduced by the insertion of the linker
complexes in the periphery of the columns and from the larger size
of the 1:3 complexes. The columnar stacking, hπ, is however not
affected, retaining similar shape and intensity, the clearing point
being even increased (i.e. phase stability enhanced) with respect to
the free oligomer.
Conclusions
The click chemistry based on the copper-catalyzed azide-
alkyne cycloaddition (CuAAC) has been successfully applied for
the clean and efficient construction of novel star-shaped
discotic oligomers. The effect of the spacer length on the
mesomorphism has been investigated: oligomers obtained
with the shorter spacers (4a, C3H6; 4b, C4H8) exhibit a
hexagonal columnar mesophase with three stacked
triphenylene columns per lattice, while the oligomers with
longer spacers (4c, C6H12; 4d, C10H20) do not assemble into a
mesophase, but melt in the isotropic liquid instead. The bulk
structure of 4b has moreover been compared to its self-
assembly on a surface, which was explored using high
resolution STM at the 1-octylbenzene-graphite interface: the
oligomers have been shown to self-organize in a 2-dimensional
lattice that resembles closely that of the columnar lattice
formed in the bulk structure. Based on the intuition that the
8 | J. Name., 2012, 00, 1-3
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ARTICLE
mesomorphism could be also fostered by flattening the
benzene-triazole linkers, the synthesis of flat-shaped
supramolecular complexes between the non-mesomorphic
oligomer 4d and various acids has been developed and led to
six additional mesomorphic complexes with columnar
arrangements similar to that found for 4a and 4b, without
affecting the optical properties. The approach has thus been
validated and the conditions for mesophase induction clarified.
The concept developed here, e.g. the easy synthesis of star-
shaped discotic oligomers and the convenient preparation of
liquid crystalline hydrogen-bonded supramolecular complexes,
opens the door for potential applications and fundamental
investigations in organic electronics and porous functional
materials. Furthermore, complexity and diversity can be easily
added by introducing additional functionalities within the
Experimental Section
Instruments and reagents
1H NMR was measured by a Varian UNITY INOVA-400 (400
MHz) in CDCl3, Me4Si as internal standard; 13C NMR from
Varian UNITY INOVA-400 (100 MHz). EA was measured by a
Carlo Erba 110b. POM textures were observed by OLYMPUS
BX41 with hotstage of HCS302-GXY, and INSTEC STC200
temperature controller. DSC curves were registered from TA-
DSC Q100 in nitrogen atmosphere, with heating and cooling
rate of 10 or 5 K·min-1. SAXS patterns were obtained from
Rigaku Smartlab (3) X-Ray Diffractometer, with TCU 110
temperature controller, ±1 K, Cu-K source (λ=0.154 nm), 40kV,
scanning speed is 10K·min-1. All solvents and chemical reagents
are commercial products.
Synthesis of the intermediates
1a 26
. To a mixture of 1,3-dibromopropane (1.36 g, 6.72 mmol)
and K2CO3 (3.7 g, 26.81 mmol) in acetone (50 mL), a solution of
2-hydroxy-3,6,7,10,11-pentakis(hexyloxy)triphenylene (2 g,
2.69 mmol) in acetone (50 mL) was added and refluxed for 24
h. After cooled, the inorganic salts were filtered off, and the
solvent distilled out. The crude product was purified by flash
chromatography:
silica
gel,
eluted
with
dichloromethane:petroleum ether = 1:1 (Vol/Vol), Rf = 0.2.
Recrystallization from ethanol to yield white product (2.07 g,
2.39 mmol, 88.9 %). 1H NMR (CDCl3, TMS, 400 MHz) δ: 7.89 (s,
1 H), 7.84 (s, 5 H), 4.39 (t, J = 5.6 Hz, 2 H), 4.23 (t, J = 6.4 Hz, 10
H), 3.75 (t, J = 6.4 Hz, 2 H), 2.45~2.49 (m, 2 H), 1.91~1.98 (m,
10 H), 1.54~1.62 (m, 10 H), 1.36~1.44 (m, 20 H), 0.94 (t, J = 7.2
Hz, 15 H).
1b. Synthesized and purified as 1a. TP(OC6H13)5(OH) (3.0 g,
4.03 mmol), K2CO3 (2.2 g, 15.94 mmol), acetone (100 mL), 1,4-
dibromobutane (2 g, 9.26 mmol), refluxed 24 h with stirring.
1
After workup, white product (3.23 g, 3.67 mmol, 91.2 %). H
NMR (CDCl3, TMS, 400 MHz) δ: 7.83 (s, 6 H), 4.22~4.28 (m, 12
H), 3.60 (t, J = 6.4 Hz, 2 H), 2.17~2.24 (m, 2 H), 2.07~2.13 (m, 2
H), 1.91~1.98 (m, 10 H), 1.54~1.60 (m, 10 H), 1.36~1.43 (m, 20
H), 0.94 (t, J = 6.8 Hz, 15 H).
1c 26
Synthesized and purified as 1a, TP(OC6H13)5(OH) (2.0 g,
.
2.69 mmol), K2CO3 (3.7 g, 26.81 mmol), acetone (100 mL), 1,6-
dibromohexane (2.6 g, 10.66 mmol), refluxed 24 h with
1
stirring, yielding product (2.34 g, 2.58 mmol, 96.2 %). H NMR
supramolecular architecture by using complementary acids
(CDCl3, TMS, 400 MHz) δ: 7.83 (s, 6 H), 4.23 (t, J = 6.4 Hz, 12 H),
3.45 (t, J = 6.8 Hz, 2 H), 1.90~1.97 (m, 14 H), 1.56~1.60 (m, 14
H), 1.36~1.40 (m, 20 H), 0.93 (t, J = 7.2 Hz, 15 H).
Table 5. UV-vis absorption and fluorescence emission data of compounds 4.
Compd.
absorption
λmax/nm (ε)
emission
λem/nm (I)
383 (8.22)
383 (14.07)
383 (8.78)
383 (9.59)
383 (18.99)
383 (12.51)
1d. Synthesized and purified as 1a, TP(OC6H13)5(OH) (100 mg,
0.13 mmol), K2CO3 (185.33 g, 1.34 mmol), acetone (100 mL),
1,10-dibromodecane (161.18 mg, 0.54 mmol), refluxed 24 h
with stirring, yielding white product of (117.2 mg, 0.12 mmol,
90.5 %). 1H NMR (CDCl3, TMS, 400 MHz) δ: 7.83 (s, 6 H), 4.24 (s,
12 H), 3.41 (t, J = 6.4 Hz, 2 H), 1.91~1.98 (m, 12 H), 1.81~1. 89
(m, 2 H), 1.55~1.62 (m, 14 H), 1.30~1.44 (m, 28 H), 0.94 (t, J =
6.8 Hz, 15 H).
4d
5a
5b
5c
5d
5e
240 (1.10)/280 (3.13)/308 (0.81)
242 (1.33)/280 (3.51)/308 (0.86)
242 (1.60)/280 (3.78)/308 (1.06)
238 (1.67)/280 (3.72)/308 (0.99)
238 (1.28)/280 (3.33)/308 (0.75)
240 (1.48)/280 (3.60)/308 (0.86)
a ε, absorption coefficient (x105 L·mol-1·cm-1); I, Intensity (x105).
2a 26
A mixture of TP(OC6H13)5(OC3H6Br), 1a (2.07 g, 2.39
.
bearing redox-active units, dyes, radicals or metallic
fragments.51,58
mmol) and NaN3 (1.55 g, 23.88 mmol) in DMF (15 mL) was
stirred 36 h at room temperature. Filled off the inorganic salts,
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ARTICLE
Journal Name
and organic solvents, the residue was purified by column 1.98~1.87 (m, 30 H, CH2), 1.62~1.51 (m, 30 H, CH2), 1.39~1.35
chromatography (SiO2, dichloromethane:petroether = 1:1, Rf = (m, 60 H, CH2), 0.94~0.85 (m, 45 H, CH3). 13C NMR (CDCl3,
0.3) and recrystallization from ethanol to yield white product TMS, 100 MHz) δ: 149.17, 149.12, 149.03, 148.99, 148.93,
(1.66 g, 2.00 mmol, 83.8 %). 1H NMR (CDCl3, TMS, 400 MHz) δ: 147.99, 147.07, 131.75, 124.36, 123.85, 123.49, 123.40,
7.87 (s, 1 H), 7.83 (s, 5 H), 4.33 (t, J = 6 Hz, 2 H), 4.23 (t, J = 6.4 122.30, 120.81, 108.49, 107.54, 107.38, 107.22, 107.08,
Hz, 10 H), 3.66 (t, J = 6.8 Hz, 2 H), 2.18~2.21 (m, 2 H), 1.90~1.98 106.74, 69.78, 69.73, 69.64, 69.62, 69.28, 66.29, 53.41, 47.43,
(m, 10 H), 1.58~1.62 (m, 10 H), 1.36~1.46 (m, 20 H), 0.92~0.96 31.67, 30.29, 29.45, 29.42, 29.37, 25.87, 22.65, 22.62, 14.03,
(m, 15 H).
2b. Synthesized and purified as 2a, TP(OC6H13)5(OC4H8Br), 1b (3 found C 75.16, H 9.09, N 4.78.
g, 3.41 mmol), NaN3 (2.2 g, 33.85 mmol), DMF (20 mL), to get 4b. Prepared as 4a 2b (100 mg, 0.12 mmol),
14.00. Anal. calcd for C165H237N9O18: C 75.22, H 9.07, N 4.78;
,
3 (14.05 mg, 0.04
white product (2.40 g, 2.85 mmol, 83.5 %). 1H NMR (CDCl3, mmol), sodium ascorbate (22.76 mg, 0.11 mmol), CuSO4·H2O
TMS, 400 MHz) δ: 7.83 (s, 6 H), 4.22~4.28 (m, 12 H), 3.46 (t, J = (14.34 mg, 0.06 mmol), and TBAF (30.04 mg, 0.11 mmol) in
6.8 Hz, 2 H), 2.00~2.05 (m, 2 H), 1.91~1.98 (m, 12 H), 1.55~1.60 mixed solvent (2 mL, THF and H2O in 5:1), and reacted at 25 oC
(m, 10 H), 1.40~1.45 (m, 20 H), 0.93~0.96 (m, 15 H).
2c 26
for 24 h under argon atmosphere, yielded a white product
.
Synthesized and purified as 2a. TP(OC6H13)5(OC6H12Br), 1c (76.3 mg, 74.42 %).
(2.34 g, 2.58 mmol) and NaN3 (1.44 g, 22.15 mmol) in DMF (15 1H NMR (CDCl3, TMS, 400 MHz) δ: 8.26 (s, 3 H, ArH), 8.08 (s, 3
1
mL) yields white product (2.16 g, 2.49 mmol, 96.4 %). H NMR H, NC=CH), 7.81 (s, 18 H, ArH), 4.67 (t, J = 6.8 Hz, 6 H, NCH2),
(CDCl3, TMS, 400 MHz) δ: 7.84 (s, 6 H), 4.23 (t, J = 6.4 Hz, 12 H), 4.28~4.20 (m, 36 H, OCH2), 2.33~2.30 (m, 6 H, CH2), 2.03~2.00
3.31 (t, J = 6.8 Hz, 2 H), 1.91~1.98 (m, 12 H), 1.50~1.70 (m, 16 (m, 6 H, CH2), 1.97~1.92 (m, 30 H, CH2), 1.63~1.52 (m, 30 H,
H), 1.36~1.49 (m, 20 H), 0.94 (t, J = 6.8 Hz, 15 H).
CH2), 1.42~1.32 (m, 60 H, CH2), 0.9~0.84 (m, 45 H, CH3). 13C
2d. Synthesized and purified as 2a. TP(OC6H13)5(OC10H20Br), 1d NMR (CDCl3, TMS, 100 MHz) δ: 149.06, 149.03, 148.96, 148.92,
(2 g, 2.07 mmol) and NaN3 (1.35 g, 20.74 mmol) in DMF (15 148.79, 148.35, 147.07, 131.64, 123.84, 123.72, 123.54,
1
mL) gives white product (1.61 g, 1.74 mmol, 83.7 %). H NMR 123.50, 123.36, 122.18, 120.57, 107.47, 107.36, 107.27,
(CDCl3, TMS, 400 MHz) δ: 7.84 (s, 6 H), 4.23 (t, J = 6.4 Hz, 12 107.19, 107.12, 106.52, 69.76, 69.70, 69.67, 69.25, 68.83,
H), 3.25 (t, J = 7.2 Hz, 2 H), 1.91~1.98 (m, 12 H), 1.54~1.60 (m, 53.41, 50.30, 31.70, 31.57, 29.43, 29.36, 27.67, 26.24, 26.01,
16 H), 1.33~1.45(m, 28 H), 0.94 (t, J = 6.4 Hz, 15 H).
3 59
A mixture of 1,3,5-tribromobenzene (500 mg, 1.59 mmol), C 75.38, H 9.15, N 4.71; found C 75.15, H 9.02, N 4.69.
PdCl2(PPh3)2 (33.45 mg, 0.05 mmol), PPh3 (25 mg, 0.1 mmol) , 4c. Prepared as 4a 2c (100 mg, 0.12 mmol), (13.62 mg, 0.04
25.85, 22.65, 22.62, 14.03, 14.00. Anal. calcd for C168H243N9O18:
.
,
3
CuI (9.07 mg, 0.05 mmol) in Et3N (15 mL) was stirred 20 min at mmol), sodium ascorbate (22.07 mg, 0.11 mmol), CuSO4·H2O
65 oC in argon, then trimethylsilylacetylene (624.02 mg, 6.35 (13.91 mg, 0.06 mmol), and TBAF (29.13 mg, 0.11 mmol) in
o
mmol) was added and stirred 24 h at 80 C. After the reaction mixed solvent (2 mL, THF/H2O in 5:1), and reacted at 25 oC for
was complete, the mixture was poured into dilute hydrochloric 24 h under argon. White product (81.40 mg, 79.4 %).
acid solution and extracted with CH2Cl2 three times. The 1H NMR (CDCl3, TMS, 400 MHz) δ : 8.26 (s, 3 H, ArH), 7.91 (s, 3
extracts was dried, and the solvent distilled to produce crude, H, NC=CH), 7.82 (s, 18 H, ArH), 4.45 (t, J = 6.8 Hz, 6 H, NCH2),
which was purified by flash chromatography (silica gel, n- 4.22 (t, J = 5.6 Hz, 36 H, OCH2), 2.05~2.02 (m, 6 H, CH2),
hexane:petroleum ether = 5:1) and recrystallization from 1.95~1.92 (m, 36 H, CH2), 1.70~1.64 (m, 6 H, CH2), 1.57 (s, 36
methanol to yield white product (432 mg, 1.18 mmol, 74.17 H, CH2), 1.39~1.38 (m, 60 H, CH2), 0.94~0.90 (m, 45 H, CH3). 13
C
1
%). H NMR (CDCl3, TMS, 400 MHz) δ: 7.49 (s, 3 H), 0.23 (s, 27 NMR (CDCl3, TMS, 100 MHz) δ : 149.06, 148.99, 148.95,
H).
148.92, 148.87, 148.80, 148.71, 147.09, 146.36, 132.37,
131.69, 123.71, 123.64, 123.59, 123.56, 123.53, 122.10,
Synthesis of star-shaped discotic oligomers, 4a-d
120.14, 107.38, 107.34, 107.15, 107.07, 69.81, 69.72, 69.55,
4a. A mixture of 2a (100 mg, 0.12 mmol) and
3
(14.28 mg, 0.04 69.49, 69.34, 69.28, 50.38, 31.68, 31.64, 31.60, 30.22, 29.42,
mmol) in mixed solvent (1 mL, THF and H2O in 5:1 Vol/Vol 29.39, 29.27, 26.32, 25.84, 25.66, 25,58, 25.49, 22.65, 14.04.
ratio) was stirred for 15 min. Then, a solution of sodium Anal. calcd for C174H255N9O18: C 75.69, H 9.31, N 4.57; found C
ascorbate (23.15 mg, 0.12 mmol), CuSO4·5H2O (14.59 mg, 0.06 75.77, H 9.28, N 4.66.
mmol) and TBAF (30.55 mg, 0.12 mmol) in THF (1 mL) was 4d. Prepared as 4a, 2d (500 mg, 0.54 mmol), 3 (63.90 mg, 0.17
o
added, and reacted at 25 C for 24 h under argon. After the mmol), sodium ascorbate (103.55 mg, 0.52 mmol), CuSO4·H2O
completion of the reaction, the mixture was poured into water (65.26 mg, 0.26 mmol), and TBAF (136.67 mg, 0.52 mmol) in
and extracted with CH2Cl2 three times. The extracts were mixed solvent (3 mL, THF and H2O in 5:1), and reacted at 25 oC
combined, and dried, and the solvent distilled to get crude for 24 h under argon. White product (405.4 mg, 79.4 %).
product, which was purified by flash chromatography (silica 1H NMR (CDCl3, TMS, 400 MHz) δ: 8.31 (s, 3 H, ArH), 7.95 (s, 3
gel, eluting with dichloromethane:ethyl acetate = 10:1) and H, NC=CH), 7.82 (s, 18 H, ArH), 4.39 (t, J = 7.2 Hz, 6 H, NCH2),
recrystallization from ethanol to get white product (76.5 mg, 4.22 (t, J = 6.4 Hz, 36 H, OCH2), 1.97~1.89 (m, 42 H, CH2),
74.54 %).
1.60~1.53 (m, 36 H, CH2), 1.44~1.35 (m, 90 H, CH2), 0.94~0.90
1H NMR (CDCl3, TMS, 400 MHz) δ: 8.26 (s, 3 H, ArH), 8.02 (s, 3 (m, 45 H, CH3). 13C NMR (CDCl3, TMS, 100 MHz) δ: 148.95,
H, NC=CH), 7.86~7.80 (m, 18 H, ArH), 4.77 (t, J = 6.8 Hz, 6 H, 147.06, 131.77, 123.59, 122.13, 120.15, 107.35, 107.30, 69.69,
NCH2), 4.30~4.19 (m, 36 H, OCH2), 2.60~2.54 (m, 6 H, CH2), 50.54, 31.69, 30.30, 29.49, 29.46, 29.42, 29.35, 29.04, 26.14,
10 | J. Name., 2012, 00, 1-3
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DOI: 10.1039/C5TC02576A
ARTICLE
25.85, 22.66, 14.08, 14.06. Anal. calcd for C174H255N9O18: C
76.26, H 9.60, N 4.30; found C 76.17, H 9.70, N 4.33.
Notes and References
1
T. Kato, N. Mizoshita and K. Kishimoto, Angew. Chem. Int.
Ed., 2006, 45, 38-68.
Prerparation of supramolecular complexes 5a-f by
complementary hydrogen bonding
2
3
C. Tschierske, Angew. Chem. Int. Ed., 2013, 52, 8828-8878.
J. W. Goodby, I. M. Saez, S. J. Cowling, V. Görtz, M. Draper, A.
W. Hall, S. Sia, G. Cosquer, S.-E. Lee and E. P. Raynes, Angew.
Chem. Int. Ed., 2008, 47, 2754-2787.
First, hexanoic acid, benzoic acid, and prepared 4-
hexyloxybenzoic acid, 3,4-bis(hexyloxy)benzoic acid, 3,4,5-
tris(hexyloxy)benzoic acid, were purified before use. 4d were
mixed separately with hexanoic acid, benzoic acid, 4-
hexyloxybenzoic acid 3,4-bis(hexyloxy)benzoic acid, and 3,4,5-
4
5
S. Kumar, Chem. Soc. Rev., 2006, 35, 83-109.
D. Adam, P. Schuhmacher, J. Simmerer, L. Häussling, K.
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7
8
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tris(hexyloxy)benzoic acid in
a ratio of 1:1, 1:2, 1:3
stoichiometry in CH2Cl2 followed by slow evaporation of the
solvent, the samples were ready for characterization.
1
2C5H11COOH]. H NMR (CDCl3, TMS, 400 MHz) δ: 8.28
5a
[
4d
┇
(s, 3 H, ArH), 8.05 (s, 3 H, NC=CH), 7.77 (s, 18 H, ArH), 4.44 (s, 6
H, NCH2), 4.21~4.23 (m, 36 H, OCH2), 2.36 (t, J = 7.6 Hz, 4 H,
CH2), 1.91~1.92 (m, 42 H, CH2), 1.57~1.67 (m, 40 H, CH2),
1.34~1.39 (m, 98 H, CH2), 0.90~0.95 (m, 45 H, CH3).
1
3C5H11COOH]. H NMR (CDCl3, TMS, 400 MHz) δ: 8.32
10 T. Hassheider, S. A. Benning, H. S. Kitzerow, M. F. Achard, H.
Bock, Angew. Chem. Int. Ed., 2001, 40, 2060-2063.
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5b
[
4d
┇
(s, 3 H, ArH), 8.03 (s, 3 H, NC=CH), 7.80 (s, 18 H, ArH), 4.41 (s, 6
H, NCH2), 4.21~4.22 (m, 36 H, OCH2), 2.36 (t, J = 7.6 Hz, 6 H,
CH2), 1.91~1.95 (m, 42 H, CH2), 1.55~1.61 (m, 42 H, CH2),
1.34~1.39 (m, 102 H, CH2), 0.90~0.95 (m, 54 H, CH3).
12 M. Stepien, B. Donnio and J. L. Sessler, Angew. Chem. Int.
Ed., 2007, 46, 1431-1435.
5c [4d┇
2PhCOOH]. 1H NMR (CDCl3, TMS, 400 MHz) δ: 8.34 (s, 3
13 (a) S. Kumar, Liq. Cryst., 2005, 32, 1089-1113. (b) S. K. Pal, S.
Setia, B. S. Avinash and S. Kumar, Liq. Cryst., 2013, 40, 1769–
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Martin and Z. B. Lu, J. Mater. Chem. 1999, 9, 1391-1402.
H, ArH), 8.12 (d, J = 8.4 Hz, 4 H, ArH), 8.04 (s, 3 H, NC=CH), 7.81
(s, 18 H, ArH), 7.62 (t, J = 7.2 Hz, 2 H, ArH), 7.48 (t, J = 7.2 Hz, 4
H, ArH), 4.41 (s, 6 H, NCH2), 4.21~4.22 (m, 36 H, OCH2),
1.91~1.95 (m, 42 H, CH2), 1.55~1.57 (m, 36 H, CH2), 1.38~1.39
(m, 90 H, CH2), 0.91~0.95 (m, 45 H, CH3).
5d [4d┇
3PhCOOH]. 1H NMR (CDCl3, TMS, 400 MHz) δ: 8.33 (s, 3
H, ArH), 8.11 (d, J = 8 Hz, 6 H, ArH), 7.99 (s, 3 H, NC=CH), 7.81
(s, 18 H, ArH), 7.61 (t, J = 7.2 Hz, 3 H, ArH), 7.48 (t, J = 7.6 Hz, 6
H, ArH), 4.40 (t, J = 6.8 Hz, 6 H, NCH2), 4.21~4.23 (m, 36 H,
OCH2), 1.89~1.96 (m, 42 H, CH2), 1.53~1.57 (m, 36 H, CH2),
1.39~1.44 (m, 90 H, CH2), 0.91~0.94 (m, 45 H, CH3).
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H. Ringsdorf and P. Schuhmacher, Langmuir, 1995, 11, 1666
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8.34 (s, 3 H, ArH), 8.02~8.06 (m, 7H, 3NC=CH, 4ArH), 7.82 (s, 18
H, ArH), 6.93 (d, J = 8.4 Hz, 4 H, ArH), 4.41 (s, 6 H, NCH2),
4.21~4.24 (m, 36 H, OCH2), 4.00~4.04 (m, 4 H, OCH2),
1.91~1.95 (m, 40 H, CH2), 1.79~1.82 (m, 6 H, CH2), 1.55~1.56
(m, 36 H, CH2), 1.36~1.40 (m, 104 H, CH2), 0.91~0.95 (m, 51 H,
CH3).
20 I. Paraschiv, M. Giesbers, B. V. Lagen, F. C. Grozema, R. D.
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(s, 18 H, ArH), 6.93 (d, J = 8.8 Hz, 6 H, ArH), 4.42 (s, 6 H, NCH2),
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Acknowledgements
We are grateful to the financial support of the National Natural
Science Foundation of China (Fund numbers 51273133 and
51404003). BD and BH thank CNRS for support.
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