Unsymmetric 1,3,4-oxa(thia)diazoles of quinoxaline-naphthalene conjugates

Article abstract of DOI:10.1016/j.tet.2013.08.031

Two new series of unsymmetric 1,3,4-oxa(thia)diazoles 1a,b containing both quinoxaline and naphthalene moieties were prepared and their mesomorphic properties were investigated. The mesomorphic behavior of compounds 1a,b and 2 was studied by DSC analysis

Full text of DOI:10.1016/j.tet.2013.08.031

Tetrahedron 69 (2013) 9045e9055
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Unsymmetric 1,3,4-oxa(thia)diazoles of quinoxalineenaphthalene
conjugates
,
Kuan-Ting Lin a, Hsiu-Ming Kuo a, Hwo-Shuenn Sheu b, Chung K. Lai a
*
a Department of Chemistry, National Central University, Chung-Li 32001, Taiwan, ROC
b National Synchrotron Radiation Research Center, Hsinchu 30077, Taiwan, ROC
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 27 May 2013
Received in revised form 24 July 2013
Accepted 15 August 2013
Available online 22 August 2013
Two new series of unsymmetric 1,3,4-oxa(thia)diazoles 1a,b containing both quinoxaline and naph-
thalene moieties were prepared and their mesomorphic properties were investigated. The mesomorphic
behavior of compounds 1a,b and 2 was studied by DSC analysis and polarized optical microscopy. All
compounds 1a and 2 exhibited hexagonal columnar phases (Colh), which were also confirmed by powder
XRD diffractometer. Ncell and Rar values equal to 5.23 and 22.73 A within a slice of 9.0 A thick were also
obtained for 1a (n¼16), indicating that a more disc-like structure constructed by two molecules lying
side-by-side was correlated in Colh phases. In contrast, all compounds 1b were not mesogenic, and the
lack of mesomorphic properties in 1b might be due to their unfavorable conformations. The PL spectra of
all compounds 1a,b showed one intense peak at lmax¼509e512 nm, and these photoluminescent
emissions originated from quinoxaline moiety.
2
ꢀ
ꢀ
Keywords:
1,3,4-Oxadiazoles
1,3,4-Thiadiazoles
Quinoxalines
Naphthalenes
Ó 2013 Elsevier Ltd. All rights reserved.
Hexagonal columnar phases
Liquid crystals
1. Introduction
both in melting or/and clearing points. This was an important key
factor in processing commercial display technology. Hydrogen-
1,3,4-Oxadiazole (OXD), considered as one of a few important
compounds among five-membered ring heterocycles has been paid
more attention in the field of materials chemistry due to their ex-
cellent thermal and chemical stabilities. 1,3,4-Oxadiazoles are
structurally interesting; they are bent-shaped structures, electron-
deficient rings, and good electron-acceptors. They were excellent
candidates as blue emitters, and have applications1 in OLED de-
vices. Numerous known 1,3,4-oxadiazoles with a variety of novel
structures were studied as electron transporting materials in OLED
and widely applied as organic electron conductors. The first
mesogenic asymmetric 1,3,4-oxadiazole was reported2 by Dimi-
trowa et al. Thereafter more examples of mesogenic 1,3,4-
oxadiazoles3 with either symmetrical or asymmetrical structures
were prepared and studied. Furthermore, a few mesogenic bi(1,3,4-
oxadiazoles)4 or tri(1,3,4-oxadiazoles)5 were also reported. Ne-
matic or layer smectic phases formed by these linear-shaped or
bent-shaped molecules were commonly observed. In contrast,
lesser examples exhibiting columnar phases5b,6 were also known.
1,3,4-Oxadiazole is structurally nonlinear and has a larger exocyclic
bonded mesogenic oxadiazoles8 mixed with pyridines or acids
were reported. A few examples9a 1,3,4-oxadiazoles I and their
metallomesogens II3p,9b were previously reported by this group. In
contrast, their homologue 1,3,4-thiadiazoles showed an apparently
different mesomorphic behavior. The replacement of oxygen atom
by sulfur atom often led to an improved mesomorphic behavior.9a
The reason might be twofold; (1) the larger sulfur atom in-
corporated in heterocyclic rings was more easily polarized and
better induced in the mesophases. (2) The longer CeS bond dis-
tance10 and larger CeSeC angle facilitated its formation of a more
rod-like or better linear conformation, compared to the bent-
shaped 1,3,4-oxadiazoles.
Quinoxalines were also called benzopyrazines. They were highly
p-conjugated backbones and were potentially useful in many ap-
plications such as dyes, organic light-emitting diodes, electrolu-
minescence, organic thin film transistors (TFT), and organic
photovoltaics when incorporated with an electron-donor and
electron-acceptor units via
as half-disc, elliptical or round molecules, which could easily or
spontaneously self-assemble into columns when interaction
p-bridge(s). They were also considered
bond angle7 (
3
w135ꢀ), which often resulted in a dramatic lowering
pep
or dipoleedipole interactions are accessible between neighboring
molecules. These molecules capable of forming columnar stacking
arrangements might have a dramatic impact propensity. A few
promising materials, such as liquid crystals, light-emitting diodes,
* Corresponding author. Tel.: þ886 (0)3 4259207; fax: þ886 (0)3 4277972;
e-mail address: cklai@cc.ncu.edu.tw (C.K. Lai).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.08.031

9046
K.-T. Lin et al. / Tetrahedron 69 (2013) 9045e9055
and photovoltaic devices have been explored and studied. Some
known examples11 derived from mesogenic quinoxalines IIIeV12
were studied and were investigated. Compounds III derived from
dibenzo[a,c]phenazine exhibited an improved mesomorphic be-
havior than compounds IV due to their better coplanarity. Some
quinoxalines had a higher charge carrier mobility due to their
highly conjugated structures. Substitutions and/or substituents
positions incorporated were found to play an important role on the
formation of mesophases.
peak at ca. d C
170.92 ppm assigned for eCOOH was observed on its 13
NMR spectrum. Then, 2,3-bis(3,4-bis(dodecyloxy) phenyl)-N0-(6-
(alkoxy)-2-naphthoyl)quinoxaline-6-carbohydrazides 2 isolated as
yellow-green solids were then obtained by condensation reactions
of 6-(alkoxy)-2-naphthohydrazides and 2,3-bis-(3,4-bis(dodecy-
loxy)phenyl)quinoxaline-6-carboxylic acid 3 in stirring THF at room
temperature. The reaction of 2,3-bis(3,4-bis(dodecyloxy)phenyl)-
N0-(6-(alkoxy)-2-naphthoyl)-quinoxaline-6-carbohydrazides
refluxing phosphoryl chloride gave the 1,3,4-oxadiazoles 1a. The
in
Y
Y
RO
X
OR
X
R2O
OR1
O
S
N N
O
N N
O
Cl
Cu
Pd
Cl
N N
S
N N
X
X
O
R1O
OR2
RO
OR
Y
Y
I; Cr (X = H)
Col (Y = OR)
II; SmA/SmC
R2O
OR
OR
RO
O
OR1
RO
OR1
N
N
N
OR
OR
O
N
N
X
N
N
O
X
RO
RO
OR
OR1
OR
OR1
III: Cr (X = H),
Col (X = CN, OR)
IV: Cr
V; Col
In this work, we report the preparation and mesomorphic
studies of two new series of unsymmetrical 1,3,4-oxa(thia)diazole
1a,b. These were constructed by incorporating a lateral quinoxaline
and naphthalene groups. Both lateral moieties were incorporated
to enhance the molecular polarization and/or dipole needed to
products isolated as bright yellow solids were obtained after re-
crystallization from THF/methanol with a yield of 53e65%. In con-
trast, their analogue 1,3,4-thiadiazoles 1b were prepared by the
solutions of 2,3-bis(3, 4-bis(dodecyloxy)phenyl)-N0-(6-(alkoxy)-2-
naphthoyl)-quinoxaline-6-carbohydrazides and phosphorous pen-
tasulfide in refluxing pyridine for 24 h. The products isolated as
yellow-green solids were obtained after recrystallization from THF/
methanol. All final compounds 1a,b and 2 were characterized by 1H
NMR, 13C NMR, mass and elemental analysis. For instance, two
induce the mesophases. Also,
pep interactions might be also en-
hanced. All compounds 1a and 2 exhibited hexagonal columnar
phases (Colh), which were also confirmed by powder XRD diffrac-
tometer. In contrast, all compounds 1b were not mesogenic, and the
lack of mesomorphic properties in 1b might be due to their un-
favorable conformation. The PL spectra of all compounds 1a,b were
examined.
characteristic broad singlet peaks occurred at d 9.99e10.22 ppm and
10.26e10.48 ppm, assigned for amide-H (eCONH) of compounds 2
were appeared for the formation on the 1H NMR spectra. On 13C
NMR spectra, observation of two peaks appeared, for example, at
163.84 and 165.52 ppm, and at 166.64 and 169.30 ppm was in-
dicative of the formation of compounds 1a (n¼10) and 1b (n¼10),
respectively. All data on mass and elemental analysis were well
consistent with their structures and purities.
2. Results and discussion
2.1. Synthesis and characterization
Two common synthetic routes were applied to prepare 1,3,4-
oxadiazole derivatives. In this work the synthetic procedures of
1,3,4-oxa(thia)diazoles 1a,b were given in Scheme 1. 1,2-Bis(3,4-
didodecyloxy)phenyl)-1,2-ethanedione was obtained by the re-
action of 1,2-bis (dodecyloxy)benzene with oxalyl chloride in the
presence of AlCl3 stirring in carbon disulfide at ice bath temperature,
which was then condensed with 3,4-diaminobenzoic acid stirring in
THF to give 2,3-bis-(3,4-bis(dodecyloxy)phenyl)quinoxaline-6-
carboxylic acid 3. On 1H NMR spectrum, a characteristic broad
2.2. Phase transitions, mesomorphic behavior, and thermal
stability
The mesomorphic behavior of compounds 1 and 2 was studied
and characterized by differential scanning calorimetry (DSC) and
polarizing optical microscopy (POM). The phase transitions and
thermodynamic data for compounds 1 and 2 are summarized in
Table 1. All compounds 2 (n¼8, 10, 12, 14, 16) exhibited enantio-
tropic columnar phases based on observation under polarized mi-
croscope. Under POM, a typically pseudo focal-conic or more leaf-
peak often appeared at
d w13.50 ppm assigned for eCOOH was not
observed for acids 3 due torapid exchange. However, a characteristic

K.-T. Lin et al. / Tetrahedron 69 (2013) 9045e9055
9047
HO
HO
OC12H25
HO
COOH
C12H25
O
a
O
d
O
C12H25O
HO
b
C12H25
O
C12H25O
OC12H25
COOEt
e
c
RO
OC12H25
COOEt
C12H25
O
f
N
OH
N
RO
O
C12H25
O
OC12H25
CONHNH2
3
g
OC12H25
C12H25O
OR
N
H H
N N
N
O
O
C12H25O
OC12H25
2
h
OC12H25
C12H25
O
N
OR
X
N
N N
C12H25
O
OC12H25
1a; X = O, R = CnH2n+1, n = 8, 10, 12, 14, 16
1b; X = S, R = CnH2n+1, n= 10, 12, 16
Scheme 1. Reagents and conditions: (a) RBr, K2CO3, and KI, refluxing in dry acetone for 48 h, 91e95%; (b) AlCl3, oxalyl chloride, stirring in CS2 at 0 ꢀC for 6 h, 40e42%; (c) 3,4-
diaminobenzoic acid, acetic acid, refluxing in THF for 24 h, 90e93 %; (d) ethanol, sulfuric acid, refluxing for 2 h, 72e75%; (e) RBr, K2CO3, and KI, refluxing in dry acetone for
24 h, 92e94%; (f) hydrazine monohydrate, refluxing in ethanol for 12 h, 94e97%; (g) SOCl2, refluxing for 2 h; then, triethylamine, stirring in dry THF at rt for 24 h, 71e73%; (h) X¼O,
refluxing in POCl3 for 24 h, 43e52 %; X¼S, P2S5, refluxing in pyridine for 24 h, 25e30%.
like texture (see Fig. 1) with linear birefringent defects was clearly
observed when cooling from their isotropic liquids. These observed
textures also accompanied by a large area of homeotropic domain
were characteristic for hexagonal columnar phases. The transition
temperatures of column-to-crystal for all compounds 2 were not
detectable on DSC thermographs, and they were all obtained by
POM. The melting and the isotropic temperatures were ranged
from Tmp¼130.2 to 137.0 ꢀC and Tcl¼148.4 to 156.5 ꢀC on heating
process. On the other hand, the temperature ranges of columnar
indicated in Table 1, all compounds 1a (n¼8, 10, 12, 14, 16) exhibited
monotropic columnar phases (Col), indicating that the columnar
phases were kinetically unstable. One transition of crystal-to-
isotropic on heating process and two transitions of isotropic-to-
columnar and columnar-to-crystal (Cr/Colh/I) on the cooling
process appeared on DSC thermographs. A few more transitions of
crystal-to-crystal (Cr1/Cr2) were also observed. The melting or
clearing temperatures were much lower than those of compounds
2. They were ranged from Tcl¼79.3 (n¼16) to 91.6 ꢀC (n¼10), and the
temperature ranges of columnar phases were lower with carbon
phases were ranged from
D
Tcol¼33.3 (n¼16) to 41.9 ꢀC (n¼10). As

9048
K.-T. Lin et al. / Tetrahedron 69 (2013) 9045e9055
Table 1
The phase transitions and enthalpiesa of compounds 1 and 2
148.4 (4.20)
109.7 (72.7)
133.5 (77.9)
130.2 (22.9)
135.1 (3.29)
Cr2
Cr2
Cr1
Cr1
2; n = 8
Col
Col
Col
I
I
I
108.0b
146.8 (4.06)
153.6 (4.20)
118.3 (22.2)
10
110.0b
151.9 (4.21)
156.5 (2.75)
12
Cr
Cr
Cr
Cr
112.0b
151.6 (3.00)
155.6 (4.06)
132.8 (0.84)
14
16
Col
Col
I
I
I
115.0b
137.0b
154.1 (4.09)
152.8 (4.49)
117.0b
150.3 (4.48)
90.0 (58.8)
1a; n = 8
Col
Cr2
56.6 (53.5)
88.7 (30.3)
73.9 (5.40)
91.6 (29.0)
10
12
Cr1
I
I
I
I
I
Col
Col
72.1 (4.64)
85.6 (42.0)
58.2 (58.8)
58.2 (49.3)
89.4 (18.7)
83.9 (23.2)
79.3 (32.2)
Cr2
Cr1
Cr1
Cr1
70.7 (3.26)
79.8 (1.55)
Cr2
14
16
Col
Cr2
61.9 (17.1)
46.0 (4.53)
67.0 (1.64)
Col
Cr
39.2 (2.89)
59.8 (28.2)
62.7 (1.28)
136.0 (37.6)
1b; n = 10
126.7 (35.5)
135.2 (41.9)
12
Cr
Cr
I
I
125.7 (39.6)
128.9 (34.0)
16
122.6 (32.3)
bDetermined by polarized optical microscope.
a
n¼the carbon numbers of terminal alkoxy chains; Cr1, Cr2¼crystal; Col¼columnar; I¼isotropic phases.
lengths;
D
Tcol¼17.3 (n¼8)>13.9 (n¼10)>12.5 (n¼12)>5.1 (n¼14)>
1,3,4-oxadiazole size was relatively smaller when compared to the
terminal quinoxaline moiety, leading to give an overall molecular
shape of compounds 1 and 2 as an elongated triangular shape. On
the other hand, two molecules arranged side-by-side were corre-
lated to give a more disc molecule. The relationship plot between
the melting temperatures, clearing temperatures, and the tem-
perature ranges for compounds 1a,b and 2 were given in Fig. 2. The
thermal stability of compounds 1a,b (n¼10), and 2,3 (n¼10) was
also performed by thermogravimetric analyses (TGA) under nitro-
gen atmosphere, shown in Fig. 3. All four compounds showed good
thermal stability at temperature below ca. 370 ꢀC, with a relative
thermal stability of 1a>1b>3>2 (all n¼10). The decomposition
temperatures for a 5% weight loss were listed in Table 2.
2.9 ꢀC (n¼16). A pseudo focal-conic texture (see Fig. 1) with linear
birefringent defects when slowly cooled from their isotropic liquids
was observed. The mesophase was also identified by powder XRD
experiments as hexagonal columnar phase. The monotropic be-
havior and a shorter range of columnar mesophase might be at-
tributed to their kinetically unstable conformations in the
mesophases. A non-planar conformation resulted from two non-
coplanar terminal phenyl groups on the quinoxaline moiety caused
the molecule slightly twisted and increased its overall thickness (ca.
ꢀ
3.35 A). The slightly increased thickness apparently weakened the
molecular interactions within the column; therefore, a lower
clearing temperature was obtained. Surprisingly, all 1,3,4-
thiadiazoles 1b were not mesogenic. One transition of crystal-to-
isotropic was obtained at Tcl¼128.9 (n¼16)>135.2 (n¼12)>
136.0 ꢀC (n¼10). In general, most of known 1,3,4-thiadiazoles with
a sulfur atom incorporated exhibited improved mesomorphic be-
havior than their analogue 1,3,4-oxadiazoles. This was often at-
tributed to its better linearity and/or larger dipole, resulted from
a more polarized sulfur atom than oxygen atom incorporated. The
lack of mesomorphic properties induced in 1b might be due to their
2.3. Variable-temperature powder X-ray diffractions and
packing study in columnar phase
Variable-temperature powder XRD diffraction experiments
were conducted to confirm the structure of the mesophases of
compounds 1a (n¼16). 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 69.0 ꢀC under cooling process, shown in Fig. 4. A dif-
unfavorable conformations.
A detailed crystallographic de-
termination should be informative in understanding their molec-
ular packing. Unfortunately, an attempt to obtain a good single
crystal was not successful.
The formation of columnar phases was often crucial to the side
chain density, i.e., the larger size or the more rigid is the core group,
and more side chain density is necessarily required. The central
ꢀ
fraction pattern with a d-spacing at 35.48, 20.90, 18.16 A, 13.75 and
ꢀ
ꢀ
12.26 A, and a broad diffuse peak (4.43 A) at wide-angle region was
obtained (Table 3). This diffraction pattern corresponded to a hex-
agonal columnar arrangement with a d-spacing ratio of 1, (1/3)1/2
,
(1/4)1/2, (1/7)1/2, and (1/9)1/2 corresponding to Miller indices; 100,

K.-T. Lin et al. / Tetrahedron 69 (2013) 9045e9055
9049
Fig. 1. Optical textures of columnar phases observed by: 2 (n¼10) at 149 ꢀC (top left) and 2 (n¼14) at 153 ꢀC (top right), 1a (n¼8) at 71 ꢀC (bottom left) and 1a (n¼12) at 69 ꢀC
(bottom right).
3
100
80
60
40
20
0
2 (n=10)
1b (n=10)
1a (n=10)
0
100
200
300
400
500
600
700
Temperature( )
oC
Fig. 2. Bar graphs showing the phase behavior of compounds 1a,b and 2. All tem-
peratures were taken on the cooling process.
Fig. 3. The TGA thermographs of compounds 1a,b, 2, and 3 (all n¼10) under nitrogen
gas at a heating rate of 10.0 ꢀC minꢁ1
.
Table 2
110, 200, 210, and 300, respectively. This diffraction pattern cor-
responds to an intercolumnar distance or lattice constant (i.e.,
a parameter of the hexagonal lattice) of 40.97 A. In a hexagonal
The decomposition temperaturesa of compounds 1e3 by TGA analysis
Tdec (ꢀC)
ꢀ
Compd
arrangement, the columns were located at the nodes of the hex-
agonal cell, and the columnar axes were perpendicular to the lattice
plane. The lack of any relative peaks at wide angles excluded a more
regular periodicity along the columns. However, liquid-like corre-
lations between the rigid cores occurred at wide-angle regions of
1a (n¼10)
1b (n¼10)
2 (n¼10)
3
413.5
410.4
369.3
400.3
a
Temperatures taken with a 5% weight loss.
ꢀ
4.43 A.
In order to understand the possible molecular packing13 in the
columnar phases, the number of molecules within a portion of
columnar height h was calculated by a simple model. Two impor-
tant parameters, Ncell and Rar were obtained by using XRD

9050
K.-T. Lin et al. / Tetrahedron 69 (2013) 9045e9055
molecules lying roughly side-by-side was then generated within
35.4
30000
20000
10000
0
the column. The possible molecular arrangement in columnar
phases was proposed in Fig. 5. The proposed packing style was
quite consistent with our previous studies of quinox-
alineebenzoxazole conjugates. Two molecules lying above and
below plane were arranged in an antiparallel head-to-tail into
a layer structure, and also
observed.
pep interactions as point to face were
20.9
18.1
2.4. Optical properties
13.7
12.2
The UVevis absorption and PL spectra of the compounds 1e3
(all n¼10) measured in CH2Cl2 solution at room temperature are
presented in Fig. 6. The lmax peaks of UVevis absorption and PL
spectra were listed in Table 5. The absorption lmax peaks of com-
pounds 1a,b occurred at ca. 280e287 and 402e405 nm, which
4.4
10
20
30
2 theta
Fig. 4. The powder X-ray diffraction plot of compound 1a (n¼16) measured at 69.0 ꢀ
C
were attributed to ne
p and pep transitions arising from qui-
*
*
noxaline moiety.12 The 1,3,4-thiadiazole 1b has its inherent ab-
sorption peak slightly red shifted by 28 nm over 1,3,4-oxadiazole
1a. The other peak occurred at 324e352 nm was assigned to
during the cooling process.
Table 3
Detailed indexation by powder XRD of columnar phasea for compounds 1a
ne
p . The peak occurred at ca. 306 nm was assigned to amide
*
group. The PL spectra of all compounds 1a,b showed one intense
and broad peak occurred at lmax¼509e517 nm, and this photo-
luminescent emission originated from heterocyclic quinoxaline.12
In general, the electronic natures of substitution groups; for ex-
ample, incorporated donors or acceptors often shifted the emission
peaks. An apparent red-shift was often observed when an electron-
donating group was incorporated. However, the photoluminescent
emission peaks by 1,3,4-oxadiazoles often appeared at ca.
390e418 nm4a,g,9a,b,14c were not observed in this system and in-
corporation of a highly extended-conjugated quinoxaline would
not shift its lmax. Both quinoxaline and 1,3,4-oxa(thia)diazoles were
Compd
Mesophases temp
Col at 69.0 ꢀC
d-Spacing obsd
(calcd)
Lattice
const. (A)
Miller
indices
ꢀ
1a (n¼16)
35.48 (35.48)
20.90 (20.48)
18.16 (17.74)
13.75 (13.41)
12.26 (11.83)
4.43 (br)
a¼40.97
100
110
200
210
300
Halo
a
Temperatures taken on the cooling process.
diffraction data. A columnar structure is often considered to be
constructed by columnar cross section (Scol) and the stacking pe-
riodicity along the columns (h, portion of height), according to
Vcell¼hScol¼NcellVmol. Vcell is the volume of the repeat unit (per cell),
and Vmol is the molecular volume of one molecule. Ncell is the
number of molecules within a column. Scol can be calculated from
lattice parameters of X-ray diffraction (Table 4).
often considered as
p-acceptors and fluorophore. A red-shift
emission often attributed to donoreacceptor transfer was also
not observed. The lack of an emission by 1,3,4,-oxadiazoles3 at ca.
390e418 nm was probably attributed to the so-called fluorescence
resonance energy transfer (FRET).14 Fluorescence resonance energy
€
transfer, also known as Forster resonance energy transfer, is a non-
radiative process in which the resonance energy transfers from an
excited state of a donor fluorophore (DeF) to the ground state of an
acceptor fluorophore (AeF) via a non-radiative ‘dipoleedipole
coupling’. The emission peaks of DeF were expected to have some
overlap with the absorption peaks of AeF. On the other hand, the
energy emitted by 1,3,4-oxadiazole at ca. 400 nm was absorbed by
quinoxaline, and then emitted an emission at 509e512 nm, as
shown in Fig. 7. The PL spectra of 1a,b were also obtained by using
324 nm (for 1a-10) and 352 nm (1b-10) as their excitation wave-
lengths, and the two values of lmax¼508 and 505 nm were obtained
for 1a (n¼10) and 1b (n¼10). A slightly higher quantum efficiency
ranged from 0.55 to 0.57% was obtained due to the FRET effect.
Table 4
Geometric parametersa of compound 1a (n¼16)
2
3
3
ꢀ
2
2
ꢀ
Vcell (A ) Vm (A ) Temp (ꢀC) Ncell Sar (A ) Rar (A )
ꢀ
ꢀ
ꢀ
Compd
S (A )
1a (n¼16) 1453.57 13,082.15 2499.92 69.0
5.23 406.04 22.73
a
2
3
ꢀ
ꢀ
S (A )[columnar cross section area, Vcell (A )¼volume of the column stratum
3
ꢀ
ꢀ
9 A thick, Vm(A )¼molecular volume, Ncell¼the number of molecules contained in
2
ꢀ
ꢀ
each columnar stratum 9-A thick, Sar (A )¼the surface area of hard columnar core,
2
ꢀ
Rar (A )¼the diameter of the aromatic part.
On the other hand, Vmol is equal to the rigid part Var and the
flexible chains Vch by the equation. Another parameter Rar is de-
fined as the diameter of the aromatic or hard columnar part, which
3. Conclusions
Two new series of heterocyclic 1,3,4-oxa(thia)diazoles 1a,b
constructed by quinoxalineenaphthalene conjugates incorporated
as terminal moieties were prepared and their mesomorphic prop-
erties were investigated. All precursors 2 and 1a formed hexagonal
columnar phases, in contrast, all compounds 1b were non-
can be calculated by Rar¼(4Sar/
p)
1/2. By this simple approach, the
Ncell and Rar parameters for compounds 1a (n¼16) were then cal-
2
culated. A value of Ncell¼5.23 and Rar¼22.73 A at 69 ꢀC was ob-
ꢀ
ꢀ
tained. The Rar value was close to 19.25 A, which is the size of
2
ꢀ
central core of 1a. On the other hand, an average number of ca. 5.23
mesogenic. Ncell and Rar values equal to 5.23 and 22.73 A within
ꢀ
ꢀ
molecules for 1a were stacked within a height of 9.0 A in the co-
a slice of 9.0 A thick were obtained for 1a (n¼16), indicating that
lumnar phases. Two terminal phenyl groups of quinoxaline were in
fact not coplanar, leading to give a thicker molecule. A thickness of
a more disc-like correlated structure constructed by two molecules
lying side-by-side was packed in Colh phases. The PL spectra of all
compounds 1a,b showed one intense peak occurred at ca.
lmax¼509e512 nm, which originated from quinoxaline moiety. The
lack of an emission by 1,3,4-oxadiazoles at ca. 390e418 nm was
probably attributed to the FRET process.
ꢀ
two phenyl groups twisted by an angle of approximately ca. 3.35 A
was obtained from our similar quinoxaline system.12 The molecular
shapes of compounds 1a were not perfectly round molecules.
Therefore, a more disc-like correlated structure constructed by two

K.-T. Lin et al. / Tetrahedron 69 (2013) 9045e9055
9051
Fig. 5. A schematic representation of molecular organization in columnar phase by compounds 1a (n¼16). Two tapered-shaped molecules lying side-by-side to generate a more
ꢀ
ꢀ
disc-correlated molecule was packed within a column. In a typical calculation a value of 9.0 A (2h¼9.0 A) has been assumed for most discotic molecules corresponding to the board
12
ꢀ
signal observed in the XRD diffraction patterns. A thickness of ca. 3.35 A was obtained from crystallographic data of a similar quinoxaline reported.
4. Experimental
(m, 4H, eCH2), 3.97 (t, 4H, eOCH2, J¼6.6 Hz), 6.86 (s, AreH, 4H). 13
C
NMR (75 MHz, CDCl3):
d 14.14, 22.72, 26.07, 29.38, 29.47, 29.67,
4.1. General materials and methods
29.73, 31.95, 69.29, 114.12, 121.00, 149.25.
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 DRS-300. DSC
thermographs were carried out on a Mettler DSC-822 and cali-
brated with a pure indium sample. All phase transitions are de-
termined by a scan rate of 10.0 ꢀC minꢁ1. Optical polarized
microscopy was carried out on Zeiss Axioplan 2 equipped with
a hot stage system of Mettler FP90/FP82HT. The UVevis absorption
and fluorescence spectra were obtained using a Jasco V-530 and
Hitachi F-4500 spectrometer. All spectra were measured in CH2Cl2
at room temperature, and the excitation wavelengths of the fluo-
rescent spectra were 202 nm (for 1a), 405 nm (for 1b), and 397 nm
(for 2 and 3). Elemental analyses were performed on a Heraeus
CHN-O-Rapid elemental analyzer. The powder diffraction data were
collected from the Wiggler-A beam line of the National Synchrotron
4.2.2. 1,2-Bis(3,4-bis(dodecyloxy)phenyl)-1,2-ethanedione. 1H NMR
(300 MHz, CDCl3): 0.83e0.88 (m, 12H, eCH3), 1.24e1.45 (m, 72H,
d
eCH2), 1.77e1.86 (m, 8H, eCH2), 4.01e4.05 (m, 8H, eOCH2), 6.81 (d,
2H, AreH, J¼8.4 Hz), 7.39e7.42 (m, 2H, AreH), 7.54 (d, 2H, AreH,
J¼1.8 Hz). 13C NMR (75 MHz, CDCl3):
d 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-etha-
nedione (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 for 24 h under nitrogen atmosphere.
The product, isolated as yellow solids was obtained after re-
crystallization from THF/MeOH. Yield 93%. 1H NMR (300 MHz,
ꢀ
Radiation Research Center (NSRRC) with a wavelength of 1.3263 A.
The powder samples were charged in Lindemann capillary tubes
(80 mm long and 0.01 mm thick) from Charles Supper Co. with an
inner diameter of 1.0 mm. The compounds of 1,2-di(alkoxy)ben-
CDCl3): d 0.84e0.88 (m, 12H, eCH3), 1.19e1.41 (m, 72H, eCH2),
1.68e1.83 (m, 8H, eCH2), 3.79e4.01 (m, 8H, eOCH2), 6.81 (d, 2H,
AreH, J¼8.4 Hz), 7.08e7.12 (m, 4H, AreH), 8.15 (d, 1H, AreH,
J¼8.7 Hz), 8.32 (d, 1H, AreH, J¼8.7 Hz), 8.91 (s, 1H, AreH). 13C NMR
zenes-1,2-bis(3,4-bis(alkoxy)phenyl-1,2-ethanediones),
2,3-
bis(3,4-bis(alkoxy)phenyl)quinoxaline-6-carboxylic acids,12 and
ethyl 6-(alkoxy)-2-naphthoates9a were prepared by the literature
procedures.
(75 MHz, CDCl3): d 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. Synthesis of the compounds 1aec
4.2.4. Ethyl 6-hydroxy-2-naphthoate. To the solution of 6-hydroxy-
2-naphthaoic acid (10.0 g, 0.053 mol) dissolved in 100 mL of EtOH
was added 2.0 mL of H2SO4, and this solution was refluxed for 2 h.
4.2.1. 1,2-Bis(dodecyloxy)benzene. 1H NMR (300 MHz, CDCl3):
d
0.85 (t, 6H, eCH3, J¼6.9 Hz), 1.24e1.45 (m, 36H, eCH2), 1.74e1.84

9052
K.-T. Lin et al. / Tetrahedron 69 (2013) 9045e9055
Table 5
Absorption and emission dataa of compounds 1e3
1a(n = 10)
1b(n = 10)
2
3
Compd
Adsorption
l
(nm)
Emission lmax (nm)
FF
(n = 10)
1a (n¼10)
1b (n¼10)
2 (n¼10)
3 (n¼10)
280, 324, 402
287, 352, 405
306, 394
512
509
517
517
0.55
0.57
0.44
0.42
279, 394
a
Measured in CH2Cl2 solution (1.0ꢂ10ꢁ5 M) at rt. The standard is anthracene
(
Ffs¼0.27 in hexane solution) and
n
is reflective index of solvents;
nCH
¼ 1:42440, nhexane¼1.37506.
2 Cl2
300
400
500
Wavelength (nm)
1a(n = 10)
1b(n = 10)
2
3
(n = 10)
500
600
Wavelength (nm)
700
Fig. 7. Schematic diagram of the FRET operated in this system in which 1,3,4-
oxadiazole is the donor fluorophore (DeF) and quinoxaline is the acceptor fluo-
rophore (AeF). In the FRET process, blue light originally emitted from 1,3,4-oxadiazole
was absorbed by quinoxaline, then emitting yellow light.
1a(n = 10)
1b(n = 10)
AreH). 13C NMR (75 MHz, CDCl3):
d 50.00, 109.31, 118.52, 125.31,
125.91, 126.53, 127.94, 130.72, 131.24, 136.43, 155.65, 167.00.
4.2.5. Ethyl 6-(decyloxy)-2-naphthoate (n¼10). The solution of
ethyl 6-hydroxy-2-naphthoate (10.0 g, 0.06 mol) dissolved in
150 mL of acetone were added K2CO3 (4.5 g, 0.03 mol), KI (5.0 g,
0.03 mol), and 1-bromodecane (16.1 g, 0.06 mol). The solution was
refluxed for 48 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,
500
600
Wavelength (nm)
700
CDCl3): d 0.84e0.87 (t, 3H, eCH3), 1.27e1.48 (m, 14H, eCH2), 1.42 (t,
3H, eCH3, J¼7.2 Hz), 1.78e1.88 (m, 2H, eCH2), 4.05 (t, 2H, eOCH2,
J¼6.6 Hz), 4.37e4.45 (m, 2H, eOCH2), 7.11e7.24 (m, 2H, AreH), 7.71
(d, 1H, AreH, J¼8.7 Hz), 7.81 (d, 1H, AreH, J¼9 Hz), 8.01 (d, 1H,
AreH, J¼8.4 Hz), 8.51 (s, 1H, AreH). 13C NMR (75 MHz, CDCl3):
Fig. 6. Absorption (top) and fluorescent spectra (central and bottom) of the com-
pounds 1e3. The excitation wavelengths in PL spectra (central) used were 402 nm (for
1a-10), 405 nm (1b-10), 394 nm (for 2) and 394 nm (for 3). The PL spectra of com-
pound 1a,b (bottom) were obtained by using 324 nm (for 1a-10) and 352 nm (1b-10)
as excitation wavelengths and the lmax¼508 and 505 nm was obtained for 1a (n¼10)
and 1b (n¼10).
d
14.07, 14.38, 22.65, 26.05, 29.13, 29.29, 29.37, 29.54, 31.87, 60.82,
68.09, 106.30, 119.81, 125.35, 125.83, 126.66, 127.75, 130.67, 130.73,
137.13, 158.99, 166.88.
The solution was cooled and neutralized with 0.5 M of aqueous
NaOH. The solids were collected. The product isolated as white
solids were obtained after recrystallization from ethanol. Yield 85%.
4.2.6. 6-(Decyloxy)-2-naphthahydrazide (n¼10). The solution of
ethyl 6-(decyloxy)-2-naphthoate (5.0 g, 0.02 mol) dissolved in
100 mL of MeOH was added hydrazine monohydrate (7.8 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/
1H NMR (300 MHz, CDCl3):
d 3.95 (s, 3H, eOCH3), 5.74 (s, 1H,
AreOH), 7.15 (d, 2H, AreH, J¼7.6 Hz), 7.67 (d, 1H, AreH, J¼8.6 Hz),
7.83 (d,1H, AreH, J¼9.7 Hz), 7.98 (d,1H, AreH, J¼8.7 Hz), 8.51 (s,1H,

K.-T. Lin et al. / Tetrahedron 69 (2013) 9045e9055
9053
MeOH. Yield 90%. 1H NMR (300 MHz, CDCl3):
d
0.91 (t, 3H, eCH3,
Mþ: 1415.0879. Found: 1415.0874. Anal. Calcd for C92H142N4O7: C,
78.03; H, 10.11. Found C, 77.14; H, 10.28.
J¼6.9 Hz), 1.32e1.50 (m, 14H, eCH2), 1.77e1.86 (m, 2H, eCH2), 1.96
(s, 2H, eNH2), 4.03 (t, 2H, eOCH2, J¼6.6 Hz), 7.08e7.16 (m, 2H,
AreH), 7.57(m, 1H, eNH), 7.67e7.76 (m, 3H, AreH), 8.17 (s, 1H,
4.2.10. 2, 3-Bis(3,4-bis(dodecyloxy)phenyl)-N0-(6-(tetradecyloxy)-2-
AreH). 13C NMR (75 MHz, CDCl3):
d
14.19, 16.83, 22.75, 25.72, 25.90,
naphthoyl)quinoxaline-6-carbohydrazide (2, n¼14). 1H NMR
29.27, 31.73, 68.28, 120.22, 124.20, 127.32, 127.68, 127.95, 128.42,
130.54, 136.62, 158.87.
(300 MHz, CDCl3): d 0.84e0.88 (m, 15H, eCH3), 1.24e1.44 (m, 94H,
eCH2), 1.66e1.83 (m, 10H, eCH2), 3.73e3.99 (m, 10H, eOCH2),
6.69e6.80 (m, 2H, AreH), 6.97e7.05 (m, 6H, AreH), 7.50e7.57 (m,
2H, AreH), 7.80 (d, 1H, AreH, J¼8.4 Hz), 8.00 (d, 1H, AreH,
J¼8.7 Hz), 8.14 (d, 1H, AreH, J¼8.7 Hz), 8.23 (s, 1H, AreH), 8.65 (s,
1H, AreH), 10.22 (br s, 1H, eNH), 10.48 (br s, 1H, eNH). 13C NMR
4.2.7. 2,3-Bis(3,4-bis(dodecyloxy)phenyl)-N0-(6-(alkoxy)-2-
naphthoyl)quinoxaline-6-carbohydrazide (2, n¼10). 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 atmo-
sphere. The excess of thionyl chloride was removed under reduced
vacuum. The compound prepared was then used directly for the
following step. The solution of 6-(decyloxy)-2-naphthalhydrazide
(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
(75 MHz, CDCl3):
d 14.08, 22.67, 26.04, 29.16, 29.24, 29.37, 29.47,
29.68, 31.92, 68.09, 69.12, 106.21, 112.86, 112.96, 115.20, 119.92,
122.89, 122.98, 123.85, 125.87, 127.02, 128.33, 128.79, 129.46, 130.51,
131.08, 131.25, 131.99, 136.66, 139.97, 142.44, 148.53, 148.66, 150.03,
150.18, 154.05, 154.58, 164.32, 165.36. MS (HRFAB): calcd for Mþ:
1443.1192. Found: 1443.1201. Anal. Calcd for C94H146N4O7: C, 78.18;
H, 10.19. Found C, 78.90; H, 10.35.
4.2.11. 2,3-Bis(3,4-bis(dodecyloxy)phenyl)-N0-(6-(hexadecyloxy)-2-
naphthoyl)quinoxaline-6-carbohydrazide (2, n¼16). 1H NMR
(300 MHz, CDCl3):
d 0.84e0.88 (m, 15H, eCH3), 1.24e1.44 (m, 98H,
ethyl acetate. Yield 75%. 1H NMR (300 MHz, CDCl3):
d
0.84e0.87
eCH2), 1.64e1.81 (m, 10H, eCH2), 3.74e4.03 (m, 10H, eOCH2),
6.73e6.81 (m, 2H, AreH), 7.00e7.10 (m, 6H, AreH), 7.58e7.64 (m,
2H, AreH), 7.82 (d, 1H, AreH, J¼8.4 Hz), 8.10 (d, 1H, AreH,
J¼8.7 Hz), 8.15 (d, 1H, AreH, J¼8.7 Hz), 8.26 (s, 1H, AreH), 8.65 (s,
1H, AreH), 9.99 (br s, 1H, eNH), 10.26 (br s, 1H, eNH). 13C NMR
(m, 15H, eCH3), 1.26e1.44 (m, 86H, eCH2), 1.62e1.83 (m, 10H,
eCH2), 3.73e4.03 (m, 10H, eOCH2), 6.72e6.81 (m, 2H, AreH),
6.99e7.10 (m, 6H, AreH), 7.55e7.62 (m, 2H, AreH), 7.82 (d, 1H,
AreH, J¼8.4 Hz), 8.04 (d, 1H, AreH, J¼8.7 Hz), 8.15 (d, 1H, AreH,
J¼8.7 Hz), 8.26 (s, 1H, AreH), 8.66 (s, 1H, AreH), 10.07 (br s, 1H,
(75 MHz, CDCl3):
d 14.10, 22.69, 26.05, 29.17, 29.24, 29.38, 29.47,
eNH), 10.33 (br s, 1H, eNH). 13C NMR (75 MHz, CDCl3):
d
14.07,
29.68, 31.93, 68.14, 69.14, 106.28, 112.99, 115.20, 120.08, 122.90,
123.00, 123.82, 125.86, 127.16, 127.51, 127.70, 128.27, 128.71, 129.60,
130.54, 131.11, 131.23, 131.97, 136.76, 140.04, 142.51, 148.61, 148.69,
150.09, 150.22, 154.15, 154.68, 158.92, 163.88, 164.88. MS (HRFAB):
calcd for Mþ: 1471.1505. Found: 1471.1505. Anal. Calcd for
22.67, 26.05, 29.19, 29.27, 29.37, 29.46, 29.60, 29.68, 31.92, 68.15,
69.20, 106.33, 113.05, 113.12, 115.36, 120.00, 122.97, 123.06, 123.87,
125.94, 127.10, 127.60, 127.71, 128.31, 128.71, 129.49, 130.53, 131.08,
131.22, 132.08, 136.74, 139.96, 142.41, 148.66, 148.76, 150.19, 150.33,
154.06, 154.59, 158.91, 164.09, 165.12. MS (HRFAB): calcd for Mþ:
1387.0566. Found: 1387.0566. Anal. Calcd for C90H138N4O7: C,
77.87; H, 10.02. Found C, 77.21; H, 9.83.
C96H150N4O7: C, 78.32; H, 10.27. Found C, 77.94; H, 10.17.
4.2.12. 2-(2,3-Bis(3,4-bis(dodecyloxy)phenyl)quinoxalin-6-yl)-5-(6-
(decyloxy)naphthalen-2-yl)-1,3,4-oxadiazole (1a, n¼10). The solu-
tion of 2,3-bis(3,4-bis(dodecyloxy)phenyl)-N0-(6-(decyloxy)-2-
naphthoyl)-quinoxaline-6-carbohydrazide (1.0 g, 0.36 mmol) dis-
solved 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 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 re-
crystallization from THF/methanol or by silica gel chromatography
eluting with hexane/ethyl acetate. Yield 55%. 1H NMR (300 MHz,
4.2.8. 2,3-Bis(3,4-bis(dodecyloxy)phenyl)-N0-(6-(octyloxy)-2-
naphthoyl)quinoxaline-6-carbohydrazide
(300 MHz, CDCl3):
(2,
n¼8). 1H
NMR
d
0.84e0.88 (m, 15H, eCH3), 1.26e1.44 (m, 82H,
eCH2), 1.64e1.83 (m, 10H, eCH2), 3.72e4.02 (m, 10H, eOCH2),
6.72e6.81 (m, 2H, AreH), 6.99e7.10 (m, 6H, AreH), 7.54e7.60 (m,
2H, AreH), 7.81 (d, 1H, AreH, J¼8.7 Hz), 8.03 (d, 1H, AreH,
J¼8.7 Hz), 8.15 (d, 1H, AreH, J¼8.7 Hz), 8.24 (s, 1H, AreH), 8.65 (s,
1H, AreH), 10.15 (br s, 1H, eNH), 10.40 (br s, 1H, eNH). 13C NMR
(75 MHz, CDCl3):
d 14.08, 22.66, 26.03, 29.16, 29.24, 29.37, 29.46,
29.68, 31.91, 68.10, 69.13, 106.23, 112.88, 112.97, 115.20, 119.97,
122.88, 122.98, 123.84, 125.86, 127.06, 127.52, 127.66, 128.31, 128.76,
129.50, 130.51, 131.09, 131.24, 131.98, 136.69, 140.00, 142.46, 148.56,
148.66, 150.05, 150.19, 154.08, 154.61, 158.85, 164.16, 165.16. MS
(HRFAB): calcd for Mþ: 1359.0253. Found: 1359.0265. Anal. Calcd
for C88H134N4O7: C, 77.71; H, 9.93. Found C, 77.81; H, 9.33.
CDCl3):
d 0.84e0.87 (m, 15H, eCH3), 1.25e1.45 (m, 86H, eCH2),
1.69e1.90 (m, 10H, eCH2), 3.80e4.12 (m, 10H, eOCH2), 6.82e6.87
(m, 2H, AreH), 7.10e7.23 (m, 6H, AreH), 7.83e7.88 (m, 2H, AreH),
8.18 (d, 1H, AreH, J¼8.7 Hz), 8.26 (d, 1H, AreH, J¼8.7 Hz), 8.52 (d,
1H, AreH, J¼8.7 Hz), 8.57 (s, 1H, AreH), 8.89 (s, 1H, AreH). 13C NMR
4.2.9. 2,3-Bis(3,4-bis(dodecyloxy)phenyl)-N0-(6-(dodecyloxy)-2-
naphthoyl)quinoxaline-6-carbohydrazide (2, n¼12). 1H NMR
(75 MHz, CDCl3): d 14.07, 22.67, 26.05, 29.18, 29.25, 29.37, 29.45,
(300 MHz, CDCl3):
d
0.84e0.86 (m, 15H, eCH3), 1.25e1.44 (m, 90H,
29.57, 29.68, 31.92, 68.27, 69.28, 106.76, 113.23, 115.45, 118.62,
120.43, 122.96, 123.11, 123.80, 124.75, 127.19, 127.39, 127.64, 127.78,
128.23, 130.09, 130.39, 131.17, 136.52, 140.58, 142.24, 148.85, 150.34,
150.44, 154.50, 159.04, 163.84, 165.52. MS (HRESI): calcd for Mþ:
1370.0773. Found: 1370.0542. Anal. Calcd for C90H136N4O6: C,
78.78; H, 10.14. Found C, 78.76; H, 10.10.
eCH2), 1.66e1.80 (m, 10H, eCH2), 3.73e4.02 (m, 10H, eOCH2),
6.71e6.80 (m, 2H, AreH), 6.98e7.10 (m, 6H, AreH), 7.54e7.61 (m,
2H, AreH), 7.81 (d, 1H, AreH, J¼8.4 Hz), 8.03 (d, 1H, AreH,
J¼8.7 Hz), 8.15 (d, 1H, AreH, J¼9.0 Hz), 8.25 (s, 1H, AreH), 8.65 (s,
1H, AreH), 10.15 (br s, 1H, eNH), 10.41 (br s, 1H, eNH). 13C NMR
(75 MHz, CDCl3):
d 14.10, 22.68, 26.05, 29.17, 29.24, 29.38, 29.47,
29.69, 31.92, 68.12, 69.14, 106.26, 112.99, 115.22, 120.02, 122.99,
123.85, 125.89, 127.09, 127.53, 127.68, 128.31, 128.76, 129.52, 130.53,
131.11, 131.24, 132.01, 136.72, 140.02, 142.47, 148.58, 148.68, 150.07,
150.21, 154.11, 154.63, 158.88, 164.10, 165.24. MS (HRFAB): calcd for
4.2.13. 2-(2,3-Bis(3,4-bis(dodecyloxy)phenyl)quinoxalin-6-yl)-5-(6-
(octyloxy)naphthalen-2-yl)-1,3,4-oxadiazole (1a, n¼8). 1H NMR
(300 MHz, CDCl3):
d 0.83e0.88 (m, 15H, eCH3), 1.25e1.47 (m, 82H,
eCH2), 1.67e1.90 (m, 10H, eCH2), 3.80e4.12 (m, 10H, eOCH2),

9054
K.-T. Lin et al. / Tetrahedron 69 (2013) 9045e9055
6.82e6.87 (m, 2H, AreH), 7.09e7.22 (m, 6H, AreH), 7.83e7.89 (m,
2H, AreH), 8.18 (d, 1H, AreH, J¼8.7 Hz), 8.25 (d, 1H, AreH,
J¼8.7 Hz), 8.52 (d, 1H, AreH, J¼8.7 Hz), 8.57 (s, 1H, AreH), 8.88 (s,
after recrystallization from THF/methanol or by silica gel chroma-
tography eluting with hexane/ethyl acetate. Yield 45%. 1H NMR
(300 MHz, CDCl3):
d 0.84e0.89 (m, 15H, eCH3), 1.25e1.43 (m, 86H,
1H, AreH). 13C NMR (75 MHz, CDCl3):
d
14.09, 22.69, 26.05, 29.18,
eCH2), 1.67e1.89 (m, 10H, eCH2), 3.80e4.10 (m, 10H, eOCH2),
6.81e6.86 (m, 2H, AreH), 7.09e7.22 (m, 6H, AreH), 7.78e7.85 (m,
2H, AreH), 8.10 (d, 1H, AreH, J¼8.4 Hz), 8.23 (d, 1H, AreH,
J¼8.7 Hz), 8.39 (s, 1H, AreH), 8.52 (d, 1H, AreH, J¼8.4 Hz), 8.64 (s,
29.25, 29.38, 29.46, 29.70, 31.83, 31.93, 68.27, 69.25, 106.74, 113.21,
115.38, 118.64, 120.44, 122.90, 123.04, 123.81, 124.69, 127.13, 127.39,
127.79, 128.23, 130.18, 130.40, 131.29, 131.39, 136.52, 140.68, 142.39,
148.82, 150.25, 150.35, 154.47, 154.58, 159.04, 163.89, 165.51. MS
(HRESI): calcd for Mþ: 1342.0147. Found: 1342.0214. Anal. Calcd for
1H, AreH). 13C NMR (75 MHz, CDCl3):
d 14.08, 22.67, 26.04, 29.17,
29.23, 29.37, 29.45, 29.57, 29.69, 31.92, 68.22, 69.25, 106.66, 113.20,
115.39,120.32,122.94,123.09,125.06, 127.74,128.00,128.20,128.42,
128.73, 129.87, 130.24, 131.12, 131.26, 136.26, 140.57, 141.99, 148.82,
150.30, 150.35, 154.16, 158.77, 166.64, 169.30. MS (HRESI): calcd for
Mþ: 1386.0231. Found: 1386.0323. Anal. Calcd for C90H136N4O5S: C,
77.87; H, 10.02. Found C, 77.81; H, 10.02.
C
88H132N4O6: C, 78.76; H, 9.91. Found C, 78.90; H, 10.09.
4.2.14. 2-(2,3-Bis(3,4-bis(dodecyloxy)phenyl)quinoxalin-6-yl)-5-(6-
(dodecyloxy)naphthalen-2-yl)-1,3,4-oxadiazole (1a, n¼12). 1H NMR
(300 MHz, CDCl3):
d 0.84e0.87 (m, 15H, eCH3), 1.25e1.45 (m, 90H,
eCH2), 1.69e1.82 (m, 10H, eCH2), 3.80e4.12 (m, 10H, eOCH2),
6.82e6.87 (m, 2H, AreH), 7.10e7.23 (m, 6H, AreH), 7.83e7.89 (m,
2H, AreH), 8.18 (d, 1H, AreH, J¼8.7 Hz), 8.27 (d, 1H, AreH,
J¼8.7 Hz), 8.53 (d, 1H, AreH, J¼8.7 Hz), 8.57 (s, 1H, AreH), 8.90 (s,
4.2.18. 2-(2,3-Bis(3,4-bis(dodecyloxy)phenyl)quinoxalin-6-yl)-5-(6-
(dodecyloxy)naphthalen-2-yl)-1,3,4-thiadiazole (1b, n¼12). 1H NMR
(300 MHz, CDCl3):
d 0.84e0.89 (m, 15H, eCH3), 1.25e1.45 (m, 90H,
1H, AreH). 13C NMR (75 MHz, CDCl3):
d
14.08, 22.68, 26.05, 29.19,
eCH2), 1.61e1.87 (m, 10H, eCH2), 3.80e4.11 (m, 10H, eOCH2),
6.81e6.86 (m, 2H, AreH), 7.09e7.23 (m, 6H, AreH), 7.79e7.86 (m,
2H, AreH), 8.10 (d, 1H, AreH, J¼8.7 Hz), 8.21 (d, 1H, AreH,
J¼8.7 Hz), 8.39 (s, 1H, AreH), 8.52 (d, 1H, AreH, J¼8.7 Hz), 8.62 (s,
29.25, 29.38, 29.46, 29.69, 31.93, 68.27, 69.28, 106.75,113.23,115.44,
118.61, 120.42, 122.95, 123.11, 123.79, 124.75, 127.19, 127.39, 127.63,
127.78, 128.23, 130.08, 130.39, 131.22, 136.51, 140.58, 142.21, 148.84,
150.34, 150.44, 154.42, 154.49, 163.84, 165.51. MS (HRESI): calcd for
Mþ: 1398.0773. Found: 1398.0854. Anal. Calcd for C92H140N4O6: C,
79.03; H, 10.09. Found C, 79.18; H, 10.10.
1H, AreH). 13C NMR (75 MHz, CDCl3):
d 14.08, 22.68, 26.04, 29.17,
29.23, 29.37, 29.45, 29.68, 31.92, 68.22, 69.23, 106.67, 113.22, 115.31,
115.38, 120.33, 122.86, 123.01, 125.07, 127.75, 127.89, 128.19, 128.43,
128.93, 129.98, 130.24, 131.15, 131.33, 131.42, 136.26, 140.80, 142.15,
148.81, 150.19, 150.26, 154.22, 154.28, 158.77, 166.73, 169.27. MS
(HRESI): calcd for Mþ: 1414.0544. Found: 1414.0617. Anal. Calcd for
4.2.15. 2-(2,3-Bis(3,4-bis(dodecyloxy)phenyl)quinoxalin-6-yl)-5-(6-
(tetradecyloxy) naphthalen-2-yl)-1,3,4-oxadiazole (1a, n¼14). 1H
NMR (300 MHz, CDCl3):
d
0.84e0.88 (m, 15H, eCH3), 1.25e1.45 (m,
C92H140N4O5S: C, 78.14; H, 9.98. Found C, 78.39; H, 9.99.
94H, eCH2), 1.72e1.88 (m, 10H, eCH2), 3.82e4.12 (m, 10H, eOCH2),
6.82e6.87 (m, 2H, AreH), 7.11e7.23 (m, 6H, AreH), 7.83e7.89 (m,
2H, AreH), 8.18 (d, 1H, AreH, J¼8.7 Hz), 8.31 (d, 1H, AreH,
J¼8.4 Hz), 8.54 (d, 1H, AreH, J¼8.1 Hz), 8.58 (s, 1H, AreH), 8.92 (s,
4.2.19. 2-(2,3-Bis(3,4-bis(dodecyloxy)phenyl)quinoxalin-6-yl)-5-(6-
(hexadecyloxy)naphthalen-2-yl)-1,3,4-thiadiazole (1b, n¼16). 1H
NMR (300 MHz, CDCl3):
d 0.84e0.88 (m, 15H, eCH3), 1.19e1.31 (m,
1H, AreH). 13C NMR (75 MHz, CDCl3):
d
14.09, 22.68, 26.05, 29.18,
98H, eCH2), 1.54e1.90 (m, 10H, eCH2), 3.80e4.12 (m, 10H, eOCH2),
6.81e6.86 (m, 2H, AreH), 7.09e7.23 (m, 6H, AreH), 7.80e7.86 (m,
2H, AreH), 8.12 (d, 1H, AreH, J¼8.4 Hz), 8.22 (d, 1H, AreH,
J¼8.7 Hz), 8.40 (s, 1H, AreH), 8.53 (d, 1H, AreH, J¼8.7 Hz), 8.63 (s,
29.23, 29.38, 29.45, 29.68, 31.93, 68.27, 69.28, 106.75, 113.18, 115.40,
118.57, 120.45, 123.03, 123.19, 123.81, 124.88, 127.36, 127.44, 127.80,
128.23, 129.95, 130.42, 130.77, 130.94, 136.54, 140.43, 141.99, 148.85,
150.42, 154.41, 159.05, 163.80, 165.57. MS (HRESI): calcd for Mþ:
1426.1086. Found: 1426.1179. Anal. Calcd for C94H144N4O6: C, 79.16;
H, 10.18. Found C, 79.11; H, 10.39.
1H, AreH). 13C NMR (75 MHz, CDCl3):
d 14.08, 22.68, 26.03, 29.17,
29.23, 29.37, 29.45, 29.68, 31.92, 68.23, 69.23, 106.67, 113.22, 115.37,
120.33, 122.85, 123.01, 125.07, 127.75, 127.89, 128.19, 128.43, 128.93,
129.98, 130.24, 131.15, 131.33, 131.42, 136.26, 140.80, 142.16, 148.80,
150.18, 150.25, 154.22, 154.28, 158.77, 166.73, 169.27. MS (HRESI):
calcd for Mþ: 1470.1170. Found: 1470.1237. Anal. Calcd for
4.2.16. 2-(2,3-Bis(3,4-bis(dodecyloxy)phenyl)quinoxalin-6-yl)-5-(6-
(hexadecyloxy) naphthalen-2-yl)-1,3,4-oxadiazole (1a, n¼16). 1H
NMR (300 MHz, CDCl3):
d
0.83e0.88 (m, 15H, eCH3), 1.18e1.43 (m,
C96H148N4O5S: C, 78.42; H, 10.15. Found C, 78.42; H, 9.72.
98H, eCH2), 1.65e1.90 (m, 10H, eCH2), 3.82e4.12 (m, 10H, eOCH2),
6.82e6.86 (m, 2H, AreH), 7.10e7.22 (m, 6H, AreH), 7.83e7.89 (m,
2H, AreH), 8.18 (d, 1H, AreH, J¼8.4 Hz), 8.28 (d, 1H, AreH,
J¼8.1 Hz), 8.53 (d, 1H, AreH, J¼7.8 Hz), 8.58 (s, 1H, AreH), 8.91 (s,
Acknowledgements
We thank the National Science Council of Taiwan, ROC (NSC-
100-2113-M-008-00-MY2) for generous support of this work.
1H, AreH). 13C NMR (75 MHz, CDCl3):
d 14.08, 22.67, 26.04, 29.17,
29.23, 29.37, 29.45, 29.68, 31.92, 68.25, 69.27, 106.72, 113.18, 115.40,
118.57, 120.43, 122.99, 123.15, 123.79, 124.79, 127.26, 127.40, 127.57,
127.78, 128.21, 130.03, 130.40, 131.10, 136.51, 140.50, 142.11, 148.82,
150.35, 154.45, 159.03, 163.81, 165.52. MS (HRESI): calcd for Mþ:
1454.14. Found: 1454.15. Anal. Calcd for C96H148N4O6: C, 79.18; H,
10.38. Found C, 79.26; H, 10.36.
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