Fluorocarbon and hydrocarbon N-heterocyclic (C5-C7) difluorooxymethylene-bridged liquid crystals

Article abstract of DOI:10.1002/ejoc.201301067

A series of new fluorocarbon and hydrocarbon N-heterocyclic (C ₅-C₇) difluorooxymethylene-bridged liquid crystals have been prepared. The impact of ring (C₅-C₇) as end group was investigated. Compounds with term

Full text of DOI:10.1002/ejoc.201301067

FULL PAPER
DOI: 10.1002/ejoc.201301067
Fluorocarbon and Hydrocarbon N-Heterocyclic (C5–C7) Difluorooxymethylene-
Bridged Liquid Crystals
Hongren Chen,*[a] Peilian Liu,[a] Huijuan Li,[a] Hong Zhang,[a] Stelck Daniel,[b] and
Zhuo Zeng[a,c]
Keywords: Fluorine / Heterocycles / Liquid crystals / Mesophases / Phase transitions
A series of new fluorocarbon and hydrocarbon N-hetero-
cyclic (C5–C7) difluorooxymethylene-bridged liquid crystals
have been prepared. The impact of ring (C5–C7) as end group
was investigated. Compounds with terminal N-heterocyclic
5- or 6-membered rings such as 3,4-difluoropyrrole, pyrrol-
idine, or pyridine, exhibited nematic phases (N). Whereas the
terminal 3,3,4,4-tetrafluoropyrrolidine and 3,3,4,4,5,5-hexa-
cation of the ring size with different length alkyl groups and
variation of the chains from alkyl to polyfluoroalkyl markedly
changed the properties of these compounds. It is possible
that these N-heterocycles (C5–C7) could replace fluorobenz-
ene as terminal groups to form valuable difluorooxymeth-
ylene-bridged liquid crystals. Compounds with 3,4-di-
fluoropyrrole as terminal group showed strongly positive di-
electric anisotropy (Δε), moderate birefringence (Δn), and
relatively low viscosity (γ1), thus meeting the criterion for
high-performance liquid-crystalline materials.
fluoropiperidine derivatives exhibited smectic
C and B
phases; the mesomorphic behavior weakened with increas-
ing ring size. These new compounds also exhibited promis-
ing physicochemical and electro-optical properties. Modifi-
Introduction
Thin-film transistor (TFT) type liquid crystal devices
have been developed and commercialized in recent years as
a result of its outstanding features. Advantages of the AM-
LCDs driven by TFTs include low power consumption,
light weight, flicker-free image, thin profile, low-voltage op-
eration, and large dynamic range of screen luminance.[1] Re-
duction of driving voltage and response time is the most
important aim for the TFT driving mode, and developing
compounds with an high dielectric anisotropy (Δε) is one
of the common approaches to reduce driving voltage.[2] The
insertion of a difluorooxymethylene bridge into the liquid
crystalline compounds increases dielectric anisotropy with-
out increasing viscosity.[3] The resultant highly dielectric an-
isotropy and low viscosity of compounds with a difluoro-
oxymethylene bridge make them promising candidates for
the development of new liquid crystalline materials. Some
of these commercial liquid crystal molecules are shown in
Scheme 1.[2–5]
Scheme 1. Typical difluorooxymethylene-bridged molecules.
In designing new liquid crystals, an alternative method
to increase the polarity and Δε value has been the introduc-
tion of a polar ring into the liquid crystalline core struc-
ture.[6] Over the years, a large number of LC compounds
containing heterocyclic units have been synthesized. For ex-
ample, molecules containing a heterocyclic ring incorporat-
ing trans-1,3-dioxane or 1,3,2-dioxaborinane, 1,3,4-oxadi-
azole or a benzofuran group exhibit promising physico-
chemical and electro-optical properties and can be used as
components of nematic liquid crystalline materials
(LCMs).[7] Mesogenic N-heterocyclic derivatives have been
extensively investigated both within our own research
group[8] and by others.[9] Thus, a promising approach to
the design of novel thermotropic liquid crystals (TLCs) for
applications in advanced functional materials involves the
introduction of a polar ring into the liquid crystalline core.
Such structures should prove to be highly valuable for fur-
ther investigation because: (a) These compounds have a
[a] College of Chemistry & Environment, South China Normal
University,
Guangzhou 510006, China
E-mail: zhuoz@scnu.edu.cn
http://sce.scnu.edu.cn/department/50.html
[b] Department of Chemistry, University of Idaho,
Moscow, ID 83844-2343, USA
[c] Department Key Laboratory of Organofluorine Chemistry,
Shanghai Institute of Organic Chemistry, Chinese Academy of
Sciences,
Shanghai, 200032, China
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201301067.
Eur. J. Org. Chem. 2013, 7517–7527
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
7517

H. Chen, P. Liu, H. Li, H. Zhang, S. Daniel, Z. Zeng
FULL PAPER
large dielectric constant that gives the liquid crystal the ap-
propriate dipole moment, as well as good thermal stability
and electron transport properties.[10] (b) The introduction
of heterocyclic moieties into the rigid unit of thermotropic
liquid crystals is of great importance due to their ability to
impart lateral and/or longitudinal dipoles in addition to the
accompanied changes in their molecular geometry.[9c,11]
(c) In particular, fluorinated N-heterocyclic liquid crystals
have strong electron-withdrawing properties that impart
novel characteristics to the materials.[8b] (d) Further novel,
potentially valuable liquid crystals may be derived from
these heterocycles by varying the size of the ring or substit-
uents on the ring. Studies on N-heterocycle-based liquid
crystals having a difluoromethyleneoxy moiety as a linker
chain, however, have been relatively scarce. Because some
liquid crystals derived from O-heterocycles exhibit relatively
high viscosity,[4] we hope these new molecules will combine
the advantages of both the N-heterocycle and difluoro-
methyleneoxy groups, which have displayed high absolute
values of dielectric anisotropy, improved solubility, broad
nematic phase range, and a favorable ratio of viscosity.
Herein, we report the design and synthesis of novel ther-
motropic fluorocarbon and hydrocarbon N-heterocyclic li-
quid crystals with a difluoromethyleneoxy moiety as a link-
age group for applications in advanced functional materials;
the approach involves the selection of a suitable central
core, linking group, and terminal functionality.
Results and Discussion
Synthesis
Novel liquid crystals 3CCA5H–3CCA7H, 5CCA5H–
5CCA7H and their fluorinated derivatives 3CCA5F–
3CCA7F, 5CCA5F–5CCA7F, 3CCA5–2F, and 5CCA5–2F
were synthesized as shown in Schemes 2, 3, 4, 5, and 6.
Details of the synthesis and characterization of the materi-
als are given in the experimental section.
Our efforts were directed towards the development of N-
heterocyclic compounds as potential bioactive molecules as
Scheme 2. Synthesis of trifluoromethanesulfonic acid alkyldiyl and
polyfluoroalkyldiyl esters.
Scheme 3. Synthesis of 4-{difluoro[(trans,trans)-4Ј-alkyl(1,1Ј-bicyclohexyl)-4-yl]methoxy}benzenamines 3CCANH2 and 3CCANH2.
7518 Eur. J. Org. Chem. 2013, 7517–7527
www.eurjoc.org
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Difluorooxymethylene-Bridged Liquid Crystals
well as functional materials. Trifluoromethanesulfonic acid toxic, corrosive, give low yields, and are difficult to purify
alkyldiyl (1h–3h) and polyfluoroalkyldiyl esters 1f–3f were due to the presence of intermediate species preceding for-
prepared by our group earlier by using the combination of mation of the target compound.[14,16] In this article, the in-
trifluoromethanesulfonic acid and alkyl diol (1a–3a) or termediates 3CCANO2 and 5CCANO2, having the di-
polyfluoroalkyl diol (1b–3b), respectively (Scheme 2).[8]
fluoromethyleneoxy moiety as a linkage group were synthe-
A variety of synthetic methods for the preparation the sized by oxidative fluorodesulfuration as described by Kirch
difluoromethyleneoxy moiety have been presented in pre- et al.[17] These nitro compounds can be reduced by Zn and
vious reports.[12] Two methods have been developed for the NH4Cl in CH3OH/THF solution to give 3CCANH2 or
introduction of a difluoromethyleneoxy moiety. The first is 5CCANH2 in ca. 93% yield (Scheme 3).
[13]
the use of fluorinating agents, such as SF4 or DAST;[14]
Trifluoromethanesulfonic alkyldiyl and fluoroalkyldiyl
the second is the indirect introduction by oxidative fluoro- esters 1f and 1h, were treated with arylamines (3CCANH2
desulfuration.[15] The fluorinating reagents, SF4 and DAST or 5CCANH2) in the presence of Et3N in CH3CH2OH to
have the drawbacks of usually being extremely reactive and give the five-membered heterocyclic compounds 3CCA5F
Scheme 4. Synthesis of N-heterocyclic (C5) liquid crystals.
Scheme 5. Synthesis of N-heterocyclic (C6) liquid crystals.
Eur. J. Org. Chem. 2013, 7517–7527
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
7519

H. Chen, P. Liu, H. Li, H. Zhang, S. Daniel, Z. Zeng
FULL PAPER
Scheme 6. Synthesis of N-heterocyclic (C7) compounds.
or 5CCA5F, and 3CCA5H or 5CCA5H (Scheme 4). Subse- similar conditions to those described above, as depicted in
quent dehydrofluorination of 3CCA5F or 5CCA5F with Scheme 6. However, when 3CCA7F reacted with an excess
excesss tBuONa in dimethyl sulfoxide (DMSO) at 100 °C of tBuONa in DMSO under a range of temperatures (50–
for 12 h generated the corresponding ether 3CCA5–2F or 150 °C), a mixture of six compounds was observed by TLC
5CCA5–2F.
that could not be separated by normal column chromatog-
Six-membered heterocyclic compounds (3CCA6F, raphy due to their similar polarities.
5CCA6F, 3CCA6H, and 5CCA6H) were obtained as de-
scribed for the five-membered heterocyclic analogues
(Scheme 5). When 3CCA6F reacted with five equivalents
Liquid Crystalline Properties
tBuONa in DMSO at 120 °C for 4 h, the dehydrofluorin-
As a preliminary investigation, the phase transitions and
ation product 3CCA6–2F (Scheme 5) was obtained. This thermodynamic data of the synthesized compounds were
appears to be an untried, but straightforward single-step investigated by differential scan calorimetry (DSC), and the
route to fluorinated N-heterocyclic 3,5-difluoro-pyridin- mesophases exhibited were examined with a polarizing op-
4(1H)-one, which is, to the best of our knowledge, the first tical microscope (POM).
example of a difluoro-substituted pyridin-4(1H)-one.
Transition temperatures and enthalpies of transition for
Seven-membered heterocyclic compounds 3CCA7F, the compounds, which differ in structure at the terminal
5CCA7F, 3CCA7H, and 5CCA7H were obtained under position, are given in Table 1. Their enthalpy values were
Table 1. Thermal behavior of the compounds.
Transition temp. (°C)[a] [enthalpies of transition, J g–1]
Td (°C)[b]
3CCA5H
3CCA5F
3CCA5–2F
3CCA6H
3CCA6F
3CCA7H
3CCA7F
3CCA6–2F
5CCA5H
5CCA5F
5CCA5–2F
5CCA6H
5CCA6F
5CCA7H
5CCA7F
Cr 155.5 [6.38]
Cr 154.9 [3.69]
Cr 124.8 [3.50]
Cr 116.4 [1.18]
Cr 126.2 [4.90]
Cr 122.6 [7.44]
Cr 134.0 [2.35]
Cr 226.9 [5.70]
Cr 154.8 [7.58]
Cr 149.4 [3.67]
Cr 98.3 [10.61]
Cr 157.9 [0.78]
Cr 109.4 [0.87]
Cr 120.5 [2.42]
Cr 140.9 [2.43]
N 237.1 [0.99]
SmC 174.3 [2.53]
N 242.9 [0.07]
SmB 134.6[2.61]
SmB 138.0 [1.86]
Iso
Iso
Iso
Iso
Iso
Iso
Iso
Iso
Iso
Iso
Iso
Iso
Iso
Iso
Iso
294.2
280.1
288.1
269.3
266.9
331.5
281.8
362.8
339.0
301.9
307.6
334.7
282.0
334.5
289.6
N 187.3 [0.89]
N 232.8 [0.52]
SmC 184.4 [2.27]
N 228.9 [2.64]
N 187.1 [0.03]
CrЈ 119.4 [2.42]
SmB 146.2 [2.37]
[a] Transition temperature and enthalpy change (in square brackets) were determined on the basis of DSC (peak temperature, first heating
scan, 5 K min–1) and confirmed by POM. Cr = crystalline solid, N = nematic phase, SmB = smectic B, SmC = smectic C, Iso = isotropic
liquid state. [b] Decomposition temperature.
7520
www.eurjoc.org
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2013, 7517–7527

Difluorooxymethylene-Bridged Liquid Crystals
determined on the basis of the differential scan calorimetry (Cr 154.8 °C, N 232.8 °C) or 5CCA6H (Cr 157.9 °C, N
(DSC) thermograms. These novel difluorooxymethylene- 187.1 °C). The mesomorphic phases of 3,4-difluoropyrrole
bridged molecules all show thermotropic liquid crystalline compounds also have a broader range than those with
phases, with the exception of the terminal seven-membered 3,3,4,4-tetrafluoropyrrolidine, 3,3,4,4,5,5-hexafluoropiper-
ring N-heterocyclic compounds 3CCA7H, 3CCA7F, idine, or 3,3,4,4,5,5,6,6-octafluoroazepane [e.g., 3CCA5–2F
5CCA7H, and 5CCA7F, and terminal 3,5-difluoro-pyridin- (Cr 124.8 °C, N 242.9 °C), 3CCA5F (Cr 154.9 °C, SmC
4(1H)-one compound 3CCA6–2F. Some of these com- 174.3 °C), 3CCA6F (Cr 126.2 °C, SmB 138.0 °C), 3CCA7F
pounds have a very wide nematic range; for example, (Cr 122.6 °C)].
3CCA5–2F has a nematic phase range of 118.1 °C. As can
be seen from Figure 1, as the terminal N-heterocycle size difluoropyrrole,
In general, the introduction of terminal fluorinated 3,4-
3,3,4,4-tetrafluoropyrrolidine, and
increases from a five- to a seven-membered ring, the range 3,3,4,4,5,5-hexafluoropiperidine causes a decrease of the
of mesomorphic phases narrows rapidly [e.g., 3CCA5H, (Cr melting temperature when compared with nonfluorinated
155.5 °C, N 237.1 °C), 3CCA6H, (Cr 116.4 °C, SmB pyrrolidine or piperidine compounds, for example 5CCA5H
134.6 °C, N 187.3 °C); see Table 1]; 3CCA7H melted into (m.p. 154.8 °C), 5CCA5F (m.p. 149.4 °C), 5CCA6H (m.p.
an isotropic liquid at 122.6 °C directly with no texture of 157.9 °C), and 5CCA6F (m.p. 119.4 °C), whereas 3CCA6H
liquid crystal being observed. The mesomorphism of the has a lower melting point (116.4 °C) and an SmB of be-
fluorocarbon and hydrocarbon N-heterocyclic liquid crystal tween 116.4 and 134.6 °C. However, the new compounds
compounds also changed dramatically [Figure 2; e.g., with 3,3,4,4,5,5,6,6-octafluoroazepane as terminal group
3CCA5F (Cr 154.9 °C, SmC 174.3 °C), 3CCA5–2F (Cr unexpectedly exhibit higher melting points than those with
124.8 °C,
N
242.9 °C), 3CCA5H, (Cr 155.5 °C
N
an azepine group (e.g., 5CCA7H: m.p. 120.5 °C, 5CCA7F:
237.1 °C)]. The existence of a nematic phase was evidenced m.p. 140.9 °C). Compound 3CCA6–2F, with a 3,5-di-
based on the schlieren texture observed by POM, and their fluoropyridin-4(1H)-one terminal group, has an extraordi-
smectic phase was investigated by POM and ascertained by narily high melting point (226.9 °C), but no liquid crystal-
variable-temperature X-ray diffraction (VTXRD).
line phase.
The new compounds with 3,4-difluoropyrrole as terminal
group exhibit the highest clearing point, compared with the
analogous pyrrolidine and 3,3,4,4-tetrafluoropyrrolidine
terminal compounds (e.g., 3CCA5–2F and 5CCA5–2F at
c.p. 242.9 and 228.9 °C, respectively, and 3CCA5H and
5CCA5H at c.p. 237.1 and 232.8 °C). Lower melting tem-
perature and higher clearing point is a fundamental prere-
quisite for all types of commercially significant LCDs.[4] It
can be seen that different lengths of the alkyl substituents
of the bicyclohexane building block has no significant effect
on these novel difluorooxymethylene-bridged molecules.
X-ray Diffraction
Smectic phases were observed for 3CCA5F, 3CCA6H,
3CCA6F, 5CCA5F, and 5CCA6F by POM. To obtain fur-
ther information on the molecular arrangements in the me-
sophase, variable-temperature X-ray diffraction (VTXRD)
experiments were performed on 3CCA5F, 3CCA6H, and
3CCA6F (see the Supporting Information). The diffraction
patterns obtained for compounds 3CCA5F and 3CCA6H
are shown in Figures 3 and 4, respectively.
Figure 1. DSC heating curves of compounds 3CCA5H, 3CCA6H,
and 3CCA7H.
Figure 3 presents the temperature-dependent X-ray dif-
fraction diagrams obtained from samples of 3CCA5F at
180, 160, and 50 °C. At 180 °C (Figure 3, a), the plot shows
only a wide diffraction peak in the wide angle region and
no diffraction peak was found in the small angle region;
combined with POM, these results indicate an isotropic
phase at this temperature. At 160 °C (Figure 3, b), a sharp
scattering at 5.30° is observed corresponding to a d spacing
of 16.65 Å given in the small angle region; a diffuse scat-
Figure 2. Optical texture (a) for 3CCA5F the broken focal-conic of
SmC upon cooling to 156 °C, and (b) for 3CCA5H schlieren of a
nematic phase upon cooling to 224 °C.
The nematic phase of 5CCA5–2F, for example, ranges tering at 17.52°, corresponding to a d spacing of 5.06 Å,
from 98.3 to 228.9 °C and is broader than that of 5CCA5H was also obtained. These results indicate the formation of
Eur. J. Org. Chem. 2013, 7517–7527
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
7521

H. Chen, P. Liu, H. Li, H. Zhang, S. Daniel, Z. Zeng
FULL PAPER
tion peak was found in the small angle region; combined
with POM, these results indicate the material was isotropic
at this temperature. At 140 °C (Figure 4, b), again, only a
wide diffraction peak was observed in the wide angle region
and no diffraction peak was found in the small angle re-
gion, indicating that no lamellar ordering exists in the me-
sophase. Combined with the results of POM analysis (Fig-
ure 5), it can be concluded that there is a nematic phase at
140 °C. When the measuring temperature was reduced from
140 to 130 °C, two sharp reflections at 3.58 and 7.22° were
seen with corresponding d-spacings of 24.65 and 12.23 Å in
the small angle region. These reflections are in the ratio 2:1
or 4:2, indicating a lamellar ordering in the mesophase. The
presence of a single strong sharp outer diffraction peak
(17.56°) indicates the formation of a smectic B phase (Fig-
ure 4, c). The liquid crystal state for SmB shows a single
sharp outer diffraction peak, whereas SmE, SmI, SmG, and
SmH exhibit several sharp outer rings, as previously re-
ported.[18] The layer thickness of 3CCA6H is larger than the
molecular length (d/L = 1.04, see Table 2), but significantly
smaller than twice the length, indicating bilayer structures.
When the measuring temperature was further cooled to
50 °C, a crystalline substance was obtained.
Figure 3. X-ray diffraction pattern of compound 3CCA5F at
(a) 180 °C, (b) 160 °C, and (c) 50 °C (before heating). (*) The dif-
fraction peak at 2θ = 25.54° is from the glass sample holder.
Table 2. X-ray diffraction analysis data of 3CCA5F, 3CCA6F, and
3CCA6H.
T
(°C)
d1
d2
d3
Molecular
Ratio Phase
(Å) (Å)
(Å) length (l, Å)[a] d1/l
3CCA5F 160
3CCA6F[b] 130
3CCA6H 130
16.65
13.14
/
/
5.04 23.16
5.04 23.11
0.72
0.57
1.04
SmC
SmB
SmB
24.65 12.23 5.04 23.69
[a] Length l was calculated for the fully extended conformation (es-
timated with Gaussian03). [b] See the Supporting Information.
Figure 4. X-ray diffraction pattern of compound 3CCA6H at
(a) 190 °C, (b) 140 °C, (c) 130 °C, and (d) 50 °C (before heating).
(*) The diffraction peak at 2θ = 25.54°is from the glass sample
holder.
a smectic phase at 160 °C; smectic A, smectic C, and smec-
tic F show a diffuse outer ring accompanied by a strong
inner diffraction as observed in previous reports.[18] The op-
tical polarizing micrograph (Figure 2, a) reveals a broken
focal-conic for 3CCA5F in this temperature range. Both re-
sults are consistent with a smectic C structure. The calcu-
lated molecular length of a molecule of 3CCA5F is 23.16 Å,
which is larger than the experimentally obtained layer
Figure 5. Optical texture for 3CCA6H (a) the mosaic texture of
SmB upon cooling to 110 °C, and (b) Schlieren texture of a nematic
phase upon cooling to 169 °C.
Thermal Stability
Thermal stabilities, which range from 266.9 to 362.8 °C
thickness (Table 2); this suggests that the mesogens are and depend on the N-heterocycle and the cyclohexane
packed in a monolayer structure. The diffraction plot mea- building block, were determined by thermal gravimetric
sured at 50 °C (Figure 3, c) demonstrates that the smectic C analysis (TGA). Data show that the decomposition tem-
phase has been quenched at this temperature. Figure 4 peratures were higher than the clearing points for these
shows the diffraction diagram of the phase transitions of compounds. The decomposition temperatures of the new
3CCA6H taken at 190, 140, 130, and 50 °C. The plot re- compounds, shown in Table 1, were correlated with the
corded at 190 °C (Figure 4, a) presents only a wide diffrac- structures of the N-heterocyclic (C5–C7) difluorooxymeth-
tion peak observed in the wide angle region and no diffrac- ylene-bridged compounds (Figure 6). In general, the new
7522
www.eurjoc.org
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2013, 7517–7527

Difluorooxymethylene-Bridged Liquid Crystals
compounds with [trans-4-(trans-4-n-propylcyclohexyl)cyclo-
Liquid crystal compounds 3CCA5–2F, 3CCA5F–
hexane]difluoromethyl (3CCA) building blocks were ther- 3CCA6F, and 3CCA5H–3CCA6H show positive dielectric
mally less stable than those constructed from the n-pentyl anisotropy, especially compounds with a 3,4-difluoropyr-
analogues 5CCA. The new compounds with a fluorocarbon role group, i.e., 3CCA5–2F, show strongly positive dielectric
N-heterocycle (3,3,4,4-tetrafluoropyrrolidine, 3,3,4,4,5,5- anisotropy (Δε 16.9). The Δε value of 3CCA5–2F is larger
hexafluoropiperidine, 3,3,4,4,5,5,6,6-octafluoroazepane and than those of polar terminal trifluoromethoxy-based com-
3,4-difluoropyrrole) as terminal group were less stable than pounds, i.e., 4-{difluoro[(trans,trans)-4Ј-propyl(1,1Ј-bicyclo-
those with a hydrocarbon N-heterocycle (pyrrolidine, piper- hexyl)-4-yl]methoxy}-2-fluoro-1-(trifluoromethoxy)benzene
idine, azepane) as terminal group. This suggests that the (A2; Δε 8.3) and the 3,4,5-trifluorobenzene derivative A1
rigidity of the molecule also influences its thermal stability, (Δε 10.5). This shows that compounds with fluorinated N-
for example, changing the pyrrolidine to piperidine, leads heterocycles as a terminal group have large permanent di-
to a decrease in thermal stability.
pole moments running parallel to their long molecular axis.
Another key performance parameter relevant for the ap-
plication of liquid crystals is the optical anisotropy or bi-
refringence (Δn).[19] Compound 3CCA5–2F exhibits a large
optical anisotropy (Δn 0.149), whereas 3CCA5H, 3CCA5F,
and 3CCA6H have more moderate Δn values of 0.131,
0.109, and 0.109, respectively. Aromatic compounds (which
have large induced polarizability of their highly conjugated
π-electron system) exhibit optical anisotropy (Δn = ne – no)
that is much larger than that of nonaromatic compounds.
Compound 3CCA6F exhibits remarkably low Δn values.
The Δn values of fluorinated N-heterocycles 3CCA5F (Δn
0.109) and 3CCA6F (Δn 0.069) are lower than that of non-
fluorinated N-heterocycles 3CCA5H (Δn 0.131) and
3CCA6H (Δn 0.109); thus, the introduction of fluorine
atoms into the terminal group leads to a decrease in bire-
fringence (Δn).
The most prominent and positive feature of the new
compounds containing a difluoromethyleneoxy bridge is
their viscosity.[20] Compounds 3CCA5–2F and 3CCA6H
exhibit relatively low viscosities (γ1 181 mPas for the latter)
that are lower than some commercially available liquid crys-
talline compounds, for example A2 (γ1 243 mPas), whereas
the viscosity of 3CCA5H is significantly higher (305 mPas).
Compounds 3CCA5F and 3CCA6F show higher viscosities
(428 and 829 mPas, respectively).
Figure 6. Correlation between thermal stability and the structure of
N-heterocyclic (C5–C7) difluorooxymethylene-bridged compounds.
Physical Properties of Liquid Crystals
In the study of liquid crystal chemistry, it is essential to
measure physical and electro-optical properties of liquid
crystalline compounds to obtain optimal performance of
commercially-successful liquid crystal displays. These speci-
fications include the nematic phase range, dielectric anisot-
ropy (Δε), birefringence (Δn), and rotational viscosity
(γ1).[4] A high clearing point, low viscosity, and high po-
larity are key LC properties for LCD products.[19] The phys-
ical properties of 3CCA5–2F, 3CCA5F–3CCA6F, and
3CCA5H–3CCA6H are listed in Table 3.
Theoretical Study
The geometry optimization of the structures of 3CCA5F,
3CCA6F, and 3CCA7F were performed by using density
functional theory (DFT), with Becke’s three-parameter
hybrid function and nonlocal correlation of Lee–Yang–Parr
(B3LYP) method in the gas phase.[21] The corresponding
frequency analyses were computed at the same level of
theory to characterize them as minima (no imaginary fre-
quencies) with help of the Gaussian03 (Revision D.01) suite
of programs.[22] All of above calculations used a 6-31+G
basis set. The computed structures were visualized by using
the GaussView program.[23] The conformation expression is
mainly a thermodynamic problem, so the total energy of
each different conformation can reflect the stability of the
structure. Six-membered-ring N-heterocycles have two dif-
ferent conformations, chair and boat form, their total ener-
gies being –1978.20574172 and –1978.19885694 a.u.,
respectively. The molecular total energy of the chair form
Table 3. Dielectric anisotropy (Δε), birefringence (Δn), and vis-
cosity (γ1) of 3CCA5–2F, 3CCA5F–3CCA6F, and 3CCA5H–
3CCA6H.
[a]
Δε[a]
Δn[a]
γ1 (mPas)
3CCA5–2F
3CCA5F
3CCA5H
3CCA6F
3CCA6H
A1[b]
16.9
8.4
4.4
3.9
2.4
10.5
8.3
0.149
0.109
0.131
0.069
0.109
0.066
0.080
181
428
305
829
181
145
243
A2[b]
[a] Extrapolated from 5 wt.-% solution in nematic host mixture
BYLC3014–000 (the nature of the host matrix: Δε = +10.4, Δn =
0.129, γ1 = 35 mPas). [b] See Scheme 1.
Eur. J. Org. Chem. 2013, 7517–7527
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
7523

H. Chen, P. Liu, H. Li, H. Zhang, S. Daniel, Z. Zeng
FULL PAPER
was lower than that of the boat form by approximately the terminal 3,3,4,4,5,5-hexafluoropiperidine compound
18.08 kJ/mol (1 a.u. = 2625.51 kJ/mol), indicating that the should exist in the chair conformation. The 3,3,4,4,5,5,6,6-
chair conformation of the terminal 3,3,4,4,5,5-hexa- octafluoroazepane (C7) adopts the twist-boat conformation
fluoropiperidine compound is more stable than the boat in comparison with 3,3,4,4,5,5-hexafluoropiperidine (C6)
conformation from a thermodynamic point of view. Thus and 3,3,4,4-tetrafluoropyrrolidine (C5), which decreases the
Figure 7. The optimized geometry of 3CCA5F–3CCA7F.
Table 4. Geometrical parameters of 3CCA5F–3CCA7F calculated with Gaussian03.
Dihedral angles (°)
Bond angles (°)
Bond lengths (10–1 nm)
Dipole (Debye)
3.3363
3CCA5F C2–C3–N19–C12
C3–N19–C13–C16
6.14
–168.24
151.01
C3–N19–C11
C3–N19–C12
C3–N19–C13
C3–N19–C16
123.15
123.18
161.00
160.54
N19-C11
C11-C13
C13-C16
C16-C12
C12-N19
1.468
1.520
1.537
1.520
1.468
C1–C6–O24–C25
3CCA6F C2–C3–N20–C11
C3–N20–C11–C13
–46.24
–108.44
–96.26
C3–N20–C11
C3–N20–C12
C3–N20–C13
C3–N20–C19
C3–N20–C16
121.87
122.33
125.80
141.06
126.16
N20-C12
C12-C16
C16-C19
C19-C13
C13-C11
C11-N20
1.457
1.528
1.537
1.537
1.530
1.458
4.9652
3.6694
C1–C6–O27–C28
3CCA7F C2–C3–N21–C11
C3–N21–C11–C13
–4.33
–93.88
–74.50
C3–N21–C11
C3–N21–C12
C3–N21–C13
C3–N21–C19
C3–N21–C20
C3–N21–C16
122.72
122.10
118.54
129.24
113.32
115.37
N21-C11
C11-C13
C13-C19
C19-C20
C20-C16
C16-C12
C12-N21
1.453
1.523
1.544
1.548
1.550
1.534
1.454
C1–C6–O30–C31
7524
www.eurjoc.org
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2013, 7517–7527

Difluorooxymethylene-Bridged Liquid Crystals
molecular ordered arrangement from five- to a seven-mem- active matrix displays.[25] Possessing highly conjugated π-
bered ring. This shows that the mesomorphic behavior is electron system, compounds with 3,4-difluoropyrrole such
dominated by the size of the N-heterocycle ring.
as 3CCA5–2F, exhibits large optical anisotropy and
It can be seen from geometrical parameters (Figure 7) strongly positive dielectric anisotropy, which are the most
that the coplanar structure of the molecule is destroyed promising physicochemical and electro-optical properties of
upon expansion of the terminal N-heterocycle; this is mani- components of nematic liquid crystalline materials.
fested in their dihedral angles and bond angles (Table 4)
and comes about as a result of the increase in the size of
Influence of the Difluoromethyleneoxy Bridge on the
Molecules
the ring, which leads to a decrease in the number of inter-
molecular interactions. Consequently, these factors lead to
a deterioration of the liquid crystalline phase range and a
lowering of the clearing point.
Compounds 3CCA5–2F and 3CCA6H exhibit relatively
low viscosity (181 mPas), and 3CCA5H has acceptable vis-
cosity (305 mPas). In comparison to other linking groups,
such as esters or dimethylenes, the two lateral fluorine
atoms in the difluoromethyleneoxy linkage chain are con-
ducive to reducing the intermolecular force, which can ef-
fectively reduce the viscosity of these liquid crystalline ma-
terials. The introduction of the difluoromethyleneoxy moi-
ety as a linkage group also favors a positive dielectric an-
isotropy (Δε). This arises from the fact that the fluorine
atoms contribute to the inductive effect of the molecule in
the long axis direction, which induces an increase in the
molecular dipole moment, a rise of Δε, and a higher specific
voltage holding ratio. For example, compound 3CCA5–2F
has good attributes for use in displays with a fairly high
positive dielectric anisotropy, acceptable viscosity, and a
reasonably high nematic phase stability.
Evaluation of the Influence of the Terminal N-Heterocycle
Investigations have centered on assessing the effect of the
terminal N-heterocycle on the melting point, transition
temperatures, mesophase morphology, and various physical
properties. With expansion of the terminal N-heterocycle
from a five- to a seven-membered ring, the range of meso-
morphic phases narrowed rapidly [e.g., 3CCA5H (Cr
155.5 °C, N 237.1 °C) and 3CCA6H (Cr 116.4 °C, SmB
134.6 °C, N 187.3 °C]; 3CCA7H melted into isotropic li-
quids at 122.6 °C directly with no texture of liquid crystal
being observed. This may be because with the expansion of
the terminal N-heterocycle, the coplanar structure of the
molecular is destroyed, on the other hand, the expansion
also induces an increase in the width of the molecule,
thereby increasing the distance between molecules and re-
sulting in a decrease in the number of intermolecular inter-
actions. These factors lead to a reduction in both the liquid
Conclusions
A series of novel fluorocarbon and hydrocarbon N-
crystalline phase ranges and the clearing point. Moreover, heterocyclic (C5–C7) difluorooxymethylene-bridge liquid
the type of mesomorphism observed for fluorinated N- crystals have been prepared in good yield by oxidative
heterocycle liquid crystal compounds and nonfluorinated fluorodesulfuration. Their melting points, decomposition
N-heterocycle liquid crystal compounds changed dramati- temperatures, clearing points, mesomorphism type, dielec-
cally [e.g., 3CCA5F (Cr 154.9 °C, SmC 174.3 °C), 3CCA5– tric anisotropy (Δε), birefringence (Δn), and viscosity (γ1)
2F (Cr 124.8 °C, N 242.9 °C), 3CCA5H (Cr 155.5 °C, N were determined. Their mesomorphic behavior, physico-
237.1 °C)]. This is because fluorine has the highest elec- chemical and electro-optical properties are affected by alter-
tronegativity of all the elements, and increasing the amount ing the polarity of the terminal N-heterocycle. The hydro-
of fluorine atoms in the terminal N-heterocycle increases carbon N-heterocyclic (C5–C6) difluorooxymethylene-
the polarization and thus the lateral attraction between mo- bridged liquid crystals, for example 3CCA5H and
lecules. When the lateral attraction is greater than the ter- 3CCA6H, display broad nematic phases range, high clear-
minal attraction, the smectic phase forms preferentially, ing points, moderate birefringence (Δn), neutral dielectric
however, dehydrofluorination of 3CCA5F or 5CCA5F anisotropy (Δε), and moderate viscosity (γ1), whereas
causes a reduction in lateral attraction, and hence increases fluorocarbon N-heterocyclic (C5–C6) difluorooxymeth-
the terminal attraction. When the terminal attraction is ylene-bridged liquid crystals, for example 3CCA5F and
greater than the lateral attraction, the nematic phase forms 3CCA6F, exhibit different mesomorphism type, positive di-
preferentially.
electric anisotropy, and relatively low Δn values. It is notice-
A comparison with nonfluorinated N-heterocyclic liquid able that compounds with 3,4-difluoropyrrole as terminal
crystal compounds shows that the fluorinated N-hetero- group show relatively low viscosities and strongly positive
cyclic liquid crystal compounds have a larger positive di- dielectric anisotropy in combination with reasonable or
electric anisotropy. This is because the terminal fluoro sub- good values for the other relevant parameters (phase transi-
stituent has a reasonable polarity, which provides positive tions and optical anisotropy). These novel liquid crystals
dielectric anisotropy, and yet has a very low polarizability, can be used in a range of applications, such as precise ad-
which tends to impart a high resistivity.[24] Hence, terminal justment of electroopic properties, reduction of the rota-
fluoro-substituted liquid crystals have become the subject tional viscosity, or raising the clearing temperature of mix-
of extensive research for their use in nematic mixtures for tures for LCDs.
Eur. J. Org. Chem. 2013, 7517–7527
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
7525

H. Chen, P. Liu, H. Li, H. Zhang, S. Daniel, Z. Zeng
FULL PAPER
0.01 mol) or 5CCANO2 (4.24 g, 0.01 mol), Zn (3.92 g, 0.06 mol),
NH4Cl (3.21 g, 0.06 mol), and CH3OH (60 mL) in THF (30 mL)
was placed in a Pyrex glass tube and sealed at room temp. for 24 h.
The mixture was then filtered through Celite (2.5 g), the solvent
was removed under vacuum, and the residue was purified by
chromatography on silica gel to give the target product [Rf = 0.4
(PE/CH2Cl2, 1:2)].
Experimental Section
General: All the reagents were of analytical grade, purchased from
commercial sources, and used as received. H and 19F NMR spec-
1
tra were recorded with a 400 MHz spectrometer operating at 400
and 376 MHz, respectively. Chemical shifts are reported relative to
Me4Si for 1H, and CCl3F for 19F; the solvent was CDCl3 unless
otherwise specified. Thermogravimetric analysis (TGA) measure-
ments were performed at a heating rate of 10 °C min–1 with a
Netzsch STA409PC (Germany) instrument. DSC plots were re-
corded at a scan rate of 5 °C min–1 with a Netzsch DSC200PC
apparatus. Optical micrographs were observed with a polarizing
optical microscope (POM) (Nikon LINKAM-THMSE600)
equipped with a heating plate (HCS601). Variable-temperature X-
Preparation of 2,2,3,3-Tetrafluoro-1,4-butanediyl Trifluoromethane-
sulfonate (1f), 2,2,3,3,4,4-Hexafluoro-1,5-pentanediyl Trifluoro-
methanesulfonate (2f), 2,2,3,3,4,4,5,5-Octafluoro-1,6-hexanediyl
Trifluoromethanesulfonate (3f) and 1,4-Butanediyl Trifluoro-
methanesulfonate (1h), 1,5-Pentanediyl Trifluoromethanesulfonate
(2h), 1,6-Hexanediyl Trifluoromethanesulfonate (3h): A solution of
2,2,3,3-Tetrafluoro-1,4-butanediol (1a), 2,2,3,3,4,4-hexafluoro-1,5-
pentanediol (2a), 2,2,3,3,4,4,5,5-octofluoro-1,6-hexanediol (3a),
1,4-butanediol (1b), 1,5-pentanediol (2b), or 1,6-hexanediol (3b)
(1 mmol), and pyridine (3 mmol) in CH2Cl2 (20 mL) was stirred at
room temperature. After 30 min, trifluoromethanesulfonic anhy-
dride (2.5 mmol) in CH2Cl2 (10 mL) was slowly added over 1 h.
The mixture was stirred for 12 h, then washed with water (3ϫ
30 mL), and dried with anhydrous sodium sulfate. The solvent was
removed under vacuum to give 1f (white solid, 95%), 2f (yellow
liquid, 93%), 3f (white solid, 93%), 1b (white solid, 90%), 2b (yel-
low liquid, 91%), or 3b (white solid, 90%).
ray diffraction (XRD) experiments were performed with
a
RIGAKU D-MAX 2200 VPC X-ray diffractometer (using Cu-Kα1
radiation of a wavelength of 1.54 Å) with temperature controller.
The dielectric anisotropy (Δε), the birefringence (Δn), and the vis-
cosity (γ1) were measured with a mixture of 5 wt.-% of each com-
pound and 95 wt.-% of base LC mixture (BYLC3014–000, Beijing
Bayi Space LCD Materials Technology Co., Ltd.). Elemental
analyses were performed with an EXETER CE-440 Elemental An-
alyzer.
Typical Procedure for the Preparation of 5,6-Dihydro-2-
[(trans,trans)-4-(4-propylcyclohexyl)cyclohexyl]-4H-1,3-dithiinium
Trifluoromethanesulfonate (3CCB) and 5,6-Dihydro-2-[(trans,trans)-
4-(4-pentylcyclohexyl)cyclohexyl]-4H-1,3-dithiinium Trifluorometh-
anesulfonate (5CCB): Compound 3CCA (10.1 g, 0.04 mol), toluene
(10 mL), isooctane (10 mL), and 1,3-propanedithiol (5.6 g,
0.52 mol) were added to a two-necked flask. The mixture was
stirred and heated to 50 °C, and trifluoromethanesulfonic acid
(7.8 g, 0.52 mol) was added over 30 min. The resulting solution was
heated to 102–104 °C and water was removed azotropically for
about 2h. The solution was cooled to 90 °C, and methyl tert-butyl
ether (100 mL) was added over 20 min at 90–70 °C. The suspension
was cooled to 0 °C and filtered under a dry nitrogen atmosphere.
The crystals were washed with methyl tert-butyl ether (50 mL) and
filtered under a dry nitrogen atmosphere to obtain white crystals
(17.47 g, 93%).
Preparation of N-Heterocyclic Liquid Crystalline Compounds (Ex-
cept 3CC5–2F and 5CCA5–2F): A solution of ester 1f, 2f, 3f, 1h, 2h,
or 3h (1 mmol), and 3CCANH2 (366 mg, 1 mmol) or 5CCANH2
(394 mg, 1 mmol), in Et3N (3 mmol) and ethanol (20 mL) was
placed in a Pyrex glass tube, sealed, and heated at 90 °C for 24 h.
After cooling, the solvent was removed under vacuum, CH2Cl2
(50 mL) was added and the mixture was washed with water (3ϫ
50 mL) and dried with anhydrous Na2SO4. After removal of the
solvent, the residue was purified by chromatography on silica gel
to give the target product [Rf = 0.2–0.4 (PE/CH2Cl2, 10:1)].
Preparation of N-Heterocyclic Liquid Crystalline Compounds
3CC5–2F and 5CCA5–2F: Compound 3CCA5F (491 mg, 1 mmol)
or 5CCA5F (520 mg, 1 mmol), and sodium tert-butoxide (720 mg,
8 mmol) in dimethyl sulfoxide (5 mL) were placed in a Pyrex glass
tube, sealed, and heated at 100 °C for 12 h. After cooling, CH2Cl2
(30 mL) was added and the mixture was washed with water (3ϫ
30 mL) and dried with anhydrous Na2SO4. The solvent was re-
moved and the residue was purified by chromatography on silica
gel to give the target product [Rf = 0.2–0.4 (PE/CH2Cl2, 10:1)].
Preparation of 1-{Difluoro[(trans,trans)-4Ј-propyl(1,1Ј-bicyclohexyl)-
4-yl]methoxy}-4-nitro-benzene (3CCANO2) and 1-{Difluoro-
[(trans,trans)-4Ј-pentyl(1,1Ј-bicyclohexyl)-4-yl]methoxy}-4-nitro-
benzene (5CCANO2): A solution of 3CCB (18.98 g, 0.04 mol) or
5CCB (20.10 g, 0.04 mol) in CH2Cl2 (40 mL) was cooled to –70 °C,
and a solution of p-nitrophenol (6.67 g, 0.048 mol) in a mixture of
triethylamine (5.66 g, 0.056 mol) and CH2Cl2 (40 mL) was added
over 30 min, keeping the temperature below –70 °C. After stirring
for 1 h, NEt3·3HF (32 mL, 0.4 mol) was added over 10 min, then
a solution of bromine (10.25 mL, 0.4 mol) in CH2Cl2 (30 mL) was
added at –70 °C. The mixture was stirred for 1 h at –70 °C, then
warmed to 0 °C. The solution was poured into a mixture of 30%
aqueous NaOH (60 mL) and ice (100 g). The pH was adjusted to
7–8 by addition of 30% aqueous NaOH. The aqueous layer was
extracted with CH2Cl2 (50 mL), and the combined organic extracts
were filtered through Celite (2.5 g), washed with water (3 ϫ
100 mL), and dried with anhydrous sodium sulfate. The solvent was
removed under vacuum, and the residue was purified by
chromatography on silica gel to give the target product [Rf = 0.3
(PE/CH2Cl2, 10:1)].
Preparation of 1-{Difluoro[(trans,trans)-4Ј-propyl(1,1Ј-bicyclohexyl)-
4-yl]methoxy}-4-(3,5-difluoro-4-oxo-1-pyridyl)benzene (3CC6–2F):
Compound 3CCA6F (541 mg, 1 mmol), sodium tert-butoxide
(450 mg, 5 mmol) and dimethyl sulfoxide (5 mL) were placed in a
Pyrex glass tube, sealed, and heated at 120 °C for 4 h. After cool-
ing, CH2Cl2 (30 mL) was added and the mixture was washed with
water (3ϫ 30 mL) and dried with anhydrous Na2SO4. The solvent
was removed and the residue was purified by chromatography on
silica gel to give the target product [Rf = 0.3 (PE/EtOAc, 1:2)].
Supporting Information (see footnote on the first page of this arti-
cle): Experimental data and analytical (DSC, TGA, POM,
1
VTXRD) figures and copies of the H and 19F NMR spectra.
Acknowledgments
Preparation of 4-{Difluoro[(trans,trans)-4Ј-propyl(1,1Ј-bicyclohexyl)-
4-yl]methoxy}benzenamine (3CCANH2 ) and 4-{difluoro- The authors gratefully acknowledge the support of the National
[(trans,trans)-4Ј-pentyl(1,1Ј-bicyclohexyl)-4-yl]methoxy}- Natural Science Foundation of China (NSFC) (grant number
benzenamine (5CCANH2): A mixture of 3CCANO2 (3.96 g, 21272080), Department of Science and Technology, Guangdong
7526
www.eurjoc.org
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2013, 7517–7527

Difluorooxymethylene-Bridged Liquid Crystals
DE-A 19946228, 1998; d) S. Dandapani, in: Handbook of Fluo-
rous Chemistry, Highlights of Applications in Synthesis and Ca-
talysis (Eds.: J. A. Gladysz, D. P. Curran, I. T. Horváth), Wiley-
VCH, Weinheim, Germany, 2005, p. 175–182.
Province (grant numbers 2010A020507001-76, 5300410, FIPL-05-
003), and The Scientific Research Foundation for the Returned
Overseas Chinese Scholars, State Education Ministry.
[13] B. Ekkehard, H. Reinhard, K. Hans-Adolf, P. Herbert, P. Eike,
US Pat 5045229, 1991.
[14] W. H. Bunnelle, B. R. McKinnis, B. A. Narayanan, J. Org.
Chem. 1990, 55, 768–770.
[1] I.-W. Wu, J. Soc. Inf. Display 1994, 2, 1–14.
[2] S. Matsui, T. Kondo, K. Sago, Mol. Cryst. Liq. Cryst. 2004,
411, 127–137.
[3] D. Pauluth, K. Tarumi, J. Mater. Chem. 2004, 14, 1219–1227.
[4] P. Kirsch, M. Bremer, Angew. Chem. 2000, 112, 4384; Angew.
Chem. Int. Ed. 2000, 39, 4216–4235.
[5] a) E. Bartmann, K. Tarumi (Merck KGaA), DE-B 19531165,
1995; b) T. Ando, K. Shibata, S. Matsui, K. Miyazawa, H.
Takeuchi, Y. Hisatsune, F. Takeshita, E. Nakagawa, K. Kobay-
ashi, Y. Tomi (Chisso Corp), EP-B 0844229, 1998.
[6] a) H. M. Vorbrodt, J. Vogel, H. Zaschke, G. Pelzl, D. Demus,
Mol. Cryst. Liq. Cryst. 1985, 123, 137–141; b) C. Tschierske,
H. Altmann, H. Zaschke, G. Brezesinski, F. Kuschel, Mol.
Cryst. Liq. Cryst. 1990, 191, 295–300; c) V. S. Bezborodov, V. F.
Petrov, V. I. Lapanik, Liq. Cryst. 1996, 20, 785–796.
[7] a) C.-R. Wen, Y.-J. Wang, H.-C. Wang, H.-S. Sheu, G.-H. Lee,
[15] M. Kuroboshi, K. Kanie, T. Hiyama, Adv. Synth. Catal. 2001,
343, 235–250.
[16] a) B. S. Pederson, S. Scheibye, K. Clausen, S. O. Lawesson,
Bull. Soc. Chim. Belg. 1978, 87, 293–297; b) M. Kuroboshi, T.
Hiyama, Synlett 1994, 251–252.
[17] a) P. Kirsch, M. Bremer, A. Taugerbeck, T. Wallmichrath, An-
gew. Chem. 2001, 113, 1528; Angew. Chem. Int. Ed. 2001, 40,
1480–1482; b) P. Kirsch, in: Modern Fluoroorganic Chemistry:
Synthesis Reactivity, Applications, Wiley-VCH, Weinheim, Ger-
many, 2004, p. 25–192.
[18] a) W. R. Krigbaum, J. Watanabe, T. Ishilawa, Macromolecules
1983, 16, 1271–1279; b) A. D. Vries, Mol. Cryst. Liq. Cryst.
1973, 24, 337–345.
C. K. Lai, Chem. Mater. 2005, 17, 1646–1654; b) S. Qu, X. [19] D. Pauluth, K. Tarumi, J. Soc. Inf. Display. 2005, 13, 693–702.
Chen, X. Shao, F. Li, H. Zhang, H. Wang, P. Zhang, Z. Yu,
K. Wu, Y. Wang, M. Li, J. Mater. Chem. 2008, 18, 3954–3964;
c) C. V. Yelamaggad, A. S. Achalkumar, D. S. S. Rao, S. K.
Prasad, J. Org. Chem. 2009, 74, 3168–3171; d) V. F. Petrov, Liq.
Cryst. 2001, 28, 217–240.
[20] E. Bartmann, Adv. Mater. 1996, 8, 570–573.
[21] a) D. Feller, J. Chem. Phys. 1990, 93, 579–590; b) A. D. Becke,
J. Chem. Phys. 1993, 98, 5648–5652; c) C. Lee, W. Yang, R. G.
Parr, Phys. Rev. B 1988, 37, 785–789; d) P. Kirsch, M. Bremer,
ChemPhysChem 2010, 11, 357–360.
[8] a) J. Tao, J. Zhong, P. Liu, S. Daniels, Z. Zeng, J. Fluorine
Chem. 2012, 144, 73–75; b) H. Chen, P. Liu, H. Li, S. Daniel,
Z. Zeng, Tetrahedron 2013, 69, 5129–5135.
[22] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, J. A. Montgomery Jr, T. Vreven,
K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar, J. Tom-
asi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega,
G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota,
R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,
O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratch-
ian, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gom-
perts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C.
Pomelli, J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A.
Voth, P. Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dap-
prich, A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick,
A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q.
Cui, A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov,
G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. L. Martin,
D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayak-
kara, M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen,
M. W. Wong, C. Gonzalez, J. A. Pople, Gaussian 03, revision
D.01, Gaussian, Inc., Wallingford CT, 2004.
[9] a) F. Ma, X. Chen, Y. Zhao, X. Wang, B. Jing, F. Gao, H. Qiu,
Chem. Lett. 2009, 38, 240–241; b) G. Karel, L. Kathleen, N.
Peter, V. H. Kristof, V. M. Luc, D. Kris, G.-W. Christiane, B.
Koen, C. Thomas, Chem. Eur. J. 2009, 15, 656–674; c) H. Gal-
lardo, G. Conte, P. A. Tuzimoto, B. Behramand, F. Molin, J.
Eccher, I. H. Bechtold, Liq. Cryst. 2012, 39, 1099–1111; d)
R. T. W. Huang, W. C. Wang, R. Y. Yang, J. T. Lu, I. J. B. Lin,
Dalton Trans. 2009, 35, 7121–7131; e) Y. Li, L. Hao, H. Fu, W.
Pisula, X. Feng, Z. Wang, Chem. Commun. 2011, 47, 10088–
10090; f) D. W. Bruce, S. Estdale, D. Guillon, B. Heinrich, Liq.
Cryst. 1995, 19, 301–305; g) C. Cruz, J. L. Gallani, B. Heinrich,
D. W. Bruce, D. Guillon, Mol. Cryst. Liq. Cryst. 1999, 330,
151–158; h) X. Wang, M. Sobota, F. T. U. Kohler, B. Morain,
B. U. Melcher, M. Laurin, P. Wasserscheid, J. Libuda, K.
Meyer, J. Mater. Chem. 2012, 22, 1893–1898; i) J. Han, S.-S.-
Y. Chui, C.-M. Che, Chem. Asian J. 2006, 1, 814–825.
[10] a) S. Torgova, L. Karamysheva, A. Strigazzi, Braz. J. Phys.
2002, 32, 593–601; b) M. Parra, P. Hidalgo, J. Alderete, Liq.
Cryst. 2005, 32, 449; c) M. Parra, P. Hidalgo, E. Carrasco, J.
Barbera, L. Silvino, Liq. Cryst. 2006, 33, 875–882.
[11] a) A. Seed, Chem. Soc. Rev. 2007, 36, 2046–2069; b) H. Gal-
lardo, R. Cristiano, A. A. Vieira, R. A. W. Neves Filho, R. M.
Srivastava, I. H. Bechtold, Liq. Cryst. 2008, 35, 857–863.
[12] a) A. Haas, M. Spitzer, M. Lieb, Chem. Ber. 1988, 121, 1329–
1340; b) E. Bartmann, Adv. Mater. 1996, 8, 570–573; c) T.
Kondo, K. Kobayashi, S. Matsui, H. Takeuchi (Chisso. Co.),
[23] R. Dennington, T. Keith, J. Millam, K. Eppinnett, W. L. Hov-
ell, R. Gilliland, 2003, GaussView, version 3.09, Semichem,
Inc., Shawnee Mission.
[24] a) S. Inoue, T. Yanai, S. Ando, A. Nakazawa, K. Honda, Y.
Hoshino, T. Asai, J. Mater. Chem. 2005, 15, 4746–4752; b) P.
Kirsch, M. Bremer, M. Heckmeier, K. Tarumi, Angew. Chem.
1999, 111, 2174; Angew. Chem. Int. Ed. 1999, 38, 1989–1992.
[25] M. Hird, Chem. Soc. Rev. 2007, 36, 2070–2095.
Received: July 18, 2013
Published Online: September 24, 2013
Eur. J. Org. Chem. 2013, 7517–7527
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
7527