End functionalised liquid crystalline bent-core molecules and first DAB derived dendrimers with banana shaped mesogenic units

Article abstract of DOI:10.1039/b415910a

New series of non-symmetric bent-core compounds with a terminal carboxylic function as well as its benzyl esters and pentafluorophenyl esters have been synthesised. For most pentafluorophenylesters and for a benzylester with fluorine atoms in the ortho po

Full text of DOI:10.1039/b415910a

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PAPER
www.rsc.org/materials | Journal of Materials Chemistry
End functionalised liquid crystalline bent-core molecules and first DAB
derived dendrimers with banana shaped mesogenic units{{
Dorota Kardas,§a Marko Prehm,a Ute Baumeister,b Damian Pociecha,c R. Amaranatha Reddy,a
Georg H. Mehld and Carsten Tschierske*a
Received 14th October 2004, Accepted 24th December 2004
First published as an Advance Article on the web 31st January 2005
DOI: 10.1039/b415910a
New series of non-symmetric bent-core compounds with a terminal carboxylic function as well as
its benzyl esters and pentafluorophenyl esters have been synthesised. For most
pentafluorophenylesters and for a benzylester with fluorine atoms in the ortho positions to the
alkoxy chain different types of columnar ribbon phases (ColrPA and ColobPA) and a polar smectic
SmCPA phase have been observed. Both the columnar and the smectic phases show
antiferroelectric switching behaviour. Based on these functionalised banana-shaped molecules the
first example of an amphiphilic bent-core molecule with a terminal 1-acylaminopropane-2,3-diol
unit and DAB derived dendrimers of the first as well as the second generation have been
synthesised and their physical properties have been investigated. Neither the diol-terminated
bent-core molecule nor the dendrimers show any electrooptical response. Dendrimers with long
aliphatic chains as well as the amphiphile form non-polar bilayer smectic phases, whereas
dendrimers with shorter chains organise into a mesophase with a 2D lattice (Col). It seems that
hydrogen bonding at the periphery of the bent-core units is unfavourable for the formation of
polar smectic phases.
report about dendrimers with disc-like mesogenic units has
recently been presented.10 Though there are few reports
Introduction
about bent-core units incorporated in polymer structures,11
Until recently, most liquid crystals have been designed to be
either low molecular weight for display applications or high
molecular weight for prototypical polymers.1 Dendritic liquid
work concerning attachment of banana-shaped molecules
according to the best of our knowledge, there is only one
crystals,2,3 on the other hand, combine the unique features of
to a dendritic core, more precisely to a first generation
carbosilane core.12
low molecular weight materials with those of polymers.
Moreover, dendrimers exhibit a variety of physical properties
Bent-core molecules are of prime interest in contemporary
that make them attractive for applications in different fields
liquid crystal research, due to their special properties provided
of science.4 They offer a very elegant and effective way
of adding funtionalisation together with an unprecedented
level of control of the precise nature and location of specific
functionalities and overall molecular architectures.5
by the distinct molecular shape.13,14 The fascinating features of
these materials are the occurrence of a polar order within the
layers and the appearance of different types of structural
chirality in these systems composed of configurationally non-
chiral molecules.15,16 The polar order, which is a consequence
of the restricted rotation of these molecules due to their bent
shape, gives rise to interesting application properties of such
materials, e.g. as ferroelectric16,17 or antiferroelectric15 switch-
ing materials which can be used for display devices,18 highly
efficient switchable NLO materials19 and as components for
optical wave guides. The occurrence of chirality in these
systems is of fundamental scientific interest, especially as it has
recently been found that this chirality can be switched in
external electric fields.20 Another interesting feature concerns
the modulation of the mesophase structure by the formation of
ribbon-like aggregates or undulated layers, which organise into
So far, a variety of mesogens have been connected to a
dendrimeric matrix.2 In most cases the mesogenic cores were
fixed to the periphery of a dendrimer,6,7 but also some reports
have appeared where mesogenic units are incorporated into the
dendrimer core8 or into a hyperbranched polymer architec-
ture.9 There are very few reports concerning liquid crystalline
(LC) dendrimeric materials in which mesogenic groups are
laterally attached to a dendrimeric core,7 and a relatively large
group of materials in which a dendrimeric core is connected
with mesogens via one of their terminal positions.6 Also a first
{ This work was funded as part of the EU Research Training Network
‘‘LCDD’’, Supermolecular Liquid Crystal Dendrimers.
{ Electronic supplementary information (ESI) available: Procedures
and analytical data, tables with X-ray data, 2D diffraction pattern of
I-Pfp16, and DSC traces of 1-Pfp14. See http://www.rsc.org/suppdata/
jm/b4/b415910a/
§ Present address: Agricultural University SGGW, Department of
Biophysics, Nowoursynowska 159/34, 02776 Warsaw, Poland.
E-mail: kardas@alpha.sggw.waw.pl
˜
different columnar and modulated smectic phases (SmC
phases, B1 phases and B7 subtypes).21,20c This modulation of
the smectic layers can be due to an escape from a macroscopic
polarisation, due to splay modulation22 or due to steric reasons
as a result of the different space filling of distinct molecular
parts.20c Hence, it was decided to investigate novel super-
molecular systems containing banana-shaped units joined to a
*carsten.tschierske@chemie.uni-halle.de
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The designation of the compounds is as follows: The end-
functionalized bent-core molecules are grouped into two
classes (I and II) depending on the spacer length. Additional
F substituents at the rigid core are indicated by an additional
letter F (e.g. IF). The functional end group is indicated by a
letter code (H 5 COOH, Bz 5 benzylester, Pfp 5 penta-
fluorophenyl ester) and this is followed by a number indicating
the length of the terminal chain (12, 14, 16). The dendrimers
are described by the generation number as a roman number,
followed by the length of the terminal chains (e.g. 1-12).
Synthesis
The general synthetic procedure to get the COOH terminated
bent-core compounds and their pentafluorophenyl esters is
outlined in Scheme 1. 49-Benzyloxy-3-biphenylol (A) and the
4-benzoyloxybenzoic acids (B) were obtained according to
methods described elsewhere.16,23b Esterification of A with B
using DCC/DMAP, followed by hydrogenolytic debenzylation
gave the intermediates C16a which were used for the
etherification with the funtionalised benzoic acids D (for the
synthesis, see the electronic supplementary information
(ESI){) to yield the benzyl esters I-Bzn, IF-Bzn and II-Bzn.
Hydrogenolysis of these benzyl esters lead to the carboxylic
acids I-Hn, IF-Hn and II-Hn, which were used for the
preparation of the corresponding pentafluorophenyl esters
I-Pfpn, IF-Pfpn and II-Pfpn using DCC in the presence of
the acylation catalyst DMAP as condensation agent.
Fig. 1 Cartoon of a dendrimer with terminally attached bent-core units
and possible organisation of this dendrimer within a smectic phase.
DAB core via a terminal carboxylic function. Fig. 1 shows a
cartoon of the general structure of the target systems; the
structures of the unsymmetrical bent-core molecules used for
the synthesis of the dendrimers are shown in Fig. 2.
This paper is divided into two parts. The first part is
devoted to the synthesis and the physical properties of new
series of unsymmetrical banana-shaped molecules, which will
be attached in the further step to the dendritic system. As is
shown in Fig. 2, these new banana-shaped compounds consist
of five aromatic rings. The bent 3,49-biphenyldiol core23,11d is
connected with two different aromatic branches. One of them
carries an alkoxy chain with either 12, 14 or 16 carbon atoms.
Most important from the further functionalisation point of
view, these monomeric molecules contain a free carboxylic
end-group (R4 5 H). This kind of compound is relatively
easy to convert in further steps, for example, into ester or
amide derivatives to design new supermolecular architectures
incorporating bent-core mesogenic units. The bent-core unit
was additionally modified by introduction of lateral fluorine
substituents positioned at the peripheral benzene rings (R1, R2
and R3 5 H or F), because such substituents are known to
influence the mesomorphic properties of bent-core molecules
significantly.17c,24 The length of the spacer unit which connects
the bent aromatic core with the terminal carboxyl group was
altered as well, whereby C4 (m 5 3) or C10 (m 5 9) alkyleneoxy
spacers have been chosen.
The way to get the dendrimeric compounds of the first and
the second generation is outlined in Scheme 2. The final
compound 1-16 was obtained via condensation reaction of
the DAB dendrimer of the first generation with the penta-
fluorophenyl ester derivative I-Pfp16.6c The second generation
Having the monomers prepared, these building blocks
could be used to finally obtain the dendrimer compounds.
The second part of this report concerns the synthesis and
physical properties of DAB dendrimers of the first and the
second generation and also of an amphiphilic, diol-terminated,
bent-core molecule.
Fig. 2 The general structure of unsymmetrical banana-shaped
compounds, where: m 5 9 (series I), m 5 3 (series II); n 5 12, 14 or
16; R1, R2, R3 5 H or F (series IF); R4 5 Bz (benzyl), H (free
carboxylic acid) or Pfp (pentafluorophenyl).
Scheme 1 Synthesis of the unsymmetrical banana-shaped compounds
(R1–R3 5 H, F; m 5 3, 9; n 5 12, 14, 16).
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(pentafluorophenylester method6c). The syntheses of the end
functionalised bent-core molecules I-Bz16, I-H16 and I-Pfp16
as well as the dendrimers 1-16 and 2-16 are described in the
experimental section. The other experimental procedures and
analytical data are collated in the ESI.{
Results and discussion
The bent shaped precursors are reported first, followed by the
dendrimers. Some of the bent shaped building blocks show
liquid crystalline properties, which are in most cases mono-
tropic (metastable). Therefore, in Tables 1–4 the transition
temperatures are given for the cooling process and the melting
points obtained in the first heating (mp) are also provided in
Tables 1–3.
Banana-shaped compounds with terminal carboxylic groups
Series I. In the compounds of series I, a decamethyleneoxy
spacer separates the bent aromatic core and the carboxylic
group (11-substituted derivatives of the undecanoic acid).
Three groups of compounds have been obtained in this series:
either with 14 or 16 carbon atoms in the terminal alkoxy group
and without fluoro substituent (R1, R3 5 H). The third group
consists of compounds with 14 carbon atoms in the alkoxy
chain and with one fluorine atom in the ortho position to this
terminal alkoxy chain (see Table 1). To check the influence of
shortening the spacer length for the compounds of series II the
length of the oxyalkylene spacer was reduced to four carbon
atoms (5-substituted derivatives of pentanoic acid, see Table 2).
For the obtained compounds polarised light optical micro-
scopic (POM) investigation, as well as differential scanning
calorimetric (DSC) measurements have been performed. The
transition temperatures and associated enthalpy values are
shown in Tables 1 and 2.
Scheme 2 Synthesis of the first and second generation DAB
dendrimers 1-16 and 2-16 with peripheral bent-core mesogenic units.
The synthesis of the dendrimers 1-12 and 2-12 with shorter end chains
(n 5 12) and spacers (m 5 3) was done in the same way as described for
1-16.
dendrimer was achieved by coupling of the carboxylic acid
I-H16 to the DAB-(8) dendrimer in the presence of diphenyl
(2,3-dihydro-2-thioxo-3-benzoxazolyl)-phosphateas acondens-
ing agent.25 A 1.1 molar excess amount of either I-Pfp16 or
I-H16 for every primary amino end group present in the
dendrimer was used. The synthesis of the dendrimers 1-12 and
2-12 with shorter alkyl chains and shorter spacer units was
done using the same method as for the synthesis of 1-16
The benzyl ester (Bz) compounds in all three series do not
reveal liquid crystalline phases. The carboxylic acids I-H14 and
I-H16 have much higher melting temperatures than their benzyl
ester analogues. The samples can be slightly supercooled and
Table 1 Melting points (T/uC, first heating), phase transition temperatures (T/uC), and, in parentheses, their enthalpy values (DH/kJ mol21) given
for the second scan of cooling (DSC, 10 K min21) for compounds of series I (R3 5 H)a
Comp.
R1
R4
n
mp
Phase transitions
I-Bz14
I-H14
I-Pfp14
I-Bz16
I-H16
I-Pfp16
IF-Bz14
IF-H14
IF-Pfp14
a
H
H
H
H
H
H
F
Bz
H
C6F5
Bz
H
C6F5
Bz
14
14
14
16
16
16
14
14
14
98
127
88
100
126
80
91
126
92
Iso 67 [70.9] Cr
Iso 120 [46.6] M1 91 [41.3] Cr2
Iso 76 [13.1] ColrPA 59 [0.9] ColobPA 50 [17.9] Cr
Iso 74 [83.4] Cr
Iso 122 [44.0] M1 94 [41.5] Cr
Iso 83 [13.9] ColobPA 59 [30.5] Cr
Iso 71 [17.2] Cr1 60 [51.8] Cr2
Iso 120 [43.9] M2 65 [11.5] Cr
Iso 82 [14.4] ColrPA 61 [12.6] M 41 [10.9] Cr
F
F
H
C6F5
Abbreviations: Iso 5 isotropic liquid; ColobPA 5 antiferroelectric switching polar oblique columnar mesophase; ColrPA 5 antiferroelectric
switching polar rectangular columnar mesophase; M, M1, M2 5 not identified mesophases; Cr 5 crystalline solid.
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transition from the isotropic liquid is of rather low viscosity
and appears with the typical texture as shown in Fig. 3a. The
lower temperature phase exhibits well-developed spherulites
(Fig. 3b,c). In the circular domains the extinction brushes
are inclined by +h and 2h from the direction of the polarisers,
indicating a tilted arrangement with a tilt angle of about
h y 18u. The textures of both mesophases are characteristic
for some variants of columnar ribbon phases of bent-core
molecules. The material shows antiferroelectric switching
under an applied electric field, as demonstrated in Fig. 4. At
the transition from the isotropic liquid into the high tem-
perature mesophase, two well-separated peaks per half period
of the applied triangular wave voltage arise and the texture
shown in Fig. 3d develops. Decreasing the temperature leads
to the development of two new peaks between the peaks of the
high temperature phase. Upon further decreasing the tem-
perature the two peaks of the high temperature phase dis-
appear and only the two new peaks remain. The value of the
spontaneous polarisation increases from 45 nC cm22 in the
high temperature phase to PS 5 450 nC cm22 in the low tem-
perature phase. The textural features and the switching
behaviour of this material are very similar to phases of some
bent-core molecules investigated by Szydlowska et al.21b These
two phases were denoted as B1rev phase (non-tilted, high
Table 2 Melting points (T/uC, first heating), phase transition
temperatures (T/uC), and, in parentheses, their enthalpy values
(DH/kJ mol21
)
given for the second scan of cooling (DSC,
10 K min21) for compounds of series IIa
Comp. R4
mp Phase transitions
II-Bz12 Bz
102 Iso 66 [36.1] Cr
140 Iso 122 [14.1] M1 83 [17.9] Cr
II-H12
II-Pfp12 C6F5 94 Iso 76 [29.3] Cr1 59 [11.9] Cr2
H
II-Bz14 Bz
II-H14
II-Pfp14 C6F5 95 Iso 80 [16.3] SmCPA 65 [15.5] Cr1 48 [8.2] Cr2
116 Iso 89 [53.4] Cr
H
145 Iso 129 [19.7] M1 95 [17.6] Cr1 87 [2.0] Cr2
a
M1 5 not identified mesophase; SmCPA 5 antiferroelectric switch-
able, tilted, polar smectic mesophase.
Table 3 Melting points (T/uC, first heating), phase transition
temperatures (T/uC), and, in parentheses, their enthalpy values
(DH/kJ mol21
)
given for the second scan of cooling (DSC,
10 K min21) for fluorine substituted compounds of series I
temperature phase) and B1rev,
phase (low temperature
tilted
phase; tilted analogue of B1rev), and are made up by broken
layers (ribbons), in which the 2D density modulations are in
the plane perpendicular to the spontaneous polarisation
vectors. Thus, it was considered that in the case of I-Pfp14
the same phases occur, i.e., the upper phase is an orthogonal
B1rev mesophase and the lower one is a B1rev, tilted version with
a tilted organisation of the molecules. It should be pointed out
that the structure of columnar phases with a polarisation
direction along the columns cannot be adequately described by
the 17 plane groups, because, due to the polar direction, the
Comp.
R1 R2 R3 mp Phase transitions
IF-Bz14
F
F
F
F
H
H
F
H
F
H
F
91
97
85
89
Iso 71 [17.2] Cr1 60 [51.8] Cr2
Iso 74 [15.6] ColX 64 [23.3] Cr
Iso 76 [48.5] Cr
IFa-Bz14
IFb-Bz14
IFc-Bz14
F
Iso 82 [45.0] Cr
Table 4 Phase transition temperatures (T/uC), and, in parenthesis,
their enthalpy values (DH/kJ mol21) given for the second scan of
cooling (DSC, 10 K min21) for the synthesised dendrimers.
Comp.
G
n
m
Phase transitions
1-12
1-16
2-12
2-16
First
First
Second
Second
12
16
12
16
3
9
3
9
Iso 151 [25.5] Colr 104 [5.0] Cr
Iso 144 [32.5 ] Sm 113 [41.0] Cr
Iso 162 [12.2] Colr 120 [29.3] Cr
Iso 149 [24.0] Sm 122 [105.0 ] Cr
upon cooling a crystallisation can be seen, but the apparently
crystalline material is still soft and it is possible to shear these
samples. This (soft crystalline) mesophase is assigned as M1.
The carboxylic acid IF-H14, which has one lateral fluoro
substituent at the rigid core, exhibits a monotropic liquid
crystalline phase (M2). However, due to rapid crystallisation it
was not possible to investigate any of these carboxylic acids in
more detail.
Fig. 3 Optical textures (crossed polarisers) of compound I-Pfp14: (a)
ColrPA phase at 76 uC, (b) phase transition between ColrPA and
ColobPA at 58 uC, (c) ColobPA phase at 57 uC), (d) ColrPA phase at
76 uC. Pictures (a–c) were taken upon cooling from the isotropic liquid
without applying an electric field, and (d) after applying an electric
field (60 Vpp mm21). The arrows indicate the positions of polariser and
analyser.
The most interesting liquid crystalline properties reveal the
pentafluorophenylester (Pfp) derivatives I-Pfp14, I-Pfp16, and
IF-Pfp14. For compound I-Pfp14 two monotropic mesophases
were detected (DSC traces are shown in Fig. S2 of the ESI{).
The phase transition is clearly visible during POM studies as
the texture drastically changes. The mesophase formed at the
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Fig. 4 Spontaneous polarisation measurements for compound
I-Pfp14 in the ColobPA phase at 58 uC (B) and in ColrPA phase at
75 uC (A). The current response in one half period of the triangular
wave voltage is shown. Changing of value of PS as well as the position
of the peaks confirms the existence of two different phases. The
occurrence of two current peaks within one half period of the applied
triangular wave voltage indicates an antiferroelectric switching process
in both phases.
upper and the lower ends of the columns become different.
Therefore, it was suggested21c to use the 80 layer groups
instead.26 However, as shown in the ESI{ (Fig. S3), there are
different ways to organise the polar columns in an antiferro-
electric manner within a rectangular or an oblique lattice and
these correspond to different settings in the layer groups
number 46 (pmmn, orthorhombic/rectangular) and number 7
(p112/a, monoclinic/oblique). Because the precise organisation
within the columns is not completely clear, and hence an
unique assignment to a specific set of lattice parameters is not
possible, the more general descriptions ColrPA and ColobPA
are used here for the assignment of polar columnar phases with
a polarisation direction perpendicular to the 2D lattice. Hence,
the B1rev phase is assigned as ColrPA, whereas the B1rev,tilted
phase is assigned as ColobPA. Models showing the arrange-
ment of the molecules in these columnar mesophases are
shown in Fig. 5b,c.
Fig. 5 Models of some columnar banana phases. (a) Model for non-
switchable Colr phases (B1 phase) as suggested for short chain bent-
core molecules, here the 2D lattice is in the plane of the polarisation
vectors (corresponding to the bend direction), the molecules are non-
tilted. (b) ColrPA phase (compound I-Pfp14, high temperature phase),
here the 2D-lattice is perpendicular to the plane of the polarisation
vectors, the molecules are non-tilted; the 2D lattice is rectangular. (c)
The ColobPA phase (compound I-Pfp14, low temperature phase,
compound I-Pfp16) is related to the ColrPA phase, but the molecules
are additionally tilted, resulting in an oblique type lattice. Only one of
the three possible models, differing in the polarisation direction in
adjacent ribbons is shown, all three structures are compared in Fig. S3
in the ESI{. Only the aromatic bent-core units are shown. The space
between the ribbons is filled by the conformationally disordered
terminal chains. The polarisation directions are indicated by dots (out
of the plane) and crosses (into the plane).
according to Vcell 5 ab(sin c)heff 5 5.1 nm3 with a height
heff 5 0.52 nm.27 Using the volume increments of Immirzi and
For compound I-Pfp16, which has a terminal hexadecyloxy
chain, only one liquid crystalline phase was detected. During
cooling from the isotropic phase the characteristic texture of a
columnar phase grows (similar to the texture shown in Fig. 3c).
All these features are very similar to those of the low
temperature phase of I-Pfp14 (which is a ColobPA phase).
The X-ray diffraction pattern of an aligned sample of this
mesophase (see Fig. S1 of the ESI{) can be indexed on the
basis of an oblique lattice (see Fig. 5c) and the lattice
parameters for the plane group p2, neglecting the polarisation
directions are a 5 4.2 nm, b 5 2.35 nm and c 5 95u (T 5 80 uC,
see also Table S1 in ESI{). The angle between the preferred
direction of the outer scattering (caused by the lateral mole-
cular arrangement within the ribbons) and the 10-reflection
indicates a 46u tilt of the molecules with respect to the normal
to the b-axis, i.e. to the normal to the broken layers. The para-
meter a is in rather good agreement with the total molecular
length of I-Pfp16 (d10/L 5 4.2 nm/6.1 nm 5 0.69 5 cos 46u,
L 5 6.1 nm in a 120u bent V-shaped conformation with all
trans alkyl chains). The unit cell volume was calculated
Perini28 the volume of a molecule was calculated to Vmol
5
1.47 nm3, and from these values, according to n 5 Vcell/Vmol, a
number of about 3–4 molecules (n 5 3.5) in the cross section of
each ribbon is calculated. This columnar phase, similarly to
those described above, responds to the electric field. Two
current peaks indicate an antiferroelectric switching with a
spontaneous polarisation value of about 500 nC cm22, hence
this phase is designated as ColobPA.
The third material in this group of compounds, IF-Pfp14,
has a tetradecyloxy terminal chain as I-Pfp14, but it possesses
a fluorine atom in the ortho position to this alkoxy chain. In
the POM studies lancet-like textures (see Fig. 6a) with some
circular domains were observed, where the extinction brushes
are parallel to the direction of polariser and analyser (see
Fig. 6b). This texture is very similar to that of the high
temperature phase of I-Pfp14, suggesting that this mesophase
is also a columnar phase. The position of the extinction crosses
parallel to polariser and analyser points to a non-tilted
molecular alignment in the ribbons. Applying a triangular
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Fig. 6 The textures (crossed polarisers) of the columnar phase of
compound IF-Pfp14 taken at 80 uC (a) cooled from the isotropic
phase, (b) circular domain with extinction brushes parallel to the
polarisers, (c) after applying an electric field, (d) under d.c. electric field
(30 V mm21); note the pronounced change of birefringence. The arrows
indicate the positions of polariser and analyser.
voltage to the sample does not cause any brush movement,
however, two current peaks per half period of the applied a.c.
voltage are visible. The switching process is accompanied by
pronounced changes of the birefringence (Fig. 6c,d). This
points to a switching process by rotation around the molecular
long axis, as seen in the SmAPA phases29,24b and in some
columnar type banana phases.21b,d,20b,c The antiferroelectricity
of the phase is additionally confirmed by the low value of the
static dielectric constant. Only a weak (De y 5) high-frequency
mode (above 10 kHz), most probably related to the collective
rotation around the long molecular axis, is observed, as seen in
Fig. 7. From all these investigations it can be concluded that
the mesophase of IF-Pfp14 is the same as the high temperature
phase of I-Pfp14 (ColrPA), i.e. the introduction of the fluoro
substituent suppresses the tilted ColobPA phase.
Fig. 7 3-D frequency–temperature dependence of the real (top) and
imaginary (bottom) parts of the dielectric constant for compound
IF-Pfp14.
Series II: influence of shortening of the spacer unit
spacer length a transition from polar columnar phases
(ColrPA, ColobPA) to a polar smectic phase (non-modulated
layers, SmCPA) takes place. In the microscopic studies, upon
cooling from the isotropic state under an applied d.c. field of
10 V mm21 the characteristic circular domains can be grown.
The extinction brushes are directed along the polariser
directions, indicating an anticlinic molecular organisation.
Moreover, the birefringence of the textures obtained in a
thin glass cell, estimated from the tabulated interference
colours of a quartz wedge, was Dn 5 0.06. This can suggest
that the molecules are aligned with their banana planes on the
glass surface. Application of a low frequency a.c. electric field
influences the texture. For some small domains a brush
rotation appears (see Fig. 8). Removing the field pushes the
brushes immediately back to their initial orientation, which
is an indication of an antiferroelectric switching process
taking place by a collective rotation of the molecules around
a tilt cone. This behaviour could reflect the molecular
switching from an anticlinic-antiferroelectric (SmCAPA) to
In the series II the alkyl chain carrying the carboxylic function
was shortened to five carbon atoms. The transition tempera-
tures as well as the enthalpy values for these materials are
shown in Table 2. Similar to the analogous compound I-Bz14,
the benzyl ester derivatives II-Bz14 and II-Bz12 do not exhibit
mesogenic properties. The difference for the corresponding
free acids and the pentafluorophenylester derivatives is not so
significant, considering both the melting and clearing tem-
peratures. However, a slight decrease of the melting tempera-
ture and a small increase of the clearing temperature for
compounds II-H14 and II-Pfp14 in comparison with com-
pounds I-H14 and I-Pfp14, respectively, was observed. The
most important difference in the mesomorphic behaviour
reveals the pair of pentafluorophenyl ester derivatives I-Pfp14
and II-Pfp14. Whereas the homologue I-Pfp14 with long
spacer shows two columnar phases (see above), its counterpart
with the short spacer exhibits a SmCPA phase, as indicated by
the very typical texture. This means that on reducing the
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Fig. 9 The textures (crossed polarisers) of compound IFa-Bz14 at
73 uC (a, b) during the growing process and (c) as a fully developed
texture (different region).
Fig. 8 Changes of the extinction brush direction of the domains of
the SmCPA phase of II-Pfp14 in a 5 mm ITO cell under an electric field
(¡200 V) at 79 uC.
carbosilane31 end groups, for example, lead to a transition
from the antiferroelectric switching behaviour, which is usually
observed for the tilted smectic phases of banana molecules
(SmCPA-phases) to a ferroelectric switching.16 For such com-
pounds a strong decoupling of the smectic layers driven by
microsegregation of the branched units is discussed to be
mainly responsible for the stabilisation of the macroscopic
polar ferroelectric states.16
synclinic-ferroelectric (SmCSPF) arrangement, i.e. the homo-
geneous chiral state seems to be the preferred organisation of
II-Pfp14 under the given experimental conditions.
In contrast to II-Pfp14 the homologous compound II-Pfp12
with shorter terminal alkyl chain shows no liquid crystalline
phase.
Influence of the number and position of lateral fluorine atoms
The free COOH groups, capable of hydrogen bonding, seem
to be not advantageous for the formation of mesophases in the
case of bent-core molecules. All synthesised compounds with
terminal COOH groups show rather high melting points and
only highly ordered (soft crystalline) mesophases (M1, M2)
were observed. Compound III (Fig. 10), which was obtained
from the pentafluorophenylester I-Pfp16 and 1-amino-2,3-
propandiol has a hydrogen bonding 1-acylaminopropane-2,3-
diol group at its end. Textural investigations of the mesophase
of III indicate small focal conic defects, surrounded by dark
areas. Shearing leads to a birefringent texture, similar to that
shown in Fig. 11b. When the material III was used as dopant
for a SmC* matrix, it did not induce an antiferroelectric
SmCA* phase, as proven with other bent-core materials.32
Furthermore, the phase is not switchable under an applied
electric field. The X-ray diffraction pattern (Guinier method,
powder pattern) showed layer reflections from second up to
the sixth order (first order reflection is hidden by the beam
stop; for details, see Table S2 in ESI{), indicating a layer
structure with quite sharp interlayer interfaces. This is possibly
due to the mesophase stabilising effect of the diol unit by
intermolecular hydrogen bonding and due to the fact that
these polar end groups can segregate into distinct sublayers.33
The layer distance is d 5 9.2 nm. This amounts to about
1.5 times the molecular length (L 5 6.1 nm in a 120u bent
V-shaped conformation with all trans alkyl chains), indicating
a bilayer structure in which the molecules III adopt an
antiparallel end to end packing. The formation of a bilayer
structure is in accordance with the suggested segregation of the
To evaluate the role of fluorine atoms on the properties of the
investigated system, additionally to IF-Bz14, three compounds
with lateral fluoro substituents have been synthesised (see
Table 3). To compare the properties of the fluorinated
compounds the benzyl ester derivatives with tetradecyloxy
terminal chains were chosen. The fluorine atoms are either
attached in ortho position to the alkoxy terminal chain (one or
two fluorine atoms) and/or one fluorine atom is connected in
ortho position to the spacer chain. Only one of these
derivatives, compound IFa-Bz14, exhibits a liquid crystalline
phase. In the microscopic study, upon cooling from the
isotropic liquid the growing of a texture characteristic for
columnar mesophases is observed, as shown in Fig. 9.
However, due to its monotropic character more detailed mea-
surements were impossible (therefore it is assigned as ColX).
Banana-shaped amphiphile III: the influence of hydrogen
bonding
Because of the end functionalisation, the monomeric banana-
shaped materials described here are attractive on their own.
Particularly, the pentafluorophenylester derivatives exhibit
interesting liquid crystalline behaviour, possibly due to the
bulky pentafluorophenyl end groups, located at the interlayer
interfaces (and inter-ribbon interfaces). The engineering of
the interlayer interfaces seems to be an important tool to
modify the mesophase structures of bent-core molecules.30
Branched end chains,17a,b,f as well as bulky oligosiloxane16 or
Fig. 10 Compound III, the phase transition temperatures (T/uC) and their enthalpy values (DH/kJ mol21) on cooling are: Iso 155 [47.4 kJ mol21
]
Sm 96 [42.0 kJ mol21] Cr. The melting point in the first heating is at 156 uC.
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Fig. 11 Textures (crossed polarisers) of the first generation dendrimer
1-16 at: (a) 118 uC, (b) 108 uC, after shearing.
polar 1-acylaminopropane-2,3-diol groups from the aliphatic
and aromatic molecular segments. However, because no
aligned samples could be obtained, it is not completely clear
if the molecules are tilted within the smectic layers or not
(hence this mesophase is designated as Sm). In addition, this
compound is not stable, because the diol groups give rise to a
transesterification reaction with the ester groups within the
mesogenic core at higher temperatures and especially upon
applying an electric field. Therefore additional compounds of
this type were not synthesised.
Fig. 12 MALDI-TOF spectrum of 1-16 CH2Cl2 solvent, HABA
matrix.
the material was too high to fill the cells for electrooptical
measurements. In the small angle region, the X-ray diffraction
pattern of a non-oriented sample of 1-16 (Guinier pattern)
showed three reflections corresponding to the second, third
and fourth order reflections of a layer periodicity, correspond-
ing to a distance d 5 9.1 nm (first order reflection is hidden by
the beam stop, for details, see Table S2 in ESI{). Remarkably,
this distance is nearly the same as found for the mesophase of
the amphiphilic compound III. In the wide angle region a
diffuse scattering was found, confirming the liquid crystalline
character of this mesophase. If a layer structure is assumed, the
measured layer thickness d is smaller than the molecular
dimension of the complete dendrimer (Lden 5 12.2 nm,
defined by the molecular diagonal of the whole dendrimer,
as estimated by molecular modelling, ChemDraw 3D),
but about 1.5 times as large as the bent mesogenic units
(Lmes 5 6.1 nm in a 120u bent V-shaped conformation with all
trans alkyl chains). This can be explained by a layer structure
where the dendritic parts and the terminal alkyl chains are
segregated into distinct sublayers, similar as suggested for the
amphiphilic compound III. Folding of the alkyl chains and
the dendrimeric part should be responsible for the reduction of
the layer distance (d/Lden # 0.75), but as in the case of III, a
tilted organisation of the molecules cannot be completely
excluded. The textures of the second generation dendrimer
2-16 are similar to those seen for compound 1-16. The viscosity
of the liquid crystalline phase is slightly lower in comparison
with the first generation dendrimer, and in this case it was
possible to fill the measurement cells by means of capillary
forces. However, the electrooptical measurements for these
dendrimers show no response to the applied electric field up to
an applied voltage of 400 V in a 5 mm cell.
Dendrimeric compounds
Though the mesomorphic properties of some of the fluorinated
derivatives were quite promising, non-substituted derivatives
have been chosen for further functionalisation to get
dendrimeric materials, because these unsubstituted bent-core
derivatives are available in larger quantities due to the much
shorter synthetic routes. The dendrimeric compounds 1-16 and
2-16 were obtained as shown in Scheme 2. The dendrimers 1-12
and 2-12 were synthesised using the same method as for 1-16.
The structures of the final dendrimeric compounds were
1
characterised by H, 13C NMR by elemental analysis, as well
as by MALDI-TOF mass spectrometry. For 1-12 and 2-12
ESI-MS was used in addition. The MALDI-TOF mass
spectrum of compound 1-16 (see Fig. 12), for example, shows
one signal that is clearly due to the formation of the desired
dendrimer with four banana-shaped units. The m/z value
(4086.9 2 22.9 5 4064.0) corresponds to the calculated value
of 4086.9 (molecular mass + Na+). The results for the other
dendrimers are listed in the experimental part and the ESI{.
However, attempts to prepare the third and fourth generation
dendrimers 3-12 and 4-12 using one of the methods
mentioned above leads to an incomplete functionalisation of
the dendrimeric core and hence no sufficiently pure products
could be obtained.
The transition temperatures of the dendrimers are
recorded in Table 4. Generally, the clearing temperatures
of the dendrimers are significantly higher than those of the
corresponding bent-core precursors (acids, benzyl esters and
pentafluorophenyl esters). Furthermore, there is only partial
and very slow crystallisation upon cooling. Therefore, defined
melting temperatures cannot be given, but all mesophases are
enantiotropic. For dendrimer 1-16 a non-specific, grainy
texture was observed upon cooling from the isotropic liquid,
which might represent a not well developed fan texture of a
smectic phase (see Fig. 11a). Though it was possible to shear
the sample between glass plates (see Fig. 11b), the viscosity of
The dendrimers 1-12 and 2-12 with shorter alkyl chains and
spacer units show textures (see Fig. 13) which are different
from those of the dendrimers 1-16 and 2-16. These textures
are more similar to those observed for non-switchable Colr
phases (see models shown in Fig. 5a,b). The powder X-ray
diffraction pattern of 2-12 (see Table S3 in the ESI{) is
characterised by six sharp Bragg reflections in the small angle
region and a diffuse scattering in the wide angle region. The
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showing non-polar smectic phases with bilayer structures. The
dendrimers 1-12 and 2-12 with shorter aliphatic segments
form modulated smectic phases (rectangular columnar ribbon
phases Colr). Also these mesophases are non-switchable. It
seems that hydrogen bonding at the periphery of bent-core
molecules is unfavourable for the formation of polar smectic
phases with bent-core molecules.34
Experimental
General
The mesophase identification was based on microscopic
examination of the textures formed by samples between two
glass plates. A Nikon Optiphot-2-Pol polarising microscope
equipped with a Mettler FP82HT hot stage was used. The
temperatures and enthalpies of the phase transitions were
determined by calorimetric measurements performed with
a Perkin-Elmer DSC-7 apparatus at the cooling rate of
10 K min21. The changes of textures under electric field,
spontaneous polarisation and dielectric dispersion were
studied in glass cells with ITO electrodes, 5 mm thick, supplied
by Linkam. The dielectric dispersion studies were performed
with a Solartron SI 1260 Impedance Analyser in the frequency
range 10 Hz–10 MHz. Spontaneous electric polarisation was
measured using the switching current method under triangular
wave voltage. Tilt angle was estimated as an angle between
the directions that give extinctions of light that propagates
through the planar cell placed between crossed polarises.
Molecular dimensions were estimated by molecular modelling
(ChemDraw 3D) or by CPK models. The X-ray investigations
on non-oriented samples were carried out in capillary tubes
(diameter: 1 mm) using a Guinier film camera (HUBER
Diffraktionstechnik, Germany). X-Ray patterns of the par-
tially oriented sample (drop on a glass plate, surface aligned
at the sample–air interface) of I-Pfp16 were taken by a
2D-detector HI-Star (Siemens, Germany).
Fig. 13 Texture (crossed polarisers) of the first generation dendrimer
1-12 as it grows upon cooling from the isotropic liquid (dark areas) at
151 uC.
small angle reflections exclude a simple layer structure and can
be indexed on the basis of a rectangular lattice with the
parameter 7.4 nm and 5.6 nm (Colr). Attempts to get aligned
samples with 1-12 or 2-12 were not successful and therefore a
more precise assignment of the phase structure was not
possible. Both dendrimers show no response to an applied
electric field up to an applied voltage of 400 V in a 5 mm cell.
Conclusions
To conclude, three new series of monomeric banana-shaped
compounds have been synthesised and their physical pro-
perties have been investigated. Most of the benzyl protected
acid derivatives exhibit exclusively crystalline phases, whereas
most pentafluorophenylester derivatives exhibit monotropic
banana phases. For the compounds with long spacer units
(I-Pfp14, I-Pfp16 and IF-Pfp14) two different antiferroelectric
switchable columnar phases (ColrPA and ColobPA) have been
identified, whereas for the counterpart with shorter spacers an
antiferroelectric SmCPA phase (SmCAPA) has been observed.
Reduction of the alkyl chain length to C12 leads to a complete
loss of the liquid crystalline properties. These end function-
alised bent-core molecules represent valuable starting materials
for the further functionalisation, leading to supermolecular LC
materials. Preliminary attempts in this direction have been
made. One bent-core molecule with a polar diol group at one
terminus was synthesised, which shows a non-switchable
smectic phase with bilayer structure. Four dendrimeric com-
pounds with DAB cores of the first and the second generations
and bent-core molecules at the periphery have also been
synthesised. All dendrimers exhibit rather high viscosities,
which is unfavourable for detailed investigation of these
materials. Maybe the viscosity is due to a reduced flexibility
of the central dendrimeric cores because of the presence of the
amide groups (linking groups between the dendrimer cores
and the bent mesogenic units), which introduce hydrogen
bonding interactions. For none of the synthesised dendrimers a
switching process could be found. From these investigations it
can be concluded that the amphiphilic molecule III as well as
the two dendrimers 1-16 and 2-16 behave quite similarly,
Solvents were purified and rigorously dried over appropriate
drying agents and distilled prior to use. All atmosphere-
sensitive reactions were carried out under dry argon using
standard Schlenk techniques. DAB dendrimers (ALDRICH)
were used as received.
In order to confirm the molecular structure of the
synthesised compounds the following analytical methods were
applied. 1H NMR spectra were recorded on a spectrometer
operating at 400 (Varian Gemini 2000) or 500 (Varian Inova)
MHz, whereas 13C spectra were recorded at 100 and 125 MHz.
As the internal standard the signals of the residual protonated
species of the deuterated solvent were used. Chemical shifts are
given in ppm. Analytical TLC was performed on silica gel,
F-254 precoated silica gel glass or aluminium plates (Merck).
Visualisation was accomplished with UV light and/or using
iodine vapour. Column chromatography was carried out
either at atmospheric pressure or under flash conditions using
silica gel (230–400 mesh, Merck). Silica gel 60 PF254 (with
gypsum, Merck) was used for centrifugal force mediated
preparative thin layer chromatography in conjunction with a
Chromatotron from Harrison Research Europe (Muttenz).
Composition of the synthesised compounds, determined by
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elemental analysis performed on CHNS elemental analyser
(Leco & Co), confirmed expected molecular structures.
General procedures for the synthesis of the benzylesters,
carboxylic acids and the pentafluorophenylesters are given
together with the analytical data for the hexadecylsubstituted
derivatives. The synthesis of the dendrimers 1-16 and 2-16 and
their analytical data are also given here, whereas the analytical
data of all other molecules are collected in the ESI{.
Abbreviations: DCC: N,N9-dicyclohexylcarbodiimide; DMAP:
4-(dimethylamino)pyridine; NMP: N-methylpyrrolidone; TEA:
triethylamin.
4H, CH2); 1.63 (quintet, 2H, CH2, J 5 7.5 Hz); 1.78–1.84 (m,
4H, CH2); 2.34 (t, 2H, OOCCH2, J 5 7.5 Hz); 4.03 (t, 2H,
OCH2, J 5 6.5 Hz); 4.04 (t, 2H, OCH2, J 5 6.5 Hz); 6.96 (dd,
2H, Ar–H, J1 5 9.0 Hz, J2 5 5.0 Hz); 6.97 (dd, 2H, Ar–H,
J1 5 9.0 Hz, J2 5 5.0 Hz); 7.20–7.22 (m, 1H, Ar–H); 7.28 (dd,
2H, Ar–H, J1 5 8.5 Hz, J2 5 4.5 Hz); 7.37 (dd, 2H, Ar–H,
J1 5 8.5 Hz, J2 5 4.5 Hz); 7.44 (bs, 1H, Ar–H); 7.49 (d, 2H,
Ar–H, J 5 5.0 Hz); 7.63 (dd, 2H, Ar–H, J1 5 8.5 Hz,
J2 5 4.5 Hz); 8.14 (dd, 4H, Ar–H, J1 5 9.0 Hz, J2 5 5.0 Hz);
8.29 (dd, 2H, Ar–H, J1 5 9.0 Hz, J2 5 4.5 Hz); 13C NMR (d
ppm, CDCl3): 14.05, 22.67, 24.71, 25.97, 25.99, 29.04, 29.12,
29.18, 29.30, 29.31, 29.34, 29.44, 29.55, 29.58, 29.65, 29.67,
29.68, 31.92, 33.65, 68.38, 68.47, 114.40, 114.51, 120.43,
120.54, 121.12, 121.64, 122.10, 122.17, 124.66, 126.97, 128.23,
129.82, 131.83, 132.32, 132.43, 137.81, 142.23, 150.98, 151.49,
155.53, 163.65, 163.91, 164.30, 164.46, 164.89, 177.71;
Elemental analysis: Calcd. for C60H74O10: C 75.44, H 7.81%;
Found: C 75.38, H 7.48%.
Synthetic procedures and analytical data
Benzylesters. The appropriate carboxylic acid (5.0 mmol),
phenol (5.0 mmol) and DMAP (0.1 mmol) were dissolved in
dry CH2Cl2 (50 ml). The reaction mixture was cooled down to
0 uC and DCC (5.5 mmol) dissolved in dry CH2Cl2 (10 ml) was
slowly added. After adding the last portion of DCC the
cooling bath was removed and the mixture was stirred at room
temperature for 2–5 days. The precipitated solid was removed
by filtration, and the solvent was evaporated. The crude
product was purified by sequential column chromatography or
centrifugal thin layer chromatography on a Chromatotron
with CH2Cl2 and CH2Cl2–MeOH mixtures (up to 10%
MeOH), followed by repeated crystallisation from methanol
and hexane. Yield was between 80 and 95%. I-Bz16: 1H NMR
(d ppm, CDCl3): 0.87 (t, 3H, CH3, J 5 7.0 Hz); 1.25–1.34 (m,
34H, CH2); 1.45–1.47 (m, 4H, CH2); 1.57–1.69 (m, 2H, CH2);
1.79–1.83 (m, 4H, CH2); 2.34 (t, 2H, OOCCH2, J 5 7.6 Hz);
4.03 (t, 2H, OCH2, J 5 6.5 Hz); 4.04 (t, 2H, OCH2, J 5 6.8 Hz);
5.10 (s, 2H, OCH2Bzl); 6.96 (dd, 2H, Ar–H, J1 5 9.0 Hz,
J2 5 4.8 Hz); 6.97 (dd, 2H, Ar–H, J1 5 8.8 Hz, J2 5 5.2 Hz);
7.18–7.23 (m, 1H, Ar–H); 7.28 (dd, 2H, Ar–H, J1 5 8.8 Hz,
J2 5 5.2 Hz); 7.32–7.35 (m, 5H, Ar–H); 7.37 (dd, 2H, Ar–H,
J1 5 8.8 Hz, J2 5 4.4 Hz); 7.44 (bs, 1H, Ar–H); 7.49 (d, 2H,
Ar–H, J 5 5.2 Hz); 7.64 (dd, 2H, Ar–H, J1 5 8.8 Hz,
J2 5 4.8 Hz); 8.14 (dd, 4H, Ar–H, J1 5 8.8 Hz, J2 5 4.8 Hz);
8.29 (dd, 2H, Ar–H, J1 5 8.4 Hz, J2 5 4.4 Hz); 13C NMR (d
ppm, CDCl3): 14.12, 22.71, 24.97, 26.00, 29.12, 29.22, 29.33,
29.36, 29.37, 29.46, 29.57, 29.60, 29.67, 29.71, 31.94, 34.35,
66.05, 68.33, 68.42, 114.31, 114.42, 120.38, 120.50, 120.98,
121.49, 122.06, 122.13, 124.63, 126.86, 128.10, 128.18, 128.48,
129.78, 131.78, 132.26, 132.37, 136.14, 137.71, 142.12, 150.84,
151.30, 155.40, 163.54, 163.79, 164.23, 164.40, 164.83, 173.55;
Elemental analysis: Calcd. for C67H78O10: C 77.42, H 7.18%;
Found: C 77.38, H 7.15%.
Pentafluorophenylesters. The appropriate carboxylic acid
(5.0 mmol), pentafluorophenol (5.0 mmol) and DMAP
(0.1 mmol) were dissolved in dry CH2Cl2 (50 ml). The reaction
mixture was cooled down to 0 uC and DCC (5.5 mmol)
dissolved in dry CH2Cl2 (10 ml) was slowly added. After
adding the last portion of DCC the cooling bath was removed
and the mixture was stirred at room temperature for 2–5 days.
The precipitated solid was removed by filtration, and the
solvent was evaporated. The crude product was purified by
centrifugal thin layer chromatography on a Chromatotron
(eluent CH2Cl2), followed by repeated crystallisation from
isopropanol and hexane. Yield was between 80 and 95%.
I-Pfp16 1H NMR (d ppm, CDCl3): 0.87 (t, 3H, CH3, J 5
6.8 Hz); 1.20–1.52 (m, 38H, CH2); 1.73–1.85 (m, 6H, CH2);
2.65 (t, 2H, OOCCH2, J 5 7.6 Hz); 4.04 (t, 2H, OCH2,
J 5 6.4 Hz); 4.04 (t, 2H, OCH2, J 5 6.6 Hz); 6.96 (d, 2H,
Ar–H, J 5 8.8 Hz); 6.97 (d, 2H, Ar–H, J 5 9.2 Hz); 7.21 (td,
1H, Ar–H, J1 5 4.6 Hz, J252 Hz); 7.27 (dd, 2H, Ar–H,
J1 5 8.8 Hz, J2 5 4.8 Hz); 7.37 (dd, 2H, Ar–H, J1 5 8.8 Hz,
J2 5 4.4 Hz); 7.44 (bs, 1H, Ar–H); 7.49 (d, 2H, Ar–H, J 5
5.2 Hz); 7.64 (dd, 2H, Ar–H, J1 5 8.8 Hz, J2 5 4.8 Hz); 8.14
(dd, 4H, Ar–H, J1 5 8.8 Hz, J2 5 4.8 Hz); 8.29 (dd, 2H, Ar–H,
J1 5 8.8 Hz, J2 5 4.4 Hz); 13C NMR (d ppm, CDCl3): 14.15,
22.74, 24.81, 26.03, 28.87, 29.14, 29.34, 29.40, 29.46, 29.60,
29.63, 29.70, 29.74, 31.97, 33.39, 68.33, 68.43, 114.31, 114.42,
120.39, 120.50, 120.99, 121.52, 122.07, 122.12, 124.64, 126.85,
128.19, 129.78, 131.78, 132.26, 132.37, 137.72, 142.12, 150.83,
151.30, 155.39, 163.51, 164.23, 164.39, 164.81; Elemental
analysis: Calcd. for C66H73F5O10: C 70.70, H 6.56%; Found:
C 70.67, H 6.93%.
Carboxylic acids. The appropriate benzyl ester (5.0 mmol)
was dissolved in THF (50 ml). The solution was flashed with
nitrogen and 200 mg of Pd/C (10% Merck) was added. After
flushing with hydrogen the hydrogenation was carried out at
2 atm. with shaking (Parr hydrogenation apparatus) for 4 h.
Then the solution was filtered, THF evaporated under reduced
pressure and the crude product was purified by column
chromatography (eluent CH2Cl2/10% MeOH). The repeated
crystallisation from methanol gave the desired products with
yields of 80 to 90%. I-H16: 1H NMR (d ppm, CDCl3): 0.87 (t,
3H, CH3, J 5 7.0 Hz); 1.26–1.36 (m, 34H, CH2); 1.44–1.48 (m,
Dendrimer of the first generation 1-16. To a solution of BAB-
(4) dendrimer (54 mg, 0.17 mmol), TEA (5 ml) in dichloro-
methane (10 ml) the pentafluorophenylester I-Pfp16 (841 mg,
0.75 mmol) in CH2Cl2 (5 ml) was added. The solution was
stirred at room temperature for 7 days. After that the reaction
mixture was washed with water (6 2), aqueous sodium
hydroxide, water (6 2), and finally with brine. Crystallisation
from MeOH–EtOH–CHCl3 (10 : 9 : 1), isopropanol and
sequential chromatographic separations (CH2Cl2) followed by
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crystallisation from methanol gave a colourless solid with yield
40%. 1H NMR (d ppm, CDCl3): 0.87 (t, 12H, CH3, J 5 6.8 Hz);
1.20–1.47 (m, 154H, CH2); 1.59–1.62 (m, 16H, CH2); 1.76–1.84
(m, 18H, CH2); 2.15 (t, 8H, NHOCCH2, J 5 7.6 Hz); 2.34 (bs,
4H, NCH2); 2.39 (t, 8H, NCH2, J1 5 6.4 Hz); 3.27 (td, 8H,
NHCH2, J1 5 6.4 Hz, J2 5 6.4 Hz); 4.01 (t, 8H, OCH2,
J 5 6.8 Hz); 4.03 (t, 8H, OCH2, J 5 6.8 Hz); 6.46 (t, 4H, NH,
J 5 5.6 Hz); 6.96 (d, 16H, Ar–H, J 5 8.8 Hz); 7.18–7.21 (m,
4H, Ar–H); 7.26 (d, 8H, Ar–H, J 5 8.8 Hz); 7.36 (d, 8H,
Ar–H, J 5 8.8 Hz); 7.43 (bs, 4H, Ar–H); 7.48 (d, 8H, Ar–H,
J 5 4.8 Hz); 7.62 (d, 8H, Ar–H, J 5 8.8 Hz); 8.12 (d, 8H,
Ar–H, J 5 8.8 Hz); 8.14 (d, 8H, Ar–H, J 5 8.8 Hz); 8.28 (d,
8H, Ar–H, J 5 8.4 Hz); 13C NMR (d ppm, CDCl3): 14.14,
22.73, 25.91, 26.02, 27.15, 29.14, 29.39, 29.47, 29.51, 29.59,
29.62, 29.68, 29.72, 31.95, 36.84, 38.20, 51.97, 53.88, 68.33,
68.41, 106.32, 114.29, 114.39, 120.34, 120.48, 120.96, 121.46,
122.04, 122.10, 124.60, 126.83, 128.15, 129.76, 131.74, 132.23,
132.34, 137.68, 142.06, 150.79, 151.27, 155.36, 163.48, 163.75,
164.19, 164.35, 164.77, 173.18; MALDI-TOF MS: molecular
weight calc. for C256H328N6O36: m/z: 4086.9 [M + Na]+;
found: m/z: 4086.9 [M + Na]+; Elemental Analysis: Calcd. for
C256H328N6O36: C 75.63, H 8.13, N 2.07%; Found: C 74.32, H
7.83, N 2.10%.
‘‘Supermolecular Liquid Crystal Dendrimers’’ under contract:
HPRN-CT-2000-00016 and the Deutsche Forschungs-
gemeinschaft (GRK 984). Physical studies were supported by
Grant KBN 4T09A 00425. R.A.R. is grateful to the Alexander
von Humboldt Foundation for research fellowship.
Dorota Kardas,§a Marko Prehm,a Ute Baumeister,b Damian Pociecha,c
R. Amaranatha Reddy,a Georg H. Mehld and Carsten Tschierske*a
aInstitute of Organic Chemistry, Martin-Luther University,
06120 Halle, Kurt-Mothes Str.2, Germany.
E-mail: carsten.tschierske@chemie.uni-halle.de; Fax: +49 345 5527346;
Tel: +49 345 5525664
bInstitute of Physical Chemistry, Martin-Luther-University
Halle-Wittenberg, Mu¨hlpforte 1, D-06108 Halle, Germany
cWarsaw University, Department of Chemistry, Al. Zwirki i Wigury
101, 02089 Warsaw, Poland
dThe Hull University, Department of Chemistry, Cottingham Road,
HU7 6RX, Hull, UK
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The precipitate was filtered out, washed with water and dried.
Crystallisation from methanol, column chromatography (silica
gel, CH2Cl2) followed by crystallisation from methanol gave a
slightly yellow solid with yield 40%. 1H NMR (d ppm, CDCl3):
0.81 (t, 24H, CH3, J 5 6.8 Hz); 1.20–1.43 (m, 886H, CH2);
1.20–1.43 (m, 24H, CH2); 1.54–1.64 (bs, 16, CH2); 1.70–1.78
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(m, 16H, NH, Ar–H); 7.25 (d, 16H, Ar–H, J 5 8.8 Hz); 7.37
(d, 16H, Ar–H, J 5 8.8 Hz); 7.41 (bs, 8H, Ar–H); 7.47 (d, 16H,
Ar–H, J 5 4.8 Hz); 7.60 (d, 16H, Ar–H, J 5 8.8 Hz); 8.11 (d,
16H, Ar–H, J 5 8.8 Hz); 8.12 (d, 16H, Ar–H, J 5 8.8 Hz); 8.27
(d, 16H, Ar–H, J 5 8.4 Hz); 13C NMR (d ppm, CDCl3): 14.35,
22.93, 26.22, 29.34, 29.60, 29.73, 29.83, 29.90, 29.92, 29.93,
32.16, 38.12, 51.58, 52.24, 54.32, 68.56, 68.64, 114.57, 114.67,
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128.46, 130.09, 132.55, 132.66, 137.98, 142.35, 151.09, 151.58,
155.68, 163.82, 164.09, 164.55, 164.72, 165.14; MALDI-TOF
MS: molecular weight calc. for C520H672N14O72: m/z: 8294.1
[M + Na]+; found: m/z: 8294.1 [M + Na]+; Elemental Analysis:
Calcd. for C520H672N14O72: C 75.51, H 8.19, N 2.37%; Found:
C 75.16, H 8.15, N 2.60%.
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The authors thank the European Union for funding of
this work within the framework of the RTN network
1732 | J. Mater. Chem., 2005, 15, 1722–1733
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