The effect of intermolecular actions on the mesomorphic properties of alkenoxy biphenyl-based liquid crystals

Article abstract of DOI:10.1016/j.molliq.2019.111880

Two series of alkenoxy-biphenyl compounds have been synthesized and characterized for investigating the relationship between intermolecular actions (e.g., π-π stacking, dipole-dipole interactions, and van der Waals interactions) and the mesomorphic properties. Firstly, their mesophases were determined by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X-ray diffraction (XRD). Then, Density Functional Theory (DFT) calculations, UV absorption spectra and fluorescence (FL) emission spectra were also conducted to assist in analyzing their mesomorphic properties. The results show that the type and stability of liquid crystal mesophases are dependent on the intermolecular actions. Moreover, suitably modifying intermolecular actions by the terminal groups has been proved to be an effective approach to regulate the formation and stability of nematic/smectic mesophases.

Full text of DOI:10.1016/j.molliq.2019.111880

Journal Pre-proof
The effect of intermolecular actions on the mesomorphic properties of alkenoxy
biphenyl-based liquid crystals
Shengbo Zhu, Jin Chigan, Wei Li, Jingyu Yang, Weixing Chen, Wenzhi Zhang,
Xiaoling Niu, Xinbing Chen, Zhongwei An
PII:
S0167-7322(19)33621-9
DOI:
https://doi.org/10.1016/j.molliq.2019.111880
MOLLIQ 111880
Reference:
To appear in: Journal of Molecular Liquids
Received Date: 29 June 2019
Revised Date: 30 September 2019
Accepted Date: 4 October 2019
Please cite this article as: S. Zhu, J. Chigan, W. Li, J. Yang, W. Chen, W. Zhang, X. Niu, X. Chen, Z. An,
The effect of intermolecular actions on the mesomorphic properties of alkenoxy biphenyl-based liquid
crystals, Journal of Molecular Liquids (2019), doi: https://doi.org/10.1016/j.molliq.2019.111880.
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Graphical abstract

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The effect of intermolecular actions on the mesomorphic properties
of alkenoxy biphenyl-based liquid crystals
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Shengbo Zhua, Jin Chigana, Wei Lia, Jingyu Yangb, Weixing Chena, Wenzhi Zhanga,
Xiaoling Niua, Xinbing Chenb and Zhongwei Anb
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a
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Shaanxi Key Laboratory of Photoelectric Functional Materials and Devices, School
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of Materials and Chemical Engineering, Xi'an Technological University, Xi'an 710021,
China
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b
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School of Materials Science and Engineering, Shaanxi Normal University, Xi'an
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710062, China
Corresponding Authors
(1) Shengbo Zhu
E-mail: zhushengbo@xatu.edu.cn
(2) Weixing Chen
E-mail: chenwx@xatu.edu.cn
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Abstract
Two series of alkenoxy-biphenyl compounds have been synthesized and characterized
for investigating the relationship between intermolecular actions (e.g., π-π stacking,
dipole-dipole interactions, and Van der Waals interactions) and the mesomorphic
properties. Firstly, their mesophases were determined by differential scanning
calorimetry (DSC), polarizing optical microscopy (POM) and X-ray diffraction
(XRD). Then, Density Functional Theory (DFT) calculations, UV absorption spectra
and fluorescence (FL) emission spectra were also conducted to assist in analyzing
their mesomorphic properties. The results show that the type and stability of liquid
crystal mesophases are dependent on the intermolecular actions. Moreover, suitably
modifying intermolecular actions by the terminal groups has been proved to be an
effective approach to regulate the formation and stability of nematic / smectic
mesophases.
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KEYWORDS: Alkenoxy biphenyl-based compounds; nematic mesophase; smectic
mesophase; intermolecular actions; DFT calculations
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1. Introduction
Liquid crystals (LCs) have been playing significant roles in many emerging fields due
to their unique physical and optical properties[1-3], such as liquid crystal displays[4],
liquid crystal thermosets[5], sunlight-driven polymer actuators[6], photovoltaic
devices[7], etc.. In order to meet higher application requirements, molecular
engineering is often an effective approach. Sometimes a slight structural adjustment is
likely to cause considerable changes in the mesomorphic properties[8]. Therefore,
researches on regulating mesomorphic properties by molecular modifications will be
an ongoing challenge.
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Generally, LC molecules consist of four sections, i.e., mesogenic cores, linking
groups, terminal groups, and lateral substituents[9]. Up to now, continuous molecular
engineering has been proposed to modify these four sections for forming stable LC
mesophases. In addition, intermolecular actions (e.g., π-π stacking, dipole-dipole
interactions, and van der Waals forces) should also be concerned because of their
decisive effects on the formation of mesophase types. At present, biphenyl fragment is
usually employed as the mesogenic core due to the rod-like shape, structural rigidity,
and low cost[10, 11]. Moreover, its π-π stacking feature is helpful for the well-ordered
arrangements, hence facilitating the formation of semetic mesophase. However, too
much strong π-π interactions is often unhelpful for the formation of nematic
mesophase[12-14]. To obtain desirable mesophases in π-conjugated molecules, a
perfect balance of intermolecular actions is necessary. Therefore, molecular
modifications become particularly important. One simple way is just to modify the
terminal moieties, e.g., changing the kind of terminal groups or the length of terminal
chains[15, 16].
In the previous researches, it is gradually clear that the effect of the intermolecular
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actions on mesomorphic properties, including π-π interaction[17], dipole-dipole
interaction[18] and hydrogen bond interaction[19]. In particular, the recent result[20],
that is the enhanced induced dipole-induced dipole interactions could result in
multiple reversible smectic mesophases (i.e., SmA, SmB and SmE) and wider
mesophase ranges by fine-tuning the terminal groups, has given us more research
motivation. Based on this, we will go deeper into the formation and stability of
mesophases from the view of intermolecular actions in this paper. To facilitate
discussion, two series, VmOBC (m = 1, 2, 3, 4) with cyano terminals and V1OBEn
(n = 6, 8, 10, 12) with alkyl ester terminals, have been designed and synthesized, as
shown in Figure 1 and Scheme 1. Meanwhile, Density Functional Theory (DFT)
calculations and photophysical measurements were conducted to assist in analyzing
the structure-property relationship.
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2. Results and discussion
2.1. Synthesis and characterization
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Two series, VmOBC (m = 1, 2, 3, 4) and V1OBEn (n = 6, 8, 10, 12), have been
synthesized through simple reactions, and their synthetic routes are shown in Scheme
1. Compounds VmOBC were prepared from 4'-hydroxy-[1,1'-biphenyl]-4-carbonitrile
and the corresponding olefin bromide via an etherification reaction. For series
V1OBEn, 4'-hydroxy-[1,1'-biphenyl]-4-carboxylic acid and 3-bromoprop-1-ene are
employed as the starting materials via two-step reactions (i.e., etherification followed
by esterification) to obtain the target compounds. The final products were purified by
column chromatography and confirmed by 1H-nuclear magnetic resonance (1H NMR),
13C-nuclear magnetic resonance (13C NMR), gas chromatography with electron
impact-mass spectrometry (GC/EI-MS), and infrared (IR) spectroscopy, as described
in the experimental section. Taking V1OBC and V1OBE6 as examples, IR spectra
were chosen to confirm the characteristic groups. As can be seen from Figure 2, the
simultaneous peaks at 1602 cm-1 in the cases of V1OBC and V1OBE6 are assigned to
the stretching vibration of the vinyl group. The peak at 2223 cm-1 is the stretching
vibration of the cyano group in V1OBC, and the peak at 1718 cm-1 is attributed to the
carbonyl group in V1OBE6, which demonstrates that the target compounds are
successfully obtained.
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2.2. DFT Calculations
To investigate the geometry and polarizability of series VmOBC (m = 1, 2, 3, 4) and
V1OBEn (n = 6, 8, 10, 12), density functional theory (DFT) studies based on
quantum mechanical calculations were conducted without imposing any constraints
using the Gaussian 09 program package[21]. Spin-restricted DFT calculations were
carried out in the framework of the generalized gradient approximation (GGA) using
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B3LYP exchange-correlation functional and the 6-31G (d, p) basis set[22, 23]. All the
calculated results are shown in Figure 3 and Figure S1. From Table 1, it can be found
that the molecular aspect L/W ratios of series VmOBC increase first and then
decrease with the extension of the flexible alkenoxy chains. Compared with the L/W
ratio (3.25) of V3OBC, V4OBC gives a smaller L/W ratio (2.88) in spite of the
longest alkenoxy chain, meaning that it may exhibit a greater steric repulsion and Van
der Waals interaction. Meanwhile, the L/W ratios of series V1OBEn show an
increased trend from 3.31 to 4.03. Although these two series contain distinct terminal
groups, the inter-ring twist angles (θ) of biphenyl units do not display significant
changes. However, the molecular dipole moments (ꢀ) of series VmOBC and
V1OBEn are quite different, i.e., 6.42-6.64 D and 2.43-2.48 D, respectively. This
may be caused by electron-withdrawing abilities of the terminal cyano and ester
groups. Overall, the above parameters are of great importance for analyzing the
mesomorphic and photophysical properties below.
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2.3. Mesomorphic properties
Differential scanning calorimetry (DSC) and polarizing optical microscopy (POM)
are utilized to identify mesomorphic properties of series VmOBC and V1OBEn.
Mesophase identification is determined by comparing the observed textures in the
reported literature[24]. The corresponding data are summarized in Table 2. The
representative DSC curves of compound V1OBC and V1OBE6, as examples, are
depicted in Figure 4(a) and Figure 5(a), respectively, and those of the other analogs
can be found in the Supporting Information.
2.3.1. The effects of terminal alkenoxy chain lengths on mesophase stability of
biphenyl carbonitrile-based LCs
In the DSC curve of V1OBC, there are two obvious peaks at 80.91 ℃ and 63.72 ℃,
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corresponding to the melting point and the freezing point, respectively. In addition, a
small exothermic peak at 76.48 ℃ can also be found, and the corresponding
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enthalpy is 0.64 kJ mol-1. Generally, the enthalpy value is lower than 1 kJ mol-1,
suggesting the transition between nematic mesophase and isotropic phase[25, 26].
And, this has been proved from POM observation in Figure 4(b). In order to improve
mesophase stability, the terminal alkenoxy chains are further extended from 3 carbon
atoms to 6. Unfortunately, V2OBC and V3OBC have still no mesophases on heating.
Along with the further extension of the terminal alkenoxy chain, surprisingly,
V4OBC displays enantiotropic nematic mesophases. This may be attributed to the
decrease in molecular length (L) and the increase in molecular width (W) (see Table 1),
thereby maximizing the steric repulsion of molecules and loosening π-π stacking,
which support the formation of nematic mesophase[12]. On the other hand, the longer
alkenoxy chain can also favour Van der Waals interactions, which promotes the
stacking of mesogens.[3, 27, 28] Furthermore, from Figure 6(a and b), it can be found
that all compounds VmOBC give nematic mesophases on cooling, but only V4OBC
possesses nematic mesophase on heating. Their melting, clearing, and freezing points
exhibit obvious odd-even effects. In addition, the even-terminal compounds (V2OBC
and V4OBC) show wider nematic mesophases on cooling compared to those of the
odd-terminal compounds (V1OBC and V3OBC). Among them, V4OBC gives the
widest nematic mesophase range (68.51 ℃).
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2.3.2. The effects of terminal alkyl chain lengths on mesophase stability of allyloxy
biphenyl ester-based LCs
Compared with V1OBC, V1OBE6 shows enantiotropic mesophases in spite of the
same allyloxy biphenyl moiety. In addition, mesophase-mesophase transitions are also
found, which is proved to be the transition between the fan-shaped texture of SmA
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mesophase and the striated fan-shaped texture of SmE mesophase, as shown in Figure
5(b-d). This is because the strong intramolecular π-conjugation and large L/W ratios of
series V1OBEn (n = 6, 8, 10, 12) are beneficial to the π-π overlap between adjacent
biphenyl cores and the orderly side-by-side molecule arrangements, which is of
importance to the formation smectic mesophases[3, 27, 29]. From Figure 6(c), it can
be found that the clearing points decrease with the extension of the terminal alkyl
chains, while their melting points show regular wave changes. On the whole, the
mesophase ranges gradually narrow down with the extension of molecular lengths. By
contrast, most of the compounds give wider mesophase ranges on cooling except
V1OBE6. There are two possible reasons for this: (i) Longer terminal alkyl chains
may result in crystallization hysteresis; (ii) The wider mesophase may be caused by
supercooling phenomenon[30].
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2.4. Photophysical properties
UV-vis absorption spectra and fluorescence (FL) emission spectra of V1OBC and
V1OBE6 in dichloromethane (DCM) as examples[31], are depicted in Figure 7. From
Figure 7(a), it can be seen that V1OBC and V1OBE6 show similar absorption bands
with the maximum absorption wavelengths (λmax) at 294 nm and 298 nm, respectively.
The absorption band of V1OBC is slightly blue-shifted by 4 nm in comparison to that
of V1OBE6. From the FL emission spectra in Figure 7(b), at the same time, it can be
observed that V1OBC and V1OBE6 deliver the maximum emission wavelengths (λem)
at 365 nm and 381 nm, respectively, when excited at 300 nm. The emission peak of
V1OBC is blue-shifted by 16 nm compared with that of V1OBE6. The blue-shifted
absorption and emission spectra may be because that the stronger
electron-withdrawing ability of cyano group makes electron clouds deviate from the
biphenyl section and further reduces the intramolecular π-conjugation level, which not
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only increases molecular dipole moments (6.64 D for V1OBC vs. 2.47 D for
V1OBE6) but also decreases π-π stacking[17, 32]. This phenomenon could also
verify the aforementioned fact that terminal groups affect the intermolecular actions
and the formation of mesophase.
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2.5. Thermal stability evaluation
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Thermal stability is an important parameter for evaluating LC application, which is
usually determined by thermo-gravimetric analysis (TGA)[8, 17, 33]. Normally,
homologues have similar decomposition behaviors, so the TGA curves of V1OBC
and V1OBE6 are taken as examples here. From Figure 8, it can be seen that the onset
decomposition temperatures of them are about 200 ºC, and almost decomposed
completely at the range of 300-450 ºC. It is worth noting that V1OBC shows one-step
decomposition from 200 ºC to 320 ºC, while V1OBE6 loses 75% of weight between
200 and 330 and follows a small shoulder platform until 450 ºC. To be specific,
the temperatures at which 5% weight loss occurred (T5%) of V1OBC and V1OBE6
are 221.6 ºC and 244.9 ºC, respectively, which is much higher than their melting and
clearing points in Table 2. The results could prove that these two series are stable up
to their clearing points, which are in accordance with DSC data.
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3. Conclusions
This study has highlighted the importance of intermolecular actions (e.g., π-π stacking,
dipole-dipole interactions, and Van der Waals interactions) on determining the type
and stability of LC mesophases, where the intermolecular actions could be tuned by
the terminal groups. In these alkenoxy-biphenyl-carbonitrile compounds, the cyano
terminal group can give rise to the increase in intermolecular dipole-dipole
interactions and the decrease in π-π interactions because of the strong
electron-withdrawing ability, while the longer terminal alkenoxy chain can also
loosen π-π stacking and promote Van der Waals interactions, which would be crucial
to the formation and stability of nematic mesophase. When the cyano group is
replaced by alkyl-ester groups, by contrast, the π-conjugated levels of the biphenyl
cores are strengthened obviously, which are beneficial to the π-π overlap between
adjacent biphenyl cores and the orderly side-by-side molecule arrangements, thereby
resulting in the formation of smectic mesophase. Hence, modifying intermolecular
actions by the terminal groups has been proved to be an effective approach to regulate
the formation and stability of LC mesophases.
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4. Experimental section
4.1. Materials
4'-hydroxy-[1,1'-biphenyl]-4-carbonitrile (1), 4'-hydroxy-[1,1'-biphenyl]-4-carboxylic
acid (3), 3-bromoprop-1-ene (2a), 4-bromobut-1-ene(2b), 5-bromopent-1-ene(2c),
6-bromohex-1-ene (2d), 1-bromohexane, 1-bromooctane, 1-bromodecane,
1-bromododecane were purchased from Aladdin-reagent Co. (Shanghai, China) and
used as received. All chromatographic separations were conducted on silica gel
(200-300 mesh). All the chemicals and solvents used in this work were of analytical
grade and used without further purification unless otherwise stated.
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4.2. Characterization and measurements
The structures of the final products and intermediate were confirmed by 1H NMR and
13C NMR spectra (Bruker AV-400 MHz instrument), mass spectra (GC/EI-MS
Thermo DSQ II), and IR spectra (Thermo-Nicolet Nexus spectrometer). The phase
transition temperatures and enthalpy data of the final products were measured by DSC
(Mettler Toledo DSC1) under nitrogen atmosphere at heating and cooling rates of
5 °C min-1. Mesophase textures were examined by POM (Leica DM2500P) with a
Linkam THMS600 hot-stage at a heating and cooling rate of 0.5 °C min−1. XRD
experiments were performed on a Small &. Wide Angle X-Ray Scattering System
(Anton Paar, SAXSess mc2) using the linear monochromatic Cu Kα beam (λ = 0.154
nm). TGA was carried out with Thermoanalyzer systems (Q1000DSC+LNCS+FACS
Q600SDT) at a scanning rate of 10 °C min-1 under a nitrogen atmosphere (flow rate:
100 cm3 min−1). UV-vis absorption spectra of compounds V1OBC and V1OBE6 in
dichloromethane (DCM) (1×10-5 mol L-1) were measured with a Shimadzu UV-3600
spectrophotometer. FL emission spectra of compounds V1OBC and V1OBE6 in
DCM (2×10-7 mol L-1) were obtained by a Hitachi F-7000 Fluorescence
spectrophotometer.
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4.3. Synthesis
4.3.1. Synthesis of series VmOBC
As
an
example,
the
preparation
procedure
of
4'-(allyloxy)-[1,
1'-biphenyl]-4-carbonitrile (V1OBC) is described below.
In a 100 mL 3-necked flask, 4'-hydroxy-[1, 1'-biphenyl]-4-carbonitrile (1) (5.00 g,
25.61 mmol), 3-bromoprop-1-ene (2a) (3.72 g, 30.74 mmol), K2CO3 (7.43 g, 53.79
mmol), and N, N-dimethylformamide (DMF) (50 mL) were added in turn. Following
this, the reaction mixture was stirred for 12 h at 60 °C, and then poured into DCM.
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The organic layer was washed with water. After removing the solvent, the crude
product obtained was purified through column chromatography (DCM/PE = 1/3, v/v;
where PE is petroleum ether, boiling range: 60-90 ºC) to give white crystals (5.08 g,
84 % yield). 1H NMR (400 MHz, CDCl3, TMS): δ (ppm) 7.68 (d, J = 8.8 Hz, 2H,
phenyl-H), 7.62 (d, J = 8.9 Hz, 2H, phenyl-H), 7.52 (d, J = 9.1 Hz, 2H, phenyl-H),
7.00 (d, J = 9.0 Hz, 2H, phenyl-H), 6.10-6.02 (m, 1H, CH2=CH), 5.44 (d, J = 17.3 Hz,
1H, CH2=CH), 5.31 (d, J = 11.1 Hz, 1H, CH2=CH), 4.58 (dt, J = 5.4, 1.6 Hz, 2H,
OCH2). 13C NMR (100 MHz, CDCl3, TMS) δ (ppm) 159.25, 145.19, 132.97, 132.57,
131.65, 128.35, 127.12, 119.09, 117.94, 115.37, 110.16, 68.92. GC-MS (EI, m/z)
calcd. for (C16H13NO): 235.1. Found: 235.2 (M+, 100%), 220.1 (12%), 194.1 (65%),
166.1 (47%), 140.1 (29%). IR (KBr, pellet, cm-1): 3108, 2898, 2223, 1606, 1495,
1245, 1174, 826, 530.
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The synthesis methods of the other compounds (V2OBC-V4OBC) resemble that
of V1OBC, and the detailed characteristic data are described below.
V2OBC: The yield is 42 % of white crystals. 1H NMR (400 MHz, CDCl3, TMS):
δ (ppm) 7.65 (d, J = 8.4 Hz, 2H, phenyl-H), 7.60 (d, J = 8.9 Hz, 2H, phenyl-H), 7.50
(d, J = 8.9 Hz, 2H, phenyl-H), 6.97 (d, J = 9.0 Hz, 2H, phenyl-H), 5.95-5.85 (m, 1H,
CH2=CH), 5.17 (d, J = 17.3 Hz, 1H, CH2=CH), 5.11 (d, J = 10.4 Hz, 1H, CH2=CH),
4.04 (t, J = 6.9 Hz, 2H, OCH2), 2.58-2.53 (m, 2H, CH2). 13C NMR (100 MHz, CDCl3,
TMS) δ (ppm) 159.61, 145.22, 134.26, 132.57, 131.47, 128.35, 127.09, 119.10,
117.23, 115.20, 110.12, 67.40, 33.60. GC-MS (EI, m/z) calcd. for (C17H15NO): 249.1.
Found: 249.1 (M+, 64%), 221.0 (10%), 195.1 (100%), 166.0 (14%), 140.0 (13%). IR
(KBr, pellet, cm-1): 3075, 2950, 2872, 2223, 1606, 1495, 1239, 1173, 1035, 826, 530.
V3OBC: The yield is 68 % of white crystals. 1H NMR (400 MHz, CDCl3, TMS):
δ (ppm) 7.68 (d, J = 8.8 Hz, 2H, phenyl-H), 7.62 (d, J = 8.9 Hz, 2H, phenyl-H), 7.52
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(d, J = 9.0 Hz, 2H, phenyl-H), 6.98 (d, J = 9.0 Hz, 2H, phenyl-H), 5.90-5.80 (m, 1H,
CH2=CH), 5.07 (d, J = 17.2 Hz, 1H, CH2=CH), 5.01 (d, J = 11.1 Hz, 1H, CH2=CH),
4.01 (t, J = 6.6 Hz, 2H, OCH2), 2.28-2.22 (m, 2H, CH2), 1.94-1.87 (m, 2H, CH2). 13C
NMR (100 MHz, CDCl3, TMS) δ (ppm) 159.76, 145.28, 137.69, 132.57, 131.38,
128.34, 127.09, 119.10, 115.34, 115.14, 110.11, 67.35, 30.09, 28.40. GC-MS (EI, m/z)
calcd. for (C18H17NO): 263.1. Found: 263.1 (M+, 45%), 195.1 (100%), 166.0 (9%),
140.0 (8%). IR (KBr, pellet, cm-1): 2930, 2223, 1600, 1488, 1252, 1180, 1058, 911,
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813, 530. V4OBC: The yield is 62 % of white crystals. H NMR (400 MHz, CDCl3,
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TMS): δ (ppm) 7.68 (d, J = 8.5 Hz, 2H, phenyl-H), 7.62 (d, J = 8.9 Hz, 2H, phenyl-H),
7.51 (d, J = 9.0 Hz, 2H, phenyl-H), 6.98 (d, J = 9.0 Hz, 2H, phenyl-H), 5.88-5.78 (m,
1H, CH2=CH), 5.04 (d, J = 17.2 Hz, 1H, CH2=CH), 4.98 (d, J = 11. 5Hz, 1H,
CH2=CH), 4.00 (t, J = 6.7 Hz, 2H, OCH2), 2.16-2.11 (m, 2H, CH2), 1.86-1.78 (m, 2H,
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CH2), 1.62-1.54 (m, 2H, CH2). C NMR (100 MHz, CDCl3, TMS) δ (ppm) 159.80,
145.28, 138.46, 132.57, 131.32, 128.34, 127.08, 119.11, 115.12, 114.85, 110.09, 67.97,
33.42, 28.68, 25.34. GC-MS (EI, m/z) calcd. for (C19H19NO): 277.1. Found: 277.2
(M+, 24%), 195.2 (100%), 166.1 (11%), 140.0 (8%). IR (KBr, pellet, cm-1): 2944,
2223, 1606, 1495, 1245, 1180, 826, 530.
4.3.2. Synthesis of series V1OBEn
As an example, the preparation procedure of hexyl 4'-(allyloxy)-[1,
1'-biphenyl]-4-carboxylate (V1OBE6) is described below.
Synthesis of the intermediate 4'-(allyloxy)-[1, 1'-biphenyl]-4-carboxylic acid (4):
In a 150 mL 4'-hydroxy-[1, 1'-biphenyl]-4-carboxylic acid (3) (10.00 g, 46.68 mmol),
3-bromoprop-1-ene (2a) (6.78 g, 56.02 mmol), K2CO3 (16.13 g, 116.70 mmol), and
DMF (100 mL) were added in turn. Following this, the reaction mixture was stirred
for 12 h at 60 °C, and then poured into DCM. The organic layer was washed with
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water. After removing the solvent, the crude product obtained was purified through
column chromatography (EA/PE = 1/4, v/v; where EA is ethyl acetate) to give white
crystals (8.00 g, 68 % yield). 1H NMR (400 MHz, CDCl3, TMS): δ (ppm) 8.09 (d, J =
8.8 Hz, 2H, phenyl-H), 7.60 (d, J = 8.8 Hz, 2H, phenyl-H), 7.51 (d, J = 8.9 Hz, 2H,
phenyl-H), 6.92 (d, J = 8.9 Hz, 2H, phenyl-H), 6.10-6.00 (m, 1H, CH2=CH), 5.31 (d,
J = 17.2 Hz, 1H, CH2=CH), 5.27 (d, J = 10.6 Hz, 1H, CH2=CH), 4.84-4.83 (m, 2H,
OCH2). 13C NMR (100 MHz, CDCl3, TMS) δ (ppm) 166.40, 156.05, 145.37, 132.64,
132.35, 130.27, 128.71, 128.29, 126.57, 118.33, 115.94, 65.66. GC-MS (EI, m/z)
calcd. for (C16H14O3): 254.1. Found: 253.9 (M+, 56%), 196.9 (100%), 168.9(11%),
140.9 (11%), 114.9 (9%).
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Synthesis of V1OBE6: In a 50 mL 3-necked flask, intermediate 4 (0.45 g, 1.77
mmol), 1-bromohexane (1.17 g, 7.08 mmol), K2CO3 (1.47 g, 10.62 mmol), and DMF
(20 mL) were added in turn. Following this, the reaction mixture was stirred for 14.5
h at 40 °C, and then poured into DCM. The organic layer was washed with water.
After removing the solvent, the crude product obtained was purified through column
1
chromatography (EA/PE = 1/15, v/v) to give white crystals (0.53 g, 88 % yield). H
NMR (400 MHz, CDCl3, TMS): δ (ppm) 8.09 (d, J = 8.7 Hz, 2H, phenyl-H), 7.61 (d,
J = 8.7 Hz, 2H, phenyl-H), 7.55 (d, J = 8.8 Hz, 2H, phenyl-H), 6.97 (d, J = 8.8 Hz, 2H,
phenyl-H), 6.10-6.00 (m, 1H, CH2=CH), 5.42 (d, J = 17.2 Hz, 1H, CH2=CH), 5.29 (d,
J = 10.4 Hz, 1H, CH2=CH), 4.84 (dt, J = 5.6, 1.4 Hz, 2H, OCH2), 3.99 (t, J = 6.6 Hz,
2H, COOCH2), 1.83-1.76 (m, 2H, CH2), 1.51-1.43 (m, 2H, CH2), 1.37-1.32 (m, 4H,
CH2), 0.91 (t, J = 6.6 Hz, 3H, CH3). 13C NMR (100 MHz, CDCl3, TMS) δ (ppm)
166.21, 159.51, 145.39, 132.40, 132.14, 130.18, 128.33, 128.21, 126.44, 118.14,
114.98, 68.16, 65.49, 31.62, 29.26, 25.76, 22.64, 14.06. GC-MS (EI, m/z) calcd. for
(C22H26O3): 338.2. Found: 338.4 (M+, 55%), 281.2 (10%), 254.1 (40%), 197.1 (100%),
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169.1 (9%), 141.1 (9%). IR (KBr, pellet, cm-1): 2937, 2865, 1718, 1606, 1278, 1200,
1101, 826, 773.
3
The synthesis methods of the other compounds (V1OBE8-V1OBE12) resemble
that of V1OBE6, and the detailed characteristic data are described below.
V1OBE8: The yield is 92 % of white crystals. 1H NMR (400 MHz, CDCl3, TMS):
δ (ppm) 8.09 (d, J = 8.7 Hz, 2H, phenyl-H), 7.61 (d, J = 8.9 Hz, 2H, phenyl-H), 7.55
(d, J = 9.0 Hz, 2H, phenyl-H), 6.97 (d, J = 9.0 Hz, 2H, phenyl-H), 6.10-6.00 (m, 1H,
CH2=CH), 5.42 (d, J = 17.2 Hz, 1H, CH2=CH), 5.29 (d, J = 10.5 Hz, 1H, CH2=CH),
4.85-4.82 (m, 2H, OCH2), 3.99 (t, J = 6.7 Hz, 2H, COOCH2), 1.83-1.76 (m, 2H, CH2),
1.59-1.24 (m, 10H, CH2), 0.88 (t, J = 7.2 Hz, 3H, CH3). 13C NMR (100 MHz, CDCl3,
TMS) δ (ppm) 166.23, 159.48, 145.39, 132.37, 132.15, 130.17, 128.32, 128.19,
126.44, 118.15, 114.96, 68.17, 65.49, 31.83, 29.37, 29.27, 29.25, 26.06, 22.67, 14.10.
GC-MS (EI, m/z) calcd. for (C24H30O3): 366.2. Found: 366.2 (M+, 64%), 309.1 (12%),
254.0 (47%), 197.0 (100%), 169.0 (7%), 141.0 (8%). IR (KBr, pellet, cm-1): 2924,
2852, 1718, 1600, 1272, 1199, 1108, 826, 773.
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1
V1OBE10: The yield is 85 % of white crystals. H NMR (400 MHz, CDCl3,
TMS): δ (ppm) 8.09 (d, J = 8.7 Hz, 2H, phenyl-H), 7.61 (d, J = 8.7 Hz, 2H, phenyl-H),
7.55 (d, J = 8.9 Hz, 2H, phenyl-H), 6.97 (d, J = 8.9 Hz, 2H, phenyl-H), 6.10-6.00 (m,
1H, CH2=CH), 5.42 (d, J = 17.2 Hz, 1H, CH2=CH), 5.29 (d, J = 10.4 Hz, 1H,
CH2=CH), 4.84 (dt, J = 5.6, 1.4 Hz, 2H, OCH2), 3.99 (t, J = 6.6 Hz, 2H, COOCH2),
1.83-1.76 (m, 2H, CH2), 1.50-1.43 (m, 14H, CH2), 0.88 (t, J = 7.2 Hz, 3H, CH3). 13C
NMR (100 MHz, CDCl3, TMS) δ (ppm) 166.22, 159.48, 145.39, 132.37, 132.15,
130.16, 128.32, 128.19, 126.44, 118.15, 114.96, 68.17, 65.49, 31.91, 29.59, 29.57,
29.41, 29.33, 29.27, 26.06, 22.69, 14.11. GC-MS (EI, m/z) calcd. for (C26H34O3):
394.3. Found: 394.2 (M+, 75%), 337.1 (12%), 254.0 (55%), 197.0 (100%), 169.0 (7%),
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141.0 (7%). IR (KBr, pellet, cm-1): 2918, 2852, 1711, 1600, 1278, 1193, 1107, 826,
767.
1
3
V1OBE12: The yield is 90 % of white crystals. H NMR (400 MHz, CDCl3,
4
TMS): δ (ppm) 8.09 (d, J = 8.2 Hz, 2H, phenyl-H), 7.61 (d, J = 8.5 Hz, 2H, phenyl-H),
7.55 (d, J = 8.8 Hz, 2H, phenyl-H), 6.97 (d, J = 8.8 Hz, 2H, phenyl-H), 6.05 (dt, J =
16.1, 5.6 Hz, 1H, CH2=CH), 5.42 (d, J = 17.2 Hz, 1H, CH2=CH), 5.29 (d, J = 10.4 Hz,
1H, CH2=CH), 4.84 (d, J = 5.6 Hz, 2H, OCH2), 3.99 (t, J = 6.6 Hz, 2H, COOCH2),
1.84-1.76 (m, 2H, CH2), 1.49-1.25 (m, 18H, CH2), 0.87 (t, J = 6.7 Hz, 3H, CH3). 13C
NMR (100 MHz, CDCl3, TMS) δ (ppm) 166.23, 159.49, 145.40, 132.38, 132.16,
130.17, 128.32, 128.20, 126.44, 118.15, 114.97, 68.18, 65.49, 31.94, 29.68, 29.65,
29.62, 29.60, 29.42, 29.37, 29.28, 26.07, 22.70, 14.12. GC-MS (EI, m/z) calcd. for
(C28H38O3): 422.3. Found: 422.2 (M+, 86%), 365.1 (12%), 254.0 (62%), 197.0 (100%),
169.0 (6%), 141.0 (6%). IR (KBr, pellet, cm-1): 2918, 2846, 1718, 1606, 1285, 1193,
826, 767.
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Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This work was financially supported by the National Natural Science Foundation of
China (Nos. 61704133, 21673134, and 51773112), the Natural Science Foundation of
Shaanxi Province (No. 2018JM6087, 2019JM-225), the President’s Key Foundation
of Xi’an Technological University (No. XAGDXJJ16001), and the Natural Science
Foundation of Shaanxi Provincial Department of Education (Nos. 16JS043, 18JS051).
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Figures
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Figure 1. Molecular structures of compounds VmOBC (m = 1, 2, 3, 4) and V1OBEn (n = 6, 8, 10,
4
5
6
12).
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Figure 2. IR spectra of V1OBC and V1OBE6.
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Figure 3. Molecular structures of V4OBC and V1OBE6 optimized at the DFT/B3LYP/6-31G (d,
13
p) level of theory.
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Figure 4. DSC trace and POM image (×200) of V1OBC: (a) DSC trace; (b) the marble texture of
nematic mesophase at 75.4 ℃ on cooling. Herein (-) denotes cooling process.
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Figure 5. DSC trace and POM images (×200) of V1OBE6: (a) DSC trace; (b) the striated
fan-shaped texture of SmE mesophase at 71.1℃ on heating; (c) the fan-shaped texture of SmA
mesophase at 76.0℃ on heating; (d) the striated fan-shaped texture of SmE mesophase at 75.4℃
on cooling; (e) the fan-shaped texture of SmA mesophase at 88.5℃ on cooling. Herein (+) denotes
heating process, and (-) denotes cooling process.
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Figure 6. Phase transition temperature of series VmOBC in the heating (a) and cooling (b)
processes, and series V1OBEn in the heating (c) and cooling (d) processes. Cr: crystal; N:
nematic mesophase; Sm: smectic mesophase; I: isotropic liquid.
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Figure 7. (a) UV-vis absorption spectra of V1OBC and V1OBE6 in DCM (1×10-5 mol L-1); (b)
FL emission spectra of V1OBC and V1OBE6 in DCM (2×10-7 mol L-1).
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Figure 8. TGA curves of V1OBC and V1OBE6. Inset shows corresponding partial curves.
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Scheme 1. Synthetic routes of series VmOBC (m = 1, 2, 3, 4) and V1OBEn (n = 6, 8, 10, 12).
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Tables
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Table 1. Molecular length (L), molecular width (W), molecular aspect L/W ratio, inter-ring twist
angle (θ), and molecular dipole moment (ꢀ) calculated by DFT for series VmOBC (m = 1, 2, 3, 4)
and V1OBEn (n = 6, 8, 10, 12).
Compound
V1OBC
L (Å)
16.33
16.43
18.74
17.87
23.80
26.15
28.68
31.19
W (Å)
5.49
5.46
5.76
6.21
7.19
7.56
7.64
7.74
L/W
2.97
3.01
3.25
2.88
3.31
3.46
3.75
4.03
θ (°)
ꢀ (D)
6.64
6.42
6.63
6.60
2.47
2.48
2.45
2.43
35.49
35.73
35.49
35.67
35.99
35.90
35.73
35.39
V2OBC
V3OBC
V4OBC
V1OBE6
V1OBE8
V1OBE10
V1OBE12
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Table 2. Phase transition, temperature, and corresponding enthalpy obtained by POM and DSC for
series VmOBC (m = 1, 2, 3, 4) and V1OBEn (n = 6, 8, 10, 12).
Transition temperature (℃) (enthalpy change (kJ mol-1))
Compound
Heating process
Cr 80.91 (20.68) I
Cooling process
I 76.48 (-0.64) N 63.72 (-19.12) Cr
I 35.24 (-0.16) N -2.89 (-9.15) Cr
I 69.27 (-0.41) N 63.69 (-24.67) Cr
I 52.39 (-0.30) N -16.12 (-3.16) Cr
V1OBC
V2OBC
V3OBC
V4OBC
Cr 65.56 (24.19) I
Cr 84.91 (30.27) I
Cr 35.79 (16.15) N 52.60 (0.20) I
Cr 67.41 (11.41) SmE 75.92 (3.63)
SmA 101.25 (7.47) I
I 96.62 (-6.33) SmA 75.4* SmE 73.12
(-3.46) Cr
V1OBE6
V1OBE8
I 93.53 (-6.65) SmA 65.77 (-1.20) SmE
52.15 (-1.77) Cr
Cr 71.48 (24.97) SmA 95.20 (6.59) I
Cr 63.56 (30.62) SmA 92.03 (7.42) I I 92.1 SmA 54.5 SmE 32.9 Cr*
Cr 70.5 SmA 91.4 I* I 90.8 SmA 56.7 Cr*
V1OBE10
V1OBE12
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Note: (1) * data obtained by POM. (2) Cr: crystal; I: isotropic liquid; N: nemetic; SmA: smectic A;
SmE: smectic E. (3) The phase transition temperature is the peak value of the transition on DSC
curve.
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Highlights:
ꢀ Regulating the formation and stability of liquid crystalline mesophases by
intermolecular actions.
ꢀ Investigating the relationship between molecular dipole moments and the
formation of nematic mesophase.
ꢀ Investigating the relationship between π-π stacking and the formation of smectic
mesophase.
1 / 1

Title: The effect of intermolecular actions on the mesomorphic properties
of alkenoxy biphenyl-based liquid crystals
Conflict of interest: none.