Vinyl Groups Containing Tetraphenylethylene Derivatives as Fluorescent Probes Specific for Palladium and the Quenching Mechanism?

Article abstract of DOI:10.1002/cjoc.202000746

We previously reported that a series of tetraphenylethylene (TPE)-containing all-hydrocarbon conjugated polymers exhibited a specific fluorescence quenching by palladium ions (Pd²⁺). To understand the quenching mechanism, herein we investigate

Full text of DOI:10.1002/cjoc.202000746

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中
国 化 学
Cite this paper: Chin. J. Chem. 2021, 39, 1599—1605. DOI: 10.1002/cjoc.202000746
Vinyl Groups Containing Tetraphenylethylene Derivatives as
Fluorescent Probes Specific for Palladium and the
Quenching Mechanism†
Xiaoqing Liu,‡,a,b Yuxuan Shang,‡,a and Zhong-Ren Chen*,a,b
a Shenzhen Grubbs Institute and Department of Chemistry, Southern University of Science and Technology, Shenzhen, Guangdong 518005,
China
b Guangdong Provincial Key Laboratory of Catalysis, Southern University of Science and Technology, Shenzhen, Guangdong 518055, China
Keywords
Aggregation-induced emission | Fluorescent probes | Palladium detection | Electron transfer | Time-resolved spectroscopy
Main observation and conclusion
We previously reported that a series of tetraphenylethylene (TPE)-containing all-hydrocarbon conjugated polymers exhibited a spe-
cific fluorescence quenching by palladium ions (Pd2+). To understand the quenching mechanism, herein we investigate the quenching
behaviors of three TPE derivatives in the presence of Pd2+. Each TPE derivative, consisting of TPE unit and terminal vinyl groups, shows
an aggregation-induced emission (AIE) and its fluorescence turns off specifically to Pd2+. The sensitivity is enhanced with increasing
numbers of vinyl groups in the molecules. By time-resolved fluorescence measurement, a dynamic quenching is observed where the
fluorescence lifetime is reduced with Pd2+. Specifically, the quenching occurs via the electron transfer in the excited states, as sug-
gested by the disappearance of the stimulated emission band in transient absorption spectra. A theoretical calculation on the excited
states identifies intermolecular electron transfer from TPE derivatives to Pd, especially for electron–rich TPE derivative. The mecha-
nism can be general for the design of novel AIE active chemosensors.
Comprehensive Graphic Content
*E-mail: chenzr@sustech.edu.cn
View HTML Article
Supporting Information
‡ These authors contributed equally to this work.
† Dedicated to Department of Chemistry, SUSTech, on the Occasion of Her
10th Anniversary.
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Concise Report
triyl)tribenzene (TPE-1), two for 1,2-diphenyl-1,2-bis(4-vinylphe-
nyl)ethene (TPE-2), and four for 1,1,2,2-tetrakis(4-vinylphenyl)-
ethene (TPE-4), as indicated by the numbers in the abbreviations.
All three TPE derivatives show a turning-off fluorescence response
specific to Pd2+. The sensitivity depends on the numbers of vinyl
groups. The fluorescence quenching mechanism is revealed by a
combination of time-resolved fluorescence spectra, transient
absorption spectra, and theoretical calculation.
Background and Originality Content
Palladium (Pd) plays an indispensable role as metal catalyst in
chemical,[1] pharmaceutical,[2] and automobile[3] industry. With its
extensive usage, increased Pd emissions to water sources and
soils have been recognized, which pose serious health threats to
plants, animals, and humans.[4] A proposed maximum dietary
intake of Pd is limited to < 2 μg per day per person.[5] Some labor-
atory analytical methods are developed to fast determine the
levels of Pd residual in diverse matrices, but they rely on experi-
enced operators and sophisticated instruments such as atomic
absorption spectrometry,[6] inductively coupled plasma mass
spectroscopy,[7] and X-ray fluorescence.[8] Many researchers are
seeking to detect Pd (especially in the form of Pd2+) in a low cost,
easy handling, and non-destructive fashion.[9-10]
Chart 1 Chemical structures of TPE derivatives
Fluorescent chemosensors can exhibit a fluorescence “turning
on” or “turning off” behavior based on the interaction between
the molecules and Pd, enabling a fast and naked-eye detection
just with the assistance of a portable lamp. According to the
sensing mechanism, fluorescent chemosensors are categorized
into chemical-reaction[11-12] and coordination[13-14] based sensors.
A Pd-targeted catalytic reaction site or binding site[15] (e.g., het-
ero-atoms such as N, O, and S) in the probe, which often requires
tedious synthesis, is thus prerequisite for high sensitivity and se-
lectivity. A number of conventional organic fluorophores, such as Results and Discussion
rhodamine, fluorescein, and BODIPY, have been reported for Pd
sensing in the solution,[10] yet few of them can be easily operated
for real-life applications. Newly emerging probes with aggrega-
tion-induced emission (AIE) characteristics become competitive
candidates in broad application fields, such as in solutions, in
aggregate states, and even in cells and organisms.[16-19] Some
AIE-probes for metal ions such as Zn2+ and Hg2+ have been de-
signed,[20-21] but their usage for Pd2+ detection is less explored.[22-23]
We recently reported a series of AIE-active all-hydrocarbon
conjugated polymers and their potential usage as specific Pd2+
sensors in quasi-aqueous solution.[24] As these polymers were
prepared from diene monomers based on AIE-active tetra-
phenylethylene (TPE, Chart 1), they were highly emissive in
THF/water mixture (fw = 90%). Surprisingly, their fluorescence was
quenched by Pd2+, even none of Pd-catalytic reactions or specific
coordination interactions exist in this system. Considering that
the polymers are electron-rich and Pd2+ is electron-deficient, we
proposed a dynamic quenching mechanism arising from photoin-
duced electron transfer from the excited state of the polymer to
Pd2+. This finding is completely distinct from a static quenching
observed in coordination based sensing systems, in which fluo-
rescence intensity is reduced as a consequence of the formation
of a non-emissive ground-state complex between the fluorophore
and the quencher. The solid evidence for a dynamic or static
quenching is provided by the fluorescence lifetime measurement,
i.e., lifetime changed in a dynamic quenching while unchanged in
a static quenching.[25] As a dynamic quenching works via the in-
teraction between the quencher and the fluorophores in the ex-
cited state, the details on the electron or energy transfer process
are far to know. On the molecular level, Pd sensors arising from a
dynamic quenching process do not require specific coordination
sites in the molecules, so what kind of chemical structure is cru-
cial to the fluorescence quenching? The answer to this question
would be valuable for the molecular design of novel chemosen-
sors, especially AIE-active sensors.
Synthesis of TPE derivatives. Synthesis procedures of TPE-1,
TPE-2 and TPE-4 are shown in Scheme 1. Briefly, TPE-1 was ob-
tained via a one-step Suzuki-Miyaura cross-coupling reaction from
(2-bromoethene-1,1,2-triyl)tribenzene (1) with 4-vinylphenyl-
boronic acid. TPE-2 and TPE-4 were the products of Suzuki cou-
pling reactions from the bromide substituted TPEs (3 and 5) with
potassium vinyltrifluoroborate. Successful attachment of terminal
1
vinyl groups on TPEs was verified by H NMR spectra, which dis-
play three proton resonance peaks at δ 6.60, 5.69, and 5.20, re-
spectively. Details of the characterization on their chemical
structures (NMR, high resolution mass spectra and IR data) are
provided in Supported Information.
Scheme 1 Synthesis of TPE derivatives containing terminal vinyl groups
Optical spectra. Like TPE, all the molecules show characteris-
tic absorption in UV region and AIE behaviors in the aggregation
states. As shown in Figure 1 and Table 1, the wavelengths of
maximum absorbance (λabs) for TPE-1, TPE-2, and TPE-4 are 326,
334, 354 nm, indicative of higher conjugation degrees with in-
creasing number of vinyl groups in the molecules. Accordingly,
the wavelengths of maximum emission (λem) in THF/H2O mixture
(water contents fw = 90 %) are 501, 512, and 535 nm, respectively.
Starting from TPE, the basic construction unit, herein we de-
sign three TPE derivatives (Chart 1) as a model system to investi-
gate their fluorescence quenching by Pd2+. Considering that TPE
units were linked by double bonds in the conjugated polymers,[24]
TPE derivatives have different numbers of terminal vinyl groups
attached on TPE units: one for (2-(4-vinylphenyl)ethene-1,1,2-
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Chin. J. Chem.
Table 1 Summary of optical properties of TPE derivatives
c
Compound
λabsa/nm
λemb/nm
τ0 /ns
τd/ns
TPE
308e
326
334
354
470
501
512
535
3.02
2.29
2.69
2.83
2.68
0.91
0.68
0.50
TPE-1
TPE-2
TPE-4
a The wavelength of maximum absorbance measured in THF. b The wave-
length of maximum emission recorded in THF/H2O mixture (fw = 90 %)
with the excitation wavelength of 330 nm. c τ0, fluorescence lifetime in
THF/H2O mixture (fw = 90 %). d τ, fluorescence lifetime with 10 μmol/L Pd2+.
All the measurements were performed with a molecular concentration of
10 μmol/L. e Data from Ref [26].
Figure 2 Fluorescence responses of TPE derivatives to Pd(OAc)2 in
THF/water mixtures (fw = 90%). (a), (b), (c), and (d) are emission spectra of
TPE, TPE-1, TPE-2, and TPE-4 upon the addtion of Pd(OAc)2 (0—100
μmol/L); (e) Stern-Volmer plots of (I0/I) versus the concentration of
Pd(OAc)2. I and I0 are fluorescence intensities recorded at the maximum
emission wavelengths with and without Pd(OAc)2. (f) A test paper method
illustrates fluorescence response of TPE-4 with different concentrations of
Pd(NO3)2 under the irradiation of UV light (365 nm).
Figure 1 Optical spectra of TPE derivatives. (a) Normalized absorption
spectra in THF solutions. Emission spectra were recorded in THF/water
mixtures (fw = 0—90% from bottom to up) for TPE-1 (b), TPE-2 (c), and
TPE-4 (d), which are plotted in grey, red, and blue, respectively.
We then used the filter paper as a substrate to show a solid-
state detection of Pd ions. TPE-4 (10 μmol/L in THF) was coated
on the paper by drop-casting. To avoid the dissolution of TPE-4 on
the filter paper during the test, organic solvents (such as THF)
should not be involved in Pd solution. According to Figure S3, the
fluorescence responses of TPE derivatives are weakly dependent
on the form of Pd ions. Thus, Pd(NO3)2, instead of Pd(OAc)2, was
used due to its good water solubility. Stock solutions of Pd(NO3)2
(5 μL) were then dropped in different quadrants. Figure 2f shows
the photo taken under UV illumination. With increasing Pd2+ con-
centrations from 0.5 to 10 mmol/L, fluorescence quenching spots
appear darker, demonstrating the potential application for a
qualitative assessment of Pd2+.
Fluorescence responses. In the previous work, the fluores-
cence of TPE-containing conjugated polymers was quenched by
Pd2+ in the absence of specific coordination interaction or chemi-
cal reaction.[24] Using the same procedure, fluorescence spectra of
small TPE molecules to Pd(OAc)2 are examined in THF/H2O mix-
ture (fw = 90%). The molecular concentration is 10 μmol/L. Fluo-
rescence intensities (I) at the peak position are recorded at dif-
ferent concentrations of Pd2+ ([Pd]).The initial intensity without
Pd2+ is denoted by I0. As expected, fluorescence intensities from
TPE and its derivatives decrease with increased amount of Pd2+
(Figure 2). Interestingly, the quenching degree was enhanced with
increasing numbers of vinyl groups in the fluorophores, following
the sequence of TPE < TPE-1 < TPE-2 < TPE-4. For examples, at [Pd]
= 100 μmol/L, the fluorescence intensity of the four fluorophores
were reduced by 52%, 61%, 79%, and 90%, respectively.
Moreover, the addition of other metal ions such as Na+, Ca2+,
Al3+, Cr2+, Mn2+, Fe2+, Fe3+, Co2+, Ni2+, Cu2+, Ag+, and Cd2+ brought
about minor changes in fluorescence spectra for all TPE deriva-
tives (Figure 3), implying their remarkable selectivity for Pd2+.
The fluorescence quenching degrees are compared by the
Stern-Volmer plot (Figure 2e). Each plot shows a growth regime at
low [Pd] and then levels off at high concentrations. At low [Pd] up
to 1.0 μmol/L, a linear fitting (Figure S1) according to I0/I =
Ksv[Pd]+1 gives a Stern-Volmer constant (Ksv) of 3.6104, 5.1105,
6.3105, and 9.7105 L·mol–1 for TPE, TPE-1, TPE-2, and TPE-4,
respectively. The enhanced Ksv means a higher sensitivity for the
sensor molecules with more terminal vinyl groups. The detection
limit of TPE-4 was calculated to be 0.38 μmol/L (Figure S2). The
flattening trend of the Stern-Volmer plot at higher concentrations
indicates that a heterogeneity of multi-fluorophores exists in the
system, which is indeed our case since TPEs are in aggregation
form in THF/water mixtures (fw = 90%).
Figure 3 Fluorescence quenching degree (I0/I–1) of TPE derivatives in the
presence of different metal ions (cion = 100 μmol/L). The quenching by
metal ions other than Pd2+ is negligible as the quenching degrees are in
the range of 0.2.
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Time resolved fluorescence spectra. To understand the
quenching mechanism, we performed time-resolved measure-
ments of fluorescence decays for TPE derivatives with and with-
out Pd2+ in THF/H2O mixture (fw = 90%). As shown in Table 1 and
Figure 4, TPE derivatives have typical fluorescence lifetimes of
2—3 ns. When Pd2+ is added (10 μmol/L), the curve follows a
faster decay process, as suggested by the reduced lifetime (τ). For
example, τ of TPE has a minor decrease from 3.02 to 2.68 ns,
while the value of TPE-4 exhibits a remarkable decay from 2.83 to
0.50 ns. It is noted that the decay degree of fluorescence lifetime
(τ0/τ) agrees with the quenching degree of fluorescence intensi-
ties (I0/I) (Table S1), which is the characteristic of a dynamic
quenching.
A dynamic quenching works via the interaction between the
quencher and the fluorophores in the excited state, offering a
non-radiative relaxation pathway, which reduces both the fluo-
rescence yield and the lifetime. The unchanged absorbance spec-
tra (Figure S4) prove that there are no ground-state complex
formed either. Therefore, the photo-induced excited state of TPEs
must be probed by ultrafast spectroscopy to gain more insight on
the interaction between TPE derivatives and Pd2+.
Transient absorption spectra. The excited state dynamics of
TPE have been extensively studied by ultrafast spectroscopy in
the past four decades.[27-31] The rotation around the elongated
C=C bond and the formation of photocyclized intermediates are
responsible for the non-emission of TPE in the solution, while the
inaccessibility of such dynamic in solids helps to preserve elec-
tronic energy for fluorescence.[27,28] Transient absorption spec-
trum (TAS) is a powerful technique to “see” ultrafast processes.
For TPE in the solution, two excited-state absorption (ESA) bands,
one at 420 nm and the other at about 620 nm, were observed in
the literatures.[30] The two bands were ascribed to the
Franck-Condon relaxed excited S1 state and the vibrationally re-
laxed planar S1 state.
Figure 4 Time-resolved fluorescence signals for TPE-derivatives with and
without the addition of 10 μmol/L Pd2+ in THF/H2O mixture (fw = 90%). (a)
TPE, (b) TPE-1, (c) TPE-2, (d) TPE-4. Red and blue dots correspond to ob-
served signals with and without Pd, respectively, while fits of signals are
lines. The instrument response function (IRF) is drawn in black dots. The
excitation wavelength is 365 nm, while the emission wavelength is the
maximum emission wavelength for each TPE derivative.
We also observed these two states for TPE-derivatives (Figures
5, S5, and S6). Note that the samples are in aggregation states in
THF/H2O mixture (fw = 70%), the corresponding wavelengths are
red-shifted compared to those reported in TPE.[30] The red-shift
becomes more evident for TPE-derivatives with more vinyl groups.
Taken TPE-4 as an example, one ESA band appears from 1.1 ps at
a wavelength longer than 730 nm (band I, longer wavelength not
shown because of the cut-off the laser intensity around 800 nm).
The second ESA band locates at 570 nm (band Ⅱ). Its intensity
reaches a maximum in 1.4 ps. At longer time scale, it decays with
Figure 5 Transient absorption spectra of TPE-4 with and without the addition of Pd2+ with a pump wavelength of 350 nm. (a) and (b) are the ultrafast
spectra of TPE-4 at short and long time scales. (c) Kinetic traces of TPE-4 at 535 nm (green square) and 730 nm (red triangle). (d) and (e) are the ultrafast
spectra of TPE-4 with Pd2+ (0.3 mmol/L) at short and long time scales. (f) Kinetic traces of TPE-4 with Pd2+ at 535 nm (green square) and 730 nm (red tri-
angle). TPE samples are prepared in THF/H2O mixture (fw = 70%) with a concentration of 0.3 mmol/L. The dip at 700 nm in each spectra was caused by the
laser scattering of TPE-4 particles.
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Fluorescent Probes Specific for Palladium
Chin. J. Chem.
a blue-shift to 550 nm (Figures 5a and 5b). Figure 5c shows
typical kinetic traces of the two ESA bands. The evolution of
the signals is related to intramolecular relaxations such as the
twisting of C=C bond and the torsion of phenyl rings,[28] which
are still active even in the aggregation state. However, it is not
our interest to interpret the dynamics associated with these
non-radiative relaxations in this work.
Interestingly, there are two additional negative absorption
bands at shorter wavelengths, i.e., 476 nm and 410 nm, which
are termed as band Ⅲ and Ⅳ. They actually appear earlier
than ESA bands. According to the absorption and fluorescence
spectra in steady state (Figure 1), it is inferred that band Ⅲ is
related with stimulated emission (SE) of TPE-4 (partly over-
lapped with the positive band Ⅱ), and band Ⅳ arises from
the ground state bleaching (GSB).[32] The SE and GSB bands
preserve during the experiment timescale (~1 ns).
After the addition of Pd2+, TAS recorded at each timescale
(Figures 5d—5f) are almost identical to those of pure TPE-4,
suggesting that the presence of Pd2+ does not influence the
ESA bands of TPE-4. However, a difference can be spotted
when SE bands are compared, especially at a short time scale
(Figure 6). For TPE-4 with Pd2+, the SE emerges at 0.9 ps and
the emission intensity is weaker than that of TPE-4, indicated
by the negative amplitudes at 476 nm. As time goes to 1.4 ps,
the signal of 476 nm turns from negative to positive, while it
remains nearly unchanged for TPE-4 (Figure 6b). This observa-
tion demonstrates that there is a reduced population of fluo-
rescent species in the system with Pd2+. It agrees with the re-
sults from steady-stated and time resolved fluorescence
measurements.
The disappearance of SE signature can be interpreted as
several electronic relaxation processes, e.g., the formation of
intermediates, the energy transfer, and electron transfer be-
tween TPE-4 and Pd. However, the first two mechanisms can
be ruled out, because they often lead to both the disappear-
ance of existing bands (GSB, SE, and ESA) and the formation of
new band.[33] Here, GSB signatures are not influenced by Pd2+.
An electron transfer most probably occurs from the excited
TPE-4 (donor) to Pd2+ (acceptor) at the early stage. Theoreti-
cally, the ESA bands of the acceptor should appear when the
electron transfers. Unfortunately, we could not discern the ESA
bands of Pd acceptor. Instead, systematic blue shifts of ESA
bands of TPE-4 are observed after adding Pd2+ (Figure 6a). The
reason is not clear yet.
Figure 6 (a) Comparison of TAS of TPE-4 (grey line) and TPE-4 with
Pd2+ (red line) at short time scales from 0.9 to 1.4 ps. (b) Kinetic traces
of TPE-4 (grey line) and TPE-4 with Pd2+ (red line) at the wavelength of
476 nm.
change is shown on the spectra.
Electron transfer mechanism. To investigate the interac-
tion between TPE-4 and Pd2+, theoretical calculations on the
excited states of TPE-4 with Pd(OAc)2 were carried out using
time dependent density functional theory (TD-DFT).[34] On the
basis of TD-DFT calculation, a hole–electron analysis[34-35] (Fig-
ure 7b) clearly shows an electron transfer from the center of
TPE-4 molecule to Pd, indicated by the distributions of holes
(blue) and electrons (green). We also calculated the wave
functions of the electron–hole pairs from the transition density
matrix.[35-36] The two-dimensional color-filled map (Figure 7c) is
plotted to represent the probability of finding the electron and
hole in the atomic orbitals localized on each non-hydrogen
atom. Electron transfer can be inferred from the off-diagonal
region. Carbon atoms on the central and terminal double
bonds are labeled as 1, 2 and 29, 33 (Figure 7a). We observe
that the electron flows from C1=C2, crossing the phenyl ring
(Atom 5, 11, 19, 25) and vinyl group C29=C33, and eventually to
Pd (Atom 35). For TPE-4 itself, the electron density flows
mainly from the central C=C bond to the adjacent C—C bonds
(Figure S7).
Similar to TPE-4, two ESA bands are also found on TAS for
TPE-1 and TPE-2 (Figures S5 and S6). However, their SE bands
cannot be resolved because SE signatures are overlapped with
ESA bands around 500 nm. After adding Pd2+, no apparent
Figure 7 Electron transfer between the excited state of TPE-4 and Pd2+ (in the form of Pd(OAc)2). (a) Molecular model shows the label of atoms. (b)
Hole-electron distribution of TPE-4 with Pd(OAc)2. The source and destination of electron density flow are indicated with blue wireframe and green
wireframe. (c) The transition density matrix map of the excited state of TPE-4 with Pd(OAc)2.
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The electron transfer is observed for the other TPE deriva-
tives with Pd as well (Figures S8—S10). Note that there is no
vinyl group in TPE, both intramolecular electron flowing and
intermolecular electron transfer are found in the excited state
of TPE with Pd (Figure S8). With increased number of terminal
vinyl groups on TPE, the electron density of TPE becomes rich,
the transfer is more pronounced (Figures S9—S10). Therefore,
we experimentally observed a higher fluorescence sensitivity
to Pd2+ for TPE derivatives with abundant vinyl groups. It is
proposed that terminal vinyl group is essential in a TPE-based
chemosensors for Pd, because it not only increases the elec-
tron density but also acts as a “bridge” for the flowing of elec-
trons.
photoluminescence spectrometer equipped with a picosecond
pulsed diode laser (EPL365). Ultrafast spectra were measured
using the pump-probe transient absorption spectrometer (TAS)
(Newport). The femtosecond laser has a central wavelength of
800 nm with a pulse width of 100 fs and a repetition rate of 1
kHz. The 350 nm pump laser was generated by the frequency
multiplication of the BBO crystal with a 800 nm laser. The
probe pulses (white light, 320—800 nm) were generated from
a thin CaF2 plate under the excitation of a 800 nm laser. The
changes in absorbance were measured between every two
successive laser shots by chopping the pump beam at 500 Hz.
Theoretical calculations. The quantum chemical calcula-
tions were carried out by the Gaussian 09 software package,[37]
under PCM implicit solvation model[38] and DFT-D3 dispersion
correction.[39] The details are given in the Supporting Infor-
mation.
Conclusions
In summary, using TPE derivatives containing different
numbers of vinyl groups, we have studied their fluorescence
quenching mechanism by Pd2+ with steady-state and time-
resolved spectroscopy. We find that electron transfer from TPE
derivatives to Pd provides an efficient nonradiative relaxation
pathway for electronic excitation. The attachment of vinyl
groups on the periphery TPE unit proves to be efficient to im-
prove the sensitivity to Pd2+, because vinyl groups not only
make TPE molecules more electron-rich but also facilitate the
intermolecular electron flow as a “bridge”, as revealed by the-
oretical calculation. The dynamic quenching mechanism in this
work is distinct from those conventional systems based on
coordination or chemical reactions. Following this mechanism,
a wide variety of AIE-active chemosensors can be chosen from
the database of AIE molecules and be developed for a real-life
application in Pd sensing.
Supporting Information
The supporting information for this article is available on
the WWW under https://doi.org/10.1002/cjoc.202000746.
Acknowledgement
This work is supported by the National Natural Science
Foundation of China (22075124, 21902073), Shenzhen Special
Fund (JCYJ20190809115013348), and Guangdong Provincial
Key Laboratory of Catalysis (No. 2020B121201002). This work
is also supported by Center for Computational Science and
Engineering of Southern University of Science and Technology.
The authors thank Prof. He, T. C. and Mr. Xiao, S. Y. (Shenzhen
University) for the measurement of transient absorption spec-
tra. The authors also thank Prof. Liu, Y. and Mr. Feng, Y.
(Shenzhen University) for the help during the synthesis.
Experimental
Materials. Tetrahydrofuran (THF) and toluene were puri-
fied by the solvent purification system (MBRAUN, MB SPS-5).
Other commercially available solvents (Shenzhen Changtai
Chemical Co.) and chemicals were directly used without any
further purification. Triphenylphosphine, 4-vinylphenylboronic
acid, 4-bromobenzophenone, bis(4-bromophenyl)methanone,
caesium carbonate, and (2-bromoethene-1,1,2-triyl)tribenzene
were obtained from Alfa. TiCl4 were bought from J&K Scientific.
Potassium vinyltrifluoroborate, palladium acetate, and tetra-
butylammonium bromide were obtained from Acros. Zinc
powder was bought from Tianjin DAMAO Chemical Reagent Co.
Ltd. Inorganic salts such as NaCl, CaCl2, CdCl2, CuCl2·2H2O,
AgNO3, FeSO4·7H2O, FeCl3, CrCl2, Pd(OAc)2, Pd(NO3)2, PdCl2,
CoCl2, NiCl2, MnCl2·4H2O, and Al2(SO4)3·18H2O were purchased
from Aladdin. Synthesis details of TPE derivatives were pre-
sented in the Supporting Information.
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1
Instruments and measurements. H NMR (400 MHz) and
13C NMR (100 MHz) spectra were recorded on a Bruker
AscendTM spectrometer at room temperature using deuter-
ated chloroform (CDCl3) as the solvent and tetramethylsilane
(TMS) as the internal standard. IR spectra were recorded on a
Bruker V80 FT-IR spectrophotometer. Mass spectra were rec-
orded on a Thermo Scientific™ Q Exactive™ Mass spectrometer.
The ultraviolet-visible (UV-vis) absorption spectra were col-
lected in a 1.0 cm path length cell with Agilent Cary 60 UV-vis
spectrophotometer. Sample concentrations were typically 10
μmol/L. The fluorescence measurements were performed on
Edinburgh FS5 spectrofluorometer equipped with a xenon arc
lamp. The excitation wavelength was 330 nm, and the emis-
sion was collected in the 380—800 nm region. Fluorescence
lifetime measurements were conducted on fluorescenceS1000
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Chin. J. Chem. 2021, 39, 1599—1605

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Manuscript received: January 5, 2021
Manuscript revised: February 4, 2021
Manuscript accepted: February 5, 2021
Accepted manuscript online: February 7, 2021
Version of record online: XXXX, 2021
Chin. J. Chem. 2021, 39, 1599—1605
© 2021 SIOC, CAS, Shanghai, & WILEY-VCH GmbH
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