Chemical programming of the domain of existence of liquid crystals

Article abstract of DOI:10.1002/chem.201503420

This work illustrates how enthalpy and entropy changes responsible for successive phase transitions of cyanobiphenyl-based liquid crystals can be combined to give cohesive free energy densities. These new parameters are able to rationalize and quantify the demixing of the melting and clearing processes that occur in thermotropic liquid crystals. Minor structural variations at the molecular level can be understood as pressure increments that alter either the melting or clearing temperatures in a predictable way. This assessment of microsegregation operating in amphiphilic molecules paves the way for the chemical programming of the domain of existence of liquid-crystalline phases. Changing states: The cohesive free energy density concept (CFED) is applied to thermotropic cyanobiphenyl-based liquid crystals to establish predictive quantitative correlations between each antagonist segments of the amphiphilic molecules (flexible alkyl tail/rigid aromatic core) and their transition temperatures (solid→liquid crystalline/liquid crystalline→ isotropic liquid; see figure).

Full text of DOI:10.1002/chem.201503420

DOI: 10.1002/chem.201503420
Full Paper
&
Thermodynamics
Chemical Programming of the Domain of Existence of Liquid
Crystals
Thibault Dutronc,[a] Emmanuel Terazzi,*[a] Laure GuØnØe,[b] Kerry-Lee Buchwalder,[a]
SØbastien Floquet,[c] and Claude Piguet*[a]
Abstract: This work illustrates how enthalpy and entropy
changes responsible for successive phase transitions of cya-
nobiphenyl-based liquid crystals can be combined to give
cohesive free energy densities. These new parameters are
able to rationalize and quantify the demixing of the melting
and clearing processes that occur in thermotropic liquid
crystals. Minor structural variations at the molecular level
can be understood as pressure increments that alter either
the melting or clearing temperatures in a predictable way.
This assessment of microsegregation operating in amphiphil-
ic molecules paves the way for the chemical programming
of the domain of existence of liquid-crystalline phases.
Introduction
intermolecular potentials operating between interacting mole-
cules in liquid crystals,[5] were able to explain the occurrence of
order–disorder phase transitions involving nematic organiza-
tions, but gave few insights into the prediction of the associat-
ed transition temperatures. A more recent model considers the
two nanospaces of the incompatible components of a binary
AÀB amphiphilic molecule, which can be related to the macro-
scopic segregation (demixing) of two liquids with molecular
structures similar to the two segments A and B that form the
amphiphile (see Figures 1 and 2, below, for molecular illustra-
tions).[6] Because the empirical Trouton’s rule fixes a value of
DSvap =85–88 JmolÀ1 KÀ1 for the entropy of vaporization of any
After more than a century of scientific interest in liquid crystals,
the prediction and fine-tuning of mesomorphism, as well as
the design of new liquid-crystalline materials, is still a vast and
fascinating issue.[1] Because most existing applications for infor-
mation display are based on liquid-crystal mixtures,[2] decisive
advances in the design of pure compounds and control of
their properties would have significant industrial repercussions.
So far, guidelines for the preparation of new mesomorphic ma-
terials have come from extensive empirical observations and
pattern recognitions. If characteristic factors, such as molecular
shapes, interfacial curvatures, or intermolecular interactions,
have been clearly identified and can be selectively worked
upon, studied, or even predicted by analogy, there is no uni-
fied route for the design of liquid crystals.[3] From a chemical
point of view, the industrially relevant[2] thermotropic meso-
phase corresponds to a liquid-crystalline phase thermally in-
duced by the melting of the solid, but separated from the iso-
tropic liquid by the clearing process. Classical theories based
on entropically driven hard-rod models,[4] or on statistical treat-
ments of long-range enthalpic contributions to the attractive
liquid, its enthalpy of vaporization, DHvap, is linearly related to
[7]
its vaporization temperature, Tvap =DHvap/DSvap
.
Therefore,
DHvap has been exploited as a quantitative index to estimate
the intermolecular cohesive energy densities, d2 =DHvap/Vmol
,
within liquids (Vmol is the molar volume and d is known as the
Hildebrand solubility parameter).[8] The difference, dAÀdB, be-
tween the two segments A and B of the amphiphile thus re-
flects their incompatibility and decides whether nanoscale seg-
regation could take place.[6] This approach is analogous to that
originally developed for the miscibility of block copolymers,[9]
an analogy noted 40 years ago,[10] which has found a renewal
of interest[11] for understanding the formation of mesophases
in unconventional liquid-crystalline molecules.[12] The basic
concept considers the free energy of mixing for the formation
of polymer blends, which includes standard entropy of mixing
that arises from regular solution theory, together with an extra
enthalpic contribution to monitor intermolecular interactions.[9]
The Flory and Huggins theory, in terms of solubility parame-
ters, shows that the latter interaction factor depends on
(dAÀdB)2 weighted by the thermal energy.[6,12] Quantitative ap-
plications to mesogenic calamitic cyanobiphenyls,[9a] cubic-
phase-forming liquid-crystalline molecules,[9c] and polycatenar
pentaerythritol derivatives[11b] successfully rationalized phase
segregation, leading to specific mesomorphism. However, con-
[a] T. Dutronc, Priv.-Doz. Dr. E. Terazzi, K.-L. Buchwalder, Prof. Dr. C. Piguet
Department of Inorganic, Analytical and Applied Chemistry
University of Geneva, 30 quai E. Ansermet
1211 Geneva 4 (Switzerland)
E-mail: Emmanuel.terazzi@unige.ch
Claude.Piguet@unige.ch
[b] Dr. L. GuØnØe
Laboratory of Crystallography
University of Geneva, 24 quai E. Ansermet, 1211 Geneva 4 (Switzerland)
[c] Dr. S. Floquet
Institut Lavoisier de Versailles, UMR 8180
University of Versailles Saint-Quentin-en-Yvelines
45 av. des Etats-Unis, 78035 Versailles (France)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201503420.
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trary to Trouton’s rule for the vaporization of liquids, the entro-
py changes, DStr, accompanying the melting process that
transforms a solid into a liquid or a liquid crystal, or the iso-
tropization process that transforms a liquid crystal into an iso-
tropic liquid, are not constant. They depend on the nature of
the material and contribute to the stabilization of the different
states of matter.[13] For instance, the large and variable entropic
contributions of the molten flexible chains to the Gibbs free
energy have been exploited for the stabilization of the nanose-
gregated liquid-crystalline phases found in alkylcyanobiphenyls
(smectic A mesophase),[14] bis-alkyloxybenzoylhydrazines (cubic
mesophase),[15] and alkylisothiocyanatibiphenyls (smectic E
mesophase).[16]
Consequently, the square of the Hildebrand solubility param-
eter, d2, pertinent to the vaporization of liquids, has been re-
placed by the concept of cohesive free energy density, CFED=
ref
tr
ref
tr
ÀDG /Vmol in liquid crystals, in which DG =DHtrÀTrefDStr
measures the intermolecular cohesion free energy in the solid
or in the liquid-crystalline phase estimated at a fixed reference
temperature, Tref (DHtr and DStr are the enthalpy and entropy
changes of the incriminated phase transition, respectively).[17]
Applied to the melting of solid linear alkanes, alkanoic acids,
organosilanes, transition metals, or metal oxides, plots of CFED
with respect to the melting temperatures systematically dis-
play linear correlations, as further illustrated in Figure 1 for
methyl-substituted cyanobiphenyls 12-OCBi’,j, which simply
melt to give isotropic liquids, despite their amphiphilic charac-
ter.[18] To extend the use of the CFED concept into the field of
thermotropic liquid crystals, which display successive melting
and isotropization transitions, it is necessary to increase the
polarity difference (Dd=dtailÀdhead) between the antagonist
segments originally included in the substituted cyanobiphenyls
12-OCBi’,j. The introduction of an additional para-substituted
benzoate group gives the n-LCi’,j family (Figure 2), for which an
8–29% increase in Dd can be computed (Appendix 1 in the
Supporting Information). We report herein on the syntheses
and structures of the mesogenic extended cyanobiphenyls n-
LCi’,j, together with their thermal behavior and liquid-crystalline
properties, which are analyzed within the frame of the CFED
concept. We believe that its predictive aspects would help in
the rational design of the domain of existence of pure liquid-
crystalline materials.
Figure 1. Plot of the CFEDs (Tref =298 K) versus the melting temperatures for
the substituted cyanobiphenyls 12-OCBi’,j. Redrawn from ref. [18].
aromatic stacking and hydrogen bonding produces a distance
of 9.6(2) Š between the planes defined by the nitrogen atoms
of the opposite cyano groups; these planes are tilted by
46.4(6)8 with respect to the molecular axis of the rodlike cya-
nobiphenyl units (Figure 3 and Appendix 4 in the Supporting
Information).
Upon methylation of n-LCi’,j (i¼ 0 or j¼ 0), the intermolecular
packing interactions observed in the crystalline state are drasti-
cally altered. This perturbation produces variable molecular or-
ganizations in the solid state with severely reduced (if any)
head-to-head interdigitations of the rigid cyanobiphenyl cores
(Appendices 3 and 4 in the Supporting Information). This diver-
sity in intermolecular interactions found in the solid state is
mirrored by the formation of various fluidic birefringent tex-
tures upon heating solid samples of n-LCi’,j (except for 12-
LC2’,2; Figure 4).
Results and Discussion
Standard organic syntheses, relying on Suzuki–Myaura cou-
pling strategies for the preparation of substituted cyanobi-
phenyls cores,[17] eventually lead to a complete set of extended
cyanobiphenlys n-LCi’,j (Scheme 1; details are given in Appen-
dix 2 in the Supporting Information).
All compounds were characterized by XRD in the crystalline
state (Appendix 3 in the Supporting Information). For the non-
methylated calamitic molecules n-LC0’,0 (A=B=C=D=H in
Scheme 1),[19] which differ only in the length of the linear ali-
phatic chains, the crystal structures show long-range polar/
apolar segregation and two-dimensional molecular layering
(Figure 3). Opposite head-to-head interdigitation stabilized by
This behavior is characteristic of the implementation of spe-
cific organizations of the molecules in the liquid-crystalline
phases, which could be assigned to smectic and nematic or-
ganization by polarized optical microscopy (POM; Figure 5).
Temperature-dependent small-angle X-ray scatterings con-
firmed these assignments because no low-angle diffraction
pattern could be detected for the nematic mesophases, where-
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Figure 3. Segregated layer organization in the crystal of 8-LC0’,0, which
shows interdigitation between the opposite aromatic cyanobiphenyls and
the orientation of the rodlike units in nonsubstituted n-LC0’,0 compounds.
as a single sharp peak was assigned to the d001 reflection in
the smectic mesophases (Appendix 5 in the Supporting Infor-
mation). The calculated interlamellar distances (34.7–41.5 Š)
are much shorter than twice the total length estimated for the
rodlike molecules in the crystalline state (54–64 Š), which sug-
gests the occurrence of head-to-head interpenetration in the
smectic mesophases, probably combined with partial interdigi-
tation of the molten alkyl chains (Table S1 and Figure S1 in the
Supporting Information).
Differential scanning calorimetry (DSC) traces were recorded
at 0.5 KminÀ1 for n-LCi’,j to minimize deviations from thermo-
dynamic equilibria (Figure 6). Transition enthalpies and entro-
Figure 2. Chemical structures of the substituted cyanobiphenyls n-LCi’,j con-
sidered herein.
pies for melting (DHm, DSm,) and isotropization (DHclearing,
DSclearing) were estimated at the respective transition tempera-
tures by integration of the DSC signals recorded during the
heating runs (Table S2 in the Supporting Information). For the
nonmethylated calamitic molecules n-LC0’,0, our observations
corroborate those previously reported by Hardouin et al.,[19]
except for some minor differences in the transition tempera-
tures measured by POM, although we refer to the onset of the
heat-flow peak monitored by DSC herein (Table S3 in the Sup-
porting Information). Beyond the first-order melting and iso-
tropization transitions, which confirm the thermal behavior es-
tablished by POM (Figure 5), DSC analyses also reveal some
minor solid–solid transitions, cold crystallizations, pretransition-
al effects, and kinetically enlarged transitions, which are not
considered herein because of their negligible enthalpic contri-
butions (Appendix 5 in the Supporting Information).
As previously reported for the nonmesogenic parent mole-
cules 12-OCBi’,j,[17] the minor perturbation induced by methyl
substitution and chain-length increments in 12-LCi’,j are not ex-
pected to drastically alter the minimum intermolecular contact
distances in the condensed phases. Consequently,[20] both
melting and isotropization processes obey local linear enthal-
py/entropy compensations (Figure 7). The melting tempera-
tures at which solid samples of n-LCi’,j transform into liquid
crystals cover a narrow range, 343ꢀTm ꢀ376 K (Figure 5), re-
gardless of 1) the length of the alkyl tail (for nꢁ7 methylene
rotors) or 2) substitution of the rigid aromatic head. On the
contrary, the clearing temperatures at which the liquid-crystal-
line phases transform into isotropic liquids present a stepwise
decrease from 491ꢀTclearing ꢀ519 K for nonsubstituted
cyanobiphenyls n-LC0’,0 (left side of Figure 5) toward
Scheme 1. Syntheses of n-LCi’,j: dppf=1,10-bis(diphenylphosphino)ferro-
cene, Cy2NH=dicyclohexylamine; A=H or CH3; B=H or CH3 (see Figure 2).
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Figure 5. Mesomorphic ranges and observed thermotropic mesophases for
n-LCi’,j (scan rate 0.5 KminÀ1).
Figure 6. DSC thermograph of 12-LC0’,0 (scan rate 0.5 KminÀ1, heating cycle
with upward peaks, cooling cycle with downward peaks). Cr=crystal,
SmA=smectic A, I=isotropic liquid.
406ꢀTclearing ꢀ426 K for monomethylated cyanobiphenyls 12-
LCi’,j (i¼ 0 or j¼ 0; central part of Figure 5) and finally toward
352ꢀTclearing ꢀ372 K for dimethylated cyanobiphenyls 12-LCi’,j
(i¼ 0 and j¼ 0; right side of Figure 5).
Reasonably assuming[17] that the transition enthalpies and
entropies determined at Tm and Tclearing, respectively, are not
significantly altered when expressed at a common reference
temperature, Tref, taken as the average of the observed
phase transition processes (Trmef =360.6 K and Tcrelefaring =443.4 K),
the
CFEDs
in
the
solid
state,
CFEDsolid =ÀDGm/
V
mol =À(DHmÀTrmefDSm)/Vmol (left part of Figure 8), and in
the liquid-crystalline state, CFEDliq-cryst =ÀDGclearing/Vmol
=
À(DHclearingÀTcrelefaringDS)/Vmol (right part of Figure 8), can be easily
computed with the help of the specific molar volumes, Vmol, of
n-LCi’,j taken as the Connolly volume estimated in the crystal
structures (Appendix 3 in the Supporting Information).[21] The
plots of CFED versus transition temperatures immediately
show that the melting and clearing processes are decorrelated,
each is characterized by its specific linear trend line (Figure 8).
According to the fundamental Gibbs equation of chemical
thermodynamics, S=À(@G/@T)P,[22] the slopes of these linear
correlations correspond to cohesive entropy densities,
Figure 4. Polarized optical micrographs of 12-LC0’,0 at 487 K (top, smectic A
phase), 12-LC0’,3 at 358 K (center, smectic C phase), and 12-LC0’,2 at 416 K
(bottom, nematic phase).
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rigid cores in 12-LCi’,j (i.e., zero!mono-!dimethylation) re-
sults in three well-separated series that display stepwise de-
creases in clearing temperatures (Figure 8). The simple but te-
dious mathematical developments collected in Appendix 6 in
the Supporting Information show that 1) the CFED parameter
has pressure units (1 JcmÀ3 =106 Pa) and 2) application of the
Clapeyron equation[23] leads to CFED=ÀldP, in which l is the
relative molar volume expansion at the transition temperature
(DVtr/Vmol) of the series of compounds obeying the linear CFED
versus Ttr correlation. The increment in pressure units for
a given member of the series, dP, thus reflects the “chemical
changes” or “chemical efforts” required to shift its specific
melting temperature toward the reference temperature, Tref, of
the family (Figure A6-2 in Appendix 6 in the Supporting Infor-
mation).
Conclusion
Plots of CFED as a function of the transition temperatures
bring quantitative support to chemical intuition[10] that a ther-
motropic liquid-crystalline phase is the result of melting of the
apolar lipophilic parts of an amphiphilic molecule, while the
rigid cores remain partially correlated. For the lipophilic cyano-
biphenyls n-LCi’,j, a chain length of nꢁ7 is sufficient for the
demixing of the apolar parts, leading to nanoscale segregation
and the formation of thermotropic liquid-crystalline phases for
each member of the series (except for 12-LC2’,2; Figure 5). As
expected, substitution (i.e., methylation) of the rigid aromatic
core has only a minor influence on the melting temperatures
controlled by the entropic contribution of the molten flexible
alkyl chains.[13,16] With the help of the CFED concept, the latter
effect can be associated with a cohesive entropy density of
DSm/Vmol =0.253(8) JKÀ1 cmÀ3. On the other hand, the clearing
temperatures correspond to decorrelations of the rigid aromat-
ic cores, and thus, strongly depend on the methylation of the
aromatic part of the cyanobiphenyls in n-LCi’,j. Again, the appli-
cation of the CFED concept provides a quantitative assessment
of the effect of peripheral methylation onto the clearing tem-
Figure 7. DStr versus DHtr plots for a) melting and b) isotropization of n-LC0’,0
(n symbol) and 12-LCi’,j (monomethylated compounds and dimethylated
compounds with i’,j symbols), showing local linear H/S compensation. The
dashed lines represent reciprocal Hill fits, which obey thermodynamic boun-
dary conditions when DHtr!0.[18]
perature with
a cohesive entropy density of DSm/Vmol =
0.0054(9) JKÀ1 cmÀ3. In simpler words, methyl substitution of
the cyanobiphenyl core can be exploited to tune the clearing
temperatures (Tclearing), while the melting temperatures (Tm) are
essentially invariant (the relative effect can be estimated as
0.253/0.0054ꢂ47). Finally, the CFED versus Ttr correlation high-
lighted in Figure 8 can be combined with the associated local
linear H/S compensations (Figure 7) to give a set of two empiri-
cal equations [Eqs. (1) and (2)], which define the domain of ex-
istence (TclearingÀTm) of the liquid-crystalline phases.[17]
Figure 8. CFEDs versus transition temperatures. CFEDsolid versus melting tem-
~
*
( ), and CFEDliq-cryst versus clearing temperatures, Tclearing ( ), are
perature, Tm
displayed for successive phase transitions that occur in non- (n-LC0’,0; black),
mono- (12-LCi’,j with i¼ 0 or j¼ 0; blue), and dimethylated (12-LCi’,j with i¼ 0
and j¼ 0; red).
DStr/Vmol. The steep value of DSm/Vmol =0.253(8) JKÀ1 cmÀ3 ob-
served for the melting of the solids into their liquid-crystalline
phases (left part of Figure 8) implies that chemical substitu-
tions of the rigid cyanobiphenyl core in 12-LCi’,j have minor ef-
fects on the melting temperature. On the contrary, the flat
slope of DSclearing/Vmol =0.0054(9) JKÀ1 cmÀ3 found for isotropi-
zation of the liquid-crystalline phases into the isotropic liquids
(right part of Figure 8) indicates that methylation of the rigid
aromatic cores produces large changes in clearing tempera-
tures. Furthermore, we note that successive methylation of the
DHtr À TtrrefDStr
ð1Þ
ð2Þ
ÀCFED ¼
¼ aTtr þ b
Vmol
DHtr ¼ gDStr þ f
For the specific perturbation brought about by successive
methylation of the rigid cores of the cyanobiphenyls in 12-
LCi’,j, Figure S2 in the Supporting Information illustrates the
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tor. Variable temperatures were achieved with a nitrogen cryo-
streamer (Oxford Cryosystem; available temperatures: 100–500 K).
prediction that mesogenic behavior requires a minimal molar
volume of Vmol =200 cm3 molÀ1; a much smaller value than
those found for non- (489 cm3 molÀ1), mono- (503 cm3 molÀ1),
and dimethylated 12-LC (519 cm3 molÀ1).[24]
2) A STOE STADI P transmission powder diffractometer system with
a focused monochromatic CuKa1 beam obtained from a curved Ger-
manium monochromator (Johann-type) and collected on a curved
image plate position-sensitive detector (IP-PSD). A calibration with
silicon and copper laurate standards, for high- and low-angle do-
mains, respectively, was preliminarily performed. Sample capillaries
were placed in the high-temperature attachment for measure-
ments in the range of desired temperatures (from À30 to 2408C)
within 0.058C. Periodicities up to 50 Š could be measured.
Experimental Section
General
The syntheses and characterizations (NMR spectroscopy, ESI-MS, el-
emental analysis) of the lipophilic cyanobiphenyls n-LCi’,j are col-
lected in Appendix 2 in the Supporting Information.
Spectroscopic and analytical measurements
Acknowledgements
1H and 13C NMR spectra were recorded at 258C on a Bruker Avance
400 MHz spectrometer. Chemical shifts are given in ppm with re-
spect to tetramethylsilane (TMS). Pneumatically assisted electro-
spray (ESI-MS) mass spectra were recorded from 10À4 m solutions
on an Applied Biosystems API 150EX LC/MS system equipped with
a Turbo Ionspray source. Elemental analyses were performed by
K. L. Buchwalder at the Microchemical Laboratory of the University
of Geneva. Thermogravimetric analyses were performed with
a thermogravimetric balance by Mettler Toledo Star Systems
(under N2). DSC traces were obtained with a Mettler Toledo DSC1
Star Systems differential scanning calorimeter from 3–5 mg sam-
ples (5 and 0.58CminÀ1, under N2). Conversion: T(K)=T(8C)+
273.15. The characterization of the mesophases and isotropic liq-
uids were performed with a Leitz Orthoplan-Pol polarizing micro-
scope with a Leitz LL 20”/0.40 polarizing objective, and equipped
with a Linkam THMS 600 variable-temperature stage. Mathematical
analyses were performed by using Igor Pro (WaveMetrics, Inc.) and
Excel (Microsoft) software.
This work was supported through grants from the Swiss Na-
tional Science Foundation.
Keywords: cyanobiphenyls · liquid crystals · phase transitions ·
structure elucidation · thermodynamics
[1] S. Chandrasekhar, Liquid Crystals, Cambridge University Press, New York,
1992.
[2] W. O’Mara, Liquid Crystal Flat Panel Displays: Manufacturing Science &
Technology, Reinhold Van Nostrand, New York, 1993.
[3] T. Thiemann, V. Vill, in Handbook of Liquid Crystals Set (Eds.: D. Demus, J.
Goodby, G. W. Gray, H. W. Spiess , V. Vill), Wiley-VCH, Weinheim, 2008,
p.87.
[4] a) L. Onsager, Ann. N. Y. Acad. Sci. 1949, 51, 627–659; b) G. J. Vroege,
H. N. W. Lekkerkerker, Rep. Prog. Phys. 1992, 55, 1241–1309.
[5] a) W. Maier, A. Saupe, Z. Naturforsch. A 1959, 13, 564–570; b) W. Maier,
A. Saupe, Z. Naturforsch. A 1959, 14, 882–900; c) W. Maier, A. Saupe, Z.
Naturforsch. A 1960, 15, 287–292; d) A. Saupe, Angew. Chem. Int. Ed.
Engl. 1968, 7, 97–118; Angew. Chem. 1968, 80, 99–115; e) G. R. Luck-
hurst, C. Zannoni, Nature 1977, 267, 412–414.
X-ray crystallography
Single crystals: Summaries of crystal data, intensity measurements,
and structure refinements for compounds n-LCi’,j are collected in
Tables A3–1 to A3–14 in the Supporting Information. Crystals were
mounted on a Kapton loop with protective oil. Cell dimensions
and intensities were measured at 180 K on a Supernova (Rigaku)
diffractometer with mirror monochromated CuKa radiation (l=
1.54184 Š) and an Atlas charge-coupled device (CCD) camera. Data
were corrected for Lorentz and polarization effects and for absorp-
tion. The structures were solved by direct methods (SIR97,[25]
SHELXS[26]) or the charge flipping method (SUPERFLIP);[27] all other
calculations were performed with SHELXL97[26] and ORTEP[28] pro-
grams.
[6] a) C. Tschierske, Ann. Rep. Prog. Chem. Ser. C 2001, 97, 191–267; b) C.
Tschierske, Top. Curr. Chem. 2011, 318, 1–108.
[7] F. T. Trouton, Philos. Mag. 1884, 18, 54–57.
[8] a) J. H. Hildebrand, R. L. Scott, The Solubility of Nonelectrolytes, 3rd Ed.,
Reinhold Pub Group, New York, 1950; b) C. M. Hansen, Solubility Param-
eters: A User’s Handbook, 2nd ed., CRC Press, Boca Raton, 2007, Chap-
ter 1.
[9] a) E. Bialecka-Florjanczyk, J. Phys. Chem. B 2006, 110, 2582–2592; b) M.
Yoneya, K. Araya, E. Nishikawa, H. Yokoyama, J. Phys. Chem. B 2004, 108,
8099–8101; c) M. Yoneya, Chem. Rec. 2011, 11, 66–76.
[10] a) A. Skoulios, Advances in Liquid Crystals (Ed.: G. Brown), Academic
Press, New York, 1975, part 1, p. 169; b) D. Guillon, A. Skoulios, J. Phys.
1976, 37, 797–800; c) A. Skoulios, D. Guillon, Mol. Cryst. Liq. Cryst. 1988,
165, 317–332. For a comprehensive review, see C. Tschierske, Angew.
Chem. Int. Ed. 2013, 52, 8828–8878; Angew. Chem. 2013, 125, 8992–
9047.
[11] a) C. Tschierske, J. Mater. Chem. 1998, 8, 1485–1508; b) A. Pegenau, T.
Hegmann, C. Tschierske, S. Diele, Chem. Eur. J. 1999, 5, 1643–1660; c) C.
Tschierske, J. Mater. Chem. 2001, 11, 2647–2671.
[12] C. Tschierske in Handbook of Liquid Crystals, Vol. 5, 2nd ed. (Eds.: J. W.
Goodby, P. J. Collings, T. Kato, C. Tschierske, H. F. Gleeson, P. Raynes),
Wiley-VCH, Weinheim, 2014, pp. 1–43.
[13] K. Saito, T. Miyazawa, A. Fujiwara, M. Hishida, H. Saitoh, M. Massalska-
Arodz, Y. Yamamura, J. Chem. Phys. 2013, 139, 114902.
CCDC-1412272, 1412273, 1412274, 1412275, 1412276, 1412277,
1412278, 1412279, 1412280, 1412281, 1412282, 1412283, 1412285,
and 1412285 contain the supplementary crystallographic data for
this paper. These data are provided free of charge by The Cam-
bridge Crystallographic Data Centre.
Low-angle powder diffraction: For all samples, the crude powder
was filled in Lindemann capillaries of 0.8 mm in diameter. Low-
angle powder XRD experiments at various temperatures were per-
formed by using two different diffractometers, depending on the
compounds:
[14] Y. Yamaoka, Y. Tanigushi, S. Yasuzuka, Y. Yamamura, K. Saito, J. Chem.
Phys. 2011, 135, 044705.
[15] Y. Nakazawa, Y. Yamamura, S. Kutsumizu, K. Saito, J. Phys. Soc. Jpn.
2012, 81, 094601.
1) An Empyrean (PANalytical) diffractometer in capillary mode, with
a focusing X-ray mirror for Cu radiation and a PIXcel3D area detec-
[16] T. Miyazawa, Y. Yamamura, M. Hishida, S. Nagatomo, M. Massalska-
Arodz, K. Saito, J. Phys. Chem. B 2013, 117, 8293–8299.
Chem. Eur. J. 2016, 22, 1385 – 1391
www.chemeurj.org
1390
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
[17] T. Dutronc, E. Terazzi, L. GuØnØe, K.-L. Buchwalder, A. Spoerri, D. Emery,
J. Mareda, S. Floquet, C. Piguet, Chem. Eur. J. 2013, 19, 8447–8456.
[18] T. Dutronc, E. Terazzi, C. Piguet, RSC Adv. 2014, 4, 15740–15748.
[19] F. Hardouin, A. M. Levelut, N. H. Tinh, G. Sigaud, Mol. Cryst. Liq. Cryst.
1979, 56, 35–41.
[24] The very limited range of molecular volumes spanned by the experi-
mental data collected for molecules 12-LCi’,j in this work results in rela-
tively large uncertainties that affect the coefficients a, b, g, and f of
the linear correlations depicted in Equations (1) and (2). Hence, only
trend lines for the phase boundaries are accessible in Figure S2 in the
Supporting Information.
[25] A. Altomare, M. C. Burla, M. Camalli, G. Cascarano, C. Giacovazzo, A.
Guagliardi, G. Moliterni, G. Polidori, R. Spagna, J. Appl. Crystallogr. 1999,
32, 115.
[26] G. M. Sheldrick, SHELXL97 Program for the Solution and Refinement of
Crystal Structures, University of Gçttingen, Germany, 1997.
[27] L. Palatinus, G. Chapuis, J. Appl. Crystallogr. 2007, 40, 786.
[28] ORTEP3, L. J. Farrugia, J. Appl. Crystallogr. 1997, 30, 565.
[20] a) D. M. Ford, J. Am. Chem. Soc. 2005, 127, 16167–16170; b) C. Piguet,
Dalton Trans. 2011, 40, 8059–8071.
[21] The molecular volumes are taken as the Connolly volumes, which are
obtained by building the Connolly surface around the molecular struc-
tures of complexes observed in the crystal structures with a probe
radius of 1.4 Š to model water solvent molecules (M. L. Connolly, Sci-
ence 1983, 221, 709–713. M. L. Connolly, J. Appl. Crystallogr. 1983, 16,
548–558).
[22] P. W. Atkins, J. de Paula, Physical Chemistry, 9th ed., W. H. Freeman and
Company, New York, 2010, p.124.
Received: August 28, 2015
Published online on December 14, 2015
[23] P. W. Atkins, J. de Paula, Physical Chemistry, 9th ed., W. H. Freeman and
Company, New York, 2010, p.147.
Chem. Eur. J. 2016, 22, 1385 – 1391
www.chemeurj.org
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ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim