Ferroelectric liquid crystals induced by atropisomeric dopants: Dependence of the polarization power on the core structure of the smectic C host

Article abstract of DOI:10.1021/ja990965m

A series of 11 chiral dopants with an atropisomeric core derived from 4,4′-dihydroxy-2,2′,6,6′-tetramethyl-3,3′- dinitrobiphenyl were synthesized in optically pure form. These compounds were doped into five different smectic C (S_C) liquid crystal hosts to induce a ferroelectric S_C* liquid crystal phase, and the reduced polarization P_o was measured as a function of the dopant mole fraction x_d over the range 0.005 < x_d ≤ 0.05. The polarization power δ_p was found to strongly depend on the core structure of the S_C host. For example, the dopant (+)-2,2′,6,6′-tetramethyl-3,3′-dinitro-4,4′-bis[(4- octyloxybenzoyl)oxy]biphenyl gave δ_p values of <30 nC/cm² in a phenyl benzoate S_C host and 1738 nC/cm² in a phenylpyrimidine S_C host; the latter is one of the highest polarization power values reported thus far in the literature. In the phenylpyrimidine S_C host, the polarization power was found to depend on the length of the dopant side chains and on the position of the atropisomeric core with respect to those of the surrounding S_C host molecules, on the time average. The polarization power followed a trend opposite to that followed by the S_C* helical pitch. Analysis of these results suggests that chirality transfer from the atropisomeric core of the dopant to those of the Sc host molecules plays a key role in amplifying the polarization induced in the phenylpyrimidine host. It is likely that such intercore chirality transfer results in an asymmetric distortion of the S_C* lattice, which in turn, further increases the conformational asymmetry of the chiral dopant by virtue of increased diastereomeric bias between the S_C* lattice and the chiral conformations of the dopant.

Full text of DOI:10.1021/ja990965m

J. Am. Chem. Soc. 1999, 121, 8229-8236
8229
Ferroelectric Liquid Crystals Induced by Atropisomeric Dopants:
Dependence of the Polarization Power on the Core Structure of the
Smectic C Host
Despina Vizitiu, Carmen Lazar, Brian J. Halden, and Robert P. Lemieux*
Contribution from the Department of Chemistry, Queen’s UniVersity, Kingston, Ontario, Canada K7L 3N6
ReceiVed March 24, 1999. ReVised Manuscript ReceiVed July 1, 1999
Abstract: A series of 11 chiral dopants with an atropisomeric core derived from 4,4′-dihydroxy-2,2′,6,6′-
tetramethyl-3,3′-dinitrobiphenyl were synthesized in optically pure form. These compounds were doped into
five different smectic C (SC) liquid crystal hosts to induce a ferroelectric SC* liquid crystal phase, and the
reduced polarization Po was measured as a function of the dopant mole fraction xd over the range 0.005 < xd
e 0.05. The polarization power δp was found to strongly depend on the core structure of the SC host. For
example, the dopant (+)-2,2′,6,6′-tetramethyl-3,3′-dinitro-4,4′-bis[(4-octyloxybenzoyl)oxy]biphenyl gave δp
2
2
values of <30 nC/cm in a phenyl benzoate SC host and 1738 nC/cm in a phenylpyrimidine SC host; the latter
is one of the highest polarization power values reported thus far in the literature. In the phenylpyrimidine SC
host, the polarization power was found to depend on the length of the dopant side chains and on the position
of the atropisomeric core with respect to those of the surrounding SC host molecules, on the time average. The
polarization power followed a trend opposite to that followed by the SC* helical pitch. Analysis of these
results suggests that chirality transfer from the atropisomeric core of the dopant to those of the SC host molecules
plays a key role in amplifying the polarization induced in the phenylpyrimidine host. It is likely that such
intercore chirality transfer results in an asymmetric distortion of the SC* lattice, which in turn, further increases
the conformational asymmetry of the chiral dopant by virtue of increased diastereomeric bias between the SC*
lattice and the chiral conformations of the dopant.
Introduction
A chiral smectic C (SC*) liquid crystal phase, which is
ferroelectric as a surface-stabilized thin film (vide infra), can
be obtained by doping an achiral smectic C (SC) liquid crystal
1
host with a chiral additive that may or may not be mesogenic.
On the time average, the symmetry elements of an achiral
smectic C (SC) liquid crystal phase include a C2 axis normal to
the tilt plane (defined by the molecular long axis n and the layer
normal z) and a reflection plane of symmetry σ congruent with
the tilt plane, as shown in Figure 1. The introduction of a chiral
dopant into a SC liquid crystal breaks the reflection symmetry
and results in the polar ordering of transverse molecular dipoles
along the C2 axis, which is now a polar axis, thus resulting in
Figure 1. Schematic representation of the smectic C phase. The vectors
z and n are in the plane of the page.
2
a net spontaneous polarization (PS). In the absence of external
E across the glass slides, a SSFLC can be switched between
two degenerate surface-stabilized states corresponding to op-
posite tilt orientations, thus producing a change in birefringence
when the SSFLC film is placed between crossed polarizers. This
effect is now being exploited in high-resolution display ap-
constraints, however, a chiral SC* liquid crystal forms a
macroscopic helical structure in which the spontaneous polariza-
tion rotates from one layer to the next, thus averaging to zero
in the bulk.
4
plications. The switching time (τs) of a SSFLC light valve is
Clark and Lagerwall have shown that the helical structure of
a SC* liquid crystal spontaneously unwinds between polyimide-
coated glass slides with a spacing of 1-5 µm to give a surface-
stabilized ferroelectric liquid crystal (SSFLC) with a net
spontaneous polarization along the polar C2 axis, which is
a function of PS, the orientational viscosity (η), and the applied
4
c
field (E) according to eq 1. Because SC* mesogens with high
PS tend to have high orientational viscosities, commercial SC*
mixtures suitable for SSFLC display applications are normally
3
perpendicular to the glass slides. By applying an electric field
(4) (a) Lagerwall, S. T. In Handbook of Liquid Crystals; Demus, D.,
Goodby, J. W., Gray, G. W., Spiess, H. W., Vill, V., Ed.; Wiley-VCH:
Weinheim, 1998; Vol. 2B. (b) Walba, D. M. Science 1995, 270, 250. (c)
Goodby, J. W.; Blinc, R.; Clark, N. A.; Lagerwall, S. T.; Osipov, M. A.;
Pikin, S. A.; Sakurai, T.; Yoshino, K.; Zeks, B. Ferroelectric Liquid
Crystals: Principles, Properties and Applications; Gordon & Breach:
Philadelphia, 1991. (d) Dijon, J. In Liquid Crystals: Applications and Uses;
Bahadur, B., Ed.; World Scientific: Singapore, 1990; Vol. 1, Chapter 13.
*
To whom correspondence should be addressed. E-mail: lemieux@
chem.queensu.ca.
(
(
1) Kuczynski, W.; Stegemeyer, H. Chem. Phys. Lett. 1980, 70, 123.
2) Meyer, R. B.; Liebert, L.; Strzelecki, L.; Keller, P. J. Phys. (Paris)
Lett. 1975, 36, L69.
3) Clark, N. A.; Lagerwall, S. T. Appl. Phys. Lett. 1980, 36, 899.
(
1
0.1021/ja990965m CCC: $18.00 © 1999 American Chemical Society
Published on Web 08/31/1999

8230 J. Am. Chem. Soc., Vol. 121, No. 36, 1999
Vizitiu et al.
obtained by mixing a chiral dopant with a propensity to induce
high PS into an achiral SC liquid crystal mixture with a low
viscosity and a wide temperature range.
τ ∝ η/P E
(1)
s
S
The spontaneous polarization and tilt angle (θ) of a SC* phase
are related by eq 2 to the reduced polarization (Po), which is
intrinsic to the chiral component of the SC* liquid crystal at a
fixed temperature difference below the SC*-SA* or SC*-N*
1
phase transition (T - TC). The propensity of a chiral dopant to
induce a spontaneous polarization in a SC host can be expressed
as the polarization power (δp) according to eq 3, in which xd is
5
the dopant mole fraction. This relationship is generally found
to be linear when xd < 0.1. It is now well established that the
magnitude and sign of Po in induced SC* liquid crystals depend
on the molecular structure and absolute configuration of the
chiral dopant, respectively.6 More recently, studies have shown
that, for certain types of chiral dopants, the induced polarization
transverse dipole with respect to the polar axis due to so-called
hard core (steric) interactions with the SC host. However, due
to the limited amount of experimental data reported for type II
dopants, it is difficult to fully assess the validity of each model.
To further investigate the host dependence of type II chiral
dopants, and possibly exploit this phenomenon in the formula-
tion of fast-switching FLC mixtures through the design of
dopants with increasingly high polarization power,10 we have
undertaken the study of a new class of axially chiral dopants
with atropisomeric biphenyl cores.
,7
8
can also depend on the nature of the SC host. To rationally
design chiral dopants with high δpsand achieve fast switching
in SSFLC display applicationssa detailed understanding of these
structure-property relationships must be achieved.
P ) P /sin θ
(2)
o
S
dP (x )
o
d
δp )
(3)
(
)
dxd
xdf0
To contribute to PS, a polar functional group must be oriented
with its dipole perpendicular to the molecular long axis of the
dopant, and it must be sterically coupled to an adjacent
asymmetric center (stereopolar coupling). By reducing the
conformational symmetry of the polar functional group, stere-
opolar coupling results in a net orientational bias of the dipole
along the polar axis, thus giving rise to a spontaneous polariza-
tion. The dependence of PS on the conformational asymmetry
of chiral side chains, which comprise the vast majority of
stereopolar units in chiral dopants, has been investigated in a
6
number of different systems and is reasonably well understood.
Stegemeyer has shown that the polarization power of dopants
with chiral side chains (e.g., 1) is generally independent of the
nature of the SC host; these chiral dopants are classified as Type
8
b
I.
Recent studies have shown that the polarization power of
several new dopants with rigid chiral cores (e.g., 2) varies with
the nature of the SC host; these dopants are classified as type
Only a few examples of axially chiral SC* mesogens are
8
II. The dependence of δp on the nature of the SC host has been
11
known; these include allene and alkylidenecyclohexane de-
explained on the basis of two models.8b In the first model,
intermolecular chirality transfer leads to a polar ordering of the
SC host, which results in higher δp values in SC hosts with large
transverse dipole moments. In the second model, which is
rivatives,12 butadiene iron tricarbonyl complexes,13 and atropi-
(10) For examples of chiral dopants with high polarization power, see:
(
a) Ikemoto, T.; Sakashita, K.; Kageyama, Y.; Terada, F.; Nakaoka, Y.;
Ichimura, K.; Mori, K. Chem. Lett. 1992, 567. (b) D u¨ bal, H. R.; Escher,
C.; G u¨ nther, D.; Hemmerling, W.; Inogushi, Y.; M u¨ ller, I.; Murakami, M.;
Ohlendorf, D.; Wingen, R. Jpn. J. Appl. Phys. 1988, 27, L2241. (c) Nishide,
K.; Nakayama, A.; Kusumoto, T.; Hiyama, T.; Takehara, S.; Shoji, T.;
Osawa, M.; Kuriyama, T.; Nakamura, K.; Fujisawa, T. Chem. Lett. 1990,
623. (d) Kusumoto, T.; Sato, K.; Ogino, K.; Hiyama, T.; Takehara, S.;
Osawa, M.; Nakamura, K. Liq. Cryst. 1993, 14, 727. (e) Sakashita, K.;
Ikemoto, T.; Nakaoka, Y.; Terada, F.; Sako, Y.; Kageyama, Y.; Mori, K.
Liq. Cryst. 1993, 13, 71. (f) Kobayashi, S.; Ishibashi, S.; Takahashi, K.;
Tsuru, S.; Yamamoto, F. AdV. Mater. 1993, 5, 167. (g) Ikemoto, T.;
Kageyama, Y.; Onuma, F.; Shibuya, Y.; Ichimura, K.; Sakashita, K.; Mori,
K. Liq. Cryst. 1994, 17, 729.
9
derived from the microscopic model of Zeks, variations in δp
arise from different rotational distributions of the dopant
(
(
5) Siemensmeyer, K.; Stegemeyer, H. Chem. Phys. Lett. 1988, 148, 409.
6) Walba, D. M. In AdVances in the Synthesis and ReactiVity of Solids;
Mallouck, T. E., Ed.; JAI Press: Ltd.: Greenwich, CT, 1991; Vol. 1.
(7) (a) Goodby, J. W.; Chin, E.; Leslie, T. M.; Geary, J. M.; Patel, J. S.
J. Am. Chem. Soc. 1986, 108, 4729. (b) Goodby, J. W.; Chin, E. J. Am.
Chem. Soc. 1986, 108, 4736.
(
8) (a) Osipov, M. A.; Stegemeyer, H.; Sprick, A. Phys. ReV. E 1996,
5
4, 6387. (b) Stegemeyer, H.; Meister, R.; Hoffmann, U.; Sprick, A.; Becker,
A. J. Mater. Chem. 1995, 5, 2183 and references therein. (c) Vizitiu, D.;
Halden, B. J.; Lemieux, R. P. Chem. Commun. 1997, 1123. (d) Yang, K.;
Campbell, B.; Birch, G.; Williams, V. E.; Lemieux, R. P. J. Am. Chem.
Soc. 1996, 118, 9557.
(11) (a) Lunkwitz, R.; Tschierske, C.; Langhoff, A.; Geisselmann, F.;
Zugenmaier, P. J. Mater. Chem. 1997, 7, 1713. (b) Stichler-Bonaparte, J.;
Kruth, H.; Lunkwitz, R.; Tschierske, C. Liebigs Ann. 1996, 1375.
(12) Poths, H.; Schonfeld, A.; Zentel, R.; Kremer, F.; Siemensmeyer,
K. AdV. Mater. 1992, 4, 351.
(9) Urbanc, B.; Zeks, B. Liq. Cryst. 1989, 5, 1075.

Ferroelectric Liquid Crystals
J. Am. Chem. Soc., Vol. 121, No. 36, 1999 8231
Figure 2. Structures representing two conformational minima of
3
2
-methyl-5-nitrophenyl benzoate (X ) NO
2
, Y ) H) and 3,5-dimethyl-
) according to AM1
-nitrophenyl benzoate (X ) Me, Y ) NO
2
calculations.
someric 5,7-dihydro-1,11-dimethyldibenzo[c,e]thiepine deriva-
14
tives. In the first three cases, relatively small PS values ranging
2
from 12 to 38 nC/cm were reported for the neat SC* liquid
crystals; no PS data were reported for the fourth one. Our first
report of ferroelectric induction by an atropisomeric dopant
focused on compound 3, which exhibited a pronounced type II
behavior in the SC hosts PhB and NCB76.8d We proposed that
polar ordering of dopant 3 in the SC lattice originates from a
very small conformational energy bias associated with rotation
of the biphenyl core about the ester C-O bond (Figure 2), which
was estimated by AM1 calculations on the model compound
3
-methyl-5-nitrophenyl benzoate to be 0.4 kcal/mol. We have
extended this conformational analysis to other phenyl benzoate
model compounds and found that shifting the symmetry-
breaking NO2 group to the 2-position raises the conformational
energy bias to 1.2 kcal/mol, as shown in Figure 3. According
to our hypothesis, this should result in a higher polarization
power for the corresponding atropisomeric dopant. To test the
validity of this conformational analysis in predicting relative
δp values in chiral dopants with atropisomeric cores, and to
investigate the origin(s) of the observed type II host dependence,
we have synthesized the atropisomeric dopants 4a-j and 5 and
measured their polarization power in five SC liquid crystal hosts
representing four distinct structural classes of mesogens.
Figure 3. Energy profiles for 3-methyl-5-nitrophenyl benzoate (top)
and 3,5-dimethyl-2-nitrophenyl benzoate (bottom) as a function of the
torsional angle defined by C-6, C-1, O, C(O) and C-2, C-1, O, C(O),
respectively, according to AM1 calculations.
Results and Discussion
Scheme 1a
The atropisomeric dopants 4a-j were obtained by diesteri-
fication of the optically pure dihydroxybiphenyl 8 using the
corresponding 4-alkoxybenzoic acids. The dihydroxybiphenyl
8
was first obtained as a racemic mixture by conversion of the
15
known tetramethylbenzidene 6 to the dihydroxybiphenyl 7 via
the bis-diazonium salt, followed by dinitration under mild
conditions (Scheme 1). Resolution of 8 was achieved by
semipreparative chiral stationary-phase HPLC using a Daicel
Chiralcel OJ column to give both enantiomers in optically pure
form. The unsymmetrical dopant 5 was obtained by mono-
esterification of racemic 8 using 4′-octyloxy-4-biphenylcar-
boxylic acid to give 9, which was resolved by semipreparative
chiral stationary-phase HPLC and esterified using decanoic acid
to give 5 in optically pure form.
a
Key: (a) NaNO
2
, 10% H
2
SO
4
, 5 °C; (b) reflux; (c) Fe(NO
3 3 2
) ‚9H O,
EtOH; (d) chiral stationary-phase HPLC resolution, Daicel Chiralcel
OJ column, 9:1 hexanes/EtOH, 3 mL/min.
<
xd e 0.05 to give an induced SC* liquid crystal phase.16 Each
mixture was introduced into a polyimide-coated ITO glass cell
with a 4 µm gap and aligned by slow cooling from the isotropic
liquid phase to the SC* phase at 5 K below the SC*-SA* phase
transition temperature (T - TC ) -5 K). Spontaneous polariza-
tion and tilt angle values were measured as a function of xd by
the triangular wave method (80-100 Hz, 6V/µm), and Po values
were calculated using eq 2. At least four different samples were
prepared for each dopant-host combination.
The dopants 4a-j were mixed into the SC hosts PhB, NCB76,
DFT, and PhP1 (Figure 4) over the mole fraction range 0.005
(
(
(
13) Jacq, P.; Malthete, J. Liq. Cryst. 1996, 21, 291.
14) Solladi e´ , G.; Hugel e´ , P.; Bartsch, R. J. Org. Chem. 1998, 63, 3895.
15) Carlin, R. B. J. Am. Chem. Soc. 1945, 67, 928.
(16) Doping compounds 3-5 into any of the SC hosts caused the
temperature range of the resulting SC* phase to decrease with increasing
dopant mole fraction, thus limiting the useful range to xd e 0.05.

8232 J. Am. Chem. Soc., Vol. 121, No. 36, 1999
Vizitiu et al.
Table 1. Polarization Power δ
p
of Dopants 3 and 4a-j in the S
C
Hosts PhB, DFT, NCB76, and PhP1 Measured at T - T
δpa,b (nC/cm2)
C
) -5 Κ
dopant
PhB
DFT
NCB76
170 (+)c
PhP1
c,d
63 (+)e
(
(
(
(
(
(
(
(
(
(
(
-)-3 <20 (-)
161 ( 11 (+)
d
d,g
<27 (-)d
-)-4a <30
103 ( 14 (-) <43 (-)
+)-4b <30 (-)d
<30 (+)e
d
183 ( 6 (+)
274 ( 12 (-) 1199 ( 81 (-)
373 ( 54 (+) 1738 ( 95 (+)
505 ( 51 (+)
-)-4c 171 ( 11 (+)
98 (-)
d
124 (+)e
+)-4d <30 (-)
-)-4e <34 (-)d
312 ( 32 (-) 514 ( 38 (-) 1555 ( 119 (-)
+)-4f 250 ( 11 (+) 602 ( 37 (+) 768 ( 23 (+) 1423 ( 149 (+)
-)-4g 496 ( 43 (-) 817 ( 54 (-) 856 ( 73 (-) 1392 ( 140 (-)
+)-4h 449 ( 42 (+) 550 ( 44 (+) 940 ( 71 (+) 1329 ( 60 (+)
+)-4i 506 ( 8 (+)
500 ( 78 (+) 634 ( 70 (+) 998 ( 18 (+)
454 ( 39 (-) 280 ( 26 (-)
-)-4j 388 (-)e
f
a
in parentheses. b Uncertainty is ( standard error
Sign of induced P
S
of least-squares fit. c From ref 8d. Estimated upper limit based on a
detection limit of 0.3 nC/cm at the highest dopant mole fraction.
Values extrapolated from a single P
.04. The temperature range of the S * phase was less than 5 K.
d
2
e
o
measurement at x
C
d
) 0.03-
f
0
g
S
Unable to determine the sign of P .
Figure 4. Structures of liquid crystal hosts and phase transition
temperatures in °C.
Figure 6. Polarization power δ
p
as a function of alkoxy chain length
n for dopants 4a-j in the S hosts PhB (triangles), DFT (squares),
C
NCB76 (circles), and PhP1 (filled circles). Error bars represent (SE.
hosts, except for (-)-4a in DFT and PhP1 and (+)-4b in DFT.
The results in Table 1 show that the sign of PS induced by 4a-j
in the SC hosts DFT, NCB76, and PhP1 correlates with the
relative configuration of the atropisomeric core: all dopants
derived from (+)-8 induced a positive polarization and all those
derived from (-)-8 induced a negative polarization. In PhB,
PS sign inversions were observed for the C4-C8 derivatives (+)-
Figure 5. Reduced polarization P
for the dopant (-)-4e in the S
squares), and PhP1 (circles) at T - T
o
as a function of dopant mole fraction
hosts DFT (triangles), NCB76
) -5 Κ.
4
b,d and (-)-4c.
x
(
d
C
Inspection of the results in Table 1 reveals three important
C
trends. First, the polarization power of the 2,2′-dinitro dopant
(-)-3 is significantly less than that of the corresponding 3,3′-
dinitro dopant (+)-4d in NCB76, DFT, and PhP1, which is
consistent with an increase in the conformational energy bias
for rotation about the ester C-O bond (vide supra). Second,
the polarization power of all dopants strongly depends on the
nature of the SC host, as predicted by Stegemeyer et al., although
Plots of Po vs xd gave good linear fits, as shown in Figure 5
for dopant (-)-4e, from which δp values were obtained
according to eq 3. These results are presented in Table 1, along
with new data for dopant (-)-3 in DFT and PhP1. As
previously observed with dopant (-)-3,8d dopants in series 4
with short to medium chain lengths, except for (-)-4c, produced
no measurable spontaneous polarization in the SC host PhB even
though the characteristic Goldstone-mode switching of a SC*
phase was evident upon applying an AC field across the cell.
Upper limit values for δp were estimated from tilt angle
8
b
on a larger scale than reported heretofore. For example, the
polarization power of (+)-4d in PhP1 is at least 55 times that
estimated for (+)-4d in PhB. Third, the polarization power of
dopants in series 4 varies with the length of the alkoxy chains,
as shown in Figure 6. The highest polarization power was
recorded in the SC host PhP1 for the C8 derivative (+)-4d
measurements at T - TC ) -5 K assuming a detection limit of
2
0
.3 nC/cm at a maximum dopant mole fraction of 0.05.
2
Measurable spontaneous polarizations were obtained in PhB
for dopants with chain lengths C12 and longer. All dopants gave
a measurable spontaneous polarization in the other three SC
(+1738 nC/cm ), which is one of the highest δp values reported
1
0
thus far in the literature for a chiral dopant. A plot of PS vs
temperature for a 2 mol % mixture of (+)-4d in PhP1 (Figure

Ferroelectric Liquid Crystals
J. Am. Chem. Soc., Vol. 121, No. 36, 1999 8233
Figure 8. Schematic view of the chiral core along the molecular long
axis: ψ
o
⊥
is the angle between the transverse dipole µ and the molecular
reference axis m, and ψ is the angle between m and the polar axis y.
The tilt plane is in the xz plane.
S
Figure 7. Spontaneous polarization P as a function of temperature
for a 2 mol % mixture of (+)-4d in PhP1.
7
) shows a supercooling of the induced SC* phase to 40 °C
Figure 9. Model for intercore chirality transfer between the atropi-
someric dopant and the S host PhP1.
C
(pure PhP1 crystallizes at 58 °C) and gives a maximum
2
spontaneous polarization PS(max) of +18 nC/cm , which
corresponds to an extrapolated PS(max) value for dopant (+)-
However, simple calculations17 show that the rotational
distribution model alone cannot account for the wide variations
in δp values reported in Table 1, especially the high δp values
obtained in PhP1. For example, assuming µ⊥ to be coincident
with the molecular reference axis (cos ψo ) 1), this model
predicts a polar order parameter 〈cos ψ〉 of 0.58 for dopant (+)-
4d in PhP1 at T - TC ) -40 Κ, which is remarkably large
considering the relatively small degree of conformational
asymmetry expected for such a dopant in the SC lattice (vide
2
4
d of +900 nC/cm .
To explain these results, we consider the models proposed
8b
for the molecular origins of Type II behavior. In a general
sense, the polarization power of Type II dopants is thought to
be strongly influenced by interactions between the chiral core
of the dopant and the achiral cores of the surrounding host
molecules. This is reasonable since the core region of a smectic
liquid crystal phase is more highly ordered than the tail regions,
and intermolecular interactions in the former are expected to
affect macroscopic bulk properties to a much greater extent than
intermolecular interactions in the latter. Such intercore interac-
tions may or may not result in substantial chirality transfer
depending on the complementarity of the core structures. An
extension of Zeks’ microscopic model9 suggests that the
spontaneous polarization induced by a type II chiral dopant is
influenced by steric interactions with the surrounding SC host
molecules that affect the orientation of the core transverse dipole
with respect to the polar axis (rotational distribution). The
spontaneous polarization is expressed as a function of the core
transverse dipole moment µ⊥ by eq 4:
1
8
supra). In this case, it is likely that dopant-host interactions
do more than simply influence the rotational distribution of the
core transverse dipole; such interactions may also amplify the
conformational asymmetry of the chiral dopants via chirality
transfer.
Semiempirical calculations suggest that the core structures
of all four SC hosts adopt twisted chiral conformations that
should be in rapid equilibrium with their enantiomeric mirror
1
9
images at ambient temperature. Interactions with a dopant
chiral core favoring one handedness can shift such conforma-
tional equilibrium toward one of the two enantiomeric states
and result, in some cases, in a nonlinear amplification of chiral
2
0
bulk properties. As shown in Figure 9, conformational
interactions between the atropisomeric core of an orientationally
ordered dopant such as 4 and the cores of neighboring SC host
molecules should result in an effective transfer of molecular
chirality to favor, or induce, one twisted conformation of the
P ) N µ cos ψ 〈cos ψ〉
(4)
S
1
⊥
o
where N1 is the dopant number density, ψo is the angle between
µ⊥ and a reference axis m defined by the shape of the chiral
core, and 〈cos ψ〉 is a polar order parameter ranging from 0 to
2
1
SC host. In principle, this intercore chirality transfer could
amplify the induced spontaneous polarization by (i) inducing a
1
that is related to the conformational asymmetry of the chiral
8
b
8b
polar ordering of the SC host transverse dipole, and/or (ii)
core about the molecular long axis (Figure 8). According to
this model, the relatively small δp values obtained in PhB could
be due to a rotational distribution that brings the transverse
dipole of the chiral core near the tilt plane. In such a situation,
small changes in 〈cos ψ〉 could change the sign of PS by rotating
the vector µ⊥ through the tilt plane. This would be consistent
with the fact that dopant (-)-3 and some of the shorter chain
dopants in series 4 show a sign inversion in PS going from PhB
to the other three SC hosts (see Table 1). Conversely, the higher
δp values obtained in DFT, NCB76, and PhP1 and the lack of
PS sign inversion in these SC hosts could be explained by a
shift in rotational distribution that brings the core transverse
dipole closer to the C2 polar axis.
(17) Dunmur, D. A.; Grayson, M.; Roy, S. K. Liq. Cryst. 1994, 16, 95.
(18) The polar order parameter 〈cos ψ〉 was calculated using eq 4. A µ⊥
value of 2.49D was obtained by ab initio calculation at the HF/3-21G*
level on the AM1-minimized model system 4,4′-dibenzoyl-2,2′,6,6′-
tetramethyl-3,3′-dinitrobiphenyl in its lowest energy conformation. The
dopant number density N of a 2 mol % mixture of (+)-4d in PhP1 was
1
estimated as 2% of the molecular number density of PhP1. The density of
3
PhP1 was assumed to be 1.1 g/cm .
(19) Low-level ab initio calculations at the STO-3G level suggest that
the global minimum of 2-phenylpyrimidine, which forms the core structure
of PhP1, adopts a planar conformation in the gas phase: Barone, V.;
Commisso, L.; Lelj, F.; Russo, N. Tetrahedron 1985, 41, 1915.
(20) Green, M. M.; Zanella, S.; Gu, H.; Sato, T.; Gottarelli, G.; Jha, S.
K.; Spada, G. P.; Schoevaars, A. M.; Feringa, B.; Teramoto, A. J. Am.
Chem. Soc. 1998, 120, 9810.

8234 J. Am. Chem. Soc., Vol. 121, No. 36, 1999
Vizitiu et al.
Table 2. Polarization Power δ
p
of Dopant (-)-4e at T - T
C
) -5
Κ and Helical Pitch of the Induced S
C
* Phase in the Liquid Crystal
Hosts PhB, DFT, NCB76, and PhP1 and a 1:1 PhP1/PhP2
Mixture
a
(nC/cm2)
pitchb,c (µm)
d
S
C
Host
δ
p
⊥
µ (D)
PhB
DFT
NCB76
PhP1
<34e
4.3 ( 0.2
7.4 ( 0.6
5.9 ( 0.6
2.9 ( 0.3
1.5 ( 0.1
2.4
3.2
3.8
0.92
2.9
312 ( 32
514 ( 38
1555 ( 119
1063 ( 76
1
:1 PhP1/PhP2
a
b
Uncertainty is ( standard error of least-squares fit. Measured at
c
a dopant mole fraction x
d
) 0.02. Uncertainty is ( one standard
deviation. Transverse dipole moment of the S host calculated at the
HF/3-21G* level. Estimated upper limit based on a detection limit of
d
C
e
2
0
.3 nC/cm at the highest dopant mole fraction.
inducing an asymmetric distortion of the SC lattice that would
increase the conformational asymmetry of the atropisomeric core
by a feedback mechanism.
Figure 10. Polarization power δ
p
(filled circles) and S
C
* helical pitch
(
circles) as a function of alkoxy chain length n for dopants 4a-i in the
host PhP1. Error bars represent (SE (δ ) and (one standard
deviation (pitch).
S
C
p
An induced polar ordering of the SC host can be ruled out as
the main cause of polarization amplification by comparing δp
values with transverse dipole moments (µ⊥ ) of the corresponding
SC host core structures. The latter values were obtained by single
point ab initio calculations at the HF/3-21G* level using
structures minimized at the semiempirical AM1 level and are
Another way to assess the importance of intercore chirality
transfer is to study the effect of varying the length of the dopant
side chains on the polarization power. As shown in Figure 6,
the polarization power of dopant 4 increases with increasing
alkoxy chain length n in all four SC hosts, reaching a maximum
at a value n(max) that varies with the SC host. The subsequent
decrease in δp with a further increase in n has been observed
before with some type I dopants but remains largely unex-
22
listed in Table 2. The results show that there is no correlation
between the polarization power and the host transverse dipole
moment: the highest δp values are obtained in the SC host with
the smallest transverse dipole moment, PhP1, which is incon-
sistent with polar ordering of the SC host. The polarization power
of (-)-4e was also measured in a 1:1 mixture of PhP1 and the
difluoro derivative PhP2, which has a transverse dipole moment
of 5.03 D in its lowest energy conformation. In the 1:1 mixture,
24
plained. The increase in δp with increasing chain length is
consistent with an increase in positional/orientational ordering
of the atropisomeric core in the SC lattice, which should improve
intercore chirality transfer as well as increase the contribution
of the ester asymmetric conformational mode toward polar
2
the dopant (-)-4e gave a polarization power of -1063 nC/cm ,
23
which is about 30% less than that obtained in pure PhP1. This
is also inconsistent with polar ordering of the SC host and
suggests that polarization amplification in PhP1 may be due in
large part to an increase in conformational asymmetry of the
dopant as a result of intercore chirality transfer.
25
ordering by anchoring the side chains in the transoid SC lattice.
The variation in n(max) as a function of the SC host may be
related to differences in the SC layer spacing and/or differences
in the length of the SC host core structure. Measurements of
SC* helical pitch were also carried out for 2 mol % mixtures of
To assess the importance of intercore chirality transfer in
polarization amplification, the polarization power of the unsym-
metrical dopant (-)-5 was measured in the SC host PhP1.
Although (-)-5 has the same length as the symmetrical dopant
4
a-i in PhP1. As shown in Figure 10, the SC* helical pitch
follows a trend that is opposite to that followed by δp as a
function of n, except at very long chain lengths. This observation
further supports the claim that polarization amplification in PhP1
is strongly linked to intercore chirality transfer.
(+)-4d, the position of its atropisomeric core should be offset
with respect to the core region of the SC layer on the time
average. As a result of this positional shift, and the expected
reduction in chiral conformational interactions between the core
of the dopant and those of the surrounding host molecules, the
polarization power of (-)-5 should be lower than that of the
symmetrical dopant (+)-4d. Indeed, the polarization power of
However, when the SC* helical pitch is measured as a function
of the SC host (Table 2), we find that there is essentially no
correlation between the SC* pitch and δp. Given these and other
experimental results presented herein, we conclude that one
cannot rationalize the variations in polarization power as a
function of the SC host on the basis of a single microscopic
model. Indeed, the two models described above are not mutually
exclusive, and it is likely that differences in δp values for an
atropisomeric dopant in any two SC hosts can be explained by
variations in both the rotational distribution of the transverse
dipole and intercore chirality transfer. Nevertheless, the results
obtained in PhP1 may be singled out as a unique case in which
intercore chirality transfer plays a key role in amplifying the
induced spontaneous polarization. We propose that polarization
amplification takes place via a feedback mechanism in which
intercore chirality transfer results in an asymmetric distortion
(
-)-5 proved to be ca. 35% less than that obtained for (+)-4d:
2
2
-
1101 nC/cm vs +1738 nC/cm , respectively. Furthermore, a
comparison of SC* helical pitch values for 2 mol % mixtures
in PhP1 showed that (+)-4d induces a tighter helical pitch than
(
-)-5, which is also consistent with a decrease in dopant-host
chirality transfer: 1.5 ( 0.3 µm vs 2.4 ( 0.5 µm, respectively.
(21) A similar mechanism of chiral induction was proposed for cholesteric
phases induced by atropisomeric biaryl dopants in order to account for the
correlation found between helical twist sense of the cholesteric phase and
that of the dopant: Gottarelli, G.; Hibert, M.; Samori, B.; Solladi e´ , G.;
Spada, G. P.; Zimmermann, R. J. Am. Chem. Soc. 1983, 105, 7318.
(22) A plot of experimental dipole moments vs dipole moments calculated
at the HF/3-21G* level for a series of monosubstituted benzenes gave an
(24) Loseva, M.; Chernova, N.; Rabinovitch, A.; Poshidaev, E.; Narkevitch,
J.; Petrashevitch, O.; Kazachkov, E.; Korotkova, N.; Schadt, M.; Bucheker,
R. Ferroelectrics 1991, 114, 357.
2
excellent linear correlation (R ) 0.994).
(23) The decrease in δp may be ascribed to a difference in polarizability
anisotropy of the phenylpyrimidine cores that should, in principle, affect
the strength of dopant/host chiral conformational interactions. A systematic
investigation of this relationship is underway, and results will be published
elsewhere.
(25) A similar effect was reported for a more conventional type I dopant
and accounted for by considering the “rotational damping” of the stereo-
polar unit with increasing chain length: Goodby, J. W.; Patel, J. S.; Chin,
E. J. Phys. Chem. 1987, 91, 5151.

Ferroelectric Liquid Crystals
J. Am. Chem. Soc., Vol. 121, No. 36, 1999 8235
of the SC* lattice that, in turn, further increases the conforma-
tional asymmetry of the atropisomeric dopant by virtue of
increased diastereomeric bias between the SC* lattice and the
chiral conformations of the dopant. Further studies aimed at
providing additional experimental and theoretical support for
this hypothesis are in progress.
332.1008, found 332.1015. The second eluant was collected and
concentrated to give (+)-8 in optical purity of 96% ee.
General Procedure for the Preparation of Dopants 4a-i. The
procedure described for the preparation of (-)-2,2′,6,6′-tetramethyl-
3
,3′-dinitro-4,4′-bis[(4-nonyloxybenzoyl)oxy]biphenyl ((-)-4e) is rep-
resentative. Dopants (-)-4a,c,e,g were derived from (-)-8; dopants
(+)-4b,d,f,h,i were derived from (+)-8.
Under an Ar atmosphere, solid DCC (35 mg, 0.17 mmol) was added
Experimental Section
to a stirred solution of (-)-8 (26 mg, 0.08 mmol), 4-nonyloxybenzoic
acid (45 mg, 0.17 mmol) and DMAP (21 mg, 0.17 mmol) in dry CH Cl
General Methods. 1H and 13C NMR spectra were recorded on
2
2
Bruker ACF-200 and AM-400 NMR spectrometers in deuterated
chloroform (CDCl ) and deuterated dimethyl sulfoxide (DMSO-d ). The
3 6
(5 mL). The mixture was stirred at room temperature for 24 h and
then filtered and concentrated. The solid residue was redissolved in
EtOAc, washed with 2 M aqueous HCl, H O, and brine, dried (MgSO ),
2 4
and concentrated. Purification by flash chromatography on silica gel
(7:3 hexanes/EtOAc) gave 56 mg (88%) of (-)-4e as a white solid.
Prior to doping into liquid crystal hosts, the compound was recrystal-
chemical shifts are reported in δ (ppm) relative to tetramethylsilane as
internal standard. Low-resolution EI mass spectra were recorded on a
Fisons VG Quattro triple quadrupole mass spectrometer; peaks are
reported as m/z (percent intensity relative to the base peak). High-
resolution EI mass spectra were performed by the University of Ottawa
Regional Mass Spectrometry Center. Optical rotations were measured
on a Perkin-Elmer 241 polarimeter at room temperature. Semiprepara-
tive chiral stationary-phase HPLC separations were performed using a
lized from hexanes after filtration through a 0.45 µm PTFE filter: mp
1
116-118 °C; [R]
D
-7.32 (c 1.1, CHCl
3
); H NMR (400 MHz, CDCl
3
)
δ 0.89 (t, J ) 7.0 Hz, 6H), 1.30-1.54 (m, 24H), 1.76-1.89 (m, 4H),
1.99 (s, 6H), 2.03 (s, 6H), 4.05 (t, J ) 6.5 Hz, 4H), 6.97 (d, J ) 8.9
Hz, 4H), 7.34 (s, 2H), 8.08 (d, J ) 8.9 Hz, 4H); 13C NMR (100 MHz,
CDCl ) δ 14.1, 15.1, 20.4, 22.7, 26.0, 29.1, 29.3, 29.4, 29.5, 31.9, 68.4,
3
114.6, 120.0, 123.6, 129.7, 132.7, 136.2, 140.0, 142.0, 143.4, 163.6,
164.1.
2
5 cm × 10 mm i.d. Daicel Chiralcel OJ column. Elemental analyses
were performed by Guelph Chemical Laboratories Ltd (Guelph,
Ontario) and by MHW Laboratories (Phoenix, AZ). Melting points were
measured on a Mel-Temp II melting point apparatus and are uncor-
rected.
Anal. Calcd for C48
60 2
H N O10: C, 69.88; H, 7.33; N, 3.40. Found:
Materials. All reagents, chemicals, and liquid crystal hosts were
obtained from commercial sources and used without further purification
C, 69.69; H, 7.13; N, 3.17.
(-)-4,4′-Bis[(4-methoxybenzoyl)oxy]-2,2′,6,6′-tetramethyl-3,3′-
1
unless otherwise noted. Methylene chloride (CH
under N . Tetrahydrofuran (THF) was distilled from sodium/
benzophenone under N . (-)-2,2′-Dimethyl-6,6′-dinitro-4,4′-bis[(4-
octyloxybenzoyl)oxy]biphenyl ((-)-3), 4,4′-diamino-2,2′,6,6′-tetra-
2 2
Cl ) was distilled from
dinitrobiphenyl ((-)-4a): white solid (80%); mp 185-186 °C; H
P
2
O
5
2
3
NMR (400 MHz, CDCl ) δ 1.99 (s, 6H), 2.03 (s, 6H), 3.90 (s, 6H),
1
3
7.00 (d, J ) 8.8 Hz, 4H), 7.34 (s, 2H), 8.10 (d, J ) 8.8 Hz, 4H);
C
2
8
d
NMR (100 MHz, CDCl ) δ 15.1, 20.4, 55.6, 114.1, 120.3, 123.5, 129.7,
3
1
5
methylbiphenyl (6), (()-4-[(4-methylhexyl)oxy]phenyl 4-decyloxy-
27
132.7, 136.2, 140.0, 141.9, 143.4, 163.5, 164.4.
26
benzoate (PhB), 2′,3′-difluoro-4-heptyl-4′′-nonyl-p-terphenyl (DFT),
(+)-4,4′-Bis[(4-butyloxybenzoyl)oxy]-2,2′,6,6′-tetramethyl-3,3′-
28
1
and 4-octyloxy-4′-biphenylcarboxylic acid were synthesized according
to published procedures and shown to have the expected physical and
spectral properties. The liquid crystal host NCB76 was provided by
Prof. H. Stegemeyer.
dinitrobiphenyl ((+)-4b): white needles (40%); mp 155-157 °C; H
NMR (400 MHz, CDCl ) δ 1.00 (t, J ) 7.4 Hz, 6H), 1.46-1.61 (m,
3
4H), 1.74-1.89 (m, 4H), 1.99 (s, 6H), 2.03 (s, 6H), 4.06 (t, J ) 6.5
Hz, 4H), 6.98 (d, J ) 8.8 Hz, 4H), 7.34 (s, 2H), 8.08 (d, J ) 8.8 Hz,
4H); 13C NMR (100 MHz, CDCl
) δ 13.8, 15.1, 19.2, 20.4, 31.1, 68.1,
4
,4′-Dihydroxy-2,2′,6,6′-tetramethylbiphenyl (7). A solution of
NaNO (0.27 g, 4.0 mmol) in H O (2 mL) was added dropwise to a
solution of 6 (0.48 g, 2.0 mmol) in 10% aqueous H SO (10 mL) cooled
3
114.5, 119.9, 123.5, 129.7, 132.7, 136.1, 140.0, 141.9, 143.4, 163.6,
164.1.
2
2
2
4
to 5 °C. The mixture was stirred at 5 °C for 30 min, then refluxed with
stirring overnight. After cooling, the mixture was extracted with EtOAc
(-)-4,4′-Bis[(4-hexyloxybenzoyl)oxy]-2,2′,6,6′-tetramethyl-3,3′-
1
dinitrobiphenyl ((-)-4c): white needles (71%); mp 120-122 °C; H
(
2 × 20 mL), and the combined extracts were washed with H
brine, dried (MgSO ), and concentrated. The solid residue was purified
by sublimation (0.06 Torr, 125 °C) to give 0.20 g (41%) of 7 as a
2
O and
3
NMR (400 MHz, CDCl ) δ 0.92 (t, J ) 6.8 Hz, 6H), 1.34-1.50 (m,
4
12H), 1.75-1.89 (m, 4H), 4.05 (t, J ) 6.5 Hz, 4H), 6.98 (d, J ) 8.8
Hz, 4H),7.34 (s, 2H), 8.08 (d, J ) 8.8 Hz, 4H); 13C NMR (100 MHz,
2
9
1
white solid: mp 172-174 °C (lit. mp 183 °C); H NMR (200 MHz,
DMSO-d
3
CDCl ) δ 14.0, 15.1, 20.4, 22.6, 25.6, 29.0, 31.5, 68.4, 114.5, 119.9,
123.5, 129.7, 132.6, 136.1, 140.0, 141.9, 143.3, 163.6, 164.1.
1
3
6
) δ 1.73 (s, 12H), 6.52 (s, 4H), 9.05 (s, 2H); C NMR (50
MHz, DMSO-d
6
) δ 19.7, 114.2, 130.1, 136.4, 155.5; MS (EI) m/z 242
(+)-2,2′,6,6′-Tetramethyl-3,3′-dinitro-4,4′-bis[(4-octyloxybenzoyl)-
+
1
(M , 100), 227 (64), 212 (74) 105 (28); HRMS (EI) calcd for C16
H O
18 2
oxy]biphenyl ((+)-4d): white needles (44%); mp 112-114 °C; H
2
42.1307, found 242.1302.
-)- and (+)-4,4′-Dihydroxy-2,2′,6,6′-tetramethyl-3,3′-dinitrobi-
phenyl ((-)-8 and (+)-8). A mixture of 6 (2.16 g, 8.95 mmol) and
Fe(NO ‚9H O (2.53 g, 6.26 mmol) in absolute EtOH (60 mL) was
3
NMR (400 MHz, CDCl ) δ 0.90 (t, J ) 6.7 Hz, 6H), 1.30-1.55 (m,
(
20H), 1.76-1.89 (m, 4H), 1.99 (s, 6H), 2.03 (s, 6H),4.05 (t, J ) 6.5
Hz, 4H), 6.97 (d, J ) 8.8 Hz, 4H), 7.34 (s, 2H), 8.08 (d, J ) 8.8 Hz,
4H); 13C NMR (100 MHz, CDCl
3
)
3
2
3
) δ 14.1, 15.1, 20.4, 22.6, 26.0, 29.0,
refluxed with stirring overnight. After cooling, the mixture was
concentrated to a solid residue that was dissolved in EtOAc (20 mL),
29.2, 29.3, 31.8, 68.4, 114.5, 120.0, 123.5, 129.7, 132.7, 136.1, 140.0,
142.0, 143.4, 163.6, 164.1.
washed with 2 M aqueous HCl, water, and brine, dried (MgSO
concentrated. Purification by flash chromatography on silica gel (CHCl
gave 1.39 g (47%) of (()-8 as a bright yellow solid. After recrystal-
lization from 10% CHCl /hexanes, the product was resolved by
semipreparative chiral stationary-phase HPLC (9:1 hexanes/EtOH, 3
mL/min). The first eluant was collected and concentrated to give (-)-8
4
), and
(+)-4,4′-Bis[(4-dodecyloxybenzoyl)oxy]-2,2′,6,6′-tetramethyl-3,3′-
1
3
)
dinitrobiphenyl ((+)-4f): white solid (71%); mp 92-94 °C; H NMR
(400 MHz, CDCl ) δ 0.89 (t, J ) 6.7 Hz, 6H), 1.27-1.50 (m, 36H),
3
3
1.75-1.89 (m, 4H), 1.99 (s, 6H), 2.03 (s, 6H), 4.05 (t, J ) 6.5 Hz,
4H), 6.97 (d, J ) 8.8 Hz, 4H), 7.34 (s, 2H), 8.08 (d, J ) 8.8 Hz, 4H);
13
3
C NMR (100 MHz, CDCl ) δ 14.1, 15.1, 20.4, 22.7, 26.0, 29.0, 29.4,
29.55, 29.58, 29.64, 31.9, 68.4, 114.5, 119.9, 123.6, 129.7, 132.7, 136.1,
140.0, 141.9, 143.4, 163.6, 164.1.
in optically pure form: mp 128-130 °C; [R]
D
-99.4 (c 1.1, CHCl
) δ 1.89 (s, 6H) 2.16 (s, 6H), 7.01 (s, 2H),
0.04 (s, 2H); C NMR (100 MHz, CDCl ) δ 18.0, 21.0, 118.6, 132.1,
34.2, 134.8, 145.7, 153.9; MS (EI) m/z 332 (M+, 100), 315 (87), 165
3
);
1
H NMR (400 MHz, CDCl
3
13
1
1
3
(-)-2,2′,6,6′-Tetramethyl-3,3′-dinitro-4,4′-bis[(4-tetradecyloxy-
benzoyl)oxy]biphenyl ((-)-4g): white solid (52%); mp 94-96 °C;
1
(67), 152 (65), 128 (75), 115 (88); HRMS (EI) calcd for C16
H
16
N
2
O
6
3
H NMR (400 MHz, CDCl ) δ 0.88 (t, J ) 6.7 Hz, 6H), 1.26-1.49
(
6
m, 44H), 1.78-1.89 (m, 4H), 1.99 (s, 6H), 2.03 (s, 6H), 4.05 (t, J )
(
(
26) Keller, P. Ferroelectrics 1984, 58, 3.
27) Gray, G. W.; Hird, M.; Lacey, D.; Toyne, K. J. J. Chem. Soc., Perkin
.5 Hz, 4H), 6.99 (d, J ) 8.9 Hz, 4H), 7.34 (s, 2H), 8.10 (d, J ) 8.9
13
Hz, 4H); C NMR (100 MHz, CDCl ) δ 14.1, 15.1, 20.4, 22.7, 26.0,
3
Trans. 2 1989, 2041.
(
(
28) Gray, G. W.; Hartley, J. B.; Jones, B. J. Chem. Soc. 1955, 1412.
29) Nomura, Y.; Takeuchi, Y. J. Chem. Soc. B 1970, 956.
29.0, 29.4, 29.55, 29.59, 29.66, 31.9, 68.4, 114.5, 119.9, 123.6, 129.7,
132.7, 136.1, 140.0, 141.9, 143.4, 163.6, 164.1.

8236 J. Am. Chem. Soc., Vol. 121, No. 36, 1999
Vizitiu et al.
(
+)-4,4′-Bis[(4-hexadecyloxybenzoyl)oxy]-2,2′,6,6′-tetramethyl-
EtOAc (20 mL), washed with 2 M aqueous HCl, H
(MgSO
silica gel (7:3 hexanes/EtOAc) gave 13 mg (99%) of (-)-5 as a light
2
O, and brine, dried
4
), and concentrated. Purification by flash chromatography on
1
3
,3′-dinitrobiphenyl ((+)-4h): white solid (14%); mp 88-90 °C; H
NMR (400 MHz, CDCl ) δ 0.88 (t, J ) 6.7 Hz, 6H), 1.26-1.50 (m,
2H), 1.78-1.89 (m, 4H), 1.99 (s, 6H), 2.03 (s, 6H), 4.05 (t, J ) 6.5
Hz, 4H), 6.97 (d, J ) 8.8 Hz, 4H), 7.34 (s, 2H), 8.08 (d, J ) 8.8 Hz,
H); C NMR (100 MHz, CDCl
9.4, 29.57, 29.60, 29.66, 31.9, 68.4, 114.5, 119.9, 123.6, 129.7, 132.7,
3
1
5
brown solid: mp 81-82 °C; [R]
D
3
-11.0 (c 0.3, CHCl ); H NMR (400
MHz, CDCl ) δ 0.86-0.91 (m, 6H), 1.25-1.48 (m, 22H), 1.72-1.84
3
1
3
4
2
1
3
) δ 14.1, 15.1, 20.4, 22.7, 26.0, 29.1,
(m, 4H), 1.97 (s, 6H), 2.01 (s, 6H), 2.57 (t, J ) 7.5 Hz, 2H), 4.02 (t,
J ) 6.6 Hz, 2H), 7.00 (d, J ) 8.7 Hz, 2H), 7.15 (s, 1H), 7.35 (s, 1H),
7.59 (d, J ) 8.7 Hz, 2H), 7.70 (d, J ) 8.4 Hz, 2H), 8.17 (d, J ) 8.4
36.1, 140.0, 141.9, 143.4, 163.6, 164.1.
(
+)-4,4′-Bis[(4-octadecyloxybenzoyl)oxy]-2,2′,6,6′-tetramethyl-
Hz, 2H); 13C NMR (100 MHz, CDCl
3
) δ 14.1, 15.2, 20.4, 20.4, 22.7,
1
3
,3′-dinitrobiphenyl ((+)-4i): white solid (65%): mp 90-92 °C; H
) δ 0.88 (t, J ) 6.7 Hz, 6H), 1.26-1.50 (m,
0H), 1.78-1.89 (m, 4H), 1.99 (s, 6H), 2.03 (s, 6H), 4.05 (t, J ) 6.5
Hz, 4H), 6.97 (d, J ) 8.8 Hz, 4H), 7.34 (s, 2H), 8.08 (d, J ) 8.8 Hz,
24.2, 24.6, 26.0, 28.8, 29.0, 29.2, 29.2, 29.4, 29.4, 31.8, 31.9, 34.0,
35.3, 68.2, 115.0, 123.5, 123.5, 125.9, 126.8, 128.4, 129.8, 131.0, 131.7,
136.3, 140.1, 141.7, 141.9, 143.3, 146.7, 159.7, 163.8, 171.1.
NMR (400 MHz, CDCl
3
6
Anal. Calcd for C47
58 2 9
H N O : C, 71.01; H, 7.35; N, 3.52. Found:
1
3
4
2
1
3
H); C NMR (100 MHz, CDCl ) δ 14.1, 15.1, 20.4, 22.7, 26.0, 29.1,
9.4, 29.57, 29.60, 29.66, 31.9, 68.4, 114.5, 119.9, 123.6, 129.7, 132.7,
36.1, 140.0, 141.9, 143.4, 163.6, 164.1.
C, 71.14; H, 7.12; N, 3.37.
Ferroelectric Measurements. Texture analyses and transition
temperature measurements for the doped liquid crystal mixtures were
carried out using a Nikon Labophot-2 polarizing microscope fitted with
(
-)-4,4′-Bis[(4-eicosanoyloxybenzoyl)oxy]-2,2′,6,6′-tetramethyl-
3
(
,3′-dinitrobiphenyl ((-)-4j). Under an Ar atmosphere, thionyl chloride
1.0 mL, 13 mmol) was added dropwise to a mixture of 4-eicosanoyl-
a Instec HS1-i hot stage. Spontaneous polarization (P
measured as a function of temperature by the triangular wave method
S
) values were
30
oxybenzoic acid (20 mg, 0.048 mmol) and dry benzene (2 mL) at room
temperature. After the mixture was refluxed for 2 h, it was concentrated
to give the 4-eicosanoyloxybenzoyl chloride as a colorless oil. Under
an Ar atmosphere, a solution of (-)-8 (7 mg, 0.022 mmol) and DMAP
(6 V/µm, 80-100 Hz) using a Displaytech APT-III polarization testbed
in conjunction with the Instec hot stage. For each data point taken, the
temperature of the sample was allowed to fully equilibrate in order to
rule out any temperature effect during measurement. Polyimide-coated
2
(
6 mg, 0.049 mmol) in dry THF (5 mL) was added to the acid chloride.
The mixture was stirred at room temperature overnight, diluted with
EtOAc (20 mL), washed with 2 M aqueous HCl, H O, and brine, dried
MgSO ), and concentrated. Purification by flash chromatography on
ITO glass cells (4 µm × 0.25 cm ) supplied by Displaytech Inc.
(Longmont, CO) were used for all the measurements. Good alignment
was obtained by slow cooling of the filled cells from the isotropic phase
2
(
4
A
via the N* and S * phases. Tilt angles (θ) were measured as a function
of temperature between crossed polarizers as half the rotation between
two extinction positions corresponding to opposite polarization orienta-
silica gel (7:3 hexanes/EtOAc) gave 12 mg (49%) of (-)-4j as a white
solid. Prior to doping into liquid crystal hosts, the compound was
recrystallized from absolute EtOH after filtration through a 0.45 µm
S
tions. The sign of P along the polar axis was assigned from the relative
1
PTFE filter: mp 77-80 °C; H NMR (400 MHz, CDCl
3
) δ 0.88 (t, J
configuration of the electrical field and the switching position of the
sample according to the established convention.6
)
6.7 Hz, 6H), 1.26-1.50 (m, 68H), 1.78-1.89 (m, 4H), 1.99 (s, 6H),
2
.03 (s, 6H), 4.05 (t, J ) 6.5 Hz, 4H), 6.97 (d, J ) 8.9 Hz, 4H), 7.33
S * Helical Pitch Measurements. Measurements of S * helical
C
C
1
3
(s, 2H), 8.08 (d, J ) 8.9 Hz, 4H); C NMR (100 MHz, CDCl
3
) δ
pitch were carried out at T - T ) -10 Κ on a 150 µm film of the
C
1
1
1
4.1, 15.1, 20.4, 22.7, 26.0, 29.1, 29.4, 29.57, 29.61, 29.69, 31.9, 68.4,
liquid crystal material in a planar alignment using a Nikon Labophot-2
polarizing microscope fitted with a Instec HS1-i hot stage. The helical
pitch was measured as the distance between dark fringes caused by
14.5, 119.9, 123.6, 129.7, 132.7, 136.1, 140.0, 141.9, 143.4, 163.6,
64.1.
31
4
-Hydroxy-2,2′,6,6′-tetramethyl-4′-[(4-(4-octyloxyphenyl)benzoyl)-
oxy]-3,3′-dinitrobiphenyl (9). Under an Ar atmosphere, solid DCC
15 mg, 0.07 mmol) was added to a stirred solution of (()-8 (25 mg,
.07 mmol), 4-octyloxy-4′-biphenylcarboxylic acid (24 mg, 0.07 mmol),
and DMAP (9 mg, 0.07 mmol) in dry CH Cl (5 mL). The mixture
C
the periodicity of the S * helix.
Calculations. All semiempirical calculations at the AM1 level were
3
2
(
0
carried out using the Spartan 4.0 molecular modeling program.
Rotational energy profiles of the ester linking groups in the model
systems 3-methyl-5-nitrophenyl benzoate and 3,5-dimethyl-2-nitrophen-
yl benzoate were obtained by constraining the torsional angle defined
by C-6, C-1, O, and C(O) and by C-2, C-1, O, and C(O), respectively,
and performing a full geometry optimization on the rest of the molecule.
All minima were determined by full geometry optimization and
confirmed as minima by vibrational analysis. Ab initio calculations of
transverse dipole moments were carried out as single-point calculations
on AM1-minimized structures with the HF/3-21G* basis set imple-
2
2
was stirred at room temperature for 24 h, filtered, and concentrated.
The solid residue was redissolved in EtOAc, washed with 2 M aqueous
HCl, H O, and brine, dried (MgSO ), and concentrated. Purification
2 4
by flash chromatography on silica gel (4:1 hexanes/EtOAc) gave 15
mg (32%) of racemic 9 as a white solid. The product was resolved by
chiral stationary-phase HPLC (60:40 hexanes/EtOH, 4 mL/min); the
first eluant was collected and concentrated to give 9 in optically pure
1
33
form: mp 115-116 °C; H NMR (400 MHz, CDCl
3
) δ 0.89 (t, J )
mented in Gaussian 94. The calculations were performed on a RISC-
6
1
.8 Hz, 3H), 1.30-1.49 (m, 10H), 1.79-1.84 (m, 2H), 1.95 (s, 3H),
.96 (s, 3H), 2.00 (s, 3H), 2.21 (s, 3H), 4.02 (t, J ) 6.6 Hz, 2H), 7.00
based IBM SP2 parallel processing computer.
(
d, J ) 8.8 Hz, 2H), 7.04 (s, 1H), 7.34 (s, 1H), 7.59 (d, J ) 8.8 Hz,
H), 7.70 (d, J ) 8.6 Hz, 2H), 8.17 (d, J ) 8.6 Hz, 2H), 10.05 (s, 1H);
3
Acknowledgment. We are grateful to the Natural Sciences
and Engineering Research Council of Canada for support of
this work. We also thank Profs. Mark Green, Mikhail Osipov,
and David Walba for useful discussions.
2
1
C NMR (100 MHz, CDCl ) δ 14.1, 15.2, 18.1, 20.4, 21.0, 22.7, 26.0,
3
2
1
1
9.2, 29.4, 31.8, 68.2, 115.0, 118.8, 123.4, 125.9, 126.8, 128.4, 130.1,
31.0, 131.4, 131.7, 134.0, 134.8, 137.0, 140.5, 141.7, 143.3, 145.3,
46.7, 154.1, 159.7, 163.9.
JA990965M
Anal. Calcd for C37
C, 68.90; H, 6.10; N, 3.92.
-)-4-Decanoyloxy-2,2′,6,6′-tetramethyl-4′-[(4-(4-octyloxyphenyl)-
40 2 8
H N O : C, 69.36; H, 6.29; N, 4.37. Found:
(
30) Miyasato, K.; Abe, S.; Takezoe, H.; Fukuda, A.; Kuze, E. Jpn. J.
Appl. Phys. 1983, 22, L661.
(
(31) Martinot-Lagarde, P. J. Phys. 1976, C3, 129.
benzoyl)oxy]-3,3′-dinitrobiphenyl ((-)-5). Under an Ar atmosphere,
thionyl chloride (1.0 mL, 13 mmol) was added dropwise to a mixture
of decanoic acid (3.5 mg, 0.02 mmol) and dry benzene (2 mL) at room
temperature. After the mixture was refluxed for 2 h, it was concentrated
to give decanoyl chloride as a colorless oil. Under an Ar atmosphere,
a solution of optically pure 9 (10 mg, 0.02 mmol) and DMAP (2.5
mg, 0.02 mmol) in dry THF (3 mL) was added to the acid chloride.
The mixture was stirred at room temperature overnight, diluted with
(
32) Wavefunctions, Inc., 18401 Von Karmann, #210, Irvine, CA.
(33) Gaussian 94, Rev. B.3: Frisch, M. J.; Trucks, G. W.; Schlegel, H.
B.; Gill, P. M. W.; Johnson, B. G.; Robb, M. A.; Cheeseman, J. R.; Keith,
T.; Petersson, G. A.; Montgomery, J. A.; Raghavachari, K.; Al-Laham, M.
A.; Zakrzewski, V. G.; Ortiz, J. V.; Foresman, J. B.; Peng, C. Y.; Ayala, P.
Y.; Chen, W.; Wong, M. W.; Andres, J. L.; Replogle, E. S.; Gomperts, R.;
Martin, R. L.; Fox, D. J.; Binkley, J. S.; Defrees, D. J.; Baker, J.; Stewart,
J. P.; Head-Gordon, M.; Gonzalez, C.; Pople, J. A. Gaussian, Inc., Pittsburgh,
PA, 1995.