Polar effect in columnar unsymmetric 1,3,4-oxa(thia)diazoles

Article abstract of DOI:10.1016/j.tet.2014.10.025

Three new series of heterocyclic 1,3,4-oxa(thia)diazoles 1a-c were prepared and their mesomorphic behavior studied. All compounds 1a exhibited monotropic columnar phases, which were confirmed by powder XRD diffractometer. Compounds 1b were not mesogenic.

Full text of DOI:10.1016/j.tet.2014.10.025

Accepted Manuscript
Polar effect in columnar unsymmetric 1,3,4−oxa(thia)diazoles
Tarng−Shiang Hu, Kuan−Ting Lin, Chih−Chin Mu, Hsiu−Ming Kuo, Ming−Chou Chen,
Chung K. Lai
PII:
S0040-4020(14)01452-5
10.1016/j.tet.2014.10.025
TET 26095
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 28 August 2014
Revised Date: 30 September 2014
Accepted Date: 10 October 2014
Please cite this article as: Hu T−S, Lin K−T, Mu C−C, Kuo H−M, Chen M−C, Lai CK, Polar effect in
columnar unsymmetric 1,3,4−oxa(thia)diazoles, Tetrahedron (2014), doi: 10.1016/j.tet.2014.10.025.
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ACCEPTED MANUSCRIPT
Tarng−Shiang Hu, Kuan−Ting Lin, Chih−Chin Mu, Hsiu−Ming Kuo, Ming−Chou Chen*,
Chung K. Lai*
OC12H25
C12H25
O
O
N
N
R
X
N N
C12H25
OC12H25
X = O, S; R = OCnH2n+1, H, F, NO2
Key words: polar effect, 1,3,4-oxadiazoles, columnar phases, quinoxalines
1

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Polar effect in columnar unsymmetric 1,3,4−oxa(thia)diazoles
Tarng−Shiang Hu, Kuan−Ting Lin, Chih−Chin Mu, Hsiu−Ming Kuo, Ming−Chou Chen*, and
Chung K. Lai*
Department of Chemistry, National Central University, Chung−Li, Taiwan, ROC
Abstract. Three new series of heterocyclic 1,3,4−oxa(thia)diazoles 1a−c were prepared and their
mesomorphic behavior studied. All compounds 1a exhibited monotropic columnar phases, which
were confirmed by powder XRD diffractometer. Compounds 1b were not mesogenic. The
formation of columnar phases was sensitive to the substituent groups attached on the phenyl
moiety; those with electron−donating groups (R = H, OCH3) were not liquid crystals, in contrast,
other derivatives with electron−withdrawing groups (R = F, NO2) formed enantiotropic columnar
phases. A Ncell and Rar value equal to 4.73 and 20.20 Å2 of compound 1a (n = 16) within a slice of
9.0 Å thick were obtained, indicating that two molecules was correlated to give a supplemental
more disc−like molecule within columns. This is the first example, showing that the formation of
columnar phases could be controlled by polar groups. The PL spectra of two compounds 1a−c
showed one intense peak at λmax = 505−511 nm, and these photoluminescent emissions originated
from quinoxaline moiety.
* Corresponding author. Tel.: +886 03 4259207; fax: +886 03 4277972.
E-mail address: cklai@cc.ncu.edu.tw (C. K. Lai)
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1. Introduction
2,5-Diaryl-1,3,4-oxadiazoles (OXD)1 and other related derivatives have been studied
extensively as light-emitting materials during the past decades; this might be attributed to their
good thermal and chemical stabilities, and high photoluminescence quantum yields.
1,3,4−Oxadiazoles also exhibited interesting mesogenic materials.2 Many rod−like and disc−like
liquid crystals derived from 1,3,4-oxadiazoles were known. Numerous compounds exhibiting
common phases, such as nematic, smectic A and smectic C phase, as well as lesser examples
forming columnar phases were observed. The relationship between structure−properties has been
demonstrated to be crucial in designing molecular liquid crystalline materials. When changing
molecular structures, the overall molecular shapes/sizes, core rigidities and/or electronic natures
were also altered accordingly, resulting in different mesogenic behavior. For example, phenyl and
naphthalenyl groups have been often incorporated as a structural moiety to fine tune mesogenic
structures. A few 1,3,4−oxaziazoles,3 I, II and III were prepared and studied in this group;
compounds I and II were symmetric, while compounds III are unsymmetric structures. All Ia and
III were found to form improved mesophases than their non−mesogenic homologues IIa; both Ia
and III exhibited monotropic SmC/N and SmA/N phases, respectively. In contrast, all compounds
IIa were non−mesogenic. Better aspect ratio and/or stronger π−π interactions induced in
compounds Ia and III were attributed to the improved mesophases than those in compounds IIa.
In contrast, their homologues 1,3,4−thiadiazoles Ib−IIb showed an apparently improved
mesomorphic behavior. All series of compounds Ib−IIb were mesogenic; giving a wider
temperature range of mesophases and a much higher clearing temperature. The replacement of
oxygen atom in I−IIa by sulfur atom in I−IIb much improved their liquid crystalline behavior.
The larger sulfur atom incorporated was more polarized, leading to a larger dipole moment, which
facilitated the induction of mesophases. Also, a longer C−S bond distance and a smaller C−S−C
angle of 1,3,4−thiadiazole unit favored the formation of a more linear conformation. Such better
linear conformation facilitated or favored a more efficient packing of molecules in the mesophases,
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compared to the bent−shaped 1,3,4−oxadiazoles.
In contrast, a similar more disc−like compounds IV of unsymmetric 1,3,4-oxa(thia)diazoles
derived from quinoxaline −naphthalene conjugates4 was previously reported by this group. All
compounds IVa formed monotropic columnar phases, while all compounds IVb were
non−mesogenic. In order to understand the relationship between the molecular structures and
mesomorphic properties in such columnar mesogens, in this work, we report the preparation and
mesomorphic studies of three new series of 1,3,4-oxa(thia)diazoles Ia−c. A few polar substituents
(i,e, F, NO2, OCH3) incorporated to enhance the molecular polarization and/or dipole were also
prepared. All compounds 1a and 1c exhibited columnar phases, while compounds 1b were not
mesogenic. The lack of mesomorphic properties in 1b might be due to their unfavorable
conformation. The PL spectra of all compounds 1a−b were examined.
RO
OR
RO
OR
X
X
N N
N N
R = (CH2)nH
Ia X = O; monotropic SmC or N phase
Ib X = S; enantiotropic SmC, SmA or N phase
R = (CH2)nH
IIa X = O; Cr phase
IIb X = S; SmC, N phase
RO
OR
O
N N
R = (CH2)nH
III monotropic SmA or N phase
OR1
OR1
R1O
R1O
R1O
R1O
N
N
OR2
N
N
OR2
X
X
N N
N N
∞
OR1
OR1
IVa X = O; monotropic Col phase
IVb X = S; Cr phase
1a X = O; monotropic Col phase
1b X = S; Cr phase
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2.0 Results and discussion
2.1 Synthesis and characterization
The synthetic procedures of 1,3,4-oxa(thia)diazoles 1a−c were summarized in Scheme 1.
2,3-Bis-(3,4-bis(dodecyloxy)phenyl)quinoxaline-6-carboxylic acid 3, isolated as yellow solids was
prepared by condensation reactions of 1,2-bis(3,4-didodecyloxy)phenyl)-1,2-ethanedione
condensed with 3,4-diaminobenzoic acid stirring in THF. 4−(Alkoxy)benzohydrazides and bis(3,
4−bis(dodecyloxy)phenyl)−N'−(4−(alkoxy)benzoyl)quinoxaline−6−carbohydrazides 2 were
followed by previous procedures. 1,3,4-Oxadiazoles 1a were obtained by reactions of acids 3,
refluxed first in thionyl chloride and then refluxed with 4−(alkoxy)benzohydrazides in THF.
1,3,4−Thiadiazoles 1b were similarly prepared by the solutions of approximate hydrazides 2 and
phosphorous pentasulfide in refluxing pyridine for 24 h. The products 1a−c isolated as
yellow−green solids were obtained after recrystallization from THF/methanol. All final
compounds were characterized by 1H NMR, 13C NMR, mass and elemental analysis. For instance,
two characteristic broad singlet peaks occurred at δ 9.27 and δ 9.60 ppm were assigned for
amide−H (−CONH) of compounds 2 (n = 14) in 1H NMR spectra. All data on mass and elemental
analysis were well consistent with their structures.
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OC12H25
C12H25
O
O
O
b
C12H25
O
O
O
C12H25
HO
RO
C12H25
OC12H25
COOMe
COOMe
a
d
c
HO
HO
OC12H25
C12H25
O
O
e
N
OH
N
RO
O
C12H25
OC12H25
CONHNH2
3
f
OC12H25
C12H25
O
O
R
N
H H
N N
N
O
O
C12H25
OC12H25
2a; R = OCnH2n+1, n = 8, 10, 12, 14, 16
2c; R = OCH3, H, F, NO2
g
OC12H25
C12H25O
N
N
R
X
N N
C12H25O
OC12H25
1a; X = O, R = OCnH2n+1, n = 8, 10, 12, 14, 16
1b; X = S, R = OCnH2n+1, n = 8, 12, 16
1c; X = O, R = OCH3, H, F, NO2
Scheme 1. Reagents and conditions: (a) RBr, K2CO3 and KI, refluxing in dry acetone for 48 h; (b) AlCl3,
oxalyl chloride, stirring in CS2 at 0oC for 6 h; (c) 3,4-diaminobenzoic acid, acetic acid, refluxing in THF for
24 h; (d) RBr, K2CO3 and KI, refluxing in dry acetone for 24 h; (e) Hydrazine monohydrate, refluxing in
methanol for 12 h; (f) SOCl2, refluxing for 2 h; then, triethylamine, stirring in dry THF at rt for 24 h ;(g) X =
O, refluxing in POCl3 for 24 h; X = S, P2S5, refluxing in pyridine for 24 h.
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2.2 Phase transitions, mesomorphic behavior and thermal stability of compounds 1a c
−
The mesomorphic behavior of compounds 1a−c was studied and characterized by differential
scanning calorimetry (DSC) and polarizing optical microscopy (POM). The phase transitions and
thermodynamic data for compounds 1a−c are summarized in Table 1. Under polarized optical
microscope, typical pseudo focal−conic or more leaf−like textures (see Fig. 1) with linear
birefringent defects were clearly observed when cooling from their isotropic states. Also a large
area of homeotropic domains accompanied with these observed textures were characteristic for
columnar phases. On the DSC data, all compounds 1a (n = 8, 10, 12, 14, 16) exhibited monotropic
columnar phases, indicating that the columnar phases were kinetically unstable. This monotropic
mesomorphic behavior was also obtained in similar compounds IVa. One transition of
crystal−to−isotropic (Cr→I) on heating process and two transitions of isotropic−to−columnar and
columnar−to−crystal (I→Col→Cr) on the cooling process appeared on DSC thermographs. The
clearing temperatures ranged from Tcl = 96.2 (n = 8) to 84.0 °C (n = 16) on heating process, and
they slightly decreased with increasing carbon length. The clearing temperatures were close to
those of compounds IVa. On the other hand, the temperature ranges of columnar phases were
relatively short, ranging from ∆TCol = 19.5 (n = 8) − 26.3 °C (n = 10), which were slightly wider
than those of compounds IVa (i.e ∆Tcol = 17.3 −2.9 °C). The mesophase was also identified by
powder XRD experiments as hexagonal columnar phase. Compounds IVa also formed similar
monotropic columnar phases. The monotropic mesomorphic and a shorter range of columnar
mesophases behavior observed by both compounds Ia and IVa might be attributed to their
kinetically unstable conformations in the mesophases. Two phenyl groups substituted on the
quinoxaline moiety were slightly twisted by an angle, which caused the whole molecule into a
non−planar conformation. The non−coplanar conformation also increased its overall thickness (ca.
3.35 A); consequently weakening the molecular interactions within the column. An unfavorable
packing was expected and a lower clearing temperature was obtained.
Unsurprisingly, all 1,3,4−thiadiazoles 1b were not mesogenic. One transition of
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crystal−to−isotropic occurred at Tcl = 121.8 (n = 8) −120.3 °C (n = 16), which were slightly lower
by ∆Tcl = 8.6−14.2 °C than those of compounds IVb. In general, most of known
1,3,4−thiadiazoles showed an inproved mesomorphic property than 1,3,4−oxadiazoles; such as a
wider temperature of mesophases. Mesogenic 1,3,4−thiadiazoles also often have higher clearing
temperatures than those of their homologures 1,3,4−oxadiazoles. This was often attributed to their
better linearities and/or larger dipole, inherent from a more polarized sulfur atom than oxygen
atom. The lack of mesomorphic properties observed in both compounds 1b and IVb could be due
to their unfavorable conformations. The relationship plot between the melting temperatures,
clearing temperatures, and the temperature ranges for compounds 1a−c were given in Fig. 2.
Table 1. The phase transitions and enthalpiesa of compounds 1a-1c.
96.2 (95.8)
1a; n = 8
Cr
Cr
Cr
I
I
I
Col
Col
Col
50.6 (91.3)
44.5 (77.5)
45.3 (75.8)
70.1 (6.92)
89.0 (93.9)
10
12
70.8 (6.77)
89.0 (76.9)
70.1 (5.13)
86.2 (80.9)
14
Cr
Cr
I
I
I
I
I
I
I
I
I
Col
44.3 (82.0)
45.7 (85.7)
68.7 (4.66)
84.0 (33.0)
16
Col
Cr
65.4 (3.59)
121.8 (37.8)
1b; n = 8
114.3 (36.1)
121.8 (39.7)
12
Cr
Cr
113.0 (36.8)
120.3 (36.3)
16
112.7 (34.5)
86.6 (26.4)
1c; R = OCH3
Cr
68.5 (21.2)
96.6 (52.4)
Cr
H
F
81.8 (47.3)
92.0 (6.18)
75.7 (7.27)
Cr
Cr
Col
Col
73.1 (8.02)
52.3 (8.61)
119.4 (5.19)
112.9 (39.3)
NO2
117.8 (3.93)
97.9 (37.0)
a: n = the carbon numbers of terminal alkoxy chains; Cr = crystal; Col =
columnar; I = isotropic phases.
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Fig. 1 Optical textures of columnar phases observed for compounds: 1a (n = 8) at 69 oC (top left),
1a (n = 10) at 65 oC (top right), 1a (n = 12) at 63 oC (central left), 1a (n = 14) at 65 oC (central
right), 1c (R = F) at 71 oC (bottom left), 1c (R = NO2) at 116 oC (bottom right).
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Fig. 2 Bar graphs showing the phase behavior of compounds 1a−c. All temperatures were taken
on the cooling process.
The effect5 of polar substituents on the formation of mesophases in a series of rod−like
benzoxazoles containing a variety of polar substituents was previously investigated in this group.
The results indicated that mesophases were better induced by introduction of a polar substituent.
Interestingly, all compounds with electron−donating substituents (X = CH3, OCH3, NMe2)
exhibited N phases, however, other compounds with electron−withdrawing substituents (X = F, Cl,
Br, CF3, NO2, CN, COOCH3) formed SmA phases. Electron−density distribution on the molecules
was controlled or/and determined by the polar group or substitution, which apparently affected the
intermolecular attraction between the neighboring molecules packed in the mesophases. On the
other hand, the polar effect in metallomesogenic β−diketonates containing a variety of polar
substituents was also studied by this group. Results indicated that for all compounds containing
electron−donating substituents (i.e. CH3, C2H5) a rectangular columnar phase (Colr) was observed,
however, other compounds containing electron−withdrawing substituents (i.e. Cl, Br, I) exhibited
a hexagonal columnar phase (Colh).
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The polar effect of compounds 1c on the formation of columnar phases were also studied in
this work. The mesomorphic results were interesting. The formation of columnar phases was
extremely sensitive to the polar groups attached on the phenyl moiety; compound 1c (R = H) was
not mesogenic. The only derivative with electron−donating groups (R = OCH3) was also not liquid
crystals. In contrast, the other two derivatives with electron−withdrawing groups (R = F, NO2)
formed enantiotropic columnar phases. The clearing temperatures of compounds 1a followed the
sequence of Tcl = 119.4 (NO2) > 96.6 (H) > 92.0 (F) > 86.6 °C (OCH3) on heating process. The
mesophases were identified and confirmed as hexagonal columnar phase based on the optical
textures. The optical textures are shown in Fig. 1. The temperature range of columnar phases was
close to the compounds 1a. The degree or extent of electron delocalization might be causing to the
formation of columnar phases in such molecules. The electron delocalization on both derivatives
(F, NO2) with electron−withdrawing group was better than that of the derivative with
electron-donating group (OCH3) or no polar group (H). A polar NO2 group attached to the
hydrocarbon terminal moiety changed substantially the electron affinity of the molecules, and the
strong mesogenic effect caused by the NO2 group induces a positive charge on the nitrogen atom
and increases the electronegativity of the group.
The relationship of the melting temperatures, the clearing temperatures or the temperature
ranges of the mesophases with the electronic properties of the substituents was plotted. However,
no linear correlation between the clearing temperature or the temperature range of mesophases
with Hammett constants (σp) for the substituents was found in this system (Fig. 3). This is the first
example, showing that the formation of columnar phases could be controlled by polar groups.
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150
100
50
NO2, 0.81
H, 0
F, 0.15
OCH3, -0.25
y = 30.602x + 93.218
R² = 0.9228
0
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
Hammett constant
Fig. 3 The plot of clearing temperature (°C) versus Hammett constants (σp) of polar
substituents in compounds 1c.
The thermal stability of compounds 1a−b (n = 12) was also performed by thermogravimetric
analyses (TGA) under nitrogen atmosphere, as shown in Fig. 4. All two compounds showed good
thermal stability at temperature ca. 309−412 °C and the decomposition temperatures for a 5%
weight loss were listed in Table 2. The decomposition temperatures were relatively similar to the
compounds IVa−b, while they were higher than those of compounds Ia−b.
Table 2. The decomposition temperaturesa of compounds by TGA.
Compds.
Tdec (°C)
1a (n = 12)
1b (n = 12)
Ia (n = 12)
Ib (n = 12)
IVa (n = 10)
IVb (n = 10)
411.9
409.2
358.5
366.6
413.5
410.4
a: Tdec were determined by TGA measurements at a heating rate of 10 °C/min
under nitrogen atmosphere, and temperatures were taken at a 5% weight loss.
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1a (n = 12)
1b (n = 12)
IVa (n = 10)
IVb (n = 10)
Ia (n = 12)
Ib (n = 12)
100
80
60
40
20
0
100
200
300
400
500
600
700
o
Temperature ( C)
Fig. 4 The TGA curves of compounds 1a−b, Ia−b and IVa−b.
2.3 Variable-temperature power X ray diffractions and packing study in columnar phases
−
Variable−temperature powder XRD diffraction experiments were conducted to confirm the
structure of the mesophases of compounds 1a (n = 16). A typical diffraction pattern of a
two−dimensional hexagonal lattice with one very strong diffraction peak at lower angle and four
much weaker diffraction peaks was obtained at 64.0 °C under cooling process, as shown in Figure
5. A diffraction pattern with a d−spacing at 33.09 and a broad diffuse peak (4.60 Å) at wide−angle
region was obtained (Table 3). This diffraction pattern corresponded to a hexagonal columnar
arrangement with a d−spacing ratio of 1 and (1/3)1/2, corresponding to Miller indices; 100 and 110,
respectively. This diffraction pattern corresponds to an intercolumnar distance or lattice constant
(i.e., a parameter of the hexagonal lattice) of 38.20 Å. The lack of any relatively strong peaks at
wide angles excluded a more regular periodicity along the columns. However, liquid−like
correlations between the rigid cores occurred at wide angle regions of 4.60 Å (Fig. 5).
To understand the molecular packing within the columns, two important parameters,6 Ncel and
Rar were obtained by using XRD diffraction data (Table 4). A Ncell and Rar value equal to 4.73 and
20.2 Å2 of compound 1a (n = 16) within a slice of 9.0 Å thick were obtained based on the XRD
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diffraction data. Ncell is the number of molecules within a column and Rar is defined as the
diameter of the aromatic or hard columnar part, which can be calculated by Rar = (4Sar/π)1/2. Scol
can be calculated from lattice parameters of X−ray diffraction. The Rar value was close to 19.25 Å,
which is the size of central core of 1a. On the other hand, an average number of ca. 4.73 molecules
for 1a were stacked within a height of 9.0 Å in the columnar phases, indicating that two molecules
was correlated to give a supplemental more disc-like molecule within columns. A thickness of two
phenyl groups twisted by an angle of approximately ca. 3.35° was obtained from our similar
quinoxaline system. A more disc−like correlated structure constructed by two molecules lying
roughly side−by−side was proposed within the column. The possible molecular arrangement in
columnar phases was proposed in Figure 6. The proposed packing style was quite consistent with
our previous studies of quinoxaline−benzoxazole conjugates.
33.09
30000
20000
10000
4.53
0
10
20
30
2 theta
Fig. 5 The powder X−ray diffraction plots of compound 1a (n = 16) at 64.0 oC.
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Table 3. Detailed indexation by powder XRD of columnar phasea for compounds 1a
Compd.
Mesophases
temp.
d-Spacing
obs.(calcd.)
Lattice const.
(Å)
Miller
Indices
1a (n = 16)
Col at 64.0 °C
33.09 (33.09)
4.60 (br)
a = 38.20
halo
100
a: temperature taken on the cooling process.
Table 4. Geometric parameters of compound 1a (n = 16).
Compd.
S(Å2)
Vcell(Å3)
Vm(Å3)
Temp(°C) Ncell Sar(Å2) Rar(Å2)
1a (n = 16)
1264.34 11379.03
2405.09
64.0 4.73 320.64 20.20
a: S(Å2) = columnar cross section area, Vcell(Å3) = volume of the column stratum 9−Å thick,
Vm(Å3) = molecular volume, Ncell = the number of molecules contained in each columnar stratum
9−Å thick, Sar(Å2) = the surface area of hard columnar core, Rar(Å2) = the diameter of the aromatic
part.
Fig. 6 A schematic representation of molecular organization proposed in columnar phase by
compounds 1a
2.4 Optical properties
The UV–vis absorption and PL spectra of the compounds 1a–c (all n = 12) measured in
CH2Cl2 solution at room temperature are presented in Figure 7. The λmax peaks of UV–vis
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absorption and PL spectra were listed in Table 5. The absorption λmax peaks of compounds 1a
occurred at ca. 296 and 401 nm, which were attributed to a n−π* and π−π* transitions arising from
quinoxaline moiety.4,7 The 1, 3, 4–thiadiazole 1b has its inherent absorption peak a 326 nm,
slightly red shifted by 30 nm over 1, 3, 4–oxadiazole 1a. The other peak occurred at 404 nm were
assigned to n−π*. All compounds 1c showed similar absorption peaks at 287–295 nm and 400–
404 nm. The PL spectra of all compounds 1a−c showed one intense and broad peak occurred at
λmax = 505–511 nm, which was slightly blue-shifted to similar compounds IVa–b. Compound 1c
(R = NO2) showed very weak emission peaks in intensity. These photoluminescent emissions were
attributed to the heterocyclic quinoxaline, not 1,3,4–oxadiazole moiety.8 The emission peaks were
only slightly sensitive to the nature of the polar substituents; all red-shifted by 1–6 nm. In contrast,
the photoluminescent peaks emitted by 1, 3, 4−oxadiazoles which often appeared at ca. 390−418
nm were not observed in this system and incorporation of a highly extended−conjugated
quinoxaline would not shift its λmax. Quinoxaline and 1, 3, 4−oxa(thia)diazoles were often
considered as π–acceptors and fluorophore. A red−shift emission often attributed to
donor−acceptor transfer was also not expected. The lack of emissions by 1,3,4−oxadiazoles at ca.
390−418 nm was attributed to the so−called Fluorescence Resonance Energy Transfer (FRET); the
energy emitted by 1,3,4−oxadiazole at ca. 400 nm was absorbed by quinoxaline, and then emitted
an emission at 505−511 nm.
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1a (n = 12)
1b (n = 12)
1c (R = OCH3)
1c (R = H)
1c (R = F)
1c (R = NO2)
IVa (n = 10)
IVb (n = 10)
300
400
500
Wavelengh (nm)
1a (n = 12)
1b (n = 12)
1c (R = OCH3)
1c (R = H)
1c (R = F)
IVa (n = 10)
IVb (n = 10)
500
600
700
Wavelengh (nm)
Fig. 7 Absorption (top) and PL spectra (bottom) of the compounds 1a−c and IVa-b.
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Table 5. Absorption and emission dataa of compounds 1a−c.
Compd.
Adsorption
Emission
λ (nm)
λmax (nm)
1a (n = 12)
1b (n = 12)
1c (R = OCH3)
1c (R = H)
296, 401
326, 404
295, 400
287, 401
287, 400
282, 404
324, 402
352, 405
505
505
506
507
1c (R = F)
511
1c (R = NO2)
IVa (n = 10)
IVb (n = 10)
very weak
512
509
a: measured in CH2Cl2 solution (1.0×10-5 M) at rt. The standard
is anthracene (Φfs = 0.27 in hexane solution)
3. Conclusions
Polar groups was incorporated in series of columnar 1,3,4−oxadiazoles 1c, and substitution
effect of the formation of columnar phases was investigated. The formation of columnar phases
was quite sensitive to the substituent groups attached on the phenyl moiety; one derivative with
electron−donating group (R = OCH3) was not liquid crystals, in contrast, the other derivatives with
electron−withdrawing groups (R = F, NO2) formed hexagonal columnar phases. All derivatives
showed good stabilities on TGA. This is the first example, showing that the formation of columnar
phases could be controlled by polar groups. The PL spectra of all compounds 1a−c showed one
intense peak at λmax = 505−511 nm, which was originated from the quinoxaline moiety.
4. Experimantal
3.1 General materials and methods
All chemicals and solvents were reagent grade from Aldrich Chemical Co., and solvents were
dried by standard techniques. 1H and 13C NMR spectra were measured on a Bruker DRX−300.
DSC thermographs were carried out on a Mettler DSC 822. All phase transitions are determined
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by a scan rate of 10.0 °C/min. Optical polarized microscopy was carried out on Zeiss Axioplan 2
equipped with a hot stage system of Mettler FP90/FP82HT. The UV−vis absorption and
fluorescence spectra were obtained using Jasco V-530and Hitachi F-4500 spectrometer. Elemental
analysis for carbon, hydrogen, and nitrogen was conducted at Instrumentation Center, National
Taiwan University on a Heraeus CHN−O−Rapid elemental analyzer. The powder diffraction data
were collected from the Wiggler−A beam line of the National Synchrotron Radiation Research
Center with the wavelength of 1.3263 Ǻ. The compounds of 1, 2−bis(alkoxy)benzenes,
methyl−4−(alkoxy)benzoates, 1, 2−bis(3,4−bis(alkoxy)phenyl)−1, 2−ethanediones, 2, 3-bis−(3,
4−bis(alkoxy)phenyl)quinoxaline−6−carboxylic acids, 4−(alkoxy)benzohydrazides, 2, 3−bis(3,
4−bis(dodecyloxy)phenyl)−N'−(4−(alkoxy)benzoyl) quinoxaline−6−carbohydrazide were prepared
by the literature procedures.
4.2 Synthesis of compounds 1-3
4.2.1 1, 2−Bis(dodecyloxy)benzene
1H NMR (300 MHz, CDCl3): δ 0.85 (t, 6H, −CH3, J = 6.9 Hz), 1.24−1.45 (m, 36H, −CH2),
1.74−1.84 (m, 4H, −CH2), 3.97 (t, 4H, −OCH2, J = 6.6 Hz), 6.86 (s, Ar−H, 4H). 13C NMR (75
MHz, CDCl3): δ 14.14, 22.72, 26.07, 29.38, 29.47, 29.67, 29.73, 31.95, 69.29, 114.12, 121.00,
149.25.
4.2.2 1, 2−Bis(3,4−bis(dodecyloxy)phenyl)−1, 2−ethanedione
1H NMR (300 MHz, CDCl3): δ 0.83−0.88 (m, 12H, −CH3), 1.24−1.45 (m, 72H, −CH2), 1.77−1.86
(m, 8H, −CH2), 4.01−4.05 (m, 8H, −OCH2), 6.81 (d, 2H, Ar−H, J = 8.4 Hz), 7.39−7.42 (m, 2H,
Ar−H), 7.54 (d, 2H, Ar−H, J = 1.8 Hz). 13C NMR (75 MHz, CDCl3): δ 14.14, 22.72, 25.94, 26.00,
28.93, 29.08, 29.40, 29.66, 31.95, 69.11, 69.22, 111.54, 112.19, 126.17, 149.29, 154.97, 193.83.
4.2.3 2, 3-Bis−(3, 4−bis(dodecyloxy)phenyl)quinoxaline−6−carboxylic acid 3
The solution 1, 2−bis(3, 4−bis(dodecyloxy)phenyl)−1, 2−ethanedione (4.0 g, 0.004 mol) dissolved
in 100 mL of THF was stirred with 0.5 mL of glacial acetic acid for 10 min. To the solution, 3,
4−diaminobenzoic acid (4.0 g, 0.0051 mol) dissolved in 2.0 mL of DMSO was added and stirred
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for 24 h under nitrogen atmosphere. The product, isolated as yellow solids was obtained after
recrystallization from THF/MeOH. Yield 93%, 1H NMR (300 MHz, CDCl3): δ 0.84−0.88 (m, 12H,
−CH3), 1.19−1.41 (m, 72H, −CH2), 1.68−1.83 (m, 8H, −CH2), 3.79−4.01 (m, 8H, −OCH2), 6.81 (d,
2H, Ar−H, J = 8.4 Hz), 7.08−7.12 (m, 4H, Ar−H), 8.15 (d, 1H, Ar−H, J = 8.7 Hz), 8.32 (d, 1H,
Ar−H, J = 8.7 Hz), 8.91 (s, 1H, Ar−H). 13C NMR (75 MHz, CDCl3): δ 14.15, 22.72, 26.06, 29.15,
29.22, 29.42, 29.48, 29.73, 31.96, 69.20, 113.04, 115.22, 122.98, 123.15, 129.32, 129.94, 131.08,
131.17, 132.71, 140.12, 143.37, 148.73, 150.19, 150.36, 154.36, 155.16, 170.92.
4.2.4 Methyl−4−(dodecyloxy)benzoate (n = 12)
The solution of methyl 4−hydroxybenzoate (10.0 g, 0.06 mol) dissolved in 150 mL of acetone was
added K2CO3 (4.5 g, 0.03 mol), KI (5.0 g, 0.03 mol) and 1−bromododecane (16.1 g, 0.06 mol).
The solution was refluxed for 24 h under nitrogen atmosphere. The solution was filtered while hot.
The filtrate was concentrated to give light brown solids. The products isolated as white solids were
obtained after recrystallization from CH2Cl2/MeOH. Yield 85%, 1H NMR (300 MHz, CDCl3): δ
0.85 (t, 3H, −CH3, J = 7.2 Hz), 1.24−1.42 (m, 18H, −CH2), 1.71−1.78 (m, 2H, −CH2), 3.84 (s, 3H,
−COOCH3), 3.96 (t, 2H, −OCH2, J = 6.6 Hz), 6.85 (d, 2H, Ar−H, J = 9.0 Hz), 7.93 (d, 2H, Ar−H,
J = 9.0 Hz). 13C NMR (75 MHz, CDCl3): δ 14.09, 22.66, 25.95, 29.08, 29.31, 29.34, 29.53, 31.87,
51.77, 68.13, 113.98, 122.22, 131.51, 162.91, 166.86.
4.2.5 4−(Dodecyloxy)benzohydrazide (n = 12)
The solution of methyl−4−(dodecyloxy)benzoate (5.0 g, 0.02 mol) dissolved in 100 mL of MeOH
was added hydrazine monohydrate (3.1 g, 0.2 mol). The solution was refluxed for 12 h. The
solution was concentrated to give off−white solids. The products isolated as white solids were
obtained after recrystallization from hexane/MeOH. Yield 90%, 1H NMR (300 MHz, CDCl3): δ
0.86 (t, 3H, −CH3, J = 5.7 Hz), 1.24−1.42 (m, 18H, −CH2), 1.73−1.78 (m, 4H, −CH2), 4.00 (t, 2H,
−OCH2, J = 6.3 Hz), 6.87 (d, 2H, Ar−H, J = 8.4 Hz), 7.69 (d, 1H, Ar−H, J = 8.4 Hz), 7.77 (s, 1H,
N−H). 13C NMR (75 MHz, CDCl3): δ 14.08, 22.65, 25.94, 29.07, 29.32, 29.54, 29.60, 31.87, 68.16,
114.34, 124.51, 128.63, 129.23, 162.05, 168.36.
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2, 3−Bis(3, 4−bis(dodecyloxy)phenyl)−N'−(4−(alkoxy)benzoyl)quinoxaline−6−carbohydrazide
(2; n = 12)
The solution of 2,3−bis−(3, 4−bis(dodecyloxy)phenyl)quinoxaline−6−carboxylic acid (1.0 g, 0.94
mmol) mixed with 0.3 mL of thionyl chloride (4.0 mmol) was gently refluxed for 4 h under
nitrogen atmosphere. The excess of thionyl chloride was removed under reduced vacuum. The
compound prepared was then used directly for the following step. The solution of
4−(dodecyloxy)benzohydrazide (0.322 g, 0.94 mmol) dissolved in 30 mL of THF was added
dropwise 0.14 mL of triethylamine (1.0 mmol) at ice bath. The solution was stirred at rt for 24 h.
The solution was extracted twice with 100 mL of CH2Cl2/H2O. The organic layers were combined
and concentrated to give brown solids. The products isolated as yellow−green solids were obtained
after recrystallization from ethyl acetate. Yield 75%.
4.2.6 2, 3−Bis(3, 4−bis(dodecyloxy)phenyl)−N'−(4−(tetradecyloxy)benzoyl)quinoxaline−
6−carbohydrazide (2, n = 14)
1H NMR (300 MHz, CDCl3): δ 0.84−0.88 (m, 15H, −CH3), 1.25−1.44 (m, 94H, −CH2), 1.66−1.83
(m, 10H, −CH2), 3.80−4.00 (m, 10H, −OCH2), 6.80 (d, 2H, Ar−H, J = 8.4 Hz), 6.90 (d, 2H, Ar−H,
J = 7.5 Hz), 7.08 (s, 2H, Ar−H), 7.11 (d, 2H, Ar−H, J = 10.2 Hz), 7.81 (d, 2H, Ar−H, J = 8.7 Hz),
8.15 (s, 2H, Ar−H), 8.62 (s, 1H, Ar−H), 9.27 (s, 1H, −NH, br), 9.60 (s, 1H, −NH, br). 13C NMR
(75 MHz, CDCl3): δ 14.07, 22.67, 26.04, 29.19, 29.25, 29.37, 29.46, 29.66, 31.92, 68.31, 69.24,
113.16, 114.54, 115.34, 115.40, 122.98, 123.08, 127.48, 128.42, 129.17, 129.69, 131.09, 131.17,
132.09, 140.05, 142.49, 148.82, 150.32, 150.42, 154.24, 154.76, 162.68, 163.18, 163.92.
4.2.7 2−(2, 3−Bis(3, 4−bis(dodecyloxy)phenyl)quinoxalin−6−yl)−5−(6−(dodecyloxy)phenyl) −1,
3, 4−oxadiazole (1a, n = 12)
The solution of 2, 3−Bis(3, 4−bis(dodecyloxy)phenyl)−N'−(4−(dodecyloxy)benzoyl)quinoxaline−
6−carbohydrazide (1.0 g, 0.36 mmol) dissolved in 10 mL of phosphoryl chloride was refluxed for
24 h. The solution slowly turned reddish−black in color. The solution was cooled at room
temperature, and then the solution was slowly poured into 300 mL of icy water. After stirring for 2
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ACCEPTED MANUSCRIPT
h, the orange−red solids were filtered and collected. The solids were dissolved in 25 mL of
dichloromethane and extracted with 150 mL of 1.0 M NaOH(aq) for 2 h. The yellow−brown solids
were collected. The products isolated as bright yellow solids were obtained after recrystallization
from THF/methanol or by silica gel chromatography eluting with hexane/ethyl acetate. Yield 55%,
1H NMR (300 MHz, CDCl3): δ 0.84−0.88 (m, 15H, −CH3), 1.25−1.44 (m, 90H, −CH2), 1.69−1.84
(m, 10H, −CH2), 3.82−4.06 (m, 10H, −OCH2), 6.82 (d, 2H, Ar−H, J = 6.9 Hz), 7.02 (d, 2H, Ar−H,
J = 8.7 Hz), 7.09 (s, 2H, Ar−H), 7.13 (d, 2H, Ar−H, J = 7.8 Hz), 8.08 (d, 2H, Ar−H, J = 8.7 Hz),
8.25 (d, 1H, Ar−H, J = 8.7 Hz), 8.48 (d, 1H, Ar−H, J = 8.4 Hz), 8.84 (s, 1H, Ar−H). 13C NMR (75
MHz, CDCl3): δ 14.13, 22.71, 26.05, 29.15, 29.23, 29.40, 29.47, 29.71, 31.95, 68.34, 69.20,
113.08, 115.10, 115.22, 122.93, 123.08, 124.84, 127.21, 127.45, 128.84, 130.01, 131.02, 140.51,
142.13, 148.78, 150.28, 150.37, 154.37, 154.44, 162.22 163.53, 165.15. MS (HRESI): calcd for
M+: 1348.0689. Found: 1348.0688. Anal. Calcd for C88H138N4O6: C, 78.40; H, 10.32. Found C,
78.40; H, 10.34.
4.2.8 2−(2, 3−Bis(3, 4−bis(dodecyloxy)phenyl)quinoxalin−6−yl)−5−(4−(octyloxy)phenyl)−1, 3,
4−oxadiazole (1a, n = 8)
1H NMR (300 MHz, CDCl3): δ 0.84−0.88 (m, 15H, −CH3), 1.25−1.44 (m, 82H, −CH2), 1.71−1.86
(m, 10H, −CH2), 3.80−4.06 (m, 10H, −OCH2), 6.79−6.85 (m, 2H, Ar−H), 7.02 (d, 2H, Ar−H, J =
8.7 Hz), 7.09 (s, 2H, Ar−H), 7.13 (d, 2H, Ar−H, J = 11.1 Hz), 8.08 (d, 2H, Ar−H, J = 8.7 Hz),
8.23 (d, 1H, Ar−H, J = 8.7 Hz), 8.47 (d, 1H, Ar−H, J = 8.7 Hz), 8.83 (s, 1H, Ar−H). 13C NMR (75
MHz, CDCl3): δ14.12, 22.70, 26.05, 29.16, 29.23, 29.40, 29.47, 29.71, 31.95, 68.35, 69.23, 113.08,
115.12, 115.23, 122.96, 123.10, 124.87, 127.25, 127.42, 128.86, 129.99, 130.95, 140.49, 142.08,
148.78, 150.31, 150.40, 154.48, 154.43, 162.24, 163.52, 165.18. MS (HRESI): calcd for M+:
1292.0063 Found: 1292.0110. Anal. Calcd for C84H130N4O6: C, 78.09; H, 10.14. Found C, 78.07;
H, 10.19.
4.2.9 2−(2, 3−Bis(3, 4−bis(dodecyloxy)phenyl)quinoxalin−6−yl)−5−(4−(decyloxy)phenyl)−1, 3,
4− oxadiazole (1a, n = 10)
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1H NMR (300 MHz, CDCl3): δ 0.84−0.87 (m, 15H, −CH3), 1.25−1.44 (m, 86H, −CH2), 1.71−1.84
(m, 10H, −CH2), 3.80−4.06 (m, 10H, −OCH2), 6.82−6.85 (m, 2H, Ar−H), 7.02 (d, 2H, Ar−H, J =
9.0 Hz), 7.09 (s, 2H, Ar−H), 7.13 (d, 2H, Ar−H, J = 8.4 Hz), 8.08 (d, 2H, Ar−H, J = 8.7 Hz), 8.24
(d, 1H, Ar−H, J = 8.7 Hz), 8.48 (d, 1H, Ar−H, J = 8.7 Hz), 8.83 (s, 1H, Ar−H). 13C NMR (75
MHz, CDCl3): δ14.09, 22.69, 26.04, 29.17, 29.25, 29.38, 29.46, 29.69, 31.93, 68.35, 69.24, 113.19,
115.12, 115.37, 122.89, 123.02, 124.75, 127.09, 127.57, 128.82, 130.12, 131.38, 140.67, 142.31,
148.81, 150.23, 150.33, 154.40, 154.50, 162.22, 163.57, 165.13. MS (HRESI): calcd for M+:
1320.0376. Found: 1320.0400. Anal. Calcd for C86H134N4O6: C, 78.25; H, 10.23. Found C, 78.25;
H, 10.32.
4.2.10 2−(2, 3−Bis(3, 4−bis(dodecyloxy)phenyl)quinoxalin−6−yl)−5−(4−(tetradecyloxy)phenyl)
−1, 3, 4−oxadiazole (1a, n = 14)
1H NMR (300 MHz, CDCl3): δ 0.84−0.88 (m, 15H, −CH3), 1.25−1.44 (m, 94H, −CH2), 1.67−1.84
(m, 10H, −CH2), 3.82−4.06 (m, 10H, −OCH2), 6.82−6.85 (m, 2H, Ar−H), 7.02 (d, 2H, Ar−H, J =
8.7 Hz), 7.09 (s, 2H, Ar−H), 7.13 (d, 2H, Ar−H, J = 8.1 Hz), 8.08 (d, 2H, Ar−H, J = 8.7 Hz), 8.24
(d, 1H, Ar−H, J = 8.4 Hz), 8.47 (d, 1H, Ar−H, J = 8.4 Hz), 8.84 (s, 1H, Ar−H). 13C NMR (75
MHz, CDCl3): δ 14.08, 22.68, 26.04, 29.18, 29.25, 29.37, 29.45, 29.67, 31.92, 68.36, 69.28,
113.22, 115.13, 115.40, 122.97, 123.11, 124.85, 127.19, 127.44, 128.84, 130.00, 131.12, 140.51,
142.11, 148.85, 150.36, 150.45, 154.36, 162.24, 163.53, 165.16. MS (HRESI): calcd for M+:
1376.1002. Found: 1376.0996. Anal. Calcd for C90H142N4O6: C, 78.55; H, 10.40. Found C, 78.46;
H, 10.45.
4.2.11 2−(2, 3−Bis(3, 4-bis(dodecyloxy)phenyl)quinoxalin−6−yl)−5−(4−(hexadecyloxy)phenyl)
−1, 3, 4-oxadiazole (1a, n = 16)
1H NMR (300 MHz, CDCl3): δ 0.84−0.88 (m, 15H, −CH3), 1.24−1.41 (m, 98H, −CH2), 1.67−1.92
(m, 10H, −CH2), 3.81−4.05 (m, 10H, −OCH2), 6.82−6.85 (m, 2H, Ar−H), 7.02 (d, 2H, Ar−H, J =
8.4 Hz), 7.09 (s, 2H, Ar−H), 7.13 (d, 2H, Ar−H, J = 7.8 Hz), 8.08 (d, 2H, Ar−H, J = 8.7 Hz), 8.23
(d, 1H, Ar−H, J = 9.0 Hz), 8.47 (d, 1H, Ar−H, J = 9.6 Hz), 8.83 (s, 1H, Ar−H). 13C NMR (75
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MHz, CDCl3): δ 14.12, 22.70, 26.05, 29.16, 29.22, 29.39, 29.47, 29.70, 31.94, 68.35, 69.20,
113.08, 115.12, 115.22, 123.00, 123.05, 124.92, 127.42, 127.48, 128.85, 130.88, 131.19, 140.57,
141.85, 148.79, 150.24, 150.35, 154.34, 154.38, 162.24, 163.55, 165.19. MS (HRESI): calcd for
M+: 1404.1315. Found: 1404.1304. Anal. Calcd for C92H146N4O6: C, 78.69; H, 10.48. Found C,
78.66; H, 10.52.
4.2.12 2−(2, 3−Bis(3, 4-bis(dodecyloxy)phenyl)quinoxalin−6−yl)−5−(4−(dodecyloxy)phenyl)−1,
3, 4−thiadiazole (1b; n = 12)
The solution of 2,3−bis(3,4−bis(dodecyloxy)phenyl)−N'−(4−(dodecyloxy)phenyl)−quinoxaline
−6−carbohydrazide (1.0 g, 0.36 mmol) dissolved in 10 mL of dry pyridine. The solution was
gently heated until all solids were dissolved. The solution was then added phosphorus pentasulfide
(1.12 g, 5.0 mol), and then refluxed for 24 h. The solution was extracted twice with 100 mL of
CH2Cl2/H2O. The organic layers were combined and concentrated to give brown solids. The
products isolated as yellow−green solids were obtained after recrystallization from THF/methanol
or by silica gel chromatography eluting with hexane/ethyl acetate. Yield 45%. 1H NMR (300 MHz,
CDCl3): δ 0.84−0.88 (m, 15H, −CH3), 1.25 (m, 90H, −CH2), 1.67−1.83 (m, 10H, −CH2), 3.80
−4.04 (m, 10H, −OCH2), 6.82−6.85 (m, 2H, Ar−H), 6.98 (d, 2H, Ar−H, J = 8.7 Hz), 7.08 (s, 2H,
Ar−H), 7.12 (d, 2H, Ar−H, J = 7.8 Hz), 7.95 (d, 2H, Ar−H, J = 8.7 Hz), 8.21 (d, 1H, Ar−H, J = 8.7
Hz), 8.50 (d, 1H, Ar−H, J = 8.7 Hz), 8.62 (s, 1H, Ar−H). 13C NMR (75 MHz, CDCl3): δ 14.10,
22.69, 26.04, 29.17, 29.24, 29.38, 29.45, 29.69, 31.95, 68.35, 69.24, 113.23, 115.15, 115.31,
122.47, 122.85, 123.00, 127.88, 128.84, 129.63, 129.96, 131.23, 131.36, 131.45, 140.81, 142.13,
148.81, 150.18, 150.26, 154.20, 154.27, 161.80, 166.34, 168.73. MS (HRESI): calcd for M+:
1364.0461. Found: 1364.0463. Anal. Calcd for C92H146N4O5S: C, 77.48; H, 10.20. Found C, 77.90;
H, 10.13.
4.2.13 2−(2, 3-Bis(3, 4−bis(dodecyloxy)phenyl)quinoxalin−6−yl)−5−(4−(octyloxy)phenyl)−1, 3,
4−thiadiazole (1b, n = 8)
1H NMR (300 MHz, CDCl3): δ 0.84−0.88 (m, 15H, −CH3), 1.25 (m, 82H, −CH2), 1.65−1.86 (m,
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ACCEPTED MANUSCRIPT
10H, −CH2), 3.80−4.05 (m, 10H, −OCH2), 6.82−6.85 (m, 2H, Ar−H), 6.98 (d, 2H, Ar−H, J = 8.7
Hz), 7.08 (s, 2H, Ar−H), 7.12 (d, 2H, Ar−H, J = 8.1 Hz), 7.95 (d, 2H, Ar−H, J = 8.7 Hz), 8.21 (d,
1H, Ar−H, J = 8.4 Hz), 8.49 (d, 1H, Ar−H, J = 9.3 Hz), 8.61 (s, 1H, Ar−H). 13C NMR (75 MHz,
CDCl3): δ 14.08, 22.68, 26.03, 29.17, 29.23, 29.37, 29.44, 29.68, 31.93, 68.35, 68.26, 113.25,
115.16, 115.37, 122.46, 122.95, 123.09, 128.01, 128.64, 129.64, 129.84, 131.14, 131.37, 140.58,
141.95, 148.84, 150.32, 150.38, 154.15, 161.82, 166.27, 168.79. MS (HRESI): calcd for M+:
1307.9835. Found: 1307.9842. Anal. Calcd for C92H140N4O5S: C, 77.13; H, 10.02. Found C, 77.05;
H, 9.99.
4.2.14 2−(2, 3−Bis(3, 4−bis(dodecyloxy)phenyl)quinoxalin−6−yl)−5−(4−(hexadecyloxy)phenyl)
−1, 3, 4−thiadiazole (1b, n = 16)
1H NMR (300 MHz, CDCl3): δ 0.84−0.88 (m, 15H, −CH3), 1.24 (m, 98H, −CH2), 1.67−1.83 (m,
10H, −CH2), 3.80−4.04 (m, 10H, −OCH2), 6.81−6.85 (m, 2H, Ar−H), 6.98 (d, 2H, Ar−H, J = 8.7
Hz), 7.08 (s, 2H, Ar−H), 7.12 (d, 2H, Ar−H, J = 8.1 Hz), 7.95 (d, 2H, Ar−H, J = 8.7 Hz), 8.20 (d,
1H, Ar−H, J = 8.7 Hz), 8.50 (d, 1H, Ar−H, J = 8.7 Hz), 8.60 (s, 1H, Ar−H). 13C NMR (75 MHz,
CDCl3): δ 14.10, 22.69, 26.04, 29.17, 29.25, 29.38, 29.46, 29.69, 31.93, 68.35, 69.24, 113.20,
115.14, 115.32, 122.47, 122.85, 123.01, 127.87, 128.84, 129.63, 129.95, 131.23, 131.37, 131.45,
140.81, 142.12, 148.81, 150.18, 150.26, 154.19, 154.27, 161.80, 166.33, 168.73. MS (HRESI):
calcd for M+: 1420.1087. Found: 1420.1085. Anal. Calcd for C92H146N4O5S: C, 77.80; H, 10.36.
Found C, 78.12; H, 10.19.
4.2.15 2−(2, 3−bis(3, 4−bis(dodecyloxy)phenyl)quinoxalin−6−yl)−5−(4−methoxyphenyl)−1, 3,
4−oxadiazole (1c; R = OCH3)
1H NMR (300 MHz, CDCl3): δ 0.84−0.88 (m, 12H, −CH3), 1.25 (m, 72H, −CH2), 1.66−1.83 (m,
8H, − CH2), 3.80−4.02 (m, 11H, −OCH2), 6.82−6.85 (m, 2H, Ar−H), 7.03 (d, 2H, Ar−H, J = 8.7
Hz), 7.09 (s, 2H, Ar−H), 7.13 (d, 2H, Ar−H, J = 8.4 Hz), 8.10 (d, 2H, Ar−H, J = 8.7 Hz), 8.21 (d,
1H, Ar−H, J = 8.7 Hz), 8.46−8.50 (m, 1H, Ar−H), 8.82 (s, 1H, Ar−H). 13C NMR (75 MHz, CDCl3):
δ 14.10, 22.68, 26.03, 29.15, 29.22, 29.38, 29.45, 29.69, 31.93, 55.50, 69.21, 113.13, 114.63,
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ACCEPTED MANUSCRIPT
115.30, 116.28, 122.86, 123.00, 124.70, 127.09, 127.58, 128.85, 130.12, 131.25, 131.34, 140.65,
142.31, 148.78, 150.20, 150.30, 154.42, 154.52, 162.57, 163.61, 165.04. Anal. Calcd for
C77H116N4O6: C, 77.47; H, 9.79. Found C, 77.46; H, 9.78.
4.2.16 2−(2, 3−bis(3, 4−bis(dodecyloxy)phenyl)quinoxalin−6−yl)−5−phenyl−1, 3 ,
4−oxadiazole (1c; R = H)
1H NMR (300 MHz, CDCl3): δ 0.84−0.88 (m, 12H, −CH3), 1.25−1.42 (m, 72H, −CH2), 1.66−1.84
(m, 8H, −CH2), 3.80−4.02 (m, 8H, −OCH2), 6.82−6.86 (m, 2H, Ar−H), 7.10 (s, 2H, Ar−H), 7.14
(d, 2H, Ar−H, J = 8.1 Hz), 7.52−7.57 (m, 3H, Ar−H), 8.17−8.20 (m, 2H, Ar−H), 8.26 (d, 1H,
Ar−H, J = 8.7 Hz), 8.49 (d, 1H, Ar−H, J = 7.8 Hz), 8.87 (s, 1H, Ar−H). 13C NMR (75 MHz,
CDCl3): δ 14.09, 22.67, 26.03, 29.15, 29.21, 29.37, 29.44, 29.68, 31.92, 69.22, 113.10, 115.30,
122.92, 123.07, 123.76, 124.57, 127.05, 127.14, 127.72, 129.17, 130.10, 131.03, 131.13, 131.95,
140.51, 142.24, 148.77, 150.28, 150.39, 154.43, 154.56, 164.02, 165.08. Anal. Calcd for
C76H114N4O5: C, 78.44; H, 9.87. Found C, 78.40; H, 9.84
4.2.17 2−(2, 3−bis(3, 4−bis(dodecyloxy)phenyl)quinoxalin−6−yl)−5−(4-fluorophenyl)−1, 3, 4−
oxadiazole (1c; R = F)
1H NMR (300 MHz, CDCl3): δ 0.84−0.88 (m, 12H, −CH3), 1.25−1.42 (m, 72H, −CH2), 1.64−1.84
(m, 8H, −CH2), 3.80−4.02 (m, 8H, −OCH2), 6.82−6.86 (m, 2H, Ar−H), 7.09 (s, 2H, Ar−H), 7.13 (d,
2H, Ar−H, J = 8.4 Hz), 8.16−8.21 (m, 4H, Ar−H), 8.23 (d, 1H, Ar−H, J = 9.0 Hz), 8.46−8.49 (m,
1H, Ar-H), 8.83 (s, 1H, Ar−H). 13C NMR (75 MHz, CDCl3): δ 14.09, 22.69, 26.05, 29.18, 29.24,
29.38, 29.46, 29.70, 31.93, 69.26, 113.19, 115.38, 116.42, 116.72, 120.15, 122.91, 123.05,
124.38, 127.02, 127.84, 129.30, 129.42, 130.24, 131.30, 140.62, 142.42, 148.82, 150.30, 150.39,
154.51, 154.68, 163.80, 164.12, 164.27, 165.02. Anal. Calcd for C76H113N4O5: C, 77.24; H, 9.64.
Found C, 76.83; H, 9.75.
4.2.18 2−(2, 3−bis(3, 4−bis(dodecyloxy)phenyl)quinoxalin−6−yl)−5−(4−nitrophenyl)−1, 3, 4−
oxadiazole (1c; R = NO2)
1H NMR (300 MHz, CDCl3): δ 0.83−0.88 (m, 12H, −CH3), 1.25−1.41 (m, 72H, −CH2), 1.64−1.84
26

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(m, 8H, −CH2), 3.79−4.02 (m, 8H, −OCH2), 6.82−6.86 (m, 2H, Ar−H), 7.08−7.16 (m, 4H, Ar−H),
8.25 (d, 1H, Ar−H, J = 8.7 Hz), 8.35−8.44 (d, 4H, Ar−H), 8.47−8.50 (m, 1H, Ar−H), 8.87 (s, 1H,
Ar−H). 13C NMR (75 MHz, CDCl3): δ 14.08, 22.67, 26.03, 29.16, 29.22, 29.37, 29.44, 29.68,
31.92, 69.26, 113.12, 115.33, 122.91, 123.07, 123.77, 124.50, 126.94, 127.90, 128.28, 129.22,
130.40, 131.06, 131.15, 140.53, 142.60, 148.79, 149.69, 150.36, 150.47, 154.66, 154.93, 163.28,
165.02. Anal. Calcd for C76H113N5O7: C, 75.52; H, 9.42. Found C, 74.65; H, 9.32.
Acknowledgements
We thank the National Science Council of Taiwan, ROC (NSC 102-2113-M-008-003) for
generous support of this work. Also we deeply appreciated Prof. Hwo−Shuenn Sheu for
performing powder XRD experiments at the National Synchrotron Radiation Research Center.
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