Synthesis and self-assembly of photoresponsive and luminescent polycatenar liquid crystals incorporating an azobenzene unit interconnecting two 1,3,4-thiadiazoles

Article abstract of DOI:10.1039/c6nj02604d

Novel polycatenar liquid crystals containing two 1,3,4-thiadiazole rings interconnected by an azobenzene central linkage have been synthesized and investigated by polarizing microscopy, DSC, X-ray scattering, SEM, UV-vis spectroscopy and photoluminescence measurements. These compounds can self-assemble into SmC, Col_hex/p6mm and Cub_I/Pm3n liquid crystalline phases in the bulk states and form multistimuli responsive organogels in organic solvents. They have reversible photoresponsive properties in solution, liquid crystalline states and gel states. They also show fluorescence emission with large Stokes shift in solution and binding selectivity to Cu²⁺ among a series of cations in CH₃CN-CH₂Cl₂ solution.

Full text of DOI:10.1039/c6nj02604d

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ISSN 1144-0546
PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
rsc.li/njc

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Synthesis and selfꢀassembly of photoresponsive and luminescent
polycatenar liquid crystals incorporating an azobenzene unit
interconnecting two 1,3,4ꢀ thiadiazoles
Xiongwei Peng, Hongfei Gao, Yulong Xiao, Huifang Cheng, Fanran Huang, Xiaohong Cheng*
Key Laboratory of Medicinal Chemistry for Natural Resources, Chemistry Department
Yunnan University
Kunming, Yunnan 650091,
P. R. China
Fax: (+86) 871 5032905
Eꢀmail: xhcheng@ynu.edu.cn
Abstract: Novel polycatenar liquid crystals containing two 1,3,4ꢀthiadiazole rings interconnected by an
azobenzene central linkage have been synthesized and investigated by polarizing microscopy, DSC, Xꢀray
scattering
,
SEM, UVꢀvis spectroscopy and photoluminescence measurements. These compounds can
selfꢀassemble into SmC, Colhex/p6mm and Cub / liquid crystalline phases in the bulk states and form
Pm3n
I
multistimuli responsive organogels in organic solvents. They have reversible photoresponsive properties in
solution, liquid crystalline states and gel states. They also show fluorescent emission with large Stokes shift in
solution and binding selectivity to Cu2+ among a series of cations in CH3CNꢀCH2Cl2 solution.
Key words: 1,3,4ꢀthiadiazole; azobenzene; luminescent liquid crystal; organogel; fluorescent chemosensor.
1. Introduction
The combination of heterocyclic rings into a liquid crystal molecule is essential to the design and
synthesis of advanced functional materials. Heteroatoms like nitrogen, oxygen and sulfur provide a
reduced molecular symmetry, strong lateral or longitudinal dipole and a donor–acceptor interaction
within the molecule, which in turn affects the LC selfꢀassembly and electronic behavior of the
mesogens. 1 1,3,4ꢀThiazole is an important five membered heterocycle which has a high
aromaticity and its derivatives are applied widely in pharmaceutical, agricultural and material
chemistry. With its electroꢀdeficient nature and good electronꢀaccepting ability as well as thermal
and chemical stability, 1,3,4ꢀthiazoles are widely applied in optics and electrochemistry focusing
on their photoluminescence, photoconductivity, charge transporting capacity and mesomorphism
to obtain functional liquid crystals.2
However, reports on 1,3,4ꢀthiadiazoleꢀbased mesogens are scarce, partially due to the synthetic
difficulty. Till now very few reports on 1,3,4ꢀthiadiazoleꢀbased calamitic LCs,3 bananaꢀshaped
LCs,4 hydrogenꢀbonded LCs,5 polycatenar LCs,6,7,8 starꢀshaped mesogens9 and polymeric LCs10
etc have been reported. Compared with their 1,3,4ꢀoxadiazol analogues, 1,3,4ꢀthiadiazole
derivatives are considered as more conductive to mesogens because of their higher melting points,
clear temperatures, and viscosity, as well as efficient packing, larger dipole moments
(1,3,4ꢀthiadiazole: 3.11 D, 1,3,4ꢀoxadiazo: 3.06 D) and their less bent molecular structures. 1c,4a
Most of the reported 1,3,4ꢀthiadiazole contained mesogens can self organize into nematic 3p, 4a
,

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smectic,3g,3h,3o columnar phases,7,8,9 but no thermotropic micellar cubic phases have been reported
formed by such 1,3,4ꢀthiadiazole contained mesogens.
Azobenzene derivative LCs have attracted much more attention because of their
photoresponsive properties caused by the trans–cis photoisomerization of the azobenzene units.11
A wide diversity of azobenzene derivative LCs have been designed to introduce lightꢀmodulated
functionalities, for example for application as organic lightꢀdriven actuators. 12 , 13 , 14 Most
azobenzene derivative LCs contain an azo linkage either at the periphery14,15,16,17,18 or in few
cases also at the central of the molecules.19 The azobenzene derivatives were usually non
photoluminescence (PL).20 It is possible to combine azobenzene with 1,3,4ꢀthiadiazole to design
novel LCs with both photoresponsive and luminescence properties. As far as we know, such
1,3,4ꢀthiadiazole containing polycatenar liquid crystals with an azobenzene as central links have
not ever been reported.
Therefore herein we have designed and synthesized novel symmetrical polycatenar liquid
crystals containing two 1,3,4ꢀthiadiazole rings interconnected by an azobenzene central linkage,
bearing alkyl chains at each terminus. These compounds are assigned as Im/n, where m stands for
the number of the terminal chain at one terminus, n is the alkyl chain length. Im/n have both LC
and gelation properties. Depending on the number and length of the terminal chains, different
mesophase structures including smectic C, hexagonal columnar and even micellar cubic phases
are found in these compounds. Im/n have photoresponsive ability in solution, LC states and gel
states. Im/n can also be used as fluorescence chemosensors for selective response to Cu2+ among
different metal ions in solution.
2. Results and Discussion
2.1. Synthesis
The synthetic route is shown in Scheme 1. Both thiadiazole rings in target compounds Im/n were
formed simultaneously by reaction of azobenzene dichloride
3
with appropriate
3,4,5ꢀtrialkoxybenzhydrazides 121 and subsequent cyclization with phosphorus pentasulfide.22
Azo benzene dichloride 3 was prepared from the azobenzeneꢀ4,4ꢀdicarboxylic acid 2 which was
obtained from the reduction reaction of 4ꢀnitrobenzoic acid with glucose under alkaline
environment. 23 Purification of all the products was done by column chromatography.
Experimental procedures and analytical data are collated in the Supporting Information.

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Scheme 1. Synthesis of the Im/n, Reagents and conditions: i) hydrazine hydrate, 2ꢀmethoxyethanol, 100 °C, 12 h;
ii) NaOH, glucose, 70 °C, 12 h; iii) SOCl2, 70 °C, 5 h; iv) Et3N, THF, 70 °C, 12 h; v) toluene, P2S5, 100 °C, 12 h.
2.2. Mesomorphic properties
Table 1 Transition temperatures and associated enthalpy values (in brackets) of compounds I1/n, mꢀI2/n, oꢀI2/n
and I3/n.[a]
Comp. R1, R2, R3
T/°C [ꢁH/kJ mol−1]
I1/14
mꢀI2/8
R 1= R3 = H, R2 = OC14H29
R1 = R3 = OC8H17, R2 = H
Cr 131 [50.2] SmC 167 [5.6] Iso
Cr 67 [26.8] Iso
mꢀI2/12 R1 = R3 = OC12H25, R2 = H
oꢀI2/8
R1 = H, R2 = R3 = OC8H17
oꢀI2/12 R1 = H, R2 = R3 = OC12H25
oꢀI2/14 R1 = H, R2= R3= OC14H29
Cr 54 [17.9] Iso
Cr 121 [70.8] (103[3.7] Colhex) Iso
Cr 85 [21.9] Colhex 105[b] Iso
Cr 91 [39.0] Colhex 119 [1.0] Iso
Cr 74[b] Iso
I3/8
R1 = R2 = R3 = OC8H17
R1 = R2 = R3 = OC10H21
R1 = R2 = R3 = OC12H25
R1 = R2 = R3 = OC14H29
I3/10
I3/12
I3/14
Cr 68 [47.5] Iso
Cr 61 [10.9] Cr 70 [16.9] Cub/
1
80[b] Iso
82[b] Iso
Pm3n
Pm3n
2
Cr 63 [11.0] Cr 67 [17.0] Cub/
1
2
[a] Transition temperatures were determined by DSC (peak temperature from the first heating scan, at a rate of 1 K
min−1 for I3/8, I3/10, I3/12, I3/14; 2 K min−1 for compounds I1/14, mꢀI2/8, mꢀI2/12 and 5 K min−1 for oꢀI2/8, oꢀI2/12,
oꢀI2/14). Abbreviations: Cr = crystal; SmC = smectic C phase; Colhex = hexagonal columnar phase; CubI/ Pm3n
=
micellar cubic mesophases with space groups
by POM.
; Iso = isotropic liquid. [b] Transition temperature determined
Pm3n

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The LC selfꢀassembly of compounds I1/n, mꢀI2/n, oꢀI2/n and I3/n was investigated by polarized
optical microscopy (POM), differential scanning calorimetry (DSC) and Xꢀray diffraction (XRD).
The transition temperatures are shown in Table 1.
2.2.1. Dicatenar and tetracatenar compounds (I1/n, mꢀI2/n, oꢀI2/n) and their formation of
smectic C and columnar hexagonal phases
Together ten compounds were prepared. They differ themselves in the number and length as well
as in the substituted patterns of the alkyl chains. Dicatenar compound I1/14 with one tetradecyl
chain at each terminus shows smectic C mesophase as identified by its typical SmC schlieren
texture as observed under POM (Fig. S1a†).24 The smallꢀangle Xꢀray scattering (SAXS) pattern
of this compound shows the sharp layer reflection with the thickness of d = 5.4 nm at 140 °C (Fig.
S3a†). Comparing the diffraction peak, which corresponds to the interlayer spacing, to the
molecular length L = 6.6 nm (estimated by Material Studio, version 6.0), one can infer that the
aliphatic chains are folded or the molecules are tilted within the layers. Considering the molecules
in the most extended form, the tilt angle was calculated using the relationship cos θ = d /L = 0.82
and a value of θ ≈ 37 degree was obtained, which is consistent with the value for the SmC phase.25
Tetracatenar compounds mꢀI2/n (n = 8, 12) with two metaꢀsubstituted octyl and dodecyl chains
respectively at each terminus are not LC. However, tetracatenar compounds with two
orthoꢀsubstituted alkyl chains oꢀI2/n (n = 8, 12, 14) all show columnar phases, for these
tetracatenar compounds, with the elongation of the alkyl chain, the melting temperatures decrease,
the isotropic temperatures increase, therefore the range of mesophase broadens and the stability of
mesophase increases. Compound oꢀI2/8 is monotropic columnar mesophase, the other two higher
homologues formed stable enantiotropic columnar mesophases. The columnar phases were
identified by the typical spherulitic fanlike textures under POM. Investigation of the columnar
phases by polarising microscopy between crossed polarisers with an additional λꢀretarder plate
indicates that the columnar phases of compounds oꢀI2/n (n = 8, 12, 14) are optically negative (Fig.
1b and Fig. S1bꢀ1c†). This means that the major intramolecular πꢀconjugation pathway, which is
along the long axis of the aromatic cores, is perpendicular to the column long axis. This is in line
with the proposed organization of the molecules in the columns. The columnar phases were also
investigated by SAXS. There are three small angle reflections with a ratio of their reciprocal
spacing 1: 31/2 : 2, which can be indexed to the 10, 11, 20 reflections of hexagonal lattice with
p6mm symmetry (Fig.1c, Fig. S4aꢀb† and Table S1ꢀS3†). The number of molecules organized in a
slice of the columns with a height of h = 0.45 nm (a typical value for the maximum of the diffuse
wide angle scattering) ncell could be calculated as shown in Table 2 and Table S6†. It can be
assumed that for these compounds, approximately 5 molecules selfꢀassemble into an overall
diskꢀlike stratum and they successively stack one another to form supramolecular columns, which
was similar with the reported polycatenar mesogens.26 It should be noted that the intermolecular
π–π interactions between the azobenzeneꢀthiadiazole cores as well as nanosegregation of the rigid
aromatic center from the surrounding alkyl chain moieties would promote the assembly of these
molecules into such columnar structures (Fig. 1d). Although the meta substituted compounds
mꢀI2/8 and mꢀI2/12 have very low melting points, they do not show mesophases, while all the
ortho substituted compounds are all liquid crystals. The reason is that if the two terminal alkyl
chains are not close to each other, their separation into distinct defined region is disturbed and give

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rise to disorder.27
a)
b)
d)
c)
Fig. 1 Colhex phase of compound oꢀI2/14: (a) texture as seen between crossed polarizers at T =100 °C; (b) inset
shows the same region with λꢀplate; (c) SAXS diffractogram at T = 105 °C; (d) model showing the organization of
compounds oꢀI2/n in Colhex phase.
2.2.2. Hexacatenar compounds I3/n and their formation of micellar cubic phases
Interesting micellar
cubic phase is observed in hexacatenar compounds I3/12 and I3/14 with
Pm3n
three long chains at each terminus, while the other two lower homologues (I3/8 and I3/10) are only
crystals. For this cubic phase, under POM, optically isotropic texture was observed, which is not
fluid, but soft and viscoelastic, by increasing the temperature, sharp transitions to highly fluid
isotropic liquid occur at defined temperature (Fig. S1dꢀ1e†). The isotropic mesophases of
compound I3/14 and I3/12 were investigated by XRD, indicating the fluid LC states, and several
reflections in the smallꢀangle region that could be indexed to a cubic lattice with
space
Pm3n
group (Fig. 2a and Fig. S3b†). The
lattice is the most commonly observed lattice of
Pm3n
micellar cubic phases (CubI) occurring in thermotropic systems formed by spheroidic aggregates
with soft corona.28 Hence, it is highly reasonable to illustrate that the LC phases of the compound
I3/12 and I3/14 represent
micellar cubic phases. This is in line with the position of these
Pm3n
cubic phases in the quence SmC–Colhex–CubI as observed upon increasing the number and length
of the aliphatic chains. By calculation, each micelle is built up of approximately 28 and 27
molecules in the
cubic phase of I3/12 and I3/14 respectively (Table 2 and Table S6†). The
Pm3n
πꢀconjugated azobenzeneꢀthiadiazole moieties occupy the core encapsulated by the alkyl chain
moieties in the micelles (Fig. 2b). By comparison with the reported azo free hexacatenar
analogues T3/n 7
, which can display only columnar phases (Fig. 3), the incorporation of
azobenzene unit into the thiadiazol contained rigid cores of polycatenar compounds, enhanced the
formation of CubI phase. The large volume of the flexible chain and the extended twistꢀbend

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azobenzene core should enhance the nanosegregation between the flexible tails and the extended
rigid cores and give rise to a large interface curvature, thus contribute to the emergence of the
cubic phase. The extended twistꢀbend azobenzene core and possible transꢀcis transformation of
central azobenzene unit could contribute to the formation of the softness of these spheres in cubic
phase, and this is favorable for the organization in a
lattice instead of other cubic phases.
Pm3n
T
= 65 o
C
(210)
b)
a)
(211)
2
q
I
(200)
1
2
3
4
q ( )
nm-1
Fig. 2 (a) SAXS diffractograms of compound I3/14; (b) possible molecular organization in
micellar cubic
Pm3n
phase.
Fig. 3 Bar graph summarizing the thermal behavior of researched compounds I3/n and the reported compounds T
3/n7.
Table 2 Comparison of Xꢀray data and molecular dimensions of the columnar and cubic phases[a]
Phase, Plane/space
group
L [nm]
a[nm] (T[°C] )
n
Comp.
oꢀI2/8
oꢀI2/12
oꢀI2/14
I3/12
Colhex/p6mm
Colhex/p6mm
Colhex/p6mm
5.82
6.32
6.58
4.80 (100)
5.28 (90)
5.20 (105)
4.8
5.2
4.7
Cub /
Pm3n
I
6.32
6.58
8.46 (70)
8.65 (65)
28
27
I3/14
Cub /
Pm3n
I
[a] Abbreviations: a = lattice parameter determined by XRD (ahex and acub, respectively); L = molecular length of a
molecule measured between the ends of the terminal chains and assuming a most stretched conformation with
allꢀtrans conformation of the alkyl chains; n = number of molecules in the cross section of a column in the Colhex
phases (with assumed height of 0.45 nm) or number of molecules in each aggregate of the CubI/ Pm3n lattice. For
Colhex phase: n = (a2/2) h(N /M)ρ, N = Avogadro constant, M = molecular mass, assuming a density of ρ = 1
3
A
A

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g/cm3; for CubI/ Pm3n phase: n = ncell/8.
In all cases shearing the samples led to flow which removes the textures, this confirms the LC
states of these materials. With increasing the number of alkyl chains, namely increasing the
fraction of the alkyl chains, the interface curvature between the nanosegregated regions of the
azobenzeneꢀthiadiazole cores and the flexible chains should be increased. This structural variation
gives rise to the transition from the SmC through hexagonal columnar (Colhex) to cubic
(Cub /
) LC phases, which is similar to the mesomorphism of amphiphiles and block
Pm3n
I
molecules.29
2.3. Photoisomerization behavior in liquid crystalline and solution
The effect of transꢀtoꢀcis photoisomerization caused by the UV irradiation on the thermotropic LC
phases of these compounds was investigated. All the liquid crystalline phases can respond to the
UV irradiation immediately by changing their textures to isotropic state and recoverying to their
LC textures after removing the UV source. This means that all the compounds showed trans to
cis photoisomerization under UV irradiation and cis to trans thermal isomerization under visible
light irradiation. For example, sample I1/14 was cooled from the isotropic liquid state to 145 °C in
the range of the SmC phase (Fig. 4a). After annealing for 5 minutes, the sample was exposed to
UV irradiation at 365 nm (10 mW cmꢀ2) for 1 second, the schlieren texture of the SmC phase is
disappeared and replaced by isotropic one (Fig 4aꢀb). After removal of the UV lamp, the schlieren
texture of the SmC phase renewed (Fig. 4bꢀc). It seems that the transꢀtoꢀcis photoisomerization
effect on the liquid crystalline property of the compounds reported here is very strong. Schematic
illustration of the photochemical switching possible process of SmC–Iso reversible transition of
I1/14 is shown in Fig. 5. Similarly, the compound oꢀI2/14 showed photoisomerization reversible
transition of Col–Iso (Fig. S5†). Such photoisomerizations could be useful for light sensitive
displays or data storage applications.19a,30
a)
b)
c)
Fig. 4 Textural changes as observed by POM at the photoinduced SmCꢀIso transition and the relaxation IsoꢀSmC
as observed for compound I1/14 at 145 °C: (a) before UV irradiation; (b) after UV irradiation for 1 s; (c) after
visible light irradiation for 1 s.

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Fig. 5 Schematic illustration of the photochemical switching possible process in I1/14; (a) SmC phase; (b)
SmC–Iso transition; (c) isotropic phase.
Such compounds exhibit the expected reversible transꢀtoꢀcis photoresponsive behavior in
solution (Fig. S6ꢀ8†).
2.4. Absorption and emission properties
1.2
1.0
0.8
0.6
0.4
0.2
1.2
1.0
0.8
0.6
0.4
0.2
I
1/14
2/14
3/10
1/14
2/14
3/10
o-I
I
I
o-I
I
300
350
400
450
500
550
Wavelength / nm
Fig. 6 Normalized absorption (solid line) and emission spectra (dotted line) in THF solution obtained for I1/14,
oꢀI2/14 and I3/10.
The UVꢀvis absorption and fluorescence spectroscopic data of the chosen representative
, ,
compounds I1/14 oꢀI2/14 I3/10 in THF solution (c = 10ꢀ6 mol Lꢀ1) are shown in Fig. 6. These
compounds show the maximum absorption peak at about 355 nm and maximum emission peak
range of 440ꢀ450 nm in THF solution which may be attributed to the πꢀπ* transition. It is surprised
, ,
to see that compounds I1/14 oꢀI2/14 I3/10 have a large Stokes shift of 101 nm, 100 nm and 103
nm, respectively. Compared to their polycatenar analogue T 3/10 (absorption maximum at 365
nm),7 compounds I3/10 shows hypsochromic shift for 10 nm in the absorption maximum (355 nm)
(Table S7†), indicating that the enhanced molecular transmittance (i.e. blueꢀshift of λmax) is mainly
due to the azobenzene conjugate bridge structures in chromophores.31,32 The UV–vis absorption
spectrum of compound I3/14 in the solid state exhibits a blueꢀshifted absorption with maximum at
352 nm, while its solution displays a structured absorption with a maximum at 363 nm. The
blueꢀshifted in solid state suggests the formation of πꢀstacked aggregates with a Hꢀtype parallel
stacking mode in the solid state (Fig. S9†).33
The energy band gap of compound I3/14, which was estimated from the onset of the

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absorption in film, is about 2.5 eV (Fig. S10†).34 In order to investigate the conformation and
electron distributions of I1/14 oꢀI2/14 I3/10, calculations based on density functional theory (DFT)
with the Gaussian 03 W program package at B3LYP/(6ꢀ31G, d) level were performed with the
model compounds I1/14 oꢀI2/14 I3/10. The electron distributions of the HOMO and LUMO of
,
,
,
,
I1/14
I1/14
,
,
oꢀI2/14
oꢀI2/14
,
I3/10 are shown in Fig. S11†. In the minimum energy conformation, compounds
I3/10 adopt almost a bar shaped conformation with kinks provided by the
,
azobenzene groups, linking the peripheral phenyl groups to the 1,3,4ꢀthiadiazole. As it can be seen
in the HOMO orbital, the electrons are localized on the thiadiazole unit of the centralꢀconjugated
azobenzene core. In the LUMO orbital, the electrons are mainly localized on the
azobenzeneꢀthiadiazole unit, indicating that intramolecular charge transfer (ICT) might exist in
these molecules. The bandꢀgap of the HOMO and LUMO energy levels of I3/14 (Fig. S11†)was
almost in agreement with those obtained from their absorption spectra in film.
2.5. Gelation properties
Among the synthesized polycatenar compounds Im/n, only hexacatenar compounds I3/n have
the gelation abilities. The gelation ability of the representive compound I3/10 was tested in various
organic solvents at a concentration of 6.0 mg/mL and the results are summarized in Table 3. I3/10
has the ability to gel in ethanol. A yellow gel can be obtained by cooling the heated solution of
I3/10 in ethanol quickly below 20 ºC or slowly down to room temperature (Fig. 7c). So far as we
known, there is no report about the gelation behavior of thiadiazole contained polycatenar
compounds.7 Our study has shown that the incorporation of azobenzene with thiadiazole
heterocycle induced the formation of luminescent gel of compound I3/10. π–π Interactions as well
as van der Waals forces may play an important role for the aggregation of the compounds in
solvents as exist in many azobenzene based gelators.35 Under irradiation with 365 nm light the
luminescent gel can be obtained (Fig. 7d). The organogels exhibit multiple stimuliꢀresponsive
behavior namely gel–sol reversible trans process upon exposure to a number of environmental
stimuli including light, temperature, and shear, etc (Fig. 8). Irradiation with UV light, application
of heat or shear resulted in a sol state through disruption of the nonꢀcovalent interactions between
the molecules, the gel state can be recovered by the removal of such stimuli. Such multiple
stimuliꢀresponsive behaviors could be useful for drug controlled release,36 energy transfer,37
hardeners of solvents and sensors etc.38 In order to obtain a visual insight into the morphologies
of the molecular aggregation model, the gel was investigated by scanning electron microscopy
(SEM). The SEM image of the xerogel formed by I3/10 (Fig. S12†) shows the formation of
threeꢀdimensional networks composed of entangled fibrous aggregates. The approximate diameter
of the fibers is 80ꢀ90 nm. The length is more than 25 ꢁm. On the basis of this result, it is assumed
that compound I3/10 forms fibrous aggregate in the solvent.
b)
a)
c)
d)

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Fig. 7 Photograph of solution and gels prepared with I3/10 in ethanol, 10ꢀ6 M, T = 20 °C. (a) without irradiation; (b)
under irradiation with 365 nm light; (c) without irradiation and (d) under irradiation with 365 nm light.
Table 3 Gelation properties of I3/10 [a]
Solvent
CHCl3
I
S
Solvent
CH2Cl2
I
S
S
G
S
S
S
Ethyl acetate
Hexane
S
Cyclohexane
Ethanol
P
Methanol
Acetone
DMF
PG
P
nꢀButanol
Toluene
THF
P
[a] S = solution, P = precipitation, G = gelation, PG = partial gelation, gels formed at room temperature (20 ºC).
Heating
Cooling
VisꢀLight
UVꢀLight
ThermoꢀResponsive
LightꢀResponsive
Rest
Shaking
MechanoꢀResponsive
Fig. 8 Multistimuli responsive organogels formed by compound I3/10 in ethanol (6.0 mg/mL).
2.6. Chemosensor behavior
2500
Blabk
Ag+
70
a)
b)
Cd2+
Co2+
Cr3+
Cs+
2000
1500
1000
500
0
60
50
40
30
20
10
0
Cu2+
Fe3+
Hg2+
Li+
Mg2+
Na+
Ni+
Pb2+
Zn2+
375 400 425 450 475 500 525 550 575 600
λ/nm
c)
Ag+ Cd2+ Co3+ Cr3+ Fe3+ Hg2+ Li+ Na+ Cu2+ Cs+ Pb2+ Zn2+ Mg2+ Ni+

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ꢀ
Fig. 9 Fluorescence spectra of compound oꢀI2/14 (10ꢀ6 M) at room temperature, all anions are ClO4 , at pH = 7.0. (a,
b) CH2Cl2 : CH3CN = 2 : 1 (λex = 352 nm); (F0ꢀF)/F0×100 depicts the cation selective fluorescence quenching
efficiency of compound oꢀI2/14 namely the fluorescence responses of different metal ions; abbreviation: F0 = the
fluorescence emission maximum of blank sample; F = the fluorescence emission maximum of samples with
addition of different metal ions; (c) the samples with addition of different metal ions, under irradiation with 365
nm light.
4000
blank
500000
400000
300000
200000
100000
0.5eq
1.0eq
1.5eq
2.0eq
2.5eq
3.0eq
3.5eq
4.0eq
6.0eq
12.0eq
40.0eq
3500
3000
2500
2000
1500
1000
500
a
）
b
）
400
450
500
550
0
1
2
3
4
5
6
7
2
[Cu2+] / [
O-I /14]
λ
/nm
Fig. 10 (a, b) Fluorescence spectra of compound o-I2/14 (1×10ꢀ5 M) at 20 °C upon addition of Cu2+ (from 0.5 to
40.0 equiv) in CH2Cl2 : CH3CN = 2 : 1 (λex = 360 nm).
To get insights into the binding properties of compounds Im/n toward metal ions, the
selectivity of compounds Im/n for metal ions was examined by monitoring the change of
fluorescence intensity upon the addition of various metal ions, including Ag+, Cd2+, Cr3+, Fe3+,
Hg2+, Li+, Na+, Cu2+, Cs+, Pb2+, Zn2+, Mg2+, Ni+, Co3+, the concentration of all metal ions is 10ꢀ3
mol Lꢀ1. Compounds Im/n all showed good selectivity for Cu2+. The result of the representative
compound oꢀI2/14 is shown in Fig. 9. It was found that the fluorescence intensity of the compound
oꢀI2/14 changed little in the presence of most metal ions examined, except Cu2+. The obvious
fluorescence quenching was observed upon only increasing addition of Cu2+. As is evident from
Fig. 9aꢀc, indicating that oꢀI2/14 has a high and single selectivity, and can serve as a potential
chemosensor for detection of Cu2+ in CH2Cl2 : CH3CN. Till now there are only few reports on
1,3,4ꢀthiadiazole derivatives serving as a potential chemosensor for detection of Cu2+ by
“nakedꢀeye”.39,40
For the selective response of oꢀI2/14 to Cu2+, spectral titration was performed in solution of
CH2Cl2 : CH3CN = 2 : 1; with the addition of Cu2+ (from 0.5 to 40 equiv), the emission peak at
452 nm decreased gradually and finally reached its fluorescence quenching plateau at ~ 6 equiv
(Fig. 10aꢀb).41 Therefore, compound oꢀI2/14 could be used as chemosensor exhibiting strong and
selective binding to Cu2+ in the solution of CH2Cl2 : CH3CN = 2 : 1. Cu2+ is a significant
environmental pollutant due to its widespread use. The development of chemosensors for the
detection and monitoring of Cu2+, with high sensitivity, low detection limit and quick response, is
in a great demand.42
3. Conclusion
Series of polycatenar liquid crystals containing two 1,3,4ꢀthiadiazole rings interconnected by an
azobenzene central link have been synthesized. The incorporation of azobenzene with thiadiazole
into the rigid core produced a new kind of photoresponsive and fluorescence polycatenar liquid

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crystals. With increasing the number and length of the terminal alkyl chains, not only smectic C
phase and hexagonal columnar phase, but also micellar cubic (Cub / ) phase are found in
Pm3n
I
these compounds. The formation of the micellar cubic phase is due to the larger interface
curvature between the flexible chains and rigid core. The extended twist bent azobenzene core is
flexible in some degree and lead to the formation of
cubic phase instead of other cubic
Pm3n
structures. The reversible photoresponsive behavior of these compounds in liquid crystalline,
solution states and gel states were well demonstrated. They also exhibit a lower band gap offering
great potential in organic light emitting diode applications and shows fluorescent emission with
large Stokes shift in solution and have binding selectivity to Cu2+ among a series of cations in
CH3CNꢀCH2Cl2 solution. Such multifunctional materials should have great potentials in displays,
photochemical molecular switches, chemosensor etc.
Experimental
The detailed synthetic procedures, purification of the compounds together with the analytical data
are reported in the Supporting Information. Tetrahydrofuran (THF) was distilled from sodium
prior to use. Toluene and triethylamine was distilled from calcium hydride prior to use.
1
Commercially available chemicals were used as received. H NMR and 13C NMR spectra were
recorded in CDCl3 solution on a Bruker–DRXꢀ400 spectrometer with tetramethylsilane (TMS) as
the internal standard. Elemental analysis was performed using an Elemental VARIO EL elemental
analyzer. Column chromatography was performed with silica gel 60 (230ꢀ400 mesh) from Merck.
A Mettler heating stage (FP 82 HT) was used for polarizing optical microscopy (POM, Optiphot 2,
Nikon) and DSC were recorded with a DSC 200 F3 Maia calorimeter (NETZSCH) at 5 K minꢀ1.
UVꢀvis absorption spectra were recorded on a UVꢀ240 UV–visible spectrophotometer (Shimadzu,
Japan). Fluorescence spectra were recorded using a Hitachi Fꢀ7000 fluorescence spectrometer
(Hitachi, Japan). SEM experiments were carried out on a QUNT200 scanning electron microscopy
(SEM, USA). All pictures were taken digitally. For the sample preparation, the gel was placed on
an aluminium foil for some time until the gel became dry gel. Then gold plating, finally put the
sample into the scanning electron microscopy for observation.
The smallꢀangle Xꢀray diffraction measurements were also performed in transmission mode with
synchrotron radiation at the 1W2A SAXS beam line at Beijing Accelerator Laboratory and
Shanghai Synchrotron Radiation Facility.
Acknowledgements
This work was supported by the National Natural Science Foundation of China [no. 21364017, no.
21274119, 21274132], the Yunnan Natural Science Foundation [no. 2013FA007] and Yunnan
Provincial Department of Education Foundation [no. ZD2015001] and Yunnan University
Graduate Research and Innovation Foundation Project (no. YNUY201682). The calculations were
performed with the support of the Yunnan University Supercomputer Center.
References
1
(a) V. V. Titov and A. I. Pavlyuchenko, Chem. Heterocycl. Compd., 1980, 16, 1–13; (b) M. P. Aldred, P.
Vlachos, D. Dong, S. P. Kitney, W. C. Tsoi, M. O. Neill and S. M. Kelly, Liq. Cryst., 2005, 32, 951–965; (c)
A. Seed, Chem. Soc. Rev., 2007, 36, 2046–2069; (d) B. Roy, N. De and K. C. Majumdar, Chem. Eur. J., 2012,

Page 13 of 16
New Journal of Chemistry
View Article Online
DOI: 10.1039/C6NJ02604D
18, 14560–14588; (e) J. Han, J. Mater. Chem. C., 2013, 1, 7779–7797.
2
3
Y. Hu, C.Y. Li, X. M. Wang, Y. H. Yang and H. L. Zhu, Chem. Rev., 2014, 114, 5572–5610.
(a) M. Parra, S. Hernandez, J. Alderete and C. Zuniga, Liq. Cryst., 2000, 27, 995–1000; (b) Y. Xu, W. Lu and
Z. Tai, Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A, 2000, 350, 151–159; (c) A. A. Kiryanov, P. Sampson and
A. J. Seed, J. Org. Chem., 2001, 66, 7925–7929; (d) M. W. Schroder, S. Diele, G. Pelzl, N. Pancenko and W.
Weissflog, Liq. Cryst., 2002, 29, 1039–1046; (e) M. Parra, J. Alderete and C. Zuniga, Liq. Cryst., 2004, 31,
1531–1537; (f) M. Parra, J. Vergara, P. Hidalgo, J. Barbera and T. Sierra, Liq. Cryst., 2006, 33, 739–745; (g)
B. P. Sybo, A. Bradley, S. Grubb, K. Miller, J. W. Proctor, L. Clowes, M. R. Lawrie, P. Sampson and A. J.
Seed, J. Mater. Chem., 2007, 17, 3406–3411; (h) M. Parra, S. Villouta, V. Vera, J. Belmar, C. Zuniga and H. Z.
Zunza, Z. Naturforsch., B: J. Chem. Sci., 1997, 52, 1533–1538; (i) J. Han, X. Y. Chang, L. R. Zhu, Y. M.
Wang, J. B. Meng, S. W. Lai and S. S. Y. Chui, Liq. Cryst., 2008, 35, 1379–1394; (j) J. H. Tomma, I. H.
Rou’il and A. H. AlꢀDujaili, Mol. Cryst. Liq. Cryst., 2009, 501, 3–19; (k) M. C. McCairn, T. Kreouzis and M.
L. Turner, J. Mater. Chem., 2010, 20, 1999–2006; (l) A. K. Prajapati and V. Modi, Liq. Cryst., 2011, 38,
191–199; (m) Q. Song, D. Nonnenmacher, F. Giesselmann and R. P. Lemieux, J. Mater. Chem. C, 2012, 1,
343–350; (n) P. Tuzimoto, D. M. P. O. Santos, T. D. S. Moreira, R. Cristiano, I. H. Bechtold and H. Gallardo,
Liq. Cryst., 2014, 41, 1097–1108; (o) R. C. Tandel and N. K. Patel, Liq. Cryst., 2014, 41, 495–502.
(a) M. Lehmann, J. Seltmann, A. Auer, E. Prochnow and U. Benedikt, J. Mater. Chem., 2009, 19, 1978–1988;
(b) M. Lehmann and J. Seltmann, Beilstein J. Org. Chem., 2009, 5, 73.
4
5
6
7
M. L. Parra, E. Y. Elgueta, J. A. Ulloa, J. M. Vergara and A. I. Sanchez, Liq. Cryst., 2012, 39, 917–925.
C. F. He, G. J. Richards, S. M. Kelly, A. E. A. Contoret and M. O’Neill, Liq. Cryst., 2007, 34, 1249–1267.
S. K. Pathak, S. Nath, R. K. Gupta, D. S. S. Rao, S. K. Prasad and A. S. Achalkumar, J. Mater. Chem. C.,
2015, 3, 8166–8182.
8
9
K. T. Lin, H. M. Kuo, H. S. Sheu and C. K. Lai, Tetrahedron., 2013, 69, 9045–9055.
(a) K. S. Mustafa, K. S. AlꢀMalki, A. S. Hameed and A. H. AlꢀDujaili, Mol. Cryst. Liq. Cryst., 2014, 593,
34–42; (b) F. A. Olate, J. A. Ulloa, J. M. Vergara, S. A. Sánchez, J. Barberá and M. L. Parr, Liq. Cryst., 2014,
43, 811–827; (c) S. K. Pathak, R. K. Gupta, S. Nath, D. S. Shankar Rao, S. K. Prasad and A. S. Achalkumar, J.
Mater. Chem. C., 2015, 3, 2940–2952.
10 (a) M. Sato, Macromol. Rapid Commun., 1999, 20, 77–80; (b) M. Sato and Y. Uemoto, Macromol. Rapid
Commun., 2000, 21, 1220–1225; (c) M. Sato, M. Notsu, S. Nakashima and Y. Uemoto, Macromol. Rapid
Commun., 2001, 22, 681–686; (d) M. Sato, M. Mizoi and Y. Uemoto, Macromol. Chem. Phys., 2001, 202,
3634–3641; (e) M. Sato, S. Nakashima and Y. Uemoto, J. Polym. Sci., Part A: Polym. Chem., 2003, 41,
2676–2687; (f) N. S. AlꢀMuaikel, Polym. Int., 2004, 53, 301–306; (g) M. Sato, Y. Tada, S. Nakashima, K.ꢀI.
Ishikura, M. Handa and K. Kasuga, J. Polym. Sci., Part A: Polym. Chem., 2005, 43, 1511–1525; (h) M. Sato,
Y. Matsuoka and I. Yamaguchi, Liq. Cryst., 2012, 39, 1071–1081.
11 (a) T. Ube and T. Ikeda, Angew. Chem., Int. Ed., 2014, 53, 10290–10299; (b) H. M. D. Bandarab and S. C.
Burdette, Chem. Soc. Rev., 2012, 41, 1809–1825; (c) J. H. Sung, S. Hirano, O. Tsutsumi, A. Kanazawa, T.
Shiono and T. Ikeda, Chem. Mater., 2002, 14, 385–391.
12 (a) T. Ikeda, J. Mamiya and Y. Yu, Angew. Chem., Int. Ed., 2007, 46, 506–528; (b) E. V. Fleischmann and R.
Zentel, Angew. Chem., Int. Ed., 2013, 52, 8810–8827; (c) Y. Yu, M. Nakano and T. Ikeda, Nature, 2003, 425,
145; (d) Y. Yu, M. Nakano, A. Shishido, T. Shishido and T. Ikeda, Chem. Mater., 2004, 16, 1637–1643; (e)
M. Kondo, Y. Yu and T. Ikeda, Angew. Chem., Int. Ed., 2006, 45, 1378–1382; (f) Y. Yu, T. Maeda, J.
Mamiya and T. Ikeda, Angew. Chem., Int. Ed., 2007, 46, 881–883; (g) Y. Zhang, J. Xu, F. Cheng, R. Yin, C.
C. Yen and Y. Yu, J. Mater. Chem., 2010, 20, 7123–7130.
13 (a) T. Ikeda, T. Sasaki and K. Ichimura, Nature, 1993, 361, 428–430; (b) T. Sasaki, T. Ikeda and K. Ichimura,

New Journal of Chemistry
Page 14 of 16
View Article Online
DOI: 10.1039/C6NJ02604D
J. Am. Chem. Soc., 1994, 116, 625–628; (c) H. J. Coles, H. G. Walton, D. Guillon and G. Poetti, Liq. Cryst.,
1993, 15, 551–558; (d) A. Langhoff and F. Giesselmann, Ferroelectrics, 2000, 244, 283–293.
14 N. G. Nagaveni, M. Gupta, A. Roy and V. Prasad, J. Mater. Chem., 2010, 20, 9089–9099.
15 M. L. Rahman, C. Tschierske, M. Yusoff and S. Silong, Tetrahedron Lett., 2005, 46, 2303–2306.
16 H. Adachi, Y. Hirai, T. Ikeda, M. Maeda, R. Hori, S. Kutsumizu and T. Haino, Org. Lett., 2016, 18, 924–927.
17 S. Yagai, M. Yamauchi, A. Kobayashi, T. Karatsu, A. Kitamura, T. Ohba and Y. Kikkawa, J. Am. Chem.
Soc., 2012, 134, 18205−18208.
18 (a) S. Yagai, T. Nakajima, K. Kishikawa, S. Kohmoto, T. Karatsu and A. Kitamura, J. Am. Chem. Soc., 2005,
127, 11134–11139; (b) M. Alaasar, Liq. Cryst., 2016, 43, 1–36.
19 (a) E. Westphal, I. H. Bechtold and H. Gallardo, Macromolecules., 2010, 43, 1319–1328; (b) M. Cigl, A.
Bubnov, M. Kašpar, F. Hampl, V. Hamplová, O. Pacherová and J. Svoboda, J. Mater. Chem. C., 2016, 4,
5326–5333; (c) N. G. Nagaveni, P. Raghuvanshi, A. Roy and V. Prasad, Liq. Cryst., 2013, 40, 1238–1254.
20 H. Rau, Angew. Chem., Int. Ed., 1973, 12, 224ꢀ235.
21 (a) J. C. Tang, R. Huang, H. F. Gao, X. H. Cheng, M. Prehm and C. Tschierske, RSC Adv., 2012, 2,
2842–2847; (b) X. Y. Yang, H. Dai, Q. Y. He, J. C. Tang, X. H. Cheng, M. Prehm and C. Tschierske, Liq.
Cryst., 2013, 40, 1028–1034.
22 K. Dimitrowa, J. Hauschild, H. Zaschke and H. Schubert, J. Prakt. Chem., 1980, 322, 933–944
.
23 L. H. He, G. M. Wang, Q. Tang, X. K. Fu and C. B. Gong, J. Mater. Chem. C., 2014, 2, 8162–8169.
24 I. Dierking, Textures of Liquid Crystals., WileyꢀVCH, Weinheim, 2003.
25
(a)
E.
Girotto,
I.
H.
Bechtold
and
H.
Gallardo,
Liquid
Crystals.,(2016)
DOI:10.1080/02678292.2016.1201159; (b) S. Q. Qu, X. F. Chen, X. Shao, F. Li, H. Y Zhang, H. Wang, P.
Zhang, Z. X Yu, K. Wu, Y. Wang and M. Li, J. Mater. Chem., 2008, 18, 3954–3964.
26 (a) H. T. Nguyen, C. Destrade and J. Malthête, Adv. Mater., 1997, 9, 375–378; (b) D. Fazio, C. Mongin, B.
Donnio, Y. Galerne, D. Guillon and D. W. Bruce, J. Mater. Chem., 2001, 11, 2852–2863
.
27 M. Gharbia, A. Gharbi, H. T. Nguyen and J. Malthete, Current Opinion in Colloid and Interface Science.,
2002, 7, 312–325.
28 (a) G. Ungar and X. Zeng, Soft Mater. 2005, 1, 95–106; (b) P. Ziherl and R. D. Kamien, J. Phys. Chem. B.,
2001, 105, 10147–10158.
29 (a) Handbook of Liquid Crystals (Eds: D. Demus, J. W. Goodby, G. W. Gray, H.ꢀW. Spiess and V. Vill),
WileyꢀVCH, Weinheim, 1998; (b) C. Tschierske, J. Mater. Chem., 2001, 11, 2647–2671.
30 X. P. Tan, Z. Li , M. Xia and X. H. Cheng, RSC Adv., 2016, 6, 20021–20026.
31 X. Tang, L. Pan, K. Jia and X. Z. Tang, Chem. Phys. Lett., 2016, 648,114–118.
32 X. Tang, K. Jia, X. Z. Tang, L. Chen and L. Pan, J. Mater. Sci., 2016, 27, 7174–7182.
33 (a) T. Yasuda, K. Kishimoto and T. Kato, Chem. Comm., 2006, 32, 3399–3401; (b) F. Würthner, C.
Thalacker, S. Diele and C. Tschierske, Chem. Eur. J., 2001, 7, 2245ꢀ2253.
34 R. S. Dariani and R. Zafari, J. Optoelectron. Adv. Mater., 2014, 16, 1351–1355.
35 S. S. Babu, V. K. Praveen and A. Ajayaghosh, Chem. Rev., 2014, 114, 1973−2129.
36 A. Friggeri, B. L. Feringa and J. van Esch, J. Controlled Release., 2004, 97, 241–248.
37 V. K. Praveen, S. J. George, R. Varghese, C. Vijayakumar and A. Ajayaghosh, J. Am. Chem. Soc., 2006, 128,
7542–7550.
38 R. M. Yang, S. H. Peng and T. C. Hughes, Sofe Matter, 2014, 10, 2188–2196.
39 G. R. You, G. J. Park, J. J. Lee and C. Kim, Dalton Trans., 2015, 44, 9120–9129.
40 K. R. Bandi, A. K. Singh and A. Upadhyay, Mater. Sci. Eng. C., 2014, 34, 149–157.
41 X. P. He, Z. Song, Z. Z. Wang, X. X. Shi, K. Chen and G. R. Chen, Tetrahedron, 2011, 67, 3343–3347.

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DOI: 10.1039/C6NJ02604D
42 R. Krämer, Angew. Chem., Int. Ed., 1998, 37, 772–773.

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Graphical Abstract
Synthesis and self-assembly of photoresponsive and luminescent polycatenar liquid crystals
incorporating an azobenzene unit interconnecting two 1,3,4- thiadiazoles
Xiongwei Peng, Hongfei Gao, Yulong Xiao, Huifang Cheng, Fanran Huang, Xiaohong Cheng*
Key Laboratory of Medicinal Chemistry for Natural Resources, Chemistry department, Yunnan University,
Kunming 650091, P. R. China
Target compounds can selfassemble into thermotropic LC phase sequence of SmC-Colhex-CubI,
and have binding selectivity to Cu2+
.