A multifunctional fluorescent probe for highly selective detection of hydrazine and discovering the interplay between AIE and ICT

Article abstract of DOI:10.1016/j.dyepig.2019.108111

A multifunctional luminescent material (BC–B) was synthesized, which exhibits aggregation-induced emission (AIE) enhancement property in high water fraction. The AIE shows a significant impact on the intramolecular charge transfer (ICT) process by control

Full text of DOI:10.1016/j.dyepig.2019.108111

Journal Pre-proof
A multifunctional fluorescent probe for highly selective detection of hydrazine and
discovering the interplay between AIE and ICT
Ji-hua Zhu, Hao Zhang, Yuan Liao, Jing-jiang Liu, Zheng-jun Quan, Xi-cun Wang
PII:
S0143-7208(19)32384-8
DOI:
https://doi.org/10.1016/j.dyepig.2019.108111
DYPI 108111
Reference:
To appear in: Dyes and Pigments
Received Date: 10 October 2019
Revised Date: 4 December 2019
Accepted Date: 5 December 2019
Please cite this article as: Zhu J-h, Zhang H, Liao Y, Liu J-j, Quan Z-j, Wang X-c, A multifunctional
fluorescent probe for highly selective detection of hydrazine and discovering the interplay between AIE
and ICT, Dyes and Pigments (2020), doi: https://doi.org/10.1016/j.dyepig.2019.108111.
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A multifunctional fluorescent probe for highly selective detection of
hydrazine and discovering the interplay between AIE and ICT
Ji-hua Zhu, a,c Hao Zhang, a,b Yuan Liao, a,b Jing-jiang Liu, a,b Zheng-jun Quan*,a,b and Xi-cun
Wang*,a,b
a College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou, Gansu
730070, P. R. China.
b Gansu International Scientific and Technological Cooperation Base of Water-Retention Chemical
Functional Materials, Lanzhou, Gansu 730070, P. R. China.
c College of Chemistry and Chemical Engineering，Longdong University，Qingyang 745000, P. R.
China
* Corresponding author: E-mail: quanzhengjun@hotmail.com (Zheng-jun Quan),
wangxicun@nwnu.edu.cn (Xi-cun Wang)
Abstract: A multifunctional luminescent material (BC-B) was synthesized, which
exhibits aggregation-induced emission (AIE) enhancement property in high water
fraction. The AIE shows a significant impact on the intramolecular charge transfer
(ICT) process by controlling intramolecular motion. The above result is demonstrated
by density functional theory (DFT) calculations and single-crystal X-ray diffraction.
To decrease the influence of AIE on ICT, the probe BC-B is exploited as turn-on
fluorescent probe for hydrazine (N2H4) in DMSO/PBS buffer (6/4, v/v) and displays
high sensitivity and selectivity. Besides, the fluorescence emission shows a good
linear response (R2 = 0.9960) in the range of 0 - 35 µM with the low detection limit of
1.29 ppb, which is significantly below the acceptable limit for hydrazine (10 ppb) set
by the USEPA.
Keywords: Aggregation induced emission; Intramolecular charge transfer; Hydrazine
(N2H4); Density functional theory; Fluorescent probe.
1. Introduction

Fluorescent probes have become more and more effective for monitoring
various biological and environment-specific analytes with the advantages of
easy operation, high visibility, high sensitivity and good selectivity [1, 2].
Over the past few decades, the encouraging progress of fluorescent probe was
made [3, 4]. The primary strategy relies on fluorescent changes before and
after interaction with target analytes by one or more frequently used sensing
mechanisms, such as aggregation-induced emission (AIE) [5, 6],
intramolecular charge transfer (ICT) [7], photo-induced electron transfer
(PET) [8, 9], etc. Among those, the ICT based molecules are mainly consist
of an electron donating (D) and an electron acceptor (A) group with extended
π-conjugated spacer. The push-pull structure leads to an efficient ICT from
donor to acceptor part and generation of a molecular dipole. The properties of
dipolar chromospheres can be easily adjusted by modification of the
donor-acceptor pairs [10-13]. The degrees of charge transfer in the ground
and excited-state partially depend on the ambient medium as polarity of
solution, testing temperature and nature of the electron donating and
accepting substituents. Unfortunately, these factors mentioned above can
result in an increase false probability [14]. The fluorescent probe is usually
influenced by weak interactions such as van der Waals, π···π stacking,
hydrophobic, and hydrogen-bonding interactions, which may cause the
different properties of aggregation state and individual molecule [15].
Notably, the π-conjugated molecules are always resulting fluorescence
quenched in aggregated state due to the tight π - π stacking and non-radiative
decay [16]. Most conventional photo-active organic compounds with
aggregation-caused quenching (ACQ) exhibit strong emission in dilute
solution but weak luminescence in the solid-state or in aqueous solution.
Some AIE organic molecules have the opposite results with ACQ. The AIE
provides an effective solution to the ACQ problem by restriction of
intramolecular motions [17, 18]. As a result, the molecules of AIE
mechanism or AIE plus others have been rapidly developed in optoelectronic

devices, fluorescent sensors, and stimuli-responsive materials [19-22].
However, few compounds concurrently exhibit AIE and ICT properties and
the interaction of which is rarely discussed in theory.
Hydrazine (N2H4) is widely applied in various industry areas for its
unique properties, including a strong reductant, nucleophilicity and high heat
of combustion [23, 24]. But it may lead to serious environmental pollution
problems and damage to organs and central nervous system because of high
toxicity [25]. Therefore, the development of reliable, sensitive, selective and
accurate detection methods of hydrazine is an urgent requirement for human
health and safety. Up to now, exploiting strong nucleophilicity and different
recognizing moieties, the research has acquired great achievements in
detection for N2H4 [26-30]. But the overall point of view, there are still some
defects which can limit their application. For example, some probes based on
aldehyde or ester as recognition sites were usually interfered by other
competitive amines and related species [31, 32]. Few probes were used to
detect N2H4 at high water fraction and low pH value [33].
The 4-bromo butyrate-based probes were developed for the hydrazine
detection by a substitution-cyclization-elimination reaction, as these probes usually
have excellent specificity [34- 37]. In this work, a novel luminescent material BC-B
based on ICT mechanism was designed and synthesized by grafting 4-bromo
butyrate on coumarin moiety (Scheme 1). The BC-B displayed AIE enhancement
characteristic. The intermolecular interactions (e.g. π···π stacking and
intermolecular hydrogen bonds) impacted on the ICT process, which was
confirmed by the single-crystal X-ray diffraction and DFT calculation. Furthermore,
it did not response to N2H4 in aggregation state. When the influence of AIE on ICT
was lessened, it was successfully used to detect hydrazine with high selectivity and
sensitivity in DMSO/PBS buffer (6/4, v/v, pH 7.4, 10 mM).
2. Experimental

2.1. Materials and instruments
The coumarin fluorescent dye (BC) was prepared by a modified procedure
according to the literature [38]. Dimethylsulfoxide (DMSO) was chromatographic
pure. Other chemical reagents and solvents chemicals for synthesis were provided
by commercial suppliers and used as received without further purification unless
1
otherwise stated. Ultrapure water was purified from Millipore. H NMR and 13C
NMR data analyses were performed with a Varian Mercury plus-600 instrument
unless otherwise specified. CDCl3 as solvent and tetramethylsilane (TMS) as the
internal standard were employed. HRMS data was carried out on a Thermo
Scientific Q Exactive. The UV-Vis and Fluorescence spectra were collected on a
TU-1901 spectrophotometer and
a
HORIBA FluoroMax-4. Solid-phase
fluorescence was measured using film. The fluorescent intensity was adjusted using
appropriate filters. The product of the reaction between BC-B and N2H4 was
purified, and the solid IR spectrum was recorded on NEXUS as KBr pellets. An
X-ray single-crystal diffractometer was collected on a Bruker APEX-II CCD. The
SEM measurements were obtained on an Ultra Plus scanning electron microscope.
The pH measurements were performed on a PHS-3C pH meter. Melting points were
measured with an XT-4 apparatus. TLC analyses and the applicability test of BC-B
were conducted on silica gel GF254 plates. Column chromatography was generally
performed on silica gel (200-300 mesh).
2.2. Preparation of sample solutions
The stock solution of BC-B was prepared in DMSO (2 mM). To test the AIE
property, the stock solutions (50 µL) were transferred to 10 mL volumetric flasks.
After corresponding amount of DMSO and pure water were added to afford 10 µM
solutions with different water fraction and then measured its absorption and
fluorescence spectra. For the other spectral measurement, 3 mL DMSO/PBS buffer
(6/4, v/v, pH 7.4, 10 mM) solvent was added into a quartz cuvette (1 cm×1 cm),
followed by the addition of 15 µL probe stock solution to give the sample solution
with probe concentration of 10 µM. After a certain amount of N2H4 stock solution
(10 mM) was added in titration experiments, the fluorescence spectra were recorded.

For the selectivity experiment, 10 mM relevant analytes stock solutions were
prepared in water.
O
HO
CHO
O
O
O
C2H5OH/piperidine
+
OC2H5
N
OH
N
O
O
CH3COOH/piperidine
2
3
1
O
O
4-bromobutyric acid
O
O
Br
N
O
O
N
O
O
OH
EDC,DMAP/DCM
BC
BC-B
Scheme 1. Design and synthesis of probe BC-B
2.3. Synthesis of luminescent material BC-B
The solution of compound 4-dimethylaminopyridine (DMAP, 4 mg, 0.03
mmol), 1-ethyl-3-(3-(dimethylamino)propyl) carbodiimide hydrochloride
(EDC·HCl, 100mg, 0.53 mmol) and 4-bromobutyric acid (71 mg, 0.36 mmol) in
anhydrous dichloromethane (50 mL) under N2 atmosphere was stirred for 30 min,
then the compound BC (72 mg, 0.2 mmol) was added. The mixture was constantly
stirred overnight at room temperature. After the solvent was removed under reduced
pressure, the crude product was purified by column chromatography (CH2Cl2
/CH3OH from 50/1 to 10/1, v/v) to obtain probe BC-B (66 mg, 65%). m.p. 161 ~
163 . 1H NMR (600 MHz, CDCl3) δ 8.52 (s, 1H), 8.10 (d, J = 15.7 Hz, 1H), 7.77
(d, J = 15.7 Hz, 1H), 7.67 (d, J = 8.5 Hz, 2H), 7.39 (d, J = 8.9 Hz, 1H), 7.11 (d, J =
8.5 Hz, 2H), 6.60 (dd, J = 9.0, 2.3 Hz, 1H), 6.46 (s, 1H), 3.53 (t, J = 6.4 Hz, 2H),
3.43 (q, J = 7.1 Hz, 4H), 2.77 (t, J = 7.2 Hz, 2H), 2.28 (m, 2H), 1.22 (t, J = 7.1 Hz,
6H). 13C NMR (151 MHz, CDCl3) δ 186.2, 170.7, 160.8, 158.7, 153.0, 151.9, 148.7,
141.8, 133.2, 131.8, 129.77, 125.2, 121.9, 116.5, 109.9, 108.6, 96.6, 45.1, 32.6, 32.4,
27.5, 12.5. HRMS calcd for C26H27BrNO5 [M+H]+: 512.1067 found: 512.1061,
514.1037.
3. Results and discussion
3.1. The AIE properties of BC-B
The UV-Vis absorption and fluorescent emission spectra of BC-B were

systematically investigated in various solvents (Fig. 1). The main absorption
bands located at 300-360nm and 360-500nm (Table S1) belong to π-π*
transitions and intramolecular charge transfer (ICT). With the increasing of
solvent polarity from hexane to DMSO, the absorption spectra of BC-B
demonstrated a red-shift about 29 nm, which illustrated that the BC-B
contained polar characteristic in the ground state. The fluorescent emission
displayed a large range of red-shift (95 nm) with changing the polarity from
Hexane to MeCN, demonstrating an intense ICT process in the excited-state.
With the increase of polarity from CH2Cl2 to CH3OH, the emission intensity
was gradually weakened and even invisible. It was possible because strong
polarity solvents destroyed the weak interactions which caused TICT
phenomena [39]. Such dramatic changes of emission displayed that the BC-B
had a remarkable solvatochromic effect. Further research was launched to the
relationship between the solvent polarity parameter (∆v) and the Stokes shift
(∆f). The Stokes shift was gradually increased with enhancement of solvent
polarity. The Lippert-Mataga equations (Fig. S1) showed a linear relationship.
Which further suggested the BC-B was strong dipolar characteristic with
remarkable solvatochromic effect. The UV-Vis absorption and fluorescent
emission spectra of BC were investigated (Fig. S2). The results showed that
BC also had dipolar characteristic and solvatochromic effect.
Fig. S3
(Table S2 and
)
.
Fig. 1 (a) The UV-Vis spectra and (b) fluorescent intensity of BC-B (10 µM) in different
solvents (λex = 393 nm, slit ex/ em = 2/3 nm).

To investigate the AIE performance of BC-B, the UV-Vis and
fluorescent emission spectra were carried out in H2O/DMSO mixtures as
shown in Fig. 2a. The absorption bands showed that there were little changes
at 323 nm and 465 nm as the water fraction (fw) below 40 vol%. The BC-B
mainly existed in non-aggregated state. With the increasing of fw from 60
vol% to 90 vol%, the absorbance bands disappeared at 465 nm, and new
blue-shift absorption peaks were observed at 423 nm, where the BC-B mainly
existed as molecularly aggregation state. The blue-shift was due to the
restriction of ICT process which caused the increase of π-π* transition energy
in aggregation state. Then, fluorescence emission was discussed as shown in
Fig. 2b. The BC-B showed a weak emission at 548 nm as the fw was less than
20 vol%. The emission was nearly quenched from 20 vol% to 40 vol%
because of TICT transition. The fluorescent intensity (λ em = 564 nm) was
significantly enhanced with the increasing of fw from 60 vol% to 80 vol%.
The maximum emission intensity (fw=80 vol%) was approximately 12.9-fold
increase in comparison with fw=40 vol% (Fig. S4). Meanwhile, as shown in
Fig. S5, an intense red-shifted peak (λ em = 614 nm) could be observed in
solid state, the Stokes shift (191 nm) of solid was larger than in pure water
(146 nm). These properties indicate that the BC-B could be used as a typical
AIE enhancement luminescent material. Moreover, the red-shift of emission
peaks from solvent to solid state showed that the tighter the molecular
packing was, the smaller HOMO - LUMO energy gap. However, as shown in
Fig. 3 and Table S2, the maximum emissions (525 nm and 564 nm) of BC-B
were not significant changes after the addition of 20 equiv N2H4 at high water
fraction. These results showed the ICT process was probably restricted in
aggregation state. The AIE performance of BC was also investigated, as
shown in Fig. S6. The absorption intensity of BC suddenly decreased, and the
fluorescence intensity was up to a minimum (fw=70 vol%). Then it was
increased to the maximum at 80vol%. All of these changes were like to BC-B

，but the changes of fluorescence intensity were small. The BC exhibited
weak AIE enhancement property. The scanning electron microscope (SEM)
was also exploited to investigate the formations of BC-B in solution (fw = 10
vol%) (Fig. S7a) and aggregation state (fw = 80 vol%) (Fig. S7b). The SEM
images showed that the spherical aggregation morphology could be found by
the self-assembly strategy in aggregation state.
Fig. 2 The UV-Vis spectra (a) and fluorescent intensity (b) of BC-B (10 µM) in DMSO/H2O
mixtures with different water fractions. (insert: the fluorescent changes under 365 nm UV-light)
(λex = 393 nm, slit ex/ em = 3/3 nm).
3500000
L
L+N2H4
3000000
2500000
2000000
1500000
1000000
500000
0
0
20
40
60
80
100
Water Fraction（ %）
Fig. 3 Plots of maximum emission intensity (λem= 525 nm) of BC-B (10 µM) (black)
and BC-B upon addition 20 equiv N2H4 (red) in the DMSO/ H2O mixtures with different fws.
(λex = 393 nm, slit ex/ em = 3/3 nm).
3.2. Molecular orbital calculations
In order to gain deep insights into AIE and ICT process, the theoretical
calculations using density functional theory (DFT) and time-dependent DFT
(TD-DFT) based on B3LYP/6-311G (d, p) level using the Gaussian 09

program were performed. The optimized geometry showed that the molecule
of the series adopted a nearly planar structure as shown in Fig. S8. This
structure was favorable to the aggregation of molecule. Almost all of electron
cloud of HOMO was distributed in acryloylcoumarin moiety (Fig. 4), while
the LUMO was transferred and evenly distributed in the aromatic ester group
and acryloylcoumarin moiety with an energy gap of 3.02 eV. As showed in
Table S3, the S0→S1 transition was a major contribution of HOMO-1 to
LUMO (97.7 %) at 460 nm with oscillator strength (f = 1.066). This value
was highly consistent with the experimental absorption wavelength (464 nm).
The HOMO of BC mainly was located on the coumarin unit, whereas the
LUMO was distributed throughout π-conjugated moiety. The S0→S1
transition for BC with the energy gap of 3.08 eV was a major contribution of
HOMO-1→LUMO (96.8 %) at 452 nm with oscillator strength (f =1.200).
Especially, the push-pull structure alteration led to the dipole moment which
decreased from 14.18 (BC-B) to 7.97 (BC). The above results suggested that
the probe BC-B was stronger ICT process than BC in solution, which also
provided support for the experimental prediction of solvatochromic effect for
BC-B and BC.
Fig. 4 Calculated electronic density contours and energy gaps of BC-B and BC.
3.3. Molecular and crystal structure
The AIE effect and bright solid-state fluorescence of BC-B trigger us to

elucidate their molecular conformation and arrangement in aggregation.
Fortunately, the single-crystal of BC-B was obtained by slow evaporation
from the solutions in dichloromethane/ether at room temperature. As shown
in Fig. 5a, Fig. S10 and Table S4, the single crystal structure of BC-B
contained various small dihedral angles and exhibited larger twisted
conformation than optimized geometry structure, which confirmed that the
intermolecular force of solid BC-B was more strength than that of its aqueous
solution. Which also explained the red-shift of the solid emission. As shown
in Fig. 5b and 5c, the asymmetric molecular conformations of head-to-head
stacking were linked together to form 1D zigzag chain along a-axis by
intermolecular π···π packing interactions (4.070
chains were connected into a two-dimensional molecular by two types of
intermolecular hydrogen bond with distances of 2.517 (C25-H25···O3) and
2.490 (C10-H10···O1). The overlap between electron-donating units and
Å and 3.218 Å). The 1D
Å
Å
electron-withdrawing units formed dense packing conformations, which
likely decreased the ICT process by controlling intramolecular motions.
Fig. 5 (a) X-ray crystal structure of BC-B. (b) intermolecular π-π interaction in the 1D
zigzag chain along a-axis. (c) intermolecular hydrogen bonds in the 1D zigzag chain.
3.4. Spectral response of the probe to hydrazine
Because of these, the probe BC-B can be used for the detection of N2H4

if the influence of AIE on ICT is lessened. Firstly, the time-dependent
fluorescent responses of BC-B in the absence and presence of N2H4 were
studied. As shown in Fig. S11, in the absence of N2H4, the fluorescent
emission intensity of BC-B remained no variation in 10 min, clearly
indicating its good photostability. After 20 equiv N2H4 was added into above
solution, a significant enhancement emission was observed within a few
minutes. The stable plateau emerged at 25 min later. Secondly, the
pH-dependent experiments showed (Fig. S12) that the fluorescent intensity
was nearly constant in the pH range of 3 - 12. After the addition 20 equiv
N2H4 into BC-B, the fluorescent intensity exhibited remarkable enhancement
in the pH range of 5.0 - 10.0. Therefore the probe BC-B could be used to
detect hydrazine in a wide pH value range.
Fig. 6 (a) Fluorescent response of probe BC-B (10 µM) to 20 equiv various analytes; (b)
The selectivity of fluorescent ratio (F/F0) response to various amines (n-butyl amine,
ethylenediamine, methylamine, hydroxyl amine, urea, thiourea, ammonia, Cys, GSH,
Hcy, Gly, Glu, hydrazine) in DMSO/PBS buffer (6/4, v/v, pH 7.4, 10 mM) (λex = 393
nm, λem= 525 nm, slit ex/ em = 3/3 nm).
The selectivity of probe BC-B was examined, as shown in Fig. 6 and
Fig. S13, no significant fluorescent changes were observed upon BC-B
exposure with various analytes, except hydroxyl amine (blue line) resulted in
a slight enhancement. In contrast, when N2H4 (red line) was added, the
fluorescent intensity of BC-B at 525 nm was significantly increased

approximately 10.8-fold. Moreover, most of the analytes showed little impact
on N2H4 detection. These results illustrated that the BC-B was highly
selective for N2H4 over most of analytes.
Furthermore, fluorescent titration experiments were employed for
researching the sensitivity of BC-B toward N2H4. As shown in Fig. 7, the
fluorescent intensity was increased with the increasing concentration of N2H4.
Simultaneously, the color of BC-B was changed from colorless to blue-green
under 365 nm UV-light (inset of Fig. 7a). This remarkable color change
indicates that probe BC-B can detect N2H4 by the naked eye. The fluorescent
intensity showed a good linear response (R2 = 0.9960) to N2H4 in a wide
concentration range at 0-35 µM. The detection limit was determined to be
1.29 ppb based on the general 3σ/k method, and the value was much lower
than 10 ppb suggested by EPA [40, 41], which was also equivalent or
superior to previously reported N2H4 probes (Table. S5).
Fig. 7 (a) Fluorescent intensity of BC-B (10 µM) with different concentrations of
N2H4 (0−70 µM) in DMSO/PBS buffer. Insets: the fluorescent change in the absence and
presence of N2H4 under 365 nm UV-light; (b) The linear correlation between the
fluorescence intensity and the concentration of N2H4 in the range of 0 - 35 µM (λex =
393 nm, λem= 525 nm, slit ex/ em= 3/3 nm).
After the BC-B was reacted with N2H4, as shown in Fig. S14, a new
peak was observed in IR spectra at 3248 cm−1 (−OH). The disappearance of
1699 cm-1 (-C = O) and 2927 cm-1 (-CH2) indicated that 4-bromobutyric was

eliminated. The HRMS (Fig. S15) exhibited the expected peak at 364.1538
corresponding to the BC ([M+H]+ calcd 364.1543). Therefore, the detection
mechanism toward hydrazine could be undergone a substitution- cyclization-
elimination process as shown in Scheme S1 [42].
3.5. Detection of gaseous hydrazine
To check the applicability of BC-B as an optically efficient probe for
N2H4. A solution of BC-B (100 µM) in DMSO/H2O (6/4, v/v) was prepared,
and then the letters "NWNU" were written on a glass TLC plate with a brush.
The TLC plates were dried to slightly dry before exposing to hydrazine
vapor. Next it was placed on a cushion in the sealed bottle containing vapors
of N2H4 for 30 min. Particularly, this was done in the concentrated solution of
N2H4 which was poured into the sealed bottle before 2 hours. As shown in
Fig. 8, TLC plates of BC-B showed an orange fluorescent and faint orange as
exposing to vapors of N2H4 under the daylight. Under 365nm UV light, TLC
plates of BC-B showed bright yellow fluorescent and blue-green after
interaction with hydrazine vapor. These further supported that the BC-B
could be used as potential AIE luminescent material and fluorescent probe for
N2H4 both in solution and on surface of a TLC plate.
Fig. 8 Photographs of BC-B (100
µ
M) in the sunlight (a) alone and (b) exposed to
M) under
vapors of N2H4 for 30 min later. The visible color changes of BC-B (100
µ
365 nm UV light (c) alone and (d) in the presence of hydrazine vapors. (e) The
photograph of crystal BC-B under 365 nm UV-light.

4. Conclusions
In summary, a novel luminescent material BC-B was successfully
designed and conveniently synthesized. The obtained BC-B was featured
with the AIE and ICT characteristics. In aggregation state, it mainly exhibited
AIE enhancement performance, which could be used as AIE enhancement
luminescent material with excellent photostability and significant Stokes
shift. However, the BC-B virtually showed no response to hydrazine in high
water fraction. The single-crystal X-ray diffraction and DFT calculations
investigation demonstrated that the AIE had considerable impact on ICT
process by weak interaction: π···π packing interactions and
hydrogen-bonding. As the influence of AIE on ICT was reduced, the BC-B
was employed for turn-on detecting N2H4, which showed low detection limit
(1.29 ppb), high sensitivity and selectivity. Additionally, this study provides a
valuable theoretical tool for further design of probes and selection of
detection methods.
Conflicts of interest
There are no conflicts to declare.
Acknowledgments
This work was supported by the Long Yuan Youth Innovative and
Entrepreneurial Talents Project (the Key Talent Projects of Gansu Province
(2019-39) (No. 21562036) and the Research Project of Higher Education in
Gansu Province (2018A-004).
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Highlights:
ò A novel fluorescent probe BC-B was synthesized and showed
aggregation-induced emission (AIE) enhancement performance.
ò The influences of the AIE on the ICT process were demonstrated by
density functional theory (DFT) calculations and single-crystal X-ray
diffraction.
ò The probe BC-B was applied to turn-on detection of N2H4 with high
sensitivity and selectivity by lessening the AIE influences on the ICT
process.

Conflicts of interest
There are no conflicts to declare.

author statement:
I would like to declare on behalf of my co-authors that the work described was
original research that has not been published previously, and not under
consideration for publication elsewhere, in whole or in part. Furthermore, the
publication is approved by all authors and tacitly or explicitly by the responsible
authorities where the work was carried out.