A TPE-benzothiazole piezochromic and acidichromic molecular switch with high solid state luminescent efficiency

Article abstract of DOI:10.1039/c7ra12655g

A new organic compound, namely B-TPEAN, was constructed by using tetraphenylethylene, acrylonitrile and benzothiazole as building blocks. Herein, results of single crystal structure analysis and theoretical calculation for the as-synthesized compound were

Full text of DOI:10.1039/c7ra12655g

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A TPE–benzothiazole piezochromic and
acidichromic molecular switch with high solid state
Cite this: RSC Adv., 2018, 8, 6252
luminescent efficiency†
ef
Chunping Ma,‡ab Jiajun He,‡c Bingjia Xu,d Gaoyi Xie,
Zongliang Xie,c Zhu Maoc
*
c
*
and Zhenguo Chi
A new organic compound, namely B-TPEAN, was constructed by using tetraphenylethylene, acrylonitrile
and benzothiazole as building blocks. Herein, results of single crystal structure analysis and theoretical
calculation for the as-synthesized compound were presented. Photophysical properties, including UV-
visible absorption, photoluminescence and fluorescent quantum yield, were also well studied. B-TPEAN
was found to show excellent aggregation-induced emission (AIE) properties and high quantum yield (up
to 85%) in the solid-state. These results should be attributed to the positive effect of a combination of
two typical AIE moieties in one molecule. Upon grinding, the emission color of the pristine sample for B-
TPEAN changed from bluish green (lem,max ¼ 497 nm) to yellow (lem,max ¼ 567 nm), exhibiting
a remarkable piezochromism. Moreover, by fuming with acid vapor, both of the pristine and the ground
samples of B-TPEAN showed dramatic decreases in fluorescence quantum yields and large
bathochromic shifts in PL maxima up to 53 nm and 80 nm, respectively, indicating a success in achieving
multi-stimuli-responsive luminophore with high contrast in both emission intensity and color. Further
investigation revealed that the acidifluorochormism of the samples was caused by the protonation of the
benzothiazole moiety, leading to an enhancement of ICT effect in the protonated molecules.
Received 21st November 2017
Accepted 1st February 2018
DOI: 10.1039/c7ra12655g
rsc.li/rsc-advances
emission of uorescent materials in the solid state is required.
Unfortunately, most of the organic dyes quench or weaken their
1. Introduction
uorescence in the aggregation state, due to the notorious
aggregation caused quenching (ACQ) effect.9,10 For example, Li
et al.11 reported that an imide dye based on tetrahydro[5]heli-
cene skeleton exhibited remarkable and reversible acid/base
stimulated uorescence switching properties in both solution
and solid state. However, the quantum yield of the compound
in solid state (7.4%) was much lower than that in solution
(75.2% in cyclohexane and 72.6% in toluene). A strategy to
overcome the ACQ effect is to let the aggregation play positive
instead of negative roles in enhancing the efficiency in molecule
emission.12 The substances with anti-ACQ property are called
aggregation-induced emission (AIE) compounds. A class of AIE
azobenzene derivatives prepared by Han et al.3 could turn their
emission from a twisted intramolecular charge transfer (TICT)
state to a locally excited (LE) state upon alkali treatment. The
spectral change could be rehabilitated through thermal treat-
ment. Unfortunately, the quantum yields (2.4–6.7%) of the
azobenzene derivatives were still low.
Fluorescent materials which can change their color upon
exposure to different environmental stimuli, such as light,1
acids/bases,2–4 electricity,5 mechanical force6–8 etc., are of great
importance for their potential applications in sensors, memory
devices and switches. To achieve the above applications, strong
aKey Laboratory of Light Metal Materials Processing Technology of Guizhou Province,
Guizhou Institute of Technology, Guiyang 550003, China
bSchool of Materials and Metallurgical Engineering, Guizhou Institute of Technology,
Guiyang 550003, China
cPCFM Lab, GDHPPC Lab, Guangdong Engineering Technology Research Center for
High-performance Organic and Polymer Photoelectric Functional Films, State Key
Laboratory of OEMT, School of Chemistry and Chemical Engineering, Sun Yat-sen
University, Guangzhou 510275, China. E-mail: chizhg@mail.sysu.edu.cn
dKey Laboratory of Theoretical Chemistry of Environment, Ministry of Education,
School of Chemistry and Environment, South China Normal University, Guangzhou
510006, China
eCollege of Chemical Engineering, Guizhou Institute of Technology, Guiyang 550003,
China. E-mail: xiegaoyi@126.com
fGuizhou Material Industry Technology Research Institute, Guiyang 550014, China.
E-mail: xiegaoyi@126.com
† Electronic supplementary information (ESI) available: 1H NMR (Fig. S1), 13C
NMR (Fig. S2), MS (Fig. S3), FTIR (Fig. S4) spectra and TGA curve (Fig. S5) of
B-TPEAN. CCDC 1509687. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c7ra12655g
Tetraphenylethylene (TPE), due to its propeller-shaped
molecular structure, is non-emissive in solution but becomes
highly emissive in aggregated state.13 Therefore, TPE derivatives
with varied optical properties have been hotly investigated.14–17
Recently, we have also presented a TPE-base luminophore, i.e.
TPENSOH, which contains
a
functional group of 6-
‡ These authors contributed equally to the preparation of this work.
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hydroxybenzothiazole. This new compound showed a remark- 105.96. FT-IR (KBr): 3022, 2220, 1585, 1489, 1441, 822, 762, 698.
able and reversible four-color switch based on the piezo and EI-MS, m/z: 516 ([M]+, calcd for C36H24N2, 516).
protonation–deprotonation control in the solid state.18
Although TPENSOH exhibited stronger luminescence in
comparison with most of the acid/base-stimuli-responsive
emitters, its uorescence quantum yield (around 0.3) remain
moderate among the whole AIEgen family. As reported previ-
as the internal standard]. FT-IR analyses were carried out on
ously,1,17,19,20 aromatic-substituted acrylonitrile derivatives have
been proved to be AIE-active and possess a strong uorescence
emission in solid-state. Furthermore, combining two AIE
moieties in a single molecule probably can endow the lumino-
phore with stronger uorescence emission. Accordingly, an
cence spectra (PL) were determined on a Shimadzu RF-5301PC
acrylonitrile group was introduced to link a TPE and a benzo-
thiazole fragments to create a novel molecule of B-TPEAN,
which contains two typical AIE moieties. It is expected that the
well-designed compound could show multi-color uorescent
gate thermal behaviors at both heating and cooling rates of
switch with even higher quantum yield. The molecular structure
2.3 Characterization
1H NMR and 13C NMR spectra were measured on a Mercury-Plus
300 spectrometer [CDCl3 as solvent and tetramethylsilane (TMS)
a Nicolet NEXUS 670 spectrometer (KBr pellet). Mass spectra
(MS) were obtained via a Thermo DSQ MS spectrometer (ioni-
zation method: EI). UV-visible absorption spectra (UV-vis) were
performed on a Hitachi U-3900 spectrophotometer. Fluores-
spectrometer with a slit width of 1.5 nm for excitation and 3 nm
for emission. Differential scanning calorimetry (DSC) on
a NETZSCH thermal analyzer (DSC 204F1) was used to investi-
ꢁ1
ꢀ
of B-TPEAN was fully characterized by 1H NMR, 13C NMR, FT-IR,
mass spectra and single-crystal X-ray diffraction analysis. The
optical properties of B-TPEAN were measured by UV-visible
absorption spectroscopy and uorescence spectroscopy. The
piezochromism of B-TPEAN was discussed based on the results
of PXRD and DSC measurements, which were also used to
characterize the changes of aggregation structures.
10 C min under a N2 atmosphere. Time-resolved emission
decay behaviors were measured on an Edinburgh Instruments
Ltd spectrometer (FLS 920). Powder X-ray diffraction (PAXD)
measurements were performed at 293 K on a Bruker X-ray
diffractometer (D8 ADVANCE, Germany) with an X-ray source
of Cu Ka (l ¼ 0.15406 nm) at 40 kV and 40 mA, at a scan rate of
6ꢀ (2q) per min. Fluorescence quantum yields of solid powders
were measured on an integrating sphere (C-701, Labsphere
Inc.), with a 405 nm Ocean Optics LLS-LED as the excitation
source, and the light was introduced into the integrating sphere
through optical ber.
2. Materials and methods
2.1 Material
The single crystal of the compound was grown from
a dichloromethane/ethanol mixture through slow volatilization.
X-Ray crystallographic intensity data were collected from an
Agilent Technologies Gemini A Ultra system with Cu-Ka radia-
1-Bromo-1,2,2-triphenylethene (P3Br), 4-formylphenylboronic
acid, tetrabutyl ammonium bromide (TBAB), tetrakis-
(triphenylphosphine)palladium [Pd(PPh3)4], benzothiazole-2-
acetonitrile and tetrabutylammonium hydroxide were
purchased from Alfa Aesar and were used as received. Potas-
sium carbonate (K2CO3), potassium hydroxide (KOH), toluene,
ethanol were purchased as analytical grade from Sinopharm
Chemical Reagent Co., Ltd (Shanghai, China) and used without
further purication.
ꢀ
tion (l ¼ 1.54178 A) at 150.01(10) K. The structure was solved by
the direct methods following difference Fourier syntheses, and
rened by the full-matrix least-squares method against F2 using
SHELXTL soware (CCDC 1509687†). The pictures of the
structure were produced using Diamond 3.1.
TD-DFT calculations of electronic cloud density distribution
based on the single crystal structure were performed on
Gaussian 09 program at the B3lyp 6-311+g(d,p) level of the
theory.
2.2 General procedure for B-TPEAN
The compound of P4A was prepared by using a previous litera-
ture method.17
3. Results and discussion
Synthesis of (E)-2-(benzo[d]thiazol-2-yl)-3-(4-(1,2,2-tripheny-
lvinyl)phenyl)acrylonitrile (B-TPEAN).
A solution of P4A The synthetic routes of B-TPEAN are illustrated in Scheme 1.
(1.00 g, 2.77 mmol) and benzothiazole-2-acetonitrile (0.56 g, Briey, B-TPEAN was synthesized by the Suzuki and the Knoe-
3.19 mmol) in ethanol (30 mL) was stirred at room temperature. venagel condensation reactions. The chemical structure of B-
Then tetrabutylammonium hydroxide (TBAH, 0.8 M, 10 drops) TPEAN was conrmed by 1H NMR, 13C NMR, FT-IR and MS
was added and the mixture was stirred at room temperature for analyses (Fig. S1–S4, ESI†). The temperature of weight loss at
4 h. The precipitate was collected and washed with ethanol for 5% under nitrogen was determined to be 362 ꢀC (Fig. S5, ESI†),
three times to afford a yellow-green powder (1.30 g, yield 91%). 1H indicating that B-TPEAN has high thermal stability.
NMR (300 MHz, CDCl3) d (ppm): 8.16 (s, 1H), 8.08 (d, 1H, J ¼ 7.7
Single crystals of B-TPEAN were obtained by using the slow
Hz), 7.90 (d, 1H, J ¼ 8.0 Hz), 7.79 (d, 2H, J ¼ 8.29 Hz), 7.53 (t, 1H, J volatilization method and the crystal structure was determined
¼ 7.56 Hz), 7.43 (t, 1H, J ¼ 7.59 Hz), 6.99–7.20 (m, 17H). 13C NMR by single-crystal X-ray diffraction analysis. As depicted in Table
(75 MHz, CDCl3) d (ppm): 164.40, 155.06, 149.88, 147.85, 144.47, 1, the single crystal of B-TPEAN belongs to the monoclinic
144.32, 141.21, 136.33, 133.56, 132.73, 132.64, 131.70, 131.29, system. While the single molecular conformation and the
129.35, 129.09, 128.50, 128.25, 127.27, 124.93, 123.00, 117.99, intermolecular interactions are illustrated in Fig. 1, the dihedral
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Scheme 1 Synthetic routes of B-TPEAN.
Table 2 The dihedral angles of the selected planes of the molecule in
single crystal of B-TPEAN
Table 1 Crystal data and structure refinements for the single crystal of
B-TPEAN
Plane
Dihedral angle/ꢀ
Plane
Dihedral angle/ꢀ
Compound
Formula
fw
Crystal system
T (K)
B-TPEAN
36H24N2S
516.63
Triclinic
150.01(10)
ꢁ
P1
10.3022(6)
10.3149(7)
13.7990(8)
110.494(6)
96.161(5)
98.769(5)
1336.89(14), 2
522
0.32 ꢂ 0.20 ꢂ 0.15
7270/4349 (Rint ¼ 0.0187)
3743
4349/0/352
1.239
C
A–B
A–C
A–D
B–C
56.6
76.6
75.1
74.1
B–D
C–D
D–E
79.6
59.8
2.9
Space group
ꢀ
a/A
ꢀ
b/A
ꢀ
c/A
angles between the aryl rings as dened in Fig. 1(a) were
calculated and collected in Table 2. The TPE moiety of B-TPEAN
in single crystal structure shows a twisted conformation and
thereby no obvious p/p interaction was observed between any
phenyl rings of the neighboring TPE moieties (Fig. 1(a)).
Instead, one of the phenyl rings of TPE forms weak C–H/p
(tail-to-head) interaction with the phenyl ring of benzothiazole
in the neighbouring molecule (Fig. 1(b)).
On the other hand, the benzothiazole moieties of two adja-
cent molecules adopt antiparallel coupling (dihedral angle
0.25ꢀ) and form strong p/p (tail-to-tail) interaction with each
other. Such stable molecular conformation and intermolecular
interactions could efficiently block the non-radiative pathways
(rotation) of the excitons, which is benecial for harvesting high
B-TPEAN uorescent quantum yield.
a/ꢀ
b/ꢀ
g/ꢀ
ꢀ3
V/A , Z
F (000)
Crystal size/mm3
Rens collected/unique (Rint
Obsd rens [I $ 2s(I)]
Data/restraints/parameter
Dc/mg mꢁ3
)
m/mmꢁ1
1.286
1.032
0.0320/0.0798
0.0392/0.0845
Goodness-of-t on F2
R1,a wR2b [I $ 2s(I)]
R1, wR2 (all data)
a
2
R1 ¼ S||Fo| ꢁ |Fc||/S|Fo|. b wR2 ¼ [S[w(Fo ꢁ Fc2)2]/Sw(Fo2)2]1/2, where
w ¼ 1/[s2(Fo)2 + (aP)2 + bP] and P ¼ (Fo + 2Fc2)/3.
2
Fig. 1 Crystal structure and the intermolecular interactions of B- Fig. 2 Calculated spatial electron distributions of HOMO and LUMO of
TPEAN.
B-TPEAN.
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Quantum mechanical calculations based on the density
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functional theory were performed to investigate the electron
transition behavior of B-TPEAN. As shown in Fig. 2, the highest
occupied molecular orbital (HOMO) of B-TPEAN shows
dispersed electron cloud distribution at the TPE moiety,
whereas the electron cloud of the lowest unoccupied molecular
orbital (LUMO) is principally located at the vinyl group of the AN
moiety and the neighbouring benzene ring of the TPE moiety.
The B-TPEAN molecule showed large dipole moment (3.6709 D)
and high oscillator strength (f ¼ 0.6983), implying strong
intramolecular electron push–pull effect and high uorescent
quantum yield of B-TPEAN. These theoretical calculation results
suggested that B-TPEAN had ICT characteristics, from the TPE
(donor) moiety to the benzothiazole (acceptor) moiety. In other
words, benzothiazole is electron-withdrawing compared with
the TPE moiety.
Fig. 4 UV-visible spectra of the dilute solutions of B-TPEAN in THF/
water mixtures with different water fractions (concentration: 10 mM).
To determine the AIE feature of B-TPEAN, the emission
behavior of the compound in solvent-nonsolvent system was
investigated. Fig. 3 shows the PL emission spectra of the lumi-
nophore in THF/water mixtures with different water fractions.
Under the illumination of UV lamp, the THF solution of B-
TPEAN showed a very weak bluish-green uorescence centered
at 475 nm. When water was added, the uorescence was even
quenched, probably due to the TICT effect. However, when the
water fraction increased to 80%, strong yellow-green uores-
cence (ꢃ540 nm) appeared. The photoluminescence (PL)
intensity of the B-TPEAN THF/water mixture with 90% (v/v)
water fraction (ꢃ213 a.u.) was increased by up to almost 20
times as compared with that of the pure THF solution (ꢃ11
a.u.), implying a remarkable AIE phenomenon. When the water
fraction further increased (95%), the PL intensity of the mixture
decreased slightly, attributed to the increased size of the B-
TPEAN aggregates, which reduced the number of the emission
molecules on the surface of the nanoparticles.21
Fig. 4 presents UV-vis absorption spectra of the B-TPEAN
mixtures noted above. The spectral proles signicantly
changed when the water fraction was higher than 80%. Two
absorption peaks red shied from 315 nm to 320 nm and from
402 nm to 415 nm, respectively. Moreover, the UV-visible
absorption spectra showed a Mie scattering effect for the
mixtures, which proved the existence of nanoparticles. The
results of UV-visible absorption corresponded well with the
changes of PL spectra, thus indicating that the emission
enhancement of B-TPEAN at high water content was caused by
molecular aggregation. In other words, B-TPEAN is AIE-active.
The AIE characteristic of B-TPEAN encouraged us to inves-
tigate its emission behavior in the solid state. As shown in
Fig. 5, the pristine B-TPEAN solid powder (B) exhibits a strong
blue-green-light emission centered at 497 nm, with a high
uorescence quantum yield of 50%. Aer being ground by
a pestle or sheared by a spatula, the resultant powder (G)
emitted a yellow-light and the corresponding uorescence
quantum yield decreased (FF,s ¼ 42%) slightly. Meanwhile, the
PL maximum of B-TPEAN shied to 567 nm, exhibiting
a remarkable emission wavelength change of 70 nm. Many
piezochromic compounds could recover their emission colors
upon heating or solvent fuming.17,22–24 In this system, aer
ꢀ
being heated (130 C) or fumed with CH2Cl2, the resultant B-
TPEAN powders (A and FCH Cl , respectively) displays a yellow-
2
2
green light emission centered at 541 nm or 545 nm, respec-
tively, which is almost the same with that of the single crystal
(C) of B-TPEAN (centered at 544 nm). These color changes seem
to be irreversible under these treatment conditions. However,
unexpectedly, even higher uorescence quantum yields were
observed for the annealed sample (FF,s ¼ 57%) and the fumed
sample (FF,s ¼ 85%). To gain an understanding for these
phenomena, PXRD and DSC were carried out for the samples of
B-TPEAN.
Fig. 3 PL spectra of the dilute solutions of B-TPEAN in THF/water
mixtures with different water fractions (concentration: 10 mM; excita-
tion wavelength: 365 nm). The insets depict the changes in PL peak
intensity (up) and emission images of B-TPEAN in pure THF and THF/
water (9 : 1, v/v) under 365 nm UV illumination (down).
Fig. 6 shows the PXRD patterns of the B-TPEAN powders. The
B powder exhibits sharp and intense reections. Upon grinding,
the intensity of PXRD pattern decreased, indicating that the
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Fig. 7 DSC curves of B-TPEAN: (B) the pristine powder, (G) ground
powder from B, (A) annealed (130 ꢀC, 15 min) powder from G; (FCH Cl
)
2
2
CH2Cl2 fumed (10 min) powder from G; (C) single crystal.
Fig. 5 Fluorescence images and normalized PL spectra of B-TPEAN:
(B) the pristine powder, (G) ground powder from B, (A) annealed
(130 ꢀC, 15 min) powder from G; (FCH Cl ) CH2Cl2 fumed (10 min)
scanning calorimetry (DSC) was also performed to investigate to
the thermal behaviors of B-TPEAN. As illustrated in Fig. 7, the B
powder shows an obvious endothermal peak at 205 ꢀC.
However, for the G powder, the intensity of the endothermal
peak (ꢃ203 ꢀC) decreased. Furthermore, an additional
exothermal peak at approximately 110 ꢀC was observed, fully
demonstrating that the microcrystals of the ground sample
were partially destroyed and converted to the amorphous state
by grinding treatment. An exothermal peak (ꢃ205 ꢀC), which
could be assigned to a cold crystallization peak, and a new
2
2
powder from G; (C) single crystal.
ꢀ
endothermal peak at a higher temperature (ꢃ217 C) was also
observed, suggesting that a more stable crystal structure of B-
TPEAN was formed. The appearance of the latter endothermal
peak might be attributed to the heating measurement, which
induced crystallization of B-TPEAN. Indeed, aer annealing or
fuming treatment, an obvious endothermal peak at 217–218 ꢀC
was also observed, whereas the endothermal peak at 205 ꢀC
almost disappeared. More importantly, the C powder also
shows its endothermal peak at 218 ꢀC, revealing that the
thermal behaviors of the A and FCH Cl powders are similar with
2
2
that of the C powder, but not the B powder. The PXRD and DSC
results demonstrate that the crystal structures of A and FCH Cl
powders are completely different from that of the B powder,
giving a rational explanation for the emission behaviors of the
B-TPEAN powders.
Fig. 6 The PXRD patterns of B-TPEAN: (B) the pristine powder, (G)
ground powder from B, (A) annealed (130 ꢀC, 15 min) powder from G;
(FCH Cl ) CH2Cl2 fumed (10 min) powder from G; (C) single crystal.
2
2
2
2
Considering that benzothiazole moiety can be easily
protonated by acid and then change the PL emission of the
compound,18 the emissions of the original and ground samples
of B-TPEAN were investigated aer treating with acid vapor. As
can be seen in Fig. 8, when the B powder was exposed to a HCl
vapor for 1 hour, the luminescence changed from an initial
strong blue-green light to a weak orange light with a relatively
low FF,s value (15%), which is less than one-third of the one for
the B powder. Furthermore, the PL spectrum of the FHCl powder
red shied to 550 nm with a broad emission band. The decrease
crystalline phase of B-TPEAN almost converted to amorphous
phase, which would reduce the quantum yield of the ground
powder. However, the ground sample is a metastable state, and
it will rapidly crystallize again if it is annealed or fumed by
CH2Cl2. Interestingly, compared with the B powder, both of the
PXRD patterns for A and FCH Cl are totally different, but are
accorded well with the PXRD pattern of the C powder. It seems
that the crystal state of the B powder is unstable and would
convert to a new one by grinding and subsequent annealing/
fuming treatments. To verify this hypothesis, differential
2
2
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protonation process. It is worth to note that the whole PL
emission band of the FNH sample overlapped a part of the
3
broad spectrum of the FHCl sample. This might be caused by the
tight molecular packing of B-TPEAN in the pristine crystalline
powder, which gave rise to a slightly low protonation efficiency
of B-TPEAN.
As noted above, grinding treatment could destroy the crystal
structure of the pristine B-TPEAN. Therefore, we proposed that
the G powder would be much easier to be protonated by the acid
vapor. As expected, when the G powder was exposed to HCl
vapor for about 20 min (FHCl-G), the uorescence of the powder
changed to be orange (FF,s ¼ 9%) and a narrow PL emission
band centered at 654 nm was recorded (Fig. 9). Notably, by
fuming with the NH3 vapor for 10 min (FNH -G), the uorescence
3
of the protonated ground sample could completely reverse back
to yellow (FF,s ¼ 50%), which agreed well with that of the G
powder. The large bathochromic shi up to 87 nm in emission
maxima and the recovery toward the initial state fully demon-
strate that the ground sample of B-TPEAN exhibit remarkable
and reversible uorescent switching under the stimuli of acid
and base vapor, which is promising in bioimaging and anti-
counterfeit applications.
Fig. 8 Fluorescence images and normalized PL spectra of B-TPEAN:
(B) the pristine powder; (FHCl) HCl fumed (1 h) powder from B (HCl gas
was released from a 37% concentrated hydrochloric acid solution);
(FNH ) NH3 fumed (30 min) powder from B.
3
4. Conclusions
in uorescence quantum yield and the red-shi of PL spectrum
for the FHCl sample should be attributed to the protonation of
the benzothiazole moiety, leading to the enhancement of
intramolecular charge transfer (ICT) from the TPE unit to the
benzothiazole moiety. As a result, stronger intermolecular
interactions were formed.18,25 Subsequently, the FHCl powder
was exposed to a NH3 vapor for 30 min and the resultant powder
A TPE derivative, namely B-TPEAN, was synthesized through the
reaction of Knoevenagel condensation in high yield (>90%). B-
TPEAN showed prominent AIE property that the PL intensity of
the mixture with 90% (v/v) water content was increased by up to
almost 20 times as compared with that of at a water fraction of
0%. In solid state, the B-TPEAN powders have much higher
uorescent quantum yields (up to 85%) in comparison with
most of the documented luminophores due to the rational
combination of two typical AIE moieties (i.e. TPE and aryl-
substituted acrylonitrile). PXRD and DSC analysis revealed
that, the pristine sample of B-TPEAN was crystalline and
metastable. Upon grinding and then annealing or fuming with
CH2Cl2 vapor, the original sample could convert to a new
packing mode. Moreover, under the stimulus of acid vapor,
both of the pristine and the ground samples of B-TPEAN exhibit
remarkable red-shi in PL maxima and dramatical decrease in
emission quantum yields because of the stronger ICT effect in
the protonated molecules. Additionally, compared to the pris-
tine crystals, the ground sample of B-TPEAN in amorphous state
was much easier to be protonated by HCl vapor. This work offers
a new strategy to prepare multi-stimuli-responsive uorescent
switches with high contrast in emission color and high
quantum yield.
(FNH ) was found to emit a bright yellow light with a very high
3
FF,s value (74%), conrming the quenching effect of the
Conflicts of interest
There are no conicts to declare.
Acknowledgements
Fig. 9 Fluorescence images and normalized PL spectra of B-TPEAN:
These authors contributed equally to the preparation of this
(B) the pristine powder; (G) ground powder from B; (FHCl-G) HCl fumed
(20 min) powder from G; (FNH -G) NH3 fumed (10 min) powder from G. work. This research was supported by the National Science
3
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Foundation of China (Nos. 51503046, 51603233, 51473185 and 13 Y. Dong, J. W. Y. Lam, A. Qin, J. Liu, Z. Li, B. Z. Tang, J. Sun
51603232), 863 Program (SS2015AA031701), the Guizhou Prov- and H. S. Kwok, Appl. Phys. Lett., 2007, 91, 011111.
ince Science and Technology Planning Project (Nos. [2015]2068 14 Q. Qi, X. Fang, Y. Liu, P. Zhou, Y. Zhang, B. Yang, W. Tian
and [2015]2078) and the Research Project for High-level Talents
of Guizhou Institute of Technology (XJGC201503).
and S. X.-A. Zhang, RSC Adv., 2013, 3, 16986–16989.
15 Q. Qi, Y. Liu, X. Fang, Y. Zhang, P. Chen, Y. Wang, B. Yang,
B. Xu, W. Tian and S. X.-A. Zhang, RSC Adv., 2013, 3, 7996–
8002.
16 T. Jadhav, B. Dhokale, Y. Patil, S. M. Mobin and R. Misra, J.
Phys. Chem. C, 2016, 120, 24030–24040.
17 B. Xu, M. Xie, J. He, B. Xu, Z. Chi, W. Tian, L. Jiang, F. Zhao,
S. Liu, Y. Zhang, Z. Xu and J. Xu, Chem. Commun., 2013, 49,
273–275.
18 C. Ma, B. Xu, G. Xie, J. He, X. Zhou, B. Peng, L. Jiang, B. Xu,
W. Tian, Z. Chi, S. Liu, Y. Zhang and J. Xu, Chem. Commun.,
2014, 50, 7374–7377.
References
1 J. W. Chung, S.-J. Yoon, S.-J. Lim, B.-K. An and S. Y. Park,
Angew. Chem., Int. Ed., 2009, 48, 7030–7034.
2 J. Zhang, J. Chen, B. Xu, L. Wang, S. Ma, Y. Dong, B. Li, L. Ye
and W. Tian, Chem. Commun., 2013, 49, 3878–3880.
3 L. Hu, Y. Duan, Z. Xu, J. Yuan, Y. Dong and T. Han, J. Mater.
Chem. C, 2016, 4, 5334–5341.
4 Z. Zeng, J. Wen, H. Yan, Z. Liu, Y. Xu, H. Li, C. Zhong, F. Liu
and S. Sun, RSC Adv., 2016, 6, 37385–37390.
5 H. Niu, P. Luo, M. Zhang, L. Zhang, L. Hao, J. Luo, X. Bai and
W. Wang, Eur. Polym. J., 2009, 45, 3058–3071.
6 W. Liu, S. Ying, Q. Sun, X. Qiu, H. Zhang, S. Xue and W. Yang,
Dyes Pigm., 2016, 125, 8–14.
7 M. Zheng, M. Sun, Y. Li, J. Wang, L. Bu, S. Xue and W. Yang,
Dyes Pigm., 2014, 102, 29–34.
8 K.-Y. Zhao, G.-G. Shan, Q. Fu and Z.-M. Su, Organometallics,
2016, 35, 3996–4001.
9 R. Jakubiak, C. J. Collison, W. C. Wan, L. J. Rothberg and
B. R. Hsieh, J. Phys. Chem. A, 1999, 103, 2394–2398.
10 S. W. Thomas, G. D. Joly and T. M. Swager, Chem. Rev., 2007,
107, 1339–1386.
11 M. Li, Y. Niu, H.-Y. Lu and C.-F. Chen, Dyes Pigm., 2015, 120,
184–189.
19 B.-K. An, S.-K. Kwon, S.-D. Jung and S. Y. Park, J. Am. Chem.
Soc., 2002, 124, 14410–14415.
20 B.-K. An, D.-S. Lee, J.-S. Lee, Y.-S. Park, H.-S. Song and
S. Y. Park, J. Am. Chem. Soc., 2004, 126, 10232–10233.
21 S. Dong, Z. Li and J. Qin, J. Phys. Chem. B, 2009, 113, 434–441.
22 Y. Dong, J. Zhang, X. Tan, L. Wang, J. Chen, B. Li, L. Ye,
B. Xu, B. Zou and W. Tian, J. Mater. Chem. C, 2013, 1,
7554–7559.
23 G.-G. Shan, H.-B. Li, H.-Z. Sun, D.-X. Zhu, H.-T. Cao and
Z.-M. Su, J. Mater. Chem. C, 2013, 1, 1440–1449.
24 G.-G. Shan, H.-B. Li, H.-T. Cao, D.-X. Zhu, P. Li, Z.-M. Su and
Y. Liao, Chem. Commun., 2012, 48, 2000–2002.
25 J. Chen, S. Ma, J. Zhang, L. Wang, L. Ye, B. Li, B. Xu and
W. Tian, J. Phys. Chem. Lett., 2014, 5, 2781–2784.
12 M. Chen, L. Li, H. Nie, J. Tong, L. Yan, B. Xu, J. Z. Sun,
W. Tian, Z. Zhao and A. Qin, Chem. Sci., 2015, 6, 1932–1937.
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