Induction of a ferroelectric S(C)* liquid crystal phase by an atropisomeric dopant derived from 4,4'-dihydroxy-2,2'-dimethyl-6,6'-dinitrobiphenyl

Article abstract of DOI:10.1021/ja9617505

We report the induction of a ferroelectric S(C)* phase in two S(C) liquid crystal hosts using a novel chiral dopant (-)-1 that incorporates an atropisomeric core derived from 4,4'-dihydroxy-2,2'-dimethyl-6,6'-dinitrobiphenyl. The racemic dopant was synthe

Full text of DOI:10.1021/ja9617505

J. Am. Chem. Soc. 1996, 118, 9557-9561
9557
Induction of a Ferroelectric SC* Liquid Crystal Phase by an
Atropisomeric Dopant Derived from
4,4′-Dihydroxy-2,2′-dimethyl-6,6′-dinitrobiphenyl
Kexin Yang, Bryan Campbell, Glenn Birch, Vance E. Williams, and
Robert P. Lemieux*
Contribution from the Department of Chemistry, Queen’s UniVersity,
Kingston, Ontario, Canada K7L 3N6
ReceiVed May 23, 1996X
Abstract: We report the induction of a ferroelectric SC* phase in two SC liquid crystal hosts using a novel chiral
dopant (-)-1 that incorporates an atropisomeric core derived from 4,4′-dihydroxy-2,2′-dimethyl-6,6′-dinitrobiphenyl.
The racemic dopant was synthesized in 11 steps with an overall yield of 9% and resolved by chiral stationary phase
HPLC in optically pure form. The magnitude and sign of the spontaneous polarization (PS) induced by (-)-1 were
found to depend strongly on the nature of the SC host. In a cyclohexanecarbonitrile host, (-)-1 induces a positive
polarization that is measurable over the dopant mole fraction range 0.02 < xd < 0.044; in a phenyl benzoate host,
(-)-1 induces a negative polarization that falls below detection limit at xd e 0.05. The polarization power (δp) of
(-)-1 in the cyclohexanecarbonitrile host is +170 nC/cm2, which is more than eight times that estimated as upper
limit in the phenyl benzoate host. These results are rationalized on the basis of the Boulder model for the molecular
origins of PS by modeling the conformational behavior of the biphenyl core in the achiral lattice of the SC host using
semiempirical AM1 calculations. The dependence of δp on the nature of the SC host is correlated to the large
difference in negative dielectric anisotropy (ꢀ| - ꢀ ) of the two hosts.
Introduction
The phenomenon of spontaneous polar ordering (ferroelec-
tricity) in chiral smectic C (SC*) liquid crystals has received
considerable attention over the past 15 years due to the vast
potential of these materials as active component of fast switching
electro-optical light valves and displays.1 In 1980, Clark and
Lagerwall showed that the helix of a SC* liquid crystal phase
spontaneously unwinds between polyimide-coated glass slides
to give a surface-stabilized ferroelectric liquid crystal (SSFLC).2
As predicted theoretically by Meyer and co-workers,3 the SSFLC
exhibits a finite spontaneous polarization (PS) along a polar axis
perpendicular to the tilt plane, which is defined by the orientation
of the molecular long axis n (director) and the layer normal z
(Figure 1). This spontaneous polarization is a macroscopic
manifestation of molecular chirality and is a function of the
molecular structure of the chiral component(s) of the SC* phase.4
Figure 1. Schematic representation of the SSFLC. The polar axis is
to the plane of the page.
The spontaneous polarization and tilt angle (θ) of a SC* phase
are related by eq 1 to the reduced polarization (Po), which is
intrinsic to the chiral component of the SC* phase at a fixed
temperature difference below the SC*-SA* phase transition (T-
TAC).6 The reduced polarization of an induced SC* phase
generally shows a linear dependence on the mole fraction (xd)
of the chiral dopant at a fixed T-TAC. This relationship is
expressed by eq 2, in which the polarization power (δp) is a
measure of the propensity of a chiral dopant to induce a
spontaneous polarization in a SC host. The polarization power
of most chiral dopants is independent of the nature of the achiral
SC host;6,7 these so-called Type I dopants are usually character-
ized by an acyclic stereopolar unit located in the side-chain of
the molecule. The stereopolar unit consists of the chiral center-
(s) and all sterically coupled polar functional groups contributing
to a transverse molecular dipole. Recently, there have been
several reports of SC* chiral dopants with stereopolar units
Ferroelectric liquid crystals suitable for SSFLC light valve
and display applications are usually induced SC* phases, which
are obtained by dissolving a chiral dopant with a large transverse
molecular dipole into an achiral SC liquid crystal host mixture
with low orientational viscosity and broad temperature range.5,6
* Author to whom correspondence should be addressed. Email:
lemieux@chem.queensu.ca.
X Abstract published in AdVance ACS Abstracts, September 1, 1996.
(1) (a) Walba, D. M. Science 1995, 270, 250. (b) 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. (c)
Dijon, J. In Liquid Crystals: Applications and Uses; Bahadur, B., Ed.; World
Scientific: Singapore, 1990; Vol. 1, Chapter 13.
(2) Clark, N. A.; Lagerwall, S. T. Appl. Phys. Lett. 1980, 36, 899.
(3) Meyer, R. B.; Liebert, L.; Strzelecki, L.; Keller, P. J.. Phys. (Paris)
Lett. 1975, 36, L69.
(4) Walba, D. M. In AdVances in the Synthesis and ReactiVity of Solids;
T. E. Mallouck, Ed.; JAI Press, Ltd.: Greenwich, CT, 1991; Vol. 1; pp
173-235.
(6) Siemensmeyer, K.; Stegemeyer, H. Chem. Phys. Lett. 1988, 148, 409.
(7) Stegemeyer, H.; Meister, R.; Hoffmann, U.; Kuczynski, W. Liq. Cryst.
1991, 10, 295.
(5) Kuczynski, W.; Stegemeyer, H. Chem. Phys. Lett. 1980, 70, 123.
S0002-7863(96)01750-7 CCC: $12.00 © 1996 American Chemical Society

9558 J. Am. Chem. Soc., Vol. 118, No. 40, 1996
Yang et al.
consisting of a chiral ring system located within the rigid core
of the molecule.8 In some of those cases, δp has been shown
to depend strongly on the nature of the achiral SC host; these
compounds are referred to as Type II dopants.8a
Scheme 1a
PS ) Po sin θ
(1)
dPo(xd)
δp )
(2)
(
)
dxd
xdf0
Most of the SC* mesogens and chiral dopants reported thus
far, including Type II dopants, incorporate one or more chiral
center(s) in the stereopolar unit. Only a few examples of
inherently chiral SC* mesogens have been reported, which
include allene and alkylidenecyclohexane derivatives9,10 and 1,3-
disubstituted ferrocene derivatives.11 Such compounds are of
particular interest due to their potential as high δp dopants. In
this paper, we introduce a new class of inherently chiral dopant
incorporating an atropisomeric biphenyl core with a large
transverse dipole moment as the stereopolar unit and report on
the dependence of the spontaneous polarization induced by one
such compound, (-)-1, on the nature of the SC host.12
a (a) Cl3CCH(OH)2, NH2OH‚HCl, Na2SO4, H2O, 55 °C; (b) con-
centrated H2SO4, 95 °C; (c) 30% H2O2, NaOH, H2O, 25 °C; AcOH;
(d) NaNO2, concentrated H2SO4, 0 °C; KI, H2O; (e) MeOH, H2SO4,
reflux; (f) Cu, DMF, reflux; (g) KOH, EtOH, H2O, reflux; (h) 1.0 M
BH3‚THF, 25 °C; (i) 48% HBr, AcOH, reflux; (j) NaBH3CN, HMPA,
55 °C; (k) 4-n-octyloxybenzoic acid, DCC, DMAP, CH2Cl2, 25 °C; (l)
chiral stationary phase HPLC resolution, (S,S)-Whelk-O 1 column, 40:
3:1 hexanes/IPA/CH2Cl2, 3 mL/min.
Results and Discussion
Compound 1 was prepared as a racemic mixture in an overall
yield of 9% as shown in Scheme 1. Conversion of 2 to 5 was
achieved via modification of a known procedure,13 followed
by an Ullmann coupling and hydrolysis to give the diphenic
acid 7. Selective reduction using BH3‚THF gave the diol 8,
which was converted to the dibromide 9 in a single step and
reduced under mild conditions to give the dihydroxybiphenyl
10. Following esterification, (()-1 was resolved by semiprep
chiral stationary phase HPLC using a Regis (S,S)-Whelk-O 1
column to give (-)-1 in optically pure form.
Thermal analysis by differential scanning calorimetry indi-
cated that (-)-1 does not exhibit a liquid crystal phase. The
dopant (-)-1 was mixed in the liquid crystal hosts PhBz and
NCB76 over the mole fraction range 0.01 < xd < 0.05 (Figure
2). The temperature range of the induced SC* phase in both
liquid crystal hosts was found to decrease significantly with
increasing dopant mole fraction, with the SC* phase vanishing
completely at xd > 0.05. The doped liquid crystal mixtures
were introduced into polyimide-coated ITO glass cells and
subjected to a square-wave AC voltage (6 V/µm, 1 Hz) while
in the SC* phase. In each case, the characteristic Goldstone-
mode switching of a ferroelectric SC* phase was observed.1b,c
No ferroelectric switching was observed in the absence of
dopant, nor when (()-1 was substituted for (-)-1.
Figure 2. Structures of SC hosts and phase transition temperatures in
°C.
In the SC host PhBz, the dopant (-)-1 induced a negatiVe
spontaneous polarization that fell below the detection limit of
our instrumentation (0.2 nC/cm2) at xd e 0.05. Extrapolation
of the 0.2 nC/cm2 detection limit from xd ) 0.05 to xd ) 1
(factoring in the observed tilt angle) gives an estimated upper
limit for |δp| of 20 nC/cm2 in the SC host PhBz. In the SC host
NCB76, the dopant (-)-1 induced a positiVe spontaneous
polarization that was measurable over the mole fraction range
0.02 < xd < 0.044. Spontaneous polarization and tilt angle
values were measured as a function of temperature at three
different concentrations (Figure 3). Reduced polarization values
were calculated from PS and θ values at T-TAC ) -5 °C using
eq 1. A plot of Po vs xd shows a positive deviation from linearity
(Figure 4), with a δp value of +170 nC/cm2. A similar deviation
from linearity for the function Po (xd) has been observed
previously for Type I and II mesogenic chiral dopants with
strong transverse dipole moments, albeit over a much wider
mole fraction range, and rationalized on the basis of a local
field effect.7,8a
The results can be rationalized by considering the Boulder
model for the molecular origins of spontaneous polar ordering
in SC* phases.4 According to this model, (-)-1 should fit in
the achiral lattice (binding site) of a SC host in a transoid
conformation, in which the atropisomeric biphenyl core should
be relatively free to rotate with respect to the ester side-chains,
giving rise to diastereomeric rotational states (Figure 5). In this
lowest energy conformation, (-)-1 should induce a spontaneous
(8) (a) Stegemeyer, H.; Meister, R.; Hoffmann, U.; Sprick, A.; Becker,
A. J. Mater. Chem. 1995, 5, 2183. (b) Serrano, J. L.; Sierra, T.; Gonzalez,
Y.; Bolm, C.; Weickhardt, K.; Magnus, A.; Moll, G. J. Am. Chem. Soc.
1995, 117, 8312. (c) Scherowsky, G.; Michalski, B.; Junghans, C. J. Mater.
Chem. 1995, 5, 2125. (d) Kusumoto, T.; Sato, K.; Hiyama, T.; Takehara,
S.; Ito, K. Chem. Lett. 1995, 537. (e) Ikemoto, T.; Kageyama, Y.; Onuma,
F.; Shibuya, Y.; Ichimura, K.; Sakashita, K.; Mori, K. Liq. Cryst. 1994,
17, 729. (f) Ikemoto, T.; Sakashita, K.; Kageyama, Y.; Onuma, F.; Shibuya,
Y.; Ichimura, K. Mol. Cryst. Liq. Cryst. 1994, 250, 247. (g) Scherowsky,
G.; Lotz, A. Liq. Cryst. 1993, 14, 733, 1295. (h) Kusumoto, T.; Sato, K.;
Ogino, K.; Hiyama, T.; Takehara, S.; Osawa, M.; Nakamura, K. Liq. Cryst.
1993, 14, 727. (i) Buchecker, R.; Funfshilling, J.; Schadt, M. Mol. Cryst.
Liq. Cryst. 1992, 213, 259.
(9) Zab, K.; Kruth, H.; Tschierske, C. Chem. Commun. 1996, 977.
(10) Poths, H.; Scho¨nfeld, A.; Zentel, R.; Kremer, F.; Siemensmeyer,
K. AdV. Mat. 1992, 4, 351.
(11) Deschenaux, R.; Santiago, J. Tetrahedron Lett. 1994, 35, 2169.
(12) A preliminary account of this work was presented at the 15th
International Liquid Crystal Conference, Budapest, June 1994: Yang, K.;
Lemieux, R. P. Mol. Cryst. Liq. Cryst. 1995, 260, 247.
(13) Cassebaum, H. J. Prakt. Chem. 1964, 23, 301.

Induction of a Ferroelectric SC* Phase
J. Am. Chem. Soc., Vol. 118, No. 40, 1996 9559
Figure 3. Spontaneous polarization PS (filled symbols) and tilt angle
(open symbols) as a function of temperature for the induced SC* phase
of (-)-1/NCB76 mixtures: xd ) 0.02 (triangles), 0.031 (squares), 0.044
(circles).
Figure 6. Energy profiles for 3-methyl-5-nitrophenyl benzoate (top)
and 4-benzoyloxy-2,2′-dimethyl-6,6′-dinitrobiphenyl (bottom) as a
function of the torsional angles defined by C-6, C-1, O, C(O) and C-5,
C-4, O, C(O), respectively.
3-methyl-5-nitrophenyl benzoate (11) and 4-benzoyloxy-2,2′-
dimethyl-6,6′-dinitrobiphenyl (12) are used to model the in-
tramolecular rotation of the biphenyl core in (-)-1 (Figure 6).15
Both profiles suggest a small energetic bias for intramolecular
rotation of the biphenyl core in the SC binding site, which is
consistent with the low polarization power exhibited by (-)-1
in the SC host PhBz. The energy profile calculated for 11 shows
two pairs of symmetry-related minima a, a′ and b, b′ (∆Ho )
0.4 kcal/mol). On the time average, these minima correspond
to the planar conformations I and II, respectively, which have
opposite transverse dipole moments; AM1 calculations give
dipole moment values of 4.0 D (I) and 5.3 D (II) along the
vectors shown in Figure 5. When the atropisomeric biphenyl
group is included, rotational symmetry about the ester C-O
bond is completely broken, as shown by the energy profile
calculated for 12, with the global minimum corresponding to a
conformation in which the ester carbonyl group is oriented away
from both nitro substituents.
Figure 4. Reduced polarization Po as a function of dopant mole fraction
xd for the induced SC* phase of (-)-1/NCB76 mixtures at T-TAC
-5 °C.
)
The results showing the polarization power of (-)-1 in
NCB76 to be eight times that estimated as the upper limit in
PhBz can be correlated to the difference in dielectric anisotropy
of the two hosts: NCB76 has a large transverse dipole moment
and exhibits a negative dielectric anisotropy (ꢀ| - ꢀ ) that is
ca. 10 times that of PhBz.1c This suggests that the amplification
of PS in NCB76 is a manifestation of induced polar ordering
of the SC host via transverse dipole-dipole coupling with (-)-
1. Along with polar ordering of the host, it is likely that
transverse dipole-dipole coupling between (-)-1 and NCB76
Figure 5. Transoid conformation of (-)-1 in the achiral lattice of a
SC host according to the Boulder model (left); the polar axis is to
the plane of the page. Structures representing the time-average
conformational minima of 3-methyl-5-nitrophenyl benzoate for rotation
about the ester C-O bond according to AM1 calculations (right).
(14) Dewar, M. J. S.; Zoebisch, E. G.; Healy, E. F.; Stewart, J. P. P. J.
Am. Chem. Soc. 1985, 107, 3902.
(15) It is assumed that the 2,2′-dimethyl-6,6′-dinitrobiphenyl group is
conformationally rigid. The calculated energy profile (AM1) for 360°
rotation about the central bond of the atropisomeric biphenyl is steep and
shows a single pair of symmetry-related energy minima at dihedral angles
approaching 90° and 270°, with a rotational barrier of ca. 35 kcal/mol.
polarization that is a function of the energy difference between
any two rotational states of the biphenyl core contributing
opposite dipole moments along the SC* polar axis (i.e.,
transverse to the molecular long axis). The calculated energy
profiles (AM1)14 for rotation about the ester C-O bonds of

9560 J. Am. Chem. Soc., Vol. 118, No. 40, 1996
Yang et al.
4-Methoxy-2-nitroisonitrosoacetanilide (3). A suspension of 2 (50
g, 300 mmol) in 2 M aqueous HCl (100 mL) was added to a solution
of chloral hydrate (59 g, 360 mmol), NH2OH‚HCl (74 g, 1.07 mol)
and anhydrous Na2SO4 (426 g, 3 mol) in 2 L of H2O preheated to 55
°C. The mixture was stirred mechanically at 55 °C overnight and then
allowed to cool to room temperature. The precipitated product was
collected by filtration, washed with H2O, and dried in a vacuum oven
to give 67 g (93%) of 3 as an orange solid: mp 102-104 °C; 1H NMR
(200 MHz, DMSO-d6) δ 3.83 (s, 3H), 7.37 (dd, J ) 3.0 Hz, J ) 9.1
Hz, 1H), 7.58 (d, J ) 3.5 Hz, 1H), 7.59 (s, 1H), 8.05 (d, J ) 9.1 Hz,
1H), 10.62 (s, 1H), 12.49 (s, 1H); 13C NMR (100 MHz, DMSO-d6) δ
56.0, 109.1, 121.5, 125.1, 125.6, 140.8, 143.3, 155.6, 160.6; MS (EI)
m/z 239 (M+, 16), 193 (34), 176 (15), 168 (100), 153 (38), 150 (10),
133 (8), 122 (48), 120 (37), 107 (32); HRMS (EI) calcd for
C9H9N3O5: 239.0542. Found: 239.0524.
5-Methoxy-7-nitroisatin (4). Compound 3 (67 g, 280 mmol) was
carefully added in small portion to a stirred solution of concentrated
H2SO4 (250 mL) preheated to 90 °C. The temperature was kept below
105 °C throughout the addition. The resulting dark solution was stirred
for an additional 15 min, then cooled to 60 °C, and poured onto 200 g
of crushed ice. The precipitated product was collected by filtration,
washed with H2O, and dried in a vacuum oven to give 51.5 g (83%) of
4 as an orange powder: mp 236-238 °C; 1H NMR (200 MHz, DMSO-
d6) δ 3.86 (s, 3H), 7.58 (d, J ) 1.9 Hz, 1H), 7.73 (d, J ) 1.9 Hz, 1H),
11.54 (s, 1H); 13C NMR (100 MHz, DMSO-d6) δ 56.5, 113.8, 118.3,
122.3, 131.9, 138.7, 154.3, 160.0, 181.6; MS (EI) m/z 222 (100), 205
(99), 194 (43), 175 (72), 164 (34), 147 (36), 132 (25), 120 (9), 116
(8), 104 (72), 93 (64); HRMS (EI) calcd for C9H6N2O5: 222.0277.
Found: 222.0279.
causes a significant asymmetric distortion of the achiral SC
binding site, which can further contribute to rotational ordering
of the dopant. Such distortion is also likely to affect the global
conformational minimum of the dopant, which ultimately
controls the orientation of the core with respect to the polar
axis, thus providing a possible explanation for the observed sign
inversion of PS. Another contributing factor to the sign
inversion may be a shift in the conformational equilibrium of
the biphenyl core toward conformations predicted to be of higher
energy in the gas phase (e.g., II). These conformations have
larger transverse dipole moments and should therefore be
stabilized to a greater extent by a SC host with high negative
dielectric anisotropy.
In summary, we have demonstrated for the first time the
induction of a ferroelectric SC* phase by a dopant with an
atropisomeric biphenyl core as stereopolar unit.16 The polariza-
tion power and sign of polarization induced by (-)-1 showed
a dependence on the nature of the SC host that is consistent
with the behavior of Type II dopants first reported by
Stegemeyer.8a The > 8-fold enhancement in polarization power
resulting from the change in SC host is one of the largest thus
far reported for a Type II dopant. Combined with the observed
deviation from linearity of the Po (xd) function over a relatively
narrow xd range, these results suggest that the polarization power
of (-)-1 is remarkably sensitive to the environment of the
dopant, which may be due to the unusual conformational
mobility of the stereopolar unit in (-)-1. Further work aimed
at probing the generality of this phenomenon in a wider variety
of SC hosts and at enhancing the rotational order of the biphenyl
core to produce dopants with higher δp values is in progress.
Methyl 2-Iodo-5-methoxy-3-nitrobenzoate (5). A 30% H2O2
solution (15 mL) was added dropwise to a stirred solution of 4 (14.5
g, 65 mmol) in 50 mL of 2 M aqueous NaOH cooled in an ice/H2O
bath. The mixture was stirred at room temperature overnight and then
carefully acidified with 10 mL of glacial AcOH. The solid precipitate
was collected by filtration, washed with H2O, and dried in a vacuum
oven to give 9.7 g of crude 2-amino-5-methoxy-3-nitrobenzoic acid as
a brown solid. The crude product was dissolved in concentrated H2-
SO4 (40 mL) and cooled to 5 °C, and 4.6 g of NaNO2 (67 mmol) was
slowly added while maintaining the temperature below 10 °C. The
mixture was diluted with 85% H3PO4 (80 mL), stirred at 5 °C for 1 h,
and then poured onto 350 g of crushed ice. A solution of KI (11.2 g,
67 mmol) in H2O (30 mL) was slowly added, and the mixture was
stirred at room temperature overnight. The solid precipitate was
collected by filtration, dissolved in 10% aqueous NaOH, and treated
with activated charcoal while heating over a steam bath. After cooling,
the mixture was filtered and acidified with 12 M aqueous HCl. The
resulting light brown precipitate was collected by filtration, washed
with H2O, and dried in a vacuum oven to give 11.2 g of 2-iodo-5-
methoxy-3-nitrobenzoic acid as a tan solid: 1H NMR (200 MHz,
DMSO-d6) δ 3.86 (s, 3H), 7.37 (d, J ) 2.9 Hz, 1H), 7.62 (d, J ) 2.9
Hz, 1H). The crude product was taken up in a mixture of MeOH (275
mL) and concentrated H2SO4 (30 mL) and refluxed with stirring for
12 h. After cooling, the mixture was poured into H2O and extracted
with CH2Cl2 (3 × 200 mL). The combined extracts were washed with
H2O, dried (MgSO4), and concentrated to an orange solid, which was
recrystallized from EtOH to give 10.2 g (46%) of 5 as bright orange
Experimental Section
General. 1H and 13C NMR spectra were recorded on Bruker ACF-
200 and AM-400 NMR spectrometers in deuterated chloroform and
deuterated DMSO. The 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 (% 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. Differential scanning calorimetry measurements were
carried out using a Perkin-Elmer DSC-7 instrument. 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
uncorrected.
Materials. All reagents were obtained from commercial sources
and used without further purification unless otherwise noted. Di-
methylformamide (DMF) was distilled from BaO under reduced
pressure and stored over molecular sieves. Hexamethylphosphoramide
(HMPA) was distilled from CaH2 under N2. Methylene chloride (CH2-
Cl2) was distilled from P2O5 under N2. Tetrahydrofuran (THF) was
distilled from sodium/benzophenone under N2. 4-Methoxy-2-nitro-
aniline (2) was purchased from Aldrich. The SC host PhBz was
prepared as a racemic mixture according to the published procedure17
and recrystallized twice from hexanes. The SC host NCB76 was
provided by Prof. H. Stegemeyer.
1
crystals: mp 61-62 °C; H NMR (400 MHz, CDCl3) δ 3.88 (s, 3H),
3.98 (s, 3H), 7.26 (d, J ) 3.0 Hz, 1H), 7.32 (d, J ) 3.0 Hz, 1H); 13C
NMR (50 MHz, CDCl3) δ 53.1, 56.3, 73.1, 112.2, 118.6, 140.8, 156.4,
159.9, 166.6; MS (EI) m/z 337 (M+, 100), 321 (10), 306 (33), 291
(20), 276 (31), 260 (9), 248 (12), 233 (22), 218 (12), 205 (12), 189
(9), 180 (14), 165 (12), 149 (82), 142 (38), 133 (20), 127 (37), 121
(11), 105 (64). Anal. Calcd for C9H8INO5: C, 32.07; H, 2.39; N,
4.16; I, 37.65. Found: C, 32.46; H, 2.36; N, 4.09; I, 37.26.
(16) Atropisomeric dopants have been reported on several occasions to
induce a cholesteric phase in nematic liquid crystal hosts. For recent
examples, see: (a) Gottarelli, G.; Proni, G.; Spada, G. P.; Fabbri, D.;
Gladiali, S.; Rosini, C. J. Org. Chem. 1996, 61, 2013, and references cited
therein. (b) Bhatt, J. C.; Keast, S. S.; Neubert, M. E.; Petschek, R. G. Liq.
Cryst. 1995, 18, 367. (c) Zhang, M.; Schuster, G. B. J. Phys. Chem. 1992,
96, 3063.
(17) Keller, P. Ferroelectrics 1984, 58, 3.
(18) Miyasato, K.; Abe, S.; Takezoe, H.; Fukuda, A.; Kuze, E. Jpn. J.
Appl. Phys. 1983, 22, L661.
(()-Dimethyl 4,4′-Dimethoxy-6,6′-dinitrobiphenyl-2,2′-dicarboxy-
late (6). A mixture of 5 (2.88 g, 8.5 mmol) and Cu bronze (2.71 g, 43
mmol) in 50 mL of dry DMF was refluxed with stirring under N2
overnight. After cooling, the mixture was diluted with benzene (50
mL), washed twice with 2 M aqueous HCl, dried (MgSO4), and
concentrated to give an orange solid. Purification by flash chroma-
tography on silica gel (40% EtOAc/hexane) gave 1.28 g (72%) of pure
6 as a yellow solid: mp 139-140 °C; 1H NMR (200 MHz, CDCl3) δ
(19) Wavefunction, Inc., 18401 Von Karmann, #210, Irvine, CA.

Induction of a Ferroelectric SC* Phase
J. Am. Chem. Soc., Vol. 118, No. 40, 1996 9561
3.66 (s, 6H), 3.96 (s, 6H), 7.77-7.80 (m, 4H); 13C NMR (100 MHz,
CDCl3) δ 52.7, 56.1, 113.1, 120.8, 124.2, 132.3, 150.0, 159.0, 165.1;
MS (EI) m/z 420 (M+, 5), 374 (97), 342 (31), 313 (100), 298 (72), 283
(32), 267 (11), 255 (21), 241 (8), 227 (16), 212 (12), 199 (11), 184
(14), 156 (13). Anal. Calcd for C18H16N2O10: C, 51.44; H, 3.84; N,
6.66. Found: C, 51.33; H, 4.00; N, 6.72.
(M+, 100), 258 (56), 242 (19), 240 (20), 230 (29), 228 (80), 216 (45),
214 (43), 202 (30), 190 (44), 188 (43), 184 (36), 174 (28), 160 (32),
152 (44), 147 (29), 139 (41), 128 (65), 115 (90). Anal. Calcd for
C14H12N2O6: C, 55.27; H, 3.98; N, 9.21. Found: C, 55.42; H, 4.06;
N, 8.99.
(-)-2,2′-Dimethyl-6,6′-dinitro-4,4′-bis[(4-n-octyloxybenzoyl)oxy]-
biphenyl ((-)-1). Under a N2 atmosphere, 82 mg (0.4 mmol) of solid
DCC was added to a solution of 10 (50 mg, 0.16 mmol), 4-n-
octyloxybenzoic acid (100 mg, 0.4 mmol), and DMAP (50 mg, 0.4
mmol) in 10 mL of dry CH2Cl2. The mixture was stirred at room
temperature for 24 h and then filtered. The filtrate was eluted through
a short silica gel column with CH2Cl2 to give 110 mg (89%) of (()-1
as a white solid. The product was resolved by chiral stationary phase
HPLC using a semiprep (S,S)-Whelk-O 1 column (40:3:1 hexanes/
isopropyl alcohol/CH2Cl2, 3 mL/min) and recrystallized twice from
hexanes to give (-)-1 in optically pure form: mp 130-132 °C; [R]D
(()-4,4′-Dimethoxy-6,6′-dinitrobiphenyl-2,2′-dicarboxylic Acid
(7). A mixture of 6 (2.3 g, 5.5 mmol) and NaOH (1.04 g, 26 mmol)
in 100 mL of 3:2 EtOH/H2O was refluxed with stirring overnight. After
cooling, the EtOH was removed in vacuo, and the aqueousueous phase
was acidified with 2 M aqueous HCl and extracted with EtOAc (3 ×
50 mL). The combined extracts were washed with H2O and brine,
dried (MgSO4), and concentrated to give 2.1 g (98%) of 7 as a yellow
1
solid: mp 252-254 °C; H NMR (200 MHz, DMSO-d6) δ 3.93 (s,
6H), 7.69 (d, J ) 2.7 Hz, 2H), 7.83 (d, J ) 2.7 Hz, 2H); 13C NMR
(100 MHz, DMSO-d6) δ 56.3, 112.2, 119.8, 122.6, 134.1, 150.1, 158.7,
165.8; MS (EI) m/z 392 (M+, 3), 374 (1), 360 (10), 346 (8), 330 (13),
316 (14), 298 (100), 283 (60), 270 (34), 254 (61), 241 (21), 239 (27),
226 (38), 211 (34), 199 (24), 183 (31), 171 (21), 156 (14), 140 (28).
Anal. Calcd for C16H12O10N2: C, 48.99; H, 3.08; N, 7.14. Found: C,
49.23; H, 3.00; N, 7.11.
1
) -5.01 (c 0.5, CH2Cl2); H NMR (200 MHz, CDCl3) δ 0.90 (t, J )
6.7 Hz, 6H), 1.26-1.55 (m, 20 H), 1.76-1.92 (m, 4H), 2.06 (s, 6H),
4.06 (t, J ) 6.5 Hz, 4 H), 7.01 (d, J ) 8.9 Hz, 4H), 7.52 (d, J ) 2.4
Hz, 2H), 7.93 (d, J ) 2.4 Hz, 2H), 8.14 (d, J ) 8.9 Hz, 4H); 13C NMR
(50 MHz, CDCl3) δ 14.1, 20.2, 22.6, 26.0, 29.0, 29.2, 29.3, 31.8, 68.4,
114.5, 116.3, 120.5, 128.1, 128.6, 132.5, 139.9, 148.5, 150.6, 163.9,
164.0. Anal. Calcd for C44H52N2O10: C, 68.73; H, 6.82; N, 3.64.
Found: C, 68.49; H, 6.74; N, 3.58.
(()-2,2′-Bis(bromomethyl)-4,4′-dimethoxy-6,6′-dinitrobiphenyl (9).
To a stirred solution of 7 (1.8 g, 4.6 mmol) in 40 mL of dry THF
cooled to 0 °C was added dropwise 20 mL of BH3‚THF (1M solution).
The mixture was then allowed to warm to room temperature and stirred
for 20 h. The reaction was carefully quenched by slow addition of
H2O (100 mL) and extracted with EtOAc (3 × 50 mL). The organic
extracts were combined and concentrated to an oily residue. The
residue was taken up in EtOAc (50 mL), washed with H2O (2×) and
brine, dried (MgSO4), and concentrated to give 1.5 g of the diol 8 as
a yellow solid: 1H NMR (200 MHz, CDCl3) δ 3.89 (s, 6H), 4.04 (d,
J ) 13.4 Hz, 2H), 4.19 (d, J ) 13.4 Hz, 2H), 7.31 (d, J ) 2.5 Hz,
2H), 7.48 (d, J ) 2.5 Hz, 2H). The crude 8 was taken up in a mixture
of 48% aqueous HBr (30 mL) and glacial AcOH (20 mL) and refluxed
with stirring for 24 h. After cooling, the mixture was poured into H2O
and extracted with EtOAc (3 × 50 mL), the combined extracts were
washed with H2O, dried (MgSO4), and concentrated. Purification by
flash chromatography on silica gel (5% isopropanol/hexanes) gave 1.16
g (51%) of 9 as a yellow solid: mp 215-217 °C; 1 H NMR (200 MHz,
acetone-d6) δ 4.20 (d, J ) 12 Hz, 2H), 4.36 (d, J ) 12 Hz, 2H), 7.51
(d, J ) 2.6 Hz, 2H), 7.70 (d, J ) 2.6 Hz, 2H), 9.68 (s, 2 H); 13C NMR
(100 MHz, DMSO-d6) δ 31.2, 111.8, 119.6, 123.1, 139.4, 149.1, 158.0;
MS (EI) 464 (M+4, 4), 462 (M+2, 9), 460 (M+, 4), 418 (4), 416 (8),
414 (4), 383 (5), 381 (5), 337 (24), 335 (26), 271 (62), 256 (99), 239
(100), 226 (49), 212 (47), 197 (48), 181 (43), 167 (33), 152 (75), 149
(93), 139 (57), 127 (38), 115 (75); HRMS (EI) calcd for C14H10N2O6-
Br2: 459.8910. Found: 459.8914.
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
a Instec HS1-i hot stage. Spontaneous polarization (PS) values were
measured as a function of temperature by the triangular wave method18
(6 V/µm, 60-80 Hz) using a Displaytech APT II 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 ITO glass cells (4 µm × 0.25 cm2) supplied by Displaytech
Inc. were used for all the measurements. Good alignment was obtained
by slow cooling of the filled cells from the isotropic phase via the
chiral nematic and SA* 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
orientations. The sign of PS along the polar axis was assigned from
the relative configuration of the electrical field and the switching
position of the sample according to the established convention.4
Calculations. All calculations were carried out at the semiempirical
AM1 level14 using Spartan version 3.0.1.19 Rotational energy profiles
of the ester linkages in 11 and 12 were obtained by constraining the
torsional angles defined by C-6, C-1, O, C(O) and C-5, C-4, O, C(O),
respectively, and performing a full geometry optimization on the rest
of the molecules. All minima were determined by full geometry
optimization and confirmed as minima by vibrational analysis.
(()-4,4′-Dihydroxy-2,2′-dimethyl-6,6′-dinitrobiphenyl (10).
A
mixture of 9 (2.31 g, 5 mmol) and NaBH3CN (3.2 g, 51 mmol) in 20
mL of dry HMPA was stirred at 55 °C for 20 h under N2. After cooling,
the mixture was poured carefully into 2 M aqueous HCl and extracted
with EtOAc (3 × 50 mL). The combined extracts were washed with
2 M aqueous HCl, dried (MgSO4), and concentrated. The residue was
purified by flash chromatography on silica gel (40% EtOAc/hexanes)
to give 1.16 g (76%) of 10 as a yellow solid: mp 214-215 °C (dec);
1H NMR (200 MHz, CDCl3) δ 1.96 (s, 6H), 5.28 (br s, 2 H), 7.06 (d,
J ) 2.5 Hz, 2H), 7.41 (d, J ) 2.5 Hz, 2H); 13C NMR (50 MHz, DMSO-
d6) δ 19.5, 108.2, 120.4, 121.9, 140.3, 149.2, 157.2; MS (EI) m/z 304
Acknowledgment. We are grateful to the Natural Sciences
and Engineering Research Council of Canada and to Queen’s
University for financial support of this work. We thank Prof.
H. Stegemeyer for a generous gift of NCB76 and Dr. Chris
Welch of Regis Technologies for his assistance in selecting a
suitable HPLC chiral stationary phase to resolve (()-1.
JA9617505