Triphenylamine-decorated BODIPY fluorescent probe for trace detection of picric acid

Article abstract of DOI:10.1039/c5ra12154j

Triphenylamine-decorated BODIPY derivative TBMA was designed and synthesized. Luminogen aggregation was developed by taking advantage of twisted intramolecular charge transfer (TICT) and aggregation-induced emission (AIE) processes. In non-polar solvents, the locally excited (LE) states of BODIPY luminogens emitted intense yellow light. Increasing solvent polarity brought the luminogens from an LE to a TICT state, causing a large bathochromic shift in the emission color and a dramatic decrease in emission efficiency. The red emission was greatly boosted by aggregate formation or AIE effect. We also discovered that TBMA could be applied as an efficient chemical sensor for picric acid (PA) detection. The detection limit and quenching constant (K_SV) were determined as 30 ppb and 2.1 × 10^-6 M^-1 respectively. ¹⁹F NMR and ¹H NMR titration analysis verified that F...H hydrogen bonding is demonstrated as the mode of interaction, which possibly facilitates effective exciton migration.

Full text of DOI:10.1039/c5ra12154j

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Near-IR photoactive materials TBMA demonstrated high selectivity and sensitivity towards PA
detection with low detection limit, high quenching constant.

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Triphenylamine-Decorated BODIPY Fluorescent Probe for
Trace Detection of Picric Acid
Ma Hengchang,*a Zhang Zhongwei, Jin Yuanyuan, Zha Lajia, Qi Chunxuan, Cao Haiying, Yang
Zengming, Yang Zhiwang and Ziqiang Lei*a
Abstract: TriphenylamineꢀDecorated BODIPY derivative TBMA was designed and synthesized.
Luminogen aggregations were developed through taking advantages of twisted intramolecular
charge transfer (TICT) and aggregationꢀinduced emission (AIE) processes. In nonpolar solvents,
the locally excited (LE) states of BODIPY luminogens emited intense yellow lights. Increasing
solvent polarity brought the luminogens from LE to TICT state, causing a large bathochromic shift
in the emission color and a dramatic decrease in emission efficiency. The red emission was greatly
boosted by aggregate formation or AIE effect. We also discovered that TBMA could be applied as
an efficient chemical sensor for PA detection. The detection limit and quenching constant (KSV)
were determined as 30 ppb and 2.1x10ꢀ6 Mꢀ1 respectively. 19F NMR and 1H NMR titration analysis
verified that F...H hydrogen bonding is demonstrated as the interacting mode, which is of
possibility to facilitates the effective exciton migration.
Introduction
4,4ꢀDifluoroꢀ4ꢀboraꢀ3a,4aꢀdiazaꢀsꢀindacene[1,2] or
borondipyrromꢀethene
(BODIPY)
derivatives are a group of luminogenic molecules that usually emits in the long wavelength region
(λem up to nearꢀIR) in high fluorescence quantum yields (ΦF up to unity).[3ꢀ6] Extensive studies
documented that the emission behaviors of BODIPY luminogens are sensitive to the
intramolecular rotations and the interactions of their chromophoric segments.[7] However, that is a
painstaking work to synthesize BODIPY derivatives with desirable fluorescent property from
chemical decorations.[8] Multiple synthetic steps and moderate and low isolated yield always
prevent those materials from real applications. It will be really applicable if the intramolecular
rotations can be restricted by simple physical processes, if possible, rather than by multiꢀstep
chemical modifications. Tang’s group has explored the notable aggregationꢀinduced emission
(AIE) and aggregationꢀinduced enhancement emission (AIEE).[9,10] As the terms implied that some
of luminogenic molecules, for extraordinary instances, triphenylamine (TPA) and
tetraphenylethene (TPE) with great freedom in intramolecular rotation are nonemissive when
dissolved in their good solvents but become highly luminescent when aggregated in their poor
solvents due to the physical restriction on the intramolecular rotations in the aggregates.[11ꢀ14] In
our previous works, we have been interested in exploring efficient fluorescent materials with
intriguing AIE characteristic, and several luminescent molecules have been efficiently prepared
and utilized as chemical sensors and smart soft matters.[15,16]
Picric acid (PA) has emerged as a potential explosives due to its high energy release power.[17]
In addition, PA is highly water soluble, therefore, which is estimated as major contaminate of
groundwater. PA also has been widely used in the dye industry, rocket fuel manufacturing, and the
pharmaceutical industry. Thus, for social and living beings' safety, effective monitoring and
detection of trace amounts of PA, is really important.[18]
The signal amplification effect, which was discovered for detection of trace amounts of
explosives in the solution phase by conjugated polymers, [19ꢀ22] has been applied as the traditional

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monitoring technology. However, delayed effect is inevitable because of that polymers owing to
their very high molecular weight have worse solubility in common organic solvents, leading to
reduce their sensitivity and specifity.[23] In recent years, supramolecular polymers employed as
chemical sensors turned out to be a potential alternative in this regard. Because of that lowꢀweight
molecules can easily be fabricated and modificated diversely, such applicable designing is greatly
beneficial to successful exciton migration. Although there were numerous reports on luminescent
supramolecular chemosensors for PA detection,[24ꢀ26] most detection systems were either less
selective or exhibit lowꢀtoꢀmoderate SternꢀVolmer constants. More than that the ppb level
detection in organic solvents was also a crucial but very difficult task. Herein, we report the
synthesis and characterization of TPA decorated BODIPY derivative of TBMA (Scheme 1), which
was proven to be potential candidates for picric acid sensing with high sensitivity and selectivity.
Results and Discussion
Design and Synthesis of Target Molecules
To enhance the fluorescence response capability of the probes, especially in the visible light
region, the target molecule V (abbreviated as TBMA) was designed and synthesized (Scheme 1).
There was a triphenylamine (TPA) core with two tentacles like functional group of methyl
acrylate (III), which was synthesized from intermediate II by Heck reaction with 85% yield.
Importantly, two tentacles are able to induce TPA core be more apparent fluorescent emission due
to the formation of conjugated electron donorꢀaccept system. It was also well known that TPA
derivatives are of typical AIE prosperities, methyl acrylate groups could provide stronger
intermolecular force as we reported.17 Thanks for the better aggregation ability of the intermediate
III, which could emit the desirable greenꢀyellow light under UV light (Scheme 1). Dyes bearing of
building blocks of BF2 complexes of dipyrrin ligands (BODIPYs) have diverse applications as
biolabels, artificial light harvesters, sensitizers for solar cells,[27ꢀ34] fluorescent sensors,[35,36]
molecular photonic wires, and laser dyes.[37,38] This popularity of BODIPY dyes was presumably
because of their advantageous spectroscopic properties such as high molar absorption coefficients,
narrow band shapes with tunable wavelengths, excitation/emission wavelengths above 500 nm,
large Stokes shifts (SS), high fluorescence quantum yields, and considerably high photostability.[39]
Therefore, the rigid segment of BODIPY was introduced into TPA core according to Lindsey’s
procedure by condensing compound III with excess pyrrole in the presence of a catalytic amount
of trifluoroacetic acid at room temperature.[40] Afterwards, the dehydration was carried out in
dichloromethane with DDQ for 30 min, followed by treatment with triethylamine and BF3.OEt2 at
room temperature for 10 min.[41] Thinꢀlayer chromatographic analysis shown a fluorescent red
spot of the desired compound. The crude TBMA were subjected to flash silica gel column
chromatographic purification and afforded the stable product V as darkꢀred solid in 26% yield.
Meanwhile, compound VI (abbreviated as TB) was synthesized from intermediate I following the
1
above mentioned method. H, 13C, MS and IR spectroscopies have been used to characterize
compounds III, TB and TBMA in detail.

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O
O
I
I
Methyl acrylate
0.8 mol%Pa(OAc)2
1.7 mol%DPPP
H3CO
OCH3
N
N
N
POCl3
KIO3,KI
AcOH,100 o
N
DMF, r.t. , 2h
C
Et3N , DMF, 90 o
C
CHO
I
CHO
II
TPA
III
CHO
O
O
O
O
H3CO
OCH3
H3CO
OCH3
N
N
B
N
a). CH2Cl2, DDQ
b). Et3N, BF3Et2
TFA (0.1 equiv)
excess pyrrole
O
H
N
N
N
N
NH HN
VI
B
IV
V
F
F
F
F
Scheme 1. Synthetic procedures of TBMA(V) and TB(VI), and the photographs of III, TB,
TBMA in the powder form under room light (top) and UV light illumination at 365 nm (bottom).
Photophysical properties
Solvent Effect. TBMA shown an almost similar wavelength band, which changes slightly with
the variation in solvent as can be seen from the absorption spectra (Fig. 1a). Due to the πꢀπ*
transition of the BODIPY unit, a sharp absorption peak (λabs) appears around at 500ꢀ520 nm. As
documented that BODIPY derivative with a phenyl ring at the 8 position is much less luminescent
(ΦF = 19%, EtOH), which is due to the rotational movement of the phenyl ring around the single
bond nonradiatively deactivates its excited state to a large extent.[42ꢀ45] That's to say, the less the
rotatable junctions, the higher the emission efficiency. Accordingly, as we synthesized that the
bulk junction at 8 position exerts steric effect on the rotational motion of the phenyl ring, such
effect was originated from the propellerꢀshaped TPA core and methyl acrylate groups with strong
aggregation ability. Thus, the resulted BODIPY derivative TBMA became more emissive in some
cases (as shown in Fig. 1b). The emission study of TBMA in different solvents indicated that the
luminescent properties are greatly affected by solvent polarity. The emission band is redꢀshifted
and its intensity is reduced with an increase in the solvent polarity (Fig. S1 and table S1). For
instance, fluorescence was almost quenched in the polar solvent of MeOH. However, TBMA
shown strong emission and dramatic blueꢀshift in less polar solvents like toluene (ΦF = 52%).[46ꢀ48]
a)
b)

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Fig. 1 (a) Normalized absorption spectra of TBMA in different solvents. Solution concentration:
10 µM. (b) Photographs of TBMA in different solvents taken under UV illumination at 365 nm.
TICT Process. To have a deep insight into twisted intramolecular charge transfer (TICT)
phenomenon, we serially changed the ratio of solvent by mixing polar THF and nonpolar hexane
together. Afterwards, we measured the emission property of TBMA. As can be seen from Fig. 2,
When the hexane fraction (fh) in the THF/hexane mixture was increased from 0 to 90%, the
emission color was changed from red to yellow. Meanwhile, the emission was gradually
intensified and narrowed into a more sharp band. According to the previous statements that in the
locally excited (LE), TBMA may take a more planar conformation. In a nonpolar solvent, the
excited luminogen is in equilibrium with solvent molecules and its planar conformation stabilized
by a better electronic conjugation gives a sharp emission band. Comparably, in a polar solvent,
intramolecular rotation brings the luminogen from LE state to TICT state, in the new equilibrium
state, the twisted molecular conformation is stabilized by the polar solvent. Due to the fact that
each luminogen molecule has a different twisting angle and hence emission characteristic the
collection of which thus gives rise to a broad emission band.[49] This result also could be verified
by the temperatureꢀdepended emission property in the polar solvent of THF, because the emission
of a TICT luminogen was sensitive to temperature variations.[7] From Fig. S2, we could concern
that the emission spectrum gently become into a broader band, and the intensity is reduced
obviously when the temperature is decreased from 65 to 0 oC. 1H NMR measurements
demonstrated a very different chemical shifts of TBMA in polar and nonpopar deuterium solvents
(Fig. 3). As can be seen that in nonpolar tolueneꢀd8, the crowd peaks in the range of 6.7ꢀ7.1 ppm
verify the existence of the hydrogen atoms in the C=C double bonds. However, in the solvent of
CDCl3, all of them shift to upꢀfield and separate into two cluster of peaks obviously. With
increasing the polarity of solvent, (for instance in CD3CN) two cluster of peaks shift up and down
further. Such results clearly confirmed that in the nonpolar solvent of tolueneꢀd8, a better
electronic conjugation renders TPA core with almost equal electron density, thus the nearly equal
chemical environments give all of hydrogen atoms in the C=C double bonds with the slight
difference of NMR signals. Further, we can concern that TBMA is more prefer to aggregate than
monoꢀdispersein in nonpolar solvent of toluene, because of that all of peaks shifted into upꢀfield
apparently. However, in the polar solvent, the DꢀA electron system formed and a drastic different
chemical environments generated two cluster of NMR signals, which further split with the
increasing solvent polarity. As we discussed above that TBMA is probable to take more twisted
conformation in polar solvent, therefore, a better electronic conjugation is hard to form, which
brings about a great different NMR signals. These findings were well agreed with the previous
research reports.[7]

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a)
b)
Fig. 2 (a) Emission spectra of TBMA in the THF/hexane mixtures. (b) Plots of maximum
emission intensity (Imax) and wavelength (λem) of TBMA versus hexane fraction (fh) in the
THF/hexane mixture. Solution concentration: 10 µM. Excitation wavelength: 490 nm.
Fig. 3 1H NMR spectrum (400 MHz, room temperature) of a solution of TBMA in CD3CN, CDCl3,
Tolueneꢀd8.
AIE Phenomenon. TPA derivatives are typical AIE materials.[50ꢀ52] Afterwards, we investigated
this physical property in THF/water mixtures according to the documented method. Since TBMA
is insoluble in water, they must aggregate in the aqueous mixtures with high water fractions (fw).
And as shown in Fig. 4, the absorption intensity was weaken along with the increasing water
fractions, when water fraction was up to 80% in volume, this absorption peak gradually generated
two shoulders bathochromicly and hypochromaticly. Those shoulders designated as Hꢀ and Jꢀband,
are corresponding to the different intermolecular pack modes of Hꢀ and Jꢀaggregation.[53,54] From
emission spectrum (Fig. 6a), we can see that TBMA is almost nonꢀemissive in pure THF.
However, TBMA could emit an intensified red color when 80% water is mixed. To really
1
understand the AIE property and the soft interaction between TBMAs, we carried out H NMR
titration studies in the mixture of CD3CN/D2O (4:1, v/v) and CD3CN respectively (Fig. 5).
Evidently, all of proton resonance signals shifted into up field with different value, which verified
the formation of aggregates with increasing D2O fractions. The changes of chemical shift of the
proton resonances of (Ha and Hb) in the double bond displayed the largest ꢀ value (ꢀ = 0.04 ppm),
and the other identifiable peak of “Hc” demonstrated the smaller ꢀ value (ꢁ = 0.02 ppm), such
results indicate the detectable interactions may take place between the interlaced tentacles like
functional group of methyl acrylate. More than that the obvious HꢀH NOESY correlations of
TBMA could be detected as shown in Fig. 6b, such correlations are originated from an attractive
interaction between superimposed phenyl and carbonyl groups of methyl ester. Therefore, what
could be confirmed that in the mixture of CH3CN/H2O=1:4, the wellꢀorganized aggregates are
formed in Hꢀ and Jꢀpack modes by C=O...π interactions, which results in AIE phenomenon. All
the mixed solutions were macroscopically homogeneous and transparent with visible tyndall effect,

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suggesting that the aggregates are nanosized. The formation of nanoaggregates was supported by
SEM images that when fw= 20%, uniformed nanoꢀspheres scattered on the silicon wafer, where as
long as several micrometer’s fibres enlaced each other in the case of fw= 80% (Fig. 6c).
Accordingly, reversible macroꢀgels could be easily formed. In tremendous comparison, if TBMA
doesn't possess two tentacles like methyl acrylate groups (for instance of compound TB), no fibres
could emerge, let alone gel formation (Fig. S6). The details of gelation ability could be seen in
Supporting Information.
a)
b)
Fig. 4 (a) Normalized absorption spectra of TBMA in THF/water mixtures. Solution concentration:
10 µM. (b) Normalized absorption spectra of TBMA(10 µM) in fw= 0 and 80%.
1
Fig. 5 H NMR spectrum (400 MHz, room temperature) of a solution of TBMA in CD3CN, and
CD3CN/D2O(v/v = 4:1).
a)
b)
c)
Fig. 6 (a) Emission spectra of TBMA in the THF/water mixtures. Solution concentration: 10 µM.

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Excitation wavelength: 500 nm. (b) The NOESY NMR spectrum (400 MHz, room temperature) of
a solution of TBMA in CDCl3. (c) SEM image of TBMA in the different the water fraction (fw).
In order to verify the interactions between TBMA and solvent, we prepared the gel of TBMA
in CH3CN&CH3CH2OH, then casted it on the quartz plate. The realꢀtime FTꢀIR spectra were
recorded during solvent vaporization, which clearly displayed that two identical absorption bands
around 1710 cmꢀ1 are narrowed into one sharp peak after less than 30 min, which was recognized
as C=O absorption peak. This transformation confirmed the hydrogen bonding formation between
C=O of TBMA and CH3CH2OH. Additionally, in contrast with powders of TBMA, the xerogel of
TBMA demonstrated more sharp resonance peaks in IR spectrum (Fig. S7), this difference
possibly implied that in the xerogel state (Fig. S8), TBMAs are wellꢀorganized than in the powder
state, therefore, more uniformed aggregation modes bring about the narrow distributed resonance
energy of C=O.
Fig. 7 The optimized molecular orbital amplitude plots of HOMO and LUMO energy levels of
TBMA (left), TB (right).
We performed density functional theory (DFT) calculations to gain a better understanding of
the geometric and electronic structure and optical properties of the molecules presented in this
study. Thus, quantum chemical optimization on their energy levels based on DFT/B3LYP/6ꢀ31G
(d,p) using Gaussian 09 is conducted. Fig. 11 displayed the highest occupied molecular orbital
(HOMO) and lowest unoccupied molecular orbital (LUMO) diagrams of TBMA and TB.
According to Fig. 7, both HOMO of these compounds were basically distributed over the TPA
cores, and LUMO of TBMA and TB extended across the BODIPY frames, which indicated that
these derivatives have obvious ICT tendency.[55] This result was also consistent with the observed
stronger solvent dependence fluorescence behaviours of TBMA and TB. Compared with TB,
TBMA has a lower higher energy (−5.58 eV), which is due to the existence of electron with
drawing methyl acrylate groups, and a lower LUMO energy (−2.85 eV), because of that the less
distorted structure is favorable for decreasing the LUMO energy.
Detection of Nitroaromatic Explosives in Solution
Quenching Studies
In the sensing behaviors of PA toward TBMA, the fluorescence titration for sensor with PA
revealed that fluorescence emission intensity are rapidly died down upon addition of increasing
amounts of PA solution (Fig. 8, S9), the quenching efficiency was found to be 95%. Obviously,
SEM images (Fig. 8b) demonstrated that long fibres are disrupted into cluttered sticks in the

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presence of PA. These results demonstrated the interactions of TBMA with PA possibly occurs.
a)
b)
Fig. 8 (a) Fluorescence spectrum of TBMA on addition of PA(0ꢀ500eq.) in toluene respectively.
Insets show the quenching in fluorescence of TBMA after addition of PA. Solution concentration:
10 µM. Excitation wavelength: 500 nm. All images are taken under 365 nm UV lamp. (b) SEM
images of TBMA (A) and TBMA&PA (B).
To check the portable application of the sensor in more convenient manner, we prepared the
easily available filter paper as the substrate material. For more visualized exhibitions (Fig. 9),
filter paper is cut into a Tibetan language word, then, which was moistened by TBMA solution
(10ꢀ4 M in toluene). After evaporating the solvents, the test paper is immersed into the solution of
PA (10ꢀ4 M in toluene). Obviously, the luminescent decay happened once dipping the test paper
into the solution of PA. These results clearly displayed the practical applicability of TBMA for the
instant visualization of traces of PA.
Fig. 9 Paper strips of compound TBMA (10ꢀ4 M) for PA (10ꢀ4 M) detection.
Quenching Mechanism
We explored the interaction models of TBMA with PA investigated by 19F NMR
spectroscopic analysis carried out in CDCl3 (Fig. 10). As several recently reported BODIPY
compounds that the fluorines are found to be inequvalent and show two sets of multiplets at ꢀ140
ppm.[41,56] However, in the mixture of TBMA with PA, we observed only one quartet in 19F NMR,
indicating that the fluorines are under a chemically equivalent environment. Notably, in the
presence of PA, the 19F NMR signal of TBMA exhibits obvious downfield shift. This unusual
downfield shift was probably attributed to the presence of hydrogen bonding between fluoride
ions and PA. Such observation was also consistent with the reported dipyrromethene dyes.[57]
Meanwhile, TBMA was possibly disfavor the formation of aggregates in the presence of PA due
to the huge steric hindrance after producing complex VII. Thus, the AIE process was suppressed,
and leading to the disappearance of emission color. Additionally, the significant emissive
performances represent two different “states”, where the fluorescence is “switched on” (state I)
without PA and “switched off” (state II) with PA, as shown in Scheme 2. In the presence of PA,
the intermolecular photoinduced electron transfer (PET) could be potentially enhanced after
capturing the more acidic molecules of PA, because BODIPY core turns into a more
electronꢀdeficient center. The another way, PA or picrate (P‑) ions promotes the PET quenching
of the TPA excited state effectively. Furthermore, the intermolecular bonding models were

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verified by 1H NMR titration analysis. From Fig. 11, we can see that the signals of hydrogen atom
in ꢀOH group of PA upꢀfield shifted and become broaden gradually with increasing the
concentration of sensor of TBMA. Comparably, all of rest peaks displayed negligible chemical
shift. Therefore, these results confirmed the formation of complex VII by definite interacting
patterns of F...H hydrogen bonding. What's more, this conclusion also inspired us that
dipyrromethene dyes possibly could be applied as specific chemical sensors to phenol derivatives.
Especially, more acidic the analytes, more sensitive the BODIPY sensors.
Fig. 10 19F NMR spectra of TBMA and the mixture of TBMA with PA in selected regions
recorded in CDCl3.
O
O
H3CO
OCH3
N
B
O
O
H3CO
OCH3
PET
N
PA
N
F
N
F
O2N
NO2
O
O
H
N
N
H
B
F
F
NO2
O2N
O2N
NO2
VII
Switched ON (I)
Switched OFF (II)
Scheme 2. Schematic Representation of the Fluorescence quenching.
Fig. 11 1H NMR spectra of TBMA and PA with different mol ratio in CDCl3.
Finding Detection Limit and Selective Detection of Nitroaromatics
We next investigated the fluorescence response of several other electronꢀdeficient nitro
compounds. Obviously, except PA, all other compounds shown insignificant quenching of the
emission intensity, and the quenching efficiency are less than 30% (Fig. 12). According to the
above results, BODIPY analogue of TBMA was proved as an effective and selective sensor for the
detection of PA in solution. To determine the detection limit, fluorescence titration of TBMA in
toluene with picric acid was carried out by adding picric acid solution and the fluorescence
intensity as a function of picric acid added is then plotted. From this graph the concentration at
which there is a sharp change in the fluorescence intensity multiplied with the concentration of

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TBMA gave the detection limit.[58] Equation used for calculating detection limit (DL):DL= CL ×
CT, CL = Conc. of TBMA(1×10ꢀ6 M·Lꢀ1); the datum of CT (0.03 equiv) from Fig. S10.
Thus, detection limit for picric acid DL = 1×10ꢀ6 M·Lꢀ1× 0.03 equiv = 3×10ꢀ8 M·Lꢀ1 = 30 ppb .
The quenching results could be quantitatively treated with the SternꢀVolmer equation, I0/I= 1+
Ksv[PA],[26, 59ꢀ61] where I0 and I stand for the fluorescence intensity of TBMA in the absence and
presence of PA, respectively, [PA] is concentrations of PA, and Ksv is the SternꢀVolmer constant.
The decrease in the fluorescence intensity could be an electron transfer process on the basis of
thermodynamic considerations as static and dynamic quenching. The SternꢀVolmer plots shown
two distinct regions: linear variation at a lower concentration of PA was mainly due to static
quenching, whereas a steep curve at higher concentration of PA was presumably due to dynamic
quenching. It can be seen that the SternꢀVolmer plot of the change in the intensity of TBMA with
respect to the PA concentration is linear at a lower concentration of PA and gives a quenching
constant (KSV) of 2.1×10ꢀ6 Mꢀ1, suggesting the quenching of the fluorescence of TBMA ensemble
upon the addition of PA is ascribed to the static quenching through a oneꢀtoꢀone nonfluorescent
ground state complex, which after excitation returns to the ground state without emission of light
(Fig. 13). Overall, the quenching constant and detection limit of the TBMA toward PA were
noticeably higher than those reported in previous reports.[26]
Fig. 12 Variation of fluorescence intensity (I0/I) of TBMA toward different analytes in toluene.
a)
b)
Fig. 13 (a) Stern−Volmer plots for TBMA(10 µM) using PA in toluene as quencher. (b)
Stern−Volmer plots at lower concentration region of PA in toluene.
Experimental
Materials
Triphenylamine (TPA, 99%) is purchased from Energy Chemical Company. Pyrrole (>99%) is
purchased from Energy Chemical Company. Trifluoroacetic acid (TFA, 99%) is purchased from
Aladdin Reagent Company. phosphorus oxychloride (POCl3) is purchased from Shandong Bazhou
quartz clock Reagent Company. 2,3ꢀDichloroꢀ5,6ꢀdicyanoꢀ1,4ꢀbenzoquinone(DDQ, 98%) is
purchased from Energy Chemical Company. Methyl acrylate (95%) is purchased from

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Shuangꢀshuanghg
Company.
palladium
acetate
(Pd(OAc)2,
99%),
1,3ꢀbis(diphenylphosphino)propane (DPPP, 97%), tertꢀButyl acrylate (99%), and methyl
methacrylate (99%) are brought from Aladdin Reagent Company. Triethylamine (Et3N, 99%)
were purchased from Kaixinchem Company. Quinine sulfate dehydrate is purchased from
Shanghai ZhongQin Company. Rhodamin B is purchased from Tianjin tianxin Fine chemical
industry development center. Nitrogen with a purity of 99.99% is provided from commercial
source. Other reagents, such as N,Nꢀdimethylformamide (DMF), toluene, benzene,
dichloromethane (DCM), methanol, ethanol, tetrahydrofuran (THF), ethyl acetate, diethyl ether,
chloroform, 1,4ꢀdioxane, tetrachloromethane, and acetic acid are A.R. grade.
Characterizations
1H NMR (400 MHz), 13C NMR (100 MHz), and HꢀH NOESY (400 MHz) spectra are recorded on
o
a MERCURY spectrometer at 25 C, and all NMR spectra are referenced to the solvent. Mass
spectra are recorded on a HP5989B mass spectrometer. UVꢀvisible absorption spectra are
recorded on a TUꢀ1901 spectrometer from 190 to 1100 nm. Fluorescence spectra are measured
using a PE LSꢀ55 Luminescence/Fluorescence Spectrophotometer. Emission spectra are recorded
on a PerkinꢀElmer LS 55 spectrofluorometer at room temperature (∼25 °C) as well as other
specific temperatures (0 to 65 °C). Fourier transform infrared (FTꢀIR) spectra are recorded on a
DIGIL FTS3000 spectrophotometer using KBr tablets. The morphology of compounds is observed
by scanning electron microscopy (SEM, ZEISS ULTRA PLUS). All the samples are prepared
according to the standard methods. The groundꢀstate geometries are fully optimized by using the
density functional theory (DFT) at the B3LYP / 6ꢀ31G(d,p) level, as implemented in Gaussian 09.
Synthesis
o
Synthesis of I：Phosphorus oxychloride ( 15 mL ) is added dropwise at 0 C to DMF ( 15 mL ),
and the reaction mixture is stirred for 1 h. TPA( 5g ) is added and stirring is continued for 6 hours
o
at 50 C. The reaction mixture is poured in the 100 mL water slowly, whereby a yellow solid
precipitated out. The solid is filtered, washed with water. Purification by column chromatography
on silica gel (ethyl acetate/petroleumether,1:45) followed by recrystallization (CH2Cl2/hexane)
gave II (4 g, 80%) as a yellow solid.[62,63] Mp 128ꢀ130 °C; 1H NMR (400 MHz, CDCl3) δ 9.81 (s,
1H), 7.68 (d, J = 8 Hz, 2H), 7.34 (t, J = 8 Hz, 4H), 7.16 – 7.19 (m, 6H), 7.02 (d, J = 8 Hz, 2H). 13C
NMR (100 MHz, CDCl3): δ 190.31, 153.31, 146.13, 131.24, 129.68, 129.12, 126.27, 125.06,
119.33 ppm. MS (FAB): m/z = 273.12 [M+H]+. IR (KBr): 3098, 2827, 2740, 1689, 1585, 1504,
1488, 1427, 1330, 1259, 825, 757, 696 cm–1.
Synthesis of II: In to a 100 mL, twoꢀnecked, roundꢀbottom flask equipped with a condenser are
placed 546 mg of I (2 mmol), 996 mg of potassium iodide (KI, 6 mmol), 1.284 g of potassium
iodate (KIO3, 6 mmol), and 10 mL of acetic acid. The mixture is heated to 70 oC under stirring for
10 h. The mixture is cooled to room temperature, filtration, washed consecutively with water and
ammonia water to adjust the PH of the solution to be 8. the solution is extracted with CH2Cl2, The
collected organic layer is washed with saturated sodium hydrogen sulfite and brine, dried over
anhydrous Na2SO4.[64,65] After filtration and solvent evaporation, The crude product is
recrystallized from ethanol to obtain the target II (461.1 mg, 85%) as a yellow solid. Mp
138ꢀ140 °C; 1H NMR (400 MHz, CDCl3) δ 9.84 (s, 1H), 7.71 (d, J = 8.0 Hz, 2H), 7.63 (d, J = 8.0
Hz, 4H), 7.05 (d, J = 8.0 Hz, 2H), 6.89 (d, J = 8.0 Hz, 4H) ppm. 13C NMR (100 MHz, CDCl3) δ

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190.29, 152.17, 145.71, 138.85, 131.32, 130.35, 127.59, 120.76 ppm. MS(FAB): m/z=524.91
[M+H]+. IR(KBr): 3441, 2805, 2733, 1689, 1598, 1574, 1327, 1315, 1270, 1217, 959, 819, 719
cm–1.
Synthesis of III: 4ꢀ(bis(4ꢀiodophenyl)amino)benzaldehyde（II）(2.63 g, 5 mmol), Methyl acrylate
(12 mmol), Pd(OAc)2 (18 mg, 0.08 mmol), 1,3ꢀbis(diphenylphosphino)propane (DPPP, 66 mg,
0.16 mmol) and Et3N (1.2 g, 12 mmol) are added into 10 mL of dry dimethylformamide (DMF).
After stirring for 48 h at 80 °C under N2 atmosphere. When the reaction is completed as
determined by the disappearance of II, 20 mL of water is charged, and the solution is extracted
with CH2Cl2 (3×10 mL). The organic phases are then dried with anhydrous magnesium sulfate,
filtered, and concentrated under reduced pressure.[66] Purification by column chromatography on
silica gel (ethyl acetate / petroleum ether, 1:10) followed by recrystallization (CH2Cl2/hexane)
gave III (1.78 mg, 68%) as a yellow solid. Mp 133ꢀ135 °C; 1H NMR (400 MHz, CDCl3) δ 9.88 (s,
1H), 7.76 (d, J = 8.0 Hz, 2H), 7.66 (d, J = 16.0 Hz, 2H), 7.48 (d, J = 8.0Hz, 4H), 7.15 (t, J = 8.0Hz,
6H), 6.38 (d, J = 16.0 Hz, 2H), 3.81 (s, 6H) ppm. 13C NMR (100 MHz, CDCl3): δ 190.34, 167.35,
151.99, 147.70, 143.62, 131.30, 131.09, 130.85, 129.53, 125.37, 122.28, 117.24 ppm. MS (FAB):
m/z = 441.1 6 [M+H]+. IR(KBr): 3445, 2947, 2720, 1717, 1630, 1594, 1504, 1433, 1321, 1267,
1203, 1167, 1038, 980, 825 cm–1.
Synthesis of TBMA: Pyrrole (5 mL, 72 mmol) and III (1.27 g, 2.88 mmol) are added to a dry 100
mL roundꢀbottomed flask and degassed with a stream of N2 for 5 min. TFA (22.2 ꢂL, 0.5 mmol)
was then added, and the solution is stirred under N2 at room temperature. TLC analysis indicates
that the disappearance of spots corresponds to III and appearance of a new spot corresponds to
compound IV. The solvent is removed on a rotary evaporator under vacuum, and the crude
compound is passed through flash silica gel column chromatography with a mixture of ethyl
acetate and petroleum ether as eluent (1:6 by volume). The resultant compound IV (557 mg, 1
mmol) is dissolved in freshly distilled dichloromethane and oxidized with DDQ (272.4 mg, 1.2
mmol) for 30 min at room temperature. The reaction mixture is then treated with a small amount
of Et3N (5.6 mL, 40 mmol) followed by BF3•OEt2 (6.3 mL, 50 mmol), and the mixture is stirred
for an additional 30 min at room temperature.[67] The solvent is removed in a rotary evaporator,
and the resultant crude compound is purified by silica gel column chromatography with petroleum
ether/ethyl acetate (3:1) and afforded pure TBMA (144.8mg, 26%) as a purple solid. Mp
1
205ꢀ207 °C; H NMR (400 MHz, CDCl3): δ 8.00 (s, 2H), 7.63 (d, J = 16.0 Hz, 2H), 7.41 (d, J =
8.2 Hz, 4H), 7.17 (d, J = 8.2 Hz, 2H), 7.06 (d, J = 6.7 Hz, 6H), 6.74 (s, 2H), 6.32 (d, J = 15.9 Hz,
2H), 6.18 (s, 2H), 5.94 (s, 2H), 5.46 (s, 1H), 3.80 (s, 6H) ppm. 13C NMR (100 MHz, CDCl3): δ
167.63 , 148.83 , 145.01 , 144.09 , 138.64 , 132.29 , 129.60 ,129.44 ,128.91 , 125.80 , 123.39 ,
117.36 , 115.93 , 108.49 , 107.27 , 51.58 , 43.52 ppm. MS ESI m/z: 603.22 [M+H]+. IR (KBr):
3419, 3232, 2944, 1710, 1630, 1591, 1507, 1453, 1412, 1387, 1324, 1263, 1182, 1117, 1076, 1046,
982, 911, 829, 777, 746, 715 cmꢀ1.
Synthesis of TB: Compound TB is synthesized in a manner similar to that for TBMA. Yield:
299.5 mg (77%); pure solid. Mp 212ꢀ214°C; 1H NMR (400 MHz, CDCl3) δ 7.90 (s, 2H), 7.40 (m,
6H), 7.23 – 7.06 (m, 10H), 6.55 (s, 2H) ppm. 13C NMR (100 MHz, CDCl3): δ 150.94, 147.52,
146.47, 142.77, 134.63, 132.25, 131.00, 129.67, 126.22, 125.94, 124.70, 120.02 , 117.95 ppm. MS
(FAB): m/z = 435.17 [M+H]+. IR (KBr) : 3105, 3059, 3036, 1587, 1558, 1533, 1488, 1412, 1388,
1332, 1294, 1261, 1224, 1192, 1118, 1076, 980, 911, 757, 742, 696 cmꢀ1.

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DOI: 10.1039/C5RA12154J
Conclusions
In conclusion, TPA decorated BODIPY derivative of TBMA was designed and synthesized. Two
tentacles like functional group of methyl acrylate modificated TPA core exerted huge steric
hinꢀdrance on the 8ꢀposition of BODIPY centre, therefore, TBMA exhibited emission
wavelengths above 650 nm. Additionally, due to the soft interactions between the interlaced
methyl acrylate groups, TBMA displayed notable AIE phenomenon in the mixture of THF and
H2O. We also discovered that TBMA could be applied as an efficient chemical sensor to PA
detection. The detection limit and quenching constant (KSV) are determined as 30 ppb and
1
2.1×10ꢀ6 Mꢀ1 respectively. 19F NMR and H NMR titration analysis verified that F...H hydrogen
bonding is decserved as the interacting model, which is of possibility to facilitates the effective
exciton migration.
Acknowledgements
The authors are grateful for the financial support of National Natural Science Foundation of China
(No. 21202133, 21174114, 21361023). The authors also thank the Key Laboratory of
EcoꢀEnvironmentꢀRelated Polymer Materials (Northwest Normal University), The Ministry of
Education Scholars Innovation Team (IRT 1177) for financial support.

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