D–π–A–π–D type solvatochromic fluorescence probes based on triphenylamine: Synthesis, photophysical properties and application

Article abstract of DOI:10.1016/j.saa.2020.118384

Two D–π–A–π–D type solvatochromic fluorescence probes (JT1 and JT2) based on triphenylamine have been synthesized. The photophysical and electrochemical properties of these probes as well as their solvatochromic behavior were studied. The Stokes shifts of JT1 and JT2 reach 175 nm (6417.0 cm^?1) and 218.6 nm (9916.7 cm^?1) in the acetonitrile solution, respectively. There is an excellent linear correlation between the Stokes shifts and the E_T (30) solvent polarity values in different solvents. The high responsiveness of JT1 and JT2 to solvent polarity makes them promising candidates for solvatochromic fluorescence probes, especially for the detection of the polarity of non-proton solvents or the content of water in tetrahydrofuran.

Full text of DOI:10.1016/j.saa.2020.118384

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D–π–A–π–D type solvatochromic fluorescence probes based on
triphenylamine: Synthesis, photophysical properties and
application
Zhen-E Chen, Qiang-long Qi, Hai Zhang
PII:
S1386-1425(20)30362-0
https://doi.org/10.1016/j.saa.2020.118384
SAA 118384
DOI:
Reference:
Spectrochimica Acta Part A: Molecular and Biomolecular
Spectroscopy
To appear in:
Received date: 16 March 2020
Revised date:
13 April 2020
16 April 2020
Accepted
date:
Please cite this article as: Z.-E. Chen, Q.-l. Qi and H. Zhang, D–π–A–π–D type
solvatochromic fluorescence probes based on triphenylamine: Synthesis, photophysical
properties and application, Spectrochimica Acta Part A: Molecular and Biomolecular
Spectroscopy (2020), https://doi.org/10.1016/j.saa.2020.118384
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D–π–A–π–D type solvatochromic fluorescence probes based on triphenylamine: Synthesis，
Photophysical properties and Application
Zhen-E Chen,* Qiang-long Qi and Hai Zhang*
School of Chemistry and Chemical Engineering, Zunyi Normal College, Zunyi, 563006, China.
*Corresponding Author: Tel.: +86 0851 28924799. Fax: +86 0851 28924799. E-mail:
zhenechen@vip.sina.com (Z.-E. Chen), haizhang@vip.sina.com (H. Zhang).
ABSTRACT:
Two D–π–A–π–D type solvatochromic fluorescence probes (JT1 and JT2) based on
triphenylamine have been synthesized. The photophysical and electrochemical properties of these
probes as well as their solvatochromic behavior were studied. The Stokes shifts of JT1 and JT2
reach 175 nm (6417.0 cm−1) and 218.6 nm (9916.7 cm−1) in the acetonitrile solution, respectively.
There is an excellent linear correlation between the Stokes shifts and the ET (30) solvent polarity
values in different solvents. The high responsiveness of JT1 and JT2 to solvent polarity makes
them promising candidates for solvatochromic fluorescence probes, especially for the detection of
the polarity of non-proton solvents or the content of water in tetrahydrofuran.
Keywords: Triphenylamine; Solvatochromic; Fluorescence probe; Polarity; Water
1. Introduction
Generally, solvatochromic dyes possess a D–π–A conjugated structure, which is composed of
an electron donor, a π–spacer, and an acceptor. When such molecules are stimulated by light,
intramolecular charge transfer (ICT) may occur between the electron donor and the electron
acceptor [1-3]. Simultaneously, the fluorescence spectrum of these molecules is greatly affected
by the polarity of solvents so that it is easy to exhibit solvatochromic phenomenon [4-13], which
makes these molecules have a promising future in the application of polarity-sensitive fluorescent
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probes. In the past decades, various organic solvent-sensitive probes with one-dimensional D–π–A
structure have been reported which exhibit negative or positive solvatochromism, mainly
including Aladan [14], Neutral Red [15], Prodan [16], Nile Red [17], Pyrene [18], and their
derivatives. Compared with the traditional one-dimensional D–π–A framework molecules, the D–
π–A–π–D structure molecule contains two donor moieties, which is more conducive to ICT as
well as able to reduce the bandgap of molecular energy level, thus causing a red-shift of the
spectrum [19]. Therefore, more and more attention has been paid to this type of molecules, which
have been widely used in OLEDs [20], organic solar cells, and dye-sensitized solar cells [21-23].
However, research on such molecules as the polarity probe is still scarce, and some of them are
not suitable for practical application because of their complex structures and difficult synthesis.
Based on the above considerations, a kind of novel molecules with D–π–A–π–D skeleton have
been designed. On the one hand, a single carbonyl group is chosen as an acceptor unit originating
from its non-linear bond angle can help to increase the polarity of the molecule, thereby increasing
the sensitivity to solvent response. On the other hand, to avoid instability of the fluorescence
spectrum caused by molecular aggregation, the propeller-type triphenylamine unit is selected as
the donor. Besides, a non-polar benzene ring and a polar thiophene ring are used as bridging
structures, respectively, to investigate further the effect of the π–bridge unit on the molecular
properties. Finally, two simple solvatochromic dyes JT1 and JT2 were synthesized, and their
photophysical and electrochemical properties were investigated in detail. The results show that
they are susceptible to the polarity of the environment and can be employed to detect the polarity
of aprotic solvents and the water content of organic solvents. Compared with JT1, the Stokes
shifts of the probe JT2 utilizing benzene ring as the π–bridge exhibit more variation with the
polarity of solvents, and the detection sensitivity of JT2 is higher than that of JT1.
2. Experimental section
2.1. Apparatus
1H and 13C NMR spectra were recorded in CDCl3 using a Bruker Avance 600 MHz
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spectrometer with TMS as internal reference. The IR spectra were measured on a Bruker V70
Infrared Spectrometer (Bruker Corporation). Mass spectra were obtained using an Orbitrap
analyzer spectrometer (Thermo Electron Corporation). The melting points were taken on XT4B
microscopic melting point apparatus and uncorrected. UV–Vis absorption spectra and
fluorescence spectra were measured on a Shimadzu UV-3600 Plus spectrophotometer and a
Hitachi F-4600 fluorescence spectrophotometer at the concentration 1 × 10−5 M solution.
Electrochemical redox potentials (10−3 M) were investigated by Cyclic Voltammetry (CV) on a
Modulab XM electrochemical workstation.
2.2. Materials and reagents
The N, N-dimethylformamide (DMF) solvent used in the synthesis was pretreated with 4A
molecular sieve. The tetrahydrofuran (THF) solvent was refluxed with sodium metal in an argon
atmosphere before use, then cooled and stored in sealed containers for reserve.
Bis(4-bromophenyl)methanone (4) and other reagents were obtained from Aldrich and were used
without further purification.
2.3. Synthesis of JT1 and JT2
2.3.1. Synthesis of bis(5-(4-(diphenylamino)phenyl)thiophene-2-yl)methanone (JT1)
Bis(5-bromothiophen-2-yl)methanone (3) was synthesized by the reported method [24]. mp:
119–120 oC（literature data:119 oC）.
HRMS (ESI, m/z): [M + H]+ calcd for[C9H5OBr2S2]+:350. 8143 , found: 350.8138.
Bis(5-bromothiophen-2-yl)methanone (3) (1.86 g, 5.28 mmol), 4-(diphenylamino)phenylboro-
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nic acid (1.52 g, 5.28 mmol), and tetrakis(triphenylphosphine)palladium (0) (0.302 g, 0.261 mmol)
were dissolved in dry THF (50 mL), then 2 M K2CO3 aqueous solution (10.5 mL, 21 mmol) was
added. The mixture was heated to reflux for 16 h under argon. After the mixture was cooled to
ambient temperature, the reaction mixture was poured into water and extracted with CH2Cl2. The
organic phase was washed with saturated NaCl solution, dried over anhydrous MgSO4, and then
filtered. Evaporation of the solvent was carried out under reduced pressure. Crude product was
purified by chromatography on silica gel using petroleum ether as eluent and dried under vacuum
to afford an orange-red solid (JT1) in 13.9% yield (500 mg). mp:107–108 oC.
1H NMR (600 MHz, CDCl3) δ ppm 7.87 (d, J = 4.2 Hz, 2H), 7.55–7.53 (m, 4H), 7.31–7.27 (m,
10H), 7.15–7.14 (m, 8H), 7.10–7.07 (m, 8H). 13C NMR (150 MHz, CDCl3) δ ppm 177.99, 152.57,
148.87, 147.26, 140.80, 134.16, 129.58, 127.24, 126.84, 125.18, 123.83, 122.88, 122.84.
IR(KBr), ν, cm-1:1589.31, 1436.93, 1282.63, 696.29.
HRMS (ESI, m/z): [M + H]+ calcd for[C45H33N2OS2]+: 681.2029, found: 681.2030.
2.3.2. Synthesis of bis(4'-(diphenylamino)-[1,1'-biphenyl]-4-yl)methanone (JT2)
JT2 was synthesized according to the literature [25].
mp: 253–254 oC(literature data: 249- 250 ◦C); 1H NMR (600 MHz, CDCl3) δ ppm 7.90 (d, J =
7.8 Hz, 4H), 7.69 (d, J = 8.4 Hz, 4H), 7.54 (d, J = 8.4 Hz, 4H), 7.31–7.28 (m, 8H), 7.16 (d, J = 7.2
Hz, 12H), 7.08–7.06 (m, 4H).
HRMS (ESI, m/z): [M + H]+ calcd for [C49H37ON2]+: 669.2900, found: 669.2888.
3. Results and discussion
3.1. Synthesis and characterization
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The Synthetic routes of bis(5-(4-(diphenylamino)phenyl)thiophene-2-yl)methanone (JT1) and
bis(4'-(diphenylamino)-[1,1'-biphenyl]-4-yl)methanone (JT2) are depicted in Scheme 1. JT1 and
JT2 were synthesized by Suzuki–Miyaura cross-coupling reaction. The new compounds were
characterized by 1H NMR, 13C NMR, IR and HRMS spectra (Figs. S1–S5).
Scheme 1
3.2. Optical Properties
The maximum absorption wavelength and emission wavelength of JT1 and JT2 in various
solvents are listed in Table 1. The UV–Vis absorption and fluorescence emission spectra of JT1
and JT2 in different solvents of various polarities are shown in Fig. 1 and Fig. 2. The results show
that the absorption and emission properties of two molecules can be adjusted by changing the type
of the π–bridge between triphenylamine and carbon-oxygen double bond.
As shown in Table 1 and Fig. 1, JT1 and JT2 exhibit broad absorption peaks in the wavelength
range of 350–500 nm as well as exhibit relatively high molar extinction coefficients in different
solvents, which may be attributed to the π–π* transitions in the intramolecular conjugated system.
It is worth noting that the solvatochromic shift of absorption spectra is small, which indicates that
the solvent polarity has little effect on the charge transfer of ground-state molecules due to a
relatively small dipole moment. Besides, compared with JT2, due to the smaller dihedral angle
between the carbonyl group and the π–bridge in JT1, a red-shift of about 50 nm is exhibited in the
absorption spectrum [26].
Table 1
Fig. 1
Unlike the absorption spectrum, the solvatochromic shifts of the fluorescence spectra of JT1
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and JT2 are very significant (Fig. 2). Firstly, the emission maxima of them have a significant
bathochromic shift with increasing solvent polarity. In non-polar hexane, the emission maximums
for JT1 and JT2 are 470 and 413 nm, respectively, while in polar DMSO, are 622 and 601 nm
respectively, corresponding to a red-shift of 152 or 188 nm. Secondly, the spectral width of their
fluorescent peak becomes wider with increasing solvent polarity, as shown in Fig. 2, the threshold
extended from 172 to 314 nm or 175 nm to around 325 nm for JT1 and JT2, respectively. Thirdly,
with increasing solvent polarity, the fluorescent colors of their solutions gradually change from
blue to orange under ultraviolet irradiation. The above experimental results show that JT1 and
JT2 have strong solvatochromic characteristics, and evident red-shift phenomenon (i.e., positive
solvatochromism) can be observed (Fig. 3). The relevant mechanism may be that the π–π*
electronic transition occurs when JT1 or JT2 is excited, which leads to the dipole moment of the
excited states larger than that of the ground state. Consequently, the dipole-dipole force derived
from the solvent-solute interactions also enhances as the polarity of the solvent increases and
reduces the energy of the excited state, thus facilitating the intramolecular charge transfer.
Compared to JT2, the emission wavelength of JT1 in the same solvent is red-shifted (Table 1) as
a result of the thiophene π–bridge of JT1 induces a highly polar twisted intramolecular charge
transfer (TICT) state [27]. As expected, the TICT state of JTI makes it exhibit higher stability and
longer emission wavelength than JT2 in polar solvent.
Fig. 2
Fig. 3
3.3. Stokes Shift in Different Solvents
The significant Stokes shift can avoid the interference produced by the excitation light and
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scattered light, as well as the fluorescence intensity that is reduced by self-absorption, thereby
improving the response sensitivity of fluorescent molecules [28]. To further understand the effects
of solvent on the luminescence properties of these compounds, the Stokes shifts of JT1 and JT2
in different solvents were measured (Table 1). Excitingly, the Stokes shifts of the probes JT1~2 in
the polar solvent acetonitrile reach 175 and 218.6 nm, respectively. Moreover, there is a fine linear
correlation (r ˃ 0.99) between the Stokes shifts of JT1~2 and the empirical polarity parameter ET
(30) data [29] (Fig. 4) in the aprotic solvent. The linear regression equations are y = 8.88196x –
228.44316 (r = 0.9947) and y = 12.35532 x – 341.26254 (r = 0.9955) respectively. The slope of
JT2 is greater than JT1, indicating that JT2 has a stronger solvatochromic response than that of
JT1. Undoubtedly, this reason for the difference in solvent sensitivity is mainly due to the
difference in the π–bridge and the electron polarizability of molecules. The above results
demonstrate that the maximum emission peaks of JT1~2 depend on the polarity of solvents. We
believe that the main reason for this phenomenon may be due to the strong charge transfer in the
system, and the dipole interaction between solvent molecules and solute molecules is the main
factor arising the stokes shift in fluorescence spectra of compounds.
Fig. 4
3.4. Spectra in Mixed Solvents
To further prove the solvatochromic phenomenon of JT1 and JT2, we selected two kinds of
miscible solvents: strong polar solvent acetonitrile and weak polar solvent THF. We tested the
absorption and fluorescence emission spectra of JT1and JT2 in different ratio of THF and
acetonitrile solvents. As a result, the absorption spectra of the two probes show little change (Fig.
S6), which is consistent with the results shown in Figure 1a. It can be seen from Fig. 5 and Fig.6
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that the fluorescence emission peaks red-shift gradually with increasing acetonitrile volume
fraction and solvent polarity. The emission maxima for JT1 and JT2 are 546 and 500.6 nm in THF,
617 and 592.6 nm in acetonitrile corresponding to a red-shift of 71 and 92 nm, respectively.
Besides, its fluorescence emission intensity is gradually weakened, and the single-photon
fluorescence emission intensity in THF is about five times that in acetonitrile, which is a typical
ICT effect. These phenomena are consistent with the phenomena of JT1 and JT2 in different
solvents, which further proves that JT1 and JT2 have solvatochromic characteristics.
Fig. 5
Fig. 6
3.5. Theoretical calculation and electrochemical properties of JT1 and JT2
By studying the absorption and fluorescence spectra of JT1 and JT2 molecules in different
solvents, it can be seen that these two molecules have significant charge transfer characteristics in
the excited state. To further understand this phenomenon, the density functional theory (DFT)
calculations were performed using the Gaussian 09 program suite at the B3LYP/6-31 G(d) basis
set (Fig. 7).
Fig. 7
It can be seen that in the optimized JT1 and JT2 structures, the dihedral angles of π–bridge and
carbonyl are 15.58o and 25.46o, respectively, and the torsional angles of π–bridge and
triphenylamine are 24.09o and 34.84o, respectively. The thiophene spacer on JT1 exhibits a little
less twisted structure, which enables the whole molecule to form a more effective π–conjugated
system. From the isodensity plot of the frontier molecular orbitals of the two probes, the density of
HOMO electron cloud is mainly distributed in the structure of triphenylamine, while the density of
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LUMO electron cloud is mainly distributed in π–bridge and carbonyl, and the closer to the
carbonyl group, the higher the electron cloud density. The calculation results show that the dye
molecules can undergo significant electron cloud migration from electron donors to electron
acceptors after being excited. Compared with the bandgap of JT2 (ΔEg＝3.27 eV), the bandgap of
JT1 (ΔEg＝2.94 eV) becomes much narrower, which is the main reason that the absorption
spectrum of JT1 is red-shifted than that of JT2.
CV measurements were run in a solution of tetrabutylammonium hexafluorophosphate
(TBAPF6) in DMF with the addition of ferrocene as the internal standard. An Ag/AgCl (saturated)
couple and a platinum wire were utilized as reference and counter electrodes, respectively, while a
glassy carbon electrode was used as a working electrode. The HOMO and LUMO level of JT1
and JT2 can be estimated by CV according to the following equation (1) [30]:
HOMO = –[Eox – EFc/Fc+ + 4.8]eV
LUMO = HOMO + Eg
Eg = 1240/λonset
(1)
Optical energy gaps were determined from the UV–Vis absorptions in their Hexane solutions.
As shown in Fig. S7, the ionization potential (HOMO levels) of JT1 and JT2 are –5.40 eV and –
5.36 eV, respectively. The estimated electron affinity (LUMO levels) values for JT1 and JT2 are –
2.74 eV and –2.30 eV, respectively.
It can be seen from the results that although the HOMO level of JT1 has decreased compared
with JT2, the decrease is not significant (~ 0. 04 eV). Therefore, the role of the thiophene ring is
mainly to reduce the LUMO level of the molecule (~ 0.40 eV), thus narrowing the bandgap of the
molecule level and making the absorption spectrum a red-shift.
3.6. Application of probe
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Water is the most common impurity in various organic solvents. For many sensitive chemical
reactions, water moisture in organic solvents plays a decisive role in the success of the experiment
[31]. Therefore, the development of a simple fluorescent probe for the detection of water content
in organic solvents has significant practical value. Since JT1 and JT2 are sensitive to solvent
polarity, to further study the properties and application value of probes JT1 and JT2, the
absorption spectra (Fig. S8) and fluorescence intensity (Fig.8) of THF with different water content
were measured in this experiment.
Fig. 8
Experiments show that the absorption spectra of JT1 and JT2 remain unchanged with the
increase of water content in tetrahydrofuran, but the fluorescence intensity gradually decreases,
and the maximum emission wavelength has a red-shift. The main reason for this phenomenon is
that the polarity of the system increases gradually with the addition of water, and the increasing of
polarity is beneficial to the intramolecular charge transfer, resulting in the change of the
fluorescence spectrum. For JT1, when the volume fraction of water in tetrahydrofuran increases
from 0 to 10.00%, the fluorescence intensity decreases rapidly from 1625 to 269.9. When the
volume fraction of water increases from 10.00% to 60.00%, the fluorescence intensity decreases
from 269.9 to 60.92. Based on this, further titration experiments were carried out in
tetrahydrofuran with a gradual increase of water content from 0 to 10.00% (Fig. 9).
Fig. 9
Fitting the fluorescence spectra of probes JT1 and JT2 in tetrahydrofuran solution with
different water content, we found that JT1 had an excellent linear relationship when the water
content is less than 1%, the corresponding linear equation is y = –504.10108x + 1588.79412, the
linear correlation coefficient r = 0.99614. Similarly, when the water content is less than 1.5%, JT2
also had an excellent linear relationship, the corresponding linear equation is y = –1810.8757x +
4020.10762, linear correlation coefficient r = 0.99601 (Fig. 10). It can be seen that as a fluorescent
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probe molecular for detecting water in THF, JT2 is more sensitive, and the detection range is
wider than JT1.
Fig. 10
4. Conclusion
In summary, two D–π–A–π–D type small organic molecules with the same core and carbonyl
acceptor have been successfully synthesized as solvent polarity sensitive probe. The polarity
determination of thirteen organic solvents and the detection of trace water in tetrahydrofuran were
successfully carried out. The results indicated that two compounds have strong solvatochromic
characteristics and large Stokes shifts, which can be used to detect the polarity of unknown
non-proton solvents and trace water in tetrahydrofuran. Compared with the reported probe
molecules, this novel D–π–A–π–D type small organic molecules with high sensitivity and simple
structure might be a promising research direction of solvent polarity sensitive probe in the
environment. In particular, in different solvents, the maximum absorption wavelength and the
maximum emission wavelength of JT1 are located in the visible region, which is very beneficial
for applications in the field of biological research.
Acknowledgments
We are grateful to the National Natural Science Foundation of China (21462054), Guizhou
Education Department Youth Science and Technology Talents Growth Project (KY [2019]122)
for financial support.
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Figure Captions
Scheme 1. Synthetic routes of JT1 and JT2
Fig. 1 Normalized absorption spectra of JT1(a) and JT2(b) in different solvents.
Fig. 2. Normalized emission spectra of JT1(a) and JT2(b) in different Solvents, obtained under
excitation at the maximum absorption wavelength in each solvent.
Fig. 3. The visual photographs of JT1 and JT2 in different solvents taken under visible light and
365 nm UV (from a hand-held UV lamp) irradiation at room temperature with the concentration
of 1.0 × 10−5 mol·L−1.
Fig. 4. Correlation of Stokes shifts with ET(30) for JT1 and JT2.
Fig. 5. Fluorescence spectra of JT1(a) and JT2(b) in different ratio of THF and acetonitrile
solvents.
Fig. 6. The visual photographs of JT1 and TJ2 in different ratio of THF and acetonitrile solvents
taken under visible light and 365 nm UV (from a hand-held UV lamp) irradiation at room
temperature with the concentration of 1.0 × 10−5 mol·L−1 (THF/Acetonitrile = 10/0 → 0/10).
Fig. 7. Geometrical configuration of JT1 and JT2 and electron distribution of the HOMO and
LUMO energy levels.
Fig. 8. Fluorescence spectra of JT1(a) and JT2(b) in different ratio of THF and water solvents.
Fig. 9. Fluorescence titration spectra of JT1(a) and JT2(b) in THF with water content from 0 to
10.00%.
Fig. 10. Plot of the fluorescence intensity of JT1 and JT2 in different water fractions.
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Table 1．Photophysical properties of JT1 and JT2 in different solvents and ET(30) values of
solvents.
ET(30)
(Kcal·
mol-1)
JT1
JT2
NO.
Solvent
Stokes
shift
(nm)
47
Stokes
shift
(nm)
44
abs
max
em
max
abs
max
em
max




log ε
F
log ε
F
Φ
Φ
(nm)
423
437
438
434
437
439
434
452
447
439
449
455
442
(nm)
470
500
506
516
518
546
544
574
581
590
608
622
617
(nm)
369
377
378
371
375
375
372
382
380
373
380
383
374
(nm)
413
1
2
Hexane
31.0
32.5
33.9
34.5
36.0
37.4
38.1
39.1
40.7
42.2
43.2
45.1
45.6
4.8738
4.5809
4.8089
4.6325
4.7896
4.8035
4.7459
4.5465
4.7589
4.8028
4.7796
4.738
3754
2583
3176
1809
2867
1949
1914
793
0.38
0.22
0.33
0.18
0.22
0.19
0.18
0.13
0.14
0.10
0.03
—
4.6395
4.6335
4.6284
4.6937
4.6702
4.5599
4.6656
4.6149
4.6243
4.5599
4.5378
4.5809
4.6385
296
1515
3418
4609
4240
3597
3007
3119
2200
695
0.02
0.19
0.32
0.48
0.45
0.38
0.42
0.45
0.22
0.09
0.02
—
CCl4
Toluene
Ether
63
438.8
450.6
463.4
467.8
500.6
504.4
520
61.8
3
68
72.6
4
82
92.4
5
1,4-Dioxane
THF
81
89.6
6
107
110
122
134
150
159
167
175
125.6
132.4
138
7
EA
8
CHCl3
DCM
9
1394
832
545.2
551.2
576.2
601
165.2
178.2
196.2
218
10
11
12
13
Acetone
DMF
430
364
DMSO
MeCN
224
81
4.786
176
0.03
592.6
218.6
132
0.01
abs
max

log ε: Log of the molar extinction coefficient at
.
em

F: Fluorescence intensity at
.
max
Φ: Fluorescence quantum yield. Quantum yields were determined by using quinine sulfate
(Φ = 0.54 in 0.1 M H2SO4) as a standard.
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Declaration of competing interests
We declare no competing financial interest.
Credit Author Statement
Zhen-E Chen: Conceptualization, Methodology, Resources, Writing- Reviewing and Editing.
Qiang-long Qi: Investigation, Supervision.
Hai Zhang: Conceptualization, Investigation, Resources.
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Graphical abstract
Highlights:
1. Synthesis of two simple D-π-A-π-D type solvatochromic fluorescence probes with the same
core and carbonyl acceptor.
2.The Stokes shifts of the probes have an excellent linear relationship with the ET (30) in different
solvents (r ˃ 0.99).
3.The probes were sensitive to the change of the polarity of non-proton solvents.
4.The probes can be applied for detecting the trace water content in tetrahydrofuran solution.
18