Self-assembly, AIEE and mechanochromic properties of amphiphilic α-cyanostilbene derivatives

Article abstract of DOI:10.1016/j.tet.2017.07.010

A series of amphiphilic α-cyanostilbene derivatives consisting of an α-cyanostilbene rodlike core with lipophilic and flexible alkyl chains at one end and a polar glycerol group at the opposite end have been synthesized and investigated by polarizing micr

Full text of DOI:10.1016/j.tet.2017.07.010

Accepted Manuscript
Self-assembly, AIEE and mechanochromic properties of amphiphilic α-cyanostilbene
derivatives
Yanming Ren, Ruilin Zhang, Chao Yan, Tingyan Wang, Huifang Cheng, Xiaohong
Cheng
PII:
S0040-4020(17)30727-5
10.1016/j.tet.2017.07.010
TET 28842
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 19 May 2017
Revised Date: 3 July 2017
Accepted Date: 7 July 2017
Please cite this article as: Ren Y, Zhang R, Yan C, Wang T, Cheng H, Cheng X, Self-assembly, AIEE
and mechanochromic properties of amphiphilic α-cyanostilbene derivatives, Tetrahedron (2017), doi:
10.1016/j.tet.2017.07.010.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to
our customers we are providing this early version of the manuscript. The manuscript will undergo
copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please
note that during the production process errors may be discovered which could affect the content, and all
legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT
Graphical Abstract
Self assembly, AIEE and mechanochromic
properties of amphiphilic α-cyanostilbene
derivatives
Leave this area blank for abstract info.
Yanming Ren,‡a Ruilin Zhang,‡ab Chao Yan,a Tingyan Wang,ca Huifang Cheng,a Xiaohong Cheng*a
aKey Laboratory of Medicinal Chemistry for Natural Resources, Yunnan University, Kunming 650091, P. R. China
bForensic Medicine of Kunming Medical University, Kunming 650500, P. R. China
cCollege of Science, Beijing University of Chemical Technology, Beijing 100029 , P.R.China
‡Both authors contributed equally to this work

1
ACCEPTED MANUSCRIPT
Tetrahedron
journal homepage: www.elsevier.com
Self-assembly, AIEE and mechanochromic properties of amphiphilic α-cyanostilbene
derivatives
Yanming Ren,‡a Ruilin Zhang,‡ab Chao Yan,a Tingyan Wang,ca Huifang Cheng,a Xiaohong Cheng*a
aKey Laboratory of Medicinal Chemistry for Natural Resources, Yunnan University, Kunming 650091, P. R. China
bForensic Medicine of Kunming Medical University, Kunming 650500, P. R. China
cCollege of Science, Beijing University of Chemical Technology, Beijing 100029 , P.R.China
‡Both authors contributed equally to this work
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
A series of amphiphilic α-cyanostilbene derivatives consisting of an α-cyanostilbene rodlike
core with lipophilic and flexible alkyl chains at one end and a polar glycerol group at the
opposite end have been synthesized and investigated by polarizing microscopy, DSC, X-ray
scattering, SEM, UV-vis spectroscopy and photoluminescence measurements. These compounds
Available online
can self-assemble into liquid crystalline phase sequence of SmA- Colhex/p6mm- Cub /
in
Pm3n
I
the bulk states and multistimuli responsive organogels in organic solvents. They have reversible
photoresponsive properties in solution, liquid crystalline state and gel state. They also show
aggregation-induced enhanced emission (AIEE) property, meanwhile, they present excellent
mechanochromic behavior and have a good reversibility of fluorescence conversion upon
grinding-fuming process.
Keywords:
α-Cyanostilbene derivatives
Liquid crystals
Aggregation-induced enhanced emission
Organogels
Mechanochromism
2017 Elsevier Ltd. All rights reserved.
1. Introduction
Herein we reported the design, synthesis, self-assembly as
well as AIEE, mechanochromic properties of a series of
π-Conjugated α-cyanostilbene derivatives have attracted great
interesting because of their tunable photophysical properties,
self-assembling characteristics,1,2 charming functionalities, such
as aggregation-induced enhanced emission (AIEE) effect,1,3 solid
-state emission, photochromism, 4 photovoltaics5 and biological
amphiphilic α-cyanostilbenes, consisting of a α-cyanostilbene
rodlike core with lipophilic flexible alkyl chains at one end and a
glycerol group at opposite end. Amphiphilic LCs 22 involving
glycerol units are potentially useful for the design of
nanostructured 1D, 2D or 3D ion conduction materials in
combination with ionic liquids etc.23
These amphiphilic α-cyanostilbenzes are assigned as Im/n and
IBm/n, where m stands for the number of the terminal alkyl chain,
n is the alkyl chain length, B means that the terminal alkyl chains
are the branching ones. The influence of the number, length and
type of the terminal alkyl chains on the self-assembly of these
compounds was investigated. These compounds can self-
assemble into LCs and gels. They have photoresponsible ability
in solution, LC state and gel state, additionally they show the
AIEE and excellent mechanochromic behaviors. Therefore these
compounds could be considered as multifunctional materials.
6
7
8
9
imaging
monolayers,
etc. Nanoparticles,
nanowires,
organogels,
10
11
12
quantum dots,
single crystals
and
polycrystalline films 13 based on π-conjugated α-cyanostilbene
derivatives have been reported. Relevant relationship among
molecular structure, self-assembly and optical property has been
carefully reviewed recently.1 The excellent characteristics of the
α-cyanostilbene chromophore could be combined with the self-
asmmbly of liquid crystals (LCs).14 Till now, few examples of α-
cyanostilbene based calamitic,14a,15star shaped,16 banana-shaped,17
polycatenar LCs4e,18 with formation of columnar,17,18 nematic15 or
smectic phases17,19 have been reported. These materials have led
to interesting phenomena such as fluorescence switching, 19
2. Results and discussion
photoisomerization-induced phase transitions18,19 and surface
2.1. Synthesis
20
relief gratings,7c,14e,
photoisomerization-induced phase
separation,21 and NLO17b etc. However, so far as we know there
are few amphiphilic α-cyanostilbene LCs been explored, and 3D
spherical cubic mesophase has never been observed for α-
cyanostilbene derivatives.
The target compounds Im/n and IBm/n have been synthesized
via Knoevenagel reactions between benzaldehydes 1 with
phenylacetonitrile
3 as shown in Scheme 1. Firstly 4-
hydroxybenzaldehyde was etherified with appropriate

2
Tetrahedron
ACCEPTED MANUSCRIPT
alkylsubstituted benzyl chlorides, leading to phenyl aldehydes
conjunction with a FP 82 HT heating stage, Mettler), differential
1. 3 was prepared from 2-(4-hydroxyphenyl)acetonitrile by
etherification with glycidol,24 followed by protection of the 1,2-
diol group as 1,2-isopropylidene ketal.25 Knoevenagel reactions
between benzaldehydes 1 with phenylacetonitrile 3, followed by
deprotection of the 1,2-O-isopropylidene glycerol units yielded
the final compounds.
scanning calorimetry (DSC, NETZSH 200F3) and X-ray
diffraction (XRD) techniques. The transition temperatures of the
synthesized α-cyanostilbenes Im/n and IB3/10 are reported in
Table 1.
2.2.1. Compounds (I1 /12, meta-I2 /16, I3 /n) and their
formation of smectic and columnar phases
Smectic A phase was observed in single chain compound
I1/12 and columnar phases were observed in two alkyl chain
compound meta-I2/16 and triple alkyl chain compounds Im/n (m
= 3, n = 10, 12, 14, 16, 18). Compound IB3/10 with triple
branching alkyl chains shows a cubic phase. The smectic A phase
of single chain compound I1/12 was characterized by its typical
fan-shaped focal conics textures26 (Fig. 1a). The small-angle X-
ray scattering (SAXS) pattern of I1/12 shows three equidistant
peaks (d10 = 6.731 nm, d20 = 3.407 nm, d30 = 2.281 nm) with
reciprocal d-spacing ratio of 1 : 2 : 3, which confirms a layer
structure. The layer spacing in the SmA phase of compound I1/12
is d = 6.731 nm (Table. S1). Compared with the molecular length
in the most stretched conformation (L = 3.69 nm, see Table 2),
the layer thickness is larger than the molecular length (d/L =
1.82), but slightly smaller than twice the length, indicating a
bilayer structure with slightly intercalation of the alkyl chains
(SmA2). In this SmA2 structure there is a non-intercalated
antiparallel end-to-end packing of the aromatic cores, allowing
the segregation of the polar glycerol units from the less polar
alkyl-substituted benzene rings at the opposite end, and the
reduction of the d value is in this case due to the intercalation of
the alkyl chains (Fig. 1c).
Scheme 1. Synthesis of compounds Im/n and IBm/n; Reagents and
conditions: i) DMF, K2CO3, reflux, 80 °C, 10 h, 54-89%; ii) PPTS, 2,2-
dimethoxypropane, THF, 40 °C, 3 h; iii) 4-hydroxybenzyl cyanide, tert-
butanol, potassium tert-butoxide, 70 °C, reflux, 12 h, 33-43%.
2.2. Mesomorphic properties
The LC properties of compounds Im/n and IBm/n were studied
by polarizing optical microscopy (POM, Optiphot 2, Nikon, in
Table 1. Transition temperatures and associated enthalpy values (in brackets) of compounds I1/12, meta-I2/16, I3/n and IB3/10a
Comp
R1, R2, R3
T/°C [ΔH /kJ mol−1]
I1/12
R 1= R3 = H, R2 = -OC12H25
Cr 69.4 [17.8] SmA 121.2 [2.7] Iso
Cr 70.9 [27.8] Colh 116.2 [0.2] Iso
Cr < 20 Colh 153 [0.2] Iso
meta-I2/16 R 1= R3 = -OC12H25, R2 = H
I3/10
I3/12
I3/14
I3/16
I3/18
IB3/10
R1 = R2 = R3 = -OC10H21
R1 = R2 = R3 = -OC12H23
R1 = R2 = R3 = -OC14H29
R1 = R2 = R3 = -OC16H33
R1 = R2 = R3 = -OC18H37
R1 = R2 = R3 = -OCH2CH(C10H21)2
Cr 28 [30.2] Colh 143 [0.2] Iso
Cr 43 [21.5] Colh 125 [0.1] Iso
Cr 66.4 [26.9] Colh 98.1 [0.04] Iso
Cr 60 [42.7] Colh 88 [0.2] Iso
Cr 63.5 [11.0] CubI/
85b Iso
Pm3n
aTransition temperatures were determined by DSC (peak temperature from heating scans, at a rate of 1 K min−1 for I2/16, I3/n; 2 K min−1 for compounds
I1/12, and 5 K min−1 for IB3/10, melting transitions were measured in the first heating scan), abbreviations: Cr = crystal; SmA = smectic A phase; Colh =
hexagonal columnar phase; CubI/
determined by POM.
= micellar cubic mesophase with space groups
; Iso = isotropic liquid. bTransition temperature was
Pm3n
Pm3n
a)
c)
b)
Fig. 1 (a) Texture of SmA phase as seen between crossed polarizers at T = 95 °C on cooling process; (b) SAXS diffractogram of the SmA phase at T =
90 °C; (c) model of SmA2 phase of compound I1/12.

3
Two chain compound meta-I2/16 and triple chain compounds
ACCEPTED MANUSCRIPT
I3/n (n = 10, 12, 14, 16, 18) exhibit enantiotropic columnar
phases. Increasing chain number and length leads to a dramatic
reduction of the stability of the columnar phases as seen by
comparison of compounds I3/n (n = 10, 12, 14, 16, 18), in which
the Col-to-Iso transition is reduced by more than 105 K (Table
1). The columnar phases were identified by the typical spherulitic
fanlike textures under POM (Fig. 2a and Fig. S1a-e).
Investigation of the columnar phases by POM with an additional
λ-retarder plate (Fig. 2a and Fig. S1a-e) indicates that the
columnar phases of compounds meta-I2/16, I3/n (n = 10, 12, 14,
16, 18) are optically negative. 27 This means that the major
intramolecular π-conjugation pathway, which is along the long
axis of the aromatic cores, is perpendicular to the column long
axis. The columnar phases were also investigated by small-angle
X-ray scattering (SAXS) (Fig. 2b and Fig. S3). The X-ray
diffraction pattern of compound I3/12 is shown as an example in
Fig. 2b. 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. The
lattice parameters a were calculated to be 5.6～5.9 nm for the
columnar phases of these compounds (Table 2 and Tables S2-
S7). 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) u, estimated using equation (1)
and assuming a density of ρ = 1 g/cm3 is between u = 7 to 9 for
the investigated compounds (NA = Avogadro constant; M =
molecular mass, see Table 2).
a)
b)
c)
d)
Fig. 2 Characterization of compound I3/12: (a) Texture as seen between
crossed polarizers at T =118 °C (inset shows the same region with λ-
plate); (b) SAXS diffractogram of the Colhex phase of I3/12 at T = 110
°C; (c) Reconstructed electron density map for the Colhex phase of I3/12;
(d) Model for molecular packing of compound I3/12 in Colhex phase.
Table 2. Comparison of X-ray data and molecular dimensions of the
columnar and cubic phases of compounds Im/n and IB3/10 a
Comp.
Phase, Plane/space
group
L [nm] a[nm] (T [°C] )
u
a2
(1)
 (
)
(
)
M
u
N
A
3h
I1/12
m-I2/16
I3/10
SmA
3.69
4.23
3.51
3.69
3.93
4.22
4.47
3.67
/
/
2
There is a slight decrease of this number with increasing chain
number and length, which is due to the increase of the taper angle
with the increasing space requirement of the terminal alkyl
chains.28,29 The three alkyl chains of I3/18 provide a stronger
interface curvature, leading to a clear decrease of the number of
molecules (u = 6.9) organized in the cross section of the column,
as compared to the number u = 9.2, 7.7, 7.5, 7.3 and 7.9 for I3/n
(n =10, 12, 14, 16) and meta-I2/16 respectively. The number of
molecules u = 7.9 of compound meta-I2/16 is nearly the same as
u = 7.7-7.3 for the compounds I3/n (n= 12, 14, 16) with triple
medium length of alkyl chains. Therefore it can be assumed that
the taper angle of the meta substituted double chain compound
meta-I2/16 were almost the same as those of triple chain
compounds I3/n (n = 12, 14, 16).
Colhex/p6mm
Colhex/p6mm
Colhex/p6mm
Colhex/p6mm
Colhex/p6mm
Colhex/p6mm
5.7 (100)
5.8 (90)
5.6 (110)
5.8 (115)
5.8 (90)
5.9 (80)
11.18 (75)
7.9
9.2
7.7
7.5
7.3
6.9
72.8
I3/12
I3/14
I3/16
I3/18
IB3/10
Cub /
Pm3n
I
aAbbreviations: a = lattice parameter determined by XRD (ahex and acub
respectively); L= maximum molecular length in the most extended
conformation; u = number of molecules in the cross section of a column
in the Colhex phases (with assumed height of 0.45 nm) or number of
,
Pm 3n
molecules in each aggregate of the CubI/
lattice (ucell/8).
b)
a)
The introduction of the second or the triple alkyl chains
induces a change of the molecular shape from rodlike
(compounds I1/12) to taper shape, leading to an organization of
the molecules in circular cylindrical aggregates, which can
organize into a hexagonal lattice. This is very similar to
observations made with other taper amphiphiles.30 Therefore 7-9
molecules self-assemble into an overall disk-like stratum and
they successively stack one another to form supramolecular
columns (Fig. 2d and Fig. S5). The polar units form the column
centers, which are surrounded by the rigid α-cyanostilbene
aromatic cores, and assembled on a hexagonal lattice within the
lipophilic continuum mainly formed by the terminal alkyl chains.
The effective diameters of the columns correspond to the
experimentally observed hexagonal lattice parameters ahex. These
models are also supported by the electron density maps (Fig. S4),
which were reconstructed from the small-angle X-ray scattering
(SAXS) intensities of compounds meta-I2/16 (Fig. S3a), I3/10
(Fig. S3b), I3/12 (Fig. 2b), I3/14 (Fig. S3c), I3/16 (Fig. S3d) and
I3/18 (Fig. S3e), where the column centers with high electron
density (purple) are surrounded by medium electron density
shells (blue/green/yellow).
Fig. 3 (a) SAXS diffractograms of compound IB3/10; (b) Possible model
for molecular organization micellar cubic phase.
2.2.2. Compound IB3 /10 and formation of micellar
cubic phases
Interestingly, micellar
cubic phase was observed in
Pm3n
compound IB3/10 with triple branching alkyl chains. 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 liquids occur at defined temperature (Fig. S1f). In the

4
Tetrahedron
cubic phase of compound IB3/10, the positions of the sharp
Such photoisomerizations could be useful for light sensitive
ACCEPTED MANUSCRIPT
powderlike reflections in the small-angle region can be indexed
to be a cubic phase with space group of with lattice
displays or for data storage applications.32,33
Pm3n
parameter acub = 11.18 nm (Fig. 3a and Table 2 and Table S8).
The lattice is the most commonly observed lattice of
Pm3n
a)
b)
micellar cubic phases (CubI) (Fig. 3b), occurring in thermotropic
systems formed by spheroidic aggregates with soft corona.31 In
this type of cubic phase, the molecules are organized in closed
spheroidic aggregates, and there are eight of these aggregates in
each unit cell. By calculation, each micelle is built up of
approximately 73 molecules in the
cubic phase of IB3/10.
Pm3n
The spheroids should have a core shell structure with a
hydrophilic cores formed by the polar glycerol groups which
were surrounded by π-conjugated stratum, these core-shell
spheroids are encapsulated by the terminal alkyl chain moieties
in the micelles (Fig. 3b). The large volume of the flexible chains
gives rise to a large interface curvature, thus contributes to the
emergence of the cubic phase. The twist-bend α-cyanostilbene
core and possible trans-cis transformation of central unit could
lead to the relatively flexible rigid core, contribute to the
formation of softness of these spheres in cubic phase, and this is
Fig. 4 Textural changes as observed by POM at the photo induced
Colhex-Iso transitions and the relaxation Iso-Colhex as observed for
compound I3/12 at 115 °C: (a) before UV irradiation; (b) after UV
irradiation.
2.4. Gelation properties
The gelation ability of these compounds was evaluated by
using compound I3/12 as a representative in various organic
solvents at a concentration of 5.0 mg/mL, and the results are
summarized in Table 3. I3/12 can gelate in ethanol and methanol,
solve in CHCl3, toluene and THF. Whereas it is insoluble in n-
butanol and acetone, and precipitates in cyclohexane and DMSO.
So far as we know there is few gelation behavior of α-
cyanostilbene derivatives been reported.9 Intermolecular
hydrogen bonds, π–π interactions and intramolecular hydrogen
bonds as well as van der Waals forces should play an important
role for the aggregation of the compound in solvents.34 Under
irradiation of UV lamp, the non luminescence gel become blue
luminescence (Fig. 5). The organogels exhibit multiple stimuli-
responsive behaviors namely gel–sol reversible process upon
exposure to a number of environmental stimuli including light,
temperature and shear etc (Fig. 6b). Irradiation with UV light,
application of heat or shear resulted in a sol state through
disruption of the non-covalent interactions between the
molecules. The gel state can be recovered by removal of such
stimuli. Such multiple stimuli-responsive behaviors could be
useful for drug controlled release,35 energy transfer,36 hardeners
of solvents and sensors etc.37 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 I3/12 (Fig. 6a) shows
the formation of three-dimensional networks composed of
entangled fibrous aggregates. The approximate diameter of the
fibers is 80-130 nm.
favorable for the organization in a
cubic phases.
lattice instead of other
Pm3n
Therefore the structure-property relationship of the
amphiphilic α-cyanostilbene derivatives focusing on the impact
of the number, length and type of terminal alkyl chains on the
self-assembly into lamellar, columnar, and spheroidic
supermolecular aggregates are systematically studied. By
increasing the volume ratio of the terminal alkyl chains, namely
increasing the number and length of the alkyl chains or branching
the alkyl chains, the interface curvature between the
nanosegregated regions of the α-cyanostilbene cores and the
flexible chains should be increased, the molecular shapes have
been changed from rodlike to taper shapes. This structural
variation gives rise to the transition from the bilayer smectic
phases through hexagonal columnar (Colhex
)
to cubic
(Cub / ) LC phases. So far as we know, the Cub phase as
Pm3n
I
I
well as the bilayer smectic phase are firstly realized here for the
α-cyanostilbene derivatives.
2.3. Photoisomerization behavior in liquid crystalline and
solution
The effect of trans-to-cis 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 change their
textures to isotropic states and recover to their original textures
after removing the UV source. This means that all the
compounds showed trans to cis photoisomerization under UV
irradiation and cis to trans isomerization under visible light
irradiation. For example, sample I3/12 was cooled from the
isotropic liquid state to 115 °C in the range of the Colhex phase
(Fig. 4a). After annealing for 5 minutes the sample was exposed
to UV irradiation at 365 nm (10 mW cm-2) for 3s, the
birefringence texture of the Colhex phase was disappeared and
replaced by isotropic one (Fig. 4a-b). After removal of the UV
lamp, the birefringence texture of the Colhex phase was recovered
(Fig. 4b-a). It seems that the trans-to-cis photoisomerization
effect on the liquid crystalline property of the compound reported
here is very strong. Similarly, the homologous series compounds
showed photoisomerization reversible transition of Colhex–Iso.
Additionally the homologous compounds also showed
photoisomerization reversible transition in solution (Fig. S6).
b)
a)
Fig. 5 Photograph of solution and gels prepared with I3/12 in ethanol, 10-
6 M, T = 20 °C. (a) without irradiation; (b) under irradiation with 365 nm
light.

5
130 nm
135 nm
DMF
Acetonitrile
335 nm
338 nm
465 nm
473 nm
464 nm
470 nm
ACCEPTED MANUSCRIPT
a λex = maxima absorption wavelength; λex = 330 nm; c The Stokes shift
was obtained from the difference of the emission and absorption
maximum (ΔλST = λema - λabs).
b
Table 3. Gelation properties of I3/12a
Solvent
CHCl3
Ethyl acetate
Hexane
Methanol
Acetone
DMSO
I3/12
Solvent
CH2Cl2
I3/12
S
S
S
G
I
S
P
G
I
Cyclohexane
Ethanol
wavelengths of compound I3/12 exhibited red-shifts of 11 nm,
and the emission maximum of I3/12 exhibited bathochromic
shifts of 40 nm from hexane to acetonitrile, respectively.
Meanwhile, Stokes shifts are also increased dramatically from
hexane to acetonitrile. To have a better insight into the ICT
process, the density functional of B3LYP with 6-31G* basis sets
was used to investigate the electron cloud distribution (Fig. 7c).
The electron cloud of the highest occupied molecular orbital
(HOMO) was mainly localized on the linear π-conjugated
systems, while the electron cloud of the lowest unoccupied
molecular orbital (LUMO) was localized on the α-cyanostyrene
unit due to the strong electron withdrawing ability of the cyano
group. Compound I3/12 exhibited obviously charge separation
and indicated a typical intramolecular charge transfer (ICT)
effect.
n-Butanol
Toluene
THF
S
S
P
aS = solution, P = precipitation, G = gelation, I = insoluble, gels formed
at room temperature (20 ºC).
a)
b)
Fig. 6 (a) SEM images of xerogel formed by compound I3/12 in ethanol ,
scale bar is 5 μm; (b) compound I3/12 in ethanol (5.0 mg/ml),
photograph of multistimuli responsive organogels.
2.6. Aggregation-induced emission enhancement performances
Compound I3/12 is soluble in common organic solvents in low
concentration, such as CH2Cl2, THF, ethyl acetate and almost
insoluble in water. To investigate the AIEE characteristic of
I3/12, its UV-vis and fluorescence spectra with different fraction
of water were studied (Fig. 8). The concentration of this
compound was kept at 1 × 10-5 mol L-1. For UV-vis spectra of
compound I3/12 (Fig. 8a), with an increasing fraction of water
from 0 to 30%, the absorption band almost remained at the same
position of 325 nm. With up to 40% of water content, molecules
began to form aggregates, and the absorption band showed red-
shifts slightly. The possible reasons are that the increase of the
polarity and the planarization of a twisted molecule caused the
extension of the effective conjugation lengths in the aggregated
state.39
2.5. Solvent effect
The UV-vis and fluorescence spectra of compound I3/12 in
different solvents (hexane, toluene, dichloromethane (DCM),
tetrahydrofuran (THF), acetonitrile, N,N-dimethylformamide
(DMF)) are shown in Fig. 7 and Fig S7, the corresponding
photophysical data are summarized in Table 4. As we know, the
solvents can change the energy levels of the absorption or
emission bands. As depicted in Fig. 7a, compound I3/12 shows
one characteristic absorption band at about 330 nm in varying
solvents, which is attributed to the π–π* and intramolecular
charge transfer (ICT) transitions.38 It can be obviously observed
that the absorption
For the fluorescence intensity, compound I3/12 showed a
dramatic change from weakly emitting in the monomolecular
state to strongly fluorescent in the aggregated state (Fig. 8b).
When the water fraction is inferior to 30%, the fluorescence
intensity of compound I3/12 emitted weakly fluorescence
emission, whereas in the case of 40% volume fractions of water
addition, the molecule began aggregating and the fluorescence
intensity promptly increased and reached the maximum value at
50%. Meanwhile, the aggregates exhibit an enhancement of
green-yellow emission under UV irradiation.
1.0
0.8
0.6
0.4
0.2
0.0
Hexane
Toluene
THF
CH2Cl2
DMF
b
1.0
)
a)
Hexane
Toluene
THF
CH2Cl2
DMF
0.8
0.6
0.4
0.2
0.0
Acetonitrile
Acetonitrile
400
450
500
550
300
350
400
450
/nm
/nm
c)
ΔE=3.15eV
1000
1.0
Water fraction
a)
water fraction
(vol %)
b)
(vol %)
0
800
0
0.8
0.6
0.4
0.2
0.0
10
20
30
40
50
60
70
80
90
10
20
30
40
50
60
70
80
90
Fig. 7 The UV-vis spectra (a) and fluorescence spectra (λex = 330 nm) (b)
of compound I3/12 in different solvents (1 × 10-5 mol L-1); (c) molecular
orbital amplitude plots of the HOMO and LUMO levels, energy gaps and
electron cloud distribution of I3/12 calculated using the B3LYP/6-31G*
basis set.
600
400
200
0
350
400
450
500
550
600
300
350
400
450
/nm
/nm
Table 4. UV-vis absorption and fluorescence spectroscopy data of
compound I3/12
c)
a
b
c
Compd.
Solvent
Hexane
Toluene
THF
λabs
λem
λem
ΔλST
327 nm
330 nm
331 nm
334 nm
431 nm
437 nm
445 nm
459 nm
430 nm
436 nm
444 nm
456 nm
104 nm
107 nm
114 nm
125 nm
I3/12
DCM

6
Tetrahedron
ACCEPTED MANUSCRIPT
Fig. 8 The UV-vis absorption (a) and fluorescence spectra (excited at
solutions and gels states was well demonstrated. In addition,
326 nm, 327 nm, 328 nm, 328 nm, 333 nm, 338 nm, 337 nm, 337 nm,
338 nm, 338 nm respectively) (b) of compound I3/12 in ethanol–water
mixtures with different water volume fractions; (c) optical photographs
recorded under 365 nm UV irradiation with various fractions of water.
compounds Im/n exhibited AIEE properties attributed to the
restriction of intramolecular rotation (RIR) and intermolecular
interaction. Meanwhile, the emission peak of compound Im/n was
obviously red-shifted after grinding. Such multifunctional
materials should have great potentials in displays, photochemical
molecular switches, AIEE materials and mechano fluorochromic
materials etc.
The mechanism of AIEE may be attributed to the restriction of
intramolecular rotation (RIR) and intermolecular interaction.40
When the fraction of water is higher than 60%, the fluorescence
intensity gradually decreases. This phenomenon is reasonable
that aggregates begin to form and precipitate quickly at high
water content. This process leads to the decrease of fluorescent
species and lowers the fluorescence intensity. The other
compounds I3/n have been found to display a similar behavior.
Acknowledgements
This work was supported by the National Natural Science
Foundation of China [no. 21664015, 21364017] and Yunnan
Provincial Department of Education Foundation [no.
ZD2015001], the Yunnan University Graduate Research
Foundation Project [no.YNUY201682, YNUY201620]. The
calculations were performed with the support of the Yunnan
University Supercomputer Center. We thank beamline 1W2A at
Beijing Accelerator Laboratory and beamline BL16B1 at
Shanghai Synchrotron Radiation Facility (SSRF), China.
2.7. Mechanofluorochromic properties
The AIEE feature may be suggested that those compounds
could be used as stimuli responsive smart materials. To check
whether compound I3/12 has the mechanofluorochromic
property, its emission property was studied in the solid state. It
emitted green light after grinding with a spatula for 3 min. As
shown in Fig. 9, the emission peak showed an obvious red shift
for I3/12 from 437 nm to 455 nm. When fuming with ethanol
vapor for 5 min, the emission peak almost returned to the original
fluorescence emission. For the UV-vis spectra of I3/12 in
different states (Fig. S8), it was found that the maximum
absorption peaks of the solid state showed an obvious red-shift
compared with that in dilute solution, mainly due to the reason
that effective conjugation increased through intermolecular
interaction in the solid state. Meanwhile, the absorption peak
appeared to red-shift after grinding (from 345 nm to 358 nm, Fig.
S9), which suggested that the molecular conformation became
more planarized and further increased the conjugation degree.
The results indicated that the pressure of grinding changes not
only the absorption spectra but also the emission spectra. The
conversion between the green and blue emission can be repeated
many times without fatigue due to the nondestructive nature of
the stimuli.20b
References
1. An B-K, Gierschner J, Park SY. Acc. Chem. Res. 2012; 45: 544-554.
2. Zhu LL, Zhao YL. J. Mater. Chem. C. 2013; 1: 1059-1065.
3. (a) An B-K, Kwon S-K, Jung, S. D, Park SY. J. Am. Chem. Soc. 2002;
124: 14410-14415;
(b) Gierschner J, Park SY. J. Mater. Chem. C. 2013; 1: 5818-5832.
4. (a) Chung JW, You YG, Huh HS, An B.-K, Yoon S-J, Kim SH, Lee SW,
Park SY. J. Am. Chem. Soc. 2009; 131: 8163-8172;
(b) Yoon SJ, Chung JW, Gierschner J, Kim KS, Choi M-G, Kim D, Park
SY. J. Am. Chem. Soc. 2010; 132: 13675-13683;
(c) Chung JW, Yoon S-J, An B-K, Park SY. J. Phys. Chem. C. 2013; 117:
11285-11291;
(d) Kwon MS, Gierschner J, Seo J, Park SY. J. Mater. Chem. C. 2014; 2:
2552-2557;
(e) Park JW, Nagano S, Yoon S-J, Dohi T, Seo J, Seki T, Park SY. Adv.
Mater. 2014; 26: 1354-1359.
5. (a) Mikroyannidis JA, Kabanakis AN, Sharma SS, Sharma GD. Adv.
Funct. Mater. 2011; 21: 746–755;
(b) Li XJ, Xu YX, Li F, Ma YG. Org. Electron. 2012; 13: 762-766;
(c) Jia WB, Yang P, Li JJ, Yin ZM, Kong L, Lu HB, Ge ZS, Wu YZ, Hao
XP, Yang JX. Polym. Chem. 2014; 5: 2282-2292.
6. (a) Lim C-K, Kim S, Kwon IC, Ahn C-H, Park SY. Chem. Mater. 2009;
21: 5819-5825;
a)
b)
(b) Zhang XQ, Zhang, XY, Yang B, Yang Y, Wei Y. Polym. Chem. 2014;
5: 5885-5889.
7. (a) Lim S-J, An B-K, Jung SD, Chung M-A, Park SY. Angew. Chem.,
Int. Ed. 2004; 43: 6346-6350;
(b) Nam H, Boury B, Park SY. Chem. Mater. 2006; 18: 5716-5721;
(c) Zhang Y, Sun J, Bian G, Chen YY, Ouyang M, Hu B, Zhang C.
Photochem. Photobiol. Sci. 2012; 11:1414-1421.
8. (a) An B-K, Gihm SH, Chung JW, Park CR, Kwon S-K, Park SY. J. Am.
Chem. Soc. 2009; 131: 3950-3957;
Fig. 9 (a) Emission spectra of pristine, ground and fumed with
ethanol samples of compound I3/12. (λex = 345 nm) (b)
Photographs of pristine and ground powders under 365 nm light.
(b) Kim JH, Watanabe A, Chung JW, Jung Y, An B-K, Tada H, Park
SY. J. Mater. Chem. 2010; 20: 1062-1064;
(c) Yun SW, Kim JH, Shin S, Yang H, An B-K, Yang L, Park SY. Adv.
Mater. 2012; 24: 911-915;
(d) Shin S, Gihm SH, Park CR, Kim S, Park SY. Chem. Mater. 2013;
25: 3288-3295;
(e) Jin YZ, Xia YJ, Wang S, Yan L, Zhou Y, Fan J, Song B. Soft Matter.
2015; 11: 798-805.
3. Conclusion
In summary, novel amphiphilic α-cyanostilbene derivatives
Im/n and IBm/10 have been synthesized. All of these compounds
exhibit enantiotropic liquid crystalline phases, increasing the
volumnar ratio of the terminal alkyl chains, not only bilayer
9. (a) An B-K, Lee D-S, Lee J-S, Park Y-S, Song H-S, Park SY. J. Am.
Chem. Soc. 2004; 126: 10232-10233;
(b) Chung JW, An B-K, Park SY. Chem. Mater. 2008; 20: 6750-6755;
(c) Yoon S-J, Kim JH, Chung JW, Park SY. J. Mater. Chem. 2011; 21:
18971-18973;
(d) Seo J, Chung JW, Cho I, Park SY. Soft Matter. 2012; 8: 7617-7622;
(e) Seo J, Chung JW, Kwon JE, Park SY. Chem. Sci. 2014; 5: 4845-
4850.
smectic A and columnar phases, but also
micellar cubic
Pm3n
phase are found in these compounds. The formation of the
micellar cubic phase is due to the larger interface curvature
between the flexible chains and the polar regions. The reversible
photoresponsive behavior of these compounds in liquid crystals,
10. Gulino A, Lupo F, Condorelli GG, Fragala ME, Amato ME, Scarlata G.
J. Mater. Chem. 2008; 18: 5011-5018.
11. Zhu LL, Ang CY, Li X, Nguyen KT, Tan SY, Ågren H, Zhao YL. Adv.

7
ACCEPTED MANUSCRIPT
Mater. 2012; 24: 4020-4024.
248.
12. (a) Li Y, Shen FZ, Wang H, He F, Xie ZQ, Zhang HY, Wang ZM, Liu
LL, Li F, Hanif M, Ye L, Ma YG. Chem. Mater. 2008; 20: 7312-7318;
(b) Varghese S, Yoon S-J, Calzado EM, Casado S, Boj PG, Díaz-García
MA, Resel R, Fischer R, Milián-Median B, Wannemacher R, Park SY,
Gierschner J. Adv. Mater. 2012; 24: 6473-6478;
(c) Park SK, Varghese S, Kim JH, Yoon S-J, Kwon OK, An B-K,
Gierschner J, Park SY. J. Am. Chem. Soc. 2013; 135: 4757-4764.
13. Kunzelman J, Kinami M, Crenshaw BR, Protasiewicz JD, Weder C. Adv.
Mater. 2008; 20:119-122.
36. Praveen VK, George SJ, Varghese R, Vijayakumar C, Ajayaghosh A. J.
Am. Chem. Soc. 2006; 128: 7542-7550.
37. Liu ZX, Feng Y, Yan ZC, He YM, Liu CY, Fan QH. Chem. Mater. 2012,
24, 3751-3757.
38 (a) Ding AX, Yang LM, Zhang YY, Zhang GB, Kong L, Zhang XJ, Tian
YP, Tao XT, Yang JX. Chem. Eur. J. 2014; 20: 12215-12222;
(b) Grabowski ZR, Rotkiewicz K. Chem. Rev. 2003; 103: 3899-4031.
39. (a) Levitus M, Schmieder K, Ricks H, Shimizu KD, Bunz UHF, Garibay
MAG. J. Am. Chem. Soc. 2001; 123: 4259-4265;
14. (a) Percec V, De Souza Gomes A, Lee M. J. Polym. Sci. 1991; 29: 1615-
1622;
(b) Tong H, Hong YN, Dong YQ, Ren Y, Haussler M, Lam JWY, Wong
KS, Tang BZ. J. Phys. Chem. B. 2007; 111: 2000-2007;
(c) Jia WB, Wang HW, Yang LM, Lu HB, Kong L, Tian YP, Tao XT,
Yang JX. J. Mater. Chem. C. 2013; 1: 7092-7101.
(b) Tsibouklis J, Richardson PH, Ahmed AM, Richards RW, Feast WJ.
Synth. Met. 1993; 61: 159-162;
(c) Aoki H, Mihara T, Koide N. Mol. Cryst. Liq. Cryst. 2004; 408: 53-70;
(d) Bao R, Pan M, Zhou Y, Qiu JJ, Tang HQ, Liu CM. Synth. Commun.
2012; 42: 1661-1668;
40. (a) Hong YN, Lam JWY, Tang BZ. Chem. Commun. 2009, 4332-4353;
(b) Liang GD, Lam JWY, Qin W, Li J, Xie N, Tang BZ. Chem. Commun.
2014; 50: 1725-1727;
(e) Mao WG, Chen K, Ouyang M, Sun JW, Zhou YB, Song QB, Zhang C.
Acta Chim. Sin. 2013; 71: 613-618.
(c) Peng Q, Yi YP, Shuai ZG, Shao JS. J. Am. Chem. Soc. 2007; 129:
9333- 9339.
15. (a) Wei RB, He YN, Wang XG, Keller P. Macromol. Rapid Commun.
2014; 35: 1571-1577;
(b) Morris SM, Qasim MM, Gardiner DJ, Hands PJW, Castles F, Tu G,
Huck WTS, Friend RH, Coles HJ. Opt. Mater. 2013; 35: 837-842.
16. Bao R, Pan M, Qiu JJ, Liu CM. Chin. Chem. Lett. 2010; 21: 682-685.
17. (a) Martínez-Abadía M, Varghese S, Milián-Medina B, Gierschner J,
Giménez R, Blanca Ros M. Phys. Chem. Chem. Phys. 2015; 17: 11715-
11724;
(b) Martínez-Abadía M, Robls-Hernández B, Villacampa B, Giménez R,
Ros MB. J. Mater. Chem. C. 2015; 3: 3038-3048.
18. Yoon S-J, Kim JH, Kim KS, Chung JW, Heinrich B, Mathevet F, Kim P,
Donnio B, Attias A-J, Kim D, Park SY. Adv. Funct. Mater. 2012; 22: 61-
69.
19. Lu HB, Zhang SN, Ding AX, Yuan M, Zhang GY, Xu W, Zhang GB,
Wang XH, Qiu LZ, Yang JX. New J. Chem. 2014; 38: 3429-3433.
20. (a) Zhang YJ, Sun JW, Lv XJ, Ouyang M, Fan GB, Wang W, Zhang C.
CrytEngComm. 2013; 15: 8998-9002;
(b) Zhang YY, Li HF, Zhang GB, Xu XY, Kong L, Tan YP, Yang, JX. J.
Mater. Chem. C. 2016; 4: 2971-2978.
21. Lu HB, Qiu LZ, Zhang GY, Ding AX, Xu WB, Zhang GB, Wang XH,
Kong L, Tian YP, Yang JX. J. Mater. Chem. C. 2014; 2: 1386-1389.
22. (a)Tschierske C, J. Mater. Chem. 1998; 8(7): 1485-1508;
(b)Tschierske C, Angew. Chem. Int. Ed. 2013; 52(34): 1 – 53.
23. Kato T. Angew. Chem., Int. Ed. 2010; 49: 7847-7848.
24. VanRheenen V, Cha DY, Hartley WM. Org. Synth. 1978; 58, 43-51.
25. Tan XP, Kong LY, Dai H, Cheng XH, Liu F, Tschierske C. Chem. Eur. J.
2013; 19: 16303-16313.
26. Dierking, I. Textures of Liquid Crystals, Wiley-VCH, Weinheim, 2003.
27. Cheng XH, Dng X, Wei GH, Prehm M, Tschierske C. Angew. Chem., Int.
Ed. 2009; 48: 8014-8017.
28. (a) Borisch K, Diele S, Goring P, Kresse H, Tschierske C. J. Mater.
Chem. 1998; 8: 529-543;
(b) Borisch K, Diele S, Goring P, Muller H, Tschierske C. Liq. Cryst.
1997; 22: 427-443;
(c) Borisch K, Diele S, Goring P, Kresse H, Tschierske C. Angew. Chem.
1997; 109: 2188-2190;
(d) Borisch K, Tschierske C, Goring P, Diele S. Chem. Commun. 1998,
2711-2712.
29. (a) Hudson SD, Jung H-T, Percec V, Cho W-D, Johansson G, Ungar G,
Balagurusamy VSK. Science. 1997; 278: 449-452;
(b) Percec, V.; Cho W-D, Mosier PE, Ungar G, Yeardley DJP. J. Am.
Chem. Soc. 1998; 120: 11061-11070;
(c) Percec V, Holerca MN, Uchida S, Cho W-D, Ungar G, Lee YS,
Yeardley DJP. Chem. Eur. J. 2002; 8: 1106-1117;
(d) Yeardley DJP, Ungar G, Percec V, Holerca MN, Johansson G. J. Am.
Chem. Soc. 2000; 122: 1684-1689;
(e) Rosen BM, Wilson CJ, Wilson DA, Peterca M, Imam MR, Percec V.
Chem. Rev. 2009; 109: 6275-6540.
30. Borisch K, Diele S, Goring P, Tschierske C. Chem. Commun. 1996, 237-
238.
31. (a) Ziherl P, Kamien RD. J. Phys. Chem. B. 2001; 105: 10147-10158;
(b) Grason GM, DiDonna BA, Kamien RD. Phys. Rev. Lett. 2003; 91:
058304.
32. Tan XP, Li Z, Xia M, Cheng XH. RSC Adv. 2016; 6: 20021-20026.
33. Westphal E, Bechtold IH, Gallardo H. Macromolecules 2010; 43: 1319-
1328.
34. Babu SS, Praveen VK, Ajayaghosh A. Chem. Rev. 2014; 114: 1973-2129.
35. Friggeri A, Feringa BL, Esch, JV. J. Controlled Release. 2004; 97: 241-