Transition between triangular and square tiling patterns in liquid-crystalline honeycombs formed by tetrathiophene-based bolaamphiphiles

Article abstract of DOI:10.1039/c3sc50664a

A series of 5,5′′′-diphenyl tetrathiophenes with polar glycerol groups at each end and two lateral flexible chains self-assemble into a series of liquid-crystalline honeycombs, formed by the π-conjugated rods which enclose polygonal prismatic cells filled by the lateral chains. With increasing chain length a discontinuous transition from triangular to square honeycombs takes place. At this transition a periodic honeycomb composed of a mixture of square and triangular cells in a ratio 1:2 was formed at low temperature, whereas at higher temperature a hexagonal columnar phase composed of triangular and randomly distributed rhombic cells, a new kind of cybotactic nematic phase, and also a cybotactic isotropic phase, both composed of square honeycomb fragments, represent the intermediate states. This provides an example of a dynamic self-assembled system where, depending on the molecular mobility, the transition between two periodic structures with different symmetry either leads to an increase of complexity, or to a chaotic regime with reduced order.

Full text of DOI:10.1039/c3sc50664a

Chemical Science
View Article Online
View Journal | View Issue
EDGE ARTICLE
Transition between triangular and square tiling patterns
in liquid-crystalline honeycombs formed by
tetrathiophene-based bolaamphiphiles†
a
Cite this: Chem. Sci., 2013, 4, 3317
Xiaohong Cheng, Hongfei Gao,a Xiaoping Tan,a Xueyan Yang,a Marko Prehm,b
*
b
b
*
Helgard Ebert and Carsten Tschierske
A series of 5,5000-diphenyl tetrathiophenes with polar glycerol groups at each end and two lateral flexible
chains self-assemble into a series of liquid-crystalline honeycombs, formed by the p-conjugated rods which
enclose polygonal prismatic cells filled by the lateral chains. With increasing chain length a discontinuous
transition from triangular to square honeycombs takes place. At this transition a periodic honeycomb
composed of a mixture of square and triangular cells in a ratio 1 : 2 was formed at low temperature,
whereas at higher temperature a hexagonal columnar phase composed of triangular and randomly
distributed rhombic cells, a new kind of cybotactic nematic phase, and also a cybotactic isotropic phase,
both composed of square honeycomb fragments, represent the intermediate states. This provides an
example of a dynamic self-assembled system where, depending on the molecular mobility, the transition
between two periodic structures with different symmetry either leads to an increase of complexity, or to
a chaotic regime with reduced order.
Received 9th March 2013
Accepted 7th June 2013
DOI: 10.1039/c3sc50664a
www.rsc.org/chemicalscience
representing 2D nets extended into the third dimension, have
been developed with liquid-crystalline (LC) phases formed by T-
Introduction
In recent years numerous efforts have been made to use non-
covalent interactions for the generation of nano-structured
materials by self-assembly.1 A striking feature of self-assembling
and self-organizing systems is spontaneous pattern formation,2
which can, for example, lead to periodic arrays. Two-dimensional
(2D) arrays represent useful model systems to study the funda-
mentalrelations betweenmolecular structureandself-assembled
superstructure in a systematic way starting from simple to more
complexmodes. Besidesthis fundamentalscienticinterestsuch
arrays also have a signicant potential for nanotechnological
applications, for example as components of optoelectronic or
organic electronic devices. Most work in the eld of nano-sized
pattern formation by self-assembly was done with polygonal nets
on surfaces, where rigid building blocks are interconnected into
2D nets by means of metal coordination, hydrogen bonding or
van der Waals forces, combined with surface interactions.3–6
Parallel to this development, in the eld of so matter engi-
neering 2D arrays of cylinders, forming honeycombs and thus
shaped or X-shaped polyphiles composed of a rod-like core,
incompatible end groups and laterally attached chains.7–13 Fig. 1
shows the development of representative honeycomb LC phase
structures in a series of X-shaped bolaamphiphiles 1/n, repre-
senting 5,50-diphenyldithiophenes with alkyl lateral chains and
glycerol end groups.14 In the LC honeycombs formed by these
molecules the rod-like aromatic units are arranged parallel,
forming walls. The glycerol end-groups fuse these walls to
aChemistry Department, Yunnan University, Kunming, Yunnan 650091, P. R. China.
E-mail: xhcheng@ynu.edu.cn; Fax: +86 871 5032905
bInstitute of Chemistry, Organic Chemistry, Martin-Luther University Halle-
Wittenberg, Kurt-Mothes Str. 2, 06120 Halle/Saale, Germany. E-mail: carsten.
tschierske@chemie.uni-halle.de; Fax: +49 345 55 27346
Fig. 1 Development of honeycomb LC phases of 5,50-diphenyl-2,20-dithiophene
based double-chain bolaamphiphiles depending on alkyl chain length; the
models show the cross-section through the polygonal honeycombs perpendicular
to the cylinder long axis; black: aromatic cores; blue: glycerol groups; the space in
the cells between the aromatic cores is filled by the lateral alkyl chains.14
† Electronic supplementary information (ESI) available: Synthesis, analytical data,
additional X-ray data and textures; discussion of honeycomb walls. See DOI:
10.1039/c3sc50664a
This journal is ª The Royal Society of Chemistry 2013
Chem. Sci., 2013, 4, 3317–3331 | 3317

View Article Online
Chemical Science
Edge Article
polygonal honeycombs by dynamic hydrogen-bonding networks
The focus in this work is on oligothiophenes because these
along the edges and the prismatic cells resulting inside the units have been proven to represent an interesting class of
honeycombs (the channels) are lled with the lateral organic semiconductors.27–30 In this respect it would also be of
chains.7,8,11,15 With growing volume of the lateral chains the interest to nd ways to organize this type of p-conjugated
prismatic cells change their cross-sections from triangular via aromatics into well-dened arrays. Especially their self-healing
square and pentagonal to hexagonal and beyond.8,10 Projected on capability makes LC oligothiophenes interesting materials for
an Euclidean plane these LC phases can be considered as edge-to- semiconducting organic materials.31–33 Previously reported LC
edge tiling patterns formed by congruent polygons ranging from oligothiophenes in most cases form smectic phases.34,35 There are
triangles to hexagons or, alternatively, as nets with nodes having only rare cases of polycatenar oligothiophenes forming columnar
valences between v ¼ 6 and v ¼ 3 (Fig. 1).
and spheroidic cubic phases36 and we have previously reported
In contrast to solid state net-structures (metal–organic T-shaped and X-shaped bolaamphiphilic dithiophenes with LC
frameworks (MOFs),16 covalent organic frameworks (COFs)17 and honeycomb structures (e.g. compounds 1/n in Fig. 1).14,37,38
most self-assembled nets on surfaces3), involving strictly directed
Herein we extend this work to longer oligothiophenes, the tet-
hydrogen bonding or metal coordination sites, these LC phases rathiophenes 2/n, for which only one compound (compound 3/12,
representhighlydynamicstructurescomposedofrapidlyrotating see Fig. 14) with a different substitution pattern was reported in a
andtranslatingmolecules. Duetothisconstant“noise”theseself- previous communication.37 A series of compounds 2/n, where n ¼
assembled LC structures can easily adopt to global minima on 5–14, 16 and 18 was synthesized to obtain new LC phases occurring
rugged energy landscapes.18,19 Owing to this so self-assembly at the transition between triangular and square honeycombs.
mode LC honeycombs have the ability of self-healing7,11,15 and
As a major result of the studies reported herein the (32.4.3.4)-
therefore can spontaneously form well dened arrays over quite tiling pattern7a,39 composed of square and triangular cell in a
large areas. These honeycombs do not need surface interactions ratio 1 : 2 was found as a new mode of LC self-assembly for
to be stable and can respond to external stimuli by changing their bolaamphiphiles with two lateral chains.10,40 This tiling pattern
morphology, so the change between honeycombs of different size was identied as a mode of self-assembly occurring only in a
and shape can take place as temperature-dependent phase tran- certain temperature range at the transition from triangular to
sitions, without hysteresis, inmost cases. This issupported by the square honeycombs. At higher temperature a new kind of
exibility of the nodes which can easily adapt to any valence cybotactic nematic phase (Ncyb) was found, indicating that
required for optimization of periodic self-assembly.
under these conditions the transition goes through disordered
In previous work this concept was used to obtain triangular, states.41,42 This nematic phase with negative birefringence is
square, pentagonal and hexagonal LC honeycombs. Further exten- composed of square honeycomb clusters. It is related to the NCol
sion of the lateral chain size lead to giant honeycomb LC phases, phases of disc-like molecules, but it has an inverted structure
formed by more than six molecules in the circumference of the cyl- where the aliphatic chains form the column cores and the
inders,8b–e,20 new modes of lamellar organization8b–d,21 and new aromatics are organized around them. Evidence is also provided
columnar phases formed by longitudinal rod-bundles.22 Attaching for the occurrence of rhombic honeycomb cells in the triangular
two different lateral chains gives “multicolor honeycombs”, where honeycomb, which increases the probability of emergence of
the content of adjacent honeycomb cells is different.11,15
quasi-periodic 2D tiling patterns.4a,43 An interesting observation
In the series of compounds 1/n it was observed that there is a is also, that the isotropic liquid phases occurring adjacent to the
discontinuity in the development of the honeycomb LC phases LC phases retain some of the order of the LC phases, thus being
(Fig. 1). At a certain intermediate chain length (n ¼ 8) LC phases composed of cybotactic clusters (Isocyb).44
were completely lost, indicating that these molecules are incapable
of self assembly into a well dened structure.14b Obviously the
sudden loss of long-range order is associated with the transition
Results and discussion
Synthesis
from triangular to square honeycombs. This transition is especially
interesting as numerous complex tiling patterns combining
triangles and squares can be expected in this region,23 leading to
much larger and more complex superstructures and eventually also
to LC phases with quasi-periodic24 2D tiling patterns composed of
triangular and square tiles.25,26 Therefore, it was of signicant
interest to extend this transition region over a larger chain length
range and also to avoid complete disorder by enhancing the self-
assembling forces by using elongated rod-like units.
Scheme 1 describes the synthesis of compounds 2/n using
Kumada coupling for introduction of the alkyl chains and
synthesis of the dithiophenes 9/n and Suzuki coupling reactions
for the coupling with the phenyl rings.45–50 The tetrathiophenes
14/n were obtained by oxidative homo-coupling of the func-
tionalized dithiophenes 13/n with n-BuLi and CuCl2.51 In the
nal step, the acetonide groups were cleaved (HCl in CH3OH)
and the obtained bolaamphiphiles 2/n were puried by
repeated crystallization. Detailed synthetic procedures and
analytical data are given in the ESI.†
Methods
The obtained compounds 2/n were rst investigated by polar-
izing microscopy and differential scanning calorimetry (DSC-7,
3318 | Chem. Sci., 2013, 4, 3317–3331
This journal is ª The Royal Society of Chemistry 2013

View Article Online
Edge Article
Chemical Science
Scheme 1 Synthesis of compounds 2/n. Reagents and conditions: (i) CnH2n+1MgBr, Ni(dppp)Cl2, THF, reflux, 15 h;45 (ii) NBS, THF, 25 ꢁC, 15 h;45,46 (iii) Mg, THF, reflux, 0.5
h;45 (iv) 4-methoxybenzene boronic acid, Pd(PPh3)4, NaHCO3, glyme, H2O, reflux, 15 h;47,48 (v) Ni(dppp)Cl2, THF, reflux, 15 h;45 (vi) BBr3, ꢀ78 ꢁC, CH2Cl2, 25 ꢁC, 24 h;49 (vii)
K2CO3, CH3CN, allyl bromide, reflux, 6 h;52 (viii) OsO4, NMMNO, H2O, acetone, 25 ꢁC;50 (ix) Me2C(OMe)2, PPTS' TosOH, 25 ꢁC, 24 h; (x) n-BuLi, THF, CuCl2, ꢀ60 ꢁC, reflux 15
h;51 (xi) 10% HCl, CH3OH, 25 ꢁC, 24 h.
Perkin Elmer) to determine the phase transition temperatures phase with p4gm lattice at lower temperature (Colsqu/p4gm).
and associated enthalpy values which are collated in Table 1. Compound 2/12 also shows two different LC phases, a square
Identication of the phase type and determination of the lattice phase with p4mm lattice at low temperature and a new LC phase
parameters were carried out by small and wide-angle X-ray at higher temperature, showing a Schlieren texture similar to
diffraction (XRD) on a temperature-controlled heating stage. Ni nematic (N) phases. In the homologous series the LC-to-Iso
ltered and pin-hole collimated Cu-Ka radiation was used; the transition temperatures at rst increase from 2/5 to 2/8, then
exposure time was 60 min and the sample to detector distances decrease to reach a minimum for compound 2/12 with the
were 8.8 cm and 26.9 cm for the wide-angle and small-angle nematic phase. The stability of the following Colsqu/p4mm pha-
measurements, respectively. The diffraction patterns were ses increases rst from 2/12 to 2/14 and then decreases slightly
recorded with a 2D detector (HI-STAR, Siemens). Attempts were upon further chain elongation. In the following sections the
made to align these samples by slowly cooling (rate: 0.1 K distinct phases will be discussed in more detail, especially
minꢀ1) of a small drop on a glass substrate. As for compounds focusing on the transition from Colhex to Colsqu/p4mm.
2/n no alignment could be achieved, 2D frame integration was
Though, all mesophases of compounds 2/6–2/18, with
used to convert the patterns into one-dimensional intensity exception of the high-temperature phase of compound 2/12,
proles, and the evaluated peak positions were used for phase represent honeycomb structures, these compounds ow upon
assignments as discussed below (see also Table S1, ESI†).
application of slight shear stress, indicating relatively low
viscosities, similar to those typically observed for columnar LC
phases of disc-like molecules with comparable molecular
weight. Hence, despite of their distinct honeycomb structure
these mesophases represent true liquid crystals, which is
additionally conrmed by the diffuse wide-angle scattering
observed for all these LC phases.
So self-assembly
All synthesized compounds 2/n with n ¼ 5 to n ¼ 18 self-assemble
into LC phases which are enantiotropic (thermodynamically
stable) in most cases. Compound 2/5 with the shortest lateral
chains forms a smectic phase, which upon chain elongation, is
replaced by hexagonal columnar phases (Colhex) for compounds
2/6–2/11 and by square columnar phases (Colsqu) with p4mm
Filled random mesh phase
lattice for compounds 2/12–2/18 with longest chains. The short- Compound 2/5 with the shortest lateral chain forms a non-tilted
chain compounds 2/6 and 2/7 have an additional low-tempera- smectic phase as indicated by the typical textures (fan-like
ture phase M with unknown structure. A phase transition texture and dark homeotropic regions, see Fig. 2a and b) and
between two different LC phases is also observed for compounds conrmed by XRD studies (Fig. 2c). The two relatively sharp
2/10 and 2/11 with medium chain length, in this case the Colhex reections in the small-angle region are assigned to the rst-
phase at high temperature is replaced by a square columnar and second-order reections of a layer structure (d01, d02) with
This journal is ª The Royal Society of Chemistry 2013
Chem. Sci., 2013, 4, 3317–3331 | 3319

View Article Online
Chemical Science
Edge Article
Table 1 Phase transitions, lattice parameters and other data of the tetrathiophene bolaamphiphiles 2/na
2/n
T/ꢁC [DH/kJ molꢀ1
]
a/nm (T/ꢁC)
fR
2/5
2/6
Cr 186 [45.4] (SmA+ 152 [0.8] Iso)
Cr 138[41.5] (M 108[0.2]) Colhex 161[1.7] Iso
SmA+: d ¼ 3.03 (140)
p6mm: 3.61 (150)
p6mm: 3.70 (120)
p6mm: 3.54 (160)
p6mm: 3.80 (80)
p6mm: 3.57 (160)
p6mm: 3.74 (80)
p6mm: 3.55 (160)
p6mm: 3.77 (80)
p6mm: 3.64 (140)
p4gm: 7.36 (60)
p6mm: 3.58(120)
p4gm: 6.94 (100)
N: d ¼ 3.25 (130)d
p4mm: 3.52 (110)
p4mm: 3.49 (135)
p4mm: 3.48 (140)
p4mm: 3.51 (130)
p4mm: 3.63 (60)
p4mm: 3.56 (120)
p4mm: 3.63 (80)
0.25
0.29
2/7
Cr1 96[32.4] Cr2 122[30.3] (M 71[0.33]) Colhex 169 [2.6] Iso
Cr1 93[34.7] Cr2 120[51.3] Cr3139[27.8] Colhex 171[3.0] Iso
Cr 105[36.4] Colhex 165[3.2] Iso
0.32
0.35
0.37
0.40
0.42
0.44
2/8
2/9
2/10
2/11
2/12
Cr1 89[11.6] Cr2 123[20.0] (Colsqu/p4mg 75/68b[0.7]) Colhex 162[1.3] Iso
Cr1 104 [16.9] Cr2 127 [43.4] (Colsqu/p4mg 114/104b[0.7]) Colhex 149 [1.8] Iso
Cr 138 [49.5] (Colsqu/p4mm 125 [0.8] Ncyb 135 [0.7]) Iso
2/13
2/14
2/16
Cr 147 (Colsqu/p4mm 138) Isoc
Cr 140 [47.7] Colsqu/p4mm 147 [5.3] Iso
Cr 82 [52.3] Colsqu/p4mm 146 [6.5] Iso
0.46
0.48
0.51
2/18
Cr1 82[39.1] Cr2 100[49.1] Colsqu/p4mm 141[5.9] Iso
0.54
a
Transition temperatures were determined by DSC (peak temperatures, second heating scan, 10 K minꢀ1); values in brackets identify monotropic
phase transitions; abbreviations: fR ¼ volume fraction of the lateral chains; abbreviations: Cr ¼ crystalline solid; SmA+ ¼ random mesh phase with
holes lled by the alkyl chains; M ¼ unknown mesophase; Colsqu/p4mm ¼ square columnar mesophase with p4mm lattice; Colsqu/p4gm ¼ square
columnar mesophase with p4gm lattice; Colhex/p6mm ¼ hexagonal columnar mesophase with p6mm lattice; Ncyb ¼ nematic phase composed of
d
cybotactic cluster; Iso ¼ isotropic liquid. b Transition on cooling. c Determined by polarizing microscopy. Maximum of the diffuse scattering.
angle scattering with a maximum at D ¼ 1.75 nm, which indi-
cates an additional short-range periodicity. This is thought to
result from the mean distance between nano-segregated
aliphatic domains. This means that the lateral alkyl chains are
not equally distributed between the aromatic cores, but form
distinct domains in which these chains are concentrated (see
Fig. 2d). This kind of defective smectic phase, where lipophilic
domains ll randomly distributed holes in the layers of the p-
conjugated cores is assigned as SmA+ and can be considered as
a kind of lled random mesh phase.8a,b,9 For compound 2/5 the
distortion provided by the lateral alkyl chains is obviously not
strong enough to completely break the layer structure which
takes place aer further chain elongation and leads to Colhex
phases for the following homologues.54
Triangular honeycombs
The mesophases of compounds 2/6–2/11 are characterized by
spherulitic textures as typical for columnar LC phases (see
Fig. 3a). In their XRD patterns, the ratio of the positions of the
small-angle reections is 1 : 31/2 : 2, indicating hexagonal
Fig. 2 SmA+ phase of compound 2/5: (a and b) textures as observed between
crossed polarizers at T ¼ 150 ꢁC, (a) homogeneous alignment with fan-texture and (b)
homeotropic alignment with oily streaks texture, indicating an uniaxial smectic phase;
(c) XRD pattern and (d) model of the molecularorganization in the SmA+ phase (seealso
explanations in Fig. 1, gray areas represent the regions of the segregated alkyl chains).
columnar phases (Colhex/p6mm, Fig. 4). Close to the clearing
temperature (at 150–160 ꢁC) for all compounds 2/6–2/11 the
lattice parameters are in the range between ahex ¼ 3.5–3.6 nm
(Table 1) corresponding to the maximum molecular length
(Lmax ¼ 3.6 nm).
The nearly chain length independent lattice parameters
d ¼ 3.03 nm.53 Besides the diffuse wide-angle scattering at close to the molecular length, are in line with a triangular
D ¼ 0.46 nm, which is due to the mean lateral distance between honeycomb structure of the LC phase. In this mode of self-
the molecules in LC phases, there is an additional diffuse small- assembly the positions and directions of the rod-like cores
3320 | Chem. Sci., 2013, 4, 3317–3331
This journal is ª The Royal Society of Chemistry 2013

View Article Online
Edge Article
Chemical Science
Fig. 3 Texture of the Colhex-phase of 2/6 between crossed polarizers (a) at
T ¼ 150 ꢁC, dark areas represent homeotropically aligned regions (columns
perpendicular to the substrate surfaces) and indicate the optical uniaxiality of the
columnar phases, (b) texture with l-plate (different region); the indicatrix orien-
tation in the l-compensator is shown in the inset; and (c) shows the organization
of the molecules in the spherulitic domains; the circles indicate the orientation of
the honeycomb cylinders, the bold black lines indicate the orientation of the
aromatic cores in the cylinders.
Fig. 4 (a) Small-angle and (b) wide-angle scans over the XRD patterns of
compound 2/7 with indexation, measured at different temperatures; (c) model of
the molecular organization in a Colhex phase with triangular cylinder structure
(see also the explanations in Fig. 1); and (d) small-angle XRD patterns of the
Colhex/p6mm phases of compounds 2/7, 2/9 and 2/11 at T ¼ 120 ꢁC; D indicates
the approximate position of the maximum of the broad diffuse scattering in the
small-angle region.
coincide with the hexagonal lattice and hence Lmax ꢂ ahex is
typically observed.38,55 Because in the honeycomb phases the itself) the alignment of the p-conjugation pathway, i.e. the
intramolecular p-conjugation pathway is perpendicular to the orientation of the oligothiophene cores, is perpendicular to the
column long axis these phases have negative birefringence, cylinder long axis.22,56
which was conrmed by polarizing microscopy using an addi-
The walls of the honeycombs have a thickness equal to the
tional l-retarder plate, shown in Fig. 3b; the orientations of the width of a single molecule,57,58 a more detailed discussion of the
high and low index axes of the indicatrix are shown in the inset. arrangement of the molecules in these walls is given in Section 3
In the spherulitic domains the cylinders are organized in circles of the ESI.†
around the centre (see Fig. 3c). Molecules with the p-conjuga-
An interesting feature of these triangular LC honeycomb
tion pathway along the high index axis lead to a blue shi, those phases is the presence of an additional broad diffuse scattering
with the p-conjugation pathway perpendicular to the high index in the small-angle region (D) which is especially clearly observed
axis give a yellow shi. Because green color is in the northeast for the Colhex phases of compounds with long lateral chains,
and southwest quadrants (the fans actually appear green like compound 2/11 (see further below, Fig. 6a and d). This
instead of blue due to the deep yellow colour of the compound indicates an additional short-range correlation which is
This journal is ª The Royal Society of Chemistry 2013
Chem. Sci., 2013, 4, 3317–3331 | 3321

View Article Online
Chemical Science
Edge Article
incommensurate with the hexagonal lattice. Apparently there is
only long-range order of the polar columns of the glycerol units
on a hexagonal lattice, whereas the positions of the aromatic
cores and the lateral alkyl chains are less well dened. This
suggests that there are holes in the honeycomb walls, lled by
alkyl chains and in this case the diffuse small-angle scattering
should correspond to the mean distance between these holes
along the cylinder axis (for 2/11 D ꢂ 2.2 nm at T ¼ 120 ꢁC,
corresponding to a cylinder section involving about 5 molecules
lengthwise). Formation of holes is also evident from a more
detailed analysis of the molecular packing as discussed in
Section 3 of the ESI.† This means that adjacent triangular
honeycomb cells are locally fused to rhombic cells. Hence, these
Colhex phases can be regarded as defective triangular honey-
combs combining triangular cylinder segments with orienta-
tionally randomized rhombic cylinder segments. Triangular
and rhombic segments alternate along the cylinders and the
rhombic segments are randomized with respect to their orien-
tation along the three main axes of the hexagonal 2D lattice.
Because the orientation of these rhombic cylinders is random-
ized on time and space average, the hexagonal lattice with a
ratio ahex ꢂ Lmax is retained. The formation of rhombs appears
to be advantageous as it removes some of the sharp 60ꢁ vertices
in the triangular cylinders, which are more difficult to be lled
by the alkyl chains. In addition, formation of randomly
distributed and randomly oriented rhomb segments provides
some entropic advantage4a,b in the dynamic LC structures.
In addition to this diffuse small-angle scattering there is also a
pronounced temperature dependent intensity of the small-angle
scatterings belonging to the 2D lattice. In all Colhex phases the
heightofthesmall-angle scatteringpeaksdecreases andthepeaks
Fig. 5 Colsqu/p4mm-phase of compound 2/18: (a) XRD pattern at T ¼ 120 ꢁC
with indexation to a p4mm square lattice; (b) texture between crossed polarizers
at T ¼ 140 ꢁC and (c) model of the molecular organization in the square
honeycomb phase (see also explanation in Fig. 1).
honeycombs, which is in line with the observation that for all
square honeycomb phases the temperature dependence of the
lattice parameters is much smaller (e.g. 2/16: asqu ¼ 3.51 at
T ¼ 130 ꢁC and asqu ¼ 3.63 at T ¼ 60 ꢁC) than observed for the
Colhex phases (see Table 1, for a more detailed discussion see
Section 3 in the ESI†).
Square–triangle honeycombs
become broader with rising temperature (see Fig. 4a and ESI, For compounds 2/10 and 2/11 with intermediate chain length
Fig. S1†), indicating a reduction of the correlation length of the there is a phase transition from the Colhex phase to another
hexagonal lattice formed by the polar cylinders with increasing mesophase at lower temperature, indicated by a clear change
temperature. In contrast to triangles, which are xed and cannot of the texture (Fig. 6b and e) and a small peak in the DSC
change their shape, rhombs can easily be deformed and this is heating and cooling curves (Fig. 7). The phase transition shows
thought to lead to a reduction of the long-range correlation if a a signicant hysteresis and occurs in the cooling process at
sufficiently large number of rhombic cells is incorporated.
about 7–10 K lower temperature than on heating (see Fig. 7
Before the discussion is focussed on the low-temperature and Table 1).
phases of compounds 2/10 and 2/11 and on the Colsqu–N tran-
The diffraction patterns of the low-temperature phases can
sition of 2/12, the Colsqu/p4mm phases of the long-chain be indexed to a square lattice with the plane group p4gm and a
compounds 2/13–2/18 will be shortly discussed in the following lattice parameter asqu ¼ 7.36 nm for compound 2/10 and
section.
asqu ¼ 6.94 nm for compound 2/11 (Fig. 6d). The columnar
phases with p4gm lattice can have two distinct structures.10 They
can either represent honeycombs formed by pentagonal cylin-
ders or the topological duals combining square and triangular
Square honeycombs
Based on the textures and the powder X-ray diffraction patterns cylinders in a ratio 1 : 2 (Fig. 6f).10,39,60 Because the p4gm phases
(two sharp small-angle scatterings with ratio of their d-values of of compounds 2/10 and 2/11 occur between triangular
1 : 1/21/2, see Fig. 5) the mesophases of compounds 2/13–2/18 (compounds 2/6–2/9) and square honeycomb phases
represent Colsqu/p4mm phases with lattice parameters asqu
¼
(compounds 2/12–2/18) upon increasing the lateral chain
3.5–3.6 nm, corresponding to the maximal molecular length length, they should represent honeycomb phases combining
(Lmax ¼ 3.6 nm), which is in line with a square honeycomb square and triangular cylinders in a ratio of 1 : 2. This is in line
structure.37,38,57,59 In contrast to the Colhex phases there is no with the measured lattice parameters (asqu ¼ 7.0–7.4 nm) which
indication of any diffuse small-angle scattering or any signi- amount to about twice the molecular length (asqu
¼
cant change of the line shape and intensity depending on 2 sin75ꢁ Lmax ꢂ 1.93Lmax; Lmax ¼ 3.6 nm) whereas a pentagonal
temperature. This indicates that there is no formation of holes cylinder structure (the dual) would have a larger lattice
in the cylinder walls or any other distortion in the square parameter corresponding to the ratio asqu > 2.5Lmax
.
3322 | Chem. Sci., 2013, 4, 3317–3331
This journal is ª The Royal Society of Chemistry 2013

View Article Online
Edge Article
Chemical Science
Fig. 6 Mesophases of compound 2/11: (a) XRD pattern (D indicates the maximum of the diffuse small-angle scattering), (b) texture (crossed polarizers) and (c) model
of the Colhex/p6mm at T ¼ 120 ꢁC (cut through the structure showing only one layer of molecules; the aromatic cores are indicated by bold lines, colored lines indicate
rhombic cells with distinct orientations), (d) XRD pattern, and (e) texture (crossed polarizers) and (f) model of the Colsqu/p4gm phase T ¼ 100 ꢁC.
The Colsqu/p4gm phase can thus be considered as an inter-
mediate phase at the transition from triangular honeycombs to
square honeycombs, occurring only at sufficiently low tempera-
ture. The randomly distributed rhombic segments in the Colhex
phase fuse to complete cylinders in the p4gm phase. Once
formed, these cylinders adopt a uniform square shape, leading to
a periodic honeycomb composed of square cylinders and pairs of
triangular cylinders. Hence, the Colhex–Colsqu/p4gm transition is
a special kind of disorder–order transition. As prismatic cells
with very different volume have to be lled in the p4gm phase,
some molecules must adopt an energetically less favourable P-
shape to allow both its alkyl chains to contribute to the lling of
the larger square prisms. The self-sorting of the cylinder frag-
ments according to their shape, and also the required torsion of
the conjugated p-system for achieving the P-shape, might
contribute to the experimentally observed hysteresis of the phase
transition to the p4gm lattice.
Fig. 7 DSC heating and cooling curves of compound 2/11 (10 K minꢀ1).
Having conrmed the low-temperature phase as a honey-
comb composed of square and triangular cells the question
arises why increasing the temperature, i.e. expansion of the
lateral chains, could lead to a transition to a hexagonal
columnar phase composed of triangular cells. Fig. 8 shows the
fundamental polygons representing the cross-sectional areas in
the distinct honeycomb phases. The (average) area available for
each side of the polygon (A/x ¼ area of the polygon A divided by
the number of sides x) is much larger in the p4gm lattice
combining triangles with squares (A/x ¼ 0.187) than in a p6mm
lattice exclusively composed of triangular cells (A/x ¼ 0.144).
Hence, considering thermal expansion of the alkyl chains, the
phase sequence on rising temperature is in line with the idea
that the honeycomb in the Colhex phase cannot be exclusively be
composed of cells with triangular shape, instead there should
be an excess of rhombic over triangular cells of at least ꢂ1.4 : 1
to exceed the average A/x value of the p4gm phase.
Fig. 8 Different tiles found for the cross-sectional areas in polygonal honeycomb
phases (plane groups given in the lower line) with their A/x ratios; A ¼ area of the
polygon, x ¼ number of sides of the polygon; for the p4gm lattice, composed of
more than only one polygon, the sides shared by two polygons count only half;
for the rhombs the inner angles are fixed to 60/120ꢁ. The numbers on the arrows
show the difference of the A/x values between the distinct types of tiles.
This journal is ª The Royal Society of Chemistry 2013
Chem. Sci., 2013, 4, 3317–3331 | 3323

View Article Online
Chemical Science
Edge Article
without shearing the sample; however it is more viscous than
ordinary nematic phases of rod-like LC.
Cybotactic nematic phases with honeycomb clusters
Compound 2/12 has two different LC phases; a schlieren
texture, similar to those found for nematic phases, occurs rst
(Fig. 9a and b, see also Fig. S3, ESI†), upon further cooling the
birefringence increases (Fig. 9b–e) and at T ¼ 125 ꢁC a change to
a spherulitic texture is observed (Fig. 9f and g). Both phase
transitions were also observed by DSC and have comparable
enthalpy values around 0.7–0.8 kJ molꢀ1 (Fig. 9i). The nematic
phase is less viscous than the honeycomb phases and ows also
X-Ray investigation of the low-temperature phase (Fig. 9k)
conrms a Colsqu/p4mm phase with a lattice parameter asqu
¼
3.5 nm, which is in the range of the molecular length and thus
indicates a square honeycomb phase, the same as observed for
the adjacent higher homologues 2/13–2/18.
The XRD pattern of the high-temperature phase with
nematic texture shows two diffuse small-angle scatterings and a
diffuse wide-angle scattering (Fig. 9h). The ratio of the maxima
of the diffuse small-angle scatterings at d1 and d2 is around
1 : 1/21/2, similar to the d01 and d11 reections in the low-
temperature Colsqu/p4mm phase, but the positions of the scat-
tering maxima are shied a bit to shorter distances, if compared
with the Colsqu phase. Nevertheless, the d-value (d ¼ 3.25 nm) of
the diffuse scattering maximum d01 is still in the range of the
molecular length (L ¼ 3.0–3.6 nm), so that a short-range square
lattice would be in line with the recorded diffraction pattern.
This phase can be considered as a special type of cybotactic
nematic phase (NCyb) composed of short-range ordered square
honeycomb domains. The smaller d-value most probably results
from a reduced order parameter of the rod-like cores in the
cybotactic clusters.61 This reduced orientational order parameter
is in line with microscopic investigations indicating a relatively
strong increase of the birefringence with decreasing tempera-
ture, see change of the birefringence color from red to green in
the temperature range of the nematic phase in Fig. 9b–e. So it
appears that in the nematic phase the long-range 2D lattice of
the Colsqu phase becomes short range, and the only remaining
long-range order is the orientational order of the honeycomb
cylinder fragments composed of walls of the p-conjugated
aromatics. With decreasing temperature the clusters grow in
size, which causes the order parameter of the aromatics in the
cylinder walls to increase with a distinct jump at the transition
from Ncyb to Colsqu/p4mm, when innite honeycombs are
formed and adopt long-range positional order.
Due to the xation of the aromatics perpendicular to the
cylinder long axes this nematic phase has special optical
properties. In principle, this kind of cybotactic nematic phases
can be considered as being related to the columnar nematic
phases formed by disc-like molecules62 and similar to these,
they should have negative birefringence, just like the columnar
honeycomb phases (Fig. 3). In contrast, the nematic phases
formed by rod-like molecules usually have positive birefrin-
gence as the p-conjugation pathway in most cases coincides
with the molecular long axis, which is parallel to the nematic
director. In order to conrm the cybotactic cylinder structure
with negative birefringence (i.e., that the nematic director is
perpendicular to the intramolecular p-conjugation pathway)
differently aligned samples were investigated. Fig. 9c–e shows
the high birefringent texture of the Ncyb phase indicating an
Fig. 9 Compound 2/12: (a–g) textures as observed on cooling between crossed
polarizers in a 6 mm polyimide coated planar ITO cell, rubbing direction is 45ꢁ, alignment of the square cylinders parallel to the surfaces
polarizer and analyzer are vertical, respectively horizontal: (a–e) for the nematic
(homogeneous alignment). As the rod-like cores are parallel
aligned to each other and perpendicular to the long axes of the
cylinder segments, this alignment has a relatively high bire-
fringence. At the transition to the Colsqu/p4mm phase the clus-
phase, (f) for the N-to-Colsqu/p4mm transition, and (g) for the Colsqu/p4mm
phase at the indicated temperatures; (h and k) SAXS patterns (insets show the
diffuse wide-angle scattering); (h) in the N phase at T ¼ 127 ꢁC and in the Iso
phase at T ¼ 137 and 157 ꢁC; (k) in the Colsqu/p4mm phase at 110 ꢁC; and (i)
shows the DSC-traces in the temperature range of the Colsqu–N–Iso transitions.
ters grow to honeycombs, the formed domains have fan-shaped
3324 | Chem. Sci., 2013, 4, 3317–3331
This journal is ª The Royal Society of Chemistry 2013

View Article Online
Edge Article
Chemical Science
and in some areas also spherulitic textures (see Fig. 9f and g and dominating polymeric hydrogen bonding (ꢂ3400 cmꢀ1
)
S3b, c, e and f, ESI†), conrming that the cylinders of the increases with decreasing temperature, as indicated by the
honeycombs are aligned parallel to the surfaces and perpen- difference spectra, shown in Fig. 11b. So, the size of the
dicular to the fan direction.
hydrogen-bonding networks increases from Iso (Isocyb) via Ncyb
Fig. 10 shows the nematic to Colsqu transition as observed for to Colsqu, as expected. There are distinct intensity steps at the
a homeotropic aligned sample. Here the nematic phase appears phase transition temperatures (Fig. 11a), which are disregarded
completely dark and the Colsqu phase grows with formation of here, as these are most likely due to the signicant change of
low birefringent and nearly square-shaped domains. In this the birefringence at the phase transitions involving LC phases.
region the long axis of the square cylinder fragments of the Overall, the observed change of the IR absorption bands
nematic phase is on average perpendicular to the surfaces, i.e. depending on temperature are in line with the proposed cybo-
the view is along the cylinder long axis, the aromatic cores are tactic structure of the nematic phase, but it also conrms that
parallel to the surfaces and there are 90ꢁ angles between the even in the isotropic liquid state clusters of appreciable size are
aromatics in adjacent cylinder walls (see models in Fig. 10), retained (Isocyb).
which leads to the optically isotropic appearance. This indicates
that the nematic phase is indeed composed of cylinder frag-
ments and hence, has negative birefringence. As the Colsqu
phase grows, the small cybotactic domains fuse to innite
honeycomb-cylinders, which grow perpendicular (back,
domains A) or slightly inclined (yellow, gray, domains B) to the
surfaces. If the nematic phase would be formed by the indi-
vidual molecules and hence would represent a nematic phase
with positive birefringence, then the p-conjugated aromatic
cores would have to be aligned perpendicular to the surfaces in
the optically isotropic appearing areas. If this would be the case,
then the square cylinders would grow parallel to the surfaces to
give highly birefringent domains with fan-like texture, similar to
those shown in Fig. 9f and g for the homogeneous alignment.
This is not the case and thus conrms the cybotactic cylinder
structure and negative birefringence of this nematic phase.
Temperature-dependent IR investigations of thin lms of
2/12 (see Fig. 11a) conrm the presence of large hydrogen-
bonding networks in the isotropic liquid state as well as in the
N
Cyb phase and the Colsqu phase by a broad absorption between
n ¼ 3200 and 3650 cmꢀ1
.
On decreasing the temperature the
63
shape of the nO–H bands changes. The contribution of free OH
groups (ꢂ3600 cmꢀ1) decreases and the contribution of the
Fig. 10
N
cyb–Colsqu/p4mm transition of compound 2/12 as observed at
Fig. 11 (a) Temperature-dependent IR spectra of compound 2/12 in the
temperature range between 150 and 110 ꢁC (observed on cooling every 2 K, cell
gap 13 mm) showing the region of the nOH stretching frequencies; the intensity
steps at the phase transitions, are due to the significant change of the birefrin-
gence at the phase transitions involving LC phases;63 (b) difference spectra for the
temperature ranges of the three distinct phases showing the increase of
the contribution of the polymeric hydrogen bonding (3200–3450 cmꢀ1) and the
decrease of the contribution of free OH groups (ꢂ3600 cmꢀ1) with decreasing
temperature.
T ¼ 125 ꢁC between crossed polarizers (horizontal and vertical) for a homeotropic
aligned sample with alignment of the columns/column segments perpendicular
to the surfaces (NCyb and domains A in the Colsqu phase) or slightly inclined to the
surfaces (birefringent domains B of Colsqu); the models show the view along these
cylinders, i.e. the cross-sections of the square cylinder/cylinder segments; the
birefringence of the Colsqu domains is much smaller than in Fig. 9f and g (see also
Fig. S3c, ESI† for
a direct comparison of homeotropic and homogeneous
alignment).
This journal is ª The Royal Society of Chemistry 2013
Chem. Sci., 2013, 4, 3317–3331 | 3325

View Article Online
Chemical Science
Edge Article
Cybotactic isotropic phases
In line with the IR results, the diffraction pattern of compound
2/12 does not signicantly change at the transition from the
nematic to the isotropic liquid phase (Fig. 9h). The two diffuse
small-angle scatterings at d1 and d2 are retained. The scatterings
only become more diffuse and weaker, indicating that the
correlation length further decreases. Similar scattering patterns
with two diffuse small-angle scatterings were also observed for
the isotropic phases of all other compounds 2/n as shown in
Fig. 12a for selected examples covering the chain length range
from n ¼ 7 to 18. In all cases the intensity of the diffuse small-
angle scatterings (at ꢂ10 K above the LC–Iso phase transition) is
at least equal or higher than the diffuse wide-angle scattering,
thus indicating the presence of cybotactic clusters41 in the
isotropic liquid phases occurring adjacent to the polygonal
honeycomb phases.
In Fig. 12b the position of the scattering maximum in the
isotropic phase d1 (at ꢂ10 K above the phase transition to Iso) is
plotted together with the position of the sharp d10 reection in
the columnar phase (ꢂ10 K below the phase transition to Iso or
N) as a function of the chain length. For compounds 2/7–2/11
with a Colhex phase the position of the rst diffuse scattering at
d1 is slightly shied to larger d-values if compared with the d10
diffraction peak in the corresponding Colhex phase. In contrast,
for compounds 2/12–2/18 with Colsqu/p4mm phase, d1 is shied
towards smaller d-values compared to the d10 diffraction peak in
the corresponding Colsqu/p4mm phases. Overall there is a
continuous dri of the diffuse scattering at d1 from smaller (2/7:
d1 ¼ 3.07) to larger distances with rising alkyl chain length
(2/18: d1 ¼ 3.44 nm), though the molecular length (distance
between the glycerol groups) is identical for all compounds.
Fig. 12c compares the chain length dependence of the
positions of both diffuse small-angle scattering maxima at d1
and d2 in the isotropic phase (lled dots) with the calculated d2
values, determined using the d1-value either assuming a square
lattice ((d2 ¼ d1)/21/2, non-lled circles) or a hexagonal lattice
((d2 ¼ d1)/31/2, non-lled squares). Like the d1 scattering, the
position of the second diffuse small-angle scattering d2 is also
shied to larger distances with growing chain length, but the
slope of d2(n) is not linear. The ratio d1/d2 is close to 1 : 31/3 for
compound 2/7, it increases by chain elongation and approaches
a value close to 1 : 21/2 for compounds 2/14 and 2/18. This
suggests that in the isotropic phases there is a transition of the
dominating short-range correlation from being hexagonal for
compounds 2/6 to 2/9 to square for compounds 2/11–2/18. This
could be related to the change of the shape of the cybotactic
honeycomb clusters from triangular for the short-chain
compound 2/7 to square for the long-chain compounds 2/11–
2/18. For the intermediate compounds 2/8–2/10 the clusters
seem to be formed by mixtures of triangular with square or
rhombic cells.
Fig. 12 (a) XRD patterns in the isotropic phases of compounds 2/7, 2/11, 2/14
and 2/18 at temperatures approximately 10 K above the LC–Iso transition; (b)
plots showing the development of the positions of the d10 reflection in the LC
phase and the maximum of the diffuse small-angle scattering d1 in the corre-
sponding isotropic phases depending on the alkyl chain length (n) of compounds
2/n and (c) the change of the positions of the maxima of the two diffuse small-
angle scatterings at d1 and d2 in the isotropic phases of compounds 2/n
depending on the chain length n; open symbols indicate the positions expected
for (d2 ¼ d1)/21/2 and (d2 ¼ d1)/31/2
.
the temperature dependent development of the textures in the
contact region between the Colhex/p6mm phase of compounds
2/11 and the Colsqu/p4mm phase of compound 2/14. In the
contact region the LC phase stability decreases and an isotropic
liquid phases as well as a small region of a nematic phase are
induced, which corresponds to the development of LC-phase
depending on the chain length in the series 2/n. The nematic
ꢁ
phase is induced in a small temperature (T ¼ 125–135 C) and
concentration range (X2/14 ¼ 0.25 and 0.45) and this nematic
phase occurs above a p4mm phase with square honeycomb
structure. Interestingly, not only the thermal phase sequence
Colsqu/p4mm–Ncyb–Isocyb is the same as observed for the single
compound 2/12, also the average chain volume in the nematic
region and the temperature range of the nematic phase between
Induced nematic phases in mixed systems
ꢁ
125 and 135 C correspond to compound 2/12. This indicates
Interestingly, nematic phases can also be induced in the contact that the mode of self-assembly is determined by the average
regions between short-chain compounds with Colhex phases and property of the collective of molecules and thus can be ne-tuned
long-chain compounds with Colsqu/p4mm phases. Fig. 13 shows by mixing different compounds in the appropriate ratio.
3326 | Chem. Sci., 2013, 4, 3317–3331
This journal is ª The Royal Society of Chemistry 2013

View Article Online
Edge Article
Chemical Science
has a Colsqu/p4mm–NCyb transition compound 3/12 shows
exclusively the Colsqu/p4mm phase with a lattice parameter
identical to that of 2/12 (asqu ¼ 3.52 nm). A nematic phase is
induced in the contact region between the Colhex phase of 2/11
and the Colsqu/p4mm phase of 3/12. In Fig. 14 the induced
nematic phase is clearly seen as a owing band in the contact
area between the two different honeycomb phases. The reduced
viscosity of the nematic phase compared to the honeycomb
phases excludes that it only results from a complete randomi-
zation of the direction and position of the polygonal cells in a
honeycomb structure; the honeycomb must additionally be
broken into smaller clusters and interrupted by disordered
areas. The maximum of the N–Iso transition in the contact
region is 138 ꢁC which is again similar to the transition
temperatures observed for compound 2/12 and in the contact
region between 2/11 and 2/14. This experiment indicates that
formation of a nematic phase is generally observed for this kind
of compounds at a certain and very narrow chain length to rod-
length ratio and it represents an intermediate phase at the
transition from the triangular to the square LC honeycomb. It
also appears that the peripheral chains in 3/12 require effec-
tively a bit more space than the more central chains in
compound 2/12.
Summary and conclusions
A series of new X-shaped bolaamphiphiles incorporating a rigid
rod-like 5,5000-diphenyltetrathiophene core with glycerol groups
at both ends and two laterally attached alkyl chains was
synthesized and investigated with respect to self assembly in LC
phases. Upon elongation of the chains the phase sequence
SmA+–Colhex–Colsqu/p4gm–Colsqu/p4mm was observed at lower,
and the sequences SmA+–Colhex–Ncyb–Colsqu/p4mm or SmA+–
Colhex–Isocyb–Colsqu/p4mm at higher temperatures. The
Fig. 13 Optical photomicrographs (crossed polarizers) of the different meso-
phases developing in the contact region between the Colhex phase of compound
2/11 (left) and the Colsqu/p4mm phase of compound 2/14 (right) as observed on
cooling; this figure can be read like a phase diagram and shows the regions of the
distinct mesophases, depending on the average volume of the lateral chains and
the temperature; the white dotted lines indicate the phase boundaries (two-phase
regions are not considered); the concentration limits of the induced nematic phase
region and other details were taken from investigations of discrete binary mixtures.
Fig. 14 Structure of compound 3/12 (ref. 37) with transition temperatures and
contact region between the Colsqu/p4mm phase of this compound (bottom) with
the Colhex phase of the isomeric compound 2/11 (top) at T ¼ 135 ꢁC, showing the
The previously reported compound 3/12 (ref. 37) is an isomer
of compound 2/12 having the two dodecyl chains at the outer
thiophene rings and pointing inwards. In contrast to 2/12 which formation of a nematic phase in the contact region.
This journal is ª The Royal Society of Chemistry 2013
Chem. Sci., 2013, 4, 3317–3331 | 3327

View Article Online
Chemical Science
Edge Article
formation of these series of mesophases is distinct from the and these are surrounded by the rigid aromatic units, whereas
effects usually observed by elongation of chains laterally in the Ncol phases the disc-like aromatics stack into columnar
attached to rod-like LC where it only leads to a distortion of the aggregate cores and these are organized in the continuum of the
self-assembly by replacing smectic by less ordered nematic and uid alkyl chains.
isotropic liquid phases. The effects of chain elongation is much
In the isotropic liquid phases the size of the honeycomb
more complex in the series of polyphilic molecules reported clusters is further diminished and the orientational long-range
here. Already the SmA+ phase of the short-chain compound 2/5 order of these clusters is lost. The isotropic phases occurring
is not a usual SmA phase, but a lamellar phase containing above the square honeycomb phases and the nematic phase of
clusters of the alkyl chains randomly distributed between the 2/12 can be considered as cybotactic phases with disrupted
oligothiophene cores. Only one additional methylene unit per square honeycomb structure, whereas those occurring above
chain is sufficient to break the layer structure with formation of Colhex phases (compounds 2/7–2/11) are predominately
a triangular honeycomb with hexagonal symmetry (compound composed of triangular honeycomb clusters.
2/6). In these Colhex phases the triangular honeycombs are not
It appears that the phase sequence SmA+–Colhex–Colsqu
/
defect-free and with increasing chain length and rising p4gm/Ncyb–Colsqu/p4mm, shown in Fig. 15, requires a certain
temperature a growing number of holes occur in the honey- length of the rod-like core. For molecules with shorter cores (e.g.
comb walls, effectively leading to a structure composed of compounds 1/n (ref. 14b)) the sequence occurs without the
triangular and rhombic honeycomb fragments fused together to Colsqu/p4gm phase and the nematic phase.
a defective triangular honeycomb. At a certain length of the
Overall, a fundamental understanding of the structure of the
lateral chains (n > 9) the triangular honeycombs (Colhex phases) triangular cylinder phases and the distinct modes of the tran-
become unstable and are replaced completely or partly by other sition from layers via triangular to square honeycombs is gained
LC phases. At low temperature self-sorting of rhombic and and this will facilitate the design of more complex honeycombs
triangular segments leads to a p4gm phase representing a with larger lattice parameters and a larger variety of different
(32.4.3.4)-tiling by defect-free square and triangular honeycomb tiles, leading to so matter structures with further enhanced
cells. Upon further chain elongation, for compounds 2/12–2/18, complexity.11,15 The series 2/n also provides an example for the
the triangular cells are removed completely and a square competition arising at the transition between two ordered
honeycomb with p4mm lattice is formed. At higher temperature periodic arrays with distinct symmetry (Colhex/p6mm vs. Colsqu
/
the rhomb–triangle tiling of the Colhex phase is stable over a p4mm). This either leads to increased complexity in the p4gm
broader chain length range (2/7–2/11) and it is replaced by a phase combining two different types of cylinders or to a chaotic
cybotactic nematic phase before the square honeycomb regime with reduced order in the induced Ncyb and Isocyb pha-
is formed.
ses. Hence, appropriately designed polyphilic LCs7 provide
This cybotactic nematic phase is composed of square model systems in which the mechanisms and pathways of the
cylinder honeycomb fragments of the Colsqu/p4mm phase with transition from chaos to complexity2 could be studied in detail
long-range orientational order of the cylinder long axis but only for so self-assembled systems. Probably, honeycomb LC pha-
short-range rotational and positional order of the square ses with randomized or quasi-periodic triangle/square tilings
honeycomb cells. Therefore, this nematic phase is optically (or at least their close approximates) could be achieved if the
uniaxial and has a negative birefringence, similar to the dynamics could be reduced a bit and thus a disruption of the
nematic phases formed by disc-like molecules. The presence of honeycomb into smaller clusters, leading to the cybotactic
honeycomb clusters makes this nematic phase related to the nematic phase, can be prevented.
N
col phases of disc-like molecules.62 In fact, this nematic phase
is inverted with respect to the positions of aromatic and
aliphatic units to the usual Ncol phases. In the NCyb phases
Acknowledgements
discussed here the column cores are formed by the alkyl chain This work was supported by the National Natural Science
Foundation of China (no. 21274119, 21074105 and no.
20973133), the Yunnan Science Foundation (2010CD018) and
the DFG (FG 1145). M. P. acknowledges the support by the
Cluster of Excellence “Nanostructured Materials”.
Notes and references
1 (a) G. M. Whitesides and B. Grzybowski, Science, 2002, 295,
2418–2421; (b) J. M. Lehn, Science, 2002, 295, 2400–2403;
(c) O. Ikkala and G. ten Brinke, Science, 2002, 295, 2407–
2409; (d) S. C. Glotzer and M. J. Solomon, Nat. Mater.,
2007, 6, 557–562.
2 S. A. Kauffmann, The Origins of Order, Self-Organization and
Selection in Evolution, Oxford University Press, New York,
Fig. 15 Development of the LC phases observed in the series of compounds 2/n,
depending on chain length and temperature.
1993.
3328 | Chem. Sci., 2013, 4, 3317–3331
This journal is ª The Royal Society of Chemistry 2013

View Article Online
Edge Article
Chemical Science
3 (a) L. Bartels, Nat. Chem., 2010, 2, 87–95; (b) 12 Simulations: (a) M. A. Bates and M. Walker, Phys. Chem.
J. A. A. W. Elemans, S. Lei and S. D. Feyter, Angew. Chem.,
Int. Ed., 2009, 48, 7298–7332; (c) R. Chakrabarty,
P. S. Mukherjee and P. J. Stang, Chem. Rev., 2011, 111,
6810–6918; (d) S. Klyatskaya, F. Klappenberger,
Chem. Phys., 2009, 11, 1893–1900; (b) M. A. Bates and
M. Walker, Liq. Cryst., 2011, 38, 1749–1757; (c) A. J. Crane
¨
and E. A. Muller, J. Phys. Chem. B, 2011, 115, 4592–4605;
(d) A. J. Crane, F. J. Martinez-Veracoechea, F. A. Escobedo
¨
¨
U. Schlickum, D. Kuhne, M. Marschall, J. Reichert,
and E. A. Muller, So Matter, 2008, 4, 1820–1829; (e)
R. Decker, W. Krenner, G. Zoppellaro, H. Brune, J. V. Barth
and M. Ruben, Adv. Funct. Mater., 2011, 21, 1230–1240.
4 (a) A. Stannard, J. C. Russell, M. O. Blunt, C. Salesiotis,
S. D. Peroukidis, So Matter, 2012, 8, 11062–11071.
13 Also complicated crystal structures could be analyzed and
understood by using the net-approach: (a) M. O'Keeffe and
B. G. Hyde, Philos. Trans. R. Soc. London, Ser. A, 1980, 295,
553–618; (b) A. F. Wells, Acta Crystallogr., 1954, 7, 849–853.
´
´
¨
M. C. Gimenez-Lopez, N. Taleb, M. Schroder,
N. R. Champness, J. P. Garrahan and P. H. Beton, Nat.
Chem., 2011, 4, 112–117; (b) M. O. Blunt, J. C. Russell, 14 (a) X. H. Cheng, X. Dong, G. H. Wei, M. Prehm and
´
´
¨
M. C. Gimenez-Lopez, J. P. Garrahan, X. Lin, M. Schroder,
N. R. Champness and P. H. Beton, Science, 2008, 322,
1077–1081; (c) J. F. Zhao, Y. B. Li, Z. Q. Lin, L. H. Xie,
C. Tschierske, Angew. Chem., Int. Ed., 2009, 48, 8014–8017;
(b) H. F. Gao, Y. F. Ye, X. H. Cheng, M. Prehm, H. Ebert
and C. Tschierske, So Matter, 2012, 8, 10921–10931.
N. E. Shi, X. K. Wu, C. Wang and W. Huang, J. Phys. Chem. 15 (a) B. Glettner, F. Liu, X. B. Zeng, M. Prehm, U. Baumeister,
C, 2010, 114, 9931–9937.
M. A. Bates, M. Walker, P. Boesecke, G. Ungar and
C. Tschierske, Angew. Chem., Int. Ed., 2008, 47, 9063–9066;
(b) F. Liu, R. Kieffer, X. B. Zeng, K. Pelz, M. Prehm,
G. Ungar and C. Tschierske, Nat. Commun., 2012, 3, 1104.
5 (a) A. R. Ramesh and K. G. Thomas, Chem. Commun., 2010,
46, 3457–3459; (b) S. K. Samanata, A. Pal and
S. Bhattacharya, Langmuir, 2009, 25, 8567–8578.
6 Related honeycombs on a larger length scale were reported 16 (a) D. Maspoch, D. Ruiz-Molina and J. Vecian, Chem. Soc.
for star shaped copolymers: Y. Matsushita, K. Hayashida
and A. Takano, Macromol. Rapid Commun., 2010, 31, 1579–
1587.
7 (a) C. Tschierske, Chem. Soc. Rev., 2007, 36, 1930–1970; (b)
G. Ungar, C. Tschierske, V. Abetz, R. Holyst, M. A. Bates,
F. Liu, M. Prehm, R. Kieffer, X. B. Zeng, M. Walker,
B. Glettner and A. Zywocinski, Adv. Funct. Mater., 2011, 21,
Rev., 2007, 36, 770–818; (b) J. J. Perry IV, J. A. Perman and
M. J. Zaworotko, Chem. Soc. Rev., 2009, 38, 1400–1417.
17 (a) A. P. Cote, A. I. Benin, N. W. Ockwig, M. O'Keeffe,
A. J. Matzger and O. M. Yaghi, Science, 2005, 310, 1166–
1170; (b) X. Feng, X. Ding and D. Jiang, Chem. Soc. Rev.,
2012, 41, 6010–6022; (c) E. L. Spitler, J. W. Colson,
F. J. Uribe-Romo, A. R. Woll, M. R. Giovino, A. Saldivar and
W. R. Dichtel, Angew. Chem., Int. Ed., 2012, 51, 2623–2627.
¨
1296–1323; (c) C. Tschierske, C. Nurnberger, H. Ebert,
B. Glettner, M. Prehm, F. Liu, X. B. Zeng and G. Ungar, 18 C. A. Palma, M. Cecchini and P. Samori, Chem. Soc. Rev.,
Interface Focus, 2011, 2, 669–680; (d) C. Tschierske, Top.
Curr. Chem., 2012, 318, 1–108.
2012, 41, 3713–3730.
19 D. J. Wale, Philos. Trans. R. Soc. London, Ser. A, 2012, 370,
2877–2899.
¨
8 (a) M. Kolbel, T.Beyersdorff, X. H.Cheng,C.Tschierske, J. Kain
and S. Diele, J. Am. Chem. Soc., 2001, 123, 6809–6818; (b) 20 M. Prehm, F. Liu, U. Baumeister, X. B. Zeng, G. Ungar and
X. H. Cheng, M. Prehm, M. K. Das, J. Kain, U. Baumeister, C. Tschierske, Angew. Chem., Int. Ed., 2007, 46, 7972–7975.
S. Diele, D. Leine, A. Blume and C. Tschierske, J. Am. Chem. 21 (a) M. Prehm, X. H. Cheng, S. Diele, M. K. Das and
Soc., 2003, 125, 10977–10996; (c) X. H. Cheng, M. K. Das,
U. Baumeister, S. Diele and C. Tschierske, J. Am. Chem. Soc.,
2004, 126, 12930–12940; (d) M. Prehm, C. Enders,
M. Y. Anzahaee, B. Glettner, U. Baumeister and
C. Tschierske, Chem.–Eur. J., 2008, 14, 6352–6368; (e)
C. Tschierske, J. Am. Chem. Soc., 2002, 124, 12072–12073;
(b) X. H. Cheng, M. K. Das, S. Diele and C. Tschierske,
Angew. Chem., Int. Ed., 2002, 41, 4031; (c) N. M. Patel,
I. A. Syed, C. Rosenblatt, M. Prehm and C. Tschierske, Liq.
Cryst., 2005, 32, 55–61.
R. Kieffer, M. Prehm, B. Glettner, K. Pelz, U. Baumeister, 22 M. Prehm, F. Lui, X. B. Zeng, G. Ungar and C. Tschierske, J.
F. Liu, X. B. Zeng, G. Ungar and C. Tschierske, Chem. Am. Chem. Soc., 2011, 133, 4906–4916.
Commun., 2008, 3861–3863; (f) X. H. Cheng, F. Liu, 23 (a) M. O'Keeffe and M. M. J. Treacy, Acta Crystallogr., Sect. A:
X. B. Zeng, G. Ungar, J. Kain, S. Diele, M. Prehm and
C. Tschierske, J. Am. Chem. Soc., 2011, 133, 7872–7881.
9 (a) B. Chen, X. B. Zeng, U. Baumeister, S. Diele, G. Ungar and
Found. Crystallogr., 2009, 66, 5–9; (b) P. Stampi, Helv. Phys.
Acta, 1986, 59, 1260–1263; (c) D. X. Li and K. H. Kuo, Acta
Crystallogr., Sect. B: Struct. Sci., 1986, 42, 152–159.
C. Tschierske, Angew. Chem., Int. Ed., 2004, 43, 4621–4625; (b) 24 Previously reported liquid quasicrystals (LQC) represent
B. Chen, U. Baumeister, G. Pelzl, M. K. Das, X. B. Zeng,
G. Ungar and C. Tschierske, J. Am. Chem. Soc., 2005, 127,
16578–16591.
arrangements of spherical aggregates formed by dendritic
molecules: (a) X. B. Zeng, G. Ungar, Y. Liu, V. Percec,
A. E. Dulcey and J. K. Hobbs, Nature, 2004, 428, 157–160;
(b) G. Ungar, V. Percec, X. B. Zeng and P. Leowanawat, Isr.
J. Chem., 2011, 51, 1206–1215; (c) C. Iacovella, A. S. Keys
and S. C. Glotzer, Proc. Natl. Acad. Sci. U. S. A., 2011, 108,
20935–20940; (d) S. Fischer, A. Exner, K. Zielske, J. Perlich,
10 B. Chen, X. B. Zeng, U. Baumeister, G. Ungar and
C. Tschierske, Science, 2005, 307, 96–99.
¨
11 X. B. Zeng, R. Kieffer, B. Glettner, C. Nurnberger, F. Liu,
K. Pelz, M. Prehm, U. Baumeister, H. Hahn, H. Lang,
G. A. Gehring, C. H. M. Weber, J. K. Hobbs, C. Tschierske
and G. Ungar, Science, 2011, 331, 1302–1306.
¨
S. Deloudi, W. Steuer, P. Lindner and S. Forster, Proc. Natl.
Acad. Sci. U. S. A., 2011, 108, 1810–1814.
This journal is ª The Royal Society of Chemistry 2013
Chem. Sci., 2013, 4, 3317–3331 | 3329

View Article Online
Chemical Science
Edge Article
25 (a) M. Oxborrow and C. L. Henley, Phys. Rev. B: Condens. 35 (a) A. Dell'Aquila, P. Mastrorilli, C. F. Nobile, G. Romanazzi,
Matter, 1993, 48, 6966–6998; (b) D. V. Talapin,
E. V. Shevchenko, M. I. Bodnarchuk, X. Ye, J. Chen and
C. B. Murray, Nature, 2009, 461, 964–967.
G. P. Suranna, L. Torsi, M. C. Tanese, D. Acierno,
E. Amendolae and P. Morales, J. Mater. Chem., 2006, 16,
1183–1191; (b) J. Leroy, N. Boucher, S. Sergeyev, M. Sferrazza
and Y. H. Geerts, Eur. J. Org. Chem., 2007, 1256–1261.
26 (a) K. Hayashida, T. Dotera, A. Takano and Y. Matsushita,
Phys. Rev. Lett., 2007, 98, 195502–195504; (b) T. Dotera, J. 36 T. Yasuda, H. Ooi, J. Morita, Y. Akama, K. Minoura,
Polym. Sci., Part B: Polym. Phys., 2012, 50, 155–167; (c)
T. Dotera, Isr. J. Chem., 2011, 51, 1197–1205.
M. Funahashi, T. Shimomura and T. Kato, Adv. Funct.
Mater., 2009, 19, 411–419.
¨
¨
27 (a) D. Fichow, Handbook of Oligo- and Polythiophenes, Wiley- 37 M. Prehm, C. Tschierske, G. Gotz, P. Bauerle, F. Liu,
¨
VCH, Weinheim, Germany, 1999; (b) P. Bauerle, in Electronic
X. B. Zeng and G. Ungar, Angew. Chem., Int. Ed., 2007, 46,
7856–7859.
¨
Materials: The Oligomer Approach, ed. K. Mullen and G.
Wegner, Wiley-VCH, Weinheim, Germany, 1998; (c) 38 X. H. Cheng, X. Dong, R. Huang, X. B. Zeng, G. Ungar,
D. Fichou, J. Mater. Chem., 2000, 10, 571–588; (d) S. Hotta
and K. Waragai, Adv. Mater., 1993, 5, 896–908; (e)
M. Prehm and C. Tschierske, Chem. Mater., 2008, 20, 4729–
4738.
¨
F. Garnier, A. Yassar, R. Hajlaoui, G. Horowitz, F. Deloffre, 39 B. Grunbaum and G. C. Shephard, Tilings and Patterns, W. H.
B. Servet, S. Ries and P. Alnot, J. Am. Chem. Soc., 1993, 115, Freeman, New York, 1987.
8716–8721; (f) A. Dodabalapur, L. Torsi and H. E. Katz, 40 LC honeycomb phases with p4gm lattice and representing a
Science, 1995, 268, 270–271; (g) A. Facchetti, M. Mushrush,
H. E. Katz and T. J. Marks, Adv. Mater., 2003, 15, 33–38; (h)
A. Facchetti, M. H. Yoon, C. L. Stern, G. R. Hutchison,
M. A. Ratner and T. J. Marks, J. Am. Chem. Soc., 2004, 126,
13480–13501; (i) M. Halik, H. Klauk, U. Zschieschang,
G. Schmid, S. Ponomarenko, S. Kirchmeyer and W. Weber,
square + triangle tiling have previously been observed for
star-shaped triblock copolymers6 and T-shaped facial
amphiphile, in which the position of polar and lipophilic
chains along the rigid core is exchanged compared to the
bolaamphiphiles, see ref. 9b and 10 but not for T-shaped
or X-shaped bolaamphiphiles.
Adv. Mater., 2003, 15, 917–922; (j) T. Otsubo, Y. Aso and 41 C. Keith, A. Lehmann, U. Baumeister, M. Prehm and
K. Takimiya, J. Mater. Chem., 2002, 12, 2565–2575; (k) C. Tschierske, So Matter, 2010, 6, 1704–1721.
A. Kumagai, H. Fukumoto and T. Yamamoto, J. Phys. 42 (a) A. deVries, Pramana, Suppl., n1, 1975, 1, 93–113; (b)
Chem. B, 2007, 111, 8020–8026. A. deVries, J. Mol. Liq., 1986, 31, 193–202.
28 (a) G. Horowitz, D. Fichou, X. Peng, Z. Xu and F. Garnier, 43 (a) M. Gardner, Sci. Am., 1977, 236, 110–121; (b) V. Kumar,
Solid State Commun., 1989, 72, 381–384; (b) H. E. Katz,
Z. N. Bao and S. L. Gilat, Acc. Chem. Res., 2001, 34, 359–
369; (c) F. Garnier, A. Yassar, R. Hajlaoui, G. Horowitz,
D. Sahoo and G. Athithan, Phys. Rev. B, 1986, 34, 6924–
6932; (c) Z. Zhou and K. D. M. Harris, ChemPhysChem,
2006, 7, 1649–1653.
F. Deloffre, B. Servet, S. Ries and P. Alnot, J. Am. Chem. 44 W. Chen and B. Wunderlich, Macromol. Chem. Phys., 1999,
Soc., 1993, 115, 8716–8721. 200, 283–311.
29 A. Mishra, C. Q. Ma and P. Bauerle, Chem. Rev., 2009, 109, 45 C. V. Pham, H. B. Mark and H. Zimmer, Synth. Commun.,
1141–1276. 1986, 16, 689–696.
30 (a) A. Jatsch, E. K. Schillinger, S. Schmid and P. Bauerle, J. 46 (a) T. A. Chen, X. M. Wu and R. D. Rieke, J. Am. Chem. Soc.,
¨
¨
Mater. Chem., 2010, 20, 3563–3578; (b) S. Schmid, E. Mena-
1995, 117, 233–244; (b) R. D. McCullough, R. D. Lowe,
M. Jayaraman and D. L. Anderson, J. Org. Chem., 1993, 58,
904–912.
¨
Osteritz, A. Kopyshev and P. Bauerle, Org. Lett., 2009, 11,
5098–5101.
31 (a) I. McCulloch, M. Heeney, C. Bailey, K. Genevicius, 47 Y. Huang, X. Dong, T. Zheng, L. J. He and X. H. Cheng, J.
I. Macdonald, M. Shkunov, D. Sparrowe, S. Tierney, Yunnan Univ., Nat. Sci. Ed., 2007, 29, 398–400.
R. Wagner, W. M. Zhang, M. L. Chabinyc, R. J. Kline, 48 (a) N. Miyaura, T. Yanagi and A. Suzuki, Synth. Commun.,
M. D. McGehee and M. F. Toney, Nat. Mater., 2006, 5, 328–
333; (b) M. M. Ling and Z. N. Bao, Chem. Mater., 2004, 16,
4824–4840.
1981, 11, 513–519; (b) M. Hird, G. W. Gray and K. J. Toyne,
Mol. Cryst. Liq. Cryst., 1991, 206, 187–204; (c) N. Miyaura
and A. Suzuki, Chem. Rev., 1995, 95, 2457–2483; (d)
N. Miyaura, Cross-Coupling Reactions – A Practical Guide,
Top. Curr. Chem., 2002, 219, 11–59.
32 (a) S. Sergeyev, W. Pisula and Y. H. Geerts, Chem. Soc. Rev.,
2007, 36, 1902–1929; (b) M. O'Neill and S. M. Kelley, Adv.
Mater., 2011, 23, 566–584; (c) W. Pisula, M. Zorn, J. Y. Chang, 49 J. F. W. McOmie and D. E. West, Organic Syntheses, Wiley,
¨
K. Mullen and R. Zentel, Macromol. Rapid Commun., 2009,
30, 1179–1202; (d) M. Funahashi, H. Shimura, M. Yoshio and 50 V. Van Rheenen, D. Y. Cha and W. M. Hartley, Org. Synth.,
T. Kato, Struct. Bonding, 2008, 128, 151–179. 1978, 58, 43–51.
33 (a) A. P. H. Schenning and E. W. Meijer, Chem. Commun., 51 P. Bauerle, T. Fischer, B. Bidlingmeier, J. P. Rabe and
New York, 1973, coll. vol. V, p. 412.
¨
2005, 3245–3258; (b) C. D. Simpson, J. Wu, M. D. Watson
A. Stabel, Angew. Chem., Int. Ed. Engl., 1995, 34, 303–307.
52 L. Claisen and O. Eisleb, Justus Liebigs Ann. Chem., 1913, 401,
21–119.
¨
and K. Mullen, J. Mater. Chem., 2004, 14, 494–504.
34 J. Ma and Q. Li, in Self-organized Organic Semiconductors:
From Material to Device Applications, ed. Q. Li, John Wiley & 53 This value corresponds to the shortest possible molecular
Sons, Hoboken, NJ, 2011.
length of Lmin ¼ 3.0 nm, as measured between the
3330 | Chem. Sci., 2013, 4, 3317–3331
This journal is ª The Royal Society of Chemistry 2013

View Article Online
Edge Article
Chemical Science
secondary OH groups in a molecule with most compact
conformation of the glycerol groups, whereas in the most
stretched conformation Lmax
density along the honeycomb walls (see also the discussion
in Section 3 of the ESI†).
3.6 nm is measured 59 B. Chen, U. Baumeister, S. Diele, M. K. Das, X. B. Zeng,
¼
between the ends of the primary OH groups. The layer
G. Ungar and C. Tschierske, J. Am. Chem. Soc., 2004, 126,
8608–8609.
distance d ¼ 3.03 nm is in line with a smectic monolayer
structure with the aromatic cores and the glycerol groups 60 A combination of squares and rhombs with a ratio 1 : 1 (the
organized in alternating layers. The glycerol groups could
adopt a more-or-less stretched conformation with complete
intercalation of these groups, or a compact conformation
in an end-to-end organization; in both cases space is
provided between the aromatic cores to accommodate the
lateral alkyl chains. The length of a glycerol group in the
most extend conformation is 0.65 nm; Lmax – 0.65 nm
would give d ¼ 2.95 nm for a complete intercalation of the
glycerol units; this is in good agreement with the
measured d-value.
pairs of triangles are fuse to rhombs) is another possible
structure for the p4gm phases under consideration.
However, this structure can be excluded based on the
intensity distribution of the small-angle XRD peaks. In the
square/rhomb tiling there is a reduced intensity of the 20
reection and an increased intensity of the 21 reection,
which is not observed for the diffraction patterns of the
p4gm phases of compounds 1/10 and 2/11, having an
intensity distribution as typically for square/triangle tilings
(see M. Baake and U. Grimm, Chem. Soc. Rev., 2012, 41,
6821–6843). Moreover, the reduction of the number of
honeycomb walls per unit cell would lead to values of nwall
between 2.1 and 1.8 for compounds 2/10 and 2/11,
respectively. These values are out of the range usually
observed in honeycombs formed by molecules with two
lateralchains.57
54 It is interesting to note here that sometimes also the typical
texture of the Colhex phase could be observed for compound
2/5 and in some cases the coexistence of SmA+ textures and
Colhex textures can be observed by polarizing microscopy.
This indicates that this compound is at the edge between
mesh-type lamellar and honeycomb type columnar
organization. However, in XRD experiments only the SmA+ 61 A. Gunier, X-ray Diffraction, Freeman, SanFrancisco, CA, 1963.
phase could be detected, therefore the LC phase of 2/5 is 62 (a) K. Praefcke, D. Singer, B. Kohne, M. Ebert, A. Liebmann
assigned as SmA+; it seems that slight change of the
conditions, as for example surface effects, uptake of
moisture and others can easily induce the triangular
cylinder structure.
and J. H. Wendorff, Liq. Cryst., 1991, 10, 147–159; (b)
H. Bengs, O. Karthaus, H. Ringsdorf, C. Baehr, M. Ebert
and J. H. Wendorff, Liq. Cryst., 1991, 10, 161–168; (c)
¨
S. Laschat, A. Baro, N. Steinke, F. Giesselmann, C. Hagele,
55 F. Liu, B. Chen, U. Baumeister, X. B. Zeng, G. Ungar and
C. Tschierske, J. Am. Chem. Soc., 2007, 129, 9578–9579.
56 P. Oswald and M. Kleman, J. Phys., 1981, 42, 1461–1472.
57 R. Kieffer, M. Prehm, B. Glettner, K. Pelz, U. Baumeister,
F. Liu, X. B. Zeng, G. Ungar and C. Tschierske, Chem.
Commun., 2008, 3861–3863.
G. Scalia, R. Judele, E. Kapatsina, S. Sauer, A. Schreivogel
and M. Tosoni, Angew. Chem., Int. Ed., 2007, 46, 4832–4887.
63 There is a distinct maximum located at n ¼ 3430 cmꢀ1 which
does not change its position. It is at lower frequencies
compared to the possible modes of intramolecular
hydrogen bonding (5-ring: 3612–3619 cmꢀ1 for ethylene
58 With decreasing temperature the d-values of the small-angle
reections are shied to larger distances. For compound 2/7
as an example, ahex increases from ahex ¼ 3.54 nm at T ¼ 160
glycol,
6-ring:
3558
for
propane-1,3-diol;
(a) W. K. Buseld,
3-
methoxypropanol 3554 cmꢀ1
;
M. P. Ennis and I. J. McEwen, Spectrochim. Acta, Part A,
1973, 29, 1259–1264; (b) L. P. Kuhn, J. Am. Chem. Soc.,
1952, 74, 2492–2499; (c) A. B. Foster, A. H. Haines and
M. Stacey, Tetrahedron, 1961, 16, 177–184. The insolubility
of compounds 2/n in non-polar solvents inhibited IR
investigation in solution and therefore the origin of this
maximum cannot be assigned unambiguously.
ꢁ
ꢁC to ahex ¼ 3.80 nm at T ¼ 80 C (see Table 1 and Fig. 4).
This indicates a shrinkage of the lattice parameter with
rising temperature, which is oen observed for polygonal
honeycomb phases8b,d and can be explained if the thermal
expansion of the lateral chains occurs predominately along
the cylinder long axes, thus reducing the core packing
This journal is ª The Royal Society of Chemistry 2013
Chem. Sci., 2013, 4, 3317–3331 | 3331