Thermotropic MIDA Boronates as a Case Study for the Role of Dipolar Interactions in Liquid Crystalline Self-Assembly

Article abstract of DOI:10.1002/chem.201605648

A series of MIDA (N-methylimino diacetic acid) boronates carrying 4-alkoxy, 3,4-bisalkoxy, or 3,4,5-trisalkoxyphenyl substituents were synthesized and their mesomorphic properties characterized by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction (XRD) techniques such as small- and wide-angle X-ray scattering (SAXS and WAXS, respectively). Most derivatives were liquid crystalline. In the case of mono- and bisalkoxy-substituted derivatives, C₆ chains already induced smectic A (SmA) mesophases despite the bulky MIDA head group. With increasing chain length, columnar hexagonal (Col_h) phases replaced SmA phases in the disubstituted series. Quantum chemical calculations on a series of MIDA boronates show that the B?N bond is a dative bond with a positive charge on the boron atom and negative charges on the nitrogen and oxygen atoms. In addition, no π-interaction between the aryl moiety and B?N bond was found, thus the mesogenic unit is electronically decoupled from the MIDA head group. These theoretical findings were supported by IR and Raman spectra as well as by asingle crystal structure analysis of 4-ethoxyphenyl MIDA boronate. Calculations of the electrostatic potential of the MIDA boronate reveal a special polarity pattern that can support the formation of a two-dimensional network and is likely to explain the liquid crystalline self-assembly. The absence of any electronic cross-talk between the MIDA head group and B-aryl or B-alkyl substituents allows the efficient tailoring of the mesophase type through variation of the substituents.

Full text of DOI:10.1002/chem.201605648

A Journal of
Accepted Article
Title: Thermotropic MIDA boronates as a case study for the role of
dipolar interactions in liquid crystalline self-assembly
Authors: Tobias Wöhrle, Rafet Gündemir, Wolfgang Frey, Friederike
Knecht, Andreas Köhn, and Sabine Laschat
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10.1002/chem.201605648
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Thermotropic MIDA boronates as a case study for the role of dipolar interactions in liquid
crystalline self-assembly
Tobias Wöhrle,a Rafet Gündemir,a Wolfgang Frey,a Friedericke Knecht,b Andreas Köhn,c,*
Sabine Laschata,*
a Institut für Organische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart,
Germany
E-mail: sabine.laschat@oc.uni-stuttgart.de
b Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart,
Germany
c Institut für Theoretische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart,
Germany
Abstract
A series of MIDA (N-methylimino diacetic acid) boronates carrying 4-alkoxy, 3,4-bisalkoxy, or
3,4,5-trisalkoxyphenyl substituents were synthesized and their mesomorphic properties
characterized by differential scanning calorimetry (DSC), polarizing optical microscopy (POM)
and X-ray diffraction (WAXS, SAXS). Most derivatives were liquid crystalline. In the case of
mono- and bisalkoxy-substituted derivatives, already C6 chains induced SmA mesophases despite
the bulky MIDA head group. With increasing chain lengths Colh phases replaced SmA phases in
the disubstituted series. Quantum chemical calculations of a series of MIDA boronates show that
the B-N bond is a dative bond with a positive charge on the boron atom and negative charges on
the nitrogen and oxygen atoms, respectively. In addition, no π-interaction between aryl moiety and
B-N bond was found, thus the mesogenic unit is electronically fully decoupled from the MIDA
head group. These theoretical findings were supported by IR and Raman spectra and a single crystal
structure analysis of 4-ethoxyphenyl MIDA boronate. Calculations of the electrostatic potential of
the MIDA boronate reveal a special polarity pattern that can support the formation of a two-
dimensional network and is likely to explain the liquid crystalline self-assembly. The absence of
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any electronic cross talk between MIDA head group and B-aryl or B-alkyl substituents allows the
efficient tailoring of the mesophase type through variation of the substituents.
Key words: MIDA, Boronate, Liquid Crystal, Smectic, Columnar, Quantum Chemical Calculation
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Introduction
Boron containing materials have received increasing interest during the last decade due to their
specific properties. For example, tris-coordinated boron compounds are Lewis acidic, isoelectronic
with carbeniumions, possess  electron acceptor as well as inductive  electron donor capacity,
undergo formation of tetracoordinate borates and conjugate adjacent -systems, while compounds
containing B-N bonds are isoelectronic with the corresponding C-C analogues and display strong
luminescence.[1-7] With regard to thermotropic liquid crystals most work has been devoted to
borondifluoride -diketonates (or -enaminoketonates),[8-14] borondipyrromethene (BODIPY)
derivatives (1)[15-27] and boron clusters (2)[28-35] (Fig. 1). In diketonate and BODIPY derivatives
such as 1 or subphthalocyanines, the boron atom is surrounded by a flat mesogenic -system, which
not only contributes to the liquid crystalline self-assembly, but also adds favorable absorption and
emission characteristics. In contrast, the bulky closo-carboranes 2 are incorporated into rigid rod-
like units in order to obtain suitable mesomorphic properties. These boron clusters are not only
suitable for liquid crystal display applications due to their high dielectric anisotropy 31,36,37] but
also as battery electrolytes.[38] Moreover, they provided insight into fundamental aspects of soft
matter such as the contribution of Coulomb and dipolar interactions on the stabilization of
mesophases.[7,32]
Figure 1.
Discotic BODIPY 1[21], calamitic boron cluster 2[32], discotic borolane 3[48] and
boroxine 4[49]
In contrast, boronic acids, boronates and derivatives thereof are much less explored regarding
liquid crystalline properties despite their extensive use as highly versatile building blocks for
transition metal-catalyzed cross-coupling reactions.[39-42] Based on early work by Seto[43-47]
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electron deficient discotic triphenylene borolanes 3 have been developed by King.[48] During our
previous studies on discotic boroxines 4[49,50] we noticed that neither of the synthetic precursors,
i.e. pinacol borolanes 5[51,52], boronic acids 6[49] and diethanolamine boronates 7 respectively,
displayed any mesomorphism despite their wedge shape in case of 3,4,5-trisalkoxy-substituted
derivatives and the possibility to enforce nanosegregation through hydrogen bonding for the latter
two cases 6 and 7 (Fig. 2). In agreement with our own work a literature survey revealed that
boronate derivatives 5 – 7 with only two or one side chain were not liquid crystalline.[53-55,48,56]
Much to our surprise the tetragonal N-methyliminodiacetic acid (MIDA) boronates 8 showed
double melting, which was taken as evidence for mesophase formation.
[49]
Figure 2. Pinacol borolanes 5 (Cn)3 with n = 10 – 12[51,52], boronic acid 6 (C11)n
and
diethanolamin boronates 7 (Cn)3 with n = 10 – 12 showing no liquid crystalline
behaviour and liquid crystalline MIDA-boronates 8 (Cn)m (n = 6 – 14, m = 1 – 3)
presented in this work.
MIDA boronates are air stable Lewis acid/base complexes pioneered by Contreras[57,58] and
Burke[59] as organoboron species, which are protected against transmetallation and can be
reactivated for further cross coupling by simple saponification giving access to a great diversity of
compound classes.[60] Based on variable temperature NMR studies Contreras calculated an
activation enthalpy of >90 kJ/mol for the cleavage of the B-N dative bond,[57] indicating the
remarkable stability. Further insight came from experimental and theoretical vibrational
spectroscopy studies by Tschumper, Hemmer and coworkers.[61] However, liquid crystalline self-
assembly of MIDA boronates has not been reported in the literature.
For the formation of thermotropic liquid crystalline phases several factors are important. For
example space filling, i.e. minimization of free volume, and shape anisotropy of the mesogenic
molecules, i.e. disk- or rod-shaped mesogens with attached hydrophobic alkyl chains, are
parameters, which lead to nanosegregation because structurally or chemically incompatible parts
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do not mix with each other but occupy different domains.[62-70] Other parameters such as -
interactions, hydrogen bonds or fluorophobic interactions also contribute to the stability of the
mesophase.[62-70] For example, hydrogen bonding determines the phase behaviour of
supramolecular liquid crystal dimers as reported by Imrie.[71] In addition, dimer formation of
molecular dipoles has been identified as the origin for the reentrant behaviour of 4-alkoxy- and 4-
alkyl-4-cyanobiphenyl binary mixtures.[72] Polar interactions play a stabilizing role in bent-core
molecules.[73] For amphiphilic, ionic or zwitterionic liquid crystals nanosegregation of charged
molecular subunits and less polar groups together with electrostatic interactions are the major
driving forces for mesophase formation. Besides chemical incompatibility the difference in
molecular flexibility contributes to nanosegregation.[74] It should be emphasized that the presence
of mesogenic units is not required in order to obtain liquid crystalline phases.[74a] Prominent
examples are lyotropic,[75,76] amphotropic[77] and ionic liquid crystals.[66-70,78] As demonstrated by
Saito, even classical thermotropic systems such as 4-alkylcyanobiphenyls display amphiphilic
properties upon mixing with n-alkanes.[77]
However, these various parameters did not provide an obvious explanation for the unique liquid
crystalline self-assembly of MIDA boronates 8 with respect to boronic acid derivatives 5 – 7. The
above-mentioned lack of knowledge on the materials properties of MIDA boronates 8 motivated
us to explore them as a novel class of thermotropic liquid crystals. Our aim was to understand the
different phase behaviour of MIDA boronates 8 as compared to boronic acid derivatives 5 – 7. By
a combined theoretical and experimental study, we hoped to gain insight into the role of dipolar
interactions on the liquid crystalline self-assembly of such Lewis acid/base complexes and to obtain
design principles useful for other thermotropic liquid crystals. The results are described below.
Results and Discussion
Synthesis
Three series of MIDA boronates 8 (Cn), 8 (Cn)2 and 8 (Cn)3 (n = 4, 6, 8, 10, 12, 14) with one, two
or three alkoxy side chains at the phenyl ring were prepared (Figure 3). Mono-, di- and
trisalkoxybromobenzenes 9 – 11 were lithiated with n-BuLi, followed by sequential treatment with
boron triisopropyl borate and MIDA according to the method by Burke[79] and the resulting MIDA
boronates 8 (Cn)m were isolated in 20 - 75 % yield. For comparison, biphenyl derivative 13 (C12)
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carrying a typical calamitic mesogenic subunit was prepared from the respective 4’-bromo-4-
dodecoxy-biphenyl 12 accordingly.
Figure 3.
Synthesis of MIDA boronates 8 (Cn)m and 13 (C12).
Mesophase Behaviour
Mesomorphic properties were investigated by differential scanning calorimetry (DSC), polarizing
optical microscopy (POM) and X-ray diffraction (WAXS, SAXS). A typical DSC curve is shown
in Figure 4a for decyloxyphenyl MIDA boronate 8 (C10). Upon 1st heating two endothermal phase
transitions were visible, the melting from the crystalline to the liquid crystalline at 111 °C and the
clearing into the isotropic liquid at 178 °C. Upon 1st cooling only the formation of the liquid
crystalline phase at 179 °C was observed. Upon 2nd heating and 2nd cooling only the clearing points
were observable. Due to the fact, that melting (or crystallization) peaks could not be clearly
identified for most of the MIDA boronates, these transitions were determined via POM. For this
purpose, the respective sample was heated and cooled with the same rates as in the DSC
experiments (Δ = 5K·min-1). If a phase transition occurred, heating and cooling was reiterated in
that temperature range with lower heating and cooling rates (Δ = 2K·min-1).
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Figure 4.
a) DSC traces of first, second and third heating / cooling cycle of 8 (C10), b) DSC
traces of first heating and cooling of 13 (C12) (heating / cooling rate 5 K·min-1), c)
DSC traces of first, second and third heating / cooling cycle of 8 (C10)2 (heating /
cooling rate 5 K·min-1).
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Figure 5.
Phase widths of the MIDA boronates 8 (Cn)m and 13 (C12) obtained by DSC and
POM (heating/cooling rate 5 K/min). Phase transition temperatures were taken upon
second heating, exceptions: 8 (C6) was taken upon second cooling, 13 (C12) was
taken upon first heating. The following phases were observed: ■ crystalline (Cr),
■ smectic A (SmA), ■ hexagonal columnar (Colh).
The complementary DSC and POM results are summarized in Figure 5 (for details of DSC traces
see Supp. Info). Compounds 8 (C4), 8 (C5), and 8 (C6)3 with short side chains were non-
mesomorphic. All other MIDA boronates showed enantiotropic mesomorphism regardless of the
number and lengths of side chains. For the monoalkoxyphenyl series 8 (Cn) mesophase widths and
stabilities increased with increasing chain lengths n from 19 K (n = 6) to 96 K (n = 14). In order to
check, whether the high clearing temperatures between 179 °C for 8 (C10) and 200 °C for 6 (C14)
might lead to decomposition, TGA measurements for 8 (C10) were carried out. As shown in Figure
S18b, TGA revealed that the compound was stable up to 300 °C. For comparison, the mono-
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substituted biphenyl 13 (C12) was studied by DSC (Fig. 4b). Upon 1st heating three endothermal
transitions were observed, at 116 °C a melting transition from crystalline to crystalline phase, at
161 °C to the liquid crystalline phase, and at 246 °C from the mesophase to the isotropic liquid.
The phase width of 85 K is similar to the respective alkoxyphenyl derivative 8 (C12), although, at
elevated temperatures. During subsequent cooling no more phase transitions were visible.
Presumably, clearing to the isotropic liquid lead to decomposition, which is in contrast to the
thermal stability of the alkoxyphenyl derivative 8 (C10). Under the POM strong homeotropic
alignment was detected for the 8 (Cn) series and for 13 (C12). After shearing filament-like textures
were visible, suggesting the presence of a SmA phase (Figure 6). Presumably, homeotropic
alignment is enforced by the polar head group interacting with the glass surface.
Figure 6.
POM images: a) homeotropic aligned sample of 8 (C10) at 170 °C, b) same sample
of 8 (C10) after shearing at 170 °C, c) 8 (C12) after shearing at 150 °C, d) 13 (C12)
after shearing at 200 °C, e) 8 (C10)2 after shearing at 120 °C, f) 8 (C10)2 at 100 °C
after cooling from the SmA phase, g) 8 (C10)3 at 105 °C, h) 8 (C12)3 at 100 °C. All
images were taken during 2nd cooling from the isotropic liquid (except 13 (C12)
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which was investigated during 1st heating), heating/cooling rate was 5 K·min-1,
100x magnification.
DSC and POM experiments of the dialkoxyphenyl series 8 (Cn)2 showed in each case mesophases
of similar phase widths as compared to the monoalkoxyphenyl series 8 (Cn), albeit decreased
melting and clearing points. With increasing chain lengths n the clearing temperatures increased.
More importantly, the phase type changed with increasing chain lengths. While the shortest
member of the series 8 (C6)2 displayed a crystalline to SmA transition at 65°C and a clearing
transition at 120°C upon heating, the higher homologue 8 (C10)2 displayed a melting point at 49°C,
followed by a transition to the SmA phase at 111°C and a clearing transition at 130°C. The phase
sequence is reproducible as can be seen in Figure 4c, however the melting point from crystalline
state to the low temperature mesophase is broadened significantly during cooling and not visible
in the 2nd and 3rd heating cycles. Under the POM 8 (C6)2 and 8 (C8)2 displayed strong homeotropic
alignment with filament like textures after shearing. This indicates the presence of a SmA
mesophase. The high temperature phase of 8 (C10)2 showed a similar behaviour implying a SmA
phase as well (Figure 6e). Subsequent cooling to the low temperature mesophase gave an obvious
change to fan-shaped textures which are typical for Colh phases (Figure 6f). The higher homologues
of the dialkoxyphenyl series, 8 (C12)2 and 8 (C14)2, each showed only one broad liquid crystalline
phase with temperature ranges of 85 K and 108 K respectively. POM investigations showed focal
conic and broken fan-like textures with, especially for 8 (C14)2, large homeotropic areas, suggesting
Colh phases.
All members of the trisalkoxyphenyl series 8 (Cn)3 with a minimum chain length of C8 showed
broad Colh phases. The addition of a third side chain at the phenyl ring led to a further decrease of
melting and clearing points as compared to the 8 (Cn)2 series, while mesophase widths remained
between 61 K and 121 K. For derivatives with longer alkyl chains (n = 10, 12, 14) stable room
temperature Colh phases were detected. The melting point of 8 (C12)3 was even below 0 °C at -
15 °C, with a clearing point at 106 °C 8 (C12)3 showed the broadest mesophase (121 K) of all
examined MIDA boronates. Under the POM fan-shaped textures of the Colh phase revealed
homeotropically aligned areas. Typical examples are shown for 8 (C10)3 (Figure 6g) and 8 (C12)3
(Figure 6h) respectively.
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Crystal Structure
Fortunately, the non-mesomorphic MIDA boronate 8 (C4) provided single crystals suitable for
X-ray crystal structure determination (Figure 7a).[80] MIDA boronate 8 (C4) crystallized in the
monoclinic centrosymmetric space group P21/c with one molecule in the asymmetric unit (full
XRD data see Supporting Information). Crystal quality was only sufficient, indicated by a R(int)
of 0.14, which is mainly caused by thermal fluctuations of the alkyl chains. In addition, the carbonyl
function in the MIDA unit shows a slight rotational disorder with equivalent population factors
(C3A=O3A / C3B=O3B). With respect to these conditions, the angles and distances at the boron
and at the nitrogen are in good agreement with a tetrahedral surrounding. The angles at the boron
are with values of O1-B1-O2 = 109.4(4)°, O1-B1-C6 = 113.0(5)° and O2-B1-C6 = 114.4(4)° close
to the ideal tetrahedral angle. The same applies to the angles at the nitrogen atom,
C4-N1-C5 = 111.1(5)°, C4-N1-C2 = 113.5(6)° and C5-N1-C2 = 108.5(5)°. The B-O distances are
identical with 1.464(7) Å and 1.467(7) Å, respectively. The B-N distance is with a value of 1.658 Å
in the same range as reported before for phenyl MIDA-boronate derivatives.81 The distance of the
boron to the phenyl moiety is 1.573(7) Å. The packing diagram of the unit cell (Figure 7b) reveals
a lamellar structure, in which polar and hydrophobic domains are formed by the MIDA boronate
head groups and the alkoxy phenyl moieties, respectively. It should be emphasized that in the solid-
state phenyl rings are involved in the interdigitated side chains. Thus, a polar MIDA boronate
bilayer is sandwiched between two non-polar alkoxyphenyl bilayers, strongly resembling a smectic
bilayer geometry.
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Figure 7.
a) Molecular structure of 8 (C4) in the crystalline state. b) View of the unit cell along
the b axis with distinct bilayer-like structure.
Quantum Chemical Calculations
As discussed in the previous section, the single crystal data of 8 (C4) gives an idea of how the
molecules are arranged in the liquid-crystalline phase. With this information at hand, we wanted to
understand the role of the MIDA head group. In particular, we wanted to investigate, whether there
is any cross talk between the head group and the phenyl-alkoxy residues and understand the
difference between MIDA boronates 8 and pinacol borolane 5, boronic acids 6 and diethanolamine
boronates 7 regarding phase behaviour.
The TURBOMOLE program package[82,83] was employed for all quantum chemical calculations.
Equilibrium structures were computed with Møller-Plesset second-order perturbation theory (MP2)
and the def2-TZVPP basis sets for all atoms.[84] The resolution-of-the-identity approach was used
to speed up two-electron integral evaluations using the appropriate auxiliary basis sets.[85,86]
Relaxed MP2 electron densities were used for the natural population analysis (NPA)[87] of the
charge distribution and for computing dipole moments. As TURBOMOLE does not support
computation of natural bond orbitals, we resorted to intrinsic bond orbitals (IBOs)[88] based on the
Hartree-Fock orbitals, which serve about the same purpose and for which an in-house
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implementation is available. Graphical representations of the quantum chemical results were
prepared with the TmoleX program.[89]
The MP2 approach, in particular in connection with basis sets of triple- type as used in this study,
is known to give reliable structures for main group compounds with typical errors not exceeding
0.02 Å relative to highly accurate reference computations.[90,91] We also note that the B-N bond
distance computed with this approach is in much better agreement with the experimental value
determined above for 8 (C4) as compared to density functional theory approaches. Details about
this issue, further validation studies and the relevant parameters that characterize the bonding to
the boron atom are given in the Supporting Information. All important structure parameters of the
single crystal structure are well reproduced. Computed and experimental bond lengths agree within
0.02 Å, bond angles agree within 4 degrees. This confirms that the method describes the electronic
structure of the molecules sufficiently well.
In order to shed further light on the bonding situation in the MIDA boronate head group,
particularly around the boron atom, we computed the partial charges by a natural population
analysis (NPA). The results are shown in Figure 8 (left).
Figure 8.
Left: Computed partial charges on the head group of 8(C4). The charges refer to the
indicated atoms or to CH2 and CH3 groups. Right: Intrinsic bond orbitals
characterizing the bonding to boron. Isosurfaces are shown in the top row, while the
bottom contains a color-coded contour plot in a plane containing boron and the
corresponding neighboring atom.
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According to the NPA, the boron atom is strongly charged with nearly one positive unit charge
accumulated on this center. All surrounding atoms carry negative partial charges, indicating
significantly polarized bonds to boron. This result clearly suggests to address the B–N bond as a
dative bond (where the two electrons are still formally counted for nitrogen), as a Lewis-structure
with a shared electron pair implies a negative formal charge on boron and a positive formal charge
on nitrogen, clearly in contrast with the above result.
To further elucidate the bonding situation, we computed the intrinsic bond orbitals (IBOs) of the
molecule. The orbitals representing the bonding to boron are shown in Figure 8 (right). The IBO
corresponding to the B–N bond clearly shows strong nitrogen sp3 character and little contribution
from boron and should be thus addressed as a dative bond. The IBOs corresponding to the B–O
and B–C bonds are also polarized but to a lesser degree. No further IBO indicating π-conjugation
of the alkoxyphenyl ring and the MIDA boronate head-group is found.
Figure 9.
Derivatives computed for natural population analysis.
For closer investigation of the influence of the substituents the analysis of the partial charges was
extended to seven different MIDA boronates carrying methyl (14), phenyl (15), 4-ethoxyphenyl
(8 (C2)) 4-butoxyphenyl (8 (C4)), 4-hexyloxyphenyl 8 (C6), 3,4-diethoxyphenyl (8 (C2)2) and
3,4,5-triethoxyphenyl (8 (C2)3) units at the boron atom (Figure 9). This study revealed that the
substituents have a negligible influence on the electronic structure of the MIDA boronate group.
Neither the type of substituent in 14, 15 and 8 (C2), i.e. methyl vs. phenyl vs. 4-ethoxyphenyl nor
the length of the side chains in 8 (C2), 8 (C4), and 8 (C6) or the number of side chains in 8 (C2),
8 (C2)2 and 8 (C2)3 give a substantial difference of the partial charges. The partial charge on boron
changes by less than 0.01 e, for the remaining atoms by even less than 0.002 e (Table 1 and
Supporting Information). We therefore conclude that the MIDA boronate head group is
electronically fully decoupled from the residue at the boron atom.
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Table 1.
Comparison of computed partial charges of boron and its neighboring atoms.
Substituent
Compound
14
15
8(C2)
8(C4)
8(C6)
8(C2)2
8(C2)3
B1
N1
O1
O2
C6
methyl
phenyl
+0.924
+0.929
+0.931
+0.931
+0.931
+0.933
+0.934
–0.361 –0.617 –0.618 –0.940a
–0.356 –0.616 –0.618 –0.362
–0.357 –0.616 –0.618 –0.382
–0.357 –0.616 –0.618 –0.382
–0.357 –0.616 –0.618 –0.382
–0.357 –0.616 –0.617 –0.376
–0.357 –0.616 –0.619 –0.358
4-ethoxyphenyl
4-butoxyphenyl
4-hexyloxyphenyl
3,4-diethoxyphenyl
3,4,5-diethoxyphenyl
aThe partial charge of the entire CH3 group is –0.274 e.
This result was further supported by IR and Raman spectroscopic studies at room temperature (for
details on the measuring conditions see Supporting Information). The following B-N stretching
modes were observed in the IR and Raman spectra respectively: (B-N) = 592 and 591 cm-1 for
8 (C10), 587 and 589 cm-1 for 8 (C10)2, 587 and 593 cm-1 for 8 (C10)3. The values do not show any
differences between mono-, di- and tri-substituted phenyl derivatives further supporting the
absence of any electronic communication between the aryl ring and the B-N bond.
From the above theoretical and experimental data, we anticipated that the distinct mesomorphic
behaviour of MIDA boronates 8 – as compared to structurally related boron compounds 5 – 7,
which carry the same aryl moiety – should be somehow related to the polar character of the head
group. Therefore, the electronic properties of the MIDA group in the model system 8 (C2) were
compared with the other boron containing groups: diethanolamine boronate 7 (C2), boronic acid 6
(C2), and pinacol borolane 5 (C2). Note that our findings in Table 1 strongly suggested that we
could confine our study to the ethoxy group (abbreviated as C2), as the length of the alkyl chain
did not have any significant influence on the electronic structure of the head group.
Our computations showed that the head groups of compounds 5 – 8 indeed have a significantly
different polar character, see Figure 10. The strongly alternating partial charges on the MIDA
boronate 8 (C2) as shown in Figure 8, already suggested that this group carries a strong dipole
moment. This is in fact the case, we computed a dipole moment of 7.6 Debye units. More detailed
insight is gained from inspecting the electrostatic potential of the molecule, Figure 10a. The oxygen
atoms of the carboxyl groups accumulate negative charge and give rise to a strongly negative
potential in this region. Positive charge is accumulated near the opposite methyl group and
methylene bridges. As indicated in Figure 10a, the charge distribution can be qualitatively
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addressed as originating from two distributed dipoles. As we will discuss below, this charge
distribution may in fact rationalize the formation of a layered structure.
Replacing the carboxyl units in MIDA boronate 8 (C2) by alkoxy groups in diethanolamine
boronate 7 (C2) resulted in a much less polar charge distribution (Figure 10b). The overall dipole
moment is still 5.9 Debeye units, but the negative charges accumulate in a much smaller area.
Hence we do not get the distributed dipoles as discussed for 8 (C2). The same is observed for
boronic acid 6 (C2) and pinacol borolane 5 (C2) which also have much smaller dipole moments of
2.8 and 1.4 Debeye units, respectively (Figure 10c,d).
Figure 10.
Visualization of the electrostatic potential of different boron containing head-groups
in MIDA boronate 8 (C2), diethanolamine boronate 7 (C2), boronic acid 6 (C2) and
pinacol borolane 5 (C2) with a 4-ethoxy-phenyl ring as further residue at the boron
atom. The electrostatic potential is color coded (red = –1.9 eV to blue = +1.9 eV) on
an isosurface of the electron density (0.0067 Å–3). Two different perspectives are
shown (from the side and from below). Computed dipole moments are given on the
bottom of each column. For (a) the electrostatic potential may be qualitatively
described as originating from two distributed dipoles as indicated in the bottom
view.
16
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Figure 11.
Schematic distribution of dipoles in the MIDA boronate packing scheme according
to crystal structure of 8 (C4).
As indicated above, the charge distribution computed for 8 (C4) can be interpreted as two
distributed dipoles. This charge distribution is compatible with a 2D packing of the molecules as
derived from the crystal structure of 8 (C4), see Figure 11. Note that cofacially arranged dipoles
prefer an antiparallel alignment while dipoles arranged in a linear chain prefer parallel alignment.
The schematic distribution of the dipoles in Figure 11 also gives a hint on the mechanisms of the
mesophase formation from MIDA boronates 8. On the one hand, the different polarities of the
MIDA and the alkoxyphenyl group lead to phase separation and formation of the bilayer structure.
On the other hand, the strong dipolar interactions of the MIDA groups stabilizes the sublayer as
shown in Figure 11, whereby a layer-like mesophase can be formed. In the case of 5, 6, and 7 either
weaker tendencies of phase separation or weaker dipolar interactions do not support a stable bilayer
structure. With the results of the quantum chemical calculations in hand it was possible to deduce
a general understanding on the mesophase formation of the MIDA boronates 8 which was utilized
to explain the following X-ray investigations.
Mesophase Geometries
To gain further insight in the phase geometries of the liquid crystalline MIDA boronates small
(SAXS) and wide angle (WAXS) X-ray scattering experiments were conducted (for full XRD data
see Supporting Information). First, the derivatives for which the POM investigations suggested a
17
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layer-like mesophase were investigated. Therefore, the samples were investigated via SAXS at
different temperatures during cooling from the isotropic liquid. From the obtained (001) XRD
reflexes the respective layer spacings d were determined. In Figure 12a the results of
monoalkoxyphenyl derivative 8 (C10) and bisalkoxyphenyl derivative 8 (C10)2, in the high
temperature mesophase, are depicted. During cooling the layer spacing gradually increased, which
is typical for SmA mesophases, presumably because of a decreasing interdigitation of the alkoxy
chains.[92] Interestingly, the layer spacing of 8 (C10) is larger than that of 8 (C10)2 although the latter
has two side chains which should require more space than the one of the mono substituted
derivative.
For better comparison, the layer spacings at the reduced clearing point dred (at 0.95 × Tc)[92] were
calculated for all derivatives 8 (Cn) (n = 6 – 14) and 8 (Cn)2 (n = 6 – 10) using the equations of the
trendlines of the respective SAXS layer spacing temperature dependency. Additionally, for each
compound the molecular lengths L (and 2L) between the outer most atoms in the stretched all-
trans conformation were calculated by using the Avogadro 1.1.1 software (Figure 12b).[93] The dred
values for both substitution patterns 8 (Cn) and 8 (Cn)2, and for 13 (C12) are between L and 2L
indicating the formation of smectic bilayers SmA2 for both series. However, the observed layer
spacings differ increasingly with longer alkyl chains from the calculated bilayer distances
indicating a stronger interdigitation with increasing alkyl chain lengths. Therefore, a comparison
of the dred values with the maximal interdigitated bilayers is of interest. The size of the MIDA
boronate head group together with the attached phenyl ring is Lcore = 8.15 Å. For maximum
interdigitation it is assumed that the layer spacing is Lmax = L + Lcore, since the alkoxy side chains
are completely interleaved (Fig. 12c). The values of Lmax are very close to those of the respective
layer spacings dred indicating a strong interdigitation especially for longer chain lengths. For
8 (C12), 8 (C14), 13 (C12), and 8 (C10)2 the calculated interdigitation give values of 99 %, indicating
a complete interdigitation at the reduced clearing point. However, these findings do not suggest the
participation of the core structure in the interdigitation as implied in the single crystal structure of
8 (C4) (Fig. 7b).
18
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Figure 12.
a) Layer spacing temperature dependency of ● 8 (C10) and ■ 8 (C10)2 in the SmA2
phase derived from SAXS experiments (* transition from the SmA2 phase to the low
temperature Colh phase), b) layer spacing at reduced clearing points ● dred compared
to single (▲, L) and double (■, 2L) molecular lengths, and to maximal interdigitation
(×, Lmax), c) illustration of the molecular dimensions.
According to the DSC and POM studies (Figure 4c, Figure 6e,f) bisdecyloxy-substituted derivative
8 (C10)2 displayed a second mesophase at lower temperatures in addition to the SmA2 phase. The
results of the XRD experiments of this lower temperature mesophase are shown in Figure 13a. The
SAXS profile only displays one reflection indexed as (10) which is not sufficient for the assignment
of the phase. However, the Colh phase geometry was confirmed by the WAXS experiment shown
in the inset of Figure 13a. In addition to the broad halo at 4.5 Å caused by the molten alkyl chains,
a hexagonal orientation of the (10) reflection was detected, which is typical for Colh mesophases.
19
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Figure 13.
a) SAXS profile of 8 (C10)2 at 90 °C and WAXS diffraction pattern at 90 °C (left),
magnification of inner signals of the WAXS pattern (right), b) SAXS profile of
8 (C8)3 at 90 °C and WAXS diffraction pattern at 90 °C (left), magnification of inner
signals of the WAXS pattern (right).
For the remaining dialkoxy- and trialkoxyphenyl MIDA boronates 8 (Cn)2 (n = 12, 14) and 8 (Cn)3
(n = 8 – 14) XRD investigations confirmed the assignment of Colh phase geometries. For
derivatives 8 (C14)2, 8 (C8)3, and 8 (C10)3 hexagonal orientations of the (10) reflection were found
either in the WAXS or SAXS experiments. Figure 13b shows the results of the XRD experiments
for 8 (C8)3. The SAXS profile displays three reflexes in the ratio of 1 : 1/√3 : 1/2 indexed as (10),
(11), and (20).[94] Moreover, the depicted WAXS pattern displays a halo in the wide angle region
and six distinct reflexes in the small angle region arranged in a hexagonal manner supporting the
assignment of the Colh phase.
In order to rationalize the transition from the smectic mesophases observed for mono- 8 (Cn) (n = 6
– 14) and dialkoxy-substituted derivatives 8 (Cn)2 (n = 6 – 10) to columnar hexagonal mesophases
for 8 (Cn)2 (n = 10 – 14) and trialkoxy-substituted MIDA boronates 8 (Cn)3 (n = 8 – 14)
minimization of free volume and increasing sterical demand of the alkyl chains seem to govern
20
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mesophase formation. Presumably for one or two side chains a lamellar organization is preferred
resulting in SmA2 bilayers (Figure 14). However, as the lengths of the two alkoxy chains exceed
C10 or an additional third chain is attached to the phenyl ring, the bilayer cannot accommodate any
longer the MIDA boronates 8 (Cn)m in an anti-parallel interdigitated fashion, but a micellar-like
aggregate of the wedge-shaped mesogens is favoured, resulting in the Colh phase. The number of
molecules per disk Z could be calculated according to 푍 = 휌·푁 ·퐴·ℎ, where ρ is the density
퐴
푀
(considered close to 1), NA is Avogadro’s constant, A is the columnar cross section, h is the height
of a disc (approximately the d-value of the respective halo), and M is the molecular weight of a
single molecule.[95]
The results of these calculations are summarized in Table 2. For 8 (C10)2, a Z-value of 6 was
calculated. Therefore, in a hexagonal lattice with a lattice parameter ahex = 38.3 Å one disc consists
of 6 molecules forming a micellar-like aggregate. Upon increase of the side chain lengths to n = 12
and n = 14 respectively, the lattice parameters remained relatively constant at ahex = 37.7 Å and
ahex = 38.3 Å respectively, while the number of molecules per disc decreased to Z = 5 for 8 (C12)2
and 8 (C14)2, presumably due to increased interdigitation and increased volume requirements of a
single molecule within the micellar aggregate. For the trisalkoxy-substituted MIDA boronate
8 (C8)3 with C8 chains a lattice parameter ahex = 31.2 Å was obtained and the calculated Z-value
was 4. Upon increasing the side chain lengths to n = 10 and n = 12, the lattice parameters increased
steadily to ahex = 33.5 Å and ahex = 36.3 Å respectively, while the calculated Z-values remained
constant at Z = 4. Probably due to the increased volume fraction of the trisubstituted MIDA
boronates, e.g. 8 (C12)3 as compared to the corresponding disubstituted counterpart 8 (C12)2 fewer
molecules can be accommodated in the micellar aggregate, thus the Z-value decreases from 6 and
5 in the disubstituted series to 4 in the trisubstituted series. However, constant Z-values for 8 (C8)3,
8 (C10)3 and 8 (C12)3 are only possible, if the lattice parameter increases with increasing chain
lengths. Surprisingly, in case of MIDA boronate 8 (C14)3 with three C14 chains a significantly larger
lattice parameter of ahex = 50.1 Å was detected. In order to accommodate such a lattice, the number
of molecules with the micellar aggregate needs to be increased considerably from Z = 4 to Z = 7.
21
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Table 2.
XRD data for MIDA boronates displaying hexagonal columnar mesophases 8 (C10)2
– 8 (C14)2 and 8 (C8)3 – 8 (C14)3.
Mesophase
ahexa / Å
dexp (dcalc) / Å hk
Zb
6
8 (C10)2 Colh at 90 °C
p6mm
a = 38.3
33.1
4.5
(10)
halo
(10)
8 (C12)2 Colh at 120 °C
p6mm
a = 37.7
32.6
5
16.3 (16.31) (20)
4.1
halo
(10)
halo
(10)
8 (C14)2 Colh at 140 °C
p6mm
a = 38.3
a = 31.2
33.2
4.6
5
4
8 (C8)3 Colh at 90 °C
p6mm
27.0
15.6 (15.60) (11)
13.4 (13.51) (20)
4.2
halo
(10)
halo
(10)
halo
(10)
8 (C10)3 Colh at 90 °C
p6mm
a = 33.5
a = 36.3
a = 50.1
29.0
4.6
4
4
7
8 (C12)3 Colh at 70 °C
p6mm
31.5
4.7
8 (C14)3 Colh at 60 °C
p6mm
43.4
21.7 (21.71) (20)
14.4 (14.47) (30)
10.1 (9.96)
9.5 (9.48)
8.8 (8.68)
4.7
(32)
(41)
(50)
halo
a The parameter ahex corresponds to the column diameter and was
calculated with ahex = 2·d10 / √3. b Rounded to integers.[95]
The X-ray diffraction data together with the observation, that even MIDA boronates with relatively
short alkyl chains, i.e. C6 for 8 (Cn), 8 (Cn)2 and C8 for 8 (Cn)3 displayed mesomorphic properties
suggested that the dipolar interactions between the MIDA boronate head groups play an important
role in the stabilization of the mesophase, even in the absence of either strong van der Waals
interactions exerted by long alkoxy chains or strong -interactions.
22
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Figure 14.
Proposed self-assembly of the MIDA boronates 8 into SmA2 or Colh mesophases
depending on the number and lengths of the alkoxy side chains.
Conclusion
In conclusion, we have demonstrated for the first time that MIDA boronates can indeed induce
thermotropic liquid crystalline properties even when the MIDA boronate head group is connected
to a mono-, di- or trialkoxyphenyl unit with relatively short alkyl chain lengths of C6 for 8 (Cn),
8 (Cn)2 or C8 for 8 (Cn)3. In order to understand, why MIDA boronates 8 form stable mesophases,
whereas the corresponding pinacol borolanes 5, boronic acid 6 or diethylamino boronates 7 are
devoid of any liquid crystalline self-assembly, quantum chemical calculations were carried out.
The calculations clearly revealed a charge distribution at the B-N bond, where the positive charge
is located at the boron atom, while the negative charge is positioned at the nitrogen atom,
suggesting that the bonding situation in the MIDA boronate should be characterized by a dative
bond rather than a zwitterionic Lewis structure. According to the calculations the MIDA head
group is electronically fully decoupled from the remaining substituent at the boron, regardless
whether the phenyl ring carries ethoxy substituents or longer alkoxy chains. This allowed us to use
non-mesomorphic 4-ethoxyphenyl MIDA boronate 8 (C2) as a mimic for higher homologues
8 (Cn) (n ≥ 6) capable of liquid crystalline self-assembly in subsequent calculations, where the
unique properties of the MIDA head group in comparison with diethylamino boronate, boronic
acid and pinacol borolane head group were assessed. According to the calculations the overall
dipole moment decreases in the series 8 (C2) > 7 (C2) > 6 (C2) > 5 (C2), suggesting that dipolar
interactions between mono-alkoxy-substituted MIDA boronates 8 (Cn) play a prominent role in the
stabilization of smectic mesophases. Dipolar interactions even seem to overrule hydrophobic
interactions or hydrogen bonds which are present in the boronic acid derivatives 5 (Cn) - 7 (Cn).
Experimental results showed that for MIDA boronates 8 (Cn)m the mesophase type is determined
by the number and lengths of alkoxy chains, i.e. for one or two short alkoxy chains smectic A
23
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phases were observed, while two longer or three alkoxy chains led to hexagonal columnar
mesophases. Thus, the scope of MIDA boronates has been extended far beyond cross-coupling
reagents into tailor-made soft matter. It should be emphasized that our work on dipolar interactions
in liquid crystalline MIDA boronates complement recent studies by Kaszynski,[96] who was able to
quantify the contribution of dipolar interactions to the clearing temperature of carborane clusters
via isosteric and isoelectronic replacement. Future work must demonstrate, whether dipolar
interactions can be employed to generate other novel thermotropic materials.
Acknowledgement
Generous financial support by the Deutsche Forschungsgemeinschaft, the Ministerium für
Wissenschaft, Forschung und Kunst des Landes Baden-Württemberg and the Bundesministerium
für Bildung und Forschung is gratefully acknowledged.
References
[1] Review: Z. Liu, T. B. Marder, Angew. Chem. Int. Ed. 2008, 47, 242.
[2] Review: G. Vancoille, R. Hoogenboom, Polymer Chem. 2016, 7, 5484.
[3] Review: Y. Weng, X. Wang, X. Wang, Y. Bando, D. Golberg, Chem. Soc. Rev. 2016, 45, 3989.
[4] Review: C. D. Entwistle, T. B. Marder, Angew. Chem. Int. Ed. 2002, 41, 2927.
[5] Review: D. Bonifazi, F. Fasano, M. Mercedes Lorenzo-Garcia, D. Marinelli, H. Oubaha, J.
Tasseroul, Chem. Comm. 2015, 51, 15222.
[6] Review: T. Tanaka, Y. Chujo, Macromol. Rapid Commun. 2012, 33, 1235.
[7] Review: T. B. Marder, Science 2006, 314, 69.
[8] I. Sanchez; C. Nunez, J. A. Campo, M. R. Torres, M. Cano, C. Lodeiro, J. Mater. Chem. C
2014, 2, 9653.
[9] Y. Bando, T. Sakurai, S. Seki, H. Maeda, Chem. Asian J. 2013, 8, 2088.
[10]Y. Terashima, M. Takayama, K. Isozaki, H. Maeda, Chem. Commun. 2013, 49, 2506.
[11]M. J. Mayoral, P. Ovejero, J. A. Campo, J. V. Heras, E. Oliveira, B. Pedras C. Lodeiro, M.
Cano, J. Mater. Chem. 2011, 21, 1255.
[12]I. Sanchez, M. J. Mayoral, P. Ovejero, J. A. Campo, J. V. Heras, M. Cano, C. Lodeiro, New J.
Chem. 2010, 34, 2937.
[13]O. A. Turanova, E. V. Kaledyaeva, O. I. Gnezdilov, S. I. Nikitin, A. N. Turanov, Russ. J.
General Chem. 2010, 80, 258.
24
This article is protected by copyright. All rights reserved.

10.1002/chem.201605648
Chemistry - A European Journal
[14]O. A. Turanova, A. N. Turanov, D. V. Lapaev, O. I. Gnezdilov, S. V. Lobkov, Y. G.
Gayametdinov, Russ. J. General Chem. 2006, 76, 730.
[15]S. Mula, S. Frein, V. Russo, G. Ulrich, R. Ziessel, J. Barbera, R. Descheneaux, Chem. Mater.
2015, 27, 2332.
[16]H. Gopee, X. Kong, Z. He, I. Chambrier, E. L. Hughes, G. J. Tizzard, S. J. Coles, A. N.
Cammidge, J. Org. Chem. 2013, 78, 9505.
[17]A. Florian, M. J. Mayoral, V. Stepanenko, G. Fernandez, Chem. Eur. J. 2012, 18, 14957.
[18]J.-H. Olivier, J. Barbera, E. Bahaidarah, A. Harriman, R. Ziessel, J. Am. Chem. Soc. 2012, 134,
6100.
[19]M. Benstead, G. A. Rosser, A. Beeby, G. H. Mehl, R. W. Boyle, New J. Chem. 2011, 35, 1410.
[20]M. Benstead, G. A. Rosser, A. Beeby, G. H. Mehl, R. Boyle, Photochem. Photobiol. Sci. 2011,
10, 992.
[21]J.-H. Olivier, F. Camerel, G. Ulrich, J. Barbera, R. Ziesse Chem. Eur. J. 2010, 16, 7134.
[22]S. Frein, F. Camerel, R. Ziessel, J. Barbera,R. Deschenaux, Chem. Mater. 2009, 21, 3950.
[23]F. Camerel, G. Ulrich, J. Barbera, R. Ziessel, Chem. Eur. J. 2007, 13, 2189.
[24]E. Cavero, D. P. Lydon, S. Uriel, M. R. de la Fuente, J. L. Serrano, R. Gimenez, Angew. Chem.
Int. Ed. 2007, 46, 5175.
[25]E. Cavero, M. R. de la Fuente, E. Beltran, P. Romero, J. L. Serrano, R. Gimenez, Chem. Mater.
2007, 19, 6230.
[26]F. Camerel, L. Bonardi, G. Ulrich, L. Charbonniere, B. Donnio, C. Borgogne, D. Guillon,
Chem. Mater. 2006, 18, 5009.
[27]F. Camerel, L. Bonardi, M. Schmutz, R. Ziessel, J. Am. Chem. Soc. 2006, 128, 4548.
[28]B. Ringstrand, P. Kaszynski, Acc. Chem. Res. 2013, 214.
[29]B. Ringstrand, Liq. Cryst. Today 2013, 22, 22.
[30]B. P. Dash, R. Satapathy, J. A. Maguire, N. A. Hosmane, New J. Chem. 2011, 35, 1955.
[31]B. Ringstrand, P. Kaszynski, J. Mater. Chem. 2011, 21, 90.
[32]B. Ringstrand, P. Kaszynski, J. Mater. Chem. 2010, 20, 9613.
[33]M. Nieuwenhuyzen, K. R. Seddon, F. Teixidor, A. V. Puga, C. Vinas, C. Inorg. Chem. 2009,
48, 889.
[34]M. Jasinski, A. Jankowiak, A. Januszko, M. Bremer, D. Pauluth, P. Kaszynski, Liq. Cryst.
2008, 35, 343.
[35]P. Kaszynski, J. Huang, G. S. Jenkins, K. A. Bairamov, D. Lipiak, Mol. Cryst. Liq. Cryst. A
1995, 260, 315.
25
This article is protected by copyright. All rights reserved.

10.1002/chem.201605648
Chemistry - A European Journal
[36]J. Pecyna, P. Kaszynski, B. Ringstrand, M. Bremer, J. Mater. Chem. C 2014, 2, 2956.
[37]J. Pecyna, D. Pociecka, P. Kaszynski, J. Mater. Chem. C 2014, 2, 1585.
[38]B. Ringstrand, H. Monoku, P. Kaszynski, J. Mater. Chem. 2009, 19, 4805.
[39]V.Coeffard, X. Moreau, C. Thomassigny, C. Greck, Angew. Chem. 2013, 125, 5794.
[40]A. Suzuki, Angew. Chem. Int. Ed. 2011, 50, 6722.
[41]N. Miyaura, N. Bull. Chem. Soc. Jpn. 2008, 81, 1535.
[42]N. Miyaura, Topics Curr. Chem. 2002, 219, 11.
[43]K. Seto, S. Takahashi, T. Takara, J. Chem. Soc., Chem. Commun. 1985, 122.
[44]K. Seto, H. Matsubara, S. Takahashi, M. Murakami, S. Miyake, T. Masumi, T. Ando, A.
Fukami, J. Chem. Soc., Chem. Commun. 1988, 56.
[45]M. Murakami, S. Miyake, T. Masumi, T. Ando, A. Fukami, S. Takahashi, K. Seto, T. Takara,
Mol. Cryst. Liq. Cryst. 1988, 162B, 149.
[46]H. Matsubara, K. Seto, H. Tabushi, H. Imazaki, S. Takahashi, Chem. Lett. 1989, 1519.
[47]H. Matsubara, K. Seto, S. Takahashi, S. Mol. Cryst. Liq. Cryst. A 1994, 241, 9.
[48]L. A. Tatum, C. J. Johnson, A. A. P. Fernando, B. C. Ruch, K. K. Barakoti, M. A. Alpuche-
Aviles, B. T. King, Chem. Sci. 2012, 3, 3261.
[49]T. Wöhrle, A. Baro, S. Laschat, Materials 2014, 7, 4045.
[50]M. Belloni, M. Manickam, Z.-H. Wang, J. A. Preece, Mol. Cryst. Liq. Cryst. 2003, 399, 93.
[51]T. Yasuda, T. Shimizu, F. Liu, G. Ungar, T. Kato, J. Am. Chem. Soc. 2011, 133, 13437.
[52]T. Wöhrle, J. Kirres, M. Kaller, M. Mansueto, S. Tussetschläger, S. Laschat, J. Org. Chem.
2014, 79, 10143.
[53]Y. Wang, Y. Liu, J. Luo, H. Qi, X. Li, M. Nin, M. Liu, D. Shi, W. Zhu, Y. Cao, Dalton Trans.
2011, 40, 5046.
[54]T. Wöhrle, S. J. Beardsworth, C. Schilling, A. Baro, F. Giesselmann, S. Laschat, Soft Matter
2016, 12, 3730.
[55]M. Belloni, M. Manickam, P. R. Ashton, B. M. Kariuki, J. A. Preece, N. Spencer, J. Wilkie,
Mol. Cryst. Liq. Cryst. 2001, 369, 17.
[56]C. Sauer, S. Diele, N. Lindner, C. Tschierske, Liq. Cryst. 1998, 25, 109.
[57]R. Contreras, T. Mancilla, J. Organomet. Chem. 1986, 307, 1.
[58]N. Farfán, T. Mancilla, D. Castillo, G. Uribe, L. Carrillo, P. Joseph-Nathan, R. Contreras, J.
Organomet. Chem. 1990, 381, 1.
[59]E. P. Gillis, M. D. Burke, J. Am. Chem. Soc. 2007, 129, 6716.
26
This article is protected by copyright. All rights reserved.

10.1002/chem.201605648
Chemistry - A European Journal
[60]J. Li, A. S. Grillo, M. D. Burke, Acc. Chem. Res. 2015, 48, 2297.
[61]D. N. Reinemann, A. M. Wright, J. D. Wolfe, G. S. Tschumper, N. I. Hammer, J. Phys. Chem.
A 2011, 115, 6426.
[62] a) C. Tschierske, in Handbook of Liquid Crystals, J. W. Goodby, P. J. Collings, T. Kato, C.
Tschierske, H. F. Gleeson, P. Raynes, (eds.), 2nd ed., Wiley-VCH: Weinheim, 2014; vol. 5,
pp. 45. b) C. Tschierske, ibid, vol. 5, pp. 1. c) C. Tschierske, Angew. Chem. Int. Ed. 2013, 52,
8828. d) C. Tschierske, Isr. J. Chem. 2012, 52, 935.
[63]J. W. Goodby, E. J. Davies, R. J. Mandle, S. J. Cowling, in Handbook of Liquid Crystals, J.
W. Goodby, P. J. Collings, T. Kato, C. Tschierske, H. F. Gleeson, P. Raynes, (eds.), 2nd ed.,
Wiley-VCH: Weinheim, 2014; vol. 1, pp. 231.
[64]J. W. Goodby, R. J. Mandle, E. J. Davis, T. Zhong, S. Cowling, Liq. Cryst. 2015, 42, 593.
[65]D. Chen, M. R. Tuchband, B. Horanyi, E. Korblova, D. M. Walba, M. A. Glaser, J. E.
MacLennan, N. A. Clark, Nature Comm. 2015, 6, 7763.
[66]K. V. Axenov, S. Laschat, Materials 2011, 4, 206.
[67]M. Mansueto, S. Laschat, in Handbook of Liquid Crystals, J. W. Goodby, P. J. Collings, T.
Kato, C. Tschierske, H. F. Gleeson, P. Raynes, (eds.), 2nd ed., Wiley-VCH: Weinheim, 2014;
vol. 6, pp. 231.
[68]S. Chen, S. H. Eichhorn, Isr. J. Chem. 2012, 52, 830.
[69]L. Douce, J.-M. Suisse, D. Guillon, A. Taubert, Liq. Cryst. 2011, 38, 1653.
[70]a) K. Goossens, K. Lava, C. W. Bielawski, K. Binnemans, Chem. Rev. 2016, 116, 4643. b)
K. Binnemans, Chem. Rev. 2005, 105, 4148.
[71]A. Martinez-Felipe, C. T. Imrie, J. Mol. Struct. 2015, 1100, 429.
[72]S. Fujimura, Y. Yamamura, M. Hishida, S. Nagatomo, K. Saito, Liq. Cryst. 2014, 41, 927.
[73]a) M. A. Osipov, G. Pajak, Liq. Cryst. 2016, doi: 10.1080/02678292.2016.1247474. b) G.
Pajak, M. A. Osipov, Phys. Rev. E 2013, 88, 012507.
[74]a) K. Saito, M. Hishida, Y. Yamamura, Soft Matter 2015, 11, 8493. b) K. Horiuchi, Y.
Yamamura, R. Pelka, M. Sumita, S. Yasuzuka, M. Massalska-Arodz, K. Saito, J. Phys. Chem.
B 2010, 114, 4870. c) Y. Yamamura, T. Adachi, T. Miyazawa, K. Horiuchi, M. Sumita, M.
Massalska-Arodz, S. Urban, K. Saito, J. Phys. Chem. B 2012, 116, 9255. d) T. Miyazawa, Y.
Yamamura, M. Hishida, S. Nagatomo, M. Massalska-Arodz, K. Saito, J. Phys. Chem. B 2013,
117, 8293.
[75]Review on lyotropic liquid crystals: C. Fong, T. Le, J. Drummond, Chem. Soc. Rev. 2012, 41,
1297.
[76]K. Sadakane, H. Seto, M. Nagao, Chem. Phys. Lett. 2006, 426, 61.
27
This article is protected by copyright. All rights reserved.

10.1002/chem.201605648
Chemistry - A European Journal
[77]Y. Yamaoka, Y. Taniguchi, S. Yasuzuka, Y. Yamamura, K. Saito, J. Chem. Phys. 2011, 135,
044705.
[78]C. M. Gordon, J. D. Holbrey, A. R. Kennedy, K. R. Seddon, J. Mater. Chem. 1998, 8, 2627.
[79]S. G. Ballmer, E. P. Gillis, M. D. Burke, Org. Synth. 2009, 86, 344.
[80]CCDC-1486006 contains the supplementary crystallographic information for 8 (C4). The data
can be obtained free of charge from The Cambridge Crystallographic Data Center via
https://summary.ccdc.cam.ac.uk/structure-summary-form.
[81]T. M. Percino, R. M. F. Ancona, M. L. Martìnez, Polyhedron 2009, 28, 2771.
[82]TURBOMOLE V7.0.1 2015, a development of University of Karlsruhe and
Forschungszentrum Karlsruhe GmbH, 1989-2007, TURBOMOLE GmbH, since 2007;
available from http://www.turbomole.com.
̈
[83]F. Furche, R. Ahlrichs, C. Hattig, C. Klopper, M. Sierka, F. Weigend, Comput. Mol. Sci. 2013,
4, 91.
[84]F. Weigend, R. Ahlrichs R. Phys. Chem. Chem. Phys. 2005, 7, 3297.
[85]F. Weigend, M. Häser, Theor. Chem. Acc. 1997, 97, 331.
[86]F. Weigend, M. Häser, H. Patzelt, R. Ahlrichs, Chem. Phys. Lett. 1998, 294, 143.
[87]A. Reed, R. Weinstock, F. Weinhold, J. Chem. Phys. 1985, 83, 735.
[88]G. Knizia, J. Chem. Theory. Comput. 2013, 9, 4834.
[89]C. Steffen, K. Thomas, U. Huniar, A. Hellweg, O. Rubner, A. Schroer, J. Comput. Chem.
2010, 31, 2967.
[90]K.L. Bak, J. Gauss, P. Jørgensen, J. Olsen, T. Helgaker, and J.F. Stanton, J. Chem. Phys. 2001,
114, 6548.
[91]1 S. Coriani, D. Marchesan, J. Gauss, C. Hättig, T. Helgaker, and P. Jørgensen, J. Chem. Phys.
2005, 123, 184107.
[92]P. H. J. Kouwer, T. M. Swager, T. M. J. Am. Chem. Soc. 2007, 129, 14042.
[93]Avogadro: an open-source molecular builder and visualization tool. Version 1.1.1. M. D.
Hanwell, D. E. Curtis, D. C. Lonie, T. Vandermeersch, E. Zurek, G. R. J. Hutchison,
Cheminformatics 2012, 4, 17.
[94]S. K. Prasad, D. S. S. Rao, S. Chandrasekhar, S. Kumar, Mol. Cryst. Liqui. Cryst. 2003,
396, 121.
[95]M. Lehmann, C. Köhn, H. Meier, S. Renker, A. Oehlhof, J. Mater. Chem. 2006, 16, 441.
[96]A. Jankowiak, A. Sivaramamoorthy, D. Pociecha, P. Kaszynski, RSC Adv. 2014, 4, 53907.
28
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