The nitro aromatic compounds detection by triazole carboxylic acid and its complex with the fluorescent property

Article abstract of DOI:10.1016/j.tet.2017.03.057

The 5-methyl-1-(4-nitrophenyl)-1H-1, 2, 3-triazole-4-carboxylic acid (1) was synthesized by an improved method. By using the compound 1 as ligand, a new complex [Cu(L)₂][Cu(L)₂(H₂O)₂] (2) was prepared firstly under hydrothermal condition. Both 1 and 2 were all used as exclusive fluorescence sensor for 2, 4, 6-trinitrophenol (TNP) for the first time. The fluorescence exploration demonstrated that they exhibit highly selective and sensitive (K_SV?=?393685?M^?1 and K_SV?=?213269?M^?1, respectively) sensing to TNP from other nitro aromatic compounds (NACs) with high quenching efficiency QP value of 96.76% and 93.37%, as well as low detection limit (0.68?μM and 0.37?μM, respectively). It means that complex 2 had higher selectivity due to the less interference by 4-NT and 2-NP compared with 1. Moreover, the fluorescence quenching phenomenon of sensor 1 with TNP was analyzed by density functional theory (DFT).

Full text of DOI:10.1016/j.tet.2017.03.057

Accepted Manuscript
The nitro aromatic compounds detection by triazole carboxylic acid and its complex
with the fluorescent property
Jie Yan, Jue Chen Ni, Jin Xin Zhao, Li Xian Sun, Feng Ying Bai, Zhan Shi, Yong
Heng Xing
PII:
S0040-4020(17)30306-X
10.1016/j.tet.2017.03.057
TET 28563
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 13 January 2017
Revised Date: 17 March 2017
Accepted Date: 21 March 2017
Please cite this article as: Yan J, Ni JC, Zhao JX, Sun LX, Bai FY, Shi Z, Xing YH, The nitro aromatic
compounds detection by triazole carboxylic acid and its complex with the fluorescent property,
Tetrahedron (2017), doi: 10.1016/j.tet.2017.03.057.
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ACCEPTED MANUSCRIPT
The Nitro aromatic compounds detection by triazole
carboxylic acid and its complex with the fluorescent
property
Jie Yanaꢀ, Jue Chen Niaꢀ, Jin Xin Zhaoa, Li Xian Sunb, Feng Ying Baia, *
Zhan Shic and Yong Heng Xinga, *
ꢀ
These authors contributed equally.
aCollege of Chemistry and Chemical Engineering, Liaoning Normal University,
Dalian City, 116029, P.R. China
bGuangxi Key Laboratory of Information Materials, Guilin University of Electronic
Technology, Guilin City, 541004, P.R. China
cState Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of
Chemistry, Jilin University, Changchun City, 130012, P.R. China
E-mail: xingyongheng2000@163.com
Tel: +86-411-82156987
We firstly reported a triazole compound and its new complex as exclusive
fluorescence sensor for TNP.

ACCEPTED MANUSCRIPT
Graphical Abstract
The Nitro aromatic compounds detection by
triazole carboxylic acid and its complex with
the fluorescent property
We firstly reported a triazole compound
and its new complex as exclusive
fluorescence sensor for TNP.
Jie Yanaꢀ, Jue Chen Niaꢀ, Jin Xin Zhaoa, Li Xian Sunb, Feng Ying Baia, * Zhan Shic and Yong Heng Xinga, *
ꢀThese authors contributed equally.
aCollege of Chemistry and Chemical Engineering, Liaoning Normal University, Dalian City, 116029, P.R.
China
bGuangxi Key Laboratory of Information Materials, Guilin University of Electronic Technology, Guilin City,
541004, P.R. China
cState Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin
University, Changchun City, 130012, P.R. China

1
ACCEPTED MANUSCRIPT
Tetrahedron
journal homepage: www.elsevier.com
The Nitro aromatic compounds detection by triazole carboxylic acid and its complex
with the fluorescent property
a
a
a
b
a
c
a1
ꢀ
Jie Yan ꢀ, Jue Chen Ni , Jin Xin Zhao , Li Xian Sun , Feng Ying Bai * Zhan Shi and Yong Heng Xing *
ꢀThese authors contributed equally.
aCollege of Chemistry and Chemical Engineering, Liaoning Normal University, Dalian City, 116029, P.R. China
bGuangxi Key Laboratory of Information Materials, Guilin University of Electronic Technology, Guilin City, 541004, P.R. China
cState Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun City, 130012, P.R. China
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
The 5-methyl-1-(4-nitrophenyl)-1H-1, 2, 3-triazole-4-carboxylic acid (1) was synthesized by an
improved method. By using the compound 1 as ligand, a new complex [Cu(L)2][Cu(L)2(H2O)2]
(2) was prepared firstly under hydrothermal condition. Both 1 and 2 were all used as exclusive
fluorescence sensor for 2, 4, 6-trinitrophenol (TNP) for the first time. The fluorescence
exploration demonstrated that they exhibit highly selective and sensitive (KSV = 393685 M-1 and
KSV = 213269 M-1, respectively) sensing to TNP from other nitro aromatic compounds (NACs)
with high quenching efficiency QP value of 96.76% and 93.37%, as well as low detection limit
(0.68ꢀM and 0.37ꢀM, respectively). It means that complex 2 had higher selectivity due to the
less interference by 4-NT and 2-NP compared with 1. Moreover, the fluorescence quenching
phenomenon of sensor 1 with TNP was analyzed by density functional theory (DFT).
Available online
Keywords:
Fluorescence sensor
Synthesis
Triazole
Nitro aromatic compounds
2, 4, 6-Trinitrophenol
2017 Elsevier Ltd. All rights reserved
.
1. Introduction
various π- conjugated heterocyclic compounds, triazoles have
attracted attention in medicinal chemistry due to their numerous
biological activities.10 Triazoles are 5-membered rings, which
contain two carbon and three nitrogen atoms.11 According to the
position of nitrogen atoms, the triazoles exist in two isomeric
forms which are the 1, 2, 3-triazole and the 1, 2, 4-triazole.12 In
the past two decades, a large amount of drugs containing 1, 2, 3-
triazole group such as Tazobactam, Cephalosporin and
Cefatrizine have been synthesized.13 They are clinically used for
the treatment of bacterial infections.14 In recent years, complexes
containing metal Cu(Ⅱ) and 1,2,3-triazole ligands also have been
extensively investigated.15
Nitro aromatic compounds (NACs), in particular 2, 4, 6-
trinitrophenol (TNP), are of great current concerns in both
national security and environmental pollution because they are
not only explosives but also recognized as toxic pollutants.1 TNP
is firstly synthesized as explosive used in militarily, which has
strong explosion ability and low safety coefficient.2 Its extensive
appearance in the soil and ground water near military and
industrial facilities may lead to serious environmental pollution.3
Moreover, its ingestion can cause severe poisoning in humans,
including headache, nausea, vomiting, abdominal pain and
destruction of erythrocytes.4 Thus, the sensing of TNP is highly
essential for protecting personal safety and for controlling
environmental pollution.5 Recently, various techniques have
been developed for the detection of TNP: mass spectrometry, ion
Until now, there have been lots of reports on the synthesis of
1, 2, 3-triazoles and 1, 2, 3-triazole complexes,16 but less efforts
have been made to use them as fluorescence sensor to detect
TNP. In this paper, we improved the method of synthesizing 5-
methyl-1-(4-nitrophenyl)-1H-1, 2, 3-triazole-4-carboxylic acid
(1) and increased the yield (85%) in contrast to the previous
literature (yield 67%). Then, we utilized compound 1 as a ligand
to develop a new complex [Cu(L)2][Cu(L)2(H2O)2] (2). To
extend the functional properties of them, we show that compound
1 and complex 2 exhibit highly selective and low detection limit
of 2, 4, 6-trinitrophenol (TNP), over other NACs such as
nitrobenzene (NB), 4-nitrotoluene (4-NT), 4-nitrobenzaldehyde
(4-NBA), 1,2-dinitrobenzene (1,2-DNB), 1,4-dinitrobenzene
mobility
spectrometry,
electrochemical
Compared with these analytical techniques,
methods,
and
colorimetry.6
fluorescence-based detection offers several advantages such as
high sensitivity, specificity and real-time monitoring with short
response time.7 Thereby, it is necessary to develop a rapid and
sensitive fluorescence sensor to detect TNP.8
π- Conjugated heterocyclic compounds, such as oxadiazoles,
thiadiazoles and triazoles constitute an important class of
compounds in medicinal and pharmaceutical chemistry.9 Among
———
Corresponding author Tel.: +86-411-82156987; E-mail: baifengying2000@163.com, xingyongheng2000@163.com; ꢀ: These authors
contributed equally.

2
Tetrahedron
ACCEPTED MANUSCRIPT
(1,4-DNB), 2-nitrophenol (2-NP), 2,4-dinitrochlorobenzene
that C-N single bond distorting between benzene ring and the
(DNCB), 4-chloronitrobenzene (4-CNB) via a “turn-off ”
fluorescence quenching in the dispersed state. In addition, the
density functional theory (DFT) calculations also help us to
understand the nature of interactions between compound 1 and
TNP for its superior selectivity.
triazole ring is strong. For 1 ligand, it adopts a terminal
monodentate coordination mode in Cu1 moiety and bidentate
chelating coordination mode in Cu2 moiety, the bond length of
Cu–NL is 1.988(2) Å and the distance of Cu–OL are 1.938(2) and
1.963(2) Å. In the packing structure of complex 2, there are
three kinds of hydrogen bonds: (i) hydrogen bond (O5–H5A⋯
O2) between the oxygen (donor) from coordinated water
molecule and the oxygen (acceptor) from 1 ligand; (ii) hydrogen
bond (C–H⋯O) between the carbon (donor) and the oxygen
(acceptor) from 1 ligand: C4–H4B···O4 and C18–H18C···O7;
(iii) hydrogen bond (C13–H13···N1) between the carbon (donor)
from benzene ring and the nitrogen (acceptor) from triazole ring.
Through the hydrogen bond of O5–H5A⋯ O2, a 1D chain
structure is formed. By the hydrogen bonding of C4–H4B···O4,
the 1D chains are further connected to form a 2D supramolecular
sheet structure.
2. Results and discussion
2.1. Synthesis of compound 1
According to literature method, compound 1 and intermediate
was synthesized in Scheme 1.17 In the literature, aromatic azide
was prepared from p-nitroaniline by diazotization reaction with
sodium nitrite in HCl media acceding to sodium azide. Then,
ethyl acetoacetate and the appropriate azide were slowly added
together to the obtained MeOH/MeONa solution. 1, 3-dipolar
cycloaddition was conducted by refluxing the aryl azide with
ethyl acetoacetate under basic conditions for 1h using ethanol as
solvent (67% yield). Based on plenty of experimental and data
analysis, modified the order of the added was found as an
efficient way to get higher yield. In this paper, ethyl acetoacetate
was kept in the alkaline conditions for 30 minutes to make sure
that the ethyl acetoacetate was deprotonated completely.
Through the above-mentioned means, it could facilitate the
formation of enol structure and 1, 3-dipolar cycloaddition would
be reacted more fully with the aryl azide (yield increased to
85%). Meanwhile, X-ray single crystal structure (Fig. 1) of the
compound 1 was firstly achieved.
2.3. Fluorescence sensing of nitro aromatic compounds
The emission spectra of the compound 1 and the complex 2
were shown in Fig. S9-S10 and the luminescent spectra of them
were analyzed under excitation wavelength 320 nm and 300nm,
respectively. The fluorescence quantum yield (ΦF) of the
compound 1 and the complex 2 were 0.068 and 0.047,
respectively. Compound 1 and complex 2 are highly soluble in
DMSO and the sensing study on them was carried out in VDMSO
:
VH2O =1:1. When small amount of 2, 4, 6-trinitrophenol (TNP)
was added to the 10ꢀM solution of them, the initial fluorescence
intensity was quenched considerably, which inspired us to
systematically establish the applicability of sensor 1 (compound
1) and sensor 2 (complex 2) for the detection of nitro aromatic
compounds (NACs).
2.2. Structural description of complex 2
X-ray single crystal study shows that complex 2 is crystallized
in a monoclinic system with P21/c space group. The structure of
2 comprises two moieties: Cu(L)2 and Cu(L)2(H2O)2, which are
combined by electrostatic attraction and hydrogen bonds. The
coordination environment of the copper atoms is shown in Fig. 2.
Cu1(II) and Cu2(II) are both four-coordinated with a flat square
geometry, but their coordination environments are different.
Cu1(II) is coordinated by four oxygen atoms (O3, O3# and O5,
O5#; #: 2−x, -y, 1− z), which are from two compound 1 ligands
and two coordinated water molecules, respectively; Cu2(II) is
coordinated by two N atoms (N6, N6#; #: 2−x, -y, 1− z) and two
oxygen atoms (O2, O2#; #: 2−x, -y, 1− z) from two 1 ligands.
The bond length of Cu–N is 1.988(2) Å and those of Cu–O are in
the range of 1.938(2)–1.963(2) Å. The angles of the O–Cu–O,
O–Cu–N and N–Cu–N are in the range of 88.92(9)–180.0°,
82.66(9)–97.34(9)° and 180.0°, respectively. The dihedral angle
between benzene rings (C5, C6, C7, C8, C9, C10; C11, C12, C14,
C15, C16, C13) and the triazole rings (C2, C3, N3, N2, N1; C17,
C19, N6, N5, N4) are 38.95 (0.08) ° and 54.62 (0.08) °, showing
Scheme 1. Synthetic routes of compound 1
Figure 1. The crystal structure of compound 1(hydrogen atoms and
the lattice water molecule are omitted for clarity)
Figure 2. (a) The coordination environment of the Cu (II) ion in complex 2 (the hydrogen atoms have been omitted for clarity. Symmetry code:
#1: -x+1,-y,-z+2; #2: -x+2,-y,-z+1). (b) The 1D chain structure of complex 2 along the a-axis (Symmetry code: #3: –x+2, –y, –z+2). (c) A
view of the hydrogen bonds of complex 2 (part of the hydrogen atoms are omitted for clarity. Symmetry code: #3: –x+2, –y, –z+2; #4: 1-x, -y,
1-z; #5: x, y, -1+z; #6: 1+x, y, 1+z).

3
To gain a better understanding on the quenching efficiency
and quenching rate (sensitivity) in the presence of NACs,
fluorescence quenching titrations were performed by gradual
addition of 1 or 2 ppm solution of several analytes to 10ꢀM
solution of the sensors. In the study, the NACs including 2,4,6-
trinitrophenol (TNP), nitrobenzene (NB), 4-nitrotoluene (4-NT),
4-nitrobenzaldehyde (4-NBA), 1,2-dinitrobenzene (1,2-DNB),
1,4-dinitrobenzene (1,4-DNB), 2-nitrophenol (2-NP), 2,4-
dinitrochlorobenzene (DNCB) and 4-chloronitrobenzene (4-CNB)
are used to evaluate the quenching efficiency of sensing for nitro
aromatic compounds. The representative titrations with TNP for
sensors 1 and 2 are given in Fig. 3 and the titration with the other
analytes are provided in the supporting information (Fig.S11-
S12). In all cases, the initial fluorescence intensity of the sensors
decreased dramatically upon gradual addition of the NACs. As
shown in Fig. 4, the quenching percentage (QP = (I0 − I)/I0 ×
100%, I0 and I are luminescence intensity of sensor before and
after exposure to the nitro compound) of sensor 1 was 96.76% for
TNP, 70.44% for 4-NT, 63.44% for 2-NP, 46.36% for 4-NBA,
45.15% for 1, 2-DNB, 43.48% for 1, 4-DNB, 42.21% for 4-CNB,
40.56% for NB, 29.66% for DNCB. Correspondingly, the QP of
sensor 2 was 93.37% for TNP, 48.79% for 2-NP, 46.28% for 4-
NBA, 46.05% for 4-NT, 44.42% for NB, 37.15% for 4-CNB,
29.20 for DNCB, 27.08% for 1, 2-DNB, 24.00% for 1, 4-DNB.
The experiments revealed that, both sensor 1 and 2 have
significantly fluorescence quenching efficiency for the detection
of TNP. Considering the interference by 4-NT and 2-NP, sensor
2 had better selectivity for the detection of TNP.
Enthused from these interesting outcomes, TNP selectivity
ACCEPTED MANUSCRIPT
in the presence of other nitro explosives was thoroughly checked.
We studied the competing experiment in presence of other nitro
analytes, of which DNCB was added initially to the VDMSO: VH2O
=1:1 solution of sensor 1 and 2, then, TNP and DNCB were
alternately added. Similarly, the process was performed for other
competing analytes. The experimental results show that DNCB
merely lead to a minor fluorescent quenching effect, subsequent
addition of TNP results in a strikingly prompt and noteworthy
response for fluorescent quenching. The similar results are also
observed for the other competing analytes, all of which have a
similar plot (Fig. 8) of stepwise increase of quenching efficiency
against the alternative addition of competing analytes and TNP.
Consequently, high selectivity of sensor 1 and 2 for TNP is
confirmed. For this result, we speculate that the high selectivity
of sensor 1 and 2 for TNP was owing to the outstanding
properties of triazole ligand. Besides, the selective experiments
further support the conclusion of fluorescence quenching
experiments that sensor 2 have higher selectivity due to the less
interference by 4-NT and 2-NP than sensor 1. The detection
limit of the sensors for the TNP was calculated by following
equation: detection limit = 3σ/k. Where, σ is the standard
deviation of the blank measurement and k is the slope between
the fluorescence intensity versus TNP concentration. The
detection limit of the sensor 1 and sensor 2 are calculated to be
0.68 ꢀM for TNP, 0.37 ꢀM for TNP, respectively.18
Furthermore, the sensitivity is evaluated through the Stern–
Volmer equation (I0/I = KSV [Q] + 1), where KSV is Stern–Volmer
constants indicating the sensors sensitivity; I0 and I are the
fluorescence intensities before and after the addition of the
analytes, [Q] is the concentration of the analytes. As shown in
Fig. 5, all nitro analytes at low concentrations (up to 5 ppm)
show linear proportional in (I0/I-1). The SV plots began to bend
upwards with the increase of the nitro analytes concentration,
diverging from linearity (Fig. 6). The linear relationship at lower
concentrations is mainly due to static quenching, whereas the
deviation from linearity at higher concentrations is presumably
due to dynamic quenching. The static quenching can be
attributed to the ground state interaction between the analytes and
the sensors. The dynamic quenching is mainly due to the energy
and electron-transfer process between the analytes and sensors.
Fitting of linear parts allows the quenching constants (KSV) of
sensor 1 to be 393685 M-1 for TNP, 28092 M-1 for 4-NT, 23077
M-1 for 2-NP, 15953 M-1 for 1,2-DNB, 13478 M-1 for 4-NBA,
12490 M-1 for 1,4-DNB, 9171 M-1 for NB, 8353 M-1 for 4-CNB,
7622 M-1 for DNCB and of sensor 2 to be 213269 M-1 for TNP,
16386 M-1 for 2-NP, 14808 M-1 for 4-NBA, 14587 M-1 for 4-NT,
13380 M-1 for 4-CNB, 10968 M-1 for NB, 9427 M-1 for DNCB,
8439 M-1 for 1,2-DNB, 5396 M-1 for 1,4-DNB, respectively. The
larger KSV values observed reveals high sensitivity, which made
sensor 1 and 2 be the candidate of fluorescent sensor compounds
for detection of TNP. The determination of the individual Stern-
Volmer constants indicates that the fluorescence quenching
mainly occurs through electron transfer. To further establish the
formation of electron transfer, NMR titration of sensor 1 with
TNP was performed. Sensor 1 was added into 5 ppm and 10 ppm
solution of TNP in DMSO-d6 that gives the NMR spectrum as
shown in Fig. 7, significant chemical shifts of HA and HB protons
for the sensor 1, in addition to TNP, are observed in the 1H NMR
spectra (Table 1). The chemical shift of hydrogen protons on
phenyl ring moves more prominently in comparison to other
hydrogen protons. This observation suggests an electron transfer
interaction between TNP and sensor 1.
Figure 3. Reduction of the fluorescence emission intensity of the
sensor 1 and 2 upon gradual addition of TNP (1-10 ꢀl, 10-3 g/mL
TNP were added to 3 mL sensor 1 and sensor 2 solution
respectively).

4
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Figure 6. Stern–Volmer plots of analytes in higher concentration
ranges of analytes (up to 10 ppm) (1-10 ꢀl, 10-3 g/mL analytes were
added to 3 mL sensor 1 and sensor 2 solution respectively).
Figure 4. The column graph of reduction in fluorescence
intensity (plotted as quenching efficiency) upon the addition of
different analytes (10 ꢀl, 10-3 g/mL NACs were added to 3 mL
sensor 1 and sensor 2 solution respectively).
Figure 7. NMR with addition TNP to sensor 1 in DMSO-d6 (5ꢀl and
10 ꢀl, 10-3 g/mL TNP were added to 3 mL sensor 1 solution
respectively).
Figure 5. Stern–Volmer plots of analytes in lower concentration
ranges of analytes (up to 5 ppm) (1-5 ꢀl, 10-3 g/mL analytes were
added to 3 mL sensor 1 and sensor 2 solution respectively).
Figure 8. Fluorescence quenching of sensor 1 and 2 upon addition of
DMSO/H2O solutions of different nitro compounds followed by TNP
(1-10 ꢀl, 10-3 g/mL different NACs and TNP were alternately added
to 3 mL sensor 1 and sensor 2 solution respectively).

5
Table 1. The NMR chemical shifts of sensor 1 with TNP in DMSO-d6
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Chemical shift
Sensor 1
TNP/ppm
HA/ppm
HB/ppm
-
8.440
8.434
8.424
8.423
8.417
8.407
7.943
7.936
7.927
7.926
7.919
7.910
Sensor 1 +5ppm TNP
Sensor 1 +10ppm TNP
8.543
8.547
resulting in initial fluorescence quenching. Estimation of the
HOMO and LUMO energy of the sensor as well as for TNP by
density functional theory (DFT) revealed that the LUMO of the
electron deficient TNP is situated in between the HOMO and
LUMO of the sensor. Hence, an excited-state electron transfer is
expected from the LUMO of the sensor to TNP. The difference
in the energy between the LUMO of the sensor and TNP
implicate that TNP has good fluorescence quenching ability. In
addition, to support the experimental charge-transfer mechanism
between the sensor and TNP, a series of computational
calculations was carried out employing DFT. The geometry
optimization of the sensor in the presence of TNP revealed that
the most favorable location (in terms of energy) for TNP
interacting with the sensor was related to the carboxyl of triazole
ring moiety. If TNP formed a charge-transfer complex with the
sensor, the LUMO of the newly formed complex should be lower
in energy compared to the sensor itself. However, the energy
level of HOMO kept almost the same comparing to that of the
sensor. In Fig. 10, a representative energy diagram of sensor 1,
TNP and [sensor 1 +TNP] indicated that the initial HOMO and
LUMO energy difference of sensor 1 (4.57 eV) is reduced to 3.61
eV in the presence of TNP. In this process, the energy of the
LUMO of sensor 1 (-2.92 eV) decreases firmly by 0.91 eV to the
newly formed LUMO (-3.83 eV) of the [sensor 1 +TNP] adduct,
however, the HOMO energy does not change significantly. To
our expectation, the LUMO of [sensor 1 +TNP] has the
contribution mainly on the TNP moiety and the HOMO is located
on the carboxyl of triazole ring moiety of sensor 1.
Figure 9. Photo stability test: Fluorescence spectra of sensor 1 and
sensor 2 in presence of 10 ppm of TNP at different time scale (10 ꢀl,
10-3 g/mL TNP were added to 3 mL sensor 1 and sensor 2 solution
respectively).
In addition to the sensitivity and selectivity for TNP, the photo
stability required for sensing is also very significant for practical
application. The fluorescence response of TNP is quick
quenching process.
fluorophore does not have any photo stability that leads to
fluorescence activity changes with time. The quenching
Typically, the inorganic and organic
fluorescence intensity in presence of TNP does not show any
change in fluorescence spectrum with temporal variation as
demonstrated in Fig. 9. The present sensors for TNP detection
are comparable or superior to the methods reported earlier.19
2.4. Mechanism for detection of TNP
The fluorescence quenching phenomenon can be described by
a donor–acceptor electron transfer mechanism between the sensor
and TNP.20 One can anticipate that the electron transfer could
take place upon excitation if the LUMO of the electron deficient
analytes resides in between the HOMO and the LUMO of the
sensors. Upon excitation of the sensor, a charge transfer takes
place from the LUMO of the sensor to the LUMO of TNP, thus,
Figure 10. Calculated energy level diagram of sensor 1, TNP and
[sensor 1 + TNP]

6
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3. Conclusions
on Hitachi F-7000 fluorescence spectrophotometer. For this
experiment, a 10-5M solution of the individual sensor was
prepared in DMSO/H2O (1:1) and subsequently 3 mL solution
was placed in quartz cuvette. The geometries of all compounds
were optimized by density functional (DFT) methods by using
the Gaussian 09 program. For optimization, B3LYP functional
was used employing 631G* basis set.
In summary, aiming at developing and enriching inorganic
and organic fluorescent materials, we prepared a triazole
derivative with carboxylic acid group (compound 1) by modified
method and utilized it as a ligand to develop a new metal copper
complex (complex 2). Compound 1 was characterized by
elemental analysis, H NMR and 13C NMR. Correspondingly,
1
4.2. Synthesis
Complex 2 was characterized by spectroscopy elemental analysis,
IR, UV–vis spectroscopy and powder X-ray diffraction (PXRD).
Both of them showed high sensitivity, selectivity and low
detection limit for TNP. Then we had a discussion about the
fluorescence quenching mechanism of the sensor 1 (compound 1)
with TNP based on the density functional theory (DFT)
calculations. Therefore, the syntheses of this kind of compounds
were very successful, whose potential applications in inorganic
and organic fluorescent materials were widespread and valuable.
5-Methyl-1-(4-nitrophenyl)-1H-1, 2, 3-triazole-4-carboxylic
acid (1): Sodium nitrite (3.45 g, 0.05mol) in cold distilled water
(15 mL) was slowly added to the p-nitroaniline (6.91g, 0.05mol)
in concentrated hydrochloric acid (25 mL) at 0oC with stirring for
50 minutes. Then, the mixture was stirred around 0oC (no more
than 5oC) for 30 minutes. After filtration, sodium azide (3.25 g,
0.05mol) dissolved in distilled water (10 mL) was added to the
solution. The solution was stirred at room temperature for 2 h.
The white solid was collected by filter. Metallic sodium (0.5 g,
0.02mol) was added to cold absolute ethanol (10mL). After the
reaction was completely finished, ethyl acetoacetate (1.31 g,
0.01mol) was added dropwise into mixture at 0oC with stirring.
When the system was reacted for 30 minutes, the organic azide
(1.63 g, 0.01mol) was added to mixture with stirring in the ice
water bath. The mixture was heated to the boiling point slowly
and kept the temperature at the boiling point for 1 hour. Hot
water was added to the solution until the precipitation
disappeared. The mixture was kept heating for 10 minutes and
then cooled to room temperature. The resulting solution was
acidified with 2M HCl. The crude product was recrystallized in
ethanol to give compound 1 as white solid (2.10 g, 85%). Anal.
Calc. for C10H8N4O4 (248.19): C, 48.67; H, 3.29; N, 22.46%.
Found: C, 48.39; H, 3.25; N, 22.57%. IR data (KBr, cm-1): 3480,
4. Experimental section
4.1. Materials and methods
Compound 1 was synthesized according to the modified
literature method.17 All other chemicals were purchased from
commercial sources and used as received. Solvents were dried
and distilled prior to use by standard procedure. IR spectra were
recorded on a Bruker AXS TENSOR-27 FT-IR spectrometer
with pressed KBr pellets in the range of 4000-400 cm-1. H NMR
1
and 13C NMR were recorded in DMSO-d6 on a Bruker AV 500 O
FT-NMR spectrometer operating at 500 and 125 MHz,
respectively. The high resolution mass spectrum was recorded
with an Agilent 6540. The elemental analyses for C, H, and N
were carried out on a Perkin Elmer 240C automatic analyzer.
UV-vis absorption spectra were recorded with a JASCO V-570
UV/VIS/NIR spectrophotometer in the range of 200-2500 nm.
X-ray powder diffraction (PXRD) patterns were obtained on a
Bruker Advance-D8 equipped with Cu Kα radiation, in the range
of 5° < 2θ < 60°, with a step size of 0.02° (2θ) and a count time
of 2 s per step. Fluorescence emission studies were carried out
1
3125, 2866, 1714, 1580, 1513, 1445, 1346, 1268, 1228, 1114. H
NMR (500 MHz, DMSO-d6): δ (ppm) 13.19 (s, 1H), 8.44-8.42
(d, J = 8.6 Hz, 2H), 7.94-7.93 (d, J = 8.6 Hz, 2H), 2.54 (s, 3H).
13C NMR (125 MHz, DMSO-d6): δ (ppm) 162.82, 148.32,
140.56, 139.94, 137.46, 126.96, 125.51, 10.25. HRMS (ESI):
m/z calcd for C10H8N4O4 [M+H]+ 249.0625, found 249.0624.
Table 2. Crystallographic data and the structure refinement for compound 1 and complex 2*
Compound/Complex
Formula
M (g·mol-1)
Crystal system
Space group
a (Å)
1
2
C10H10N4O5
266.22
C40H32N16O18Cu2
1151.90
Monoclinic
P21/c
Monoclinic
P2(1)/n
11.656(2)
7.7162(16)
14.086(3)
90
7.7352(9)
35.847(4)
8.4927(10)
90
b (Å)
c (Å)
α (°)
β (°)
108.360(4)
90
108.903(2)
90
γ (°)
V (Å3)
1202.4(4)
4
2227.9(4)
2
Z
Dcalc (g·cm-3)
Crystal size (mm)
F(000)
1.471
1.717
0.41 x 0.22 x 0.19
552
0.40 x 0.35 x 0.31
1172
ꢀ(Mo-Kα) mm-1
Reflections collected
Independent reflections
Parameters
ꢁ(ρ) (e Å-3)
Goodness of fit
Ra (Rb)
0.120
1.054
7527
13549
2933
5149
174
348
0.269, -0.262
1.012
0.470, -0.668
1.048
0.0553 (0.1138)
0.1237 (0.1468)
0.0456 (0.0784)
0.1200 (0.1417)
b
wR2a (wR2 )
*a R = Σ||Fo| − |Fc||/Σ|Fo|, wR2 = [Σ(w(Fo2 - Fo2)2/Σ(w(Fo2)2)]1/2; [Fo > 4σ(Fo)]. b Based on all data.

7
Table 3. The detailed attribution of IR (cm-1) for compound 1 and complex 2
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Compound/ Complex
1
2
ν(O-H)
ν(Ar-H)
ν(CH3)
ν(C=O)
νas(COO )
νs(COO )
3480
3125
2866
1714
-
-
3443
3085
2864
-
1636
1434
-
-
ν(phenyl)
ν(triazole)
νas(NO2)
νs(NO2)
1580, 1445
1346, 1228, 1114
1513
1617
1348, 1252, 1127
1521
1268
1300
Table 4. The detailed attribution of UV-vis (nm) for compound 1 and
complex 2
[Cu(L)2][Cu(L)2(H2O)2] (2): CuCl2·2H2O (0.017 g, 0.10 mmol)
and compound 1 (0.025 g, 0.10 mmol) were mixed in a beaker
with the mixture of water (10 mL) and EtOH (5 mL) then stirred
for 3 h. The final reaction mixture was sealed in a 25 mL Teflon-
lined stainless steel vessel under autogenous pressure and heated
at 160 °C for 4 days, and then followed by slow cooling to room
temperature. After filtration, the product was washed with
distilled water and then dried at room temperature. Some blue
crystals suitable for X-ray diffraction analysis were obtained.
Yield: 32% (based on Cu). Anal. Calc. for C40H32N16O18Cu2
(1151.90): C, 41.71; H, 2.80; N, 19.46%. Found: C, 41.70; H,
2.85; N, 19.42%. IR data (KBr, cm-1): 3443, 3085, 2864, 1636,
1617, 1521, 1434, 1348, 1300, 1252, 1127.
Compound/ Complex
π–π*/ n–π*
LMCT
1
2
217, 260, 306
-
-
219, 262, 339
415
720 2Eg → 2T2g
d–d*
4.5. UV-vis spectra
The electronic absorption spectra of compound 1 and complex
2 were recorded at room temperature in the form of a solid
sample. As shown in Fig. S6–S7, electronic absorption spectra
of compound 1 and complex 2 have similar absorption patterns.
There are three sharp and strong high-energy absorption bands in
the region of 200-350 nm. Bands at 217, 260, 306 nm for
compound 1 and 219, 262, 339 nm for complex 2 could be
ascribed to n–π* or π–π* transition. The peak observed at 415
nm for complex 2 is attributed to the charge transitions from the
ligand to the Cu (II) atoms (LMCT). The absorption band at 720
of complex 2 is caused by the d-d* transition of Cu2+. Compared
with compound 1, it is found that complex 2 shows slight red
shifts about the high-energy absorption bands, indicating that the
N-heterocyclic ligand of compound 1 was coordinated to metal
center. The detailed appointments of the UV-vis spectra data for
compound 1 and complex 2 are listed in Table 4.
4.3. X-ray crystallographic determination
Suitable single crystals of the compound 1 and complex 2
were mounted on glass fibers for X-ray measurement,
respectively. Reflection data were collected at room temperature
on a Bruker AXS SMART APEX Ⅱ CCD diffractometer with
graphite monochromatized Mo Kα radiation (λ = 0.71073 Å).
All absorption corrections were performed using the SADABS
program. Crystal structures were solved by the direct method.
All non-hydrogen atoms were refined anisotropically. All
hydrogen atoms were fixed at calculated positions with isotropic
thermal parameters except for the coordinated water molecules,
which were located by difference Fourier map. All calculations
were performed using the SHELX-97 program. Crystal data and
details of the data collection and the structure refinement of
compound 1 and complex 2 are given in Table 2. For compound
1 and complex 2, the selected bond lengths and bond angles are
listed in Table S1; the hydrogen bonds of complex 2 are shown in
Table S2. The drawings were made with Diamond 3.2.
4.6. PXRD analysis
The PXRD pattern of complex 2 is shown in Fig. S8. All the
peaks presented in the measured patterns closely match the
simulated patterns generated from the single crystal diffraction
data, which indicate that the complex is phase pure.
Acknowledgments
4.4. IR spectra
This work was supported by the grants of the National Natural
Science Foundation of China (Nos. 21571091, 21371086), State
Key Laboratory of Inorganic Synthesis and Preparative
Chemistry, College of Chemistry, Jilin University, Changchun
130012, P.R. China (No. 2016-02) and Guangxi Key Laboratory
of Information Materials, Guilin University of Electronic
Technology, P. R. China (Project No. 151002-K) for financial
assistance for financial assistance. Furthermore, we also give
thanks to the High-Performance Computing Platform of Guangxi
University for generous support of our computational chemistry
research.
The IR spectra of compound 1 and complex 2 are examined
(Fig.S4-S5).
For compound 1, a broad absorption band
appearing at 3480 cm-1 can be attributed to the O–H stretching
vibrations of the carboxyl group. Absorption band at 3125 cm-1
should be assigned to the stretching vibrations of the =C–H in the
phenyl ring. Weak absorption band observed at 2866 cm-1 is
features of the νC–H vibration modes of –CH3 group. Strong
Absorption at 1714 cm-1 is the characteristic stretching vibration
of the νC=O bond. The bands at 1580, 1445, 1346, 1228, and 1114
cm-1 are attributed to the characteristic stretching vibrations of
the phenyl and triazole rings. The peaks at 1513 and 1268 cm-1
are the characteristic absorptions for the asymmetric and
symmetric stretching vibrations of –NO2 group, respectively.
Because the stretching vibrations of –NO2 group and the
characteristic stretching vibrations of the phenyl and triazole
rings both appear at 1600-1200 cm-1, and overlap partially, the
absorption bands in this region are comparatively broad. IR
spectral characteristic of complex 2 is similar to compound 1,
except the peaks at 1636 and 1434 cm-1 are the characteristic
absorptions for the asymmetric and symmetric stretching
vibrations of the carboxylate group in the triazole ligand. The
detailed appointments of the IR spectra data for compound 1 and
complex 2 are listed in Table 3.
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Supplementary Material
1
Figures of H NMR, 13C NMR, IR spectra, UV-vis spectra,
PXRD, fluorescence spectra and tables of crystal data are
presented in the supplementary material. CCDC 1511387 for
compound 1, CCDC 1511372 for complex 2.
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