English

• 0.   Introduction

  Nitroaromatic compounds (NACs) are often used as important materials in the industrial production of dye intermediates, explosives, medicines, and pesticides. However, as an important NACs, p-nitrophenol (4-NP) is also a toxic pollutant. The high concentration of 4-NP waste liquid discharge leads to its long-term residue in soil and water, causing pollution and serious harm to the human body. Therefore, it is crucial to establish a sensitive and convenient 4-NP detection method^[1-5]. On the other hand, metal ions play important roles in biological and environmental systems, in which Fe(Ⅲ) plays an important role in many biochemical processes such as DNA replication, hemoglobin formation, and cellular metabolism. Excessive intake and deficiency of Fe(Ⅲ) lead to people's health problems. Not only that, but the extensive use of Fe(Ⅲ) in the industry also causes environmental pollution, so it is urgent to find an efficient method for detecting Fe(Ⅲ)^[6-10].

  Scientists have tried many methods to detect these two species, including electrochemical methods, inductively coupled plasma atomic emission spectroscopy (ICP-OES), HPLC, atomic absorption spectroscopy (AAS), MS, etc^[11-17]. These methods have problems such as complicated instrument operation, high cost, time-consuming, and insensitivity. Therefore, it is imperative to find a detection technology with simple operation and sensitive response. The photochemical method is considered to be an effective detection method because of its low cost, high sensitivity, and good selectivity^[18-24]. Some coordination polymers (CPs), as a class of 2D or 3D porous materials^[25-29], have excellent luminescence properties; therefore, CPs are a good choice for detecting 4-NP and Fe(Ⅲ) as fluorescence sensors^[30-36].

  The 2, 2', 3, 4', 5-diphenyl ether pentacarboxylic acid (H₅depa) ligand has five carboxyl groups, which can be completely or partially deprotonated, providing hydrogen bond donors and acceptors, which are useful for building diverse supramolecular structures. The luminescence sensors of CPs based on H₅depa ligands still have great potential and are also a great challenge. Therefore, it is necessary to explore the CPs and fluorescence sensing properties of H₅depa ligands. From this, we synthesized a CP, {[Cu₂(Hdepa) (2, 2'-bpy)₂ (H₂O)₂]·2H₂O}_n (1) (2, 2'-bpy=2, 2'-bipyridine), and its synthesis, structure, thermal stability, and fluorescence properties are also described here.

  1.   Experimental

  1.1   Reagents and instruments

  All reagents were purchased commercially and not purified, and reactions are carried out under solvothermal conditions. IR spectra were recorded as KBr pellets on a Bruker EQUINOX55 spectrophotometer in a 4 000-400 cm^-1 region. Thermogravimetric analysis (TGA) was performed in a nitrogen atmosphere with a heating rate of 10 ℃·min^-1 with a NETZSCHSTA 449C thermogravimetric analyzer. The powder X-ray diffraction pattern (PXRD) was recorded with a Rigaku D/Max Ⅲ diffractometer operating at 40 kV and 30 mA using Cu Kα radiation (λ =0.154 18 nm) at a scanning rate of 2 (°)·min-1 from 5° to 50°.

  1.2   Synthesis of CP 1

  CuCl₂·2H₂O (17.1 mg, 0.1 mmol), H₅depa (19.5 mg, 0.05 mmol), 2, 2'-bpy (7.8 mg, 0.05 mmol), DMSO (1 mL), H₂O (2 mL), and NaOH (100 µL, 0.5 mol·L^-1) were put into a 10 mL vial, heated to 95 ℃ for 72 h. The blue bulk crystals were obtained with a yield of 61% based on Cu. Anal. Calcd. for C₃₇H₃₀Cu₂N₄O₁₅(%): C, 49.46; H, 3.34; N, 6.23. Found(%): C, 49.48; H, 3.33; N, 6.21. FT-IR (KBr, cm^-1) for 1: 3 658(w), 3 608 (w), 3 432(m), 3 088(w), 2 365(w), 1 705(s), 1 607(s), 1 446(s), 1 374(s), 1 277(m), 1 221(s), 1 164(w), 1 074 (w), 1 032(w), 898(w), 764(s), 427(w).

  1.3   Fluorescence sensing experiments

  For the NACs sensing experiments, CP 1 (3 mg) was dissolved in different NACs solutions (1 mmol· L^-1): 4-NP, 2, 4-dinitrophenylhydrazine (DNP), nitrobenzene (NB), 3-nitroaniline (3-NT), p-nitrobenzoic acid (PNBA), 2, 4, 6-trinitrophenylhydrazine (TRI), paranitrophenylhydrazine (4-NPH), o-nitroaniline (O-NT), and 2, 4, 6-trinitrophenol (TNP). After ultrasonic treatment for 30 min and aging for 3 d, a stable suspension was formed, and the fluorescence experiment was performed.

  For the inorganic cation sensing experiments, CP 1 (3 mg) was dissolved in the solutions of Ag⁺, Al³⁺, Ba²⁺, Ca²⁺, Cd²⁺, Co²⁺, Cu²⁺, Dy³⁺, Er³⁺, Fe³⁺, Eu³⁺, K⁺, La³⁺, Mg²⁺, Nd³⁺, Ni²⁺, Pb²⁺, Pr³⁺, Tb³⁺, Y³⁺, and Zn²⁺. After ultrasonic treatment for 30 min and aging for 3 d, a stable suspension was formed, and the fluorescence experiment was performed.

  1.4   Single-crystal X-ray diffraction analysis

  The intensity data were collected on a Bruker Smart APEX Ⅱ CCD diffractometer using graphite monochromatic Mo Kα radiation (λ =0.071 073 nm) at room temperature. Using the SHELXTL-2016 program and the OLEX program, the structure was solved and refined by the direct method. All non-hydrogen atoms were refined anisotropically and hydrogen atoms of organic ligands were generated geometrically. The crystal parameters of CP 1 are listed in Table 1, the main bond lengths and bond angles are listed in Table 2, and the hydrogen bond parameters are listed in Table 3.

  Table 1

  

  Table 1.  Crystal data and structure refinement for CP 1

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  Parameter	1		Parameter	1
  Empirical formula	C37H30Cu2N4O15		V/nm3	1.822 4(13)
  Formula weight	897.73		Z	2
  Temperature/K	296(2)		Dc/(g·cm-3)	1.636
  Crystal system	Triclinic		μ/mm-1	1.248
  Space group	P1		F(000)	916
  a/nm	1.039 9(4)		Crystal size/mm	0.240×0.160×0.120
  b/nm	1.111 6(5)		Reflection collected	7 853
  c/nm	1.717 6(7)		S on F2	1.088
  α/(°)	7.949 0(7)		R1, wR2*[I > 2σ(I)]	0.039 4, 0.113 4
  β/(°)	83.708(6)		R1, wR2(all data)	0.046 4, 0.119 3
  γ/(°)	69.180(6)
  * R1=∑‖Fo|-|Fc‖/∑|Fo|, wR2=[∑w(Fo2-Fc2)2/∑w(Fo2)2]1/2.

  Table 2

  

  Table 2.  Selected bond distances (nm) and bond angles (°) for CP 1

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  Cu1—O7#1	0.197 6(2)	Cu1—O1	0.199 2(3)	Cu(1)—N(2)	0.201 8(3)
  Cu1—N1	0.203 0(3)	Cu1—O12	0.234 7(3)	Cu(2)—O(10)	0.195 4(3)
  Cu2—O4#2	0.201 0(2)	Cu2—N3	0.201 5(3)	Cu(2)—N(4)	0.204 3(3)
  Cu2—O13	0.225 7(3)
  O7#1—Cu1—O1	93.03(11)	O7#1—Cu1—N2	95.12(12)	O1—Cu1—N2	163.67(11)
  O7#1—Cu1—N1	175.13(13)	O1—Cu1—N1	90.65(12)	N2—Cu1—N1	80.54(13)
  O7#1—Cu1—O12	95.58(11)	O1—Cu1—O12	90.43(12)	N2—Cu1—O12	102.81(13)
  N1—Cu1—O12	87.56(13)	O10—Cu2—O4#2	93.34(10)	O10—Cu2—N3	173.39(12)
  O4#2—Cu2—N3	92.03(11)	O10—Cu2—N4	92.76(12)	O4#2—Cu2—N4	162.4(12)
  N3—Cu2—N4	81.01(12)	O10—Cu2—O13	91.36(10)	O4#2—Cu2—O13	100.25(10)
  N3—Cu2—O13	91.50(12)	N4—Cu2—O13	96.06(11)
  Symmetry codes: #1: 1+x, -1+y, z; #2: -1+x, y, z.

  Table 3

  

  Table 3.  Hydrogen bond parameters for CP 1

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  D—H⋯A	d(D—H)/nm	d(H⋯A)/nm	d(D⋯A)/nm	∠DHA/(°)
  O9#3—H9#3⋯O4#4	0.082	0.185	0.264 4(4)	163
  O12#5—H12A#5⋯O14#3	0.085	0.196	0.281 1(6)	175
  O14#3—H14B#3⋯O6#3	0.085	0.244	0.289 4(6)	114
  O15#3—H15A⋯O6#3	0.085	0.199	0.284 4(5)	179
  O15#3—H15B#3⋯O8#6	0.085	0.216	0.300 8(6)	172
  Symmetry codes: #3: 1-x, 1-y, 1-z; #4: -1+x, y, 1+z; #5: -1+x, 1+y, z; #6: x, y, 1+z.

  2.   Results and discussion

  2.1   Structural analysis

  CP 1 belongs to the triclinic system, space group P1. The asymmetric unit of 1 contains two Cu(Ⅱ) ions, one Hdepa^4- ion, two 2, 2'-bpy molecules, two coordinated water molecules, and two lattice water molecules. As shown in Fig. 1a, the central metal Cu1 coordinates with O1, O7, O12, N1, and N2. The O1 and O7 atoms (Cu1—O1 0.199 2(3) nm, Cu1—O7#1 0.197 6(2) nm) are from the Hdepa^4- ion, and the O12 (Cu1—O12 0.234 7(3) nm) atom is from the coordinated water molecule. The N1 and N2 atoms (Cu1—N1 0.203 0(3) nm, Cu1—N2 0.201 8(3)nm) are from the 2, 2'-bpy molecule. The coordination environment of Cu2 is similar to Cu1: two oxygen atoms (O4 and O10) from Hdepa^4-(Cu2—O4#2 0.201 0(2) nm, Cu2—O10 0.195 4(3) nm), one oxygen atom (Cu2 —O13 0.225 7(3) nm) from the coordinated water, and two nitrogen atoms (N1 and N2) from 2, 2'-bpy (Cu2—N3 0.201 5(3) nm, Cu2—N4 0.204 3(3) nm). It is worth noting that both Cu1 and Cu2 adopt a five-coordination mode with triangular bipyramid geometry.

  Figure 1

  

  Figure 1.  (a) Coordination environment of Cu(Ⅱ) ion in CP 1; (b) Coordination modes of Hdepa^4- in 1; (c) 2D structure of 1; (d) 3D network of 1 where the dotted lines represent hydrogen-bond interactions

  Symmetry codes: #1: 1+x, -1+y, z; #2:-1+x, y, z

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  The Hdepa^4- ion adopts a μ₄-η¹-η¹-η¹-η¹ bridging coordination mode, and the four carboxyl groups of it connect four Cu(Ⅱ) ions by bridging monodentate (Fig. 1b). According to the coordination mode, each pair of Cu(Ⅱ) ions are linked by one Hdepa^4- ion from two directions to form a 2D network (Fig. 1c). Interestingly, O4 and O9 atoms form hydrogen bonds (O9#3⋯O4#4 0.264 4(4) nm) between adjacent 2D networks. The oxygen atoms (O14#3 and O15#3) in free water molecules form hydrogen bonds with the oxygen atoms (O6#3, O8#6, and O12#5) of the carboxyl group (O12#5⋯ O14#3 0.281 1(6) nm, O14#3⋯O6#3 0.289 4(6) nm, O15#3⋯O6#3 0.284 4(5) nm, O15#3⋯O8#6 0.300 8(6) nm). It can be seen that the two 2D layers, which are mirror images of each other, act as repeating units and assemble through weak hydrogen bond interactions to form a 3D supramolecular structure (Fig. 1d)^[37-41].

  2.2   TGA and PXRD characterization

  To explore the thermal stability of CP 1, TGA was performed, as shown in Fig. 2a. The weight loss at 135 ℃ was about 8%, presumably due to the loss of all water molecules. The second weight loss was 71% in a temperature range of 260-400 ℃, corresponding to the decomposition of Hdepa^4- and 2, 2'-bpy (Calcd. 74.2%).

  Figure 2

  

  Figure 2.  (a) TGA curve and (b) PXRD patterns of CP 1

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  Then, the PXRD patterns of simulated, experimental, and after selective experiments of Fe³⁺ and 4-NP were obtained, as shown in Fig. 2b. It can be seen from the figure that the peak position and peak intensity of the experimental data were in good agreement with the simulated data, which indicates the high purity of CP 1 and the stability after the fluorescence experiment.

  2.3   Fluorescence quantum yield of CP 1

  In order to study the luminescence intensity of CP 1, the fluorescence quantum yields before and after the response were measured. Using the reference method and quinine sulfate as the standard substance, the relevant data of the fluorescence quantum yield before and after the response were measured and obtained by Eq.1. The calculated fluorescence quantum yield of 1 was 75%, and the fluorescence quantum yields^[42-43] after the addition of 4-NP and Fe³⁺ were 6% and 14%, respectively (Table 4).

  $ Y_{\mathrm{u}}=Y_{\mathrm{s}} \times \frac{F_{\mathrm{u}}}{F_{\mathrm{s}}} \times \frac{A_{\mathrm{s}}}{A_{\mathrm{u}}} $

  (1)

  Table 4

  

  Table 4.  Fluorescence quantum yield of CP 1

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  Sample	λex/nm	λem/nm	A	Fintegral	Y
  Quinine sulfate	313	449	0.049 34	942 398.769	0.55
  CP 1	315	433	0.047	1 226 998.480	0.75
  CP 1+4-NP	315	433	0.046 08	91 177.786	0.06
  CP 1+Fe3+	315	433	0.047 86	231 272.066	0.14

  where F_u, Y_u, and A_u represent the fluorescence quantum yield, integrated fluorescence intensity, and absorbance of the analyte; F_s, Y_s, and A_s represent the fluorescence quantum yield, integrated fluorescence intensity, and absorbance of the reference substance.

  2.4   Fluorescence detection of CP 1 for different NACs

  The copper complexes reported in the literature have good luminescent properties^[44-45]. The liquid fluorescence of CP 1 was obtained, and the emission of 1 was 433 nm at the excitation of 315 nm (Fig. 3). Due to the microporous structure and excellent fluorescence properties of CP 1, we further explored the possibility of CP 1 as a fluorescence sensor to detect NACs. As shown in Fig. 4a, the results show that the luminescence of CP 1 had different quenching degrees for different NACs. It is worth noting that the quenching Fig. 3 Fluorescence excitation and emission peaks of CP 1 effect of 4-NP was the most obvious, and the fluorescence of 3-NT and DNP was slightly enhanced.

  Figure 3

  

  Figure 3.  Fluorescence excitation and emission peaks of CP 1

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  Figure 4

  

  Figure 4.  (a) Fluorescence intensities of CP 1 at 433 nm in the presence of various NACs; (b) Fluorescence spectra of 1 in water upon the addition of 4-NP; (c) Linear relationship of I₀/I-1 with c_4-NP in the fluorescence detection of 1 to 4-NP; (d) Comparison of the luminescence intensity of CP 1 in the presence of 4-NP-mixed NACs

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  Therefore, the effect of different concentrations of 4-NP on the fluorescence quenching of CP 1 at room temperature was further investigated. With the increasing concentration of 4-NP (0-220 µmol·L^-1), the fluorescence intensity gradually decreased until the fluorescence was almost completely quenched when the concentration increased to 220 µmol·L^-1 (Fig. 4b). In order to study the relationship between the concentration of 4-NP and the fluorescence intensity more precisely, we made a plot of I₀/I-1 vs c_4-NP according to the Stern-Volmer (SV) equation: I₀/I=1+K_SVc_Q, where I₀ represents the initial luminescence intensity, and I represents the luminescence intensity after adding 4-NP, c_Q is the concentration of quencher, and K_SV is the quenching constant. As shown in Fig. 4c, a linear relationship was observed in the low concentration range of 5×10^-5-9×10^-5 mol·L^-1: y=8.144×10⁴x-2.740 (R²=0.996 6). Using the equation LOD=3σ/K, the limit of detection (LOD) was calculated as 0.44 µmol·L^-1 for 4-NP, which was better than the reported value^[36].

  In addition, 4-NP can be selectively detected in the interference term of other NACs. A solution of 4-NP (20 µL, 10 mmol·L^-1) was added to the mixture containing other NACs (20 µL, 10 mmol·L^-1) in the CP 1 suspension. The fluorescence intensity did not drop drastically upon the addition of other NACs, but after the addition of 4-NP, the fluorescence was almost completely quenched, as shown in Fig. 4d. The anti-interference experiment showed that the quenching effect of 4-NP was not affected by other selected competing NACs, proving that CP 1 demonstrated better selectivity for 4-NP.

  2.5   Fluorescence detection of CP 1 for different cations

  We further investigated the luminescence sensing of CP 1 to detect cations. As shown in Fig. 5a, the results show that the luminescence of CP 1 had different quenching degrees for different cations. It is worth noting that Fe³⁺ has the most obvious quenching effect.

  Figure 5

  

  Figure 5.  (a) Fluorescence intensities of CP 1 at 433 nm in the presence of various cations; (b) Fluorescence spectra of 1 in water upon the addition of Fe³⁺; (c) Linear relationship of I₀/I-1 with c_Fe(Ⅲ) in the fluorescence detection of 1 to Fe³⁺; (d) Comparison of the luminescence intensity of CP 1 in the presence of Fe³⁺-mixed cations

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  Therefore, the effect of different concentrations of Fe³⁺ on the fluorescence quenching of CP 1 at room temperature was further investigated, and a titration experiment was carried out. The fluorescence intensity gradually decreased until the concentration increased to 760 µmol·L^-1 and the fluorescence was almost completely quenched, as shown in Fig. 5b. According to the SV equation, there was a linear relationship in the low concentration range of 5×10^-6-3×10^-5 mol·L^-1 (Fig. 5c): y=8.136×10⁴x-0.126 9 (R²=0.990 1). The calculated LOD of Fe³⁺ was 0.44 µmol·L^-1, which was better than the value reported in the literature^[32-33].

  In addition, Fe³⁺ can be selectively detected in the interference term of other cations. A solution of Fe³⁺ (20 µL, 5 mmol·L^-1) was added to the CP 1 suspension containing other cations (20 µL, 5 mmol·L^-1). The fluorescence intensity did not drop significantly when other cations were added, but after adding equimolar Fe³⁺, the fluorescence was almost completely quenched, as shown in Fig. 5d. Anti-interference experiments show that after adding Fe³⁺, the quenching effect was not affected by other selected competing cations, which proves that CP 1 had better selectivity to Fe³⁺.

  2.6   Fluorescence quenching mechanism

  Since low concentrations of 4-NP showed a good linear relationship for CP 1, suggesting that static or dynamic quenching was taking place. Both quenching mechanisms could be predicted by examining the fluorescence lifetime. If the fluorescence lifetime of the sensing material decreases after adding a quencher, the quenching process is regarded as dynamic, and if the fluorescence lifetime remains unchanged after adding a quencher, it is static quenching^[46-49]. The amplitude-weighted mean lifetime (τ_α) was calculated by substituting the fluorescence lifetime τ₁ (τ₂, τ₃) and the corresponding fluorescence lifetime ratio α₁ (α₂, α₃) into the formula (Eq.2): $\tau_\alpha=\sum\limits_{i=1}^n \alpha_i \tau_i $. Time-resolved fluorescence experiments (Fig. 6a) showed that the average excited-state lifetime (τ_avg) shortened from 2.52 to 0.29 ns before and after the addition of 4-NP (Table 5), which suggests that the nature of the quenching process is dynamic, and the shortening of fluorescence lifetime is consistent with the fluorescence quenching results of CP 1 on 4-NP.

  Figure 6

  

  Figure 6.  Fluorescence lifetime decay profiles of CP 1 before and after the addition of (a) 4-NP or (b) Fe³⁺

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  Table 5

  

  Table 5.  Excited-state lifetime values of CP 1 before and after the addition of 4-NP or Fe³⁺

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  Sample	α1/%	α2/%	α3/%	τ1/ns	τ2/ns	τ3/ns	τavg/ns
  CP 1	66.03	7.14	26.83	0.13	1.85	8.57	2.52
  CP 1 treated by 4-NP	93.92	3.52	2.55	0.09	0.75	7.20	0.29
  CP 1 treated by Fe3+	88.83	9.55	1.63	0.10	0.75	5.23	0.25

  We also investigated the quenching mechanism of Fe³⁺ by the fluorescence lifetime test, and the data (Fig. 6b) showed that the τ_avg before and after adding Fe³⁺ shortened from 2.52 to 0.25 ns (Table 5), which indicates that the quenching process is dynamic in nature, and the shortening of the fluorescence lifetime is basically consistent with the fluorescence quenching result of Fe³⁺ by CP 1.

  A possible quenching mechanism is the collapse of the crystal structure resulting in fluorescence quenching. To test this idea, PXRD measurements of CP 1 were performed after sensing experiments. The PXRD pattern matched the simulated pattern well (Fig. 2b). Therefore, the collapse of the CP 1 structure is not responsible for the fluorescence quenching.

  When studying the quenching mechanism, we usually compare the UV-Vis absorption spectrum of the analyte with the excitation or emission spectrum of CP and then speculate that the quenching mechanism is resonance energy absorption or competitive absorption. It is assumed that the UV-Vis absorption spectrum of the analyte overlaps with the emission spectrum of CP, which can lead to quenching of the luminescence of CP, and the quenching mechanism is resonance energy transfer^[48]. When the absorption spectrum of the analyte overlaps the excitation spectrum of the CP, competitive absorption between the CP and the analyte is likely to occur^[49-50].

  When we investigated the quenching mechanism of NACs, the UV-Vis absorption spectrum of 4-NP almost completely overlapped with the excitation spectrum of CP 1 (Fig. 7a) compared with the other eight NACs. So, it is speculated that the fluorescence quenching mechanism of 4-NP is competitive absorption. The quenching mechanism of cations is similar to NACs. The UV-Vis absorption spectrum of Fe³⁺ overlapped with the excitation spectrum of CP 1 (Fig. 7b), while the UV-Vis spectra of other cations did not overlap with the excitation spectra. So, we speculate that the quenching mechanism of 1 is competitive absorption.

  Figure 7

  

  Figure 7.  (a) UV-Vis absorption spectra of the NACs and the emission spectrum of CP 1; (b) UV-Vis absorption spectrum of the cations and the emission spectrum of CP 1

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  3.   Conclusions

  CP 1 was synthesized based on H₅depa and 2, 2'-bpy ligands under hydrothermal conditions. CP 1 exhibits a unique 3D supramolecular network structure, and could rapidly and sensitively detect Fe³⁺ and 4-NP. The results show that CP 1 is expected to become a new type of multifunctional fluorescent sensing material.

  
  
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  Figure 1  (a) Coordination environment of Cu(Ⅱ) ion in CP 1; (b) Coordination modes of Hdepa^4- in 1; (c) 2D structure of 1; (d) 3D network of 1 where the dotted lines represent hydrogen-bond interactions

  Symmetry codes: #1: 1+x, -1+y, z; #2:-1+x, y, z

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  Figure 2  (a) TGA curve and (b) PXRD patterns of CP 1

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  Figure 3  Fluorescence excitation and emission peaks of CP 1

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  Figure 4  (a) Fluorescence intensities of CP 1 at 433 nm in the presence of various NACs; (b) Fluorescence spectra of 1 in water upon the addition of 4-NP; (c) Linear relationship of I₀/I-1 with c_4-NP in the fluorescence detection of 1 to 4-NP; (d) Comparison of the luminescence intensity of CP 1 in the presence of 4-NP-mixed NACs

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  Figure 5  (a) Fluorescence intensities of CP 1 at 433 nm in the presence of various cations; (b) Fluorescence spectra of 1 in water upon the addition of Fe³⁺; (c) Linear relationship of I₀/I-1 with c_Fe(Ⅲ) in the fluorescence detection of 1 to Fe³⁺; (d) Comparison of the luminescence intensity of CP 1 in the presence of Fe³⁺-mixed cations

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  Figure 6  Fluorescence lifetime decay profiles of CP 1 before and after the addition of (a) 4-NP or (b) Fe³⁺

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  Figure 7  (a) UV-Vis absorption spectra of the NACs and the emission spectrum of CP 1; (b) UV-Vis absorption spectrum of the cations and the emission spectrum of CP 1

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  Table 1.  Crystal data and structure refinement for CP 1

  Parameter	1		Parameter	1
  Empirical formula	C37H30Cu2N4O15		V/nm3	1.822 4(13)
  Formula weight	897.73		Z	2
  Temperature/K	296(2)		Dc/(g·cm-3)	1.636
  Crystal system	Triclinic		μ/mm-1	1.248
  Space group	P1		F(000)	916
  a/nm	1.039 9(4)		Crystal size/mm	0.240×0.160×0.120
  b/nm	1.111 6(5)		Reflection collected	7 853
  c/nm	1.717 6(7)		S on F2	1.088
  α/(°)	7.949 0(7)		R1, wR2*[I > 2σ(I)]	0.039 4, 0.113 4
  β/(°)	83.708(6)		R1, wR2(all data)	0.046 4, 0.119 3
  γ/(°)	69.180(6)
  * R1=∑‖Fo|-|Fc‖/∑|Fo|, wR2=[∑w(Fo2-Fc2)2/∑w(Fo2)2]1/2.

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  Table 2.  Selected bond distances (nm) and bond angles (°) for CP 1

  Cu1—O7#1	0.197 6(2)	Cu1—O1	0.199 2(3)	Cu(1)—N(2)	0.201 8(3)
  Cu1—N1	0.203 0(3)	Cu1—O12	0.234 7(3)	Cu(2)—O(10)	0.195 4(3)
  Cu2—O4#2	0.201 0(2)	Cu2—N3	0.201 5(3)	Cu(2)—N(4)	0.204 3(3)
  Cu2—O13	0.225 7(3)
  O7#1—Cu1—O1	93.03(11)	O7#1—Cu1—N2	95.12(12)	O1—Cu1—N2	163.67(11)
  O7#1—Cu1—N1	175.13(13)	O1—Cu1—N1	90.65(12)	N2—Cu1—N1	80.54(13)
  O7#1—Cu1—O12	95.58(11)	O1—Cu1—O12	90.43(12)	N2—Cu1—O12	102.81(13)
  N1—Cu1—O12	87.56(13)	O10—Cu2—O4#2	93.34(10)	O10—Cu2—N3	173.39(12)
  O4#2—Cu2—N3	92.03(11)	O10—Cu2—N4	92.76(12)	O4#2—Cu2—N4	162.4(12)
  N3—Cu2—N4	81.01(12)	O10—Cu2—O13	91.36(10)	O4#2—Cu2—O13	100.25(10)
  N3—Cu2—O13	91.50(12)	N4—Cu2—O13	96.06(11)
  Symmetry codes: #1: 1+x, -1+y, z; #2: -1+x, y, z.

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  Table 3.  Hydrogen bond parameters for CP 1

  D—H⋯A	d(D—H)/nm	d(H⋯A)/nm	d(D⋯A)/nm	∠DHA/(°)
  O9#3—H9#3⋯O4#4	0.082	0.185	0.264 4(4)	163
  O12#5—H12A#5⋯O14#3	0.085	0.196	0.281 1(6)	175
  O14#3—H14B#3⋯O6#3	0.085	0.244	0.289 4(6)	114
  O15#3—H15A⋯O6#3	0.085	0.199	0.284 4(5)	179
  O15#3—H15B#3⋯O8#6	0.085	0.216	0.300 8(6)	172
  Symmetry codes: #3: 1-x, 1-y, 1-z; #4: -1+x, y, 1+z; #5: -1+x, 1+y, z; #6: x, y, 1+z.

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  Table 4.  Fluorescence quantum yield of CP 1

  Sample	λex/nm	λem/nm	A	Fintegral	Y
  Quinine sulfate	313	449	0.049 34	942 398.769	0.55
  CP 1	315	433	0.047	1 226 998.480	0.75
  CP 1+4-NP	315	433	0.046 08	91 177.786	0.06
  CP 1+Fe3+	315	433	0.047 86	231 272.066	0.14

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  Table 5.  Excited-state lifetime values of CP 1 before and after the addition of 4-NP or Fe³⁺

  Sample	α1/%	α2/%	α3/%	τ1/ns	τ2/ns	τ3/ns	τavg/ns
  CP 1	66.03	7.14	26.83	0.13	1.85	8.57	2.52
  CP 1 treated by 4-NP	93.92	3.52	2.55	0.09	0.75	7.20	0.29
  CP 1 treated by Fe3+	88.83	9.55	1.63	0.10	0.75	5.23	0.25

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