New mesogenic compounds containing a terminal-substituted benzoxazole unit

Article abstract of DOI:10.1080/15421406.2013.837997

A series of novel mesogenic 2-(4-alkoxyphenyl-1-yl)-benzoxazole derivatives bearing different substituents (H, NO₂, CH₃, Cl, coded as nPB-H, nPB-N, nPB-M, and nPB-C, respectively) at the 5-position were prepared and characterized. nPB-N, nPB-M, and nPB-C exhibited enantiotropic smectic mesophases with the mesophase ranges 3 °C-32 °C and 3 °C-82 °C on heating and cooling processes, whereas nPB-H showed no mesophases. The substituents with the stronger electron withdrawing effect let to the wider mesomorphic temperature domain. The nPB-M, nPB-C, and nPB-H displayed intense emission in CH₂Cl₂ solutions with λ_max peaks of the photoluminescence spectra at 350-355 nm when excited at their absorption maxima. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/15421406.2013.837997

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New Mesogenic Compounds Containing a
Terminal-Substituted Benzoxazole Unit
Pei Chena, Yiwei Xua, Weisong Dub, Guangping Zhangb, Xinbing Chena
& Zhongwei Anac
a Key Laboratory of Applied Surface and Colloid Chemistry (MOE),
School of Materials Science and Engineering, Shaanxi Normal
University, Xi’an, P. R. China
b Xi’an Caijing Opto-Electrical Science & Technology Co. Ltd., Xi’an,
P. R. China
c Xi’an Modern Chemistry Research Institute, Xi’an, P. R. China
Published online: 28 Apr 2014.
To cite this article: Pei Chen, Yiwei Xu, Weisong Du, Guangping Zhang, Xinbing Chen & Zhongwei An
(2014) New Mesogenic Compounds Containing a Terminal-Substituted Benzoxazole Unit, Molecular
Crystals and Liquid Crystals, 592:1, 44-62
To link to this article: http://dx.doi.org/10.1080/15421406.2013.837997
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Mol. Cryst. Liq. Cryst., Vol. 592: pp. 44–62, 2014
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2013.837997
New Mesogenic Compounds Containing
a Terminal-Substituted Benzoxazole Unit
PEI CHEN,1 YIWEI XU,1 WEISONG DU,2 GUANGPING
ZHANG,2 XINBING CHEN,1,∗ AND ZHONGWEI AN1,3
1Key Laboratory of Applied Surface and Colloid Chemistry (MOE), School of
Materials Science and Engineering, Shaanxi Normal University, Xi’an, P. R.
China
2Xi’an Caijing Opto-Electrical Science & Technology Co. Ltd., Xi’an, P. R.
China
3Xi’an Modern Chemistry Research Institute, Xi’an, P. R. China
A series of novel mesogenic 2-(4-alkoxyphenyl-1-yl)-benzoxazole derivatives bearing
different substituents (H, NO2, CH3, Cl, coded as nPB-H, nPB-N, nPB-M, and nPB-
C, respectively) at the 5-position were prepared and characterized. nPB-N, nPB-M,
and nPB-C exhibited enantiotropic smectic mesophases with the mesophase ranges
3 ◦C–32 ◦C and 3 ◦C–82 ◦C on heating and cooling processes, whereas nPB-H showed
no mesophases. The substituents with the stronger electron withdrawing effect let to the
wider mesomorphic temperature domain. The nPB-M, nPB-C, and nPB-H displayed
intense emission in CH2Cl2 solutions with λmax peaks of the photoluminescence spectra
at 350–355 nm when excited at their absorption maxima.
Keywords Benzoxazole derivative; mesomorphic property; photophysical property
1. Introduction
Heterocyclic rings used as central cores generate numerous novel compounds that exhibit
mesophases, which is attributed to their electronic unsaturation and/or their significant
polarizability [1]. Among them, five- and six-membered rings have been most studied,
due to their wide range of structural templates as well as their optical and photochemical
properties, such as benzothiazoles [2], flavones and isoflavones [3,4], coumarins [5–7], ben-
zothiadiazoles [8,9], and benzoxazoles [10,11]. The field involving the design and synthesis
of mesogenic heterocyclic compounds has emerged as an area of active research, since such
materials are attractive from both a fundamental research and practical application point of
view.
For benzoxazole-based mesogenic and metallomesogenic materials, there are a few re-
ports [10–13]. The formation of mesophases for benzoxale-based compounds was found to
∗Address correspondence to Xinbing Chen, Key Laboratory of Applied Surface and Col-
loid Chemistry (MOE), School of Materials Science and Engineering, Shaanxi Normal University,
Xi’an 710062, P. R. China. Tel.: +86-29-81530719; Fax: +86-29-85310230. E-mail: chenxinbing@
snnu.edu.cn
44

Benzoxazole Liquid Crystals
45
be greatly affected by polar substituents and on intramolecular and/or intermolecular forces
[14,15]. There are very few reports on liquid crystals containing a terminal-substituted
benzoxazole group, and recently, we studied a series of mesogenic 2-arylbenzoxazole
derivatives with different polar substituents at the 5-position of terminal benzoxazole unit,
where biphenyl and benzoxazole units are used as mesogenic core [16]. It is commonly
accepted that molecular order in liquid crystal phases depends largely on the mesogenic
core structure: its geometry, polarizability, molecular conformation, and length-to-breath
ratio as well as the number and position of permanent dipole moments in the core. For
this reason, altering the core structure has been regarded as one of the factors that bring
significant changes to mesomorphic properties [17]. Here, a series of novel mesogenic com-
pounds, 2-(4-alkoxyphenyl-1-yl)-benzoxazole derivatives (nPB-x), with a short mesogenic
core composed of benzene and benzoxazole-terminated unit bearing different substituents
(H, NO2, CH3, Cl, coded as nPB-H, nPB-N, nPB-M, and nPB-C, respectively) at the 5-
position, was designed and synthesized. The structure–property relationships of the novel
benzoxazole-based liquid crystals were investigated.
2. Results and Discussion
2.1 Synthesis and Characterization
A synthetic route toward nPB-x is illustrated in Scheme 1, where nucleophilic substi-
tution, nucleophilic addition of 2-aminophenols with benzaldehydes, and subsequent in-
tramolecular cyclization were carried out in turn. As a result, the objective compounds
nPB-x bearing carbon atoms of alkoxy chain from 3 to 18 and containing polar sub-
stituents at benzoxazole unit were obtained with purities higher than 98% (high perfor-
mance liquid chromatography (HPLC) or gas chromatography (GC)) and overall yields of
47%–59%. In our case, condensation of ortho-aminophenols and aldehydes under oxida-
tive conditions was adopted to construct 2-substituted benzoxazole skeletons, where 2,3-
dichloro-5,6-dicyanobenzoquinone (DDQ) was chosen as an oxidative reagent with a good
result.
The structures of the products and intermediates were characterized by IR, 1H-NMR,
GC/electron ionization-mass spectrometry (EI-MS), and elemental analysis. From the IR
data of compound 14PB-C, the peaks at 1596, 1524, and 1471 cm−1 were attributed to the
vibrations of aromatic ring skeleton. It was noted that the absorption band of C N in the
Scheme 1. Synthesis of nPB-x (nPB-N, nPB-H, nPB-M, and nPB-C series).

46
P. Chen et al.
benzoxazole moiety was observed obviously with a blueshift to 1618 cm−1. Three peaks
1
appeared at 7.72, 7.48, and 7.30 ppm in H-NMR spectrum of 14PB-C were assigned to
the protons of phenyl ring in 5-chlorobenzoxazole group. Two kinds of protons appeared at
8.19 and 7.03 ppm were attributed to the protons of phenyl ring. The proton in CH2 group
adjacent to oxygen atom was assigned at 4.06 ppm, and other protons in alkoxyl group
appeared at 0.80–2.00 ppm. The peak of the positively charged molecular ion appeared at
m/z 441.32 with relative intensity of 9% in GC/EI-MS spectrum for 14PB-C, which was
consistent with the theoretical one (441.24). Elemental analysis result of 14PB-C (C 74.15,
H 8.23, and N 3.22) was in accordance with the calculated data (C 73.36, H 8.21, and N
3.17). All of these results provide clear evidence that nPB-x series are consistent with the
proposed structures.
2.2 Mesomorphic Properties
Mesomorphic properties of nPB-x were determined by differential scanning calorimetry
(DSC) and polarizing optical microscopy (POM). DSC curves obtained under the same
condition overlapped with each other, indicating that the reproducibility of the measure-
ments was satisfactory. The phase transition temperatures reported in this paper are the peak
values of the transition on DSC curves. Phase identification was made by comparing the
observed textures with those reported in the literature. The phase transition temperatures,
the associate enthalpy changes, and mesophase textures of nPB-N and nPB-M series are
summarized in Tables 1 and 2, respectively. Clear-cut transition temperatures and textures
could be obtained from DSC curves and POM observations, and they were in good agree-
ment with each other for the multiple heating/cooling cycles. Because sliver-coated cell was
obviously corrupted after DSC measurement of the samples nPB-C, the phase transition
temperatures and mesophase textures were only determined via POM.
nPB-N, nPB-M, and nP◦B-C exhibited enan◦tiotropi◦c smectic mesophases, where the
◦
mesophase ranges were 11 C–31 C and 20 C–49 C on heating and cooling pro-
◦
◦
◦
◦
cesses for compounds nPB-N, 3 C–18 C and 3 C–37 C for compounds nPB-M, and
Table 1. Types of phase transitions, temperatures, and corresponding enthalpies obtained
by POM and DSC methods for compounds nPB-N
Transition temperature/◦C (enthalpy change/kJ mol−1
)
Compounds
Heating process
Cooling process
I 98.7–97.3 Cr
6PB-N
7PB-N
Cr 99.0–100.2 (n.d.) I
Cr 90.9 (17.1) SmC 100.2 (1.8)
N 101.7 (0.2) I
I 98.4 (−0.2) N 97.3 (1.6) SmC
78.3(−16.3) Cr
8PB-N
Cr 92.8 (18.5) SmC 106.0 (1.9) I I 103.2 (−1.7) SmC 75.5 (−17.8) Cr
Cr 82.1 (22.1) SmC 110.1 (2.6) I I 108.1 (−2.2) SmC 58.7 (−15.7) Cr
Cr 80.2 (26.1) SmC 111.2 (3.1) I I 108.9 (−2.9) SmC 64.7 (−25.7) Cr
Cr 89.5 (34.6) SmC 111.4 (3.0) I I 107.8 (−2.8) SmC 67.4 (−26.7) Cr
Cr 93.1 (39.2) SmC 108.8 (3.0) I I 106.1 (−3.0) SmC 71.3 (−31.2) Cr
10PB-N
12PB-N
14PB-N
16PB-N
18PB-N
Cr 99.0–100.2 (n.d.) I
I 99.1-97.9 Cr
Cr: crystal; SmC: smectic C mesophase; I: isotropic liquid.

Benzoxazole Liquid Crystals
47
Table 2. Types of phase transitions, temperatures, and corresponding enthalpies obtained
by POM and DSC methods for compounds nPB-M
Transition temperature/◦C (enthalpy change/kJ mol−1
)
Compounds
Heating process
Cooling process
I 67.4–66.1 Cr
7PB-M
Cr 68.5–69.8 (n.d.) I
8PB-M
Cr 72.6 (50.3) SmC 75.7 (8.3) I
Cr 65.3 (40.2) SmC 80.7 (7.5) I
Cr 69.8 (46.8) SmC 82.3 (9.0) I
Cr 65.3 (33.5) SmC 83.5 (7.9) I
Cr 72.5 (28.3) SmC 81.2 (4.4) I
Cr 99.5–100.7 (n.d.) I
I 72.8 (−7.9) SmC 69.5 (−47.2.) Cr
I 77.7 (−7.5) SmC 41.1 (−33.4) Cr
I 78.5 (−9.0) SmC 52.4 (−46.0) Cr
I 80.1 (−6.9) SmC 48.9 (−30.5) Cr
I 77.2 (−3.9) SmC 57.9 (−7.2) Cr
I 99.2–97.8 Cr
10PB-M
12PB-M
14PB-M
16PB-M
18PB-M
Cr: crystal; SmC: smectic C mesophase; I: isotropic liquid.
Figure 1. DSC traces and photomicrographs (×200) of 8PB-N. (a) DSC traces at a scanning rate
5 ◦C min−1; (b) focal conic textures of the smectic mesophase at 98 ◦C on heating; and (c) focal conic
textures of the smectic mesophase at 80◦C on cooling.

48
P. Chen et al.
Figure 2. X-ray scattering diagram of 8PB-N obtained at 98◦C on the sample gradually cooled from
the isotropic state.
7 ◦C–32 ◦C and 12 ◦C–82 ◦C for compounds nPB-C, respectively, whereas nPB-H showed
no mesophase at all.
As shown in Table 1, compounds nPB-N with a too short or a too long terminal alkoxy
chain (n < 7 or n > 16) exhibited no mesophase at all on heating or cooling, while the other
compounds only showed the smectic C mesophase. The phases of 8PB-N were assigned
from the typical fan-shaped textures during both heating and cooling processes, respectively,
as shown in Fig. 1. The lamellar structure of this mesophase was also confirmed by the
X-ray diffraction (XRD) method. A sharp peak corresponding to an interlayer spacing
distance of 2.88 nm in the small angle region and a broad reflection centered near 0.44 nm
were observed in XRD diagrams of 8PB-N at 98 ◦C (Fig. 2). The calculated dimension of
the dimer of 8PB-N in the longest direction was higher than the experimental interlayer
spacing, suggesting its smectic C layer characteristic.
Similar to compounds nPB-N, nPB-M with proper terminal alkoxy chain (7 < n
< 18) exhibited smectic C mesophase in heating/cooling processes (Table 2), in which
the phases of 12PB-M were assigned from the typical fan-shaped textures during both
heating and cooling processes, respectively, as shown in Fig. 3. 5-Chlorobenzoxazole-
terminated compounds nPB-C with carbon number of the alkoxy chain from 5 to 18
exhibited enantiotropic smectic mesophase (Table 3), which were assigned from the typ-
ical fan-shaped or focal conic textures in heating/cooling processes, as shown in Fig. 4.
It is noted that a supercooled phenomena was observed in cooling process for nPB-N,
nPB-M, and nPB-C series. This phenomenon is common for calamitic liquid crystalline
materials.
Compared with other series, nPB-H showed no mesophase at all whether with short or
long terminal alkoxy chain during both heating and cooling, which indicated that the sub-
stituents (NO2, CH3, and Cl) at benzoxazole moiety were helpful to increase the mesophase
stability. It is obvious that the substituents with the stronger electron-withdrawing effect let
to the wider mesomorphic temperature domain for nPB-x due to the stronger dipole–dipole
interaction between the molecules, i.e., NO2 > Cl > CH3, as shown in Tables 1–3 and
Fig. 5, which was in accordance with the reference results [16]. It was noted that nPB-x

Benzoxazole Liquid Crystals
49
Figure 3. DSC traces and photomicrographs (×200) of 12PB-M. (a) DSC traces at a scanning rate
5 ◦C min−1; (b) focal conic textures of the smectic mesophase at 82 ◦C on heating; and (c) focal conic
textures of the smectic mesophase at 70◦C on cooling.
exhibited much worse mesophase stability than 2-(4ꢀ-alkoxybiphenyl-4-yl)-benzoxazole
derivatives, which maybe due to their short mesogenic cores composed of only benzene
and substituted benzoxazole.
2.3 Thermal Stability
The thermal stability of nPB-x was determined by thermogravimetric analysis (TGA) mea-
surements. Figure 6 depicts the TGA curves of the samples 10PB-N and 10PB-M, which
◦
◦
were recorded at 30 C–500 C under N2 atmosphere. TGA measurement of compound
10PB-C was not carried out to avoid the corruption of test cell resulted from chloro. It can
be seen that both the compounds 10PB◦-N and 10PB-M were almost completely decom-
◦
posed by a one-step process from 180 C to 350 C, whereas 10PB-N showed a higher
onset decomposition temperature at 245 ◦C than 10PB-M (205 ◦C). This indicated that the
decomposition temperature increased with the increase of the polarity of the molecules,
where polar nitro substituent in nPB-N structure enhanced the dipole–dipole interaction

50
P. Chen et al.
Table 3. Types of phase transitions and temperatures obtained by POM for compounds
nPB-C
Transition temperature/◦C
Compounds
Heating process
Cooling process
3PB-C
5PB-C
6PB-C
7PB-C
8PB-C
10PB-C
12PB-C
14PB-C
16PB-C
18PB-C
Cr 120.1–121.8 I
I 119.3–117.8 Cr
Cr 79.8 SmC 105.6 I
Cr 86.7 SmC 107.8 I
Cr 77.7 SmC 110.1 I
Cr 86.1 SmC 115.3 I
Cr 77.3 SmC 107.8 I
Cr 78.1 SmC 106.9 I
Cr 79.3 SmC 103.4 I
Cr 82.5 SmC 99.6 I
Cr 86.3 SmC 93.1 I
I 103.4 SmC 55.7 Cr
I 104.3 SmC 68.3 Cr
I 107.6 SmC 36.9 Cr
I 112.1 SmC 29.8 Cr
I 104.4 SmC 49.4 Cr
I 102.6 SmC 63.4 Cr
I 101.5 SmC 60.7 Cr
I 96.9 SmC 62.3 Cr
I 90.8 SmC 78.9 Cr
Cr: crystal; SmC: smectic C mesophase; I: isotropic liquid.
between the molecules, resulting in high thermal stability. All the results showed that
nPB-x series are stable before their clearing point. Those are consistent with the DSC
results.
2.4 The Effects of Alkoxy Chain and Polar Substituents on Liquid
Crystalline Properties
It is clear that the length of the alkoxy chain influenced not only the nature of the mesophases
but also the mesomorphic temperature ranges. Figures 7–9 plot the transition temperatures
of compounds nPB-N, nPB-M, and nPB-C as a function of the number of methylenic units
(n) in the alkoxy chain during the heating process, respectively.
Figure 4. DSC traces and photomicrographs (×200) of 16PB-C. (a) Focal conic textures of the
smectic mesophase at 88◦C on heating and (b) focal conic textures of the smectic mesophase at 67 ◦C
on cooling.

Benzoxazole Liquid Crystals
51
Figure 5. The effect of substituents on the mesophase range of compounds 12PB-X during heating
and cooling.
As shown in Figs. 7–9, a decreasing trend in the melting temperature was observed
for the compounds nPB-N, nPB-M, and nPB-C series with alkoxy chain length from 6 to
12 (Fig. 7), 7 to 14 (Fig. 8), and 3 to 10 (Fig. 9), respectively, whereas by ascending the
homologs further, an increase in the melting temperature was found. The SmC-isotropic
liquid transition temperature increased obviously first, and then decreased smoothly for
nPB-x with ascending the homologues. As a result, the elongation of the terminal alkoxy
chain produced an enhancement of the mesomorphic temperature ranges first, and then
followed by a decrease in mesophase range.
Figure 6. TGA curves of compounds 10PB-x.

52
P. Chen et al.
Figure 7. Transition behavior of the compounds nPB-N series: dependence of the transition tem-
peratures on the number (n) of methylene units of the alkoxy chain.
Generally, the calamitic compounds substituted with polar groups, such as nitro group,
might lead to a higher clearing temperature [15]. In our case, compounds nPB-x with
electron-withdrawing substituents (x = NO2, Cl) displayed higher clearing temperatures
(Tcl) than those of other corresponding homologs with electron-donating substituents, and
the higher Tcl was attributed to an enhanced conjugative interaction.
2.5 Photophysical Properties
The absorption spectra of compounds 10PB-x recorded in CH2Cl2 are shown in Fig. 10.
All of the compounds exhibited a broad absorption band (λmax = 315 nm for 10PB-N,
315 nm for 10PB-C, 313 nm for 10PB-M, and 306 nm for 10PB-H) attributable to the
electronic transition originating from the π-molecular orbitals. Compared with 10PB-H,
the polar substituents at benzoxazole moiety result in a slight redshift of the absorption
Figure 8. Transition behavior of the compounds nPB-M series: dependence of the transition tem-
peratures on the number (n) of methylene units of the alkoxy chain.

Benzoxazole Liquid Crystals
53
Figure 9. Transition behavior of the compounds nPB-C series: dependence of the transition tem-
peratures on the number (n) of methylene units of the alkoxy chain.
band in a sequence, which is similar to the effect of the substituents on the mesophase.
This phenomenon is related to the strength of π-conjugation resulted from the substituents,
for instance, nitro-, chloro-, and methyl-substituted compounds 10PB-N, 10PB-C, and
10PB-M exhibited a slight redshift due to the stronger π–π, p–π, and σ–π conjugation,
respectively.
Figure 10. UV spectra of 10PB-x in CH2Cl2 (2.1×10−3 mol L−1).

54
P. Chen et al.
Figure 11. FL spectra of 10PB-x in CH2Cl2 (2.1×10−5 mol L−1).
The fluorescence spectra of compounds 10PB-x were recorded and shown in Fig. 11.
The compounds exhibited intense emission in CH2Cl2 solutions when excited at their
absorption maxima, where the peaks of the emission bands appeared at 350 nm (10PB-
H), 353 nm (10PB-M), and 355 nm (10PB-C), respectively, whereas 10PB-N led to a
significant decrease in emission, which was a common phenomenon for nitro-substituted
fluorophores. Compared with 10PB-H, the substituted benzoxazole-terminated compounds
showed slight redshifted emission peaks, which was consistent with the trend observed in
the absorption spectra.
3. Conclusions
In summary, nPB-x bearing different polar substituents (i.e., H, NO2, CH3, Cl) at 5-position
of benzoxazole moiety were synthesized and characterized. The substituents had obvious
effects on the liquid crystal mesophase ranges and the UV absorption bands of nB-x with
the same sequence. The elongation of the terminal alkoxy chain produced different effects
on the melting and clearing points, which resulted in an enhancement of the mesomorphic
temperature ranges first, and then followed by a decrease in mesophase range with ascending
the homologs. Compared with 2-(4ꢀ-alkoxybiphenyl-4-yl) -benzoxazole derivatives, nPB-x
exhibited much worse mesophase stability due to their short mesogenic cores composed of
only benzene and substituted benzoxazole.

Benzoxazole Liquid Crystals
55
4. Experimental
4.1 Materials
4-Hydroxybenzaldehyde, bromoalkanes, 2-amino-4-nitrophenol, 2-amino-4-chlorophenol,
2-amino-4-methylphenol, 2-aminophenol, and DDQ were purchased from Aladdin-Reagent
Co. (Shanghai, China) and used as received. Tetrahydrofuran, silica gel, petroleum ether
(PE), ethyl acetate (EA), absolute ethanol, N,N-dimethylformamide (DMF), chloroform
and anhydrous potassium carbonate were purchased from Sinopharm Chemical Reagent
Co. (Shanghai, China) and anhydrous potassium carbonate was dried at 150 ◦C in vacuum
prior to use. Chloroform was dehydrated by pre-dried 4 Å molecular sieves that were
activated at 350 ◦C for 4 hr prior to use.
4.2 Characterization and Measurements
The structures of the final products and intermediates were confirmed by a variety of spectral
methods. IR spectra were recorded on a Nicolet Avatar360E spectrometer. 1H-NMR spectra,
with tetramethylsilane (TMS) as internal standard, were recorded on a Bruker AV 300
(300 MHz) and AV 400 (400 MHz) instruments. Some of the mass spectra were obtained
by GC/EI-MS Thermo DSQ II with m/z 50–650. Elemental analysis was performed for C,
H, and N in an Elementar Vario EL III instrument. The phase transition temperatures of
the target compounds were measured by DSC, Shimatsu DSC-60 in nitrogen at a heating
◦
and cooling rate of 5 C min−1, and POM, Changfang XPN-300E with a heating stage
and a control unit. TGA was carried out with a TA 600SDT in helium (flow rate: 100 cm3
min−1) at a heating rate of 10 ◦C min−1. UV-vis absorption spectra were recorded using a
Hitachi U-3900UV spectrometer. The emission spectra were recorded using a Cary Eclipse
spectrometer.
4.3 Synthesis
As an example, the preparation procedure of 2-(4-tetradecyloxyphenyl-1-yl)-5-methyl-
benzoxazole (14PB-M) is described below.
4.3.1 Synthesis of 4-tetradecyloxybenzaldehyde. To a 50 mL, three-neck, round-bottom
flask equipped with an overhead stirrer and condenser, 12.2 g (0.1 mol) of 4-hydroxy
benzaldehyde, 30.5 g (0.11 mol) of 1-bromotetradecane, 27.6 g (0.2 mol) of anhydrous
potassium carbonate, 0.5 g of KI, and 150 mL of DMF were added. Then the reaction
◦
system was stirred at 100 C for 4 hr. After completion of the reaction, the mixture was
diluted with water and filtered. The solid was recrystallized from◦ethanol.
1
The yield was 95% of pale white crystals. M.p. 50.6–51.8 C. H-NMR (300 MHz,
CDCl3, TMS): δ (ppm) 9.88 (s, 1H), 7.84 (d, J = 8.7 Hz, 2H), 7.04 (d, J = 8.7 Hz, 2H),
4.04 (t, J = 6.3 Hz, 2H), 1.84 (m, 2H), 1.47–1.28 (m, 22H), 0.90 (t, J = 6.6 Hz, 3H). IR
(KBr, pellet, cm−1): 2918, 2844, 1687, 1595, 1502, 1464, 1379, 1252, 1159, 1028, 827,
719. Elemental analysis: calcd. C21H34O2: C 79.19, H 10.76, N 10.05; found C 80.03, H
10.65, N 9.98.
4.3.2 Synthesis of 2-(((4-tetradecyloxyphenyl-1-yl)methylene)amino)-4-methylphenol
(14PB-S-M). To a 100 mL round-bottom flask equipped with an overhead stirrer and
condenser, 1.69 g of 4-tetradecyloxy-benzaldehyde (4.0 mmol), 0.54 g of (4.4 mmol)

56
P. Chen et al.
2-amino-4-methylphenol, and 40 mL of ethanol were added. The reaction system was
stirred at reflux for 6 hr. Then the mixture was cooled to room temperature, it was filtered
through Celite. The solid was washed with 15 mL ethanol for several times to give the
object with the HPLC purity more than 98%.
◦
1
The yield was 90% of pale white crystals. M.p. 68.7–69.8 C. H-NMR (300 MHz,
CDCl3 TMS): δ (ppm) 8.60 (s, 1H), 7.87 (d, J = 8.7 Hz, 1H), 7.08 (s, 1H), 6.99 (m, 3H),
6.91 (d, J = 8.1 Hz, 2H), 4.05 (t, J = 6.3 Hz, 2H), 2.31 (s, 3H), 1.84 (m, 2H), 1.47–1.28
(m, 22H), 0.90 (t, J = 6.6 Hz, 3H). IR (KBr, pellet, cm−1): 3378, 2953, 2916, 2849, 1620,
1603, 1593, 1568, 1514, 1498, 1473, 1451, 1394, 1382, 1337, 1311, 1254, 1248, 1218,
1035, 1023, 1007, 828, 802. Elemental analysis: calcd. C28H41NO2: C 79.39, H 9.76, N
3.31; found C 80.06, H 9.65, N 3.26.
4.3.3 Synthesis of 2-(tetradecyloxyphenyl-1-yl)-5-methylbenzoxazole (14PB-M). To a
100 mL round-bottom flask equipped with an overhead stirrer and condenser, 0.85 g
(2.00 mmol) of 14PB-S-M, 0.50 g (2.2 mmol) of DDQ, and 50 mL of chloroform were
added. The reaction system was stirred at reflux for 6 hr. After completion of the reaction,
the mixture was diluted with water and extracted with chloroform for three times. The
combined organic phase was dried over MgSO4. After removal of the solvent in vacuo,
the residue was purified through recrystallization from ethanol to give the object with the
HPLC purity more than 98%.
The yield was 70% of pale white crystals. M.p. 65.3 ◦C. 1H-NMR (300 MHz, CDCl3,
TMS): δ (ppm) 8.18 (d, J = 8.7 Hz, 2H), 7.52 (s, 1H), 7.43 (d, J = 8.4 Hz, 1H), 7.13 (d,
J = 8.4 Hz, 1H), 7.02 (d, J = 8.7 Hz, 2H), 4.05 (t, J = 6.6 Hz, 2H), 2.48 (s, 3H), 1.84
(m, 2H), 1.47–1.28 (m, 22H), 0.90 (t, J = 6.6 Hz, 3H). IR (KBr, pellet, cm−1): 3052, 3011,
2936, 2916, 2867, 2849, 1625, 1607, 1583, 1560, 1522, 1560, 1473, 1451, 1417, 1394,
1300, 1275, 1266, 1248, 1167, 1058, 1020, 1009, 924, 865, 809, 759, 735. EI-MS m/z (rel.
int.): 421.41 (M+, 15), 225.11 (100), 207.04 (16), 196.19 (5), 73.03 (8). Elemental analysis:
calcd. C28H39NO2: C 79.76, H 9.32, N 3.32; found C 80.26, H 9.35, N 3.37.
The other benzoxazole-terminated compounds (nPB-x) were prepared according to
the similar procedure.
nPB-M Series. 7PB-M: The yield was 69% of pale white crystals. M.p. 68.5–69.8 ◦C.
1H-NMR (300 MHz, CDCl3, TMS): δ (ppm) 8.18 (d, J = 8.4 Hz, 2H), 7.52 (s, 1H), 7.44
(d, J = 8.4 Hz, 1H), 7.14 (d, J = 8.4 Hz, 1H), 7.02 (d, J = 8.4 Hz, 2H), 4.05 (t, J = 6.6 Hz,
2H), 2.48 (s, 3H), 1.84 (m, 2H), 1.47–1.30 (m, 8H), 0.91 (t, J = 6.6 Hz, 3H). IR (KBr,
pellet, cm−1): 3049, 3017, 2941, 2920, 2863, 2850, 1616, 1605, 1582, 1561, 1532, 1502,
1476, 1466, 1431, 1417, 1390, 1314, 1300, 1275, 1253, 1166, 1052, 1031, 1000, 921, 831,
802, 745. EI-MS m/z (rel. int.): 309.18 (M+, 15.5), 211.07 (100), 183.08 (7), 154.09 (2),
63.05 (3). Elemental analysis: calcd. C21H25NO2: C 77.98, H 7.79, N 4.33; found C 78.43,
H 7.96, N 4.21.
8PB-M: The yield was 69% of pale white crystals. M.p. 72.6 ◦C. 1H-NMR (300 MHz,
CDCl3, TMS): δ (ppm) 8.18 (d, J = 8.7 Hz, 2H), 7.51 (s, 1H), 7.43 (d, J = 8.4 Hz, 1H),
7.13 (d, J = 8.1 Hz, 1H), 7.02 (d, J = 9.0 Hz, 2H), 4.05 (t, J = 6.6 Hz, 2H), 2.48 (s, 3H),
1.84 (m, 2H), 1.47–1.30 (m, 10H), 0.91 (t, J = 6.6 Hz, 3H). IR (KBr, pellet, cm−1): 3051,
3018, 2942, 2920, 2865, 2851, 1614, 1607, 1582, 1560, 1531, 1501, 1474, 1467, 1433,
1419, 1391, 1315, 1301, 1277, 1256, 1166, 1074, 1055, 1033, 999, 922, 865, 829, 805,
740. EI-MS m/z (rel. int.): 337.30 (M+, 26), 225.11 (100), 207.05 (4), 196.09 (6), 78.08 (4).
Elemental analysis: calcd. C22H27NO2: C 78.30, H 8.06, N 4.15; found C 79.55, H 8.26, N
4.23.

Benzoxazole Liquid Crystals
57
10PB-M: The yield was 68% of pale white crystals. M.p. 65.3 ◦C. 1H-NMR (300 MHz,
CDCl3, TMS): δ (ppm) 8.18 (d, J = 9.0 Hz, 2H), 7.52 (s, 1H), 7.43 (d, J = 8.4 Hz, 1H),
7.13 (d, J = 8.1 Hz, 1H), 7.02 (d, J = 9.0 Hz, 2H), 4.05 (t, J = 6.6 Hz, 2H), 2.48 (s,
3H), 1.84 (m, 2H), 1.47–1.28 (m, 14H), 0.90 (t, J = 6.6 Hz, 3H). IR (KBr, pellet, cm−1):
3063, 2978, 2918, 2865, 2847, 1618, 1606, 1584, 1557, 1502, 1482, 1469, 1466, 1449,
1423, 1384, 1309, 1291, 1271, 1254, 1173, 1130, 1118, 1108, 1058, 1010, 998, 940, 920,
874, 849, 812, 798, 738. EI-MS m/z (rel. int.): 365.30 (M+, 19), 281.09 (24), 225.11 (100),
207.05 (52), 147.07 (4).
12PB-M: The yield was 65% of pale white crystals. M.p. 69.8 ◦C. 1H-NMR (400 MHz,
CDCl3, TMS): δ (ppm) 8.19 (d, J = 8.8 Hz, 2H), 7.53 (s, 1H), 7.43 (d, J = 8.4 Hz, 1H),
7.13 (d, J = 8.4 Hz, 1H), 7.02 (d, J = 8.8 Hz, 2H), 4.05 (t, J = 6.4 Hz, 2H), 2.48 (s, 3H),
1.84 (m, 2H), 1.47–1.28 (m, 18H), 0.90 (t, J = 6.4 Hz, 3H). IR (KBr, pellet, cm−1): 3028,
2943, 2936, 2918, 2866, 2847, 1616, 1606, 1583, 1558, 1500, 1492, 1473, 1465, 1422,
1388, 1308, 1289, 1274, 1250, 1169, 1056, 1032, 1002, 922, 872, 825, 794, 738. EI-MS
m/z (rel. int.): 393.31 (M+, 16), 225.12 (100), 207.06 (5), 196.10 (6), 55.06 (4).
16PB-M: The yield was 70% of pale white crystals. M.p. 72.5 ◦C. 1H-NMR (300 MHz,
CDCl3, TMS): δ (ppm) 8.18 (d, J = 8.7 Hz, 2H), 7.51 (s, 1H), 7.42 (d, J = 8.4 Hz, 1H),
7.13 (d, J = 8.4 Hz, 1H), 7.02 (d, J = 8.7 Hz, 2H), 4.06 (t, J = 6.6 Hz, 2H), 2.48 (s, 3H),
1.84 (m, 2H), 1.47–1.27 (m, 26H), 0.90 (t, J = 6.6 Hz, 3H). IR (KBr, pellet, cm−1): 3018,
2941, 2918, 2850, 1604, 1569, 1490, 1473, 1288, 1255, 1062, 1029, 999, 923, 829, 800,
746. EI-MS m/z (rel. int.): 449.41 (M+, 12), 225.12 (100), 207.06 (9), 78.06 (4), 73.05 (4).
Elemental analysis: calcd. C30H43NO2: C 80.13, H 9.64, N 3.11; found C 80.68, H 9.71, N
3.10.
◦
1
18PB-M: The yield was 72% of pale white crystals. M.p. 99.5–100.7 C. H-NMR
(300 MHz, CDCl3, TMS): δ (ppm) 8.18 (d, J = 8.7 Hz, 2H), 7.51 (s, 1H), 7.42 (d, J =
8.4 Hz, 1H), 7.13 (d, J = 8.4 Hz, 1H), 7.02 (d, J = 8.7 Hz, 2H), 4.06 (t, J = 6.6 Hz, 2H),
2.48 (s, 3H), 1.84 (m, 2H), 1.47–1.27 (m, 30H), 0.90 (t, J = 6.6 Hz, 3H). IR (KBr, pellet,
cm−1): 3051, 3012, 2952, 2939, 2916, 2867, 2847, 1606, 1582, 1554, 1525, 1501, 1471,
1416, 1395, 1303, 1282, 1249, 1168, 1057, 1033, 1004, 924, 830, 808, 718. EI-MS m/z (rel.
int.): 357 (M+, 28), 287 (100). Elemental analysis: calcd. C32H47NO2: C 80.45, H 9.92, N
2.93; found C 80.95, H 10.19, N 2.89.
nPB-N Series. 3PB-N: The yield was 61% of pale white crystals. M.p. 167.8–169.1 ◦C.
1H-NMR (400 MHz, CDCl3, TMS): δ (ppm) 8.59 (d, 4J = 2.0 Hz, 1H), 8.29 (q, 3J = 8.8 Hz,
4J = 2.4 Hz, 1H), 8.20 (d, J = 8.8 Hz, 2H), 7.64 (d, J = 8.8 Hz, 1H), 7.05 (d, J = 8.8 Hz,
2H), 4.04 (t, J = 6.4 Hz, 2H), 1.89 (m, 2H), 1.09 (t, J = 6.8 Hz, 3H). IR (KBr, pellet, cm−1):
3123, 3106, 2972, 2937, 2918, 2870, 2850, 1619, 1603, 1578, 1562, 1522, 1500, 1468,
1456, 1428, 1397,1367, 1341, 1309, 1295, 1252, 1231, 1202, 1143, 1117, 1067, 1008, 972,
919, 870, 831, 817, 745. Elemental analysis: calcd. C16H14N2O2: C 64.42, H 4.73, N 9.39;
found C 65.29, H 5.06, N 9.33.
◦
1
5PB-N: The yield was 60% of pale white crystals. M.p. 161.5–162.3 C. H-NMR
(400 MHz, CDCl3, TMS): δ (ppm) 8.59 (d, 4J = 2.0 Hz, 1H), 8.29 (q, 3J = 8.8 Hz, 4J =
2.4 Hz, 1H), 8.20 (d, J = 8.8 Hz, 2H), 7.64 (d, J = 8.8 Hz, 1H), 7.05 (d, J = 8.8 Hz, 2H),
4.06 (t, J = 6.4 Hz, 2H), 1.85 (m, 2H), 1.49 (m 4H), 0.97 (t, J = 6.8 Hz, 3H). IR (KBr,
pellet, cm−1): 3095, 2968, 2929, 2871, 1619, 1600, 1554, 1522, 1493, 1474, 1424, 1340,
1301, 1251, 1186, 1047, 1012, 972, 810, 743. Elemental analysis: calcd. C18H18N2O2: C
66.25, H 5.56, N 8.58; found C 67.03, H 5.72, N 8.61.
◦
3
1
6PB-N: The yield was 62% of pale white crystals. M.p. 99.0–100.2 C. H-NMR
4
(400 MHz, CDCl3, TMS): δ (ppm) 8.58 (d, J = 2.0 Hz, 1H), 8.28 (q, J = 8.8 Hz,

58
P. Chen et al.
4J = 2.4 Hz, 1H), 8.19 (d, J = 8.8 Hz, 2H), 7.63 (d, J = 8.8 Hz, 1H), 7.04 (d, J = 8.8 Hz,
2H), 4.05 (t, J = 6.4 Hz, 2H), 1.84 (m, 2H), 1.51–1.36 (m 6H), 0.92 (t, J = 6.8 Hz, 3H). IR
(KBr, pellet, cm−1): 2949, 2915, 2868, 2840, 1623, 1605, 1560, 1524, 1499, 1460, 1425,
1396, 1382, 1361, 1342, 1305, 1342, 1306, 1293, 1256, 1234, 1170, 1117, 1041, 1001,
839, 823, 810, 743, 733. Elemental analysis: calcd. C19H20N2O2: C 67.05, H 5.92, N 8.23;
found C 67.78, H 6.19, N 8.27.
7PB-N: The yield was 59% of pale white crystals. M.p. 90.9 ◦C. 1H-NMR (400 MHz,
CDCl3, TMS): δ (ppm) 8.60 (d, 4J = 2.0 Hz, 1H), 8.29 (q, 3J = 8.8 Hz, 4J = 2.4 Hz, 1H),
8.20 (d, J = 8.8 Hz, 2H), 7.64 (d, J = 8.8 Hz, 1H), 7.05 (d, J = 8.8 Hz, 2H), 4.07 (t, J =
6.4 Hz, 2H), 1.86 (m, 2H), 1.52–1.32 (m 8H), 0.92 (t, J = 6.8 Hz, 3H). IR (KBr, pellet,
cm−1): 3098, 2938, 2916, 2867, 2851, 1611, 1603, 1577, 1550, 1523, 1497, 1464, 1435,
1391, 1343, 1321, 1302, 1251, 1230, 1202, 1168, 1112, 1067, 1033, 1003, 915, 841, 826,
809, 743. Elemental analysis: calcd. C20H22N2O2: C 67.78, H 6.26, N 7.90; found C 68.77,
H 6.70, N 3.94.
8PB-N: The yield was 61% of pale white crystals. M.p. 92.8 ◦C. 1H-NMR (400 MHz,
CDCl3, TMS): δ (ppm) 8.60 (d, 4J = 2.0 Hz, 1H), 8.30 (q, 3J = 8.8 Hz, 4J = 2.4 Hz, 1H),
8.21 (d, J = 8.8 Hz, 2H), 7.65 (d, J = 8.8 Hz, 1H), 7.06 (d, J = 8.8 Hz, 2H), 4.08 (t, J =
6.4 Hz, 2H), 1.86 (m, 2H), 1.49–1.30 (m 10H), 0.90 (t, J = 6.8 Hz, 3H). IR (KBr, pellet,
cm−1): 3117, 3078, 2957, 2936, 2917, 2867, 2852, 1615, 1600, 1578, 1553, 1524, 1497,
1467, 1456, 1429, 1425, 1392, 1343, 1304, 1255, 1237, 1166, 1116, 1071, 1042, 1017, 997,
938, 917, 892, 843, 808, 745. Elemental analysis: calcd. C21H24N2O2: C 68.46, H 6.57, N
7.60; found C 68.72, H 6.70, N 7.59.
10PB-N: The yield was 55% of pale white crystals. M.p. 82.1 ◦C. 1H-NMR (400 MHz,
4
3
4
CDCl3, TMS): δ (ppm) 8.60 (d, J = 2.0 Hz, 1H), 8.30 (q, J = 8.8 Hz, J = 2.4 Hz,
1H), 8.27 (d, J = 8.8 Hz, 2H), 7.65 (d, J = 8.8 Hz, 1H), 7.06 (d, J = 8.8 Hz, 2H), 4.08
(t, J = 6.4 Hz, 2H), 1.86 (m, 2H), 1.49–1.29 (m 14H), 0.89 (t, J = 6.8 Hz, 3H). IR (KBr,
pellet, cm−1): 3115, 3080, 2953, 2929, 2915, 2869, 2848, 1615, 1601, 1580, 1550, 1522,
1496, 1468, 1424, 1346, 1310, 1304, 1293, 1251, 1237, 1166, 1105, 1013, 1003, 938, 917,
893, 844, 823, 807, 745. Elemental analysis: calcd. C23H28N2O2: C 69.67, H 7.12, N 7.07;
found C 70.26, H 7.22, N 7.10.
12PB-N: The yield was 61% of pale white crystals. M.p. 80.2 ◦C. 1H-NMR (400 MHz,
CDCl3, TMS): δ (ppm) 8.60 (d, 4J = 2.0 Hz, 1H), 8.30 (q, 3J = 8.8 Hz, 4J = 2.4 Hz, 1H),
8.27 (d, J = 8.8 Hz, 2H), 7.65 (d, J = 8.8 Hz, 1H), 7.06 (d, J = 8.8 Hz, 2H), 4.07 (t, J =
6.4 Hz, 2H), 1.85 (m, 2H), 1.50–1.27 (m 18H), 0.90 (t, J = 6.8 Hz, 3H). IR (KBr, pellet,
cm−1): 3097, 3073, 3043, 2955, 2915, 2869, 2847, 1615, 1604, 1577, 1532, 1499, 1471,
1462, 1424, 1380, 1349, 1322, 1285, 1260, 1237, 1169, 1118, 1067, 1045, 1028, 1023,
1001, 973, 944, 840, 830, 811, 745. Elemental analysis: calcd. C25H32N2O2: C 70.73, H
7.60, N 6.60; found C 69.38, H 7.70, N 6.87.
14PB-N: The yield was 60% of pale white crystals. M.p. 89.5 ◦C. 1H-NMR (400 MHz,
CDCl3, TMS): δ (ppm) 8.60 (d, 4J = 2.0 Hz, 1H), 8.30 (q, 3J = 8.8 Hz, 4J = 2.4 Hz, 1H),
8.27 (d, J = 8.8 Hz, 2H), 7.65 (d, J = 8.8 Hz, 1H), 7.05 (d, J = 8.8 Hz, 2H), 4.08 (t, J =
6.4 Hz, 2H), 1.85 (m, 2H), 1.48–1.26 (m 22H), 0.89 (t, J = 6.4 Hz, 3H). IR (KBr, pellet,
cm−1): 3105, 2943, 2930, 2914, 2865, 2847, 1617, 1600, 1535, 1499, 1469, 1435, 1424,
1360, 1342, 1307, 1302, 1250, 1191, 1167, 1100, 1070, 1037, 1023, 1007, 919, 880, 830,
810, 740. Elemental analysis: calcd. C27H36N2O2: C 71.65, H 8.02, N 6.19; found C 72.51,
H 8.04, N 6.10.
16PB-N: The yield was 62% of pale white crystals. M.p. 93.1 ◦C. 1H-NMR (400 MHz,
4
3
4
CDCl3, TMS): δ (ppm) 8.60 (d, J = 2.0 Hz, 1H), 8.29 (q, J = 8.8 Hz, J = 2.4 Hz,
1H), 8.20 (d, J = 8.8 Hz, 2H), 7.64 (d, J = 8.8 Hz, 1H), 7.05 (d, J = 8.8 Hz, 2H), 4.07

Benzoxazole Liquid Crystals
59
(t, J = 6.4 Hz, 2H), 1.86 (m, 2H), 1.52–1.26 (m 22H), 0.89 (t, J = 6.8 Hz, 3H). IR (KBr,
pellet, cm−1): 3095, 2946, 2933, 2915, 2867, 2848, 1617, 1604, 1579, 1552, 1535, 1499,
1471, 1461, 1452, 1436, 1424, 1380, 1347, 1317, 1261, 1238, 1167, 1110, 1067, 1035,
1001, 918, 886, 842, 811, 759, 744. Elemental analysis: calcd. C29H40N2O2: C 72.47, H
8.39, N 5.83; found C 71.66, H 8.47, N 5.70.
◦
1
18PB-N: The yield was 61% of pale white crystals. M.p. 99.0–100.2 C. H-NMR
(400 MHz, CDCl3, TMS): δ (ppm) 8.60 (d, 4J = 2.0 Hz, 1H), 8.30 (q, 3J = 8.8 Hz, 4J =
2.4 Hz, 1H), 8.21 (d, J = 8.8 Hz, 2H), 7.65 (d, J = 8.8 Hz, 1H), 7.05 (d, J = 8.8 Hz, 2H),
4.07 (t, J = 6.4 Hz, 2H), 1.85 (m, 2H), 1.52–1.26 (m 26H), 0.90 (t, J = 6.4 Hz, 3H). IR
(KBr, pellet, cm−1): 3097, 2953, 2916, 2848, 1616, 1603, 1578, 1560, 1534, 1500, 1471,
1461, 1424, 1347, 1321, 1304, 1279, 1262, 1237, 1169, 1068, 1005, 981, 938, 919, 842,
811, 745, 735, 718, 690, 662, 518. Elemental analysis: calcd. C31H44N2O2: C 73.19, H
8.72, N 5.51; found C 73.85, H 9.01, N 5.50.
nPB-C Series. 3PB-C: The yield was 68% of pale pink crystals. M.p. 120.1–121.8 ◦C
4
.1H-NMR (400 MHz, CDCl3, TMS): δ (ppm) 8.17 (d, J = 8.8 Hz, 2H), 7.70 (d, J =
2.0 Hz, 1H), 7.46 (d, J = 8.4 Hz, 1H), 7.29 (q, 3J = 8.4 Hz, 4J = 2.0 Hz, 1H), 7.02 (d, J
= 8.8 Hz, 2H), 4.02 (t, J = 6.8 Hz, 2H), 1.86 (m, 2H), 1.08 (t, J = 7.2 Hz, 3H). IR (KBr,
pellet, cm−1): 2963, 2936, 2913, 2870, 1613, 1603, 1577, 1554, 1501, 1458, 1438, 1421,
1381, 1273, 1259, 1246, 1227, 1175, 1060, 1008, 916, 853, 838, 799, 740. EI-MS m/z (rel.
int.): 287.10 (M+, 31), 245.04 (100), 216 (7), 182.10 (2), 126.05 (3). Elemental analysis:
calcd. C16H14NClO2: C 66.79, H 4.90, N 4.87; found C 67.24, H 5.14, N 4.91.
5PB-C: The yield was 64% of pale pink crystals. M.p. 79.8 ◦C. 1HNMR (400 MHz,
CDCl3, TMS): δ (ppm) 8.17 (d, J = 8.4 Hz, 2H), 7.70 (d, 4J = 2.0 Hz, 1H), 7.46 (d, J =
3
4
8.4 Hz, 1H), 7.29 (q, J = 8.4 Hz, J = 2.0 Hz, 1H), 7.02 (d, J = 9.2 Hz, 2H), 4.05 (t,
J = 6.8 Hz, 2H), 1.85 (m, 2H), 1.49 (m, 4H), 0.95 (t, J = 7.2 Hz, 3H). IR (KBr, pellet,
cm−1): 3096, 2953, 2929, 2914, 2871, 2846, 1618, 1597, 1582, 1555, 1502, 1471, 1462,
1448, 1419, 1382, 1291, 1256, 1174, 1066, 1021, 936, 920, 877, 843, 823, 810, 768, 753,
738. EI-MS m/z (rel. int.): 315.15 (M+, 20), 245.03 (100), 216.06 (8), 153.06 (3),126.06
(3). Elemental analysis: calcd. C18H18NClO2: C 68.46, H 5.75, N 4.44; found C 69.80, H
6.05, N 4.68.
6PB-C: The yield was 60% of pale pink crystals. M.p. 86.7 ◦C. 1H-NMR (400 MHz,
CDCl3, TMS): δ (ppm) 8.17 (d, J = 9.2 Hz, 2H), 7.70 (d, 4J = 2.0 Hz, 1H), 7.47 (d, J =
8.4 Hz, 1H), 7.29 (q, 3J = 8.4 Hz, 4J = 2.0 Hz, 1H), 7.03 (d, J = 8.8 Hz, 2H), 4.06 (t, J =
6.4 Hz, 2H), 1.84 (m, 2H), 1.50 (m, 4H), 1.39 (m, 4H), 0.94 (t, J = 7.2 Hz, 3H). IR (KBr,
pellet, cm−1): 3064, 2945, 2938, 2918, 2857, 1612, 1596, 1578, 1554, 1497, 1472, 1451,
1441, 1378, 1292, 1255, 1231, 1168, 1125, 1023, 915, 881, 836, 800, 738. EI-MS m/z (rel.
int.): 329.16 (M+, 22), 245.05 (100), 216,06 (9), 153.06 (3), 126.02 (2).
7PB-C: The yield was 62% of pale pink crystals. M.p. 77.7 ◦C. 1H-NMR (400 MHz,
CDCl3, TMS): δ (ppm) 8.17 (d, J = 9.2 Hz, 2H), 7.70 (d, 4J = 2.0 Hz, 1H), 7.47 (d, J =
3
4
8.4 Hz, 1H), 7.29 (q, J = 8.4 Hz, J = 2.0 Hz, 1H), 7.03 (d, J = 8.8 Hz, 2H), 4.06 (t,
J = 6.4 Hz, 2H), 1.84 (m, 2H), 1.50 (m, 4H), 1.39 (m, 6H), 0.92 (t, J = 7.2 Hz, 3H). IR
(KBr, pellet, cm−1): 3061, 2938, 2920, 2849, 1625, 1616, 1596, 1577, 1551, 1496, 1468,
1451, 1423, 1391, 1304, 1292, 1276, 1255, 1235, 1193, 1166, 1122, 1013, 915, 881, 835,
809, 798, 738. EI-MS m/z (rel. int.): 343.17 (M+, 18), 245.03 (100), 216.05(9), 153.08 (2),
126.03 (2). Elemental analysis: calcd. C20H22NClO2: C 69.86, H 6.45, N 4.07; found C
71.30, H 6.54, N 4.16.
8PB-C: The yield was 60% of pale pink crystals. M.p. 86.1 ◦C. 1H-NMR (400 MHz,
4
CDCl3, TMS): δ (ppm) 8.17 (d, J = 8.8 Hz, 2H), 7.70 (d, J = 2.0 Hz, 1H), 7.47

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3
4
(d, J = 8.4 Hz, 1H), 7.29 (q, J = 8.4 Hz, J = 2.0 Hz, 1H), 7.03 (d, J = 8.8 Hz,
2H), 4.06 (t, J = 6.4 Hz, 2H), 1.84 (m, 2H), 1.49–1.30 (m, 10H), 0.91 (t, J = 7.2 Hz, 3H).
IR (KBr, pellet, cm−1): 3064, 2945, 2938, 2915, 2847, 1611, 1596, 1579, 1555, 1497, 1468,
1451, 1421, 1390, 1304, 1290, 1253, 1231, 1198, 1168, 1060, 1020, 914, 880, 836, 810,
798, 738. EI-MS m/z (rel. int.): 357.20 (M+, 15), 245.05 (100), 207.07 (6), 73.05 (2), 71.09
(3).
10PB-C: The yield was 59% of pale pink crystals. M.p. 77.3 ◦C. 1H-NMR (300 MHz,
CDCl3, TMS): δ (ppm) 8.17 (d, J = 8.7 Hz, 2H), 7.70 (d, 4J = 1.8 Hz, 1H), 7.47 (d, J =
3
4
8.1 Hz, 1H), 7.29 (q, J = 8.1 Hz, J = 1.8 Hz, 1H), 7.03 (d, J = 9.0 Hz, 2H), 4.06 (t,
J = 6.6 Hz, 2H), 1.84 (m, 2H), 1.48–1.28 (m, 14H), 0.91 (t, J = 6.6 Hz, 3H). IR (KBr,
pellet, cm−1): 3065, 2948, 2936, 2917, 2848, 1612, 1596, 1579, 1555, 1497, 1468, 1448,
1422, 1385, 1290, 1253, 1236, 1197, 1167, 1061, 1053, 1015, 915, 884, 837, 810, 799, 750,
737. EI-MS m/z (rel. int.): 385.20 (M+, 14), 245.05 (100), 216.05 (8), 207.04 (13), 73.07
(5).
12PB-C: The yield was 61% of pale pink crystals. M.p. 78.1 ◦C. 1H-NMR (400 MHz,
CDCl3, TMS): δ (ppm) 8.17 (d, J = 8.8 Hz, 2H), 7.70 (d, 4J = 2.0 Hz, 1H), 7.47 (d, J =
3
4
8.4 Hz, 1H), 7.29 (q, J = 8.4 Hz, J = 2.0 Hz, 1H), 7.03 (d, J = 8.8 Hz, 2H), 4.06 (t,
J = 6.4 Hz, 2H), 1.84 (m, 2H), 1.50–1.27 (m, 18H), 0.90 (t, J = 7.2 Hz, 3H). IR (KBr,
pellet, cm−1): 3064, 3037, 3020, 2916, 2846, 1616, 1597, 1580, 1554, 1535, 1497, 1470,
1451, 1421, 1390, 1378, 1350, 1305, 1288, 1253, 1236, 1197, 1168, 1063, 1052, 1032,
1015, 1002, 919, 915, 885, 837, 810, 799, 750, 738. EI-MS m/z (rel. int.): 413.26 (M+, 16),
245.05 (100), 216.07 (6), 207.07 (6), 73.05 (3).
14PB-C: The yield was 64% of pale pink crystals. M.p. 79.3 ◦C. 1H-NMR (400 MHz,
CDCl3, TMS): δ (ppm) 8.19 (d, J = 8.8 Hz, 2H), 7.72 (d, 4J = 2.0 Hz, 1H), 7.48 (d, J =
8.4 Hz, 1H), 7.30 (q, 3J = 8.4 Hz, 4J = 2.0 Hz, 1H), 7.03 (d, J = 8.8 Hz, 2H), 4.06 (t, J =
6.4 Hz, 2H), 1.84 (m, 2H), 1.49–1.27 (m, 22H), 0.90 (t, J = 6.4 Hz, 3H). IR (KBr, pellet,
cm−1): 3091, 2953, 2929, 2916, 2847, 1618, 1596, 1580, 1555, 1524, 1502, 1471, 1462,
1450, 1419, 1387, 1381, 1288, 1255, 1174, 1051, 1021, 1009, 920, 875, 842, 824, 809,
738. EI-MS m/z (rel. int.): 441.32 (M+, 9), 245.03 (100), 216.08 (4), 207.05 (13), 55.04
(7). Elemental analysis: calcd. C27H36NClO2: C 73.36, H 8.21, N 3.17; found C 74.15, H
8.23, N 3.22.
16PB-C: The yield was 65% of pale pink crystals. M.p. 82.5 ◦C. 1H-NMR (300 MHz,
CDCl3, TMS): δ (ppm) 8.17 (d, J = 8.7 Hz, 2H), 7.70 (d, 4J = 1.8 Hz, 1H), 7.47 (d, J =
8.7 Hz, 1H), 7.29 (q, 3J = 8.7 Hz, 4J = 2.4 Hz, 1H), 7.03 (d, J = 8.7 Hz, 2H), 4.06 (t, J =
6.6 Hz, 2H), 1.84 (m, 2H), 1.48–1.26 (m, 26H), 0.90 (t, J = 6.6 Hz, 3H). IR (KBr, pellet,
cm−1): 3067, 2950, 2938, 2918, 2850, 1612, 1597, 1578, 1554, 1528, 1497, 1472, 1466,
1451, 1421, 1392, 1379, 1305, 1293, 1255, 1232, 1196, 1168, 1062, 1023, 1005, 916, 881,
835, 811, 799, 750, 739. EI-MS m/z (rel. int.): 469.33 (M+, 9), 281.10 (11), 245.06 (100),
216.04 (4), 72.99 (12). Elemental analysis: calcd. C29H40NClO2: C 74.09, H 8.58, N 2.98;
found C 74.72, H 8.83, N 3.00.
18PB-C: The yield was 61% of pale pink crystals. M.p. 86.3 ◦C. 1H-NMR (400 MHz,
4
CDCl3, TMS): δ (ppm) 8.17 (d, J = 8.8 Hz, 2H), 7.70 (d, J = 2.0 Hz, 1H), 7.46 (d,
3
4
J = 8.4 Hz, 1H), 7.29 (q, J = 8.8 Hz, J = 2.0 Hz, 1H), 7.02 (d, J = 8.8 Hz, 2H),
4.05 (t, J = 6.4 Hz, 2H), 1.84 (m, 2H), 1.49–1.28 (m, 30H), 0.90 (t, J = 6.8 Hz, 3H).
IR (KBr, pellet, cm−1): 3094, 2953, 2915, 2870, 2847, 1617, 1598, 1581, 1558, 1502,
1471, 1462, 1451, 1419, 1391, 1381, 1255, 1228, 1198, 1174, 1159, 1063, 1051, 1032,
1020, 1008, 920, 880, 844, 837, 809, 750, 738, 729, 719, 702, 663, 596, 541, 527, 514.
Elemental analysis: calcd. C31H44NClO2: C 74.74, H 8.90, N 2.81; found C 75.61, H 9.03, N
2.93.

Benzoxazole Liquid Crystals
61
nPB-H Series. 7PB-H: The yield was 73% of pale white crystals. M.p. 70.1–71.2 ◦C.
1H-NMR (300 MHz, CDCl3, TMS): δ (ppm) 8.19 (d, J = 8.7 Hz, 2H), 7.74 (m, 1H), 7.56
(m, 1H), 7.33 (m, 2H), 7.05 (d, J = 8.7 Hz, 2H), 4.06 (t, J = 6.6 Hz, 2H), 1.86 (m, 2H),
1.47–1.29 (m, 8H), 0.91 (t, J = 6.6 Hz, 3H). IR (KBr, pellet, cm−1): 2948, 2939, 2916,
2867, 2847, 1606, 1582, 1554, 1525, 1501, 1471, 1416, 1395, 1303, 1282, 1249, 1168,
1057, 1033, 1009, 924, 830, 800. EI-MS m/z (rel. int.): 309.20 (M+, 26), 211.11 (100),
207.07 (6), 182.09 (7), 64.03 (2).
◦
1
8PB-H: The yield was 73% of pale white crystals. M.p. 75.3–76.6 C. H-NMR
(300 MHz, CDCl3, TMS): δ (ppm) 8.20 (d, J = 8.7 Hz, 2H), 7.75 (m, 1H), 7.56 (m,
1H), 7.34 (m, 2H), 7.03 (d, J = 9.0 Hz, 2H), 4.06 (t, J = 6.3 Hz, 2H), 1.86 (m, 2H),
1.48–1.30 (m, 10H), 0.90 (t, J = 6.6 Hz, 3H). IR (KBr, pellet, cm−1): 2949, 2916, 2867,
2847, 1618, 1604, 1580, 1554, 1525, 1500, 1465, 1453, 1416, 1395, 1303, 1264, 1240,
1168, 1054, 1033, 1000, 921, 838, 797, 743. EI-MS m/z (rel. int.): 351.27 (M+, 14), 2
(100).
◦
1
10PB-H: The yield was 73% of pale white crystals. M.p. 70.6–71.7 C. H-NMR
(300 MHz, CDCl3, TMS): δ (ppm) 8.22 (d, J = 8.7 Hz, 2H), 7.76 (m, 1H), 7.57 (m,
1H), 7.36 (m, 2H), 7.04 (d, J = 9.0 Hz, 2H), 4.07 (t, J = 6.6 Hz, 2H), 1.85 (m, 2H),
1.48–1.28 (m, 14H), 0.90 (t, J = 6.9 Hz, 3H). IR (KBr, pellet, cm−1): 2945, 2938, 2919,
2863, 2847, 1618, 1603, 1580, 1558, 1499, 1470, 1452,1419, 1395, 1301, 1280, 1252,
1241, 1161, 1050, 1016, 920, 832, 800, 746. EI-MS m/z (rel. int.): 357 (M+, 28), 287
(100).
◦
1
12PB-H: The yield was 73% of pale white crystals. M.p. 77.4–78.3 C. H-NMR
(300 MHz, CDCl3, TMS): δ (ppm) 8.20 (d, J = 9.0 Hz, 2H), 7.75 (m, 1H), 7.56 (m, 1H),
7.34 (m, 2H), 7.03 (d, J = 8.7 Hz, 2H), 4.07 (t, J = 6.3 Hz, 2H), 1.87 (m, 2H), 1.48–1.27
(m, 18H), 0.90 (t, J = 6.3 Hz, 3H). IR (KBr, pellet, cm−1): 2939, 2918, 2857, 2848, 1619,
1600, 1578, 1555, 1496, 1471, 1452, 1418, 1395, 1302, 1282, 1244, 1166, 1058, 1031,
1001, 922, 833, 800, 745. EI-MS m/z (rel. int.): 357 (M+, 28), 287 (100).
◦
1
14PB-H: The yield was 73% of pale white crystals. M.p. 77.4–78.3 C. H-NMR
(300 MHz, CDCl3, TMS): δ (ppm) 8.21 (d, J = 8.7 Hz, 2H), 7.75 (m, 1H), 7.55 (m, 1H),
7.33 (m, 2H), 7.04 (d, J = 8.7 Hz, 2H), 4.07 (t, J = 6.6 Hz, 2H), 1.87 (m, 2H), 1.48–1.27
(m, 18H), 0.90 (t, J = 6.3 Hz, 3H). IR (KBr, pellet, cm−1): 2940, 2916, 2855, 2847, 1618,
1601, 1572, 1554, 1495, 1470, 1451, 1419, 1398, 1301, 1279, 1256, 1169, 1052, 1030,
1004, 923, 833, 801, 743. EI-MS m/z (rel. int.): 357 (M+, 28), 287 (100).
◦
1
16PB-H: The yield was 73% of pale white crystals. M.p. 76.5–77.7 C. H-NMR
(300 MHz, CDCl3, TMS): δ (ppm) 8.22 (d, J = 8.7 Hz, 2H), 7.76 (m, 1H), 7.57 (m, 1H),
7.34 (m, 2H), 7.04 (d, J = 9.0 Hz, 2H), 4.06 (t, J = 6.3 Hz, 2H), 1.85 (m, 2H), 1.48–1.27
(m, 26H), 0.90 (t, J = 6.3 Hz, 3H). IR (KBr, pellet, cm−1): 2954, 2915, 2870, 2847, 1620,
1603, 1585, 1556, 1524, 1502, 1476, 1415, 1399, 1304, 1256, 1171, 1056, 1022, 1000,
921, 840, 808, 741. EI-MS m/z (rel. int.): 357 (M+, 28), 287 (100).
Acknowledgments
The authors would like to thank the National Science Foundation Committee of China
(50802058), Program for Changjiang Scholars and Innovative Research Team in Univer-
sity (IRT1070), Specialized Research Fund for the Doctoral Program of Higher Education
(20130202120010), Natural Science Foundation of Shaanxi Province (2012JM2002), Key
Technologies R&D Program of Shaanxi Province (2012K08-09), and the Fundamental Re-
search Funds for the Central Universities (GK201101003, GK201302036, GK201302037)
for financial support of this work.

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P. Chen et al.
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