Symmetrical mesogenic 2,5-bis(6-naphthalen-2-yl)-1,3,4-thiadiazoles

Article abstract of DOI:10.1016/j.tet.2012.06.092

Two series of new symmetrical 1,3,4-oxadiazoles 1a-n and 1,3,4-thiadiazoles 1b-n were prepared and their mesomorphic properties investigated by optical microscopy, differential scanning calorimetry, and powder X-ray diffractometry. Compounds 1b-n are kinetically more stable than compounds 1a-n. Compounds 1a-n exhibited monotropic nematic or smectic C phases, whereas, compounds 1b-n exhibited enantiotropic nematic or smectic A/smectic C phases. Compounds 1b-n have higher clearing temperatures and the larger temperature ranges of mesophases, which might be attributed to the better linearity and/or larger dipole, resulted from a more polarized sulfur atom than oxygen atom incorporated. The fluorescent properties of these two series of 1,3,4-thiadiazole/oxadiazole-based derivatives were also examined. The λ_max peaks of the photoluminescence spectra for compounds 1a-6 and 1b-6 measured in THF occurred at ca. 385 nm and 423 nm, respectively. Both series were blue emitters.

Full text of DOI:10.1016/j.tet.2012.06.092

Tetrahedron 68 (2012) 7331e7337
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Symmetrical mesogenic 2,5-bis(6-naphthalen-2-yl)-1,3,4-thiadiazoles
a
a
b
a,
*
Hsiu-Ming Kuo , Sih-Yeh Li , Hwo-Shuenn Sheu , Chung K. Lai
a
Department of Chemistry and Center for Nano Science Technology, National Central University, Chung-Li 32001, Taiwan, ROC
National Synchrotron Radiation Research Center, Hsinchu 30077, Taiwan, ROC
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 28 April 2012
Received in revised form 12 June 2012
Accepted 21 June 2012
Available online 28 June 2012
Two series of new symmetrical 1,3,4-oxadiazoles 1a-n and 1,3,4-thiadiazoles 1b-n were prepared and
their mesomorphic properties investigated by optical microscopy, differential scanning calorimetry, and
powder X-ray diffractometry. Compounds 1b-n are kinetically more stable than compounds 1a-n.
Compounds 1a-n exhibited monotropic nematic or smectic C phases, whereas, compounds 1b-n
exhibited enantiotropic nematic or smectic A/smectic C phases. Compounds 1b-n have higher clearing
temperatures and the larger temperature ranges of mesophases, which might be attributed to the better
linearity and/or larger dipole, resulted from
incorporated. The fluorescent properties of these two series of 1,3,4-thiadiazole/oxadiazole-based
derivatives were also examined. The max peaks of the photoluminescence spectra for compounds 1a-6
a more polarized sulfur atom than oxygen atom
l
and 1b-6 measured in THF occurred at ca. 385 nm and 423 nm, respectively. Both series were blue
emitters.
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
smectic phases were obtained by these linear-shaped or bent-
shaped molecules. In contrast, lesser examples exhibiting co-
4
1
,3,4-Oxadiazole (OXD), considered as one of the few important
lumnar phases were also reported. More interestingly, the occur-
5
compounds among five-membered heterocycles, has been studied
in the field of materials chemistry and biochemistry. Parts of such
extensive studies originated from their excellent thermal, chemical
stabilities and high photoluminescence quantum yields. The im-
portance of 1,3,4-oxadiazoles compounds is also attributed to the
simultaneous presence of a bent-shaped structure and of an electric
dipole, which are often applied as a framework constructed for
materials1 with achiral molecules; useful materials with ferro-
electric states might be obtained. The heterocyclic 1,3,4-oxadiazole
moiety was often considered as an electron-deficient and good
electron acceptor. Incorporation of appropriate electron-
withdrawing and electron-donating groups on either lateral side
might generate many potential materials valuable in organic light-
emitting diodes (OLEDs). Numerous known 1,3,4-oxadiazoles with
a variety of novel structures were studied as electron transporting
materials in OLEDs. Some of them were also used as organic elec-
tron conductors.
b
rence of biaxial nematic (N ) mesophases by some 1,3,4-oxadiazole
derivatives were observed, which were excellent candidates studied
for liquid-crystal electro-optical display technology. Surprisingly,
2,5-bis(alkoxyphenyl)-1,3,4-oxadiazoles
crystalline. 2,5-Diaryl-1,3,4-oxadiazole was considered as a non-
linear structure, which was attributed to the effect of the shape
formed by a larger exocyclic bond angle ( w135 ). A lowering of
melting or/and clearing point might be observed, and such a low-
ering of both melting and/or clearing temperature was demon-
7
a,b
3a were not liquid
6
ꢀ
3
7
a,b
7c
strated on the 2,5-bis(alkoxyphenyl)-1,3,4-oxadiazoles, 3a ec
7
d
and their metallomesogens previously reported by this group.
All derivatives 3aebwere not mesogenic, whereas, other derivatives
3c were in fact mesogenic, exhibiting room temperature columnar
hexagonal phases. The lack of mesomorphism by 3a was attributed
8
to non-linearity caused by an exocyclic bond in the 2- and 5-
positions of the oxadiazoles unit. However, the mesomorphism
could be improved by incorporation of a more polar group on either
side of lateral groups; for example, 2-(4-chlorophenyl)-5-(4-
alkoxyphenyl)-1,3,4-oxadiazoles or other similar asymmetric
structures exhibited nematic or smectic A phases over a wide
These molecules have also been investigated in the liquid crystal
field since the first mesogenic asymmetric 1,3,4-oxadiazole repor-
9
2
10
ted by Dimitrowa et al. Until now, many examples of mesogenic
1
,3,4-oxadiazoles with either symmetrical or asymmetrical struc-
range of temperatures. Interestingly, some derivatives of 2,5-diaryl-
1,3,4-oxadiazole without flexible chains showed enantiotropic
11
tures were prepared and studied. A few of them were structurally
derived from bis-(1,3,4-oxadiazoles). Typical nematic or layer
3
nematic mesophases with high melting temperatures.
6
b,12
Their homolog 1,3,4-thiadiazoles
showed an apparently
different mesomorphic behavior. The replacement of oxygen atom
by sulfur atom often led to an improvement of liquid crystalline
*
Corresponding author. Tel.: þ886 (0)3 4259207; fax: þ886 (0)3 4277972;
e-mail address: cklai@cc.ncu.edu.tw (C.K. Lai).
0
040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2012.06.092

7332
H.-M. Kuo et al. / Tetrahedron 68 (2012) 7331e7337
behavior. The larger sulfur atom incorporated in heterocyclic rings
was more easily polarized; therefore, they were better induced in
forming the mesophases. Also, the longer CeS bond distance and
a smaller CeSeC angle1 of 1,3,4-thiadiazole unit often favor the
formation of rod-like molecular conformations. Better linear con-
formations facilitated more efficient packing of molecules in the
mesophases, compared to the relatively more bent-shaped 1,3,4-
oxadiazoles.
2. Results and discussion
2.1. Synthesis and characterization
c,9
The synthetic procedures for the compounds 1a-n, 1b-n are
summarized in Scheme 1.
0
The 6-(alkoxy)-N -(6-(alkoxy)-2-naphthoyl)-2-naphthohydrazides
2-nwere prepared from 6-(alkoxy)-2-naphthoic acid chlorides with an
excess of hydrazine in dried THF at room temperature. The final 2,5-
bis(6-(alkoxy)naphthalen-2-yl)-1,3,4-oxadiazoles 1a-n were obtained
In this work, we report the preparation and mesomorphic
studies of two new series of symmetrical 1,3,4-oxadiazoles 1a-n and
0
1
,3,4-thiadiazoles 1b-n. Two substituted 4-naphthyl lateral groups
were incorporated to enhance the polarization and/or dipole
needed to induce the mesophases. Also, interactions often
by condensation reactions between 6-(alkoxy)-N -(6-(alkoxy)-2-
naphthoyl)-2-naphthohhydrazides and phosphoryl chloride (POCl
as refluxing solvent. Replacement of POCl by phosphorous trichloride
(PCl ) gave the same products with slightly lower yields. The com-
3
)
pe
p
3
existent by neighboring two fused naphthyl rings might also better
induce the formation of mesophases. Indeed, an extra smectic C
phase appeared at lower temperature in 1a-n and 1b-n was
obtained, which was not observed in other asymmetric mesogenic
diphenyl-1,3,4-oxadiazole. Compounds 1a-n indeed exhibited
monotropic nematic or smectic C phases, whereas, compounds 1b-
n exhibited enantiotropic nematic or smectic A/smectic C phases.
Compounds 1b-n have higher clearing temperatures and the larger
temperature ranges of mesophases than those of compounds 1a-n,
which might be attributed to a better linear conformation and
larger dipole13 caused by the more polarized sulfur atom. Both se-
ries of compounds 1a-n, 1b-n were blue emitters.
3
pounds 1a-n, 1b-n were isolated as pale yellow to green crystals
depending on the carbon chain length and the yields were in the range
63e74%. Most derivatives 1a-n,1b-n were characterized by H and
1
13
C
NMR spectroscopy, and elemental analysis. However, for some de-
rivatives with poor solubility in organic solvents to perform NMR
spectroscopy, mass spectroscopic data and elemental analysis were
1
obtained. The H NMR spectroscopy of compounds 2-n showed one
characteristic peak at ca. d w10.60 ppm assigned to amide eNH.
2.2. Mesomorphic properties of compound 1a-n, 1b-n
The mesomorphic properties of compounds 1a-n, 1b-n were
characterized and investigated by differential scanning calorimetry
and polarizing optical microscopy. The phase transitions and ther-
modynamic data of compounds 1a-n, 1b-n were listed in Table 1.
The DSC results indicated that compounds 1a-n were more kinet-
ically stable than compounds 1b-n. All compounds 1a-n, 1b-n
exhibited mesomorphic properties. Compounds 1a-n formed
monotropic nematic or smectic C phases, whereas, compounds 1b-
n exhibited enantiotropic nematic/smectic A/smectic C phases or
smectic A/smectic C phases.
X
X
H2n+1C O
n
OC H
n
2n+1
O
Y
Y
N N
3
a; X = Y = H
b; X = H, Y = OC H
3
3
n
2n+1
c; X = Y = OC H
n
2n+1
HO
HO
a
OCH3
COOH
O
b
H2n+1C O
n
H2n+1C O
n
c
OH
OCH3
O
O
d
H2n+1C O
n
OC H
n 2n+1
e
H2n+1C O
n
O O
OC H
n
2n+1
O
HN NH
-n
N N
2
1
a-n
n = 6, 8, 10, 12, 14, 16
f
H2n+1C O
n
OC H
n 2n+1
S
N N
1
b-n
n = 6, 8, 10, 12, 14, 16
Scheme 1. Reactions and reagents: (a) H
2
SO
4
, refluxed in CH
3
OH, 2 h, 80%; (b) RBr (1.1 equiv), K
2
CO
3
(1.5 equiv), KI, refluxed in acetone, 24 h, 90%; (c) KOH, refluxing in C
, 8 h, 72%; (f) P , refluxed in pyridine, 24 h, 70%.
2 5
H OH,
2
4 h, 93%; (d) stirred in SOCl , 4 h, 95%; then N
2
2
H
4
eH O (1.5 equiv), THF, 24 h, 80%; (e) stirred in POCl
2
3
2 5
S

H.-M. Kuo et al. / Tetrahedron 68 (2012) 7331e7337
7333
Table 1
Phase transitions and enthalpies of compounds 1a-n, 1b-n
a
9
1.2 (3.07)
168.8 (39.8)
1
1
1
a-6
Cr1
Cr2
I
N
8
1.8 (3.07)
153.9 (39.3)
156.8 (0.95)
163.8 (40.3)
1
26.4 (3.65)
04.4 (3.67)
a-8
Cr1
Cr2
Cr2
Cr2
I
I
I
1
145.4 (36.3)
147.7 (41.0)
144.3 (33.1)
139.8 (28.2)
N
N
151.3 (2.06)
158.0 (44.8)
1
19.5 (11.0)
a-10
Cr1
9
5.6 (7.23)
149.0 (3.69)
155.1 (39.0)
1
19.7 (10.4)
1
1
1
1
1
a-12
a-14
a-16
b-6
Cr1
Cr1
SmC
8
7.1 (8.06)
147.3 (6.12)
148.1 (33.4)
1
35.1 (42.0)
Cr2
Cr2
I
I
1
1
19.9 (10.9)
35.2 (72.2)
SmC 143.8 (6.53)
143.2 (35.7)
Cr1
SmC
1
10.4 (65.3)
135.8 (27.0)
213.9 (0.59)
142.7 (9.65)
b
1
1
40.4 (23.7)
10.7 (19.9)
228.0
287.7 (0.72)
Cr
Cr
SmC
SmC
SmA
SmA
N
I
I
I
I
I
I
b
197.0
198.6 (0.26)
241.3 (1.93)
281.8 (0.66)
b
1
25.9 (25.7)
05.0 (24.0)
240.0
265.1 (1.83)
b-8
N
b
1
236.0
237.2 (1.51)
244.3 (4.69)
263.0 (1.56)
b
1
24.9 (30.5)
243.0
239.0
248.3 (2.71)
1
b-10
Cr
SmC
SmA
SmC
SmC
SmC
N
b
106.2 (29.4)
240.4 (3.96)
245.4 (2.60)
b
1
27.6 (37.8)
237.0
239.6 (9.24)
1
1
1
b-12
b-14
b-16
Cr
Cr
Cr
SmA
b
1
1
15.0 (38.0)
27.8 (40.4)
234.0
237.5 (8.89)
b
231.0
234.2 (9.69)
SmA
b
1
18.0 (41.0)
228.0
231.6 (9.50)
b
1
1
24.8 (52.2)
16.2 (48.9)
215.0
218.1 (10.7)
SmA
b
213.0
216.4 (10.0)
a
:
n is the carbon number of alkoxy groups. Cr , Cr = crystal, SmC = smectic C, SmA = smectic A, nematic
1 2
b
N, and I = isotropic phase. : obtained by POM.
=
Compounds 1a-n have lower melting and clearing temperatures
than those of compounds 1b-n. The clearing temperatures of 1a-n
(
D
H¼0.95e3.65 kJ/mol) for the transition of N/I phase was
obtained. The mesomorphic behavior observed by 1a-n was slightly
improved over the nonmesogenic 2,5-(dialkoxyphenyl)-1,3,4-
oxadiazoles 3a. The reasons might be two folds. The use of two
lateral 4-naphthyl groups not only enhanced the pep interactions
but also increases its l/d aspect ratio. Both structural alternations
often can better induce the formation of respective mesophases.
In contrast, their homolog 1,3,4-thiadiazoles 1b-n showed an
apparently improved mesomorphic behavior. Compounds 1b-n
showed a more kinetically stable mesomorphic behavior than that
of compounds 1a-n. Compounds 1b-n were also mesogenic and
formed enantiotropic mesomorphic behavior over a wider tem-
perature range. The clearing temperatures of 1b-n decreased with
ꢀ
decreased with the length of the side chains; i.e., Tcl¼166.8 C
ꢀ
ꢀ
7a
(
n¼6)>155.1 C (n¼12)>143.2 C (n¼16), which indicated that van
der Waal force between the alkoxy chains might be controlling
force in deducing the mesophase. The temperature range the
mesophases, either nematic or smectic C phase of 1a-n was sur-
ꢀ
prisingly short; ranging from
D
T¼1.3 to 6.9 C during the cooling
process. The three compounds 1a-n with shorter lateral
chains (n¼6, 8, 10) formed nematic phases, in contrast, all other
compounds 1a-n (n¼12, 14, 16) exhibited smectic C phases. The
phase was characterized and identified as nematic and smectic C
phases, first by POM observation. A typical Schlieren texture or
broken focal-conics texture under the polarizing microscopy was
observed when cooled from isotropic liquid, as shown in Fig. 1. The
nematic phase was also consistent with an observation of homeo-
ꢀ
the carbon length of alkoxy chains, i.e., Tcl¼287.7 C (n¼6)>
ꢀ
ꢀ
239.6 C (n¼12)>218.1 C (n¼16), which were all much higher than
ꢀ
ꢀ
those of 1a-n by Tcl¼118.9 C (n¼6) to 74.9 C (n¼16). The tem-
tropic domain under POM.
A
relatively smaller enthalpy
perature ranges of mesophases were much wider than those of
ꢀ
ꢀ
Fig. 1. Optical textures observed on the cooling process; N phase at 149 C by 1a-10 (left) and SmC phase at 143.6 C by 1a-14 (right).

7334
H.-M. Kuo et al. / Tetrahedron 68 (2012) 7331e7337
compounds 1a-n, and they decreased with the carbon length; i.e.,
ꢀ
ꢀ
ꢀ
DT
phase¼147.3 C (n¼6)>112.0 C (n¼12)>91.3 C (n¼16) during
100
1a (n = 6)
1b (n = 6)
the cooling process. All transition temperatures in 1b-n of smectic
C4smectic A phases both on heating and cooling processes were
directly obtained by POM due to their smaller enthalpies not
detected on DSC analysis. The three compounds 1b-n with shorter
lateral chains (n¼6, 8, 10) formed nematic/smectic A/smectic C
phases, whereas, all other compounds 1b-n (n¼12,14, 16) exhibited
smectic A/smectic C phases. The nematic, smectic A, and smectic C
phases were identified by POM; a few typical textures shown in
Fig. 2. The replacement of oxygen atom in 1a-n by sulfur atom in
80
60
40
1
b-n much improved their liquid crystalline behavior. The larger
sulfur atom incorporated was more polarized, leading to a larger
dipole moment, which facilitated to the induction of mesophases.
Also, a longer CeS bond distance and a smaller CeSeC angle of
20
0
1,3,4-thiadiazole unit favored the formation of a more rod-like
0
100
200
300
400
500
600
700
molecular conformation. Such better linear conformation facili-
tated more efficient packing of molecules in the mesophases,
compared to the bent-shaped 1,3,4-oxadiazoles. The thermal sta-
bility of compounds 1a-6 and 1b-6 was also characterized by
thermogravimetric analyses (TGA), shown in Fig. 3. Two com-
pounds showed excellent thermal stability above their clearing
temperature. For example, the decomposition temperatures for
o
Temperature
(
C
)
Fig. 3. TGA curves of compounds 1a-6 and 1b-6.
a 5% weight loss for 1a-6 and 1b-6 were obtained at T
d
¼398.5 and
ꢀ
3
66.6 C, respectively.
23.2 Å
2
.3. Variable-temperature powder XRD diffraction data
27.0 Å
The powder X-ray diffraction experiment of compound 1b-6 was
29.1 Å
performed to confirm the structures of the smectic C and nematic
phases. The X-ray diffraction plot was presented in Fig. 4. Due to the
shorter temperature range of smectic A phases, the XRD diffraction
Intensity
0
C
N at 220
ꢀ
13.0 Å
0
SmC at 180 C
was performed at 180 and 220 C. As indicated, it displayed a typical
0
diffraction pattern with one strong peak at lower angle region, and
a very weak and broad diffraction peak at wider angle. The strong
Cr at 25
C
ꢀ
ꢀ
diffraction peak at 180 C with a d-spacing of 27.0 A was assigned as
01. This diffraction pattern was typically characteristic of a layer
2
Theta
0
structure or the main periodicity of the system observed for SmC
phases. Also, this d-spacing of 27.0 A was slightly smaller than
ꢀ
Fig. 4. The XRD diffraction plots of compound 1b-6 at 25.0, 180.0, and 220.0 C during
the cooling process.
ꢀ
ꢀ
ꢀ
ꢀ
Fig. 2. Optical textures observed on the cooling process. Top plates: N phase at 244.0 C (left) and SmC phase at 200.0 C (right) by 1b-10. Bottom plates: SmA phase at 236.0
C
ꢀ
(
left) and SmC phase at 210.0 C (right) by 1b-12.

H.-M. Kuo et al. / Tetrahedron 68 (2012) 7331e7337
7335
ꢀ
Table 2
3
1.5 A, which was obtained from calculated molecular length by
a
Summary of photophysical properties of compounds 1a-6 and 1b-6
MM2 model. This might indicate that the molecules were tilted and/
or the alkoxy chains were also slightly interdigitated. A very broad
and weak peak at w4.60 A was observed, and this peak was
assigned to the molten alkoxy chains. Fig. 5 shows the molecular
arrangements in crystal and smectic C phases.
Compound
a-6
labs/nm
lem/nm
Stokes shift/nm
ꢀ
264;b 273; 337
367;b 385; 406b
1
48
63
1b-6
274;b 282; 360
405;b 423; 448b
a
ꢀ
Measured in THF solution at 25 C.
Shoulder peak.
b
Fig. 5. Schematic illustration for molecular arrangements of Cr, smectic C and nematic phases in 1b-n.
2
.4. Optical properties
,3,4-Oxadiazole derivatives were long known as potential light-
attributed to a lowering of
p
e
p
*
band gap energy caused by
electron-donating ability of sulfur atom into the aromatic moieties.
These two wavelengths at
1
l
max¼337 and 360 nm were used to
emitting materials due to their photophysical and fluorescent
properties. The luminescent properties observed by such com-
pounds were often affected by the nature of substituents and/or
conjugation length. The UVevis absorption and the photo-
luminescence spectra of the two compounds 6a-6 and 6b-6 dis-
solved in THF were shown in Fig. 6. The absorption and emission
obtain the PL spectra. A similar trend was also observed in the
photoluminescence spectra. The emission peaks were much
broader, which occurred at ca. 385 and 423 nm measured in THF for
1a-6 and 1b-6, respectively. The emitting color was ranged be-
tween blue and purple. The Stokes shifts to these two compounds
are 48 nm (1a-6) and 63 nm (1b-6). The maximum at 385 and
423 nm can be attributed to the oxadiazoles and thiadiazole
emitters while the maximum can be due to the naphthalene-
containing chain segments. The carbon length of the alkoxy
group has no influence on the fluorescence emitting spectrum of
their solution states.
0.6
0.5
0.4
0.3
0.2
0.1
0.0
3000000
2500000
2000000
1500000
1000000
500000
0
1
a (n = 6)
1b (n = 6)
3. Conclusions
Two new series of 1,3,4-oxadiazoles 1a-n and thiadiazoles 1b-n
were prepared, characterized, and their mesomorphic behavior in-
vestigated. Both series were all mesogenic, exhibiting N, SmA or/and
SmC phases.1,3,4-Thiadiazoles are kinetically more stable than 1,3,4-
oxadiazoles. 1,3,4-Thiadiazoles have a wider temperature range of
mesophases over that of 1,3,4-oxadiazoles, which were attributed to
the more polarized sulfur atom incorporated. Two naphthyl rings
300
400
500
600
2,5-substituted to the central 1,3,4-oxadiazoles have better im-
Wavelength (nm)
proved the mesomorphism, over their nonmesogenic homologs, 2,5-
bis(alkoxyphenyl)-1,3,4-oxadiazoles 3a. Both series of 1a-n and 1b-n
have excellent thermal stabilities and also were excellent blue
emitters. Thisworkdemonstrated that an improved mesophasewith
a much wider temperature range could be obtained by use of sulfur
atom incorporated and naphthalene rings in 1,3,4-thiadiazoles.
Fig. 6. Absorption and PL spectra of compounds 1a-6 and 1b-6 measured in THF at
room temperature.
spectra were very similar in shape. The absorption spectra showed
two peak absorbance wavelengths at ca. 273 and 337 nm for the
1
,3,4-oxadiazoles 1a-6. The two
mately 282 and 360 nm for 1,3,4-thiadiazole 1b-6, summarized in
Table 2. The first absorption max bands at 273 and 282 nm were
lmax peaks shifted to approxi-
4. Experimental section
4.1. General
l
attributed to the transitions in the lateral naphthalene rings of the
molecule due to the high molar absorption coefficient. The second
lmax bands at 337e360 nm were due to the heteroaromatic moie-
1H and 13C NMR spectra were measured on a Bruker DRX-300.
DSC thermographs were carried out on a Mettler DSC 822. All
ties. This increase of max from 273 to 282 nm was probably
l

7336
H.-M. Kuo et al. / Tetrahedron 68 (2012) 7331e7337
ꢀ
phase transitions are determined 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
UVevis absorption and fluorescence spectra were obtained using
SHIMADZU-UV-3150 spectrometer and HORIBA-JOBIN YVON
spectrophotometer. Elemental analysis for carbon, hydrogen, and
nitrogen was conducted at Instrumentation Center, National Tai-
wan 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
123.81, 127.10, 127.66, 128.17, 130.30, 136.34, 158.87, 164.76. MS
þ
(FAB): calcd for M : C42
54
H N
2
O
3
: 634.89. Found: 635.2. Anal. Calcd
for C42
54 2 3
H N O : C, 79.45; H, 8.57. Found: C, 79.19; H, 8.58.
4.2.6. 2,5-Bis(6-(tetradecyloxy)naphthalen-2-yl)-1,3,4-oxadiazole
1
(1a-14). White solid; yield 73%. H NMR (300 MHz, CDCl
(t, eCH , 44H), 1.83e1.87 (m,
, 6H, J¼6 Hz), 1.24e1.39 (m, eCH
eCH , 4H), 4.09 (t, eOCH
3
): d 0.85
3
2
2
2
, 4H, J¼6.3 Hz), 7.16 (s, AreH, 2H),
7.20e7.21 (m, AreH, 2H), 7.85 (t, AreH, 4H, J¼9.6 Hz), 8.18 (d, AreH,
þ
2H, J¼6.9 Hz), 8.56 (s, AreH, 2H). MS (FAB): calcd for M :
ꢀ
the wavelength of 1.3263 A.
50 70 2 3 70 2 3
C H N O : 747.10. Found: 747.5. Anal. Calcd for C50H N O : C,
80.38; H, 9.44. Found: C, 80.40; H, 9.41.
4
.2. Syntheses of compounds 1a-n and 1b-n
4
.2.7. 2,5-Bis(6-(hexadecyloxy)naphthalen-2-yl)-1,3,4-oxadiazole
0
þ
4
.2.1. 6-(Hexyloxy)-N -(6-(hexyloxy)-2-naphthoyl)-2-naphthohydrazide.
(1a-16). White solid; yield 72%. MS (FAB): calcd for M :
The solution of 6-(hexyloxy)-2-naphthoic acid (5.0 g, 0.0148 mol)
was refluxed in 20 mL of thionyl chloride for 4 h under nitrogen
atmosphere. The excess thionyl chloride was removed under re-
duced pressure. The paste was redissolved in dried 20 mL of THF,
and to which hydrazine monohydrate (2.5 ml) was slowly added.
Light yellow solids were precipitated, and the mixture was stirred
for another 6 h at room temperature. The solids were then col-
C
54
H
78
N
2
O
3
: 803.21. Found: 803.4. Anal. Calcd for C54
78 2 3
H N O : C,
80.75; H, 9.79. Found: C, 80.87; H, 9.86.
4.2.8. 2,5-Bis(6-(dodecyloxy)naphthalen-2-yl)-1,3,4-thiadiazole (1b-
12). Under nitrogen atmosphere. The solution of 6-(dodecyloxy)-N -
(6-(dodecyloxy)-2-naphthoyl)-2-naphthohydrazide
1.41 mmol) dissolved in 20 mL of pyridine was added phosphorus(V)
0
(1.0 g,
lected, and the products isolated as yellow solids were obtained
sulfide (2.19 g, 9.87 mmol). The solution was refluxed for 24 h. The
1
after recrystallization twice from THF. Yield 87%.
300 MHz, DMSO): 0.90 (br, eCH
.78e1.80 (m, eCH , 4H), 4.13 (t, OCH
H, J¼8.7 Hz), 7.41 (br, AreH, 2H), 7.90e7.98 (m, AreH, 6H), 8.50
H
NMR
solution was then extracted twice with CH
layers were dried over anhydrous MgSO and concentrated to give
yellow solids. The products isolated as light yellow solids were
2 2 2
Cl /H O, and organic
(
d
3
, 6H), 1.33e1.45 (m, eCH
2
, 12H),
4
1
2
2
2
, 4H, J¼6 Hz), 7.25 (d, AreH,
1
obtained by recrystallization from CH
(300 MHz, CDCl ): 0.86 (t, eCH
, 6H, J¼6 Hz), 1.25e1.51 (m, eCH
36H),1.82e1.87 (m, eCH , 4H), 4.08 (t, eOCH
, 4H, J¼6.3 Hz), 7.15 (s,
AreH, 2H), 7.20 (d, AreH, 2H, J¼9 Hz), 7.79e7.84 (m, AreH, 4H), 8.10
2 2 3
Cl /CH OH. Yield 70%. H NMR
13
(
br, AreH, 2H), 10.60 (br, eNH, 2H). C NMR (75 MHz, DMSO):
3
d
3
2
,
d
14.97, 23.13, 26.28, 29.62, 32.05, 68.76, 107.63, 120.78, 125.59,
27.90, 128.40, 128.57, 128.97, 131.60, 137.17, 159.22, 167.06.
2
2
1
1
3
(
d, AreH, 2H, J¼8.7 Hz), 8.37 (s, AreH, 2H). C NMR (75 MHz, CDCl
3
):
4
.2.2. 2,5-Bis(6-(dodecyloxy)naphthalen-2-yl)-1,3,4-oxadiazole
d 13.92, 22.49, 25.89, 28.98, 29.15, 29.21, 29.41, 68.01, 106.43, 120.09,
0
þ
(1a-12). The mixture of 6-(dodecyloxy)-N -(6-(dodecyloxy)-2-
124.84,127.51,130.02,135.96,158.49,167.96. MS (FAB): calcd for M :
S: 707.06. Found: 707.3. Anal. Calcd for C46 S: C,
78.14; H, 8.84. Found: C, 78.01; H, 8.30.
naphthoyl)-2-naphthohydride (1.0 g, 1.41 mmol) and phosphoryl
chloride was gently refluxed for 8 h under nitrogen atmosphere.
Water was slowly added, and the solution was stirred with dilute
aqueous NaOH (1.0 M) added for 4 h. The resulting yellow-green
solids were collected. The products isolated as white solids were
C
H N O
46 62 2 2
62 2 2
H N O
4.2.9. 2,5-Bis(6-(hexyloxy)naphthalen-2-yl)-1,3,4-thiadiazole (1b-
1
6). Light yellowsolid; yield 72%. H NMR (300 MHz, CDCl
eCH , 12H), 1.76e1.86 (m, eCH
, 6H, J¼7.2 Hz), 1.33e1.50 (m, eCH
4H), 4.02 (t, eOCH
, 4H, J¼6.6 Hz), 7.07 (s, AreH, 2H), 7.16 (dd, AreH,
2H, J ¼2.4 Hz), 7.72e7.79 (m, AreH, 4H), 8.03 (dd, AreH,
¼6.6 Hz, J
2H, J
¼6.9 Hz, J
CDCl ): 14.03, 22.59, 25.74, 29.13, 31.59, 68.12, 106.52, 120.14,
3
): d 0.91 (t,
obtained after three times recrystallization from hot THF. Yield 72%.
3
2
2
,
1
H NMR (300 MHz, CDCl
3
):
d
0.85 (t, eCH
3
, 6H, J¼6.3 Hz), 1.24e1.50
2
(
m, eCH
2
, 36H), 1.79e1.89 (m, eCH
2
, 4H), 4.08 (t, eOCH
2
, 4H,
1
2
13
J¼6.3 Hz), 7.14 (s, AreH, 2H), 7.15e7.22 (m, AreH, 2H), 7.84 (t, AreH,
1
2
¼1.8 Hz), 8.28 (s, AreH, 2H). C NMR (75 MHz,
4
H, J¼9.9 Hz), 8.16 (d, AreH, 2H, J¼8.7 Hz), 8.55 (s, AreH, 2H). MS
3
d
þ
(
FAB): calcd for M : C46
H
62
N
2
O
3
: 691.00. Found: 691.2. Anal. Calcd
124.95, 125.30, 127.57, 127.82, 128.36, 130.11, 135.99, 158.52, 167.99.
þ
for C46
62
H N
2
O
3
: C, 79.96; H, 9.04. Found: C, 79.61; H, 9.01.
MS (FAB): calcd for M : C34
H
38
N
2
O
2
S: 538.74. Found: 539.1. Anal.
38 2 2
Calcd for C34H N O S: C, 75.80; H, 7.11. Found: C, 77.77; H, 7.10.
4
.2.3. 2,5-Bis(6-(hexyloxy)naphthalen-2-yl)-1,3,4-oxadiazole
(1a-
, 6H,
1
6
). White solid; yield 70%. H NMR (CDCl
,12H),1.82e1.89 (m, eCH
, 4H, J¼6.6 Hz), 7.15 (s, AreH, 2H), 7.20e7.23 (m, AreH, 2H),
.85 (t, AreH, 4H, J¼9.9 Hz), 8.17 (d, AreH, 2H, J¼8.4 Hz), 8.55 (s,
3
):
d
0.92 (t, eCH
3
4.2.10. 2,5-Bis(6-(octyloxy)naphthalen-2-yl)-1,3,4-thiadiazole (1b-
þ
J¼3.5 Hz),1.34e1.39 (m, eCH
2
2
, 4H), 4.08 (t,
8). Light yellow solid; yield 71%. MS (FAB): M : calcd for
eOCH
2
C
38
46
H N
2
O
2
46 2 2
S: 594.85. Found: 595.2. Anal. Calcd for C38H N O S: C,
7
76.73; H, 7.79. Found: C, 76.88; H, 7.90.
þ
AreH, 2H). MS (FAB): calcd for M : C34
38 2 3
H N O : 522.68. Found: 522.9.
Anal. Calcd for C34 : C, 78.13; H, 7.33. Found: C, 78.47; H, 7.42.
H
38
N
2
O
3
4.2.11. 2,5-Bis(6-(decyloxy)naphthalen-2-yl)-1,3,4-thiadiazole (1b-
1
1
0). Light yellow solid; yield 74%. H NMR (300 MHz, CDCl
(t, eCH , 20H), 1.79e1.88 (m,
, 6H, J¼6.6 Hz), 1.27e1.51 (m, eCH
eCH , 4H), 4.07 (t, eOCH
, 4H, J¼6.6 Hz), 7.13 (s, AreH, 2H), 7.19
(dd, AreH, 2H, J ¼2.1 Hz), 7.79 (t, AreH, 4H, J¼8.7 Hz),
¼6.6 Hz, J
8.08 (dd, AreH, 2H, J
¼6.9 Hz, J
NMR (75 MHz, CDCl ): 14.10, 22.67, 26.08, 29.18, 29.32, 29.41,
3
): d 0.87
4
8
.2.4. 2,5-Bis(6-(octyloxy)naphthalen-2-yl)-1,3,4-oxadiazole
(1a-
3
2
þ
). White solid; yield 71%. MS (FAB): calcd for M : C38
H
46
N
2
O
3
:
2
2
578.78. Found: 579.1. Anal. Calcd for C38
46
H N
2
O
3
: C, 78.86; H, 8.01.
1
2
13
Found: C, 78.92; H, 8.12.
1
2
¼1.5 Hz), 8.34 (s, AreH, 2H).
C
3
d
4
.2.5. 2,5-Bis(6-(decyloxy)naphthalen-2-yl)-1,3,4-oxadiazole
(1a-
0.86 (t,
31.89, 68.18, 106.61, 120.22, 125.01, 125.32, 127.64, 127.94, 128.41,
1
þ
1
0). White solid; yield 70%. H NMR (300 MHz, CDCl
eCH
, 6H, J¼6.3 Hz),1.25e1.46 (m, eCH
H), 4.07 (t, eOCH
, 4H, J¼6.6 Hz), 7.15 (s, AreH, 2H), 7.19e7.22 (m,
3
):
d
130.16,136.07,158.60,168.08. MS (FAB): calcd for M : C42
54
H N
2
O
2
S:
3
2
, 28H),1.79e1.88 (m, eCH
2
,
54 2 2
650.96. Found: 651.5. Anal. Calcd for C42H N O S: C, 77.49; H, 8.36.
4
2
Found: C, 77.94; H, 8.38.
AreH, 2H), 7.83 (t, AreH, 4H, J¼9.9 Hz), 8.16 (d, AreH, 2H, J¼7.2 Hz),
8
2
.53 (s, AreH, 2H). 13C NMR (75 MHz, CDCl
9.16, 29.32, 29.40, 29.57, 31.89, 68.21, 106.65, 118.76, 120.32,
3
):
d
14.10, 22.67, 26.08,
4.2.12. 2,5-Bis(6-(tetradecyloxy)naphthalen-2-yl)-1,3,4-thiadiazole
1
3
(1b-14). Light yellow solid; yield 73%. H NMR (300 MHz, CDCl ):

H.-M. Kuo et al. / Tetrahedron 68 (2012) 7331e7337
7337
d
0.86 (t, eCH
3
, 6H, J¼6.3 Hz), 1.24e1.49 (m, eCH
2
, 44H), 1.82e1.86
, 4H, J¼6.6 Hz), 7.13 (s, AreH, 2H), 7.19
Oyston, S.; Wang, C.; Perepichka, I. F.; Batsanov, A. S.; Bryce, M. R.; Ahn, J. H.;
Petty, M. C. J. Mater. Chem. 2005, 15, 5164e5173; (k) Hughes, G.; Bryce, M. R. J.
Mater. Chem. 2005, 15, 94e107; (l) Madsen, L. A.; Dingemans, T. J.; Nakata, M.;
Samulski, E. T. Phys. Rev. Lett. 2004, 92, 145505/1e145505/4; (m) Hughes, G.;
Kreher, D.; Wang, C.; Batsanov, A. S.; Bryce, M. R. Org. Biomol. Chem. 2004, 2,
(
m, eCH , 4H), 4.08 (t, eOCH
2
2
(
2
d, AreH, 2H, J¼8.7 Hz), 7.80 (t, AreH, 4H, J¼8.1 Hz), 8.09 (d, AreH,
13
H, J¼8.4 Hz), 8.36 (s, AreH, 2H). C NMR (75 MHz, CDCl
2.69, 26.10, 29.19, 29.67, 31.93, 68.21, 106.64, 120.27, 125.04,
25.26, 127.69, 128.03, 128.44, 130.19, 136.13, 158.67, 168.14. MS
3
): d 14.12,
3363e3367; (n) Wang, C.; Batsanov, A. S.; Bryce, M. R. Chem. Commun. 2004,
2
1
578e579.
2
3
. Dimitrowa, K.; Hauschild, J.; Zaschke, H.; Schubert, H. J. Prakt. Chem. 1980, 322,
933e944.
. (a) Qu, S.; Wang, L.; Liu, X.; Li, M. Chem.dEur. J. 2011, 17, 3512e3518; (b)
Barber ꢁa , J.; Godoy, M. A.; Hidalgo, P. I.; Parra, M. L.; Ullo, J. A.; Vergara, J. M. Liq.
þ
(
FAB): calcd for M : C50
70 2 2
H N O S: 763.17. Found: 763.6. Anal. Calcd
for C50 S: C, 78.69; H, 9.25. Found: C, 78.71; H, 9.26.
70 2 2
H N O
Cryst. 2011, 38, 679e688; (c) Zhang, P.; Bai, B.; Wang, H.; Qu, S.; Yu, Z.; Ran, X.;
Li, M. Liq. Cryst. 2009, 36, 7e12; (d) Srivastava, R. M.; Ricardo, A. W.; Filho, N.;
Schneider, R.; Vieira, A.; Gallardo, H. Liq. Cryst. 2008, 35, 737e742; (e) Wang, H.;
Zhang, F.; Bai, B.; Zhang, P.; Shi, J.; Yu, D.; Zhao, Y.; Wang, Y.; Li, M. Liq. Cryst.
4
.2.13. 2,5-Bis(6-(hexadecyloxy)naphthalen-2-yl)-1,3,4-thiadiazole
1
(
d
1b-16). Light yellow solid; yield 72%. H NMR (300 MHz, CDCl
0.84 (t, eCH , 52H), 1.83e1.84
, 6H, J¼6.3 Hz), 1.24e1.48 (m, eCH
m, eCH , 4H), 4.07 (t, eOCH
, 4H, J¼6.6 Hz), 7.14 (s, AreH, 2H), 7.20
d, AreH, 2H, J¼8.7 Hz), 7.84 (t, AreH, 4H, J¼8.4 Hz), 8.09e8.19 (m,
3
):
3
2
2
008, 35, 905e912; (f) Zhang, P.; Qu, S.; Wang, H.; Bai, B.; Li, M. Liq. Cryst. 2008,
35, 389e394; (g) Chai, C.; Yang, Q.; Fan, X.; Chen, X.; Shen, Z.; Zhou, Q. Liq. Cryst.
008, 35, 133e141; (h) Qu, S.; Li, M. Tetrahedron 2007, 63, 12429e12436.
4. (a) Tang, J.; Huang, R.; Gao, H.; Cheng, X.; Prehm, M.; Tschierske, C. RSC Adv.
012, 2, 2842e2847; (b) Vieira, A. A.; Gallardo, H.; Barbera, J.; Romero, P.;
(
(
2
2
2
13
AreH, 2H), 8.38 (s, AreH, 2H). C NMR (75 MHz, CDCl
2.69, 26.10, 29.37, 29.68, 31.92, 68.24, 106.66, 120.35, 125.04,
25.26, 127.78, 128.23, 128.39, 130.26, 136.13, 158.66, 163.20. MS
3
): d 14.11,
2
2
1
Serrano, J. L.; Sierra, T. J. Mater. Chem. 2011, 21, 5916e5922; (c) Gallardo, H.;
Ferreira, M.; Vieira, A. A.; Westphal, E.; Molin, F.; Eccher, J.; Bechtold, I. H.
Tetrahedron 2011, 67, 9491e9499; (d) Yelamaggad, C. V.; Achalkumar, A. D.; Rao,
D. S. R.; Prasad, S. K. J. Org. Chem. 2009, 74, 3168e3171.
. (a) Tschierske, C.; Photinos, D. J. J. Mater. Chem. 2010, 21, 4263e4294; (b)
Zafiropoulos, Z. A.; Lin, W.; Samulski, E. T.; Dingemans, T. J.; Picken, S. J. Liq.
Cryst. 2009, 36, 649e656; (c) Dingemans, T. J.; Madsen, L. A.; Zafiropoulos, N.
A.; Lin, W.; Samulsk, E. T. Phil. Trans. R. Soc. A 2006, 364, 2681e2696.
. (a) Picken, S. J.; Dingemans, T. J.; Madsen, L. A.; Francescangeli, O.; Samulski, E.
T. Liq. Cryst. 2012, 39, 19e23; (b) Prajapati, A. K.; Modi, V. Liq. Cryst. 2011, 38,
þ
(
FAB): calcd for M : C54
78 2 2
H N O S: 650.96. Found: 651.3. Anal. Calcd
for C54 S: C, 79.16; H, 9.60. Found: C, 79.06; H, 9.64.
78 2 2
H N O
5
Acknowledgements
6
We thank the National Science Council of Taiwan, ROC for
funding (NSC 100-2113-M-008-002-MY2) in generous support of
this work.
191e199; (c) Bates, M. A. Chem. Phys. Lett. 2007, 437, 189e192; (d) Acharya, B. R.;
Primak, A.; Dingemans, T. J.; Samulski, E. T.; Kumar, S. Pramana-J. Phys. 2003, 61,
231e237; (e) Dingemans, T. J.; Murthy, N. S.; Samulski, E. T. J. Phys. Chem. B
2001, 105, 8845e8860.
Supplementary data
7. (a) Wang, H.; Zheng, Z.; Shen, D. Liq. Cryst. 2012, 39, 99e103; (b) Wang, L.; Yu,
L.; Xiao, X.; Wang, Z.; Yang, P.; He, W.; Yang, H. Liq. Cryst. 2012, 39, 629e638; (c)
Lai, C. K.; Ke, Y. C.; Su, J. C.; Shen, C.; Li, W. R. Liq. Cryst. 2002, 29, 915e920; (d)
Wen, C. R.; Wang, Y. J.; Wang, H. C.; Sheu, H. S.; Lee, G. H.; Lai, C. K. Chem. Mater.
2005, 17, 1646e1654.
The synthetic procedures of some compounds and DSC ther-
mographs. Supplementary data associated with this article can be
found in the online version, at http://dx.doi.org/10.1016/
j.tet.2012.06.092.
8
9
. Dingemans, T. J.; Samulski, E. T. Liq. Cryst. 2000, 27, 131e136.
. Prajapati, A. K.; Modi, V. Liq. Cryst. 2010, 37, 407e415.
1
0. (a) Han, J.; Zhang, M.; Wang, F.; Geng, Q. Liq. Cryst. 2010, 37, 1471e1478; (b)
Parra, M. L.; Elgueta, E. Y.; Jimenez, V.; Hidalgo, P. I. Liq. Cryst. 2009, 36,
01e317; (c) Han, J.; Zhang, F. Y.; Wang, J. Y.; Wang, Y. M.; Pang, M. L.; Meng, J.
B. Liq. Cryst. 2009, 36, 825e833.
3
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