Selenium-linked liquid crystal dimers for twist-bend nematogens

Article abstract of DOI:10.1016/j.molliq.2019.111097

The recently discovered twist-bend nematic (N_TB) phase has become an intensively studied topic in supramolecular chemistry and condensed matter science. Herein, a new molecular design for twist-bend nematogens employing the selenoether (C–Se–C) linkage, instead of the conventional methylene or ether linkages, is introduced. We synthesized CBSenSeCB dimers, consisting of two cyanobiphenyl (CB) units connected by two selenoether linkers sandwiching an odd-numbered alkylene spacer (n = 3, 5, 7, and 9) and revealed their phase transitions and mesomorphism. CBSenSeCB (n = 5, 7, and 9) can potentially form mesophases; notably, CBSe7SeCB formed the N_TB phase from the conventional uniaxial nematic phase, which was cooled to below room temperature. The structure of the all-trans model of CBSe7SeCB, optimized by the density functional theory, suggests that the molecular bend angle between the para axes of the cyanobiphenyl moieties is ^～90°, which is more bent than those of previously reported twist-bend nematogens. Such a keen curvature is ascribed to the small C–Se–C angle of ^～101°. In addition, the molecular bend angles of the twist-bend dimers, including the present and previously reported ones, correlate linearly with their phase-transition temperatures. The present study paves the way for the molecular design of new twist-bend nematic liquid crystals based on chalcogen linkages.

Full text of DOI:10.1016/j.molliq.2019.111097

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Selenium-linked liquid crystal dimers for twist-bend nematogens
Yuki Arakawa, Hideto Tsuji
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DOI:
Article Number:
Reference:
S0167-7322(19)32430-4
https://doi.org/10.1016/j.molliq.2019.111097
111097
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29 May 2019
Please cite this article as: Y. Arakawa and H. Tsuji, Selenium-linked liquid crystal dimers
for twist-bend nematogens, Journal of Molecular Liquids, https://doi.org/10.1016/
j.molliq.2019.111097
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ACCEPTED MANUSCRIPT
Journal of Molecular Liquids
Selenium-linked liquid crystal dimers for twist-bend
nematogens
Yuki Arakawa,* and Hideto Tsuji
Abstract
The recently discovered twist-bend nematic (NTB) phase has become an intensively
studied topic in supramolecular chemistry and condensed matter science. Herein, a new
molecular design for twist-bend nematogens employing selenoether (C–Se–C) linkage,
instead of the conventional methylene or ether linkages, is introduced. We synthesized
CBSenSeCB dimers, consisting of two cyanobiphenyl (CB) units connected by two
selenoether linkers sandwiching an odd-numbered alkylene spacer (n = 3, 5, 7, and 9)
and revealed their phase transitions and mesomorphism. CBSenSeCB (n = 5, 7, and 9)
can potentially form mesophases; notably, CBSe7SeCB formed the NTB phase from the
conventional uniaxial nematic phase, which was cooled to below room temperature. The
structure of the all-trans model of CBSe7SeCB, optimized by density functional theory,
suggests that the molecular bend angle between the para axes of the cyanobiphenyl
moieties is about 90°, which is more bent than those of previously reported twist-bend
nematogens. Such a keen curvature is ascribed to the small C–Se–C angle of about 101°.
In addition, the molecular bend angles of the twist-bend dimers, including the present
and previously reported ones, correlate linearly with their phase-transition temperatures.
The present study paves the way for the molecular design of new twist-bend nematic
liquid crystals based on chalcogen linkages.

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Introduction
The breaking of chiral symmetry in achiral molecules is among the most fascinating
phenomena in supramolecular chemistry and condensed matter science. Liquid crystals,
which have properties between those of anisotropic solids and isotropic liquids, offer
rich sources of such phenomena. Over the past few decades, bent achiral liquid crystals
have gained impetus because of the discoveries of ferroelectric [1] and spontaneous
chiral segregation [2].
On the other hand, liquid crystal dimers composed of two rigid mesogenic parts
connected by an odd-numbered alkylene spacer that gives rise to a bent molecular
geometry have also gained much interest [3]. Furthermore, the most recently reported
emergent liquid crystal phase for such a bent dimer, the twist-bend nematic (NTB) phase,
has attracted a great deal of attention. This phase, which was predicted by Meyer [4]
and Dozov [5], is formed by right- and left-handed helical nanostructured molecular
aggregation and is based on symmetry breaking in achiral systems. The phase transition
from uniaxial nematic (NU) to another nematic (NX), which was subsequently
characterized as NTB [6], was experimentally observed in several bent dimers [7] and
polymers [8]. Freeze-fracture transmission electron microscopy [9] and resonant X-ray
scattering [10] experiments disclosed that the NTB phase usually has a relatively short
(~10 nm) helical pitch. Inspired by the recent discovery of the NTB phase, the
development of new twist-bend nematogens has become a major focus of
supramolecular and liquid crystal chemistry research [11]. Very recently, twist-bend
nematogens have been expanded to some oligomers [12] and polymers [8,13]. Moreover,
several applications based on the NTB phase have also been reported [14].
The molecular designs of liquid crystal dimers or oligomers that exhibit the NTB
phase are based on three parts: rigid mesogenic parts, spacers, and the linkers between
them. One of the determinants in the molecular design that induces the NTB phase is the
molecular bend or interarm angle (χ) between the para axes of the two mesogenic parts,
as shown in Figure 1, which is strongly dominated by the linker. Mandle and coworkers
have widely explored the structure-property relationships of dimers with various χ
values [15]. For example, although a few methylene-linked cyanobiphenyl (CB) dimers
(CBnCB, where n denotes the odd number of carbon atoms in the alkylene spacer) with
χ = 111° form the NTB phase, with the exception of CBO5OCB with its very narrow
NTB-phase range [16], their ether-linked counterparts, CBOnOCB, with χ = 144° are
almost conventional nematogens [17]. The difference in angle is mainly attributed to the
~
difference in the bond angles of the linkers, specifically 111° for methylene (C–CH2–
C) and ~117° for ether (C–O–C). Consequently, the methylene- and ether-linked dimers,

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CB6OCB [18] and CB8OCB [17], also form NTB phases. Watanabe et al. described a
comparative of mesogenic abilities on two-typed opposite-directed ester (COO and
OCO)-linked dimers and the NTB phase incidence [19]. In the literature, they noted that
the former has more bent molecular curvature with χ = 97°, which is a candidate for
twist-bend nematogens, and revealed that some analogues of cyclohexylbenzene-based
dimers form NTB phase. While, the latter opposite ester-linked dimers (or alkanedioates)
showing exclusive NU phase tendency [20] have a relatively large χ of 139°, which is
comparable to that of the ether-linked conventional nematogen CBOnOCB dimers.
Dawood et al. revealed that the dimer with the Schiff-base linkage and the shortest
propylene spacer forms transitioned directly from the isotropic (Iso) phase (the novel
NTB-Iso sequence), which differs to that of the usual NTB-NU-Iso sequence [21]. This is
consistent with the theory that a shorter spacer is reflected in increased molecular
curvature. Consequently, χ was suggested to be a factor responsible for the incidence of
the NTB phase. Thus far, among the large variety of twist-bend nematogenic dimers or
oligomers that have been recently developed, the atoms introduced at the linking point
have solely been carbon or oxygen.
On the other hand, while we have been homing in on the development of
alkylsulfanyl- or thioether-containing mesogens [22], we recently investigated
thioether-linked cyanobiphenyl dimers that exhibit the NTB phase, specifically,
CBSnSCB and CBSnOCB with odd-numbered alkylene spacers of length n (Figure 1)
~
[23]. This is because thioether (R–S–R) has a relatively small bond angle of 103°,
CBSnSCB and CBSnOCB have molecular geometries that are more bent (bend angles
of 109° and 126°, respectively) than the conventional ether-linked nematogen,
CBO7OCB. In addition, a thioether is believed to be more flexible because it has a
lower rotation barrier than alkylene or ether. Such curvature and flexibility would assist
the induction of the NTB phase. Consequently, our research showcased the potential of a
“chalcogen-based linkage” in the development of new twist-bend nematogens.
In this paper, we report, for the first time, twist-bend nematogens containing the
selenoether or C–Se–C. We designed and synthesized a homologous series of
selenoether-linked cyanobiphenyl dimers, CBSenSeCB, with an odd number of carbon
atoms (n = 3, 5, 7, and 9) (Figure 1). Their phase transition behavior and mesomorphism
were unlocked by polarizing light microscopy (PLM) and differential scanning
calorimetry (DSC), and the optimized molecular structure of one of these structures was
studied by density functional theory (DFT). In addition, these dimers were compared
with other twist-bend nematogens and the correlation between molecular bend angle
and phase-transition temperature determined.

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Figure 1. Molecular design concept based on chalcogen-linked liquid crystal dimers to
induce NTB phase. Ether-linked conventional nematogens CBOnOCB (a),
thioether-linked twist-bend nematogen CBSnSCB (b) and the present selenoether-linked
dimers CBSenSeCB (c).
Results and Discussion
CBSenSeCB was synthesized according to the procedure shown in Figure 2. First,
4,4’-dibromodiselenide (1) was prepared by reacting selenium with
4-bromoiodobenzene [24]. Bis(4-bromophenyl)diselenide was reduced with NaBH4 in
ethanol to afford a colorless solution of the selenide anion [25], which was subsequently
reacted with the α,ω-dibromoalkane at room temperature to afford disubstituted product
1,7-bis[(4-bromophenyl)seleno]heptane along with the monosubstituted product. Finally,
the disubstituted compound was subjected to Suzuki–Miyaura coupling [26] with the
pinacol ester of 4-cyanophenylboronic acid to afford the target CBSenSeCB. A

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representative synthetic procedure for CBSe7SeCB and its characterization data is
available in the Experimental section, and those for the other dimers are provided in the
supporting information.
The phase sequence, transition temperature, and change in enthalpy (ΔH) for
CBSenSeCB are tabulated in Table 1. The CBSenSeCB dimers (n = 5, 7, and 9) exhibit
mesophases, whereas CBSe3SeCB does not form any mesophase and has a single
melting temperature of 147.4 °C. CBSe5SeCB does not exhibit a mesophase during
~
heating but formed the monotropic NU phase during cooling, commencing at 59 °C
with subsequent crystallization starting at about 49 °C upon cooling. The emergence of
the NU phase is supported by the photomicrographs show in Figure S1. However, the
formation of the NU phase was not clearly evident by DSC owing to prior crystallization
at 75.5 °C with ΔH = 22.1 kJ mol-1, as shown in Figure S4. Notably, CBSe7SeCB forms
a NU phase as well as the NTB phase, with unusual phase-transition behavior, which is
independently described in detail below. CBSe9SeCB also exhibits a monotropic NU
phase between 61.7 and 75.9 °C Whereas, it does not form the NTB phase even at the
fast rate of 20 °C min-1 although some molecules can only induce NTB phase at a fast
rate [23].
Figure 2. Synthetic pathway of CBSenSeCB.

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Table 1. Phase transition temperatures (°C) and enthalpy changes (kJ mol-1)
at a rate of 10 °C min-1.
n
Process
2nd heat
1st cool
2nd heat
1st coola
1st heat
1st cool
2nd heatb
2nd heat
1st cool
Phase sequence
Cr 147.4 (35.8) Iso
3
Cr 105.8 (27.6) Iso
5
7
Cr 122.8 (27.5) Iso
Cr 49 (-)a NU 59 (-)a Cr 75.5 (22.1) Iso
Cr’ 80.8 (34.3) Iso’ 86.3 (6.96) Cr’’ 100.6 (9.6) Iso
G 2.39 Cr’’’ 32.4 (12.4)c NTB 43.1 (-) NU 71.9 (1.1) Iso
G 2.2 NTB 32.0 (6.8) Cr’’’ 64.9 (5.9) Cr’’ 100.6 (36.0) Iso
Cr 89.5 (40.8) Iso
9
Cr 61.7 (33.1) NU 75.9 (1.5) Iso
a Observed by POM but not clear on DSC, b NU region emerged between around 69 and
75 °C from Cr’’’ region, c Imperfect crystallization.
Figure 3. Photomicrographs of CBSe7SeCB for the NU phase at 70 °C (a), the NTB
phase at 42 °C (b) and at 30°C (c) in an untreated cell, and for the NU phase at 45 °C (d),
the NTB phase at 42 °C (e) and at 30°C (f) in an uniaxially-rubbed planarly-aligned cell
with the thickness of 3 μm. Crossed arrows and diagonal arrow represent polarizers and
rubbing directions, respectively.
We next examined the phase-transition behavior of CBSe7SeCB in detail.
Photomicrographs of the untreated, as well as uniaxially and planarly aligned cells upon

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cooling, are shown in Figure 3. Figure 3(a) reveals the NU phase with typical schlieren
textures at ~70 °C. At about 43 °C, the NU texture gradually changes to other ellipsoidal,
rope-like, and focal conic textures with partially crystallized regions [Figures 3(b) and
3(c)]. These textural changes are distinct in the images of the uniaxially and planarly
aligned cells. A monochroic birefringent texture is observed in the NU phase region,
which secures its uniaxial alignment in the NU phase [Figure 3(d)]. A line in the rubbing
direction gradually appears at 43 °C, resulting in a stripe texture, as shown in Figures
3(e) and 3(f). These optical textural changes strongly support the incidence of the NTB
phase. The striped texture is maintained with partial crystallization upon cooling to
ambient temperature. By acquiring the DSC curve at 10 °C min-1, the transition from the
NU to the NTB phase (NU-NTB) at 43 °C, and the glass transition at 2.3 °C, become
discernible, as shown in Figure 4(a), which supports the persistence of the NTB phase to
room temperature. Interestingly, CBSe7SeCB exhibits unusual phase- transition
behavior during heating, as shown in Figure 4(b). During the first heating, CBSe7SeCB
melts to the Iso phase (abbreviated as Iso’) at 80.8 °C, which is immediately subjected
to cold crystallization to Cr’’ at 86.3 °C, subsequently giving rise to melting to the Iso
phase transition at 100.6 °C. During the second heating, after first cooling to below
-10 °C, cold crystallization (to Cr’’’) is observed at 32 °C [Figures 4 and 5(b)]; this Cr’’’
phase undergoes an exothermic transition to Cr’’ [Figures 4 and 5(c)]. Moreover, it is
interesting to note that an additional NU phase emerges from the remaining Cr’’’ region
at
~69 °C, as shown in Figures 5 (c) and (d); in such a thermal process, it eventually
undergoes a transition to Cr’’ transition [Figures 5 (e) and (f)]. In other words,
CBSe7SeCB has a tendency toward a kinetics-dominated enantiotropic NU phase.
Considering the above phase-transition behavior, Cr’’ phases upon the first and second
heating are similar but Cr’ and C’’’ are derived from different crystalline species to one
another, and Cr’’’ upon heating and cooling is similar. Upon the other thermal heating
process after cooling to 30 °C from Iso phase, whereas, the following three transitions
such as the NTB to NU transition with cold crystallization (Cr’’’) at 43 °C, the Cr’’’ to NU
~
transition at 69 °C, and the NU phase to other Iso (Iso’’) phase transition at around
75 °C were clearly captured as shown in Figure 6. That is, CBSe7SeCB has an
enantiotropic NU phase between ca. 69 and 75 °C in which the latter temperature is
considered as the NU to Iso transition of CBSe7SeCB used in the bend angle
dependency later. A repeat DSC experiment after leaving the sample for two weeks
~
~
shows almost only melting at 100 °C with a subtle peak at 79 °C, too, as shown in
Figure S7, with which the former is highly analog to that upon the second heating. This

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~
suggests that the prior melting at 81 °C during the first cooling or Cr’ is ascribable to
the crystalline species that developed predominantly during solution crystallization.
Figure 4. DSC curves of CBSe7SeCB at a rate of 10 °C min-1 upon first cooling (a) and
upon first and second heating (b). NTBG: NTB glassy, Cr, Cr’, Cr’’ and Cr’’’: each crystal
phase, NTB: twist-bend nematic phase, NU: uniaxial nematic phase, and Iso and Iso’:
each isotropic phase.

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Figure 5. Photomicrographs of CBSe7SeCB at -10 °C for the NTBG (a), at 34 °C for the
NTB phase with cold crystallization to Cr’’’ (b), at 67 °C for the Cr’’’ to Cr’’ transition
(c), at 72 °C (d) and at 73 °C (e) for the NU emergence in the middle to Cr’’ transition,
and at 77 °C for Cr’’ phase (f) in an untreated cell upon heating at a rate of 10 °C min-1
from
-10 °C.
Figure 6. Photomicrographs of CBSe7SeCB at 30 °C for the NTB region (a), at 46 °C
for the NU region subjected to cold crystallization to Cr’’’ (b), at 73 °C the emergent NU
phase from the Cr’’’ region in the middle of the Cr’’ transition (c), and at 77 °C for the

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NU to the Iso transition (d) in an untreated cell upon heating at a rate of 10 °C min-1.
Finally, the molecular geometry of CBSe7SeCB with an all-trans spacer was
optimized by DFT calculations at the B3LYP [27]/6-31G(d) level using the Gaussian 16
software (Figure 7) [28]. The selenoether has an out-of-plane conformation with respect
to the benzene ring, in contrast to its in-plane conformation in the same chalcogen
family of ether- or thioether-linked dimers, in which the in-plane conformation is due to
π-π interaction between a lone pair on an O or S and the phenyl ring. On the other hand,
such an out-of-plane conformation for selenoether is rather similar to those observed for
methylene-linked dimers, which exhibit a σ-π interaction between the methylene C–H
and the phenyl ring. On the other hand, the χ value between the para axes of the two
cyanobiphenyl moieties is about 90°; intriguingly, this value is markedly smaller or
more bent than those of a conventional nematogen, namely CBO7OCB (144°) [15], as
well as twist-bend nematogens, such as CB9CB (111°) [15], CB8OCB (128°) [15],
CBS7SCB (109°) [24], and CBS7OCB (126°) [24], which have a total of nine atoms in
the spacer and linker along each chain line. The smaller χ of CBSe7SeCB is mainly
attributed to the C–Se–C bond angle of 101°. The transition temperatures for the
NTB-NU and NU-Iso phase transitions [T(NTB-NU) and T(NU-Iso), respectively] of
CBSe7SeCB, CB9CB, CBO7OCB, CB8OCB, CBS7SCB, and CBS7OCB are
summarized in Table 2 and plotted against χ in Figure 8. The T(NTB-NU) and T(NU-Iso)
values of CB9CB, CBO7OCB and CB8OCB are taken from the literature [15]. Notably,
although methylene, ether, thioether and selenoether have distinct intermolecular
interactions, the transition temperatures, especially T(NU-Iso), correlate almost linearly
with χ; that is, they decrease with decreasing χ. This observation may be an efficient
embodiment of the molecular geometry facilitated by the linkage in each aggregated
state. Although the phase-transition behavior and incidence of the NTB phase also
depend on other factors, χ provides useful plausible insight into the observed
phenomena.

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Figure 7. The optimized structure of CBSe7SeCB from its all-trans spacer model and
the molecular bend angle value (χ).
Table 1. Molecular bend angles (χ) and transition temperatures T(NTB-NU) and
T(NU-Iso) upon cooling.
Compd.
CB9CB
χ (°)
111
T(NTB-NU) (°C)
T(NU-Iso) (°C)
121.5
Refs.
15
105.4
-
CBO7OCB
CB8OCB
144
128
109
126
90
181.3
15
109.9
88.3
95.9
43.1
153.3
15
CBS7SCB
115.2
23
CBS7OCB
146.7
23
CBSe7SeCB
75a Present
a Observed by POM.
Figure 8. T(NTB-NU) and T(NU-Iso) plots against molecular bend angles (χ).
Conclusions
In summary, the present study offers a new molecular design for twist-bend nematogens
based on a selenoether linkage. Selenium-linked CBSenSeCB cyanobiphenyl dimers
were synthesized and their phase transitions and mesomorphism revealed. CBSe7SeCB
forms an NU phase, as well as an NTB phase, which was stable down to room
temperature. The DFT-optimized geometry of CBSe7SeCB revealed a χ of 90°, which is
markedly smaller than those of liquid crystalline dimers with other types of linkage. In
addition, linear correlations between the phase transition temperatures (NTB-NU

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transition and isotropic temperatures) and χ were observed. The present study provides
structural insight into phase transitions from the viewpoint of χ, and paves the way for
the molecular design of new twist-bend nematogens based on chalcogen linkages. The
selenoether-based twist-bend nematogens could exert a beneficial effect in structural
analyses by resonant X-ray scattering at the selenium K-edge [10(c)]. Furthermore,
since selenium-containing mesogens are highly rare [30], the present discussion could
be useful to design the new molecular selenium-based ones. We will further explore
selenoether-based twist-bend nematogens and mesogens in future studies.
Experimental
Chemicals
All chemicals were obtained from commercial suppliers and used without further
purification. Selenium and copper(I) oxide (CuO) were purchased from FUJIFILM
Wako Pure Chemical Co., Ltd. (Tokyo, Japan). 4-Bromoiodobenzene,
4-cyanophenylboronic acid pinacol ester (Bpin-benzonitrile), each α,ω-dibromoalkane,
sodium borohydride (NaBH4), and tetrakis(triphenylphosphine)palladium(0)
[Pd(PPh3)4] were purchased from Tokyo Chemical Industry Co., Ltd. (Tokyo, Japan),
while hexane, tetrahydrofuran (THF), dimethylsulfoxide (DMSO), dichloromethane
(DCM,) and methanol (MeOH) were purchased from Kanto Chemical Co., Inc. (Tokyo,
Japan). Anhydrous ethanol (EtOH), potassium hydroxide (KOH), potassium carbonate
(K2CO3) and cesium carbonate (Cs2CO3) were purchased from Nacalai Tesque Inc.
(Kyoto, Japan).
Synthesis
1
13
The synthesis procedure and H and C NMR (JEOL JNM ECS 500) characterization
data for CBSe7SeCB are presented below, with those for the other compounds provided
in the supporting information.
Synthesis of bis(4-bromophenyl)diselenide
Selenium powder (3.34 g, 42.4 mmol), 4-bromo-iodobenzene (6.0 g, 21.2 mmol), CuO
(0.338 g, 4.24 mmol), and KOH (2.38 g, 42.4 mmol) were placed in a flask, after which
dry DMSO (25 mL) was added under an argon atmosphere. The resulting mixture was
stirred at 90 °C for 5 h. After the reaction was complete, as evidenced by TLC, the
mixture was cooled to ambient temperature and filtered to remove the insoluble portion.
The filtrate was extracted with DCM, the extract washed with water and brine, and dried
over MgSO4. The volatiles were removed under reduced pressure, and the crude product

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was purified by silica-gel column chromatography (eluent: 1:10 DCM/hexane) to afford
1
1 as a yellow solid (2.48 g, 50%). H NMR (500 MHz, CDCl3) δ 7.44 (d, J = 7.2 Hz,
4H), 7.39 (d, J = 7.2 Hz, 4H) ppm. 13C NMR (125 MHz, CDCl3) δ 133.4, 133.4, 133.4,
133.4, 132.3, 132.3, 132.3, 132.3, 129.4, 129.4, 122.4, 122.4 ppm.
Synthesis of 1,7-bis[(4-bromophenyl)seleno]heptane
Bis(4-bromophenyl)diselenide (0.30 g, 0.638 mmol), NaBH4 (96.5 mg, 2.55 mmol), and
anhydrous EtOH (4.0 mL) were placed in a two-necked round-bottomed flask under
argon, and the resultant mixture was stirred at 0 °C for 15 min. After a colorless solution
had formed, 1,7-dibromoheptane (0.108 mL, 0.638 mmol) in anhydrous EtOH (0.5 mL)
was added dropwise to the reaction mixture with cooling at 0 °C, after which it was
stirred at room temperature for 2 h. The reaction mixture was extracted with DCM, the
extract washed with water and brine, dried over MgSO4, and concentrated under
reduced pressure. The crude product was purified by silica-gel column chromatograph
(eluent: 1:5 DCM/hexane) to afford the target compound (0.260 g, 72%) together with
1
the mono-substituted biproduct as a colorless solid. H NMR (500 MHz, CDCl3) δ 7.37
(d, J = 7.2 Hz, 4H), 7.33 (d, J = 7.2 Hz, 4H), 2.87 (t, J = 5.8 Hz, 4H), 1.66 (tt, J = 5.8
13
and 6.2 Hz, 4H), 1.37 (tt, J = 5.6 and 6.2 Hz, 4H), 1.32-1.24 (m, 2H) ppm. C NMR
(125 MHz, CDCl3) δ 134.0, 134.0, 134.0, 134.0, 132.0, 132.0, 132.0, 132.0, 129.5,
129.5, 120.8, 120.8, 29.9, 29.9, 29.5, 29.5, 28.4, 28.4, 28.1, 28.1 ppm.
Synthesis of 1-(4-cyanobiphenyl-4’-ylseleno)-7-(4-cyanobiphenyl-4’-ylseleno)heptane
(CBSe7SeCB)
1,7-Bis[(4-bromophenyl)seleno]heptane (0.232 g, 0.408 mmol), 4-cyanophenylboronic
acid pinacol ester (0.215 g, 0.938 mmol), Pd(PPh3)4 (0.108 g, 93.8 μmol), and Cs2CO3
(0.611 g, 1.88 mmol) were placed in a two-way flask, after which THF (9 mL, degassed
by argon bubbling) was added under argon. After stirring for 6 h under reflux, the
reaction mixture was extracted with DCM and the organic layer was washed with water
and brine and dried over MgSO4. After the volatiles were removed under reduced
pressure, the crude product was purified by silica-gel column chromatography (eluent:
DCM) and recrystallized from MeOH/DCM to afford CBSe7SeCB as a colorless solid
(0.120 g, 48%). 1H NMR (500 MHz, CDCl3) δ 7.72 (d, J = 6.8 Hz, 4H), 7.66 (d, J = 6.8
Hz, 4H), 7.55 (d, J = 6.8 Hz, 4H), 7.47 (d, J = 6.8 Hz, 4H), 2.96 (t, J = 5.8 Hz, 4H),
1.74 (tt, J = 5.8 and 6.2 Hz, 4H), 1.43 (tt, J = 5.6 and 6.2 Hz, 4H), 1.38-1.29 (m, 2H)
13
ppm. C NMR (125 MHz, CDCl3) δ 144.9, 144.9, 137.2, 137.2, 132.7, 132.7, 132.7,
132.7, 132.3, 132.3, 132.3, 132.3, 132.1, 132.1, 127.7, 127.7, 127.7, 127.7, 127.4, 127.4,

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127.4, 127.4, 118.9, 118.9, 110.9, 110.9, 29.9. 29.9, 29.6, 29.6, 28.5, 27.7, 27.7 ppm.
Mesophase characterization
Phase transitions were identified by variable-temperature PLM using an Olympus BX50
microscope equipped with a Linkam LK-600 PM hot stage. Detailed phase-transition
temperatures and ΔH values were obtained using a Shimadzu DSC-60 differential
scanning calorimeter with 10 °C min−1 heating/cooling/heating cycles under a 50 mL
min−1 flow of nitrogen gas.
Molecular modeling
The structure of CBSe7SeCB in its all-trans spacer form was optimized at the
B3LYP/6-
31G(d) [27] (DFT) level of theory using Gaussian 16 [28]. Gauss View 6 [29] was used
for visualization. The atom coordinates and absolute energy level obtained from the
calculations for CBSe7SeCB are provided in the supporting information.
Acknowledgements
This work was supported by Japan Society for the Promotion of Science KAKENHI
grant no. 17K14493 and a research grant from the Naito Foundation.
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