The design of liquid crystalline bistolane-based materials with extremely high birefringence

Article abstract of DOI:10.1039/c6ra14093a

We designed three new bistolanes with alkylsulfanyl groups. A symmetric derivative contains short terminal methylsulfanyl groups (-SCH₃) on both ends, while two asymmetric derivatives contain a methylsulfanyl group on one end, as well as a highly polarizable cyano (-CN) or isothiocyanate (-NCS) group on the other end. These materials exhibited a well-defined enantiotropic nematic phase, as well as an extremely high birefringence (Δn > 0.6). Most notably, the NCS derivative achieves an extremely high value of 0.77 at 550 nm. These results should be helpful for the design and synthesis of novel nematic materials with high birefringence.

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The design of liquid crystalline bistolane-based materials with
extremely high birefringence
Yuki Arakawa,a,b Sungmin Kang,a Hideto Tsuji,b Junji Watanabea and Gen-ichi Konishia
Received 00th January 20xx,
Accepted 00th January 20xx
We designed three new bistolanes with alkylsulfanyl groups.
A symmetric derivative contains short terminal
DOI: 10.1039/x0xx00000x
methylsulfanyl groups (-SC3) on both ends, while two asymmetric derivatives contain a methylsulfanyl group on one end,
as well as a highly polarizable cyano (-CN) or isothiocyanate (-NCS) group on the other end. These materials exhibited a
well-defined enantiotropic nematic phase, as well as an extremely high birefringence (Δn > 0.6). Most notably, the NCS
derivative achieves an extremely high value of 0.77 at 550 nm. These results should be helpful for the design and synthesis
of novel nematic materials with high birefringence.
www.rsc.org/
benzene ring.7 Owing to the S···S interactions and high
polarizability of the sulphur atom, these materials exhibit
Introduction
remarkable characteristics, including high ꢀn and high order
Over the last two decades, liquid crystals (LCs) have attracted
substantial attention as materials with high birefringence (ꢀn).
parameters. However, various performanceꢁlimiting issues
remain unresolved. For example, the mesophase range of these
materials is narrower compared to that of other derivatives that
Their intriguing features include selfꢁalignment, anisotropy, and
sensitivity to external fields, which provides access to a range
of optical and electric materials, as well as display films.1 So
far, these materials have been used extensively as cholesteric
(Ch) films,1(c),2 including films for selective and wide reflection,
laser emission, holographic applications,3 and LC lenses.4 Most
contain carbon or oxygen atoms.5(a),7,8 Moreover, their ꢀ
n
values are still lower than those of extremely highꢁꢀ
the soꢁcalled superꢁhighꢁꢀ
(SHB) materials.5(b)
In this study, we present novel bistolaneꢁbased LC materials
with extremely high ꢀ (ꢀ > 0.7). In order to achieve such
extremely high ꢀ , we aimed to increase the mesophase range
n materials,
n
n
n
highꢁbirefringence LC materials exhibit ꢀn values of ~0.2ꢁ0.6.
n
However, in order to improve their performance in the
aforementioned applications, values beyond this range are
required, as well as thinner LC films and a wider reflection
band for circularly polarized light from Ch films. To the best of
and the polarizability anisotropy. Therefore, we designed three
bistolaneꢁbased LC compounds: two asymmetric molecules,
containing a methylsulfanyl group at one of the terminal
positions and a highly polarizable isothiocyanato (
group ( ) at the other, as well as a symmetric methylsulfanyl
derivative ( ) with enhanced intermolecular S···S interactions.
The present molecular design uses methylsulfanyl groups, i.e.
the shortest possible alkyl chain, to realize extremely high ꢀ
1) or cyano
our knowledge, reports on such materials with ꢀ
remain extremely scarce.5
n > 0.6 still
2
3
The typical design for highꢁꢀn LC materials includes the
fabrication of rodꢁlike cores via a combination of aromatic
rings and/or unsaturated bonds.3,5,6 High molecular
polarizability anisotropies are usually attained by attaching
highly polarizable substituents, e.g. cyano (ꢁCN) and
isothiocyanato (ꢁNCS) groups, to the terminal positions of these
compounds.6
Recently, we described novel alkylsulfanyl bistolaneꢁbased
rodꢁlike LC materials, whose mesophases are induced by
introducing a fluorine atom at the lateral position of the central
n
.
Relative to longer alkyl chains, shorter ones should not only
lead to a higher density of the mesogenic moiety in direction of
the long molecular axis to provide a high extraordinary
refractive index, but also to a wider N phase for calamitic LC
molecules.
Fig. 1. Chemical structures of 1-3.
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2H), 7.15 (d,
0.25 (s, Siꢁ(C
J
= 8.8 Hz, Arꢁ
H, 2H), 2.47 (s, ArꢁSꢁCH3, 3H),
Experimental
H
3)3, 9H) ppm.
Instruments
1ꢀEthynylꢀ4ꢀmethylthiobenzene (1c). A mixture of 1b
(3.50 g, 15.9 mmol), K2CO3 (4.40 g, 31.8 mmol), MeOH (20
mL), and THF (20 mL) was stirred at room temperature for 30
min. Then, the reaction mixture was extracted with ethyl
acetate and washed with brine. After evaporating the solvent,
1H and 13C NMR spectra were measured in CDCl3 on JEOL
LNMꢁEX 400 or Bruker DPX300S spectrometers at room
temperature, using tetramethylsilane (TMS) as the internal
standard. Liquid crystalline textures were examined by
polarizing optical microscopy (POM) on a Leica DM2500P
1
1c was obtained as a colorless solid (0.72 g, >99%). H NMR
microscopy with
a Mettler FP90 hot stage. Transition
(400 MHz, CDCl3) δ 7.40 (d,
J
= 8.4 Hz, Arꢁ
H, 2H), 7.17 (d, J
temperatures and enthalpy changes were measured by
differential scanning calorimetry on a Perkin Elmer DSC7,
whereby heating and cooling scans were carried out using a
temperature gradient of 10 °C minꢁ1. Measurements of extra
= 8.4 Hz, Arꢁ
3H) ppm.
H
, 2H), 3.07 (s, C
≡
Cꢁ , 1H), 2.48 (s, ArꢁSꢁCH3,
H
4ꢀ[2ꢀ(Trimethylsilyl)ethynyl]aniline (1d). Compound 1d
was synthesized according to the generic Sonogashira coupling
conditions outlined for the preparation of 1b: 4ꢁiodoaniline
(8.00 g, 36.5 mmol), trimethylsilylacetylene (7.58 mL, 54.8
mmol), TEA (40 mL), THF (40 mL), Pd(PPh3)4 (0.420 g, 0.365
mmol), and CuI (69.5 mg, 0.365 mmol). Purification by column
chromatography on silica gel (eluent: ethyl acetate/hexane =
ordinary and ordinary refractive indices (ne and no) and of ꢀn
were carried out in uniaxially aligned nematic cells, which
contained an indium tin oxide (ITO) layer and were purchased
from EHC. The cell gaps (d) were 2 or 3 µm. The transmittance
of light under crossed nicol conditions was observed as a
function of wavelength by a microscopic/spectroscopic method
using a Nikon LV100 Pol optical microscope equipped with a
USB4000 (Ocean photonics) spectrometer.
1
1/3, v/v) afforded 1d as a pale brown solid in 77% yield. H
NMR (300 MHz, CDCl3) δ 7.23 (d,
(d, = 8.4 Hz, Arꢁ , 2H), 3.79 (brs, ꢁN
(C 3)3, 9H) ppm.
4ꢀEthynylaniline (1e). Compound 1e was synthesized
according to the method for the deprotection of trimethylsilyl
groups used for the preparation of 1c 1d (5.27 g, 27.8 mmol),
J
= 8.4 Hz, Arꢁ
H, 2H), 6.57
J
H
H
H2, 2H), 0.23 (s, Siꢁ
Synthesis
Chemicals were obtained from TCI, Wako, or Nacalai Tesque
(Japan) and used as received. The synthetic procedures for all
:
K2CO3 (5.77 g, 41.8 mmol), MeOH (30 mL), and THF (30
mL). Yield: 99%. Pale brown solid. 1H NMR (300 MHz,
compounds are described and the synthetic routes are shown in
1
Scheme 1ꢁ3. The characterization data for
1
ꢁ
3
include H NMR
CDCl3) δ 7.30 (d,
Arꢁ , 2H), 3.82 (brs, ꢁN
4ꢀ[2ꢀ(4ꢀBromoꢀ2ꢀfluorophenyl)ethynyl]aniline
J
= 8.4 Hz, Arꢁ
H
, 2H), 6.60 (d,
Cꢁ , 1H) ppm.
(1f).
J = 8.4 Hz,
spectra, as well as highꢁresolution mass spectrometry (HRMS)
data.
H
H2, 2H), 2.96 (s, C
≡ H
Compound 1f was synthesized according to the generic
Sonogashira coupling conditions outlined for the preparation of
Synthesis of 1
1ꢀBromoꢀ4ꢀ(methylthio)benzene (1a). A mixture of 4ꢁ
bromobenzenethiol (7.00 g, 37.0 mmol), iodomethane (MeI;
4.61 mL, 74.0 mmol), K2CO3 (10.2 g, 74.0 mmol), and MeCN
(60 mL) was heated to reflux for 12 h. The reaction mixture
was cooled to room temperature, extracted with ethyl acetate,
washed with water and brine, and dried over MgSO4. After
removing the solvent under reduced pressure, 1a was obtained
1b: 1e (3.26 g, 27.8 mmol), 4ꢁbromoꢁ2ꢁfluoroiodobenzene
(10.0 g, 33.4 mmol), TEA (40 mL), THF (40 mL), Pd(PPh3)4
(0.320 g, 0.280 mmol), and CuI (53.0 mg, 0.280 mmol).
Purification by column chromatography on silica gel (eluent:
ethyl acetate/hexane = 1/3, v/v) afforded 1f as a colorless solid
1
in 77% yield. H NMR (300 MHz, CDCl3) δ 7.35 (d,
J
= 8.1
Hz, Arꢁ
Arꢁ , 2H), 3.87 (brs, ꢁN
2ꢀFluoroꢀ1ꢀ[2ꢀ(4ꢀaminophenyl)ethynyl]ꢀ4ꢀ[2ꢀ(4ꢀthiophen
H, 2H), 7.33ꢁ7.22 (m, Arꢁ
H, 3H), 6.64 (d, J = 8.1 Hz,
as a colorless solid (7.41 g, 99%), which was used without
H
H2, 2H) ppm.
1
further purification. H NMR (400 MHz, CDCl3) δ 7.39 (d,
J =
8.8 Hz, Arꢁ
SꢁC 3, 3H) ppm.
1ꢀMethylthioꢀ4ꢀ[2ꢀ(trimethylsilyl)ethynyl]benzene (1b)
H, 2H), 7.12 (d, J = 8.8 Hz, ArꢁH, 2H), 2.47 (s, Arꢁ
yl)ethynyl]benzene (1g). Compound 1g was synthesized
according to the generic Sonogashira coupling conditions
outlined for the preparation of 1b: 1c (0.34 g 2.27 mmol), 1f
H
(General procedure for Sonogashira coupling)
(0.66 g, 2.27 mmol), TEA (5 mL), THF (5 mL), Pd(PPh3)4
(0.13 g, 0.11 mmol), and CuI (21 mg, 0.11 mmol). Purification
by column chromatography on silica gel (eluent:
chloroform/hexane = 1/2, v/v) afforded 1g as a pale yellow
A mixture of 1a (7.41 g, 36.5 mmol), Pd(PPh3)4 (0.42 g,
0.37 mmol), CuI (70.0 mg, 0.37 mmol), trimethylsilylacetylene
(TMSA; 7.6 mL, 54.7 mmol), triethylamine (TEA; 40 mL), and
tetrahydrofuran (THF; 40 mL; degassed by argon sparging) was
stirred at 45 °C for 24 h. After cooling to room temperature, the
reaction mixture was filtered, extracted with ethyl acetate,
washed with aqueous HCl (2 M) and brine, and dried over
MgSO4. After evaporating the solvent, the residue was purified
by column chromatography on silica gel (eluent: ethyl
acetate/hexane = 1/10, v/v) to afford a pale brown oil (7.58 g,
1
solid in 27% yield. H NMR (300 MHz, CDCl3) δ 7.46ꢁ40 (m,
Arꢁ
4H), 6.65 (d,
(s, ꢁC 3, 3H) ppm.
2ꢀFluoroꢀ1ꢀ[2ꢀ(4ꢀisothiocyanatophenyl)ethynyl]ꢀ4ꢀ[2ꢀ(4ꢀ
H
, 3H), 7.36 (d,
J
= 8.4 Hz, Arꢁ
H
, 2H), 7.25ꢁ7.17 (m, Arꢁ
H,
J
= 8.1 Hz, Arꢁ
H
, 2H), 3.86 (brs, ꢁN
H2, 2H), 2.50
H
methylthiophenyl)ethynyl] benzene (1). A mixture of 1g
(0.650 g, 1.82 mmol), CaCO3 (0.360 g, 3.64 mmol),
dichloromethane (25 mL), and water (10 mL) was cooled to 0
°C. Then, thiophosgen (0.19 mL, 2.52 mmol) was added
94%). 1H NMR (400 MHz, CDCl3) δ 7.37 (d,
J = 8.8 Hz, ArꢁH,
2 | J. Name., 2012, 00, 1-3
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dropwise, and the resulting mixture was stirred for 12 h at room ArꢁH, 2H), 3.30 (s, C≡CꢁH, 1H) ppm.
temperature. Subsequently, the mixture was extracted with
CHCl3, washed with water and brine, and dried over MgSO4. 4ꢀ[2ꢀ(4ꢀBromoꢀ2ꢀfluorophenyl)ethynyl]benzonitrile (2c)
After removing all volatiles, the residue was purified by column Compound 2c was synthesized according to the general Sonogashira
chromatography on silica gel (eluent: chloroform/hexane = 1/2, coupling conditions used for the preparation of 1b: 4ꢁ
v/v). The residue was recrystallized from CHCl3 and hexane to ethynylbenzonitrile (0.900 g, 7.08 mmol), 4ꢁbromoꢁ2ꢁ
1
afford the target compound as a pale brown solid in 77%. H fluoroiodobenzene (2.55 g, 8.49 mmol), TEA (15 mL), THF (15
NMR (300 MHz, CDCl3) δ 7.55 (d,
7.51ꢁ7.41 (m, Arꢁ , 3H), 7.30 (d, = 8.4 Hz, Arꢁ
(d, = 8.4 Hz, Arꢁ , 4H), 2.53 (s, ꢁC
3, 3H) ppm. HRMSꢁ CHCl3/hexane = 1/3, v/v); yield: 86%; colorless solid. 1H NMR (300
FAB+ (m/z): [M]+ calcd. for C24H14FNS2, 399.0552; found, MHz, CDCl3) δ 7.66 (d, J = 8.7 Hz, ArꢁH, 2H), 7.62 (d, J = 8.7 Hz,
J
= 8.4 Hz, Arꢁ
H, 2H), mL), Pd(PPh3)4 (0.245 g, 0.212 mmol), and CuI (40.4 mg, 0.212
H
J
H, 2H), 7.24 mmol); purification by column chromatography on silica gel (eluent:
J
H
H
399.0556.
ArꢁH, 2H), 7.42ꢁ7.29 (m, ArꢁH, 3H) ppm, 13C NMR (300 MHz) δ
86.4, 94.0 (d, J = 3.7 Hz), 110.5, 110.7, 112.5, 118.8, 119.8, 120.1,
124.1 (d, J = 9.0 Hz), 127.8, 128.1 (d, J = 3.7 Hz), 132.5 (d, J = 3.0
Hz), 132.5 (d, J = 3.0 Hz), 134.6 (d, J = 1.5 Hz), 161.1, 164.5 ppm.
MeI / K2CO3
Acetonitrile
SMe
SH
SMe
TMSA / Pd(PPh3)4 / CuI
TEA /THF
Br
Br
TMS
1a
1b
1c
K2CO3
SMe
2ꢀFluoroꢀ1ꢀ[2ꢀ(4ꢀcyanophenyl)ethynyl]ꢀ4ꢀ[2ꢀ(4ꢀ
methylthiophenyl)ethynyl] benzene (2)
THF / MeOH
Compound 2 was synthesized according to the general Sonogashira
coupling conditions used for the preparation of 1b: 2c (0.100 g,
0.330 mmol), 1c (53.0 mg, 0.360 mmol), TEA (5 mL), THF (5 mL),
Pd(PPh3)4 (19.0 mg, 17.0 ꢂmol), and CuI (3.10 mg, 17.0 ꢂmol);
purification by column chromatography on silica gel (eluent:
CHCl3/hexane = 1/2, v/v), followed by recrystallisation from
CHCl3/hexane; yield: 82%; colorless solid; 1H NMR (400 MHz,
CDCl3) δ 7.66 (d, J = 8.4 Hz, ArꢁH, 2H), 7.63 (d, J = 8.8 Hz, ArꢁH,
2H), 7.48 (S, ArꢁH, 1H), 7.44 (d, J = 8.8 Hz, ArꢁH, 2H), 7.30 (d, J =
9.6 Hz, ArꢁH, 1H), 7.29 (d, J = 9.6 Hz, ArꢁH, 1H), 7.22 (d, J = 8.4
Hz, ArꢁH, 2H), 2.51 (s, ꢁCH3, 3H) ppm. HRMSꢁFAB+ (m/z): [M]+
calcd. for C24H14FNS, 367.0831; found, 367.0822.
NH2
K2CO3
NH2
NH2
TMSA / Pd(PPh3)/ CuI
TEA /THF
THF / MeOH
Br
TMS
1d
1e
NH2
F
I
/ Pd(PPh3)4 / CuI
F
Br
TEA /THF
Br
1f
NH2
F
1c / Pd(PPh3)4 / CuI
TEA /THF
1g
MeS
NCS
F
Thiophosgene / CaCO3
CH2Cl2 / H2O
1
MeS
Scheme 1. Synthetic route to 1.
Synthesis of 2
1ꢀCyanoꢀ4ꢀ[2ꢀ(trimethylsilyl)ethynyl]benzene (2a)
Compound 2a was synthesized according to the general Sonogashira
coupling conditions outlined for the preparation of 1b: 4ꢁ
bromobenzonitrile (5.00 g, 27.5 mmol), trimethylsilylacetylene (5.70
mL, 41.2 mmol), TEA (20 mL), THF (20 mL), Pd(PPh3)4 (0.320 g,
0.275 mmol), and CuI (52.3 mg, 0.275 mmol); purification by
column chromatography on silica gel (eluent: CHCl3/hexane = 1/6,
v/v); yield: >99%; pale yellow solid. H NMR (300 MHz, CDCl3) δ
7.59 (d, J = 8.4 Hz, ArꢁH, 2H), 7.53 (d, J = 8.4 Hz, ArꢁH, 2H), 3.07
(s, C≡CꢁH, 1H), 0.28 (s, Siꢁ(CH3)3, 9H) ppm.
Scheme 2. Synthetic route to 2.
Synthesis of 3
1,4ꢀBis[4ꢀ(methylsulfanyl)phenyl]ethynylꢀ2ꢀfluorobenzene (3)
Compound 3 was synthesized according to the general Sonogashira
coupling conditions outlined for the preparation of 1b: 1c (0.74
mmol, 0.11 g), 1ꢁbromoꢁ3ꢁfluoroꢁ4ꢁiodobenzene (0.37 mmol, 0.11
g), Pd(PPh3)4 (37 µmol, 43 mg), CuI (37 µmol, 43 mg), TEA (5 mL),
and THF (5 mL); purification by column chromatography on silica
gel (eluent: CHCl3/hexane = 1/2, v/v), followed by recrystallisation
1
1ꢀCyanoꢀ4ꢀethynylbenzene (2b)
Compound 2b was synthesized according to the general method for
the deprotection of trimethylsilyl groups used for the preparation of
1c: 2a (5.48 g, 27.5 mmol), K2CO3 (11.4 g, 82.5 mmol), MeOH (40
1
from CHCl3/hexane; colorless solid (75.3 mg, 52%). H NMR (400
MHz, CDCl3) δ 7.49ꢁ7.42 (m, ArꢁH, 5H), 7.25ꢁ7.20 (m, ArꢁH, 6H),
2.51 (s, ꢁCH3, 6H) ppm. HRMSꢁFAB+ (m/z): [M]+ calcd. for
C24H17FNS2, 388.0756; found, 388.0746.
1
mL), and THF (40 mL); yield: 54%; colorless solid. H NMR (300
MHz, CDCl3) δ 7.62 (d, J = 8.4 Hz, ArꢁH, 2H), 7.57 (d, J = 8.4 Hz,
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0.8
0.6
0.4
0.2
Scheme 3. Synthetic route to 3.
Results and discussion
The phase transition temperatures for
1
ꢁ
3
, determined by
0
differential scanning calorimetry (DSC) and polarized optical
microscopy (POM) are summarized in Table 1, and the
corresponding DSC curves are shown in Fig. S1ꢁS3. As shown
300
350
400
450
Wavelength (nm)
Fig. 2. UV-vis spectra for
1 (red line), 2 (green line), and 3 (blue line) in DCM.
in Table 1, 1ꢁ3 exhibit solely enantiotropic nematic (N) phases
without further higherꢁordered smectic phases; the marble and
schlieren textures indicative of N phases are shown in Fig. S4ꢁ
S6. Here, it is important to note that asymmetrically substituted
Birefringence measurements
Subsequently, we evaluated the optical properties of
For that purpose, we measured the extraordinary ( e) and
ordinary refractive indices o), and calculated the
corresponding ꢀ values (ꢀ o) from target material
mediums, following a previously reported method.‡ For
measurements were conducted up to = 250 °C, as POM
measurements showed signs of decomposition beyond this
temperature, most likely on account of its high i. The
representative transmittance spectra for are shown in Fig. S7
and S8. The temperature dependence of the obtained refractive
index and ꢀ values at 550 nm are shown in Fig. 3, where TIN
and represent the transition temperatures from the isotropic
liquid to the N phase and the temperature measured upon
cooling, respectively. Fig. 3(a) shows that exhibited, on
1ꢁ3.
1
and
Relative to the corresponding hexylsulfanylꢁderivative,
a wider mesophase.7 The melting temperatures (
m), indicating
the transition from the crystal to the N phase, of (149.9 °C)
and (179.0 °C) are considerably lower than that of (203.8
°C). Conversely, the clearing temperatures ( i) for and are
higher than that for , indicating a considerable expansion of
the mesophases. Thus, during the heating scans, N phases were
observed in the following order: 140.1°C ( ) > 104.4°C ( ) >
46.3°C ( ).
2
exhibit significantly wider N phases than symmetric
3.
n
3
shows
(
n
T
n
n = ne – n
9,10
1
1
,
2
3
T
T
1
2
3
T
1
1
2
3
n
T
Table 1. DSC-derived phase-transition temperatures (°C) and enthalpy changes (ΔH in
kJ mol-1
obtained from heating (upper line) and cooling (lower line) scans; DSC
temperature gradient: 10 °C min-1
)
1ꢁ3
.
account of their highly anisotropic structures, their highly
polarizable substituents, and their short alkyl chains, extremely
Compd.
1
Cr-N/°C (ΔH)
N-Iso/°C (ΔH)
N range/°C
high refractive index values (
for e > 2.3) is particularly interesting, as it is close to that of
diamond. From a comparison of the temperature dependence of
ne > 2.1). The corresponding value
149.9 (18.1)
139.7 (17.5)
179.0 (26.9)
151.7 (25.3)
203.8 (35.5)
290.0a
140.1
144.3
104.4
132.6
46.3
1 (n
284.0a
the
and
slightly higher than that of
n
e and no values at
T
INꢁ
T
, it is apparent that the ne values of
, whereby the value of is
. In addition, the o values of and
, which explains the higher mean
>) of the former compounds with respect to
> values for (1.84) and (1.84) are
2
3
284.3 (1.6)
283.4 (1.3)
250.1 (1.3)
1
2
are higher than that of
3
1
2
n
1
2
are also higher than that of 3
refractive index (<
the latter. The <
n
n
192.8 (35.5)
246.4 (1.3)
53.5
1
2
a Observed by POM.
comparable, and relatively high (Table 2). Fig. 3(b) illustrates
the extremely high ꢀ values (>0.6) obtained for these
compounds, which are a consequence of their high ne values.
Notably, reaches a maximum (ꢀ = 0.77) at the lowest
measurement temperature (Table 2), which is, to the best of our
knowledge, the highest ꢀ value so far obtained from a single
n
UV-vis absorption
The UVꢁvis spectra for
1,
2
, and
3
were measured in
1
n
dichloromethane (DCM) and are shown in Fig.2. For
the longest absorption edges are < 400 nm, while that of
400 nm. These results indicate that are suitable mesogenic
units for optical applications, given that they exhibit low
absorption in the visible wavelength region.
1 and 3,
2
is
n
~
1ꢁ3
component system, excluding extrapolated values from roomꢁ
temperature nematic mixtures. This result demonstrates the
success of the present design strategy, which is based on a
combination of conjugation, asymmetry, and highly polarizable
substituents.
In the highꢁtemperature region
temperature dependence of ꢀ for and
However, with increasing INꢁ , the ꢀ
and , despite the fact that the molecular polarizability
(
2
T
INꢁ
is similar to that of
of surpasses those of
T < 30°C), the
n
1
3.
T
T
n
3
1
2
anisotropy follows the order NCS > CN > SCH3. This result
4 | J. Name., 2012, 00, 1-3
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implies that the ꢀ
at a higher rate than those of
n
of
3
increases with decreasing temperature
and , which could be due to the
enhanced S···S interactions of the two SCH3 (or SR)
substituents in vide infra).
The waveꢁlength dependences of the ꢀ
2.3
2.2
2.1
2
1.9
1.8
1.7
1.6
1.5
1.4
1.3
(a)
1
2
3
(
n
values at each
representative temperature are shown in Fig.S9ꢁ11, showing
positive dispersion in analogy with those for typical rodꢁlike
molecules. We compared the ne
compounds at 550 nm and 700 nm (Fig. 4). A comparison of
Fig. 3 and Fig. 4 shows that the ne o, and ꢀ values at 770 nm
are lower than those at 550 nm, due to the positive dispersion of
refractive indices for . Their temperature dependence at 700
nm exhibits a similar trend as that at 550 nm. For , the
degree of wavelength dispersion, i.e., the ꢀ ratios at 550 nm
and 700 nm (ꢀ (550 nm)/ꢀ (700 nm)), are ~ 1.2. The
, no, and ꢀn values for all
,
n
n
1
ꢁ
3
0
20
40
60
80 100 120 140
1ꢁ3
TINꢀT (oC)
n
n
n
0.70
0.60
0.50
0.40
0.30
(b)
comparable UVꢁvis absorptions (Fig. 2.) suggest that the waveꢁ
length dependence of the refractive indices should not be
affected substantially.
2.4
(a)
2.3
ne
2.2
2.1
2
1.9
1.8
0
20 40 60 80 100 120 140
TINꢀT (oC)
1.7
no
1.6
1.5
Fig. 4. Temperature dependence of (a) ne and no, as well as (b) Δn values at 700 nm for
1 (red circles), 2 (red squares), and 3 (green triangles).
0
20 40 60 80 100 120 140
Table 2. Refractive index and birefringence values for 1-3 at the lowest measurement
TINꢀT (°C)
temperature.
Compd.
1
ne
no
<n>a
Δn
0.80
0.70
0.60
0.50
0.40
0.30
(b)
2.35
1.59
1.84
0.77
2
3
2.30
2.19
1.61
1.58
1.84
1.78
0.69
0.61
a <n> = (ne + 2 no)/3
WAXD measurements for the evaluation of the order parameters
Here, the temperature dependence of ꢀ is empirically
described by the following equation: ꢀ
(1ꢁ 0 refers to ꢀ for the perfectly oriented state, i.e.,
i)β; ꢀ
= 1, while
temperature, respectively;
nematic materials.11 Accordingly, ꢀ
order parameter . Considering the aforementioned temperature
dependence of ꢀ for each compound, we speculated that the
determining factor may be the order parameters of . To
examine the correlation between the order parameter and ꢀ
we estimated the temperature dependence of by detailed XRD
n
ꢀ
n
=
S
n0, wherein
S
=
S
T
/
T
n
n
0
20 40 60 80 100 120 140
TINꢀT (°C)
T
and Ti represent measurement and clearing
is a constant characteristic for
is proportional to the
β
Fig. 3. Temperature dependence of (a) ne and no, as well as (b) Δn values at 550 nm for
1 (red circles), 2 (red squares), and 3 (green triangles).
n
S
n
1ꢁ3
n
,
S
measurements using specimens aligned through an external
magnetic field, which is described in detail elsewhere.12 The
obtained 2DꢁXRD patterns are shown in Fig. S12ꢁS14 (ESI).
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The temperature dependence of
S, using this wideꢁangle Xꢁray levels of S···S interactions relative to 1 and 2 with asymmetric
diffraction technique (WAXD), is shown in Fig. 5. The results substitution patterns including one SR group. This led to the
demonstrate that these materials exhibit highꢁorder parameters highest ꢀ value for close to INꢁ . Given their extremely
= ~ 0.5) during the isotropic to nematic transition, and high refractive index, these materials should find applications
n
3
T
T
(
S
S >
0.7 near the crystallization temperature. These values are in various optical materials.
considerably higher than those for conventional rodꢁlike LC
molecules (
anisotropic structures of
anisotropic interactions. The wide mesophase of
induces a particularly high value (0.75). Conversely, a
comparison of the temperature dependence suggests that with
decreasing temperature, the value for is much higher than
those of and , which means that this parameter is strongly
influenced by temperature. Previously, we have reported that
the optical properties of LC molecules with alkylsulfanyl
groups exhibit a high temperature dependence as a consequence
of the S···S interactions. Since the present results are consistent
with this trend, and due to the S···S interactions between the
S
= ~0.3ꢁ0.6).13 This is most likely due to the highly
, which leads to higher degrees of
(140 °C)
Notes and references
1ꢁ3
1
‡
As we could not observe clear transmittance spectra, ne values for 3 were
estimated from ne = Δn – no. In this case, the temperature dependence of Δn was
S
evaluated according to a previously described method; see: ref. 6(a).
1
2
(a) J. W. Goodby, Liq. Cryst., 2011, 38, 1363; (b) P. Kirsh and
M. Bremer, Angew. Chem. Int. Ed., 2000, 39, 4216; (c) M.
Mitov, Adv. Mater., 2012, 24, 6260; (d) R. Dąbrowski, P. Kula
S
3
1
2
and J. Herman, Crystals, 2013, 3, 443.
(a) D. J. Broer, J. Lub and G. N. Mol, Nature, 1995, 378, 467;
(b) J. Hwang, M. H. Song, B. Park, S. Nishimura, T. Toyooka, J.
W. Wu, Y. Takanishi, K. Ishikawa and H. Takezoe, Nature
Mat., 2005, 4, 383; (c) M. Funahashi and N. Tamaoki, Mol.
Cryst. Liq. Cryst., 2007, 475, 123; (d) M. G. Chee, M. H. Song,
D. Kim, H. Takezoe and I. J. Chung, Jpn. J. Appl. Phys., 2007,
46, L437; (e) M. Itoh, M. Tokita, H. Hegi, T. Hayakawa, S.
Kang and J. Watanabe, J. Mater. Chem., 2011, 21, 1697; (f) X.
Chen, L. Wang, Y. Chen, C. Li, G. Hou, X. Liu, X. Zhang, W. He
and H. Yang, Chem. Commun., 2014, 50, 691; M. Uchimura, Y.
Watanabe, F. Araoka, J. Watanabe, H. Takezoe and G.
Konishi, Adv. Mater., 2010, 22, 4473.
two symmetric SCH3 substituents, the ꢀ
higher than those for and in the low temperature region (e.g.
INꢁ = 30 °C). This result demonstrates that two symmetric
n values for 3 should be
1
2
T
T
SCH3 or SR substituents are able to induce higher levels of
S···S interactions relative to an asymmetric substitution pattern
with one SCH3 or SR substituent. This may lead to a higher ꢀ
at similar INꢁ , even though exhibited in the present case, on
account of its narrower mesophase, a lower maximum ꢀ
n
3
(a) K. Okano, O. Tsutsumi, A. Shishido and T. Ikeda, J. Am.
Chem. Soc., 2006, 128, 15368; (b) K. Okano, A. Shishido, O.
T
T
3
n
Tsutsumi, T. Shiono and T. Ikeda, J. Mater. Chem., 2005, 15
,
compared to
1
and 2.
3395; (c) K. Okano, A. Shishido and T. Ikeda, Adv. Mater.,
2006, 18, 523; (d) A. Shishido, Polym. J., 2010, 42, 525; (e) N.
Kawatsuki, H. Matsushita, T. Washio, J. Kozuki, M. Kondo, T.
Sasaki and H. Ono, Macromolecules, 2014, 47, 324.
0.8
0.7
0.6
0.5
0.4
4
5
(a) H. R. Stapert, S. del Valle, E. J. K. Verstegen, B. M. I. van
der Zande, J. Lub and S. Stallinga, Adv. Func. Mater., 2003,
13, 732; (b) P. Valley, D. L. Mathine, M. R. Dodge, J.
Schwiegerling, G. Peyman and N. Peyghambarian, Opt. Lett.,
2010, 35, 336; (c) P. Valley, M. R. Dodge, J. Schwiegerling, G.
Peyman and N. Peyghambarian, Opt. Lett., 2010, 35, 2582.
(a) D. Węgłowska, P. Kula and J. Herman, RSC Adv., 2016, 6,
403; (b) S. Gauza, C.-H. Wen, S.-T. Wu, N. Janarthanan and
C.-S. Hsu, Jpn. J. Appl. Phys., 2004, 43, 7634; (c) C. Sekine, M.
Ishitobi, K. Iwakura, M. Minai and K. Fujisawa, Liq. Cryst.,
2002, 29, 355; (d) X.-L. Guan, L.-Y. Zhang, Z.-L. Zhang, Z. Shen,
0
25
50
75 100 125 150
TINꢀT (°C)
X.-F. Chen, X.-H. Fan and Q.-F. Zhou, Tetrahedron, 2009, 65
3728; (e) Z. Zhang, L. Zhang, X. Guan, Z. Shen, X. Chen, G.
Xing, X. Fan and Q. Zhou, Liq. Cryst., 2010, 37, 69.
,
Fig. 5. Temperature dependence of the estimated order parameter (S) for 1 (red
circles), 2 (blue squares), and 3 (green triangles).
6
(a) Y. Arakawa, S. Nakajima, R. Ishige, M. Uchimura, S. Kang,
G. Konishi and J. Watanabe, J. Mater. Chem., 2012, 22, 8394;
(b) S.-T. Wu, U. Finkenzeller and V. Reiffenrath, J. Appl. Phys.,
1989, 65, 4372; (c) S.-T. Wu, C.-S. Hsu, and K.-F. Shyu, Appl.
Phys. Lett., 1999, 74, 344; (d) A. Spadło, R. Dąbrowski, M.
Filipowicz, Z. Stolarz, J. Przedmojski, S. Gauza, C. Y. H. Fan
and S.-T. Wu, Liq. Cryst., 2003, 30, 191; (e) M. Hird, A. J.
Seed, K. J. Toyne, J. W. Goodby, G. W. Gray and D. G.
Conclusions
In summary, we presented the design and synthesis of three
bistolaneꢁbased molecules with alkylsulfanyl groups (1ꢁ3).
These materials exhibit wellꢁdefined enantiotropic nematic
phases in the absence of any smectic phases. Owing to their
McDonnell, J. Mater. Chem., 1993,
Wang, Z.-C. Miao, S.-K. Jin and H. Yang, Liq. Cryst., 2012, 39
3, 851; (f) Y.-M. Zhang, D.
,
asymmetric structure, the transition temperatures of
significantly lower, and their nematic ranges are broader than
those of symmetric . With respect to optical properties, it is
noteworthy that exhibit extremely high refractive indices
and ꢀ values in their mesophases (e.g. and e > 2.3; < > =
~ 1.9). At the lowest measurement temperature, showed an
extremely high birefringence (ꢀ 0.77). Moreover,
1 and 2 are
1330; (g) C. Sekine, N. Konya, M. Minai and K. Fujisawa, Liq.
Cryst., 2001, 28, 1361; (h) O. Catanescu and L.-C. Chien, Liq.
Cryst., 2006, 33, 115; (i) P. Kula, J. Herman, S. Pluczyk, P.
Harmata, G. Mangelinckx and J. Beeckman, Liq. Cryst., 2014,
41, 503; (j) D. V. Sai, P. Sathyanarayana, V. S. S. Sastry, J.
Herman, P. Kula, R. Dabrowski and S. Dhara, Liq. Cryst., 2014,
41, 591; (k) Y. Arakawa, S. Kang, S. Nakajima, K. Sakajiri, Y.
Cho, S. Kawauchi, J. Watanabe and G. Konishi, J. Mater.
3
1ꢁ3
n
1
2
:
n
n
1
n
=
3
exhibited, due to the presence of two SR substituents, increased
6 | J. Name., 2012, 00, 1-3
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Chem. C, 2013, 1, 8094; (l) Y. Arakawa, S. Nakajima, S. Kang,
M. Shigeta, G. Konishi and J. Watanabe, J. Mater. Chem.,
2012, 22, 13908; (m) Y. Arakawa, S. Nakajima, S. Kang, M.
Shigeta, G. Konishi and J. Watanabe, Liq. Cryst., 2012, 39
,
1063; (n) Y. Arakawa, S. Kang, J. Watanabe and G. Konishi,
Chem. Lett., 2014, 43, 1858; (o) Y. Arakawa, H. Kuwahara, K.
Sakajiri, S. Kang, M. Tokita and G. Konishi, Liq. Cryst., 2015,
42, 1419; (p) Y. Arakawa, S. Kang, J. Watanabe and G. Konishi,
Phase Transit., 2015, 88, 1188; (q) E.-W. Lee, M. Hattori, F.
Uehara, M. Tokita, S. Kawauchi, J. Watanabe and S. Kang, J.
Mater. Chem. C, 2015, 3, 2266; (r) Y.-Z. Zhao, D. Wang, Z.-M.
He, G. Chen, L.-Y. Zhang, H.-Q. Zhang and H. Yang, Chinese
Chem. Lett., 2015, 26, 785; (s) Y. Arakawa, S. Nakajima, S.
Kang, G. Konishi and J. Watanabe, J. Mater. Chem., 2012, 22
14346.
,
7
8
Y. Arakawa, S. Kang, H. Tsuji, J. Watanabe and G. Konishi, RSC
Adv., 2016, , 16568.
(a) A. J. Seed, K. J. Toyne, J. W. Goodby and D. G. McDonnell,
J. Mater. Chem., 1995, , 1; (b) A. J. Seed, K. J. Toyne and J.
W. Goodby, J. Mater. Chem., 1995, , 2201; (c) G. J. Cross, A.
6
5
5
J. Seed, K. J. Toyne, J. W. Goodby, M. Hird and M. C. Artal, J.
Mater. Chem., 2000, 10, 1555; (d) A. J. Seed, K. J. Toyne, M.
Hird and J. W. Goodby, Liq. Cryst., 2012, 39, 403; (e) A. J.
Seed, K. Pantalone, U. M. Sharma and A. M. Grubb, Liq.
Cryst., 2009, 36, 329; (f) Y. Arakawa, S. Kang, J. Watanabe
and G. Konishi, RSC Adv., 2015,
Kula and J. Herman, RSC Adv., 2016,
5
, 8056; (g) D. Węgłowska, P.
, 403.
6
9
(a) R. Chang, Mol. Cryst. Liq. Cryst., 1974, 28, 1; (b) E. Hecht,
Optics, Addison-Wesley, Boston, 4th edn, 2002, pp. 416–425.
10 (a) S. Kang, S. Nakajima, Y. Arakawa, G. Konishi and J.
Watanabe, J. Mater. Chem. C, 2013, , 4222; (b) Y. Arakawa,
1
S. Kang, S. Nakajima, K. Sakajiri, S. Kawauchi, J. Watanabe
and G. Konishi, Liq. Cryst., 2014, 41, 642.
11 I. Haller, Prog. Solid State Chem. 1975, 10, 103.
12 (a) Handbook of Liquid Crystals, WILEY-VCH Verlag GmbH &
Co. KGaA, 2014,
Arakawa, M. Tokita, J. Watanabe and G. Konishi, Polym.
Chem., 2014, , 2253; (c) K. Fu, M. Sone, M. Tokita and J.
1, pp. 317-318; (b) S. Kang, S. Nakajima, Y.
5
Watanabe, Polym. J., 2006, 38, 442.
13 (a) I. Dierking, Textures of Liquid Crystals, WILEY-VCH Verlag
GmbH & Co. KGaA, 2003; (b) D. H. Chen and G. R. Luckhurst,
Trans. Faraday Soc., 1969, 65, 656.
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We designed a liquid-crystalline bistolane with alkylsulfanyl and
isothiocyanate groups that exhibited an extremely high birefringence (0.77
at 550 nm).

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