Photoluminescence intensity and polarization modulation of a light emitting liquid crystal via reversible isomerization of an α-cyanostilbenic derivative

Article abstract of DOI:10.1016/j.dyepig.2016.01.024

We found reversible photo/thermal isomerization of the α-cyanostilbenic derivative (Z)-2-(4-aminophenyl)-3-(4-(dodecyloxy)phenyl)-acrylonitrile, (Z)-CN-APHP, which is accompanied by a large decrease in compatibility when mixed with a nematic liquid crysta

Full text of DOI:10.1016/j.dyepig.2016.01.024

Accepted Manuscript
Photoluminescence intensity and polarization modulation of a light emitting liquid
crystal via reversible isomerization of an α-cyanostilbenic derivative
Hongbo Lu, Shaojun Wu, Chao Zhang, Longzhen Qiu, Xianghua Wang, Guobing
Zhang, Juntao Hu, Jiaxiang Yang
PII:
S0143-7208(16)00035-8
10.1016/j.dyepig.2016.01.024
DYPI 5077
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 27 July 2015
Revised Date: 14 December 2015
Accepted Date: 11 January 2016
Please cite this article as: Lu H, Wu S, Zhang C, Qiu L, Wang X, Zhang G, Hu J, Yang J,
Photoluminescence intensity and polarization modulation of a light emitting liquid crystal via
reversible isomerization of an α-cyanostilbenic derivative, Dyes and Pigments (2016), doi: 10.1016/
j.dyepig.2016.01.024.
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1
Photoluminescence intensity and polarization modulation of a light
emitting liquid crystal via reversible isomerization of an
α-cyanostilbenic derivative
Hongbo Lu1,2,* Shaojun Wu1,2 Chao Zhang1 Longzhen Qiu1 Xianghua Wang1
Guobing Zhang1 Juntao Hu1 Jiaxiang Yang3
1 Key Lab of Special Display Technology, Ministry of Education, National Engineering Lab of
Special Display Technology, State Key Lab of Advanced Display Technology, Academy of
Opto-Electronic Technology, Hefei University of Technology, Hefei, 230009, People’s Republic of
China.
2 Key Laboratory of Advanced Functional Materials and Devices, Anhui Province, School of
Chemistry and Chemical Engineering, Hefei University of Technology, Hefei, Anhui 230009,
People’s Republic of China.
3 College of Chemistry and Chemical Engineering, Anhui University, Hefei, 230601, People’s
Republic of China.
*Corresponding author. Tel:+8613855174354; E-mail address: bozhilu@hfut.edu.cn
Abstract
We found reversible photo/thermal isomerization of the α-cyanostilbenic derivative
(Z)-2-(4-aminophenyl)-3-(4-(dodecyloxy)phenyl)-acrylonitrile,
(Z)-CN-APHP,
which
is
accompanied by a large decrease in compatibility when mixed with a nematic liquid crystal.
Moreover, a novel optical switch using a CN-APHP doped liquid crystal that emits partially
linearly polarized light is investigated. By controlling the trans-cis isomerization of CN-APHP, it
is possibly to modulate not only photoluminescence intensity but also its polarization. This could
open possibilities to design improved optical devices.

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1. Introduction
Liquid crystal displays (LCDs) evolved rapidly over the past decades and are currently
dominating the flat panel display industry [1,2] due to their advantages such as light weight,
thinness and lower power consumption. However, the liquid crystals (LCs) in the displays do not
emit light themselves [3] directly and they require an extra light source such as a backlight [4,5],
which leads to energy consumption. The emitted light from the conventional backlight is usually
unpolarized [2] and correspondingly LCDs require polarizers, which can change the unpolarized
light into linearly or circularly polarized light [6]. The dichroic sheet polarizers used in LCDs
convert a major fraction of incident light into unwanted thermal energy, which limits the
brightness, and energy efficiency of devices with this technology.
Therefore, The polarized light source has great potential to improve the LCD performance.
By intrinsically emitting polarized light, polarizing sheets would become unnecessary and also the
power consumption could be reduced. Polarized electro- or photo-luminescent light sources have
been intensively studied [7,11]. Dyreklev et al. demonstrated that an organic electro-luminescence
(EL) device emitted polarized light based on aligned conjugated polymers [12]. Sariciftci et al.
reported that linearly polarized photoluminescence (PL) can be emitted from nematic liquid
crystals doped with photoluminescent dyes [13]. Chen et al. reported that a cholesteric liquid
crystal film doped with fluorescent materials can emit circularly polarized PL [14]. Actually, the
emitted light from a single fluorescent molecule is usually polarized, but the light from a
macroscopic EL or PL is unpolarized due to disordered molecular distribution. Hence,
polarization can be controlled by manipulating the orientation of the fluorescent molecules.
Recently, SH Joo et al. were able to selectively produce linearly polarized light, circularly

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polarized light, unpolarized light and partially polarized light from a single photoluminescent
cholesteric liquid crystal cell by controlling the molecular orientation electrically [15]. Such a
light source with tunable polarization could be useful in many optical devices such as displays or
polarization-dependent communication devices [16,17].
Currently, a common problem encountered with dye/LC mixtures is the poor solubility of the
organic dye in the liquid crystal. In addition, if the concentration of the dye is too high, the
luminescence is affected by aggregation-caused quenching (ACQ). Fortunately,
aggregation-induced emission (AIE) was discovered in both silole derivatives [18] and
α-cyanostilbenic derivatives [19]. AIE is the exact opposite of ACQ: the luminophors are highly
emissive after aggregate formation because intramolecular motion (RIM) is restricted. In order to
improve solubility and overcome the typical quenching effect at higher concentration these
AIE-active luminescent liquid crystals (LLCs) can be used. LLCs can emit linear or circular
polarized light when aligned [3], and have been widely used in information storage devices,
polarized organic lasers, anisotropic light-emitting diodes, and one-dimensional semiconductors
[20,24].
Motivated by the AIE effect, various new α-cyanostilbenic derivatives have been synthesized
[25,26]. Like in ordinary stilbene and azobenzene molecules, the Z-E isomerization process is
accompanied by a strong decrease in structural compatibility with a liquid crystal. In this paper, a
new optical switch based on AIE-active luminescent liquid crystals was developed. We find that
the fluorescence is partially linearly polarized and the degree of polarization can be continuously
controlled via conformational changes of the luminescent liquid crystal. The possibility of
photochemical patterning or image recording using these materials has also been demonstrated.

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2. Experiment
General Methods
All chemicals were purchased from Sigma Aldrich and used without further purification. The
1
synthetic route for (Z)-CN-APHP is described in the supporting information. H NMR spectra
were recorded on an Agilent VNMRS600 (600 MHz) spectrometer. UV-vis absorption spectra
were recorded with a Shimadzu UV2550 PC spectrometer using samples in solutions. PL spectra
were recorded with a HORIBA FluoroMax-4 spectrofluorometer using samples in both solution
and a liquid crystal cell. The absolute photoluminescence quantum yields of solid samples were
measured with a HORIBA FluoroMax-4 spectrofluorometer with an integrating sphere (HORIBA
Scientific, F-3092 integrating sphere). Differential scanning calorimetry (DSC) was performed on
a METTLER 82le/400 DSC at a heating and cooling rate of 5 °C min−1. Polarizing optical
microscopy was carried out with an E600POL polarizing optical microscope (Nikon, Tokyo, Japan)
equipped with a DS-5M CCD camera (Nikon) connected to a DS-L1 control unit (Nikon).
Synthesis of (Z)-2-(4-aminophenyl)-3-(4-hydroxyphenyl)acrylonitrile
This compound was synthesized according to the method described in the literature [27].
Synthesis of (Z)-2-(4-aminophenyl)-3-(4-(dodecyloxy)phenyl)-acrylonitrile ((Z)-CN-APHP)
(Z)-2-(4-aminophenyl)-3-(4-hydroxyphenyl)acrylonitrile (500 mg, 2.12 mmol) was dissolved
in DMF (10 mL) and NaOH (200 mg, 5 mmol) and stirred for 15 min at RT. Afterwards
bromooctane (1.51 g, 7.82 mmol) was added, and the mixture was stirred at 90 °C for 12 h. The
mixture was poured into 500 mL water and extracted with ethyl acetate (3 ×100 mL) three times.
After performing silica gel column chromatography (n-hexane : EtOAc = 6:1) the product was
recrystallized from ethanol and water to produce a yellow powder (304.11 mg, 0.87 mmol) with a

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yield of 60.8%.
1H-NMR ( CDCl3, 600 MHz, ppm ): δ = 7.80 ( d, 2 H, ArH, J = 8.4 Hz ), 7.47 ( d, 2 H, ArH,
J = 8.8 Hz ), 7.28 ( s, 1 H, =CH ), 6.93 ( d, 2 H, ArH, J = 8.8 Hz ), 6.65 ( d, 2 H, ArH, J = 8.4 Hz ),
4.00 ( t, 2 H, CH2, J = 6.4 Hz ), 3.85( t, 2 H, NH2, J = 7.4 Hz ), 1.77 ( m, 2H, CH2 ), 1.64 ( m, 10H,
5CH2 ), 0.88 ( t, 3 H, CH3, J = 6.0 Hz ).
HRMS (MALDI-TOF) m/z [M + H] ]+：calcd for C23H28N2O, 349.2274, found 349.2279.
Preparation
of
(E)-2-(4-aminophenyl)-3-(4-(dodecyloxy)phenyl)-acrylonitrile
((E)-CN-APHP)
(Z)-CN-APHP powders (500 mg, 1.44 m mol) were added into DMF (5 mL) and stirred at
room temperature for 10 min. Then the solution was irradiated with 440 nm light for 48 h and the
(Z)-CN-APHP isomer mostly converted to (E)-CN-APHP. (E)-CN-APHP was obtained by silica
gel column chromatography (n-hexane : EtOAc = 6:1). The product had the appearance of a
yellow grease (265.5 mg, 0.76 mmol) with 53.1% yield.
1H-NMR ( CDCl3, 600 MHz, ppm ): δ = 7.26 ( d, 2 H, ArH, J = 8.4 Hz ), 7.16 ( d, 2 H, ArH,
J = 8.8 Hz ), 7.13 ( s, 1 H, =CH ), 6.72 ( d, 2 H, ArH, J = 8.8 Hz ), 6.65 ( d, 2 H, ArH, J = 8.4 Hz ),
4.00 ( t, 2 H, CH2, J = 6.4 Hz ), 3.85( t, 2 H, NH2, J = 7.4 Hz ), 1.77 ( m, 2H, CH2 ), 1.64 ( m, 10H,
5CH2 ), 0.88 ( t, 3 H, CH3, J = 6.0 Hz ).
Device preparation
The nematic liquid crystal (E7) was purchased from Jiangsu Hecheng Display Technology.
The material used in this work consists of E7 (87%) and CN-APHP (13%). The mixture was
stirred in the isotropic phase (95 oC) for 1 hour to ensure complete dissolution. It was then injected
into an empty cell with anti-parallel rubbed polyimide alignment layers by capillary action. The
cell gap was controlled by a dispersion of 7 ꢀm spacer.
3. Result and discussion

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In order to clarify the thermodynamic, optical and photo-physical properties of the Z- and
E-isomers, CN-APHP with pure Z- and pure E-isomers were prepared separately. Fig. 1(b) shows
the images of (Z)- and (E)-CN-APHP under room and UV-light. Pure (Z)- and (E)-CN-APHP can
readily be distinguished as the PL intensity differs clearly. (Z)-CN-APHP emits bright bluish green
light with high PL quantum yields (Φf = 0.67). While, (E)-CN-APHP is barely fluorescent (PL
quantum yield is only 0.01) when excited with 365 nm UV light.
The mesomorphic properties of CN-APHP were characterized by both differential scanning
calorimetry (DSC) and polarized optical microscopy (POM). The phase-transition temperatures
o
are revealed in the DSC traces. Fig. 1(d) shows the POM photograph of (Z)-CN-APHP at 78 C
during the heating process. When (Z)-CN-APHP was heated above 73 oC, anisotropic
mesomorphic textures became clearly visible. Mesomorphic textures could also be observed
during cooling of (Z)-CN-APHP which suggests that the liquid crystal is enantiotropic. The DSC
spectra of (Z)-CN-APHP are shown in Fig. 1(c), the result agrees with the POM observation very
o
well. The liquid crystal phases appear in the temperature range from 73 to 86 C during heating
o
(Z)-CN-APHP at a rate of 5 C per minute. However, no liquid crystal phase can be observed
during heating of (E)-CN-APHP, as shown in Fig. S2. (E)-CN-APHP converts from the solid to
o
the liquid state directly at 70 C during the heating cycle. According to the calculation results
based on the density functional theory, the optimized molecular structure of the Z-isomer is
coplanar and rod-like which can be seen in Fig. S3(a). This is very beneficial if compact molecular
stacking is to be achieved. This is probably the reason why the Z-isomer exhibits liquid crystal
phases. Since the two rings of the E-isomers are significantly twisted, the optimized geometrical
structure is expected to be bent as shown in Fig. S3(b), which prevents effective molecular

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planarization and stacking in the aggregation state. In addition, the observed decrease of PL when
transitioning from the Z-isomer to E-isomer is attributed to the bent structure of the E-isomer.
Such a structure generally leads to reduced restriction of intramolecular motions (RIM).
The quite different geometry of the π-conjugated backbone significantly affects the
absorption and emission properties of (Z)- and (E)-CN-APHP. Fig. 2(a) shows that the absorption
peak (λmax) of (Z)-CN-APHP in DMF solution (2×10-5 mol·L−1) is at 379 nm with a molar
extinction coefficient (ε) of 30950 cm-1·M−1. In contrast, (E)-CN-APHP has λmax at 364 nm with ε
= 12550 cm−1·M−1. Both the hypsochromic shift (15 nm) and the decrease of the molar extinction
coefficient at λmax when transitioning from the Z-isomer to E-isomer are attributed to the bent
structure of the E-isomer. This generally causes the effective conjugation length to decrease. Fig.
2(b) shows the PL spectra of a CN-APHP solution excited at 365 nm. The PL intensity of the
Z-isomer solution is much higher than the one of the E-isomer solution.
solution, the absorption and emission changes of both pure (Z)-CN-APHP and (E)-CN-APHP
molecules in dilute DMF solution (2 × 10−5 mol·L−1) were monitored during excitation at 440 and
254 nm for the Z → E and the E → Z photoisomerization process, respectively. The absorption
peak of (Z)-CN-APHP shifts from 379 nm to 366 nm (photostationary state, PSS440
)
nm
accompanied by a gradual decrease in absorbance as a function of exposure time at 440 nm
excitation as shown in Fig. S5(a). The time-dependent PL spectra of the CN-APHP solution were
measured at 365 nm excitation wavelength. As seen from Fig. 3(b), the PL in solution decreased
considerably when 440 nm excitation was used. In contrast, λmax of (E)-CN-APHP gradually
red-shifted and its absorbance increases until the PSS254 nm when excited with 254 nm light as
shown in Fig. S5(a). Fig. S5(b) shows the intensity of the photoluminescence emission increasing

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with exposure time. These results demonstrate that both Z to E and E to Z-isomerization in
solution are reversible between the PSS440 nm and PSS254 nm as seen from Fig. 3 (c) and (d). On the
basis of the conversion equation using the absorbance values of Z- and E-isomers, it was
calculated that the resulting Z/E conversion ratio of (Z)- and (E)-CN-APHP was approximately
25/75 (PSS440 nm), and 50/50 (PSS254 nm), respectively. Since the protons in vinylene and
phenyl-rings are placed in very different chemical environments, the photoisomerization process
1
of (Z)-CN-APHP could also be clearly monitored by taking H NMR spectra as shown in Fig.
S4(a). With prolonged excitation time, the amount of the E-isomer increased gradually with a
simultaneous decrease of the Z-isomer until a photostationary state was reached. According to the
proton peaks of vinylene in the Z and E-isomers in 1H NMR spectra, Fig. S4(b) shows that the Z/E
conversion ratio of CN-APHP is 25/75 at the photo-stationary state. The results are consistent with
the conversion ratio obtained with the absorbance value.
For better understanding of the isomerization process of the CN-APHP molecules and
because the Z-E isomerization may also be triggered thermally, we also investigated the thermal
behavior of the CN-APHP solution. As presented in Fig.4, the cyanostilbene unit adopts a Z-form
(black line) in initial state. The Z-to-E photoisomerization occurs when the solution is exposed to
440 nm light and reaches equilibrium after 20 min exposure time (blue line). Most of the E-isomer
o
molecules can be converted back to the Z-form by heating at 160 C (red line). The resulting Z/E
conversion ratio at PSS160 °C was approximately 90/10, which is higher than that at PSS254 nm
.
The peculiar Z↔E isomerization process of CN-APHP molecules is very interesting for
potential use in optical memory devices. The isomerization of CN-APHP in positive liquid crystals
87 % E7 and a 13 % (Z)-CN-APHP mixture was investigated. As seen from Fig. S6, the

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phase-transition temperatures of the host LC and doped E7 are revealed in the DSC trace at a
o
heating/cooling rate of 5 C per minute and there is only one phase-transition whose temperature
changes from 58.2 °C to 63.3 °C. It means that (Z)-CN-APHP is structurally compatible with E7.
When the mixture of (Z)-CN-APHP and E7 is filled into the anti-parallel rubbed cell, Z-isomer
molecules are oriented within the template of liquid crystals due to the rod-like structure as
displayed in Fig. 5(a). During the photo-excitation at 440 nm, Z-isomers gradually convert into
E-isomers and show phase separation as a result of the poor compatibility between the E-isomers
and the E7 liquid crystals. A large number of liquid crystal domains appear within the surrounding
E-isomer matrix, forming so-called fluorescent-molecule-dispersed liquid crystals (FMDLC) as
seen from Fig. 5(b). The photoluminescence intensity of FMDLC can be switched repeatedly with
o
an electric field [27]. After the cell was heated above 160 C for 50 h, most of the E-isomer
molecules can be converted back to the Z-form. This increase the compatibility and liquid
crystalline domains disappear and convert back to the uniform planar phase as displayed in Fig.
5(c).
Fig. 5 (d) shows the emission spectra (λex=365 nm) of the cell in three states. At this excitation
wavelength, no photoluminescence from the host LC is observed and the cell emits blue light at the
maximum located between 470 - 478 nm. The cell in the initial state emits relatively strong blue light while
the peak maximum of the cell is red-shifted to 478 nm compared to the cell in PSS440 nm (470 nm) and
PSS160 °C (477 nm). This is likely due to the bent structure of the E-isomer. Even though the PL of
(E)-CN-APHP is inferior to (Z)-CN-APHP, the PL at PSS440nmshows enhanced blue emission compared to
PSS160°C. FMDLC is a highly inhomogeneous state with a large number of randomly oriented LC domains,
which strongly scatters the incident light. Photons of the incident light entering the cell have to undergo

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multiple refraction before leaving the cell. This maximizes the chances to interact with fluorescence
molecules and thereby increases fluorescence emission. Moreover, as shown in Fig. 5e and Fig. S7, the PL
intensity can be switched repeatedly between PSS440 nm and PSS160 °C and modulated by controlling the
exposure time to 440 nm light. As presented in Fig. 5(f), the CN-APHPdoped LC is suitable for recording of
images. The PSS160 °C was set as background and the letters “HFUT” appear as PSS440nmoptical features.
In addition to the controllability of PL intensity based on the isomerization of CN-APHP, the
degree of polarization of PL from CN-APHP can also be switched and operated in memory mode.
Since (Z)-CN-APHP is a luminogen with liquid crystalline properties, we suspected that
anisotropic emission could be accomplished with it. Polarized PL spectra were recorded and a
rotatable polarizer (0 o - 360 o) was placed between the sample and the detector. Fig. S8 describes
the plots of the polarized intensity of photoluminescence light parallel and perpendicular to the
rubbing direction of the liquid crystal cell versus exposure time of 440 nm light. Fig. S9(a) shows
a polar diagram of the PL intensity of the (Z)-CN-APHP doped liquid crystal cell. The cell reveals
a PL maximum for the directions of 0 ° and 180 ° - which is the rubbing direction, and a minimum
value at the directions of 90 ° and 270 ° - which is perpendicular to the rubbing direction.
Based on the above results, the dichroic ratios of polarized PL spectra of the CN-APHP
doped LC cell at PSS160 °C and PSS440 nm were studied. At PSS160 °C, the orientation of the LC
mixture was parallel to the alignment layer. The dichroic ratio is about 2.0. As shown in Fig.6(b),
the anisotropic emission almost disappeared at PSS440 nm and the dichroic ratio is only 1.2. In
addition, the dichroic ratio can change continuously by increasing the exposure time to 440 nm
light as ploted in Fig. S10.
More interesting, the PL intensity parallel to the liquid crystal direction at PSS160 °C is similar

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to that at PSS440 nm. The PL intensity normal to the liquid crystal direction at PSS440 nm is larger
than that at PSS160 °C. Based on these results, a novel pattern-recording method was demonstrated.
A UV lamp was used as light source to illuminate the mixture and a polarizer was used to analyze
the change in PL efficiency. In Fig. 6(c), we can clearly see the letters “HFUT” when the polarizer
is oriented vertically to the rubbing direction of the cell. When rotating the polarizer parallel to
the rubbing direction, the letters “HFUT” disappear.
4. Conclusions
In summary, we have synthesized an AIE-active luminescent liquid crystal, (Z)-CN-APHP,
which can be converted into E-isomers via 440 nm photoexcitation with a simultaneous decrease
in structural compatibility with a nematic liquid crystal. A new optical switching effect based on
the CN-APHP doped liquid crystals has been demonstrated. It emits partially linearly polarized
light. By controlling the reversible photo/thermal Z/E isomerization process, not only PL intensity
but also the PL polarization can be switched or modulated. Moreover, the possibility of
photochemical patterning or image recording with these materials has been demonstrated. Our
results may help create a new modulating technique for future light-switchable photonic devices
and displays.
Acknowledgments
This research was supported by Basic Research Program of China (Grant No. 2012CB723406), National
Natural Science Foundation of China (Grand No. 61107014, 51203039, 2120417, 21174036, 51103034),
Program for New Century Excellent Talents in University (Grant No. NCET-12-0839), National National
HighTechnology Research and Development Program ofChina (Grant No. 2012AA011901).

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References
[1] Moriyama M, Mizoshita N, Yokota T, Kishimoto K and Kato T. Photoresponsive anisotropic soft
solids: liquidꢀcrystalline physical gels based on a chiral photochromic gelator. Adv Mater 2003; 15;
1335ꢀ1338.
[2] Zhao D Y, Fan F, Cheng J, Zhang Y L, Tang B Z et. al. Lightꢀemitting liquid crystal displays
based on an aggregationꢀinduced emission luminogen. Adv Optical Mater 2015; 3; 199ꢀ202.
[3] Kim J H, Watanabe A, Chung J W, Jung Y, An B K, Tada H, Park S Y. Allꢀorganic coaxial nanocables
with interfacial chargeꢀtransfer layers: electrical conductivity and lightꢀemittingꢀtransistor behavior. J
Mater Chem 2010; 20; 1062.
[4]
Chen
Y,
Lin
J
,Yuan
W,
Yu
Z,
Lam
J
W
and
Tang
B
Z.
1ꢀ((12ꢀBromododecyl)oxy)ꢀ4ꢀ((4ꢀ(4ꢀpentylcyclohexyl) phenyl)ethynyl) benzene: Liquid crystal with
aggregationꢀinduced emission characteristics. Sci China: Chem 2013; 56; 1191ꢀ1208.
[5] Okumura T, Tagaya Akihiro, and Koike Y. Highlyꢀefficient backlight for liquid crystal display having no
optical films. Appl Phys Lett 2003; 83.
[6] Kim K H, Song J K. Technical evolution of liquid crystal displays. Npg Asia Mater 2009; 1; 29ꢀ36.
[7] Weder C, Sarwa C, Montali A, Bastiaansen G, and Smith P. Incorporation of photoluminescent
polarizers into liquid crystal displays science 1998; 279; 835ꢀ837.
[8] Contoret A E A, Farrar S R, Jackson P O, Khan S M, May L, O Neil lM, Nicholls J E, Kelly SM,
and Richards G J. Polarized electroluminescence from an anisotropic nematic network on a nonꢀcontact
photoalignment layer. Adv Mater 2000; 12; 971ꢀ974.
[9] Woon K L, O’Neill M, Richards G J, Aldred M P, Kelly S M, and Fox A M. Microgelꢀstabilized
metal nanoclusters: Size control by microgel nanomorphology. Adv Mater 2003; 15; 1551ꢀ1555.
[10] Yamaguchi R, Nagato H, Hafiz H, and Sato S. Sensitized fluorescence of dichroic dye in
emissive type liquid crystal displays. Mol Cryst Liq Cryst 2004; 410; 495.
[11] Salamonczyk M. , Kovarova A, Svoboda J, Pociecha D, and Gorecka E. Switchable fluorescent liquid
crystals. Appl Phys Lett 2009; 95; 171901.
[12] Dyreklev P, Berggren M, Inganäs O, Andersson M R, Wennerström O, Hjertberg T. Polarized
electroluminescence from an oriented substituted polythiophene in a light emitting diode. Adv
Mater 1995; 7; 43ꢀ45.
[13] Sariciftci N S, Lemmer U, Vacar D, Heeger A J, and Janssen R A J. Polarized photoluminescence of
oligothiophenes in nematic liquid crystalline matrices. Adv Mater 1996; 8; 651–654
[14] Chen Z H, Timothy M S. Synthesis and characterization of fluorescent acenequinonesas dyes for
guest−host liquid crystal displays. Org Lett 2007 ; 9; 997ꢀ1000.
[15] Joo S H, Kim J K, and Song J K. Fluorescent light source with continuously tunable polarization via
modification of molecular orientation. J Appl Phys 2013; 114; 083508.
[16] Empedocles S A, Neuhauser R, and Bawendi M G. Threeꢀdimensional orientation measurements of
symmetric single chromophores using polarization microscopy. Nature 1999; 399; 126ꢀ130.
[17] Lee C W, Int J. A review of polarization dependence applications for asymmetric waveguides vertical
couplers in compound semiconductor indium phosphide. Opt 2011; 164023.
[18] Du X and Wang Z Y. Donor–acceptor type silole compounds with aggregationꢀinduced deepꢀred
emission enhancement: synthesis and application for significant intensification of nearꢀinfrared
photoluminescence. Chem Commun 2011; 47; 4276–4278.

ACCEPTED MANUSCRIPT
13
[19] Chung J W, Yoon S J, An B K and Park S Y. Highꢀcontrast on/off fluorescence switching via reversible
E–Z isomerization of diphenylstilbene containing the αꢀcyanostilbenic moiety. J Phys Chem C 2013; 117;
11285–11291.
[20] Aldred M P, Eastwood A J, Kelly S M, Vlachos P, Contoret A E, Farrar S R, Mansoor B, O'Neill M, Tsoi
W C. Lightꢀemitting fluorene photoreactive liquid crystals for organic electroluminescence. Chem Mater
2004; 16; 4928ꢀ4931.
[21] Bertolotti M, Sansoni G and Scudieri F. Dye laser emission in liquid crystal hosts. Appl Opt
1979; 18; 528ꢀ531.
[22] Grell M, Bradley D D, Polarized luminescence from oriented molecular materials. Adv Mater 1999; 11;
895ꢀ905.
[23] Sagara Y, Yamane S, Mutai T, Araki K and Kato T. A stimuliꢀresponsive, photoluminescent,
anthraceneꢀbased liquid crystal: emission color determined by thermal and mechanical processes. Adv
Funct Mater 2009; 19; 1869–1875.
[24] Sa ´nchez I, Mayoral M J, Ovejero P,Campo J A, Heras J V, Cano M and Lodeiro C. Luminescent liquid
crystal materials based on unsymmetrical boron difluoride βꢀdiketonate adducts. New J Chem 2010; 34;
2937–2942.
[25] Lu H B , Zhang S N, Ding A X, Yuan M, Zhang G Y, Xu W, Zhang G B, Wang X H, Qiu L Z, Yang J X.
A luminescent liquid crystal with multistimuli tunable emission colors based on different molecular
packing structures. New J Chem 2014; 38; 3429ꢀ3433.
[26] Zhang Y L, Zhuang G L, Ouyang M, Hu B, Song Q B, Sun J W, Zhang C,Gu C, Xu Y X and Ma Y G.
Mechanochromic and thermochromic fluorescent properties of cyanostilbene derivatives. Dyes and
Pigments 2013; 98; 486–492.
[27] Lu H B, Qiu L Z, Zhang G Y, Ding A X, Xu W B, Zhang G B, Wang X H, Tian Y P, Yang J X.
Electrically switchable photoluminescence of fluorescentꢀmoleculeꢀdispersed liquid crystals prepared via
photoisomerizationꢀinduced phase separation. J Mater Chem C 2014; 2; 1386ꢀ1389.

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Fig. 1 (a) Molecular structure of (Z)-CN-APHP and (E)-CN-APHP. (b) Images of (Z)- (above) and
(E)-CN-APHP (below) under room and UV light. (c) DSC curves of (Z)-CN-APHP at a
heating/cooling rate of 5 °C per minute. (d) POM photograph of (Z)-CN-APHP at 78 °C during
heating process.
Fig. 2 Absorption (a) and photoluminescence spectra (b) of (Z)- and (E)-CN-APHP in DMF
solution (2×10-5 mol· L-1).

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Fig. 3 UV-vis absorption (a) and photoluminescence spectra of (Z)- and (E)-CN-APHP in DMF
after increasing the photoexcitation time of 440 and 254 nm light, respectively. Absorbance at 365
nm (c) and photoluminescence intensity at 505 nm (d) appear modulated during alternating
excitation at 440 nm (black circle, for 5 min) and 254 nm (red circle, for 20 min) because of the
reversible isomerization process.
Fig. 4 (a) UV-vis absorption spectra of CN-APHP in DMF solution (2×10-5 mol· L-1 ) in different
states.

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Fig. 5 Schematic illustration of the molecular arrangement and POM of the CN-APHP doped
liquid crystal cell at different states. (a) initial state (pure Z-isomer), (b) PSS440 nm and (c) PSS160 °C
(d) Photoluminescence spectra of the cell at the three states, (e) Repeated switching of PL
intensity between PSS440 nm and PSS160 °C, (f) Recorded pattern by the optical switch using two
stable states: PSS440 nm (“HFUT”) and PSS160 °C (background).
,
Fig. 6 Polarized photoluminescence spectra of the CN-APHP doped liquid crystal cell at PSS160 °C
(a) and PSS440 nm (b). The recorded pattern of CN-APHP doped LC cell under the polarizer with
the optic axis perpendicular (c) and parallel (d) to the rubbing direction of the liquid crystal cell:
PSS440 nm (“HFUT” ) and PSS160 °C (background).

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Fig. S1 Synthetic route of (Z)-CN-APHP
Fig. S2 DSC curves of (E)-CN-APHP at a heating/cooling rate of 5 °C per minute.
Fig. S3 Geometry optimization of (Z)-CN-APHP (a) and (E)-CN-APHP (b) by quantum chemical
calculations based on density functional theory.

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Fig. S4 (a) 1H NMR spectra of CN-APHP in DMF solution after various irradiation time under
440 nm light (protons in the vinylene of Z-isomer form (▼) and E-isomer form (△). (b) Changes
of Z-to-E conversion ratio as a function of UV irradiation time.
Fig. S5 The gradual changing of the absorption (a) and photoluminescence intensity (b) from
all-Z-isomer to the PSS440 nm by prolonging the illumination time of 440 nm (black square)and
all-E-isomer to the PSS254 nm by increasing the illumination time of 254 nm (red circle),
respectively.

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Fig. S6 DSC curves of host E7 and (Z)-CN-APHP doped E7 at a heating/cooling rate of 5 °C per
minute.
Fig. S7 The changing tendency of photoluminescence intensity of CN-APHP doped liquid crystal
cell by increasing exposure time of 440 nm light.

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Fig. S8 The plots of the polarized intensity of photoluminescence light parallel (red line) and
perpendicular (black line) to the rubbing direction of the liquid crystal cell versus exposure time of
440 nm light.
Fig. S9 The polar photoluminescence intensity of the CN-APHP doped liquid crystal cell at initial
state (pure Z-isomer) (a), PSS440 nm (b) and PSS160 °C (c).
Fig. S10 The changing tendency of fluorescence dichroic ratio through increasing the illumination
time.

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ꢀ A new optical switch based on AIE-active luminescent liquid crystals
was developed.
ꢀ The mixture material can emit partially linearly polarized light.
ꢀ It is possibly to modulate photoluminescence intensity and its
polarization.
ꢀ It has the potential to be used in improved optical devices.