H-Shape mesogenic dimers-the spacer parity effect

Article abstract of DOI:10.1039/c7ra02730c

It was found that for H-shape dimers, the parity of the number of atoms in the spacer linking the mesogenic cores has important influence on the mesogenic properties only for the molecules with weak mesogenic core anisotropy. In the case of stronger core

Full text of DOI:10.1039/c7ra02730c

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H-Shape mesogenic dimers – the spacer parity
effect†
Cite this: RSC Adv., 2017, 7, 20354
*
J. M. Wolska,
M. Kolpaczynska, J. Mieczkowski, D. Pociecha and E. Gorecka
It was found that for H-shape dimers, the parity of the number of atoms in the spacer linking
the mesogenic cores has important influence on the mesogenic properties only for the molecules
with weak mesogenic core anisotropy. In the case of stronger core anisotropy, the parallel
arrangement of mesogenic units is induced regardless of the spacer parity. As a result, phase
transition temperatures and layer spacing are only weakly affected by spacer parity. By studying the
properties of six new homologue series it was found that for H-shape dimers the orthogonal
smectic (SmA) is strongly disfavoured: most compounds form a tilted smectic (SmC) phase, which is
related to hindrances in molecular rotation for molecules with large breath to length ratio. For
dimers with very long spacer, and thus decoupled mesogenic units, the smectic phase is replaced by
a nematic phase, and for stiff polycatenar molecules with very short spacers the cubic phase can
appear.
Received 6th March 2017
Accepted 31st March 2017
DOI: 10.1039/c7ra02730c
rsc.li/rsc-advances
cores are connected end-to-end also other molecular geome-
tries were recently investigated, e.g. T-shape,13 U-shape14 or H-
shape15 molecules (Fig. 1).
Introduction
Liquid crystalline dimers and oligomers, as compounds with
intermediate structures between monomers and polymers,
have always been an important class of mesogenic
compounds. Their unique properties result from the addi-
tional degree of freedom due to the presence of exible chain
linking mesogenic cores.1–3 Dimers oen exhibit phases rarely
observed for monomers; they easily form modulated smec-
tics,4 polar smectics5 and broken-layer type columnar phases;6
there is also a limited number of reports that dimers might
exhibit cubic phases.7 As mesogenic cores the rod-like,2,3,8 disc-
like9 or bent-shape10 units were applied in molecular design.
For the most studied dimers, with end-to-end connected rod-
like mesogenic units, it was found the number of atoms in
spacer is of primary importance for the type of the phase
formed as well as transition temperatures.2,3,11 The parity of
spacer affects the overall molecular shape2 (Fig. 1), for even
number of atoms in the spacer molecules adopt zigzag
geometry, in which the mesogenic units are anti-parallel,
whereas the spacer with odd number of atoms results in
bent shape of the molecule, with the mesogenic units being
inclined to each other.2,3 The interest in dimers having bent
shape was strongly stimulated by recent discovery of twist-
bend nematic (NTB) phase, the heliconical phase made by
achiral molecules.8,12 Apart of dimers, in which two mesogenic
Herein, we describe 6 new series of laterally linked,
symmetric dimeric molecules (H-shape), built of rod-like
mesogenic cores interconnected through exible alkoxy
spacers of different length (n ¼ 1, 3–10) (Scheme 1).
The rod-like units having different number of phenyl rings
were used in order to study inuence of geometrical anisot-
ropy of mesogenic core on the phase properties. Further
modication of molecular geometry was obtained by a varia-
tion of number and length of terminal chains. The
phase transition temperatures for studied materials were
collected inTables 1–6 and the phase sequences are presented
in Fig. 2.
Department of Chemistry, Warsaw University, Pasteura 1, 02-093 Warsaw, Poland.
E-mail: jokos@chem.uw.edu.pl; Tel: +48 22 5526270
† Electronic
supplementary
information
(ESI)
available:
Chemical
characterization of obtained materials and detailed description of experimental
methods used for structure studies. See DOI:10.1039/c7ra02730c
Fig. 1 Types of dimers and different conformations of molecules due
to the odd–even effect.
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Scheme 1 Molecular structures of the investigated compounds.
Fig. 3 Smectic layer spacing and width of corresponding diffraction
signal vs. temperature for compound I.7.
For longer homologues with even spacers, monotropic nematic
phase was observed. Molecules with odd spacers, in general,
had better mesogenic properties, they all formed nematic
phase, and additionally for homologues n ¼ 5 and 7 a partially
bilayer smectic Ad phase was found, with the layer spacing
d slightly larger than the estimated molecular length (d/L ꢀ 1.1).
Interestingly, compound I.7 exhibited rare, for dimers, phase
sequence with re-entrant nematic phase (Nre) formed below the
smectic Ad phase. The N–SmAd–Nre phase sequence has been
conrmed by XRD measurements, the transitions between
smectic and nematic phases were signied by the broadening of
the diffraction signal related to the lamellar structure, due to
the loss of long-range positional order (Fig. 3). The half-width of
XRD signal measured in both nematic phases was similar
(Fig. 3), indicating comparable correlation length of positional
order in N and Nre phases.
The phase properties of homologues of the Series II, having
the dodecyloxy chains instead of CN group, attached to the
biphenyl units are collected in Table 2.
Compounds II.1–II.8 exhibited the SmA–SmC phase
sequence on cooling, while for the longest spacer homologues,
II.9–II.10, a SmA phase was replaced by nematic phase. The
richest polymorphism was found for even spacer compound
II.4, which formed additional orthogonal smectic B phase below
the SmC, however monotropic character of the phase prevented
its detailed characterization. The temperature dependence of
smectic layer thickness evaluated from XRD experiments
conrmed continuous character of the SmA–SmC phase tran-
sition (Fig. 4) for all the homologues. Clear odd–even effect
Fig. 2 Phase diagrams for the studied homologue Series I–VI.
Results and discussion
Most of the compounds of Series I with simple cyanobiphenyl
unit in the mesogenic cores exhibited liquid crystalline phases
(Table 1, Fig. 2) except those with short even spacers (n ¼ 4, 6).
Table 1 Series I phase transitions temperatures (in ꢁC) and in parenthesis transition enthalpies (in kJ molꢂ1
)
I.n
mp
Nre
SmA
N
Iso
I.1
I.3
I.4
I.5
I.6
I.7
I.8
I.9
I.10
121.7 (66.4)
145.6 (79.8)
156.4 (108.4)
132.8 (83.4)
139.8 (41.0)
87.9 (78.5)
114.4 (58.1)
106.2 (80.6)
113.8 (81.3)
C
C
205.2 (2.1)
144.4 (2.0)
C
C
C
C
C
C
C
C
C
C
C
116.6 (0.06)
89.8 (0.03)
C
121.8 (1.9)
C
56.7 (0.1)
C
C
C
C
110.8 (0.1)
104.5 (0.7)
103.6 (0.9)
105.0 (0.7)
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Table 2 Series II – phase transitions temperatures (in ꢁC) and in parenthesis transition enthalpies (in kJ molꢂ1
)
II.n
mp
SmB
SmC
SmA
N
Iso
II.1
II.3
II.4
II.5
II.6
II.7
II.8
II.9
II.10
117.6 (37.5)
104.3 (77.2)
118.9 (111.7)
122.0 (49.6)
94.2 (74.3)
83.1 (79.6)
96.6 (86.7)
80.3 (35.8)
78.3 (56.0)
C
C
C
C
C
C
C
C
C
150a
C
C
C
C
C
C
C
181.0 (14.8)
143.7 (16.8)
132.6 (16.6)
124.6 (15.2)
106.9 (4.0)
106.6 (9.4)
105.6 (8.6)
C
C
C
C
C
C
C
120 m
125 m
114.5 (0.1)
85 m
93 m
95 m
C
96.7 (14.1)
77.6 (0.1)
80.4 (0.4)
C
C
98.3 (3.6)
98.4 (3.4)
C
C
a
From microscopic observations.
regarding the layer spacing in smectic phase was observed
Elongation of the rigid mesogenic cores by additional phenyl
(Fig. 4), even spacer homologues showed slightly larger d values. ring attached to biphenyl unit through the ester linkage (Series
For all the homologues the layer spacing was found to be IV) caused strong increase of liquid crystalline phases stability,
much smaller than molecular length (estimated to be ꢀ60 A for the clearing temperatures for compounds IV.n were higher by
even spacer and ꢀ50 A for odd spacer homologues) showing more than 50 K comparing to their II.n analogues.
strong interdigitation of terminal chains between neighbouring
All the compounds of Series IV exhibited similar LC poly-
layers. In SmA phase the layer expansion is negative and similar morphism, smectic C and nematic phases were observed (Table
for all materials, while the thermal expansion coefficient in 4). Contrary to Series II, for the homologues of Series IV clear
SmC phase changes its sign upon elongation of the spacer, on odd–even effect was found regarding the phase transition
heating, far from SmA phase transition temperature, the temperatures, the effect is clearly visible for intermediate
contraction of the layers was found for compounds II.1 and II.3, homologues (Fig. 2), interestingly changing the parity of the
and for longer homologues layer thickness monotonically linkage chain has opposite inuence on the melting and
increased in whole temperature range (Fig. 4). The effect might clearing temperatures – the clearing temperature of even spacer
be explained by different degree of terminal chain interdigita- homologues was higher while melting temperature lower than
tion between layers, that is more signicant for molecules with for odd spacer compounds.
longer spacer between mesogenic cores.
Further modication of the molecular architecture by
For compounds of Series III, the azo group was introduced attaching additional terminal dodecyloxy chains (one in Series
into mesogenic core, such elongation of mesogenic core resul- V and two in Series VI) to each mesogenic core resulted in
ted in destabilization of the SmA phase on behave of nematic destabilization of LC phases; lowering of the clearing
phases, the phase sequence with N and SmC phase was
observed for all homologues (Table 3). Due to the presence of
Table 3 Series III – phase transitions temperatures (in ꢁC) and in
azo group the materials were photosensitive, absorption of UV
light caused the trans–cis isomerization of azo unit (see ESI†) parenthesis transition enthalpies (in kJ molꢂ1
)
that disrupted the mesogenic properties.
III.n
mp
SmC
N
Iso
III.3
III.5
III.7
III.10
104.3 (89.3)
114 (161.4)
77.6 (105.5)
106.7 (139.0)
C
C
C
C
128.3 (0.3)
104.7 (1.0)
89.5 (0.3)
87.9 (1.8)
C
C
C
C
133.5 (15.5)
110.6 (7.9)
100.6 (1.6)
100.6 (4.8)
C
C
C
C
Table 4 Series IV phase transitions temperatures (in ꢁC) and in
parenthesis transition enthalpies (in kJ molꢂ1
)
IV.n
mp
SmC
N
Iso
IV.1
IV.3
IV.4
IV.5
IV.6
IV.7
IV.8
IV.9
IV.10
132.5 (59.3)
152.2 (75.2)
88.3 (17.9)
108.4 (24.9)
94.3 (21.0)
102.7 (25.1)
90.4 (54.6)
103.6 (38.3)
122.1 (84.8)
C
C
C
C
C
C
C
C
C
215.2 (4.2)
167.8 (2.9)
170.1 (6.1)
154.3 (5.0)
159.8 (5.2)
137.8 (5.1)
150.3 (3.5)
136.0 (3.7)
142.5 (3.3)
C
C
C
C
C
C
C
C
C
258.6 (4.0)
199.6 (4.6)
188.8 (5.1)
173.0 (2.9)
183.4 (3.4)
172.1 (3.3)
180.3 (3.0)
175.4 (3.5)
178.0 (2.9)
C
C
C
C
C
C
C
C
C
Fig. 4 Smectic layer spacing vs. temperature for homologues II.n. In
the inset the layer spacing in SmA phase at the transition to SmC phase
vs. spacer length, n.
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Table
5
Series V phase transitions temperatures (in ꢁC) and in
optically isotropic, while the XRD experiments indicated pres-
ence of long-range positional order of molecules. The XRD
patterns showed series of sharp diffraction signals at low angle
range and a diffused signal at the high angle range proving the
liquid crystalline character of the phase (Fig. 5). The best tting
of the low-angle part of the diffractogram was obtained
assuming 3D crystallographic lattice of Im3m symmetry and
lattice parameter a ¼ 176.8 A (at T ¼ 50 ꢁC), corresponding
roughly to 3 molecular lengths. Assuming the density of the
cubic phase 1 g cmꢂ3, the number of dimeric molecules in the
unit cell was estimated to be as high as 1440.
parenthesis transition enthalpies (in kJ molꢂ1
)
V.n
mp
SmC
Iso
V.1
V.3
V.4
V.5
V.6
V.7
V.8
V.9
V.10
120.2 (69.2)
140.0 (69.2)
125.0 (14.7)
130.1 (6.6)
95.0 (52.4)
119.8 (52.0)
93.7 (41.1)
110.3 (37.5)
88.9 (34.9)
C
C
C
C
C
C
C
C
C
164.9 (8.3)
C
C
C
C
C
C
C
C
C
138.8 (24.6)
139.6 (22.3)
135.6 (15.3)
123.7 (20.0)
123.3 (21.6)
121.7 (14.7)
120.5 (20.5)
121.4 (21.0)
Experimental
Synthetic procedures
Table 6 Series VI phase transitions temperatures (in ꢁC) and in
parenthesis heat transition enthalpies (in kJ molꢂ1
)
Detailed synthetic procedures are shown in Scheme 2. Series I–
VI were prepared by condensation of two parts: rod-like ligands
providing liquid crystalline properties of nal compounds, and
H-shaped dimeric units with an alkyl spacer providing odd–
even behavior. Series I was prepared with commercially avail-
able 4-cyanobiphenol (9). The 4,40-biphenol (1) was used as
a main rigid fragment of rod-like compounds. The one
exemption was 4-hydroxy-40(4-octadecyloxy)diazobenzene (12)
prepared in 3-steps: alkylation of 4-nitrophenol, reduction of
nitro group to amine group (11), and nal azo coupling with
phenol (12). All alkoxy derivatives were obtained via Williamson
reaction, carried out in anhydrous DMF in presence of KI and
K2CO3 (a). All ester derivatives were prepared by esterication
reaction in anhydrous THF in presence of TEA and DMAP (b).
The compounds were puried by recrystallization from MeOH,
toluene, hexane or by column chromatography using CH2Cl2,
toluene, and mixture of MeOH/CHCl3 as eluents. All H-shaped
units were prepared via alkylation reaction of ethyl 4-
dodecyloxy-2-hydroxybenzoate (13) with appropriate dihalo-
genic alkanes. Hydrolysis and further acylation reaction allowed
receiving H-shaped acidic chlorides (16/n) common for all
Series I–VI and used in nal esterication reaction with char-
acteristic rod-like ligands. For more details see ESI.†
VI.n mp
SmC
SmA
CubIm3m
Iso
VI.1 54.1 (80.8)
C
108.0
(3.9)
C
VI.5 80.9 (13.2)
VI.7 57.6 (52.9)
C
C
C
C
61.0
(2.1)
61.4
(3.1)
VI.9 37.4 (94.8)
C
41.1
(1.6)
C
temperature was the strongest in case of molecules with three
dodecyloxy chains. Compounds of Series V showed exclusively
tilted smectic C phase, with clearing temperatures lower by 40–
90 K in comparison to analogue compounds of Series IV; while
an orthogonal smectic A phase was observed for two homo-
logues of Series VI with long spacers n ¼ 7 and 9.
For the compound VI.1, with three terminal chains and the
shortest linkage, another type of LC phase was found – instead
of lamellar phases, a cubic LC phase was formed. The phase was
Materials and methods
Temperatures and thermal effects of the phase transitions were
determined by calorimetric studies using TA Q200 calorimeter,
samples of mass 1–3 mg were sealed in aluminum pans and
kept in nitrogen atmosphere during measurement. Both heat-
ing and cooling scans with rate 10 K minꢂ1 were applied. The
optical studies were performed using Zeiss Imager A2m polar-
izing microscope equipped with Linkam heating stage. The
small angle X-ray diffraction patterns were obtained with Bruker
Nanostar system (CuKa radiation, three pinhole collimation
system, area detector VANTEC 2000, MRI TCP-U heating stage),
while wide angle diffraction experiments were performed with
Bruker GADDS diffractometer (CuKa radiation, point colli-
mator, Vantec 2000 area detector, modied Linkam heating
stage). Samples were prepared in a form of droplet on heated
surface, their temperature was controlled with precision 0.1 K.
For UV-vis experiment the Shimadzu UV-3101PC spectrometer
Fig.
5 Low angle X-ray diffractogram (black line) registered for
compound VI.1 at 50 ꢁC. The fitting curve (red line) was obtained
assuming crystallographic lattice with Im3m symmetry and unit cell
parameter a ¼ 176.8 A. In the inset 2D XRD pattern recorded in broad
diffraction angle range; diffused high angle signal evidences liquid
crystalline character of the phase.
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Fig. 6 Molecular structure of odd (II.5) and even (II.6) spacer homo-
logues of Series II, with parallel and antiparallel orientation of meso-
genic cores.
However, only for Series I, with molecules having weak core
anisotropy, the odd–even effect was pronounced; all odd
spacer homologues exhibited LC phases in broad temperature
range, while short, even spacer homologues were not meso-
genic; apparently the molecules with mesogenic units in
antiparallel and laterally shied conguration disfavoured
formation of LC phases. For other studied homologue series
the odd–even effect was less pronounced. For compounds of
Series IV the inuence of spacer parity was opposite to this
observed in Series I, the even spacer homologues had slightly
higher clearing temperatures and thus larger range of LC
phases. Since the odd–even effect is weak one can conclude
that for molecules with cores of larger anisotropy the geometry
of even and odd spacer dimers is not much different, in both
cases probably nearly parallel arrangement of mesogenic units
is obtained, for even spacers this requires gauche conforma-
tions of alkyl linkage. Similar molecular geometry of odd and
even spacer homologues is also consistent with only small
differences of the smectic layer thickness of consecutive
homologues of Series II and IV. Clear, but small parity effect
has been observed only for Series II – even spacer dimers have
slightly higher layer spacing.
Scheme 2 Synthesis of the H-dimers; (a): K2CO3, KI, DMF, (b): DMAP,
TEA, THF.
Regarding the phase situation, for all homologue series it
was observed that tilted smectic (SmC) phase is more favourable
than the orthogonal one (SmA). The formation of uniaxial SmA
phase requires that molecules rotate freely along their long
molecular axis, and such rotation for molecules with large
breath to length ratio, might be energetically disfavourable. For
molecules with hinderent rotation the packing into the biaxial
structure of SmC phase seems to be more favourable.
For the most stiff, polycatenar dimer VI.1 with three terminal
chains, instead of lamellar phase a cubic phase was observed,
indicating that efficient packing of molecules required curving
of the interface between areas occupied by aromatic cores and
alkyl tails, which is realized by formation of tri-continuous type
cubic Im3m structure.
was used and the conformational changes were induced upon
illumination with UV Hamamatsu lamp.
Conclusions
It was expected that the mesogenic properties of H-shape
dimers should depend on the length of the spacer. Indeed for
all homologue series the clearing temperature steeply decreases
with elongation of the spacer, showing that less stiff molecular
structure disfavours mesophase formation. Moreover, it was
also observed that for longer spacers the smectic A phase is
replaced by nematic phase (Series II), showing that for decou-
pled mesogenic cores formation of smectic layers is more
difficult. Also the spacer parity should affect mesogenic prop-
Acknowledgements
erties, as for odd and even number of atoms in the linkage the The studies were supported by Polish National Science Centre,
molecular geometry is expected to be much different (Fig. 6).
grant no. 2011/01/N/ST5/03314.
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9 T. Sakurai, K. Tashiro, Y. Honsho, A. Saeki, S. Seki, A. Osuka,
A. Muranaka, M. Uchiyama, J. Kim, S. Ha, K. Kato, M. Takata
and T. Aida, J. Am. Chem. Soc., 2011, 133, 6537; J. Vergara,
J. Barbera, J. L. Serrano, M. B. Ros, N. Sebastian, R. de la
Fuente, D. O. Lopez, G. Fernandez, L. Sanchez and
N. Martin, Angew. Chem., Int. Ed., 2011, 50, 12523.
Notes and references
1 C. T. Imrie andG. R. Luckhurst,Handbook of Liquid
Crystals,Wiley-VCH,Weinheim,2014,vol. 7,pp. 137–210, and
references cited therein.
2 C. T. Imrie and P. A. Henderson, Chem. Soc. Rev., 2007, 36,
2096.
´
10 N. Sebastian, N. Gimeno, J. Vergara, D. O. Lopez,
J. L. Serrano, C. L. Folcia, M. R. de la Fuente and
M. B. Ros, J. Mater. Chem. C, 2014, 2, 4027;
C. M. Hegguilustoy, M. B. Darda, R. S. Montani,
B. Heinrich, B. Donnio, D. Guillon and R. O. Garay, Liq.
Cryst., 2015, 42, 1013; M. Horcic, J. Svoboda, V. Novotna,
D. Pociecha and E. Gorecka, Chem. Commun., 2017, 53, 2721.
11 R. W. Date, C. T. Imrie, G. R. Luckhurst and J. M. Seddon,
Liq. Cryst., 1992, 12, 203.
12 D. Chen, J. H. Porada, J. B. Hooper, A. Klittnick, Y. Shen,
M. R. Tuchband, E. Korblova, D. Bedrov, D. M. Walba,
M. A. Glaser, J. E. Maclennan and N. A. Clark, Proc. Natl.
Acad. Sci. U. S. A., 2013, 110, 15931.
3 P. A. Henderson and C. T. Imrie, Liq. Cryst., 2011, 38, 1407.
4 D. Chen, M. Nakata, R. Shao, M. R. Tuchband, M. Shuai,
U. Baumeister, W. Weissog, D. M. Walba, M. A. Glaser,
J. E. Maclennan and N. A. Clark, Phys. Rev. E: Stat.,
Nonlinear, So Matter Phys., 2014, 89, 022506; D. Pociecha,
D. Kardas, E. Gorecka, J. Szydlowska, J. Mieczkowski and
D. Guillon, J. Mater. Chem., 2003, 13, 34.
5 Y. Shimbo, E. Gorecka, D. Pociecha, F. Araoka, M. Goto,
Y. Takanishi, K. Ishikawa, J. Mieczkowski, K. Gomola and
H. Takezoe, Phys. Rev. Lett., 2006, 97, 113901;
J. Mieczkowski, K. Gomola, J. Koseska, D. Pociecha,
J. Szydlowska and E. Gorecka, J. Mater. Chem., 2003, 13,
2132; H. N. S. Murthy, M. Bodyagin, S. Diele,
U. Baumeister, G. Pelzl and W. Weissog, J. Mater. Chem.,
2006, 16, 1634.
6 Y. Takanishi, M. Toshimitsu, M. Nakata, N. Takada,
T. Izumi, K. Ishikawa, H. Takezoe, J. Watanabe,
Y. Takahashi and A. Iida, Phys. Rev. E: Stat., Nonlinear, So
Matter Phys., 2006, 74, 051703; T. Izumi, Y. Naitou,
Y. Shimbo, Y. Takanishi, H. Takezoe and J. Watanabe, J.
Phys. Chem. B, 2006, 110, 23911.
7 B.-K. Cho, J.-H. Ryu, W.-C. Zin and M. Lee, Polym. Bull., 2000,
44, 393; T. Kajitani, S. Kohmoto, M. Yamamoto and
K. Kishikawa, Chem. Mater., 2005, 17, 3812; J. M. Wolska,
D. Pociecha, J. Mieczkowski and E. Gorecka, Liq. Cryst.,
2016, 43, 235.
13 A. Yoshizawa, M. Sato and J. Rokunohe, J. Mater. Chem.,
2005, 15, 3285.
14 G. S. Attard and A. G. Douglass, Liq. Cryst., 1997, 22, 349.
15 W. Weissog, D. Demus, S. Diele, P. Nitschke and
W. Wedler, Liq. Cryst., 1989, 5, 111; S.-M. Huh and J.-I. Jin,
Liq. Cryst., 1998, 25, 285; W. Wedler, D. Demus,
H. Zaschke, K. Mohr, W. Schafer and W. Weissog, J.
Mater. Chem., 1991, 1, 347; W.-S. Bae, J.-W. Lee and
J.-I. Jin, Liq. Cryst., 2001, 28, 59; J. Andersch, C. Tschierske,
S. Diele and D. Lose, J. Mater. Chem., 1996, 6, 1297;
B. Kumar, A. K. Prajapati, M. C. Varia and K. A. Suresh,
Langmuir, 2009, 25, 839; Y. Zhang, J. Martinez-Perdiguero,
U. Baumeister, C. Walker, J. Etxebarria, M. Prehm,
J. Ortega, C. Tschierske, M. J. O'Callaghan, A. Harant and
M. Handschy, J. Am. Chem. Soc., 2009, 131, 18386;
A. K. Prajapati, M. C. Varia and S. P. Sahoo, Liq. Cryst.,
2011, 38, 861; M. Kolpaczynska, K. Madrak,
8 M. G. Tamba, S. M. Salili, C. Zhang, A. Jakli, G. H. Mehl,
R. Stannarius and A. Eremin, RSC Adv., 2015, 5, 11207;
M. Cestari, S. Diez-Berart, D. A. Dunmur, A. Ferrarini,
M. R. de la Fuente, D. J. B. Jackson, D. O. Lopez,
G. R. Luckhurst, M. A. Perez-Jubindo, R. M. Richardson,
J. Salud, B. A. Timimi and H. Zimmermann, Phys. Rev. E:
Stat., Nonlinear, So Matter Phys., 2011, 84, 031704;
V. Borshch, Y.-K. Kim, J. Xiang, M. Gao, A. Jakli,
V. P. Panov, J. K. Vij, C. T. Imrie, M. G. Tamba, G. H. Mehl
and O. D. Lavrentovich, Nat. Commun., 2013, 4, 2635.
´
J. Mieczkowski, E. Gorecka and D. Pociecha, Liq. Cryst.,
2011, 38, 149; T. Sakurai, K. Tashiro, Y. Honsho, A. Saeki,
S. Seki, A. Osuka, A. Muranaka, M. Uchiyama, J. Kim,
S. Ha, K. Kato, M. Takata and T. Aida, J. Am. Chem. Soc.,
2011, 133, 6537; J. Vergara, J. Barbera, J. L. Serrano,
M. B. Ros, N. Sebastian, R. de la Fuente, D. O. Lopez,
G. Fernandez, L. Sanchez and N. Martin, Angew. Chem., Int.
Ed., 2011, 50, 12523.
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