Alternating o1igo[(2,3-O-isopropylidene-L-threitol)]-co-[(E,E)-1,4- bis(styryl)benzene]s: the linear chirality transmisson additivity relationship in nematic liquid crystals

Article abstract of DOI:10.1021/jp909286t

Alternating oligo[2,3-O-isopropylidene-L-threitol]-co-[(E,E)-l,4- bis(styryl)benzene]s (denoted as 2-6 in the article) show helical twisting power (HTP), in 4-pentoxyl-4'-biphenylcarbonitrile (5OCB), linearly proportional to the number of the chiral cores in the oligomers. The HTP per chiral core of -1.75 ??m-^l was recorded in the correlation plot with a correlation coefficient of R = 0.99. These results suggested that the C₂ chiral L-threitol cores are aligned along the same axis. The comparable linear dichroism (LD) of 0.42 ?± 0.02 obtained for (rac)-2-5 at 405 nm, and of 0.52 ?± 0.03 for E7, a commercially available room temperature nematic solvent, at 347 nm in a parallel rubbed cell indicated that the long axis of the bis(styryl)benzene segments is more or less parallel to the director of the E7 in the LC matrix. This observation is highly exciting because the HTP per core could still be maintained, no matter whether the cores are evenly spread in a form of monomer in the LC matrix or tightly confined in a polymer. Theoretical treatments about the conformations of the dopant in the nematic matrix are discussed. ? 2010 American Chemical Society.

Full text of DOI:10.1021/jp909286t

J. Phys. Chem. B 2010, 114, 2607–2616
2607
Alternating Oligo[(2,3-O-isopropylidene-L-threitol)]-co-[(E,E)-1,4-bis(styryl)benzene]s: The
Linear Chirality Transmisson Additivity Relationship in Nematic Liquid Crystals
Li-Chung Kuo,† Wan-Ting Huang,† Kuei-Hui Yang,† Hsiu-Fu Hsu,‡ Bih-Yaw Jin,† and
Man-kit Leung*,†
Department of Chemistry, National Taiwan UniVersity, Taipei, Taiwan 106, Republic of China, and
Department of Chemistry, Tamkang UniVersity, Taipei, Taiwan 251, Republic of China
ReceiVed: September 28, 2009; ReVised Manuscript ReceiVed: January 4, 2010
Alternating oligo[2,3-O-isopropylidene-L-threitol]-co-[(E,E)-1,4-bis(styryl)benzene]s (denoted as 2-6 in the
article) show helical twisting power (HTP), in 4-pentoxyl-4′-biphenylcarbonitrile (5OCB), linearly proportional
to the number of the chiral cores in the oligomers. The HTP per chiral core of -1.75 µm-1 was recorded in
the correlation plot with a correlation coefficient of R ) 0.99. These results suggested that the C2 chiral
L-threitol cores are aligned along the same axis. The comparable linear dichroism (LD) of 0.42 ( 0.02 obtained
for (rac)-2-5 at 405 nm, and of 0.52 ( 0.03 for E7, a commercially available room temperature nematic
solvent, at 347 nm in a parallel rubbed cell indicated that the long axis of the bis(styryl)benzene segments is
more or less parallel to the director of the E7 in the LC matrix. This observation is highly exciting because
the HTP per core could still be maintained, no matter whether the cores are evenly spread in a form of
monomer in the LC matrix or tightly confined in a polymer. Theoretical treatments about the conformations
of the dopant in the nematic matrix are discussed.
Introduction
Chiral-dopant-induced cholesteric liquid crystal (LC) meso-
phases are of particular important due to their technological
applications1 as well as fundamental interest of stereochemistry
and chirality.1,2 When chiral dopant molecules are introduced
into a nematic matrix, the orientation of the nematic layers would
helically rotate to form a chiral cholesteric phase (Figure 1).3
The information on the chiral molecules are therefore expressed
in the form of a long-range orientation or positional order of
the LC molecules that could be observed through amplification
of the quantities of the optical rotation or the circular dichroism.
The cholesteric phase has a periodical helicity, in which the
orientation of the long molecular axes in each successive layer
forms a given angle with that of molecules in the preceding
layer. Corresponding to the pitch p, the axis of orientation of
the molecules, known as the director, rotates through an angle
of 2π. The periodic structures were characterized by selective
reflection as well as angular dependence of the reflected
wavelength.1a The chiral-dopant effects were found even in very
dilute conditions, in which one dopant molecule would influence
hundreds of LC molecules.3 Although detection of a chiral
compound by its chiral induction of a cholesteric phase is a
very sensitive method,4 only for a few classes of organic dopants
a qualitative correlation between the molecular structure and
the induced helicity has been developed.5-12 In order to design
and develop materials with definite helical twisting power,
understanding of the factors that govern the interactions between
chiral dopants and nematic hosts is of special importance. During
the past few decades, four major classes of chiral dopants have
been designed: (1) chiral dopants without mesogenic group;3,6
(2) chiral dopants with mesogenic group tethered with a flexible
Figure 1. Chiral-dopant-induced helical twist in a nematic solvent.
TABLE 1: Calculated HTP of Dopants at 50 °C
a
ꢀM (µm-1
)
no. of chiral cores
ꢀM/core
2
3
4
5
6
7
8
9
-3.9
-5.2
-7.1
-17.6
-26.3
-6.1
-3.8
-3.1
2
3
-1.95
-1.73
-1.77
-1.76
-1.75
-6.1
4
∼10b
∼15b
1
1
1
-3.8
-3.55
a Uncertainty on tan θ of the wedge cell: (5%. b Determined by
1H NMR.
spacer;6 (3) chiral dopants with the chiral core hooked in
between two or more mesogenic groups by flexible spacers;7,8
and (4) chiral dopants with chiral core integrated as part of the
mesogenic group.9-12 Although the chiral cores are the origin
of the chiral induction, the roles of the achiral parts of the
molecules are also responsible for the chirality measurements.
The measure of the ability of a chiral molecule to produce
twisted phase is called the helical twisting power (HTP, defined
* To whom correspondence should be addressed. E-mail: mkleung@
ntu.edu.tw.
† National Taiwan University.
‡ Tamkang University.
10.1021/jp909286t  2010 American Chemical Society
Published on Web 02/08/2010

2608 J. Phys. Chem. B, Vol. 114, No. 8, 2010
Kuo et al.
SCHEME 1: Structures of the L-Threitol Based Chiral Dopants and Their Synthetic Precursors
as ꢀM in eq 1),13 that is inversely proportional to the molar
fraction of the dopant (c), the cholesteric pitch (p, in µm), and
the enantiomeric purity of the dopant (r)
ꢀM ) 1/(pcr)
(1)
When several different kinds of chiral dopants are introduced,
the contribution of each dopant on the helical twisting power
can be described in a good additive approximation5 as
(ꢀM)total
)
x (ꢀ )
(2)
∑
i
M i
i
Figure 2. GPC diagram for oligomers 5 (Mw 4100) and 6 (Mw 6100).
where xi is the mole fraction and (ꢀM)i is the HTP of the species
i.5 However, when chiral cores of a similar kind are positioned
in different locations on a mesogenic skeleton, the chiral
elements are carried into the LC matrix in different orientations.
Under these situations, the HTP of the molecules may not obey
the simple additive relationship and therefore their ꢀM cannot
be predicted on the basis of the number of chiral centers on the
molecule.9d,14 A large variation of the HTP would be found for
these compounds. For example, an elegant study of oligomeric
binaphthols has been demonstrated recently in which the ꢀM
does not follow the linear correlationship with the number of
chiral units.14a Since we are interested in developing oligochiral
dopants with predictable ꢀM, dopants with their chiral elements
being aligned in a unique direction are highly desired. It is
because their ꢀM is supposedly predictable on the basis of the
additive relationship. In addition, the polychiral dopants must
have good miscibility with the LC molecules in order to avoid
phase segregation problems.
Herein we report the study of oligochiral dopants 1-9, in
which 2-6 obey the additive relationship (Scheme 1). This class
of oligochiral dopants is derived from condensation of chiral
2,3-O-(isopropylidene)-L-threitol (L-(IPT)) with rigid-rod-like
(E,E)-1,4-bis(styryl)benzene (BSB) moieties. The L-IPT is a C2
chiral element that has chiral induction effect for cholesteric
mesophases. BSB is a linear rigid component that determines
mainly by the alignment order with the LC matrix and
accordingly the chiral elements would be carried into the matrix
in a specific direction. A model of cholesteric chiral induction
by chiral trans-4,5-dimethyl-1,3-dioxolane derivatives has been
reported in the literature8 in which the chiral 1,3-dioxolane was
aligned with its C2 axis more or less parallel to the rodlike LC
molecules; and the stereogenic fragment disturbed the parallel
alignment and imposed the helicodial arrangement. Therefore,
in our design, we adopted a flexible ether linkage to join the
chiral 1,3-dioxolane and the rigid BSB elements so that the rigid-
rod components are able to fold and align more or less parallel
with the C2 axis.
Preparation of the Chiral Dopants. The synthetic precursors
10-14 used in the present works are shown in Scheme 1. While
the oligomers 1-4 were synthesized by stepwise condensation,
the polymers 5 and 6 were obtained in a one-pot condensation
polymerization and end-capped with 3,5-dimethylphenol. In our
work, (E,E)-1,4-bis(2′-hydroxystyryl)benzenes 10-12,15 L-IPT
ditosylate (13),16 and the monotosylate 1417 were adopted as
the key building blocks for sequential condensation oligomer-
ization and one-pot polymerization reactions. The one-pot
condensation polymerization of 10 and 13 (1:1) was carried out
in DMF in the presence of K2CO3 as base and substantially
end-capped with 3,5-dimethylphenol. The polymer was purified
by precipitation from MeOH three times to give 5. The apparent
Mw obtained by GPC (American Polymer Standard AM GPC
Gel 104 Å 10 µm and 5 µm in serial) was 4100 against
polystyrene standards (Figure 2). The number-average degree
1
of polymerization (DP) of 10 was confirmed by using the H
NMR integration ratio between the dioxolane protons at δ
4.2-4.7 ppm and the terminal methyl protons at δ 2.2 ppm.
Oligomer 6 with higher apparent Mw of 6100, with the DP of

Chiral-Dopant-Induced Cholesteric LC Mesophases
J. Phys. Chem. B, Vol. 114, No. 8, 2010 2609
SCHEME 2: Synthetic Sequence for Preparation of 1-4
Figure 3. (a) Fingerprint texture of 5-doped 5OCB. (b) An enlarged image of 6 doped 5OCB in a wedge cell at 50 °C. Phase separation zones
were observed under a polarized microscope.
15 was isolated by using gel-permeation chromatography and
THF as the eluent.
The synthetic procedures for oligomers 1-4 are shown in
Scheme 2. Mono protection of 10 is done with a benzyl group
to afford 15, followed by condensation with 0.5 equiv of 13 to
give 1 in 80% yield. When 15 was treated with excess amounts
of 13, monosubstituted dioxolane 16 was obtained in reasonable
yield. By iterating the condensation strategy, 2 and 3 could
successfully be obtained. However, a practical problem was
faced when we applied this strategy for 4. When 17 was treated
with excess amounts of 13, the desired 18 and the disubstituted
Figure 4. HTP (ꢀm) and handedness of the threitol derivatives. Note
3 were simultaneously generated, which is difficult to separate.
that P twist for the D-threitol was observed by Spada, which is consistent
with the present results of M twist for the L-series.
Therefore, our strategy was detoured so that 17 was first reacted
with 14 to form the corresponding monoalcohol, followed by
tosylation to give 18, which was further coupled with 10 to
give 4. The monosubstituted dopants 7-9 were prepared in a
similar stepwise sequence, in which 15, 19, and 20 were coupled
with 14 to give 22-24, respectively, followed by methylation
to give 7-9. The spectroscopic standard 21 was prepared
through a one-step bis-benzylation of 10 under similar conditions.
Cholesteric Phase of Doped 4-Pentoxyl-4′-biphenylcarbo-
nitrile (5OCB).15 5OCB is a nematic liquid crystal with a
mesophase transition temperature (Tm) of 48 °C and isotropic
phase transition temperature (Ti) of 68 °C. When 2-6 were
doped, cholesteric fingerprint textures were observed, indicating
that helical pitches were formed in the LC matrix (Figure 3).
The left-turned helical handedness (-) was confirmed by contact
experiments with R-(-) and S-(+)-2,2′-binaphthyl-1,1′-diol as
the standards for comparison.3a,9f,18 The observation of the left-
turned helical handedness for the present L-2-6 series (i.e., M
twist for the L series) is complementary to that of reported by
Spada for 2-aryl substituted (4R,5R)-dimethyl-1,3-dioxolanes
25-27 and D-threitol 28 in E7 (Figure 4), which show right-
turned (P twist) helical handedness (i.e., P twist for the D series).8
These results imply the same chiral induction mechanism
operating for either the C2-chiral (4R,5R)-dimethyl-1,3-diox-
olanes, D-IPT, or the present L-IPT series of 2-6.
However, no fingerprint texture could be induced by 1 in
5OCB even at a high doping level of 21 wt %. The loss of the
HTP of 1 in 5OCB suggested that not only the C2-chiral
dioxolane core but also the achiral BSB parts are responsible
for the cholesteric behaviors. The effects of the BSB parts on
the HTP will be discussed in a later paper.
The HTP of the chiral dopants are also quantified by
Grandjean-Cano wedge experiments (using a cell from E.H.C.,
Japan), in which the induced pitch sizes at various dopant levels
couldbemeasuredfromthedistancebetweentheGrandjean-Cano
disclination lines.1,16 The chiral-induction capability of 2-5 in
5OCB was first compared as follows: for generation of the pitch
size of 13 µm, the mole fractions of 0.0192, 0.0148, 0.0108,
and 0.0042 for 2-5 were respectively required. The parameter
of pitch/molar fraction (p/c) was then calculated as 680, 880,
1200, and 3100 µm for 2-5. These results reflect the order of

2610 J. Phys. Chem. B, Vol. 114, No. 8, 2010
Kuo et al.
average DP of 15, was prepared by GPC for study. As shown
in Figure 7, 6 also obeys the linear relationship and shows ꢀM
of -26.3 µm-1, which could be reduced to 1.75 µm-1 per chiral
core. However, small amounts of white and bubblelike phase
segregation domains were found in the sample (Figure 3b). The
presence of these domains in the cholesteic planar texture
lowered the clearing point locally and caused some disorder of
the disclination line. We attributed these to the phase-segregation
phenomenon that is due to the lower miscibility of the high
molecular weight portions in the liquid crystal.
Temperature Dependence Experiments. The temperature
dependence of the pitch of the cholesteric phase is of particular
importance for certain LC applications.19 In dopant induced
cholesteric liquid crystals, both an increase and a decrease of
the pitch with temperature and even helix inversions have been
observed. The HTP (ꢀM) of a given dopant in a nematic LC
could be expressed as ꢀM ) (RTε)Q/2πK22νµm, where ε is the
orienting strength of the LC environment, R is the gas constant,
T is the absolute temperature, K22 is the twist elastic constant,
νm is the molar volume of the solution, and Q is the chirality
parameter which is governed by the coupling of chirality and
orientational behavior of the dopant.8,10,20 The definition of Q
could be expressed by Q ) -(2/3)1/2(QxxSxx + QyySyy + QzzSzz),
where Sꢁꢁ are the principal elements of the Saupe ordering matrix
S and Qꢁꢁ is the corresponding component of the helicity tensor
Q. Therefore, several factors that operate in opposite trends may
be responsible for the temperature dependence of the helical
twist, among which variation of order (Sꢁꢁ) of the nematic
molecules, of the elastic response (K22) of the helical twist, and
of conformational population redistribution which is related to
Q are essential for the phenomena. When temperature increases,
the elastic response (K22) of the LC matrix would become weak,
and therefore reduction of the K22 would amplify the effect of
the chiral dopants on the helical twist. The dꢀM/dT would
therefore be positive. On the other hand, the increase of
temperature is accompanied by an increase in the dynamic
conformational disorder, leading to an overall weakening of the
twisting power of the dopant molecules. Under this situation,
the dꢀM/dT would be negative. From the structural points of
view, the HTP of a chiral dopant would be governed by the
order effect and the porter effect. The dependence of the HTP
on the order of the guest and the host is known as the order
effect. However, chiral groups substituted on an achiral skeleton
possess a distinct orientational order in the liquid crystal phase,
which depends on the order of the skeleton. This effect is known
as the porter effect. Although the HTP is arising from the
contributions of all conformers of the chiral dopant, helical
conformers are expected to be the origin of the HTP effect.
When the temperature varies, redistribution of the population
of the different conformers would lead to a change of the HTPs.
In our cases, the order effect is controlled by the C2-chiral
L-threitol cores while the porter effect is coming from the rigid
BSB components. Indeed, contributions of different sign and
magnitude to the HTP can be derived from different parts in
the molecule. About the (4R,5R)-dimethyl-1,3-dioxolane sys-
tems, it was evidenced that the nematic molecules would align
along with the C2 axis (Figure 4). P twist of the chiral nematics
would lead to a positive sign (+) while M twist would lead to
a negative sign (-). In our system, observation of the negative
ꢀM for 2-9 suggested the M helicity along the C2 axis of the
chiral L-IPT cores.
Figure 5. Plot of pitch/molar fraction at the pitch size of 13 µm versus
the number of chiral L-threitol cores on the oligomers.
Figure 6. Inverse pitch (µm-1) versus molar fraction of 2-5 in 5OCB,
measured by using a Cano wedge cell at 50 °C.
Figure 7. Correlation plot of the HTP versus the number of chiral
L-threitol cores on the oligomers.
chiral-induction capability of 5 > 4 > 3 > 2. A linear correlation
plot of p/c versus the number of repeating chiral centers was
observed in this case, implying that the capability of each chiral
core on the pitch generation is essentially the same (Figure 5).
The quantitative parameter HTPs, defined as ꢀM ) 1/(pcr),13
were calculated from the slope of a plot of 1/p versus the molar
fraction (c) of the dopant, in which the enantiomeric purity (r)
equals to 1 (Figure 6). All systems almost perfectly obeyed the
linear relationship of ꢀM ) 1/(pcr) with the lines passing through
the origin.
The ꢀM values obtained for 2-5 from the linear regression
plots are -3.9, -5.2, -7.1, and -17.6 µm-1, respectively,
which are linearly proportional to the number of repeating chiral
cores on the oligomers (Figure 7). Obviously, their ꢀM obeys
the rule of summation of the HTP of each chiral unit. This could
be rationalized by assuming that the chiral cores were orienting
to the same axis so that their HTP could be maintained, without
being canceled with each other due to orientation randomness.
In order to further explore the limitation of the linear relation-
ship, another polymeric sample of 6, with an higher number
Again, as shown in Figure 8, the consistent decreasing trends
of the ꢀM versus temperature for 2-7 suggested that the chirality
transmission mechanisms for the whole series of dopants are

Chiral-Dopant-Induced Cholesteric LC Mesophases
J. Phys. Chem. B, Vol. 114, No. 8, 2010 2611
Figure 8. (a, left) Decreasing trends of the ꢀM versus temperature. (b, right) The molecular weight dependency of the temperature susceptibility
of ꢀΜ(Τ)/ꢀΜ(323 K).
Since the absorption regions of E7 (345 nm) and BSB (375
nm) segments are well resolved (Figure 9), the LD signals from
these two independent components could be directly observed.
In order to evaluate the orientation of the BSB segments with
respect to the E7 molecules, the orientation of the transition
dipole of (E,E)-4,4′-bis(2-methoxystyryl)benzene, a model
compound, was first calculated by AM1 and ZINDO.22 The
result is shown in the inset of Figure 9. By comparing the LD
signals of the BSB segments against that of E7, the relative
orientation of the BSB segment with respect to the director of
E7 could be estimated.
Figure 9. Linear dichromism of the racemic chiral dopants in E7. Inset
diagram shows the orientaion of the transition dipole moment of the
BSB segment. The orange line shows the UV-vis absorption spectrum
of a thin-liquid film of 19 in E7 as reference for comparison.
The LD experiments were performed in E7 using racemic
1-5 as dopants, which were prepared by equally mixing the
L-1-5 with their D-enantiomers. Pure E7 shows LD band at
340 nm while two positive and broad LD bands at 340 and 405
nm were observed for the (rac)-1-5 in E7. The spectral range
of the LD matches quite well with the corresponding UV
absorption spectrum of the BSB chromophore and E7. While
the LD band at 340 nm is assigned to the electronic π-π*
transition of E7, the band at 405 nm corresponds to the electronic
π-π* transition of the BSB segments. However, the spectral
shape of the band at 405 nm was slightly distorted due to the
anisotropic effects of the aligned nematic environments. Since
the value of LD ) 3Suu/(2 + Suu) is a function of the orientation
parameter, the comparable LD of 0.42 ( 0.02 for (rac)-2-5 at
405 nm, and of 0.52 ( 0.03 for E7 at 347 nm, indicated that
their long axes of the BSB segments are more or less parallel
to the director of the E7.
similar. As the temperature increases, the HTP in all plots
decreases due to the conformational disorder, leading to negative
slopes in Figure 8a. However, the temperature susceptibility of
the normalized HTP, defined as ꢀM(T)/ꢀM(323 K) per K, is found
to be slightly molecular weight dependent (Figure 8b). As shown
in Figure 8b, the macromolecular dopants would show stronger
temperature susceptibility than the small molecular dopants. The
temperature susceptibility increases from 0.0073 ( 0.0001 for
2 and 7, and reaches to a plateau of 0.015 ( 0.002 at high
molecular weight region.
Linear Dichromism (LD) in the Anisotropic Phase. Al-
though linear dichromism (LD) is a common method to provide
information about the alignment of the dopants in the LC
matrix.9a,b it was difficult to extract useful information about
the alignment of the C2-threitol chiral cores due to the lack of
the appropriate chromophores in our cases. In addition, the small
HTP value of the oligomers indicates that the interactions
between the chiral cores and the host-nematic LC might be
small. Nevertheless, the LD experiments would allow us to
understand the relative orientation of the rigid BSB segments
with respect to the director of the nematic environment. In order
to carry out the measurement at room temperature, a com-
mercially available room temperature liquid crystal named as
E7,8a instead of 5OCB,8a was adopted in these experiments.
Antiparallel rubbed polyimide coated ITO LC cells21 were
employed in order to restrict the orientation of the nematic
director. The alignment of the nematic liquid crystal could be
confirmed by the LD experiment. As shown in Figure 9, only
slightly red-shifted spectrum of 1-5 in E7, in comparison to
that of 19, was observed, indicating that the electronic π-π
interactions between BSB and E7 are weak. When the mixed
polarizations are small, a relationship linking the LD to the
Saupe order parameter (Suu) could be expressed as LD ) (ε|(λ)
- ε⊥(λ))/(ε|(λ) + ε⊥(λ)) ) 3Suu/(2 + Suu), where ε|(λ) and ε⊥(λ)
are the optical densities of the two perpendicularly plane-
polarized components of the incident radiation and the reduced
linear dichromism is denoted as LD.
On the other hand, (rac)-1 in E7 shows lower LD of 0.38 at
340 nm, indicating that the nematic alignments are less ordered
when dopant 1 was added. This observation is consistent with
the results of our previous experiment, in which no cholesteric
phase could be generated in L-1 doped 5OCB.
To further understand the behavior of oligochiral dopants
2-6, we adopted 7-9 as references to study. Perhaps the same
chiral dioxolane cholesteric phase induction mechanism is
operating in all these cases; their HTPs (ꢀM/core) and handed-
ness were found to be -6.1, -3.8, and -3.3, which are very
close to those of 2-6. However, small but observable porter
effects were recorded among 7-9. For 7 with the BSB
unsubstituted, stronger HTP (ꢀM/core) of -6.1 was observed.
On the other hand, when the BSB segments are methyl or ethyl
substituted, 8 and 9 showed HTP (ꢀM/core) of -3.8 and -3.55
that are more close to those of 2-6. Since the alkyl-substituted
BSB segments have larger length/diameter aspect ratios, we
expect that 8 and 9 are more mesogenic and would have better
alignment with the nematic matrix. Therefore, we conclude that
stronger alignment of the BSB unit with the nematic matrix
would lead to lower value of the ꢀM/core. Of course, increasing
the number of repeating units on the oligomeric dopants is essential
to provide larger driving force for the alignment. Therefore, it is

2612 J. Phys. Chem. B, Vol. 114, No. 8, 2010
Kuo et al.
culations showed that there are at least three possible conformers,
denoted as (a)-(c), respectively, when viewed along the C-O
bond. The corresponding Newman projections are shown in Figure
11. Unlike conformer (a), with the BSB matches well with the
M-twist liquid crystal alignment, conformers (b) and (c) should
be less important due to the mismatching orientation of the rodlike
BSB fragment. Therefore, we propose that the M-helical twist is
originating from conformer (a).
Figure 10. Conformational analysis of 2,3-O-(isopropylidene)-L-
threitol.
On the basis of the above discussion, a model for the
oligomeric structure could be built as illustrated in Figure 12,
in which the conformation of 7 is repeatedly extended. Our
model was built on the basis of several assumptions. (1) Spada’s
model about the alignment of the nematic LC molecules with
repsect to the C2-chiral dioxolane core is still valid. This
assumption we made is based on the fact that all molecules
have the same handedness of the cholesteric phases that matches
well with Spada’s model. (2) The BSB segments are aligned
more or less parallel to C2-chiral axis. The second assumption
is based on the results of the linear dichroism experiments, in
which the LD for the BSB segments is close to that of the E7
molecules. (3) All repeating units favor alignment on the same
axis, named as the Z-axis in our diagram. This assumption is
based on the additivity relationship, in which the ꢀM/core values
for 8, 9, and the oligomers are almost identical. (4) The local
environment of each L-threitol core should maintain the C2-
chiral symmetry. This is because the helical conformers are
expected to be the origin of the HTP effect.
no surprise that when the number of the repeating units increases,
the HTP (ꢀM/core) approaches the limit value of -1.7.
Models for the Cholesteric Phase Induction. During the
past few decades, models for the chirality transmission from a
chiral dopant to the bulk of the nematic solvent have been
extensively investigated, in which the chiral dopants are assumed
to act as templates to select chiral conformations of the LC
molecules lying next by them and therefore induce chiral
conformation in the nearest-neighbor molecules. The induced
chirality in this layer would then be passed to the next layer
through similar mechanisms and so on to the neighbor. On the
basis of this model, a chiral induction mechanism for (4R,5R)-
dimethyl-1,3-dioxolanes has been established by Spada. In this
model, the dioxolane dopant is aligned with its long axis more
or less parallel to the rodlike LC molecules (Figure 4). However,
the (4R,5R)-stereogenic fragment disturbs the parallel alignment
and imposes the P-twist helicoidal arrangement.2b This kind of
model has been applied for other systems in the past.23 Although
the chiral induction mechanism for D-threitol has not been deeply
explored, Spada obtained a similar ꢀM in the measurement with
the same helical twist handedness. These results reflected that
the chiral induction mechanisms for (4R,5R)-dimethyl-1,3-
dioxolanes and D-threitol are alike. Although theoretical calcula-
tions about the conformational structures of the chiral cores in
the gas phase may not be accurate enough to explain all
observations and phenomena in nematic liquid crystals due to
their small difference in energies as well as the perturbation
arising from the ordered host matrix, it might be still useful for
providing some insights about their relative conformational
stabilities. Since we adopted L-threitol as the chiral component
in our systems, PM5 calculations24 for L-threitol had been
performed, in which three possible C2-chiral conformations,
which are shown in Figure 10, were identified. The first one is
the gauche-in conformation with the OH groups inclining to
the C2 molecular axis. The second one is the gauche-out
conformation with the OH groups turning outward. The third
one is the anti conformation with the OH groups anti to the
dioxolane oxygens. Among them, the calculated heats of
formation of the gauche-in (-195.5 kcal/mol) and gauche-out
(-195.2 kcal/mol) conformations are almost identical but about
3 kcal/mol lower than that of the anti conformation (-192.5
kcal/mol). Therefore, the anti conformer should be the least
important for the chiral induction. On the other hand, the gauche-
out conformer should be the most significant one. Generally
speaking, chiral induction relies on the short-range intermo-
lecular interactions. Since the nematic molecules are kept off
from the C2-axis in the gauche-in conformation by the -OH
groups, small chiral-induction effect is expected. On the other
hand, the gauche-out conformation has a C2 chiral environment
similar to that of 20-22. Therefore, it is easy to perceive that
the gauche-out conformation would be the key conformation
for the M-twist chiral-induction mechanisms.
On the basis of this model, one could easily illustrate and
explain why the dopant favors to have the M-helical twist in a
nematic solvent as well as the origins of the linear ꢀM and
number of the repeating chiral cores correlationship.
In summary, we provided a strong proof for the HTP addition
rule of oligomeric and polymeric chiral dopants having the C2-
chiral cores chained alternatingly with rigid segments. This
family of dopants shows good miscibility with nematic liquid
crystals so that high molecular weight dopants could be tolerated
without significant phase segregation. The HTP of this family
obeys the addition rule so that the molar HTP is linearly
proportional to the number of repeating units. This observation
is highly exciting because the HTP per core could still be
maintained, no matter whether the cores are evenly spread in a
form of monomer in the LC matrix or being tightly confined in
a polymer. The designs of the next generation of dopant with
higher miscibility with nematic liquid crystals are ongoing.
Experimental Section
General Information. Tetrahydrofuran (THF) was distilled
from Na under N2, using benzophenone as indicator. Dimeth-
ylformamide (DMF) was dried with activated molecular sieves
(4 Å) and distilled before use. All other reagents and solvents
were of analytical or chemical grade or were purified using
standard methods. The wedge cells were ordered from E.H.C.
Japan, with the uncertainty of (5% on the value of tan θ.
1,4-(E,E)-Bis(2-hydroxystyryl)benzene Monobenzyl Ether
(15) Typical Procedure. To a solution of 10 (0.21 g, 0.65
mmol) in THF (1 mL) was added under N2 anhydrous K2CO3
(0.48 g, 3.5 mmol). The mixture was refluxed for 10 min,
followed by addition of benzyl chloride (0.082 g, 0.65 mmol)
in THF (1 mL). The reaction mixture was further refluxed for
24 h, and quenched with aqueous HCl (1 N) after cooling to
room temperature. The crude solid precipitated from the solution
were collected by filtration and purified by flash chromatography
on silica gel (toluene) to give yellow crystals (0.20 g, 0.48 mmol,
74%): mp 142-143 °C; 1H NMR (300 MHz, DMSO-d6) δ 9.77
On the other hand, conformational analysis for the less rigid
7 is more complicated. To simply our calculation, the terminal
-OBn group was replaced by hydrogen for clarity. Our cal-

Chiral-Dopant-Induced Cholesteric LC Mesophases
J. Phys. Chem. B, Vol. 114, No. 8, 2010 2613
Figure 11. Conformational analysis for a simplified 19. The terminal -OBn group was removed in order to simplify the PM5 computation.
34.5 mmol) and DMF (7 mL). The reaction mixture was reacted
at 90 °C under N2 for 3.5 h. After being cooled to room
temperature, the reaction mixture was diluted with chloroform
(20 mL) and filtered. The collected filtrate was washed with
water. The aqueous layer was re-extracted with chloroform (2
× 20 mL). The extracts were collected, dried over anhydrous
MgSO4, concentrated and purified by flash chromatography on
silica gel (toluene/ethyl acetate) to give 16 yellowish viscous
glassy solid (3.9 g, 5.1 mmol, 74%); [R]25.0 ) +1.00 (c )
D
Figure 12. Molecular model for the conformations of the oligochiral
dopants of 2-6 in 5-OCB and E7. The crossed bars represent the
orientation of the nematic layers above and under the chiral units.
1.00, CH2Cl2); 1H NMR (300 MHz, CDCl3) δ 7.74 (d, J ) 8.2
Hz, 2 H), 7.64-7.60 (m, 2 H), 7.56 (d, J ) 16.6 Hz, 1 H),
7.48-7.13 (m, 15 H), 7.12 (d, J ) 7.4 Hz, 1 H), 7.02-6.94
(m, 3 H), 6.87 (d, J ) 8.1 Hz, 1 H), 5.16 (s, 2 H), 4.27 (m, 4
H), 4.13 (m, 2 H), 2.33 (s, 3 H), 1.44 (s, 3 H), 1.39 (s, 3 H);
13C NMR (100 MHz, CDCl3) δ 156.1, 155.6, 145.0, 137.3,
137.1, 136.9, 132.6, 129.9, 129.1, 128.9, 128.61, 128.57, 127.90,
127.88, 127.23, 126.94, 126.91, 126.87, 126.85, 126.6, 126.4,
123.4, 122.7, 121.6, 121.2, 112.8, 112.4, 110.6, 77.2, 76.2, 75.7,
70.5, 69.0, 68.3, 27.0, 26.9, 21.5; HRMS (M+) calcd for
C43H42O7S 702.2651; found 702.2661.
(s, 1 H), 7.68 (d, J ) 7.4 Hz, 1 H), 7.57-7.11 (m, 17 H), 6.98
(t, 1 H), 6.36 (m, 2 H), 5.23 (s, 2 H); 13C NMR (100 MHz,
CDCl3) 156.2, 153.0, 137.4, 137.2, 136.7, 129.9, 128.9, 128.6,
127.9, 127.3, 127.2, 126.9, 126.85, 126.83, 126.7, 124.8, 123.5,
122.6, 121.2, 121.2, 115.9, 112.8, 70.5; MS m/z FAB (NBA)
404.2; HRMS (M+) calcd for C18H24O2 404.1776; found
404.1779.
1,4-(E,E)-Bis(2-hydroxy-4-methylstyryl)benzene Monoben-
zyl Ether (19). The monobenzyl ether was prepared from 11
according to the typical procedure with the yield of 50.6%. mp
Compound 1. (A Typical Coupling Procedure for 2-4).
To a double-necked flask were charged 15 (0.28 g, 0.70 mmol),
13 (0.18 g, 0.38 mmol), anhydrous K2CO3 (0.24 g, 1.75 mmol),
and DMF (1 mL). The mixture was reacted at 90 °C for 16 h
under N2. The resulting mixture was subsequently quenched with
water and extracted with ethyl acetate (3 × 20 mL). The organic
extracts were collected, washed with saturated brine, dried over
anhydrous MgSO4, concentrated by rotary evaporator, and
purified by flash chromatography on silica gel (toluene) to give
1 as yellowish solid. (0.26 g, 0.28 mmol, 80%): mp 120-125
°C [R]25.5D ) +18.98 (c ) 1.36, CH2Cl2). 1H NMR (500 MHz,
acetone-d6) δ 7.67-7.64 m, 4H), 7.59 (d, J ) 7.6 Hz, 2 H),
7.56-7.54 (m, 6 H), 7.49 (d, J ) 8.3 Hz, 4 H), 7.44-7.40 (m,
8 H), 7.36-7.33 (m, 2 H), 7.28-7.18 (m, 8 H), 7.11 (d, J )
8.4 Hz, 2 H), 7.08 (d, J ) 8.3 Hz, 2 H), 6.99-6.95 (m, 4 H),
5.24 (s, 4 H), 4.68 (s, 2 H), 4.42 (s, 4 H), 1.53 (s, 6 H); 13C
NMR (125 MHz, CDCl3) δ 156.12, 155.73, 137.15, 137.07,
136.87, 129.07, 128.94, 128.61, 128.53, 127.91, 127.30, 126.94,
126.91, 126.80, 126.72, 126.59, 126.46, 123.22, 122.80, 121.53,
121.13, 112.70, 112.35, 110.24, 77.08, 70.49, 69.00, 27.17;
HRMS (M+) calcd for C65H58O6 934.4233; found 934.4238.
Anal. Calcd for C65H58O6: C, 83.48; H, 6.25; O, 10.27. Found:
C, 83.65; H, 5.95.
1
135-137 °C; H NMR (400 MHz, DMSO-d6) δ 9.65 (s, 1H),
7.16 (d, J ) 16 Hz, 1H), 7.10 (d, J ) 16 Hz, 1 H), 7.22-7.11
(m, 2 H), 6.97 (s, 1 H), 6.80 (d, J ) 8.0 Hz, 1 H), 6.68 (s, 1 H),
6.63 (d, J ) 8.0 Hz, 1 H), 5.19 (s, 2 H), 2.31 (s, 3 H), 2.23 (s,
3 H); 13C NMR (100 MHz, DMSO-d6) δ 155.31, 154.61, 138.34,
138.02, 137.03, 136.76, 136.18, 128.30, 127.61, 127.53, 127.23,
126.34, 126.28, 126.17, 126.11, 123.27, 122.97, 122.49, 121.53,
120.87, 120.06, 116.16, 113.56, 69.57, 21.30, 21.01; HRMS
(FAB) calcd for C31H28O2 432.2089; obsd 432.2085.
1,4-(E,E)-Bis(2′-hydroxy-4′-ethylstyryl)benzene Monoben-
zyl Ether (20). The monobenzyl ether was prepared from 12
according to the typical procedure with the yield of 53.9%; mp
1
154-155 °C; H NMR (400 MHz, CDCl3) δ 7.53-7.30 (m,
13 H), 7.10 (d, J ) 16 Hz, 1 H), 7.05 (d, J ) 16 Hz, 1H), 6.82
(d, J ) 8.0 Hz, 1 H), 6.79 (s, 1 H), 6.78 (d, J ) 8.0 Hz, 1 H),
6.65 (s, 1 H), 5.14 (s, 2 H), 2.66-2.57 (m, 4 H), 1.25-1.21
(m, 6 H); 13C NMR (100 MHz, CDCl3) δ 155.92, 152.88,
145.17, 145.05, 137.06, 137.04, 136.59, 128.45, 128.39, 127.88,
127.70, 127.20, 126.75, 126.53, 126.50, 126.38, 124.22, 123.10,
122.55, 121.96, 120.57, 120.51, 115.31, 112.40, 70.55, 29.06,
28.59, 15.58, 15.42; HRMS (FAB) calcd for C33H32O2 460.2402;
obsd 460.2397.
Compound 2. Compound 10 (0.062 g, 0.20 mmol), 16 (0.25
g, 0.36 mmol), anhydrous K2CO3 (0.124 g, 0.897 mmol), and
DMF (0.5 mL) were reacted at 90 °C for 16 h under N2 to give
the crude 2 that was purified by flash chromatography on silica
gel (PhMe:EtOAc ) 1:1) to give essentially pure 2 as yellow
p-Toluenesulfonyl-4-O-{(2-(E)-{4-[2-(2-benzyloxyphenyl)-
(E)-vinyl]phenyl}vinyl)phenyl}-2,3-O-isopropylidene-L-threi-
tol (16). To an oven-dried double-necked flask were charged
15 (2.8 g, 6.9 mmol), 13 (6.49 g, 13.8 mmol), K2CO3 (4.77 g,

2614 J. Phys. Chem. B, Vol. 114, No. 8, 2010
Kuo et al.
solid (0.153 g, 0.112 mmol, 62%): mp 110-115 °C; [R]25.5
)
EtOAc ) 1:1) to give the monosubstituted threitol intermediate
D
1
+25.0° (c ) 1.02, CH2Cl2). H NMR (400 MHz, CDCl3) δ
7.80-7.65 (m, 10H), 7.60-7.57 (m, 6 H), 7.52-7.45 (m, 17
H), 7.27-7.07 (m, 21 H), 7.07-6.90 (m, 4H), 5.23 (s, 4H),
4.65 (s, 4 H), 4.39-4.31 (m, 8 H), 1.69 (s,6H), 1.68 (s, 6H);
13C NMR (125 MHz, CDCl3) δ 156.11, 155.76, 155.71, 137.14,
137.06, 136.90, 136.85, 129.11, 129.07, 128.94, 128.67, 128.61,
128.54, 127.91, 127.30, 126.93, 126.88, 126.81, 126.74, 126.72,
126.59, 126.53, 126.44, 123.22, 122.86, 122.77, 121.51, 121.13,
112.69, 112.35, 110.25, 76.88, 70.47, 69.01, 27.17; MS m/z FAB
(NBA) 1375.6. Anal. Calcd for C94H86O10: C, 82.07; H, 6.30;
O, 11.63. Found: C, 81.82, H, 6.17.
as yellowish glassy solid. (0.453 g, 0.459 mmol, 63%): [R]25.8
D
) +24.95 (c ) 1.01, CH2Cl2);1H NMR (400 MHz, CDCl3) δ
7.61- 7.46 (m, 9H), 7.42-7.34 (m, 12 H), 7.23-7.02 (m, 8
H), 7.02-6.85 (m, 8 H), 5.16 (s, 2 H), 4.55-4.54 (m, 2 H),
4.31-4.11 (m, 8 H), 3.92 (m, 1 H), 3.76 (m, 1 H), 1.95 (bs,
OH), 1.55 (s, 3 H), 1.54 (s, 3 H), 1.47 (s, 6 H); 13C NMR (100
MHz, CDCl3) δ 156.1, 155.8, 155.7, 137.16, 137.09, 137.06,
136.92, 136.88, 129.16, 129.11, 129.07, 128.96, 128.73, 128.64,
128.58, 127.95, 127.34, 126.95, 126.93, 126.82, 126.75, 126.62,
126.54, 126.50, 123.25, 123.00, 122.78, 121.56, 121.16, 112.72,
112.42, 112.37, 112.33, 110.28, 109.77, 79.30, 76.84, 75.30,
70.51, 69.04, 68.94, 68.72, 62.14, 27.20, 27.16, 27.09; HRMS
(M+) calcd for C65H64O9 988.4550; found 988.4563. The
monosubstituted threitol intermediate (0.394 g, 0.398 mmol) was
further tosylated by reaction with p-toluenesulfonyl chloride
(0.135 g, 0.764 mmol) in CH2Cl2 (0.6 mL) at 0 °C for 1.5 h,
using Et3N (0.3 mL) as the catalyst and acid scavenger. The
resulting mixture was quenched with aqueous HCl (1 N) and
extracted with EtOAc (3 × 30 mL). The organic extract was
combined, washed with saturated brine, dried over anhydrous
MgSO4, concentrated, and purified by flash chromatography on
silica gel (toluene/ethyl acetate) to give 18 as yellow glass.
1-[O-2-(2-(E)-{4-[2-(E)-(2-Hydroxyphenyl)vinyl]phenyl}-
v i n y l ) p h e n y l ] - 4 - [ O - 2 - ( 2 - ( E ) - { 4 - [ 2 - ( E ) - ( 2 -
benzyloxyphenyl)vinyl]phenyl}vnyl)phenyl]-2,3-[O-isopro-
pylidene]-L-threitol (17). Compound 10 (0.354 g, 1.13 mmol),
16 (0.549 g, 0.78 mmol), anhydrous K2CO3 (0.604 g, 4.37
mmol) in DMF (1.5 mL) were reacted at 90 °C for 19 h under
N2. The resulting mixture was subsequently quenched by
aqueous HCl (1 N) and extracted with EtOAc (3 × 20 mL).
The organic extract was collected, washed with brine (saturated),
dried over anhydrous MgSO4, and concentrated. The crude
mixture was purified by flash chromatography on pretreated
silica gel (3% triethylamine in hexane), using PhMe/EtOAc (1:
1) as eluent to give 17 as yellowish viscous oil. (0.409 g, 0.50
(0.450 g, 0.394 mmol, 99%): [R]25.8 ) +17.60 (c ) 1.00,
D
CH2Cl2); 1H NMR (400 MHz, CDCl3) δ 7.72 (d, J ) 8.3, 2 H),
7.62-7.32 (m, 22 H), 7.23-7.03 (m, 16 H), 6.87 (d, J ) 8.2,
1 H), 6.86 (d, J ) 8.2, 2H), 5.16 (s, 2 H), 4.55 (m, 2 H),
4.31-4.14 (m, 8 H), 4.14 (m, 2 H), 2.31 (s, 3 H), 1.55 (s, 3 H),
1.54 (s, 3 H), 1.42 (s, 3 H), 1.38 (s, 3 H); 13C NMR (100 MHz,
CDCl3) δ 156.10, 155.76, 155.70, 155.56, 145.02, 137.12,
137.06, 136.80, 132.50, 129.9, 129.16, 129.05, 129.02, 128.91,
128.71, 128.67, 128.61, 128.55, 128.21, 127.91, 127.3, 126.91,
126.89, 126.86, 126.81, 126.71, 126.57, 126.52, 126.46, 126.42,
123.21, 122.96, 122.75, 122.60, 121.61, 121.51, 121.49, 121.12,
112.67, 112.34, 112.32, 110.56, 110.23, 77.21, 76.79, 76.14,
75.67, 70.45, 68.99, 68.89, 68.24, 27.15, 27.02, 26.85, 21.56;
HRMS (M+) calcd for C72H70O11S 1142.4639; found 1142.4648.
Compound 4. Compound 18 (0.466 g, 0.407 mmol), 10
(0.064 g, 0.204 mmol) and anhydrous K2CO3 (0.141 g, 1.02
mmol) in DMF (0.4 mL) were heated at 90 °C for 48 h under
N2 to give a crude solid that was purified by flash chromatog-
raphy on silica gel (PhMe/EtOAc) to give 4 as yellow solid.
Compound 4 could be further recrystallized from EtOAc-hexane
mmol, 64%): mp > 170 °C dec [R]25.8 ) +15.20 (c ) 1.00,
D
CH2Cl2). 1H NMR (300 MHz, CDCl3) δ 7.65-7.25 (m, 21 H),
7.22-6.87 (m, 15 H), 6.78 (d, J ) 8.1 Hz, 1 H), 5.30 (bs, 1 H),
5.17 (s, 2 H), 4.58 (s, 2 H), 4.30 (m, 4 H), 1.59 (s, 6 H); 13C
NMR (100 MHz, CDCl3) δ 156.1, 155.7, 153.0, 137.1, 137.1,
137.0, 136.8, 136.7, 129.5, 129.1, 129.0, 128.9, 128.7, 128.6,
128.5, 127.9, 127.3, 127.0, 126.9, 126.83, 126.78, 126.7, 126.6,
126.4, 124.7, 123.2, 122.9, 122.8, 122.7, 121.5, 121.1, 121.0,
115.9, 112.7, 112.4, 112.3, 110.3, 77.05, 70.5, 69.0, 68.9, 27.2;
HRMS (M+) calcd for C58H52O6 844.3764; found 844.3764.
Compound 3. Compound 10 (0.145 g, 0.308 mmol), 13
(0.580 g, 0.686 mmol) anhydrous K2CO3 (0.094 g, 0.680 mmol)
in DMF (0.5 mL) were reacted at 90 °C under nitrogen for 48 h
to give a crude mixture that was purified by flash chromatog-
raphy on silica gel (PhMe:EtOAc ) 1:1) to give 3 as yellow
solid. (0.196 g, 0.095 mmol, 31%). The compound could be
further recrystallized from EtOAc-hexanes to afford analytical
sample: mp 110-115 °C; [R]26.7 ) +25.63 (c ) 0.96,
D
CH2Cl2).1H NMR (400 MHz, CDCl3) δ 7.30-7.55 (m, 40 H),
6.82-7.12 (m, 34 H); 5.14 (s, 4 H), 4.53 (s, 6 H), 4.30-4.21
(m, 12 H), 1.53(s, 6 H), 1.52 (s, 6 H), 1.51 (s, 6 H); 13C NMR
(125 MHz, CDCl3) δ 156.11, 155.78, 155.74, 155.71, 137.14,
137.06, 136.88, 136.85, 129.11, 129.07, 128.93, 128.67, 128.61,
128.54, 127.91, 127.30, 126.91, 126.81, 126.75, 126.72, 126.59,
126.53, 126.44, 123.22, 122.84, 122.77, 121.51, 121.13, 112.69,
112.34, 110.25, 76.88, 70.5, 69.0, 27.2; MS m/z FAB(NBA)
1815.8. Anal. Calcd for C123H114O14: C, 81.34; H, 6.33; O, 12.33.
Found: C, 81.04; H, 6.08.
to give analytically pure sample. (0.205 g, 0.090 mmol, 44%)
1
mp 120-125 °C; [R]25.6 ) +28.05 (c ) 0.93, CH2Cl2). H
D
NMR (400 MHz, CDCl3) δ 7.29-7.53 (m, 48 H), 6.85-7.11
(m, 42 H), 5.15 (s, 4 H), 4.53-4.52 (m, 8 H), 4.30-4.24 (m,
16 H), 1.535(s, 6 H), 1.528 (s, 6 H). 1.522 (s, 6 H), 1.513 (s,
6 H); 13C NMR (100 MHz, CDCl3) δ 156.2, 155.81, 155.78,
155.75, 137.2, 137.1, 136.91, 136.88, 129.15, 129.11, 128.97,
128.69, 128.62, 128.55, 127.93, 127.32, 126.95, 126.94, 126.83,
126.77, 126.74, 126.62, 126.55, 126.48, 123.26, 122.89, 122.81,
121.54, 121.16, 112.74, 112.39, 110.29, 110.27, 77.23, 76.91,
70.52, 69.06, 27.20; MS m/z FAB (NBA) 2257.4. Anal. Calcd
for C152H142O18: C, 80.90; H, 6.34; O, 12.76. Found: C, 80.59;
H, 6.26.
Two-Step Synthetic Sequence for Preparation of 18 from
17. Compound 14 (0.276 g, 0.873 mmol), 17 (0.615 g, 0.728
mmol), and anhydrous K2CO3 (0.503 g, 3.640 mmol) in DMF
(1.0 mL) were reacted at 90 °C for 12 h under N2. To secure
that the conversion was complete, additional amounts of 14
(0.060 g, 0.190 mmol) were added and reacted for another 30 h.
The resulting mixture was finally quenched with water. The
product was extracted with EtOAc (3 × 30 mL). The collected
organic extracts were washed with saturated aqueous NaCl, dried
over anhydrous MgSO4 and concentrated. The crude product
was purified by flash chromatography on silica gel (PhMe/
Polymers 5 and 6. Compound 10 (0.343 g, 1.09 mmol), 13
(0.518 g, 1.10 mmol), and anhydrous K2CO3 (0.753 g, 5.45
mmol) in DMF (1 mL) were reacted at 90 °C for 48 h under
N2. DMF (0.5 mL) was refilled once for every 12 h in order to
keep the mixture wet. 3,5-Dimethylphenol (0.027 g, 0.22 mmol)
in DMF (0.3 mL) was added to end-cap the polymer. The
mixture was further refluxed for 24 h and then diluted with
CHCl3 and filtered. The filtrate was concentrated to give a dark-

Chiral-Dopant-Induced Cholesteric LC Mesophases
J. Phys. Chem. B, Vol. 114, No. 8, 2010 2615
brown DMF solution. The polymer solution was precipitated
by addition of the solution to MeOH to give yellowish solid
that was further redissolved in CHCl3 and reprecipitated from
(s, 3 H); 13C NMR (100 MHz, CDCl3) δ 156.1, 155.8, 137.2,
137.1, 137.0, 129.0, 128.9, 128.59, 128.57, 127.9, 127.2, 126.88,
126.87, 126.79, 126.6, 126.4, 123.3, 122.9, 121.4, 121.1, 112.7,
112.3, 110.0, 77.8, 76.5, 73.3, 70.5, 68.9, 59.5, 27.12, 27.00;
HRMS (M+) calcd for C37H38O5: 562.2719; found 562.2725.
Anal. Calcd for C37H38O5: C, 78.98; H, 6.81; O, 14.22. Found:
C, 78.98; H, 7.06.
MeOH twice to give yellowish solid (0.253 g, 53%): [R]25.5
)
D
+30.6 (c ) 1.08, CH2Cl2).1H NMR (400 MHz, CDCl3) δ
6.80-7.70 (ArH, 154 H), 4.20-4.60 (alkyl protons on the
threitol moiety, 64 H), 2.20 (methyl group on the terminal unit,
s, 6 H), 1.47-1.54 (methyl groups on the threitol unit, 64 H).
The integration ratio of 10.7 between the methyl groups on the
threitol units and the methyl groups on the terminal groups
suggested that n ∼ 10-11 for the polymer; 13C NMR (100 MHz,
CDCl3) δ 155.74, 136.88, 129.10, 128.67, 126.88, 126.75,
126.52, 122,.86, 121.49, 112.34, 110.25, 77.20, 69.01, 27.17
Anal. Calcd. (for n ) 10) C314H312O44: C, 78.74; H, 6.57; O,
14.70. Found: C, 78.74; H, 6.57; O, 14.70.
Compound 8. 1,4-(E,E)-Bis(2′-hydroxy-4′-methylstyryl)ben-
zene monobenzyl ether was first coupled with 14 to give the
corresponding threitol monoether, followed by methylation to
give 8. Analytical data for the corresponding threitol monoether
intermediate 23 (69.3% yield): mp 100-102 °C; 1H NMR (400
MHz, CDCl3) δ 7.50-7.33 (m, 13 H), 7.09 (d, J ) 16 Hz, 1
H), 7.03 (d, J ) 16 Hz, 1 H), 6.81-6.78 (m, 2 H), 6.77 (s, 1
H), 6.71 (s, 1 H), 5.13 (s, 2 H), 4.37-4.34 (m, 1 H), 4.24-4.17
(m, 2 H), 4.14-4.10 (m, 1 H), 3.94-3.93 (m, 1 H), 3.81-3.78
(m, 1 H), 2.34 (d, J ) 2.8 Hz, 6 H), 1.92 (dd, J ) 5.2 Hz, 7.6
Hz, 1 H), 1.50 (s, 6 H); 13C NMR (100 MHz, CDCl3) δ 155.89,
155.41, 138.71, 138.64, 137.10, 137.06, 136.74, 128.43, 128.03,
127.84, 127.71, 127.15, 126.58, 126.51, 126.32, 126.11, 124.01,
123.12, 122.50, 122.19, 121.82, 113.51, 113.16, 109.62, 79.32,
75.31, 70.49, 68.70, 62.18, 27.25, 27.19, 21.77, 21.72; HRMS
(FAB) calcd for C38H40O5 576.2876; obsd 576.2877. Analytical
Compound 7. General Procedure for 8 and 9. A stepwise
synthetic sequence was adopted for preparation of compound
7. In this procedure, 10 was first coupled with 14 to give the
corresponding threitol monoether 22, followed by methylation
to give 7. Following is the preparation procedure of the
corresponding threitol monoether intermediate. Compound 14
(0.470 g, 1.48 mmol), 10 (0.661 g, 1.63 mmol), and anhydrous
K2CO3 (0.616 g, 4.46 mmol) in DMSO (1 mL) were reacted at
90 °C for 10 h under N2. The resulting mixture was finally
quenched with 1N HCl. The product was extracted with ethyl
acetate (3 × 30 mL). The organic extracts were collected,
washed with saturated brine, dried over anhydrous MgSO4,
concentrated, and purified by flash chromatography on silica
gel (EtOAc:PhMe ) 1:5) to give the corresponding threitol
1
data for 8 (75% yield): mp 98-100 °C; H NMR (400 MHz,
CDCl3) δ 7.54-7.36 (m, 13 H), 7.13 (d, J ) 16 Hz, 1H), 7.07
(d, J ) 16 Hz, 1H), 6.82(d, J ) 8 Hz, 2 H), 6.81 (s, 1H), 6.75
(s, 1 H), 5.14 (s, 2H), 4.27-4.23 (m, 3 H), 4.16-4.13 (m, 1
H), 3.71-3.66 (m, 2 H), 3.41 (s, 3 H), 2.37 (d, J ) 2.8 Hz, 6
H), 1.53 (d, J ) 2.8 Hz, 6 H); 13C NMR (100 MHz, CDCl3) δ
155.85, 155.43, 138.65, 138.61, 137.04, 137.00, 136.76, 128.38,
127.84, 127.77, 127.68, 127.11, 126.50, 126.29, 126.00, 123.91,
123.07, 122.62, 122.04, 121.79, 113.43, 113.03, 109.83, 77.84,
76.39, 73.34, 70.43, 68.92, 59.51, 27.21, 27.10, 21.74, 21.71;
HRMS (FAB) calcd for C39H42O5 590.3032; obsd 590.3029.
Compound 9. 1,4-(E,E)-Bis(2′-hydroxy-4′-ethylstyryl)ben-
zene monobenzyl ether was first coupled with 14 to give the
corresponding threitol monoether, followed by methylation to
give 9. Analytical data for the corresponding threitol monoether
intermediate 24 (63.1% yield): mp 120-122 °C; 1H NMR (400
MHz, CDCl3) δ 7.55-7.33 (m, 13 H), 7.12 (d, J ) 16 Hz, 1H),
7.06 (d, J ) 16 Hz, 1H), 6.84 (d, J ) 8 Hz, 2 H), 6.81 (s, 1H),
6.76 (s, 1 H), 5.16 (s, 2 H), 4.40-4.36 (m, 1 H), 4.27-4.13
(m, 3 H), 3.99-3.94 (m, 1 H), 3.84-3.78 (m, 1 H), 2.69-2.62
monoether 22 as yellowish glassy solid (0.687 g, 1.23 mmol,
1
89%); [R]26.2 ) +11.33 (c ) 0.83, CH2Cl2) H NMR (400
D
MHz, CDCl3) δ 7.61 (t, J ) 6.7 Hz, 2 H), 7.55 (d, J ) 16.5
Hz, 1 H), 7.50-7.45 (m, 7 H), 7.40 (t, J ) 7.1 Hz, 2 H), 7.34
(t, J ) 7.2 Hz, 1 H), 7.20 (t, J ) 8.3 Hz, 2 H), 7.15 (d, J )
16.4 Hz, 1 H), 7.09 (d, J ) 16.4 Hz, 1 H), 7.00 (t, J ) 6.8 Hz,
1 H), 6.96 (t, J ) 6.8 Hz, 1 H), 6.92 (d, J ) 8.2 Hz, 1 H), 6.90
(d, J ) 8.3 Hz, 1 H), 5.16 (s, 2 H), 4.39-4.35 (m, 1 H),
4.24-4.18 (m, 2 H), 4.16-4.12 (m, 1 H), 3.97-3.92 (m, 1 H),
3.81-3.75 (m, 1 H), 2.03-2.00 (m, 1 H), 1.50 (s, 6 H); 13C
NMR (100 MHz, CDCl3) δ 156.1, 156.7, 137.2, 137.1, 136.9,
129.1, 128.9, 128.6, 127.9, 127.2, 126.9, 126.8, 126.6, 126.4,
123.3, 122.7, 121.5, 121.1, 112.7, 112.3, 109.7, 79.2, 75.3, 70.4,
68.6, 62.1, 27.12, 27.05; HRMS (M+) calcd for C36H36O5:
548.2563; found 548.2554. The threitol monoether 22 was
further methylated to form 7 according to the following
procedure. To a mixture of NaH (0.018 g of 60 wt % in mineral
oil, 0.46 mmol) was prewashed with distilled hexane (3 × 3
mL) in THF (0.2 mL) at 0 °C was added the above threitol
monoether (0.110 g, 0.20 mmol) under nitrogen. After reaction
for 10 min, dimethylsulfate (0.058 g, 0.46 mmol) in THF (0.2
mL) was the added at 0 °C. The mixture is allowed to react at
room temperature overnight and quenched by addition of water.
The mixture was extracted with EtOAc (3 × 30 mL). The
extracts were collected, washed with saturated brine, dried over
anhydrous MgSO4, concentrated, and purified by flash chroma-
tography on silica gel (toluene) to give 7 as yellow solid (0.105
g, 0.18 mmol, 88%); mp 116-117 °C; [R]26.3D ) +10.34 (c )
1.47, CH2Cl2); 1H NMR (400 MHz, CDCl3) δ 7.61 (t, J ) 6.0
Hz, 2 H), 7.54 (d, J ) 16.5 Hz, 1 H), 7.51-7.46 (m, 7H), 7.41
(t, J ) 7.3 Hz, 2H), 7.34 (t, J ) 7.2 Hz, 1 H), 7.20 (t, J ) 7.3
Hz, 2 H), 7.15 (d, J ) 16.4 Hz, 1 H), 7.09 (d, J ) 16.3 Hz, 1
H), 7.01-6.98 (m, 2 H), 6.95 (d, J ) 8.4 Hz, 1 H), 6.90 (d, J
) 8.2 Hz, 1 H), 5.15 (s, 2 H), 4.25-4.22 (m, 3 H), 4.15-4.13
(m, 1 H), 3.66-3.64 (m, 2 H), 3.38 (s, 3 H), 1.50 (s, 3 H), 1.49
(m, 4 H), 2.04 (s, 1 H), 1.52 (s, 6 H), 1.29-1.24 (m, 6 H); 13
C
NMR (100 MHz, CDCl3) δ 155.92, 155.47, 145.11, 145.03,
137.06, 137.03, 136.71, 128.38, 128.03, 127.85, 127.67, 127.16,
126.55, 126.49, 126.36, 126.15, 124.20, 124.17, 123.10, 122.49,
120.90, 120.52, 112.33, 111.93, 109.57, 79.27, 75.31, 70.47,
68.63, 62.14, 29.06, 27.21, 27.16, 15.61; HRMS (FAB) calcd
for C40H44O5 604.3189; obsd 604.3193. Analytical data for 9
1
(70.3% yield): mp 84-85 °C; H NMR (400 MHz, CDCl3) δ
7.53-7.31 (m, 13 H), 7.10 (d, J ) 16 Hz, 1 H), 7.04 (d, J )
16 Hz, 1H), 6.82 (d, J ) 8.0 Hz, 2 H), 6.80 (s, 1H); 6.74 (s, 1
H), 5.14 (s, 2 H), 4.23 (d, J ) 6.0 Hz, 3 H), 4.14-4.12 (m, 1
H), 3.66-3.65 (m, 2 H), 3.37(s, 3 H), 2.67-2.61 (m, 4 H),
1.49 (d, J ) 2.8 Hz, 6 H), 1.26-1.21 (m, 6 H); 13C NMR (100
MHz, CDCl3) δ 155.98, 155.57, 145.18, 145.11, 137.11, 137.06,
136.82, 128.42, 127.97, 127.89, 127.73, 127.21, 126.54, 126.41,
126.13, 124.24, 124.21, 123.15, 122.70, 120.84, 120.57, 112.39,
111.94, 109.88, 77.93, 76.45, 73.38, 70.55, 69.00, 59.56, 29.11,
27.25, 27.14, 15.62; HRMS (FAB) calcd for C41H46O5 618.3345;
obsd 618.3340.
Acknowledgment. We thank the National Science Council
of Taiwan (NSC 95-2113-M002-021-MY3, NSC 98-2119-

2616 J. Phys. Chem. B, Vol. 114, No. 8, 2010
Kuo et al.
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M002-006-MY3, and NSC 97-3114-M002-005), Academia
Sinica (Thematic Project), Ministry of Education of Taiwan,
and National Taiwan University for financial support.
Supporting Information Available: 1H NMR spectra of
1-5, 7-12, 15-16, 19-24. This material is available free of
charge via the Internet at http://pubs.acs.org.
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