Water-soluble host-guest fluorescent systems based on fluorophores and cucurbiturils with AIE or ACQ effects

Article abstract of DOI:10.1016/j.dyepig.2021.109267

Tetraphenylethene (TPE) and pyrene as typical aggregation induced emission (AIE) and aggregation caused emission quenching (ACQ) functional groups were utilized to design and synthesize water-soluble fluorescent molecules. Through a self-assembly process

Full text of DOI:10.1016/j.dyepig.2021.109267

Dyes and Pigments 189 (2021) 109267
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: http://www.elsevier.com/locate/dyepig
Water-soluble host-guest fluorescent systems based on fluorophores and
cucurbiturils with AIE or ACQ effects
,
,**
Xinwen Bia, Wenbo Haob, Hui Liub, Xinsheng Chenb, Meiran Xiea *, Yuancheng Wangb
,
,
***
Yingjie Zhaob
a School of Chemistry and Molecular Engineering, East China Normal University, 500 Dongchuan Road, Shanghai, 200241, China
b College of Polymer Science and Technology, Qingdao University of Science and Technology, 53 Zhengzhou Road, Qingdao, 266000, China
A R T I C L E I N F O
A B S T R A C T
Keywords:
Tetraphenylethene (TPE) and pyrene as typical aggregation induced emission (AIE) and aggregation caused
emission quenching (ACQ) functional groups were utilized to design and synthesize water-soluble fluorescent
molecules. Through a self-assembly process with cucurbituril hosts, a completed opposite fluorescence response
was observed for TPE and pyrene based fluorescent molecules. The assembly processes were verified by 1H NMR,
UV–Vis, fluorescence spectroscopy. The mechanism was then studied and the aggregation-induced fluorescence
change was concluded. These new host-guest supramolecular fluorescence systems can be used as fluorescence
sensors or switches, expanding the application of fluorescence systems in biological imaging.
Aggregation induced emission
Tetraphenylethene
Pyrene
Supramolecular self-assembly
cucurbit[n]uril
1. Introduction
phenomenon [18–22]. The novel AIE effect is exactly opposite to the
traditional ACQ effect. It permits the use of dye solutions with any
The development of luminescent materials with advanced properties
is of great importance to satisfy the need of modern society and tech-
nology. The fluorescent molecules in the concentrated solution or
aggregated state, are inclined to aggregate to minimize the contact of the
concentrations for bioassays and enables the development of “turn on”
or “light up” nanosensors by taking advantage of luminogenic aggre-
gation, thus exploring their technological applications as chemosensors,
bio-probes and solid-state emitters [23–34]. Since the concept of AIE
was proposed, AIE luminogens have been judiciously utilized as sensi-
tive and selective chemosensors and bio-probes of turn-on type by
incorporating them into chemical and biological systems as labels via
chemical bonding or physical mixing. Attracted by the intriguing phe-
nomenon and its fascinating perspectives, several mechanisms have
been proposed for the AIE effects. The restriction of intramolecular
rotation (RIR) of the peripheral phenyl rings in the aggregate state is the
main cause of the AIE effect [35–40]. When the rotation of the phenyl
ring in the molecule is limited, the energy in the excited state can only be
dissipated through radiation, that is, fluorescence is generated. Thus, it
can be naturally associated with the supramolecular self-assembly
strategy especially the supramolecular host and guest chemistry which
could be taken advantage of to affect the aggregate state and the rotation
of the molecular moieties [41].
environmental medium through strong hydrophobic-hydrophobic or π-π
stacking interactions [1]. These interactions promote the formation of
closed packed excimers or exciplexes, through which the excitation
energy is relaxed non-radiatively [2]. This notorious and harmful phe-
nomenon is known as aggregation-caused quenching (ACQ) of light
emission in the condensed phase [3–11]. In the past decades, great ef-
forts have been made to tackle the ubiquitous ACQ effect to utilize flu-
orophores as a molecularly dissolved or dispersed state in dilute
solution. Different chemical, physical or engineering methods have been
applied to isolate the molecules from each other, and thus minimize the
ACQ effect [12–16]. In 2001, Tang group discovered such a system, in
which luminogen aggregation played
a constructive, instead of
destructive, role in the light-emitting process [17]. A series of molecules
such as tetraphenylethene (TPE) and hexaphenylsilole (HPS) were found
non-luminescent in the solution state but emissive in the aggregate state.
They coined “aggregation induced emission” (AIE) for this novel
Herein, we designed and synthesized two organic luminescence
molecules that have totally different fluorescence behaviors. One is a
* Corresponding author.
** Corresponding author.
*** Corresponding author.
E-mail addresses: mrxie@chem.ecnu.edu.cn (M. Xie), wangyuancheng@qust.edu.cn (Y. Wang), yz@qust.edu.cn (Y. Zhao).
https://doi.org/10.1016/j.dyepig.2021.109267
Received 14 December 2020; Received in revised form 29 January 2021; Accepted 21 February 2021
Available online 27 February 2021
0143-7208/© 2021 Published by Elsevier Ltd.

X. Bi et al.
Dyes and Pigments 189 (2021) 109267
Fig. 1. Chemical structures of the guest molecule T1, P1 and the host CB[n], and schematic representation of the formation of T1_CB[n], P1_CB[n] supramolecular
assembly structures and fluorescence enhancement and reduction. The images inserted are the fluorescence changes at endpoints of T1 and P1 in cucurbit [7]uril
titration under 365 nm UV-light.
Fig. 2. Synthesis of T1 and P1. a: CH2Cl2, Br2, room temperature (r.t.),12 h; b: methyl acrylate, Pd(OAc)2, 1,3-Bis(diphenylphosphino)propane, Et3N, N,N-Dime-
thylformamide (DMF), 110 ◦C, 72 h; c: trifluoroacetic acid, CH2Cl2, r.t., 1 h; d: NaOH, r.t.; e: methyl acrylate, Pd(OAc)2, 1,3-Bis(diphenylphosphino)propane, Et3N,
DMF, 110 ◦C, 72 h; f: trifluoroacetic acid, CH2Cl2, r.t., 1 h; g: NaOH, r.t.
TPE based molecule modified by hydrophilic carboxylate groups (T1)
which is a typical AIE fluorescent molecule. The other one is a pyrene
based molecule containing carboxylate groups (P1) which is a typical
ACQ fluorescent molecule. Both of these two fluorescent molecules are
water-soluble. Then the cucurbit[n]uril (CB[n]) as a host was utilized to
assemble with T1 and P1. The supramolecular assembly strategy is used
to combine the fluorescent guest molecules with different host mole-
cules and obtain different luminescent assemblies through non-covalent
interactions. The photophysical properties of these assemblies were then
studied. Very interestingly, the T1 and P1 show totally different fluo-
rescence behaviors after assembly with CB[n] (Fig. 1). T1 shows sig-
nificant fluorescence enhancement while P1 shows a fluorescence
reduction. It is of great significance to study the mechanisms of
aggregation-induced luminescence properties.
carried out on silica gel (200–300 mesh). The UV–vis absorbance was
measured by UV spectrometer (HITACHI, 3900). Fluorescence spectra
were recorded on fluorescence spectrometer (HITACHI, F-2700).
2.3. Synthesis
The synthesis of T1 and P1 was presented in Fig. 2. T1 and P1 were
obtained through simple quantitative neutralization of compounds 4 or
7. The deprotonation of the carboxylic acid groups leads to carboxylate
groups which bring good water-solubility of T1 and P1. The synthesis
detailed experimental procedure was presented below:
Compound 2 was synthesized from TPE following the reported
literature procedure [42]. TPE (5.0 g, 15.2 mmol) was dissolved in 300
mL CH2Cl2. 10 mL Br2 was added dropwise at room temperature. The
mixture was stirred at room temperature for 12 h, then the reaction was
quenched by ethanol and saturated Na2S2O3 solution. After neutralized
by NaOH to pH = 7, the mixture was washed by CH2Cl2, the organic
layer was dried by sodium sulfate. After filtered and concentrated, the
product was purified by column chromatography (pure petroleum) to
yield a white powder (9.3 g, 95%). 1H NMR (400 MHz, CDCl3): δ 7.25 (d,
J = 8 Hz, 8H), 6.84 (d, J = 8 Hz, 8H).
2. Experimental section
2.1. Materials
1,3-Bis(diphenylphosphino)propane, 1,3,6,8-tetrabromopyrene, Pd
(OAc)2 and other chemicals were all purchased from Energy Chemical
Company and used as received without further purification. Reagents
for synthesis were purchased commercially from Adamas Reagent and
used without further purification. Cucurbit [7]uril and cucurbit [8]uril
were purchased from Sigma. Unless otherwise specified, all aqueous
solutions were prepared with Milli-Q water.
Compound 3: Compound 2 (1.0 g, 1.6 mmol), methyl acrylate (2.0
g, 15.6 mmol), Pd(OAc)2 (75.0 mg, 0.3 mmol), 1,3-bis(diphenylphos-
phino)propane (DPPP) (260.0 mg, 0.6 mmol) and Et3N (1.0 mL, 6.2
mmol) were added into 5 mL of dry DMF. The mixture was stirred at
110 ◦C under N2 atmosphere for 72 h. When the reaction was complete
as determined by the disappearance of the 2, 20 mL of water was
charged. The solution was extracted with CH2Cl2 (3 × 20 mL). The
organic phases were then dried with anhydrous magnesium sulfate,
filtered, and concentrated under reduced pressure. The residue was
purified by column chromatography on silica gel with a mixture of ethyl
acetate and petroleum ether as eluent (1:10 by volume) [43]. A yellow
2.2. Instruments and methods
1H and 13C NMR spectra were performed on 400 MHz spectrometers
(Bruker AVANCE NEO 400 Ascend) in the indicated solvents at room
temperature. Unless otherwise indicated, column chromatography was
2

X. Bi et al.
Dyes and Pigments 189 (2021) 109267
Fig. 3. Absorption and fluorescence spectral changes of (a), (b) T1 (0.01 mM) and (c), (d) P1 (0.01 mM) upon gradual addition of CB [7] in H2O.
solid was obtained in a yield of 45%. 1H NMR (400 MHz, CDCl3): δ 7.48
(d, J = 15.9 Hz, 4H), 7.01 (s, 8H), 6.99 (s, 8H), 6.28 (d, J = 15.6 Hz, 4H),
1.51 (s, 36H). 13C NMR (100 MHz, CDCl3): δ 166.25, 144.65, 142.87,
141.09, 133.41, 131.76, 127.60, 120.29, 80.48, 28.19. HRMS (MALDI)
m/z: [M+] calcd. for C54H60O8 836.4288; found 836.4286.
NMR (400 MHz, DMSO‑d6): δ 8.94 (s, 4H), 8.69 (d, J = 3.6 Hz, 4H), 8.65
(s, 4H), 7.16 (s, 2H), 7.12 (s, 4H). 13C NMR (100 MHz, DMSO‑d6): δ
175.58, 164.55, 137.23, 129.41, 128.67, 128.03, 126.39, 122.51. HRMS
(EI) m/z: [M+] calcd. for C28H18O8 482.1002; found 482.1003.
Compound 4: Compound 3 (100.0 mg) was dissolved in 2 mL
CH2Cl2. Trifluoroacetic acid (TFA) (2 mL) was added dropwise. The
mixture was then stirred at room temperature for 30 min. After
removing the excess acid by evaporation, the mixture was washed by
CH2Cl2 to yield a yellow powder (99%).1H NMR (400 MHz, DMSO‑d6): δ
12.34 (s, 4H), 7.50 (s, 4H), 7.47 (d, J = 8.8 Hz, 8H), 7.02 (d, J = 8 Hz,
8H), 6.45 (d, J = 16 Hz, 4H). 13C NMR (100 MHz, DMSO‑d6): δ 167.95,
144.98, 143.74, 141.19, 133.36, 131.80, 128.45, 119.79. HRMS
(MALDI) m/z: [M+] calcd. for C38H28O8 612.1784; found 612.1787.
Compound 6: Compound 5 (1.0 g, 1.9 mmol), methyl acrylate (2.5
g, 19.3 mmol), Pd(OAc)2 (90.0 mg, 0.4 mmol), 1,3-bis(diphenylphos-
phino)propane (DPPP) (320.0 mg, 0.8 mmol) and Et3N (1.1 mL, 7.7
mmol) were added into 8 mL of dry dimethylformamide (DMF). The
mixture was stirred for 72 h at 110 ◦C under N2 atmosphere. When the
reaction was complete as determined by the disappearance of 5, 20 mL
of water was charged, and the solution was extracted with CH2Cl2 (3 ×
20 mL). The organic phases were then dried with anhydrous magnesium
sulfate, filtered, and concentrated under reduced pressure. The residue
was purified by column chromatography on silica gel (200–300 mesh)
with a mixture of ethyl acetate and petroleum ether as eluent (1:10 by
volume). An orange-red solid was obtained with a yield of 48%. 1H NMR
(400 MHz, CDCl3): δ 8.69 (d, J = 16 Hz, 4H), 8.56 (s, 4H), 8.50 (s, 2H),
6.69 (d, J = 16 Hz, 4H), 1.63 (s, 36H). 13C NMR (100 MHz, CDCl3): δ
165.98, 139.69, 130.26, 130.14, 125.49, 124.21, 124.14, 123.37, 81.06,
28.29. HRMS (MALDI) m/z: [M+] calcd. for C44H50O8 706.3506; found
706.3507.
3. Results and discussion
Considering the good water solubility and the intrinsic fluorescent
characteristic of T1 and P1. The photophysical properties of the fluo-
rescent molecules themselves and the self-assemblies would be very
interesting. UV–vis and fluorescence spectroscopy were then employed
to investigate the photophysical properties of the guest molecules and
the as-formed self-assembled structures. T1 is a typical AIE fluorescent
molecule, while P1 is a typical ACQ fluorescent molecule. T1 showed a
maximum absorption wavelength of 300 nm and a fluorescence wave-
length of 540 nm. A titration experiment was then employed to study the
change of the photophysical properties of the self-assembled structures.
As shown in Fig. 3a, the addition of CB [7] induced a remarkable blue
shift and hypochromism of the absorption. Besides, an obvious
enhancement of the fluorescence (10 times increase) was observed
(Fig. 3b). The quantum yield increased from 0.7% to 8.5%. This indi-
cated that the addition of CB [7] led to an aggregation of T1. The hy-
drophilic carboxylate groups were encapsulated into the cavity of the CB
[7] in H2O. As a result, the aggregation of T1 containing TPE as the
classical AIE moiety occurred which led to the fluorescence enhance-
ment. Besides, the self-assembly between the CB [7] and T1 limits the
intramolecular motion of the “arms” of T1, and the energy in the excited
state can only be dissipated in the form of fluorescence. For P1 which is a
classic ACQ molecule with a maximum absorption wavelength of 440
nm and fluorescence wavelength of 480 nm, the variation tendency of
UV–vis spectra is similar. A remarkable blue shift and hypochromism of
the absorption occurred with the addition of CB [7] (Fig. 3c). However,
an obvious quenching in the fluorescence was observed (Fig. 3d) which
is in sharp contrast with T1. The quantum yield dramatically reduced
with the addition of CB [7], from 37.7% to 0.3%. As an ACQ molecule,
Compound 7: Compound 6 (100.0 mg) was dissolved in 2 mL
CH2Cl2, TFA (2 mL) was added dropwise. The mixture was stirred at
room temperature for 30 min. After removing excess acid by evapora-
tion, the mixture was washed by CH2Cl2 to yield a red powder (99%).1H
3

X. Bi et al.
Dyes and Pigments 189 (2021) 109267
Fig. 4. Absorption and fluorescence spectral changes of (a), (b) T1 (0.01 mM) and (c), (d) P1 (0.01 mM) upon gradual addition of CB [8] in H2O.
1
Fig. 5. H NMR spectra: (a) T1 (3.0 mM) in D2O in the presence of 0, 2.0, 4.0, 10.0 equiv. of CB [7] at 25 ◦C; (b) P1 (1.0 mM) in D2O in the presence of 0, 2.0, 4.0,
10.0 equiv. of CB [7] at 25 ◦C.
the aggregation caused by the self-assembly of the CB [7] quenched the
fluorescence of P1 in H2O. To further confirmed this speculation, the
larger CB [8] as a host molecule was also tested. The CB [8] shows very
similar influence to T1 or P1 compared with CB [7]. As shown in Fig. 4,
the introduction of CB [8] led to an increase in the fluorescence of T1
and a decrease of P1. The changes in the UV–vis spectra are also similar
to the CB [7]. These results indicated that the self-assembly modes of CB
[7] and CB [8] to the T1 and P1 are similar. The CB [7] and CB [8] could
form host-guest self-assembly structures with the carboxylate in T1 and
P1. The hydrophobic peripheries of CB [7] and CB [8] induced the ag-
gregation of these fluorescent molecules. Since the well-known AIE
phenomenon of TPE and ACQ effect of pyrene, the aggregation brings a
completely opposite tendency in the fluorescence.
To clarify the self-assembly modes of the CB[n] and the fluorescent
4

X. Bi et al.
Dyes and Pigments 189 (2021) 109267
guests, we also performed the 1H NMR titration. As shown in Fig. 5, with
the increase of the CB [7], the proton signals of T1 and P1 decreased
gradually and disappeared in the end. No obvious chemical shift changes
were observed both for T1 and P1. Above all, these results indicated that
the CB[n] as hosts encapsulated only the carboxylate ending parts and
inhibited the contact of hydrophilic carboxylate groups to the H2O and
then induced the aggregation. The opposite fluorescence characteristic
of AIE for T1 and ACQ for P1 led to totally different fluorescence
response.
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4. Conclusions
Two water-soluble fluorescent molecules containing TPE as a typical
AIE functional group (T1) and pyrene as ACQ functional group (P1)
were synthesized. The self-assembly process between the CB[n] as hosts
and the fluorescent molecules as guests were then studied. Interestingly,
the T1 and P1 showed a completed opposite fluorescence response to the
CB[n]. The mechanism was then studied and the aggregation-induced
fluorescence change was concluded. These novel host-guest supramo-
lecular fluorescent systems may act as fluorescence sensors or switches.
The different fluorescence response and the different luminous mecha-
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Author statement
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We declare that this manuscript entitled “Water-Soluble Host-Guest
Fluorescent Systems Based on Fluorophores and Cucurbiturils with
AIE or ACQ Effects” is original, has not been published before and is not
currently being considered for publication elsewhere.
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together we shine, united we soar! Chem Rev 2015;21:11718–940.
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Spermine-directed supramolecular self-assembly of water-soluble AIE-active
tetraphenylethylene: nanobelt, nanosheet, globular and nanotubular structures.
New J Chem 2018;42:15379–86.
We confirm that the manuscript has been read and approved by all
named authors and that there are no other persons who satisfied the
criteria for authorship but are not listed. We further confirm that the
order of authors listed in the manuscript has been approved by all of us.
We understand that the Corresponding Author is the sole contact for
the Editorial process. He is responsible for communicating with the
other authors about progress, submissions of revisions and final
approval of proofs.
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Declaration of competing interest
[26] Chen Q, Bian N, Cao C, Qiu XL, Qi AD, Han BH. Glucosamine hydrochloride
functionalized tetraphenylethylene: a novel fluorescent probe for alkaline
phosphatase based on the aggregation-induced emission. Chem Commun 2010;46:
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The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
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Acknowledgment
[28] Yu G, Li J, Yu W, Han C, Mao Z, Gao C, Huang F. Carbon nanotube/biocompatible
bola-amphiphile supramolecular biohybrid materials: preparation and their
application in bacterial cell agglutination. Adv Mater 2013;25:6373.
[29] Zhang X, Zhang X, Yang B, Liu M, Liu W, Chen Y, Wei Y. Fabrication of aggregation
induced emission dye-based fluorescent organic nanoparticles via emulsion
polymerization and their cell imaging applications. Polym Chem 2014;5:399–404.
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nanoprobes for biomedical applications: recent advances and perspectives.
Nanoscale 2015;7:11486–508.
This work was supported by the National Natural Science Foundation
of China (21905150).
Appendix A. Supplementary data
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fluorescent cellular tracing by the aggregates of AIE bioconjugates. J Am Chem Soc
2013;135:8238–45.
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.dyepig.2021.109267.
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apoptosis and drug screening using fluorescent light-up probe with aggregation-
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