Diversified AIE and mechanochromic luminescence based on carbazole derivative decorated dicyanovinyl groups: Effects of substitution sites and molecular packing

Article abstract of DOI:10.1039/c9ce01958h

Aggregation-induced emission (AIE) properties have been widely investigated not only because they thoroughly circumvent the notorious aggregation-caused quenching effect encountered in conventional fluorophores but also due to their promising applications in organic light-emitting diodes, fluorescent sensors and bioimaging. In this work, we reported a study of the molecular packing and luminescence properties of AIE active positional isomers (m-BPCDM and p-BPCDM) with carbazole and dicyanovinyl groups. The compound m-BPCDM based on meta-substitution showed more evident AIE processes than the compound p-BPCDM based on para-substitution, which can be attributed to the strong π-π stacking effect brought by the spatial structure of p-BPCDM. Moreover, the two positional isomers also exhibited distinct mechanochromic luminescence properties.

Full text of DOI:10.1039/c9ce01958h

View Article Online
View Journal
Cr ystEngComm
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: K. Wang, H. Xiao,
L. Qian, M. Han, X. Wu, Z. Guo and H. Zhan, CrystEngComm, 2020, DOI: 10.1039/C9CE01958H.
Volume 20
Number 15
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
21
April 2018
Pages 2071-2202
CrystEngComm
Accepted Manuscripts are published online shortly after acceptance,
before technical editing, formatting and proof reading. Using this free
service, authors can make their results available to the community, in
citable form, before we publish the edited article. We will replace this
Accepted Manuscript with the edited and formatted Advance Article as
soon as it is available.
rsc.li/crystengcomm
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes to the
text and/or graphics, which may alter content. The journal’s standard
Terms & Conditions and the Ethical guidelines still apply. In no event
shall the Royal Society of Chemistry be held responsible for any errors
or omissions in this Accepted Manuscript or any consequences arising
from the use of any information it contains.
PAPER
Yuan Zhuang et al.
Structural study on PVA assisted self-assembled 3D
hierarchical iron (hydr)oxides
rsc.li/crystengcomm

Page 1 of 7
Please dC or y ns t oE tn ag dC jou ms tm margins
View Article Online
DOI: 10.1039/C9CE01958H
ARTICLE
Diversified AIE and mechanochromic luminescence based on
carbazole derivatives decorated dicyanovinyl groups: Effects of
Substitution Site and Molecular Packing
Received 00th January 20xx,
Accepted 00th January 20xx
‡
a
‡a
a
a
a
⁎,a,b
and Hongbing Zhan⁎,a
Kai Wang, Hui Xiao, Li Qian, Mingxi Han, Xianfeng Wu, Zhiyong Guo,
DOI: 10.1039/x0xx00000x
Aggregation-induced emission (AIE) properties have been widely investigated not only because they thoroughly circumvent
the notorious aggregation-caused quenching effect confronted in conventional fluorophores but also their promising
applications in organic light-emitting diodes, fluorescent sensors and bioimaging. In this work, we reported a study of the
molecular packing and luminescence properties of AIE active positional isomers (m-BPCDM and p-BPCDM) with carbazole
and dicyanovinyl groups. The compound of m-BPCDM based on the meta-substitution showed more evident AIE processes
than the compound of p-BPCDM based on the para-substitution, which can be attributed to the strong π-π stacking effect
brought by the plane spatial structure of p-BPCDM. Moreover, the two positional isomers also exhibited distinct
mechanochromic luminescence properties.
In 2001, Tang[17] et al. carried out a momentous and valuable
discovery, termed “aggregation-induced emission (AIE)” in a
series of propeller-like luminogens. They are weakly or non-
Introduction
Organic luminescent materials, because of their intense and
tunable emission intensity, have attracted tremendous
attention and been widely used in fields such as organic light-
luminescent in dilute solution, but the emission intensity and
fluorescence quantum efficiency are greatly increased in the
aggregated state. In a dilute solution, when the AIE luminogens
absorb energy and get excited, the peripheral rotors, such as
phenyl rings, rotate against the central stator and consume its
energy, which is called non-radiative transition, thereby
annihilates its excited state and attenuates its luminescence.[
In contrast, in the aggregate state, the steric hindrance
produced by the distorted molecular configuration cripples its
intermolecular π-π interaction and limits its intramolecular
rotation, as a result, enhances its luminescence intensity.[
This restriction of intramolecular rotation (RIR) is considered as
the main cause for the AIE effect. Generally, introducing
different kinds of rotatable units into its molecular structure can
be an efficient way to obtain materials with AIE effect.
[1,2]
[3-5]
emitting diodes,
biological imaging,
and fluorescent
[6-8]
sensors.
However, the common investigation of
luminescence processes is often carried out in dilute solution,
and when extended to the concentrated solution, the
luminescent behaviors of those molecules changed adversely.[9]
In the aggregation state, if the luminophores adopt a planar
conformation, which often consists of aromatic rings, those
molecules may experience strong π-π stacking interaction, and
prone to form some detrimental species such as excimers and
18]
3,19-21]
[
10,11]
H-aggregation,
thus leading to the well-known notorious
effect: aggregation-caused quenching (ACQ) effect.[12-14] Due to
the ACQ effect, conventional methods of enhancing
fluorescence quantum efficiency by increasing the number of
conjugated unit in its molecular structure cannot be effectively
implemented. Therefore, it can seriously hinder the
performance of traditional fluorophores in the lighting and
display industries. For instance, most luminescent materials are
inapplicable in working condition due to its weak emission
Among many AIE luminogens, molecules with D-π-A structure
shows advanced photoluminescence properties.[
22]
The
interaction of electron donor and electron acceptor on both
sides of the benzene ring can cause intramolecular charge
transfer (ICT), which considerably alter photophysical behaviors
of the luminogens, especially emission color tunability.[
Therefore, assembling with different types of electron donor
23,24]
[15,16]
intensity when utilized in aqueous environment.
and electron acceptor can effectively change the luminescence
process of organic luminescent materials.[
25-28]
Cyano group is
a. College of Materials Science and Engineering, Fuzhou University, Fuzhou 350108,
Fujian, PR China. E-mail: guozhy@fzu.edu.cn, hbzhan@fzu.edu.cn
Key Laboratory of Eco-materials Advanced Technology, Fuzhou University, Fujian
an ideal functional unit for the design of advanced optical
materials due to its strong electron-withdrawing ability and
structural simplicity.[ More remarkably, the steric effect of
b.
29]
Province, PR China.
1
†
Electronic supplementary information (ESI) available: H and 13C NMR spectra, FTIR
the cyano group can distort the conformation of the luminogen,
spectra and other spectra; X-ray single crystals data, theoretical calculation other
analysis data. CCDC: 1942676 (m-BPCDM), 1942677 (p-BPCDM). See DOI:
making the molecule immune to the ACQ effect.[
30,31]
Carbazole,
‡
K. W. and H. X. contributed equally.
an essential nitrogen-containing aromatic heterocyclic ring with
a special rigid fused ring, and its derivatives, exhibit many
Please do not adjust margins

Please dC or y ns t oE tn ag dC jou ms tm margins
Page 2 of 7
ARTICLE
Journal Name
unique photoelectric properties and bioactivities.[32] Owing to
its electron-donating ability, high thermal stability and
photochemical stability, carbazole groups have been widely
exploited in the design of AIEgens.[33] Herein, we synthesized
two new D-π-A types of AIEgens based on electron acceptor of
cyano groups, and electron donor of carbazole groups. These
two novel molecules exhibit similar spatial structures, except
for the meta- substitution site of m-BPCDM and para-
substitution site of p-BPCDM on central benzene which causes
different degrees of distortion of their spatial conformation,
and therefore dramatically alters their AIE properties. More
interesting, we further ascribe the significantly different AIE and
mechanochromic luminescence performance of these D-π-A
compounds to their different intermolecular packing in the
crystalline phase. Meanwhile, preliminary DFT studies
confirmed the above proposed mechanism.
View Article Online
DOI: 10.1039/C9CE01958H
Scheme 1 Synthesis of m-BPCDM and p-BPCDM.
(
9H-carbazol-9-yl)phenyl)methanone) (p-BPMCz). Compounds
1
and 2 were synthesized by classical Friedel-Crafts acylation
reaction.[ Isophthaloyl dichloride (2.52 g, 13 mmol) was
dissolved in fluorobenzene (15 mL) under nitrogen atmosphere,
and anhydrous aluminium chloride (3.50 g, 52 mmol) was added
34]
Experimental
Materials and Instrumentation
All reagents and solvents were used as received from after mixing uniformly. After 8 h, the mixture was poured into
1
commercial suppliers without further purification. The H and crushed ice and filtered to obtain a white precipitate. The
1
3
C NMR was recorded at 298 K using Bruker Advance III 500 precipitate was then washed with a 10% NaOH solution for
MHz spectrometer. Fourier-transform infrared spectroscopy several times to obtain a fluffy white powder (3.24 g) (1).
FT-IR) was performed on a Nicolet 5700 spectrometer. Compound 1 (0.65 g, 2 mmol) was mixed with carbazole (0.73 g,
(
Elemental analyses (C, H, N) were carried out on a Vario EL 4.4 mmol) in anhydrous N, N′-dimethylformamide (DMF) (25 ml)
analyzer. Mass spectra were obtained on an Agilent 6520B under nitrogen atmosphere, and t-BuOK (0.52 g, 4.6 mmol) was
spectrometer. The powder X-ray diffraction (PXRD) data were added in room temperature. The reaction system was then
collected on a Miniflex 600 diffractometer at room temperature heated to 120 °C for 24 h. The mixture was poured into crushed
using Cu Kα radiation (λ = 0.15418 nm) with 15 mA, 40 kV, and ice to obtain a yellow precipitate, and then the precipitate was
-1
a scan rate of 3° min (2θ, 5°-40°). The UV absorption spectra dissolved in dichloromethane and dried over anhydrous MgSO4.
were attained by PE LAMBDA365 at ambient temperature. The After removing the solvent, the residue was purified by silica gel
PL spectra, fluorescence lifetimes and PL quantum yields were chromatography eluting with 50% petroleum ether in
conducted on an Edinburgh FLS1000 fluorescence dichloromethane. The product (m-BPMCz, 0.92 g) was dried to
spectrophotometer at room temperature. The slit widths of afford the pure yellow solid product. The synthetic procedure
excitation and emission were set the same in AIE experiment, of p-BPMCz is like m-BPMCz. m-BPMCz: Yield 12%. Light yellow
1
and before fluorescence measurement, the solution of both solid. H NMR (500 MHz, CDCl ): δ (ppm) 8.42 (t, J = 1.7 Hz, 1H),
3
two compounds was evenly dissolved in corresponding solvents. 8.18-8.12 (m, 10H), 7.81-7.77 (m, 4H), 7.75 (d, J = 7.6 Hz, 1H),
Particle size distributions of both molecules in acetone/water 7.54 (dd, J = 8.2, 0.9 Hz, 4H), 7.42 (ddd, J = 8.2, 7.1, 1.2 Hz, 4H),
1
3
mixture were conducted by Malvern Zetasizer Nano ZS for 7.32 (td, J = 7.5, 1.0 Hz, 4H). C NMR (150 MHz, CDCl ): δ (ppm)
3
several times to attain average values.
194.79, 142.30, 140.72, 140.20, 135.24, 132.00, 129.86, 126.45,
-1
1
26.28, 123.95, 120.76, 120.54, 109.78. FTIR (KBr, cm ): 1662
Synthesis and Characterization
(
C=O), 1598, 1511, 1450, 740. Anal. calcd for C44 : C,
28 2 2
H N O
m-BPMCz and p-BPMCz were synthesized by classical Friedel-
Crafts acylation reaction and purified for the next reaction. m-
8
5.69; H, 4.58; N, 4.54. Found: C, 85.61; H, 4.60; N, 4.52. p-
1
BPMCz: Yield 15%. Yellow solid. HNMR (500 MHz, CDCl
3
): δ
BPCDM
yl)phenyl)methaneylylidene))dimalononitrile) and p-BPCDM
2,2'-(1,4-phenylenebis((4-(9H-carbazol-9-
(2,2'-(1,3-phenylenebis((4-(9H-carbazol-9-
(
ppm) 8.22-8.13 (m, 8H), 8.08 (s, 4H), 7.82 (d, J = 8.5 Hz, 4H),
7
7
1
1
.57 (dd, J = 8.3, 0.9 Hz, 4H), 7.48 (ddd, J = 8.3, 7.1, 1.2 Hz, 4H),
(
13
.36 (td, J = 7.5, 1.0 Hz, 4H). C NMR (150 MHz, CDCl
3
): δ (ppm)
yl)phenyl)methaneylylidene))dimalononitrile) were synthesized
by the respective reactions of m-BPMCz and p-BPMCz with
malononitrile in the presence of titanium tetrachloride and
pyridine (Scheme 1), and comprehensively characterized by
94.64, 142.26, 140.20, 137.93, 135.29, 133.62, 131.98, 131.04,
-1
28.80, 126.46, 126.29, 123.93, 109.79. FTIR (KBr, cm ): 1660
(
C=O), 1598, 1510, 1450, 921, 750. Anal. calcd. for C44
C, 85.69; H, 4.58; N, 4.54. Found: C, 85.63; H, 4.60; N, 4.51.
Synthesis of 2,2'-(1,3-phenylenebis((4-(9H-carbazol-9-
yl)phenyl)methaneylylidene))dimalononitrile (m-BPCDM) and
,2'-(1,4-phenylenebis((4-(9H-carbazol-9-
28 2 2
H N O :
1
Fourier transform infrared (FT-IR) spectroscopy (Fig. S1), and H
1
3
NMR and C NMR (Fig. S2-S9).
Synthesis of 1,3-phenylenebis((4-(9H-carbazol-9-
yl)phenyl)methanone) (m-BPMCz) and 1,4-phenylenebis((4-
2
yl)phenyl)methaneylylidene))dimalononitrile (p-BPCDM). m-
2
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 7
Please dC or y ns t oE tn ag dC jou ms tm margins
Journal Name
ARTICLE
BPMCz (0.25 g, 0.41 mmol) and malononitrile (0.26 g, 4 mmol)
were dissolved in anhydrous dichloromethane (20 ml). After
mixing uniformly, the mixture was cooled to 0 °C under nitrogen
atmosphere. Anhydrous titanium tetrachloride (0.52 ml, 4.8
mmol) was then slowly added to the solution via a syringe. The
mixture was stirred at 0 °C for 2 h before pyridine (1.04 ml, 13
mmol) was added dropwise to the solution. The reaction
mixture was then warmed to room temperature and then
heated to reflux for 24 h. The reaction mixture was poured into
dichloromethane and subsequently collected the filtrate. The
filtrate was extracted with 10% HCl aqueous solution (200 ml)
View Article Online
DOI: 10.1039/C9CE01958H
Fig. 1 Normalized emission spectra of m-BPCDM (a) and p-BPCDM (b) in different
solvents (10-5 M). DCM, dichloromethane; EtOAc, ethyl acetate; DMF,
dimethylformamide; excitation wavelength: 377 nm.
and 10% NaHCO
the filtrate was collected and dried over anhydrous MgSO
After removing the solvent, the residue was purified via silica
gel chromatography with dichloromethane/petroleum ether Results and discussion
3
aqueous solution (200 ml), respectively. Then
4
.
(
2:1 v/v) as eluent. The product was then dried to afford the
Solvatochromism
pure orangish solid product (0.20 g, 0.28 mmol). p-BPCDM was
The existence of electron-withdrawing dicyanovinyl groups and
electron-donating carbazole groups implies that m-BPCDM and
p-BPCDM both are typical D-π-A structure, except for a
difference in their spatial construction. Based on the
dependence of the photophysics of the D-π-A conjugates on the
polarity of the solution, the UV absorption spectra of these two
compounds in different solvents were investigated (Fig. S10).
The characteristic absorption peaks of m-BPCDM and p-BPCDM
underwent an obvious blue shift from 435 nm to 403 nm and
439 nm to 407 nm following with the polarity of the solvents,
respectively. By further investigation, the emission spectra data
of m-BPCDM and p-BPCDM were performed in Fig. 1 and Table
S1. Clearly, with the change of the polarity of different solutions
from low polar toluene to highly polar acetone, the emission of
m-BPCDM and p-BPCDM are gradually red-shifted from 555 nm
to 608 nm and 477 nm to 603 nm respectively, exhibiting an
evident bathochromic effect. These results indicate that the
fluorescence behaviours of m-BPCDM and p-BPCDM are highly
dependent on the solvent polarity, which can be ascribed to the
fact that the combination of the electron-donating carbazole
groups and the electron-accepting dicyanovinyl group enables
ICT processes in the molecule. Optical and electronic properties
of m-BPCDM and p-BPCDM and their precursors were summed
in Table 1.
also prepared by the above method. m-BPCDM: Yield 68%.
1
3
Orange solid. H NMR (500 MHz, CDCl ): δ (ppm) 8.15 (d, J = 7.8
Hz, 4H), 7.85-7.74 (m, 12H), 7.57 (d, J = 8.2 Hz, 4H), 7.46 (t, J =
13
7
.7 Hz, 4H), 7.35 (t, J = 7.4 Hz, 4H). C NMR (150 MHz, CDCl
3
): δ
(
ppm) 171.56, 142.88, 139.80, 137.13, 133.75, 132.62, 132.51,
1
1
1
31.68, 130.11, 126.66, 126.45, 124.20, 121.18, 120.57, 113.54,
-1
13.50, 109.90, 82.91. FTIR (KBr, cm ): 2223 (CN), 1598, 1512,
450, 752. Anal. calcd. for C50 : C, 84.25; H, 3.96; N, 11.79.
28 6
H N
28 6
Found: C, 84.21; H, 3.98; N, 11.76. ESI-MS: calcd. for C50H N ,
M+Cl]-
[
:
747.2064
.
Found: 747.2069. p-BPCDM: Yield 71%.
): δ (ppm) 8.22-8.06 (m,
H), 7.76 (ddd, J = 15.7, 12.3, 7.7 Hz, 8H), 7.55 (d, J = 8.1 Hz, 4H),
1
Orange solid. H NMR (500 MHz, CDCl
3
8
7
13
.48-7.37 (m, 4H), 7.33 (dt, J = 7.5, 4.0 Hz, 4H). C NMR (150
): δ (ppm) 171.43, 142.76, 139.82, 132.89, 132.28,
30.92, 126.67, 126.45, 124.18, 121.19, 120.62, 113.47, 113.39,
09.81, 83.25. FTIR (KBr, cm ): 2223 (CN), 1598, 1510, 1450,
50. Anal. calcd. for C50 : C, 84.25; H, 3.96; N, 11.79. Found:
MHz, CDCl
3
1
1
7
-1
28 6
H N
-
C, 84.22; H, 3.98; N, 11.77. ESI-MS: calcd. for C50
47.2064 Found: 747.2069.
DFT calculations
28 6
H N , [M+Cl] :
7
.
The ground-state geometries were optimized at the level of
B3LYP/6-31G(d), spatial distributions of the HOMOs and LUMOs
of the compounds were obtained from the optimized ground
state structures. Based on the optimized configuration of the
Aggregation-Induced Emission
0
ground state (S ), the high excitation energy levels of singlet and
triplet states were evaluated using B3LYP/6-31G(d).
By further inspecting the structures of these two molecules, the
single bond connecting the carbazole group and the adjacent
benzene ring entered our sight. It is well known that molecules
Table 1 Optical and electronic properties of m-BPCDM and p-BPCDM.
solna
crystal
e
e
compound
E
HOMO (eV)
E
LUMO (eV)
E
HOMO (eV)
E
LUMO (eV)
b
(%) τc (ns)
b
τc (ns)
λabs (nm)
λ
em (nm)
Ф
F
λem (nm)
Ф
F
(%)
m-BPCDM
p-BPCDM
m-BPMCz
p-BPMCz
412
420
339
336
596
592
498
550
0.30
0.20
0.50
0.20
4.51
3.97
2.81
4.22
565
609
521
565
69.74
17.39
23.45
3.72
7.89
4.43
2.50
2.04
-5.04d
-5.46
-5.36d
-5.53d
-2.43
-3.35d
-2.14
-2.37
-5.40
-5.67
-5.39
-5.51
-3.06
-3.16
-1.99
-2.34
a
Tested in a THF solution (10-5 M). b Fluorescence quantum yield determined by a calibrated integrating sphere in THF. Lifetime of the prompt component in transient
c
PL. d Calculated from cyclic voltammetry experiments calibrated by Fc/Fc and UV absorption spectra. Calculated from the B3LYP/6-31G(d) basis set.
+
e
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2019, 12, 1-3 | 3
Please do not adjust margins

Please dC or y ns t oE tn ag dC jou ms tm margins
Page 4 of 7
ARTICLE
Journal Name
fluorescent emission exhibited a certain red-shift as a result of
View Article Online
DOI: 10.1039/C9CE01958H
intramolecular charge transfer, which is a well-known
photophysical phenomenon that common exists in the D-π-A
conjugated organic dyes.[
35,36]
w
As the f continued to increase,
most of the molecules began to aggregate, which encumbered
the rotation of the carbazole units and reduced the non-
radiative transition, ultimately enhanced the PL intensity.[
After the aggregation process finished, the suspension solution
37]
was diluted as f
intensity decreased. The particle sizes of m-BPCDM and p-
BPCDM in the mixture with a f of 70% were determined to be
66 nm and 157 nm respectively, using dynamic light scattering
DLS), confirming the formation of nanoaggregates (Fig. 2e and
w
increased from 70% to 90% and thus the PL
w
1
(
f).
Crystal Structure
To further explore the underlying reasons for this significant
substitution site dependent emission behavior, an inspection of
their single crystal structures was performed (Fig. 3 and Fig. S17).
Fig. 3 presents the single x-ray crystal structures of m-BPCDM
and p-BPCDM. Crystal p-BPCDM adopted a near-planar
conformation and the torsion angles of the carbazole group
relative to the attached benzene ring, the attached benzene
ring relative to the dicyanovinyl group, the central benzene ring
towards the dicyanovinyl group were 48.13°, 36.61° and 46.49°,
respectively (Fig. 3b). In comparison, the crystal of its positional
isomer m-BPCDM showed an obvious twisted conformation in
Fig. 2 (a) PL spectra of m-BPCDM and p-BPCDM in acetone/water mixtures with different
water fractions (f
water fractions (f
). (d) Plots of the PL peak intensity of p-BPCDM vs the water fraction (f
size distribution of m-BPCDM in an acetone/water mixture with a f
Particle size distribution of p-BPCDM in an acetone/water mixture with a f
Concentration: 10-5 M (f
= 0%); excitation wavelength: 377 nm.
w
). (b) PL spectra of p-BPCDM in acetone/water mixtures with different
w
). (c) Plots of the PL peak intensity of m-BPCDM vs the water fraction
(
f
w
w
). (e) Particle its crystal structure. The torsion angle between the carbazole
value of 70%. (f) group and the attached benzene ring nearly 33.22°, while the
w
w
value of 70%.
torsion angles of the attached benzene ring towards the
dicyanovinyl, the central benzene ring towards the dicyanovinyl
group go contrary, which were 36.27° and 46.72° respectively.
Besides, the distances between two neighboring carbazole units
in m-BPCDM and p-BPCDM are 4.759 Å and 5.381 Å (Fig. 3). On
the other hand, the vertical distances between two neighboring
w
with rotors, here are carbazole groups, in the non-aggregated
state, are easy to consume energy through the rotation of the
rotors and diminish the emission subsequently. According to
the RIR mechanism of AIE, m-BPCDM and p-BPCDM could also
feature the AIE effect.
To confirm this speculation, the PL spectra of m-BPCDM and
p-BPCDM in the solid state and in acetone solution were
recorded under UV light (Fig. S13). Both m-BPCDM and p-
BPCDM are highly emissive in the solid and aggregated state
with fluorescence quantum yield of m-BPCDM and p-BPCDM is
6
9.74% and 17.39% respectively. However, both are rather
weakly emissive in liquid medium.
The above tests showed BPCDM isomers with excellent
fluorescence quantum efficiency in the solid state which
indicates the existence of the AIE effect. Hence, their AIE
properties were tested delicately in a solution of acetone and
water which served as a good and poor solvent, respectively.
For both compounds, they showed a weak emission in acetone,
and with the increase of the water infraction (f ), the emission
w
intensity boosted a lot from 30% for m-BPCDM (for p-BPCDM,
from 40%), and yielded approximately a 240-fold (30-fold for p-
BPCDM) of luminescence intensity enhancement when the f
was increased up to 70% (Fig. 2c and d). The slight increase of
the f resulted in an augment of the polarity of the solvent,
w
Fig. 3 Single crystal structures and molecular packing patterns of m-BPCDM (a) and p-
BPCDM (b), and the molecular packing viewed from the bottom and side of adjacent
w
followed by the abatement of the PL intensity. Besides, the molecules.
4
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 5 of 7
Please dC or y ns t oE tn ag dC jou ms tm margins
Journal Name
ARTICLE
to their precursors m-BPMCz and p-BPMCz (Table S3), the D-π-
View Article Online
DOI: 10.1039/C9CE01958H
A type structure in positional isomers m-BPCDM and p-BPCDM
makes the ICT effect more apparent,[ the polarization degree
more significant, accordingly resulting in an obvious red shift of
their PL spectra (Fig. 5).
40]
Intriguingly, the maximum emission peak of p-BPCDM
towards its precursor p-BPMCz, red-shifted from 504 nm to 606
nm, while for its positional isomer m-BPCDM, red-shifted from
5
00 nm to 568 nm. Thus, altering the substitution pattern of the
molecules can tune the distribution of HOMOs and LUMOs,
leading into the changes of ICT effect, and eventually, partially
changing the PL properties of the molecules.
Fig. 4 Optimized molecular structures and molecular amplitude plots of HOMO and
LUMO energy levels of m-BPCDM and p-BPCDM.
Mechanochromic Luminescence Property
molecules were calculated to be 4.309 Å and 4.886 Å (Fig. S17),
respectively. The above results suggest that p-BPCDM
encounter stronger intermolecular π-π stacking interactions
and thus resulting in weaker fluorescence in its solid state.
Adversely, m-BPCDM experiences comparative weaker
intermolecular π-π stacking interactions and therefore exhibits
higher PL intensity in the solid state (Fig. S14). The fluorescence
quantum yields of m-BPCDM and p-BPCDM were measured to
be 69.74% and 17.39%, respectively. The above results further
indicate that the quenching effect is relevant with crystal
packing style. As we assumed, the distortion of the molecular
skeleton in these D-π-A type positional isomers can induce AIE
Because of the distortion of relevant molecular structures, under
external force, the arrangement or accumulation mode of the
molecules may change and therefore alter the luminescence
[41]
properties of these compounds.
Accordingly, the luminescence
behaviors and structure changes by grinding the three compounds
under external force were investigated.
As shown in Fig. 6a and c, the pristine crystals of m-BPCDM and p-
BPCDM emitted at 565 nm and 609 nm, respectively. After grinding,
the spectra of these compounds were red-shifted to 590 nm and 617
nm. During the grinding process, the crystal lattice collapses, and the
molecules adopted a more planar conformation that altered the
luminescence behaviors. Intriguingly, as compared to p-BPCDM, m-
BPCDM with more distort structure displayed more obvious red-shift
in its fluorescence spectra. From a crystallographic point of view,
there is less free space in p-BPCDM, so its PL spectra almost keep the
same before and after grinding. As shown in Fig. 6b and d, both p-
BPCDM and m-BPCDM in their pristine form displayed sharp and
intense diffraction peaks that can be attributed to crystalline
structures. The sharp diffraction peaks disappeared after grinding,
yielding a broad band indicating that its morphology became
amorphous. After recrystallization under dichloromethane vapor for
[38,39]
effect reasonably.
Besides,
a
moderately twisted
configuration within the molecular framework may bring about
some specific luminescent behaviors, such as mechanically
responsive luminescence.
Theoretical Calculation and Analysis
Given the introduction of electron-withdrawing dicyanovinyl
groups and electron-donating carbazole groups, and the
positional isomers m-BPCDM and p-BPCDM, some evident
distinctions can be observed in their molecular structure and
their packing mode in crystal. In view of this, the molecular
orbital amplitude plots of the positional isomers (m-BPCDM and
p-BPCDM) are theoretically calculated by density functional
theory (DFT) at the level of B3LYP/6-31G(d) (Fig. 4).
6
h, the crystallinity and fluorescence of the two compounds was
The highest occupied molecular orbitals (HOMOs) of both
two compounds are mainly concentrated on the electron-rich
carbazole groups, scarcely distributed on the benzene rings. The
lowest unoccupied molecular orbitals (LUMOs) of m-BPCDM
and p-BPCDM are chiefly concentrated on the electron-
deficient dicyanovinyl groups and the benzene rings. Compared
Fig. 6 PL spectra of different processes of m-BPCDM (a) and p-BPCDM (c). Comparison
of XRD patterns of m-BPCDM (b) and p-BPCDM (d) between simulated, unground,
ground and fumed samples. Recrystallized the amorphous powder under
dichloromethane vapor for 6 h.
Fig. 5 (a) PL spectra of m-BPCDM and its precursor. (b) PL spectra of p-BPCDM and its
precursor.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2019, 12, 1-3 | 5
Please do not adjust margins

Please dC or y ns t oE tn ag dC jou ms tm margins
Page 6 of 7
ARTICLE
Journal Name
1
1
1
1 W. Z. Yuan, P. Lu, S. Chen, J. W. Y. Lam, Z. Wang, Y. LViiuew, HA.rtSic.leKOwnolinke,
resumed after fuming, indicating the reversible mechanochromic
luminescence properties of m-BPCDM and p-BPCDM in response to
external stimuli.
Y. Ma and B. Z. Tang, Adv. Mater., 2010, 22, 2159-2163.
DOI: 10.1039/C9CE01958H
2 A. Qin, J. W. Y. Lam and B. Z. Tang, Prog. Polym. Sci., 2012, 37,
182-209.
3 N. Sun, K. Su, Z. Zhou, Y. Yu, X. Tian, D. Wang, X. Zhao, H. Zhou
and C. Chen, ACS Appl Mater Interfaces, 2018, 10, 16105-16112.
Conclusions
14 W. L. Li, J. Wang, Y. X. Xie, M. Tebyetekerwa, Z. Y. Qiu, J. J. Tang,
S. Y. Yang, M. F. Zhu and Z. X. Xu, Prog. Org. Coat., 2018, 120, 1-
In summary, two carbazole derived fluorescent molecules
functionalized by strong electron withdrawing dicyanovinyl
9.
15 G. S. Beddard and G. Porter, Nature, 1976, 260, 366-367.
groups were designed and synthesized. The effects of positional 16 H. T. Lin, C. L. Huang and G. S. Liou, ACS Appl. Mater. Interfaces,
2
019, 11, 11684-11690.
isomers on AIE and mechanochromic luminescence properties
were systematically investigated. The results showed that the
space steric of bulky aromatic groups and dicyanovinyl groups
enabled the two isomers to crystallize with a twisted molecular
17 J. Luo, Z. Xie, J. W. Lam, L. Cheng, H. Chen, C. Qiu, H. S. Kwok, X.
Zhan, Y. Liu, D. Zhu and B. Z. Tang, Chem. Commun., 2001, 18,
1740-1741.
18 Z. J. Zhao, B. R. He and B. Tang, Chem. Sci., 2015, 6, 5347-5365.
conformation, which subsequently endowed them with AIE 19 Y. N. Hong, J. W. Y. Lam and B. Z. Tang, Chem. Commun., 2009,
4332-4353.
features by emitting a strong fluorescence in the aggregated
state. The single crystal X-ray analysis further confirmed that
the π-π stacking interaction in p-BPCDM is stronger than that of
m-BPCDM, therefore it exhibited much weaker emission
2
0 J. Guo, S. Hu, W. Luo, R. Hu, A. Qin, Z. Zhao and B. Z. Tang, Chem.
Commun., 2017, 53, 1463-1466.
21 J. Mei, N. L. Leung, R. T. Kwok, J. W. Lam and B. Z. Tang, Chem
Rev, 2015, 115, 11718-11940.
intensity in the solid state of p-BPCDM. Moreover, m-BPCDM 22 B. W. Xu, X. F. Wu, H. B. Li, H. Tong and L. X. Wang,
Macromolecules, 2011, 44, 5089-5092.
presented
reversible
mechanochromic
luminescence
23 Y. P. Zhang, D. D. Li, Y. Li and J. H. Yu, Chem. Sci., 2014, 5, 2710-
properties due to its non-face by face packing configuration. It
is anticipated that such positional isomer strategy can be
extended to other molecular systems allowing many new types
2716.
24 J. Shi, L. Xu, C. Chen, X. Lv, Q. Ding, W. Li, S. Xue and W. Yang,
Dyes Pigments, 2019, 160, 962-970.
of stimuli-responsive luminescent and AIE effective materials to 25 L. A. Duan, J. A. Qiao, Y. D. Sun and Y. Qiu, Adv. Mater., 2011, 23,
1137-1144.
be fabricated.
26 Z. F. Chang, L. M. Jing, B. Chen, M. Zhang, X. Cai, J. J. Liu, Y. C. Ye,
X. Lou, Z. Zhao, B. Liu, J. L. Wang and B. Z. Tang, Chem. Sci., 2016,
7, 4527-4536.
Conflicts of interest
There are no conflicts to declare.
2
2
2
3
7 A. Ekbote, T. Jadhav and R. Misra, New. J. Chem., 2017, 41, 9346-
353.
8 Y. Chen, J. Guo, X. Wu, D. Jia and F. Tong, Dyes Pigments, 2018,
48, 180-188.
9 K. A. N. Upamali, L. A. Estrada, P. K. De, X. C. Cai, J. A. Krause and
D. C. Neekers, Langmuir, 2011, 27, 1573-1580.
9
1
Acknowledgements
This work was supported by the financial support from the
National Natural Science Foundation of China (Grant Nos.
0 E. Ishow, A. Brosseau, G. Clavier, K. Nakatani, P. Tauc, C. Fiorini-
Debuisschert, S. Neveu, O. Sandre and A. Leaustic, Chem. Mater.,
2
008, 20, 6597-6599.
1 B. K. An, J. Gierschner and S. Y. Park, Acc. Chem. Res., 2012, 45,
44-554.
2 Z. Y. Yang, Z. G. Chi, T. Yu, X. Q. Zhang, M. N. Chen, B. J. Xu, S. W.
Liu, Y. Zhang and J. R. Xu, J. Mater. Chem., 2009, 19, 5541-5546.
3 Q. Zeng, Z. Li, Y. Dong, C. Di, A. Qin, Y. Hong, L. Ji, Z. Zhu, C. K. Jim,
G. Yu, Q. Li, Z. Li, Y. Liu, J. Qin and B. Z. Tang, Chem. Commun.,
5
1703031 and 51872048).
3
3
3
5
Notes and references
1
2
3
4
5
6
7
H. B. Wu, L. Ying, W. Yang and Y. Cao, Chem. Soc. Rev., 2009, 38,
391-3400.
H. Uoyama, K. Goushi, K. Shizu, H. Nomura and C. Adachi, Nature,
012, 492, 234-238.
R. Hu, N. L. Leung and B. Z. Tang, Chem. Soc. Rev., 2014, 43, 4494-
562.
X. Y. Zhang, K. Wang, M. Y. Liu, X. Q. Zhang, L. Tao, Y. W. Chen
and Y. Wei, Nanoscale, 2015, 7, 11486-11508.
Z. Yang, Z. Mao, Z. Xie, Y. Zhang, S. Liu, J. Zhao, J. Xu, Z. Chi and
M. P. Aldred, Chem. Soc. Rev., 2017, 46, 915-1016.
A. P. de Silva, T. S. Moody and G. D. Wright, Analyst, 2009, 134,
3
2
007, 70-72.
3
4 W. L. Zhao and E. M. Carreira, Org. Lett., 2006, 8, 99-102.
5 W. Qin, D. Ding, J. Liu, W. Z. Yuan, Y. Hu, B. Liu and B. Z. Tang, Adv.
Funct. Mater., 2012, 22, 771-779.
2
3
4
3
6 R. R. Hu, E. Lager, A. Aguilar-Aguilar, J. Z. Liu, J. W. Y. Lam, H. H. Y.
Sung, I. D. Williams, Y. C. Zhong, K. S. Wong, E. Pena-Cabrera and
B. Z. Tang, J. Phys. Chem. C, 2009, 113, 15845-15853.
7 J. Mei, Y. Hong, J. W. Lam, A. Qin, Y. Tang and B. Z. Tang, Adv.
Mater., 2015, 26, 5429-5479.
3
3
8 W. Z. Yuan, Y. Gong, S. Chen, X. Y. Shen, J. W. Y. Lam, P. Lu, Y. Lu,
Z. Wang, R. Hu, N. Xie, H. S. Kwok, Y. Zhang, J. Z. Sun and B. Z.
Tang, Chem. Mater., 2012, 24, 1518-1528.
2
385-2393.
A. P. de Silva, H. Q. N. Gunaratne, T. Gunnlaugsson, A. J. M.
Huxley, C. P. McCoy, J. T. Rademacher and T. E. Rice, Chem. Rev.,
1
3
4
4
9 T. Jadhav, B. Dhokale and R. Misra, J. Mater. Chem. C, 2015, 3,
997, 97, 1515-1566.
9063-9068.
8
9
1
S. W. Thomas, G. D. Joly and T. M. Swager, Chem. Rev., 2007, 107,
339-1386.
Y. N. Hong, J. W. Y. Lam and B. Z. Tang, Chem. Soc. Rev., 2011, 40,
0 J. N. Zhang, H. Kang, N. Li, S. M. Zhou, H. M. Sun, S. W. Yin, N.
Zhao and B. Z. Tang, Chem. Sci., 2017, 8, 577-582.
1
1 C. Feng, K. Wang, Y. Xu, L. Liu, B. Zou and P. Lu, Chem. Commun.,
5361-5388.
2
016, 52, 3836-3839.
0 A. C. Grimsdale, K. L. Chan, R. E. Martin, P. G. Jokisz and A. B.
Holmes, Chem. Rev., 2009, 109, 897-1091.
6
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 7 of 7
CrystEngComm
View Article Online
DOI: 10.1039/C9CE01958H
Two positional isomers exhibited noticeable different luminescence properties, which were
mainly attributed to their different molecular packing modes.
2
40 fold
NC
CN NC
CN
N
N
weak π-π stacking
strong π-π stacking
0
%
70%
0%
CN
0%
7
NC
N
N
CN
NC
3
0 fold