S. Chen et al.
Dyes and Pigments 184 (2021) 108863
doubly distilled water and ethanol, respectively. Subsequently, 6 μL of
solution or gel (the mole ratio of NDH (25 mgLꢀ 1)/Li+ = 1: 8) was
coated onto the surface of the GCE and dried naturally. The modified
GCE was directly used for the determination of CV and EIS.
2.4. Synthesis of NDH
Compounds 3 and 4 were prepared according to the literature [38,
39], respectively, and the detailed process was shown in the supporting
information. The synthetic route was shown in Scheme 1.
2.4.1. Synthesis of N-hexanoic acid methylester-4-bromo-1, 8-naphthali-
mide (1)
Triethylamine (5 mL) was added to the mixture of 4-bromo-1, 8-
naphthalic anhydride (4.2 g, 15.1 mmol), methyl 6-aminocaproate hy-
drochloride (3.0 g, 16.6 mmol) and ethanol (40 mL), then and the
mixture was stirred and refluxed for 12 h. The solvent was removed
under reduced pressure and the residue was subjected to column chro-
matography on silica gel. The product was separated with petroleum
ether/dichloromethane (3/2, v/v) to give 1 as a white powder (4.5g,
72.5%), m.p. 89–90 ◦C (lit [40]. 89–90 ◦C); 1H NMR (500 MHz, CDCl3) δ
(ppm): 8.63 (d, J = 6.8 Hz, 1H, -Nap), 8.54 (d, J = 8.4 Hz, 1H, -Nap),
8.38 (d, J = 8.0 Hz, 1H, -Nap), 8.02 (d, J = 7.6 Hz, 1H, -Nap), 7.83 (t, J
= 8.0 Hz, 1H, -Nap), 4.15 (t, J = 7.4 Hz, 2H, -NCH2), 3.64 (s, 3H, -OCH3),
2.32 (t, J = 7.6 Hz, 2H, -CH2CO), 1.78–1.66 (m, 4H, -(CH2)2), 1.48–1.41
(m, 2H, -CH2).
Fig. 1. Molecular structure of NDH.
2.4.2. Synthesis of N-hexanoic acid methylester-4- (4-formylphenoxy)-1,
8-naphthalimide (2)
2. Experimental section
Under N2 atmosphere, the mixture of compound 1 (2.0 g, 4.96
mmol), p-hydroxybenzaldehyde (0.52 g, 5.95 mmol), potassium iodide
(0.1g, 0.60 mmol) and dried DMF (40 mL) were heated to 100 ◦C and
stirred for 48 h, then was quenched with water and extracted with
dichloromethane. The organic layer was dried with anhydrous magne-
sium sulphate. Silica gel chromatography with petroleum ether/
dichloromethane (2/3, v/v) gave compound 2 as yellow solid with the
2.1. Materials and reagents
The used chemical materials in this work were purchased from
commercial companies and used without further purification. All metal
salts and other reagents used for gelation test were obtained from
Shanghai Darui fine chemical Co. Ltd. Freshly prepared 0.05 M phos-
phate buffer solution, consisting of Na2HPO4, NaH2PO4 and 0.1 M KCl
was used as the supporting electrolyte. Na2HPO4 and NaH2PO4 were
purchased from Tianjin Damao Chemical Reagent Co. (China).
yield of 87.8% (1.45 g). m.p. 47–48 ◦C; IR(KBr)
ν
/cmꢀ 1: 2957(-C=O-H),
2923(-CH2), 2852(-CH3), 1733(-COO), 1697(-CON), 1652(-CHO), 1578
(-CON), 1503(-Ph), 1462(-CH2), 1377(-CH3); 1H NMR (500 MHz, CDCl3,
Fig. S2) δ (ppm): 10.02 (s, 1H, -CHO), 8.67 (d, J = 7.0 Hz, 1H, -Nap),
8.56 (d, J = 8.5 Hz, 1H, -Nap), 8.53 (d, J = 8.5 Hz, 1H, -Ph), 7.98 (d, J =
8.5 Hz, 2H, -Nap), 7.79 (t, J = 8.0 Hz, 1H, -Nap), 7.28 (d, J = 8.5 Hz, 2H,
Ph), 7.14 (d, J = 8.0 Hz, 1H, -Nap), 4.18 (t, J = 7.5 Hz, 2H, -NCH2), 3.66
(s, 3H, -OCH3), 2.34 (t, J = 7.5 Hz, 2H, -CH2CO), 1.47–1.77 (m, 6H,
-(CH2)3); 13C NMR (125 MHz, CDCl3, Fig. S3) δ (ppm): 190.53, 174.08,
164.13, 163.52, 160.88, 157.63, 133.15, 132.44, 132.27, 132.12,
129.82, 128.24, 127.08, 124.50, 122.91, 119.81, 118.40, 113.50, 51.50,
40.21, 33.98, 27.78, 26.64, 24.67; Found: C 70.3, H 5.4, N 3.0%, mo-
lecular formula. C26H23NO6 requires C 70.1, H 5.2, N 3.1%.
2.2. Instrumentation
SEM images of the dry NDH/Li+ metallogels was measured using FE-
SEM S-4800 (Hitachi) instruments. The X-ray diffraction (XRD) data of
xerogels of NDH/Li+ aggregates were tested by a Bruker AXS D8 in-
strument (Cu target; λ = 0.1542 nm, Germany). 1H and 13C NMR spectra
were performed using Bruker instrument operating at 500 and 125 MHz
with tetramethylsilane as the internal standard. UV–Vis absorption
spectra were recored on a UH5300 spectroscope (Shimadzu). Using a Xe
lamp as an excitation source, fluorescence curves were tested on F-7000
FL spectrometer. Cyclic voltammetry (CV) were conducted via CHI760E
2.4.3. Synthesis of 6-(6-(4-(1,3-dihydroxy-4,4,5,5-
tetramethylimidazolidin-2-yl)phenoxy)-1,3- dioxo-1H-benzo[de]
isoquinolin-2(3H)-yl)hexanoate (NDH)
electrochemical workstation (ZsimpWin software) with
a three-
electrode system(the modified glassy carbon electrode (GCE) as the
working electrode, an Ag/AgCl electrode (saturated with KCl) as the
reference electrode and a platinum wire (1 mm diameter) as the counter
electrode). Electrochemical impedance spectroscopy (EIS) measurement
was performed by using the electrode in 0.1 M KCl solution containing
5.0 mM [Fe(CN)6]ꢀ 3/ꢀ 4 solution. Ion conductivity was measured using
FiveEasy Plus conductivity meter at different temperature (Mettler
Toledo).
Under N2 atmosphere, compound 4 (0.3 g, 2.25 mmol) was dissolved
in methanol (15 mL) and stirred for 10 min at room temperature, then
compound 2 (1.0 g, 2.25 mmol) and 3–4 drops of formic acid were added
to the solution. The mixture was heated to reflux for 24 h and cooled,
filtered and washed with methanol. Silica gel chromatography with
dichloromethane/ethyl acetate (2/1, v/v) gave compound NDH as pale
yellow solid with the yield of 85.1% (1.1g). m.p. 142–144 ◦C; IR(KBr)
ν
/cmꢀ 1: 3452(-OH), 3251(-OH), 2948(-CH2), 2866(-CH3), 1734(-COO),
1694(-CON), 1657(CON), 1592(-CON), 1504(-Ph), 1466(-CH2), 1388
(-CH3); 1H NMR (500 MHz, DMSO‑d6, Fig. S4) δ (ppm): 8.69 (d, J = 8.0
Hz, 1H, -Nap), 8.57 (d, J = 7.0 Hz, 1H, -Nap), 8.44 (d, J = 8.0 Hz, 1H,
-Nap), 7.92 (t, J = 8.0 Hz, 1H, -Nap), 7.84 (s, 2H, -OH), 7.63 (d, J = 8.5
Hz, 2H, -Ph), 7.26 (d, J = 8.5 Hz, 2H, -Ph), 6.95 (d, J = 8.5 Hz, 1H, -Nap),
2.3. Fabrication of modified electrodes
Before modification, the GCE was polished carefully with 0.3 and
0.05 μm α-alumina powder sequentially, and rinsed thoroughly with
2