Chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand, and preparation method and application thereof

Abstract

The invention discloses a chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand, a preparation method and application, and belongs to the field of quantum dot ligands, and the structure of the chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand is shown as a formula (I). The ligand has fluorescence and-chiral properties, a stable conjugated structure of the ligand is beneficial to electron transmission and photoelectric conduction, the ligand has excellent universality when being applied to ligand exchange on the surface of a nano quantum dot, an original ligand on the surface of the quantum dot can be replaced, chirality is transmitted to a quantum dot-ligand system, and the quantum dot-ligand system can be used for preparing the quantum dot. The quantum dot-ligand system has a circular dichroism signal which is different from a chiral raw material for synthesizing the ligand and a nitrogen-oxygen ligand of a chiral 8-hydroxyquinoline skeleton. Meanwhile, the preparation method of the ligand is simple, the reaction condition is mild, the reaction efficiency is high, and large-scale preparation and production can be realized. Formula (I)

Description

Technical Field

[0001] This invention relates to the field of quantum dot ligands, and more particularly to a chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand, its preparation method, and its application. Background Technology

[0002] Quantum dots are a class of inorganic semiconductor crystals with nanoscale dimensions. Their unique optoelectronic properties stem from the quantum confinement effect, showing broad application prospects in fields such as displays, bioimaging, and optoelectronic devices. The surface of quantum dots is typically coated with organic ligands. These ligands not only stabilize the nanostructure and prevent aggregation but also modulate its band structure and optical properties, making them key components for functional design. Among numerous ligands, compounds with an 8-hydroxyquinoline backbone are particularly promising quantum dot ligands due to their extended π-conjugated structure and excellent metal chelating ability. They can form stable complexes with metals through N,O-bident coordination.

[0003] However, despite the excellent coordination and photoelectric modulation properties of 8-hydroxyquinoline derivatives, they typically lack chiral structures and cannot induce circular dichroism signals, fundamentally limiting their application in the construction of chiral quantum dots and related spin devices. Currently, the construction of chiral quantum dots relies heavily on a few commercially available chiral small-molecule ligands, such as cysteine, penicillamine, tartaric acid, and glutathione. These molecules can bind to the surface of quantum dots through ligand exchange reactions, endowing them with chiral properties. However, these traditional chiral ligands generally lack large π-conjugated structures, resulting in poor bandgap matching with quantum dots. This limits chiral transfer efficiency and also restricts charge transport performance, impacting their application potential in chiral optoelectronic devices. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand that can replace the original ligands on the surface of quantum dots and transfer the chirality of the ligand molecules to the quantum dot-ligand system; the second purpose is to provide a method for preparing the chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand and its application.

[0005] Technical solution: The chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand with the structure shown in formula (I) of the present invention: Formula (I),

[0006] Among them, R1 and R2 are selected from hydrogen and , , Any combination of structures, where the carbon marked with * is an R-configuration or S-configuration chiral carbon.

[0007] Preferably, the chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand has a structure as shown in formula (II), (III), (IV), (V), (VI), or (VII): ,

[0008] The carbon marked with * is an R-configuration or S-configuration chiral carbon.

[0009] The method for preparing the chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand of the present invention comprises the following steps: reacting an 8-hydroxyquinoline compound with a chiral amine in an organic solvent under the catalysis of an acidic catalyst; precipitating, centrifuging, washing, and drying the precipitate to obtain the chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand; wherein the 8-hydroxyquinoline compound is selected from either 8-hydroxyquinoline-2-carboxaldehyde or 8-hydroxyquinoline-5-carboxaldehyde; and the chiral amine is selected from R-α-methylbenzylamine, S-α-methylbenzylamine, (R)-1-(1-naphthyl)ethylamine, (S)-1-(1-naphthyl)ethylamine, (R)-1-(4-nitro-phenyl)ethylamine, and (S)-1-(4-nitro-phenyl)ethylamine.

[0010] Preferably, the organic solvent is selected from one or more of methanol, ethanol, propanol, tetrahydrofuran, dioxane, N,N-dimethylformamide, and diethyl ether.

[0011] Preferably, the acidic catalyst is selected from any one of acetic acid, dilute hydrochloric acid, dilute sulfuric acid, hydrobromic acid, hydroiodic acid, and phosphoric acid.

[0012] Preferably, the molar ratio of the acidic catalyst to the 8-hydroxyquinoline compound is 0.01-1:1, more preferably 0.05-0.15:1.

[0013] Preferably, the molar ratio of the 8-hydroxyquinoline compound to the chiral amine is 1:1-2.

[0014] Preferably, the reaction temperature is 50-90℃ and the reaction time is 6-12 h.

[0015] Preferably, water is used for precipitation and washing after the reaction; more preferably, the water is deionized water.

[0016] The application of the chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand described in this invention in the surface functionalization of quantum dots.

[0017] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: 1. The chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand has excellent fluorescence performance and chiral properties, and its stable conjugated structure is conducive to electron transfer and carrier transport; 2. The ligand has excellent universality when applied to ligand exchange on the surface of quantum dots, and can replace the original ligands on the surface of quantum dots and transfer chirality to the quantum dot-ligand system, so that it has a circular dichroic signal that is different from both the chiral raw material of the synthesized ligand and the chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand; 3. The preparation method of the ligand is simple, the reaction conditions are mild, the reaction efficiency is high, and large-scale preparation can be achieved. Attached Figure Description

[0018] Figure 1 X-ray diffraction (XRD) patterns of the prepared ZnS, CdS, CdSe, and Mn-doped CdSe quantum dots are shown below. In the image, a is the XRD pattern of ZnS quantum dots, b is the XRD pattern of CdS quantum dots, c is the XRD pattern of CdSe quantum dots, and d is the XRD pattern of Mn-doped CdSe quantum dots.

[0019] Figure 2 Transmission electron microscopy (TEM) images of the prepared ZnS, CdS, CdSe, and Mn-doped CdSe quantum dots, with a scale bar of 10 nm.

[0020] Figure 3 The fluorescence emission spectra of six chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligands with structures as shown in formulas (II), (III), and (IV) are compared with the fluorescence emission spectra of ZnS, CdS, CdSe, or Mn-doped CdSe quantum dots after ligand exchange. Among them, a is the fluorescence emission spectrum of the chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand and its modified quantum dots shown in formula (II), b is the fluorescence emission spectrum of the chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand and its modified quantum dots shown in formula (III), and c is the fluorescence emission spectrum of the chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand and its modified quantum dots shown in formula (IV).

[0021] Figure 4The circular dichroism (CD) spectra of ligand-modified quantum dots (CdS) obtained by exchanging chiral ligands of two chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligands as shown in formula (II) with ZnS, CdS, CdSe, or Mn-doped CdSe quantum dots are shown. In this CD spectrum, a represents the CD spectrum of ZnS (R-ZnS) modified with (R, E)-2-(((1-phenylethyl)imino)methyl)quinoline-8-ol, ZnS (S-ZnS) modified with (S, E)-2-(((1-phenylethyl)imino)methyl)quinoline-8-ol, CdS (R-CdS) modified with (S, E)-2-(((1-phenylethyl)imino)methyl)quinoline-8-ol, and CdS (S-CdS) modified with (S, E)-2-(((1-phenylethyl)imino)methyl)quinoline-8-ol, and CdS (S-CdS) modified with (R, E)-2-(((1-phenylethyl)imino)methyl)quinoline-8-ol). Circular dichroism (CD) spectra of CdSe modified with (S, E)-2-(((1-phenylethyl)imino)methyl)quinoline-8-ol (R-CdSe), CdSe modified with (S, E)-2-(((1-phenylethyl)imino)methyl)quinoline-8-ol (S-CdSe), CdS modified with (R, E)-2-(((1-phenylethyl)imino)methyl)quinoline-8-ol (R-Mn:CdSe), and CdS modified with (S, E)-2-(((1-phenylethyl)imino)methyl)quinoline-8-ol (S-Mn:CdSe). Detailed Implementation

[0022] The technical solution of the present invention will be further described below.

[0023] Example 1: Synthesis of chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligands with the structure shown in formula (II)

[0024] The synthetic route for chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligands with the structure shown in formula (II) is as follows:

[0025]

[0026] 1. The specific synthetic steps for the chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand (R, E)-2-(((1-phenylethyl)imino)methyl)quinoline-8-ol (2-8HQ-R-MBA) are as follows:

[0027] (1) Dissolve 1 mmol of 8-hydroxyquinoline-2-carboxaldehyde (CAS No.: 14510-06-6) in 10 mL of ethanol and heat it at 78 °C to stabilize it under reflux for 30 min; inject 5 mL of ethanol solution containing 1 mmol of R-α-methylbenzylamine (CAS No.: 3886-69-9) at a flow rate of 1 mL / min, and then add 0.1 mmol of acetic acid as a catalyst. The system is then refluxed under stirring for 8 h.

[0028] (2) After the reaction was complete, 50 mL of distilled water was added to the mixture. The resulting suspension was centrifuged at 6440 × g for 10 min, and the supernatant was discarded. The obtained solid was washed three times with distilled water and dried to obtain 203 mg of brownish-black solid (R, E)-2-(((1-phenylethyl)imino)methyl)quinoline-8-ol, with a yield of 74%. Its characterization data are as follows: 1 H NMR (400 MHz, DMSO-d6) δ 8.65 (d, J = 16.0 Hz, 1H), 8.30 (d, J = 8.6 Hz, 1H), 8.20 (d, J =8.7 Hz, 1H), 7.50 (dd, J = 7.7, 2.6 Hz, 2H), 7.39 (q, J = 7.1 Hz, 3H), 7.33 –7.29 (m, 1H), 7.22 (dd, J = 7.7, 1.2 Hz, 1H), 4.74 (q, J = 6.6 Hz, 1H), 2.94(d, J = 28.8 Hz, 1H), 1.68 (d, J = 6.7 Hz, 3H).

[0029] 2. The specific synthetic steps for the chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand (S, E)-2-(((1-phenylethyl)imino)methyl)quinoline-8-ol (2-8HQ-S-MBA) are as follows:

[0030] (1) Dissolve 1 mmol of 8-hydroxyquinoline-2-carboxaldehyde (CAS No.: 14510-06-6) in 10 mL of ethanol and heat it at 78 °C to stabilize it under reflux for 30 min; inject 5 mL of ethanol solution containing 1 mmol of S-α-methylbenzylamine (CAS No.: 2627-86-3) at a flow rate of 1 mL / min, and then add 0.1 mmol of acetic acid as a catalyst. The system is then refluxed under stirring for 8 h.

[0031] (2) After the reaction was complete, 50 mL of distilled water was added to the mixture. The resulting suspension was centrifuged at 6440 × g for 10 min, and the supernatant was discarded. The obtained solid was washed three times with distilled water and dried to obtain 210 mg of brownish-black solid (S, E)-2-(((1-phenylethyl)imino)methyl)quinoline-8-ol, with a yield of 76%. Its characterization data are as follows: 1H NMR (400 MHz, DMSO-d6) δ 8.62 (d, J = 10.1 Hz, 1H), 8.35 (d, J = 8.5 Hz, 1H), 8.14 (d, J =8.7 Hz, 1H), 7.49 – 7.43 (m, 3H), 7.35 (d, J = 7.7 Hz, 2H), 7.30 – 7.26 (m,1H), 7.15 (d, J = 7.4 Hz, 1H), 4.77 (q, J = 6.6 Hz, 1H), 2.50 (s, 1H), 1.56(d, J = 6.6 Hz, 3H).

[0032] Example 2: Synthesis of chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligands with the structure shown in formula (III)

[0033] The synthetic route for chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligands with the structure shown in formula (III) is as follows:

[0034]

[0035] 1. Following the synthesis method in Example 1, the chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand R-2-[(1-naphthylethyl)iminomethyl]quinoline-8-ol (2-8HQ-R-NEA) was synthesized, except that in step 1, 5 mL of an ethanol solution containing 1 mmol (R)-1-(1-naphthyl)ethylamine (CAS No.: 3886-70-2) was injected at a flow rate of 3 mL / min.

[0036] Finally, 250 mg of a dark brown solid (R, E)-2-(((1-phenylethyl)imino)methyl)quinoline-8-ol was obtained, with a yield of 77%. Its characterization data are as follows: 1 H NMR (400 MHz, DMSO-d6) δ 8.70 (s, 1H), 8.40 – 8.32(m, 2H), 8.22 – 8.15 (m, 1H), 7.98 – 7.72 (m, 4H), 7.64 – 7.37 (m, 5H), 7.13(d, J = 7.2 Hz, 1H), 5.65 (d, J = 5.9 Hz, 1H), 1.71 (d, J = 5.6 Hz, 3H).

[0037] 2. Following the synthesis method in Example 1, the chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand S-2-[(1-naphthylethyl)iminomethyl]quinoline-8-ol (2-8HQ-S-NEA) was synthesized. The difference was that in step 1, 5 mL of an ethanol solution containing 1 mmol (S)-1-(1-naphthyl)ethylamine (CAS No.: 10420-89-0) was injected at a flow rate of 3 mL / min.

[0038] Finally, 230 mg of a dark brown solid (S, E)-2-(((1-phenylethyl)imino)methyl)quinoline-8-ol was obtained, with a yield of 71%. Its characterization data are as follows: 1 H NMR (400 MHz, DMSO-d6) δ 8.70 (s, 1H), 8.41 – 7.30(m, 2H), 8.25 – 8.14 (m, 1H), 8.01 – 7.72 (m, 4H), 7.63 – 7.40 (m, 5H), 7.13(d, J = 7.2 Hz, 1H), 5.65 (d, J = 5.9 Hz, 1H), 1.71 (d, J = 5.6 Hz, 3H).

[0039] Example 3: Synthesis of chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligands with the structure shown in formula (IV)

[0040] The synthetic route for the chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand with the structure shown in formula (IV) is as follows:

[0041]

[0042] 1. Following the synthesis method described in Example 1, the chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand (R, E)-2-[(1-(4-nitrophenyl)ethyl)iminomethyl]quinoline-8-ol (2-8HQ-R-p-nitrobenzylamine) was synthesized. The difference was that in step 1, 5 mL of an ethanol solution containing 1 mmol (R)-1-(4-nitrophenyl)ethylamine (CAS No.: 57233-86-0) was injected at a flow rate of 3 mL / min.

[0043] Finally, 245 mg of a brick-red solid (R, E)-2-[(1-(4-nitrophenyl)ethyl)iminomethyl]quinoline-8-ol was obtained, with a yield of 80%. Its characterization data are as follows: 1H NMR (400 MHz, DMSO-d6) δ 8.47 (s, 1H), 8.18 – 8.13 (m, 2H), 7.94 – 7.86 (m, 1H), 7.64 – 7.45 (m, 6H), 6.99 (dd, J =7.5, 1.6 Hz, 1H), 4.87 (q, J = 6.9 Hz, 1H), 1.55 (d, J = 6.9 Hz, 3H).

[0044] 2. Following the synthesis method described in Example 1, the chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand (S, E)-2-[(1-(4-nitrophenyl)ethyl)iminomethyl]quinoline-8-ol (2-8HQ-S-p-nitrobenzylamine) was synthesized. The difference was that in step 1, 5 mL of an ethanol solution containing 1 mmol (S)-1-(4-nitrophenyl)ethylamine (CAS No.: 132873-57-5) was injected at a flow rate of 3 mL / min.

[0045] Finally, 250 mg of a brick-red solid (S, E)-2-[(1-(4-nitrophenyl)ethyl)iminomethyl]quinoline-8-ol was obtained, with a yield of 81%. Its characterization data are as follows: 1 H NMR (400 MHz, DMSO-d6) δ 8.46 (s, 1H), 8.18 – 8.12 (m, 2H), 7.94 – 7.85 (m, 1H), 7.64 – 7.44 (m, 6H), 6.98 (dd, J =7.5, 1.6 Hz, 1H), 4.87 (q, J = 6.9 Hz, 1H), 1.54 (d, J = 6.9 Hz, 3H).

[0046] Example 4: Synthesis of chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligands with the structure shown in formula (V)

[0047] The synthetic route for chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligands with structures as shown in formula (V) is as follows:

[0048]

[0049] 1. Following the synthesis method in Example 1, the chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand (R, E)-5-(((1-phenylethyl)imino)methyl)quinoline-8-ol (5-8HQ-R-MBA) was synthesized, except that the 8-hydroxyquinoline 2-carboxaldehyde in step 1 was replaced with the same molar amount of 8-hydroxyquinoline-5-carboxaldehyde (CAS No.: 2598-30-3).

[0050] The final product was a grayish-brown solid (R, E)-5-(((1-phenylethyl)imino)methyl)quinoline-8-ol, 195 mg, with a yield of 71%. Its characterization data are as follows: 1 H NMR (400 MHz, DMSO-d6) δ 9.85 (d, J = 28.3 Hz, 1H), 8.92 (s, 1H), 8.85 (s, 1H), 7.86 (d, J = 8.0 Hz, 1H), 7.70 (dd, J = 8.7, 4.1Hz, 1H), 7.48 (d, J = 7.6 Hz, 2H), 7.35 (dd, J = 15.4, 7.5 Hz, 4H), 7.23 (d,J = 7.2 Hz, 1H), 7.14 (d, J = 7.7 Hz, 1H), 4.57 (s, 1H), 1.55 (d, J = 6.6 Hz, 3H).

[0051] 2. Following the synthesis method in Example 1, the chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand (S, E)-5-(((1-phenylethyl)imino)methyl)quinoline-8-ol (5-8HQ-S-MBA) was synthesized, except that the 8-hydroxyquinoline 2-carboxaldehyde in step 1 was replaced with the same molar amount of 8-hydroxyquinoline-5-carboxaldehyde;

[0052] Finally, 210 mg of a grayish-brown solid (S, E)-5-(((1-phenylethyl)imino)methyl)quinoline-8-ol was obtained, with a yield of 76%. Its characterization data are as follows: 1 H NMR (400 MHz, DMSO-d6) δ 10.43 (s, 1H), 9.81 (s,1H), 8.91 (d, J = 4.0 Hz, 1H), 8.86 (s, 1H), 7.86 (d, J = 8.1 Hz, 1H), 7.70(dd, J = 8.7, 4.1 Hz, 1H), 7.48 (d, J = 7.6 Hz, 2H), 7.36 (t, J = 7.5 Hz,2H), 7.25 (d, J = 7.3 Hz, 1H), 7.15 (d, J = 8.0 Hz, 1H), 4.53 (s, 1H), 1.55(d, J = 6.6 Hz, 3H).

[0053] Example 5: Synthesis of chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligands with the structure shown in formula (VI)

[0054] The synthetic route for chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligands with structures as shown in formula (VI) is as follows:

[0055]

[0056] 1. Following the synthesis method in Example 2, the chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand (R, E)-5-[(1-naphthylethyl)iminomethyl]quinoline-8-ol (5-8HQ-R-NEA) was synthesized, except that the 8-hydroxyquinoline 2-carboxaldehyde in step 1 was replaced with the same molar amount of 8-hydroxyquinoline-5-carboxaldehyde;

[0057] Finally, 270 mg of a grayish-brown solid (R, E)-5-[(1-naphthylethyl)iminomethyl]quinoline-8-ol was obtained, with a yield of 83%. Its characterization data are as follows: 1 H NMR (400 MHz, DMSO-d6) δ 8.48 (s, 1H), 8.07 (dd, J= 7.2, 1.4 Hz, 1H), 7.92 – 7.86 (m, 1H), 7.90 – 7.81 (m, 2H), 7.85 – 7.77 (m,1H), 7.65 – 7.35 (m, 8H), 7.00 (d, J = 7.5 Hz, 1H), 5.27 – 5.17 (m, 1H), 1.62 (d, J = 6.9 Hz, 3H).

[0058] 2. Following the synthesis method in Example 2, the chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand (S, E)-5-[(1-naphthylethyl)iminomethyl]quinoline-8-ol (5-8HQ-S-NEA) was synthesized, except that the 8-hydroxyquinoline 2-carboxaldehyde in step 1 was replaced with the same molar amount of 8-hydroxyquinoline-5-carboxaldehyde;

[0059] Finally, 250 mg of a grayish-brown solid (S, E)-5-[(1-naphthylethyl)iminomethyl]quinoline-8-ol was obtained, with a yield of 77%. Its characterization data are as follows: 1H NMR (400 MHz, DMSO-d6) δ 8.49 (s, 1H), 8.05 (dd, J= 7.2, 1.4 Hz, 1H), 7.92 – 7.86 (m, 1H), 7.91 – 7.81 (m, 2H), 7.86 – 7.77 (m,1H), 7.65 – 7.34 (m, 8H), 7.01 (d, J = 7.4 Hz, 1H), 5.27 – 5.15 (m, 1H), 1.61 (d, J = 7.0 Hz, 3H).

[0060] Example 6: Synthesis of chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligands with the structure shown in formula (VII)

[0061] The synthetic route for chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligands with the structure shown in formula (VII) is as follows:

[0062]

[0063] 1. Following the synthesis method in Example 3, the chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand (R, E)-5-[(1-(4-nitrophenyl)ethyl)iminomethyl]quinoline-8-ol (5-8HQ-R-p-nitrobenzylamine) was synthesized, except that the 8-hydroxyquinoline 2-carboxaldehyde in step 1 was replaced with the same molar amount of 8-hydroxyquinoline-5-carboxaldehyde;

[0064] Finally, 240 mg of a reddish-brown solid (R, E)-5-[(1-(4-nitrophenyl)ethyl)iminomethyl]quinoline-8-ol was obtained, with a yield of 78%. Its characterization data are as follows: 1 H NMR (400 MHz, DMSO-d6) δ 8.86 (d, J = 7.5Hz, 1H), 8.54 (s, 1H), 8.43 – 8.34 (m, 1H), 8.20 – 8.10 (m, 2H), 7.59 – 7.43(m, 4H), 7.03 (d, J = 7.6 Hz, 1H), 4.85 (q, J = 6.8 Hz, 1H), 1.55 (d, J = 6.9Hz, 3H).

[0065] 2. Following the synthesis method in Example 3, the chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand (S, E)-5-[(1-(4-nitrophenyl)ethyl)iminomethyl]quinoline-8-ol (5-8HQ-S-p-nitrobenzylamine) was synthesized, except that the 8-hydroxyquinoline 2-carboxaldehyde in step 1 was replaced with the same molar amount of 8-hydroxyquinoline-5-carboxaldehyde;

[0066] Finally, 220 mg of a reddish-brown solid (S, E)-5-[(1-(4-nitrophenyl)ethyl)iminomethyl]quinoline-8-ol was obtained, with a yield of 72%. Its characterization data are as follows: 1 H NMR (400 MHz, DMSO-d6) δ 8.85 (d, J = 7.5Hz, 1H), 8.55 (s, 1H), 8.43 – 8.33 (m, 1H), 8.20 – 8.11 (m, 2H), 7.59 – 7.41(m, 4H), 7.04 (d, J = 7.6 Hz, 1H), 4.86 (q, J = 6.8 Hz, 1H), 1.56 (d, J = 6.9Hz, 3H).

[0067] Experimental Example 1: Chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligands for ligand exchange on quantum dot surfaces

[0068] ZnS quantum dots were synthesized according to the method described in Xu, X.; Ji, J.; Wang, G.; You, X. Exciton Coupling of Surface Complexes on a Nanocrystal Surface. ChemPhysChem 2014, 146 (3), 445–449.

[0069] CdS quantum dots were synthesized according to the method described in Liu, H.; Cao, DB; Li, ST; Qi, F.; Li, ZY; Yuan, WK. A Generic Method for Rational Scalable Synthesis of Monodisperse Metal Sulfide Nanocrystals. Nano Lett. 2012, 12 (11), 5856–5860.

[0070] CdSe quantum dots were synthesized according to the method described in Qu, L.; Peng, X. Control of Photoluminescence Properties of CdSeNanocrystals in Growth. J. Am. Chem. Soc. 2002, 124 (9), 2049–2055.

[0071] Mn-doped CdSe quantum dots were synthesized according to the method described in Mikulec, FV; Kuno, M.; Bennati, M.; Hall, DA; Griffin, RG; Bawendi, MG Organometallic Synthesis and Spectroscopic Characterization of Manganese-Doped CdSe Nanocrystals. J. Am. Chem. Soc. 2000, 122 (11), 2532–2540.

[0072] The obtained ZnS, CdS, CdSe, and Mn-doped CdSe quantum dots were all redispersed in cyclohexane after preparation to obtain a quantum dot solution with a concentration of 30 mg / mL for later use.

[0073] The prepared quantum dot solution was dropped into the sample groove of a silicon wafer. After the sample dried, the crystal structure of the sample was characterized by X-ray diffraction. At the same time, the prepared quantum dot solution was diluted to 5 mg / mL, dropped onto a copper grid, air-dried, and then photographed using a transmission electron microscope.

[0074] The X-ray diffraction results of the prepared ZnS, CdS, CdSe, and Mn-doped CdSe quantum dots are as follows: Figure 1 As shown, the standard diffraction card (PDF card) data were obtained from MDI JADE software, and the transmission electron microscope observation results are as follows. Figure 2 As shown, the obtained quantum dots have a size of 5-7 nm, and the above results indicate that the quantum dots were successfully prepared.

[0075] Take 50 μL of the above-synthesized ZnS, CdS, CdSe, or Mn-doped CdSe quantum dot cyclohexane solution with a concentration of 30 mg / mL, mix it with 50 μL of the chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand ethanol solution obtained in Examples 1, 2, or 3 with a concentration of 25 mg / mL, add it to 3 mL of cyclohexane and mix thoroughly. Then, add 5 μL of 0.01 mol / L NaOH solution to the above mixture. After the reaction is complete, chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand modified quantum dots are obtained and stored in cyclohexane solution for later use.

[0076] 1. Fluorescence performance determination.

[0077] Take 10 μL of the six chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligands with a concentration of 30 mg / mL obtained above and add them to 3 mL of ethanol solution. Measure the fluorescence emission spectra of the six chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligands under excitation at a wavelength of 365 nm. Then take a quantum dot cyclohexane solution modified with the above six chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligands and measure the fluorescence emission spectra under excitation at a wavelength of 365 nm in the same way.

[0078] Table 1 Comparison of peak positions in fluorescence emission spectra

[0079]

[0080] The results are as follows Figure 3 As shown in Table 1, all six chiral 8-hydroxyquinoline nitrogen-oxygen ligands prepared using 8-hydroxyquinoline-2-carboxaldehyde as the backbone exhibit good fluorescence properties. Furthermore, a longitudinal comparison of the fluorescence emission peak positions of these six chiral 8-hydroxyquinoline nitrogen-oxygen ligands reveals that ligands with larger conjugated structures exhibit a greater redshift in their fluorescence emission peak positions. These data indicate that chiral 8-hydroxyquinoline nitrogen-oxygen ligands prepared using 8-hydroxyquinoline-5-carboxaldehyde as the backbone also possess good fluorescence properties.

[0081] 2. Circular Dichroism (CD) Signal Measurement

[0082] Take the prepared quantum dot cyclohexane solution modified with (R, E)-2-(((1-phenylethyl)imino)methyl)quinoline-8-ol ligand or (S, E)-2-(((1-phenylethyl)imino)methyl)quinoline-8-ol ligand and scan the circular dichroism signal in the range of 300 nm-600 nm using a circular dichroism spectrometer.

[0083] The results are as follows Figure 4 As shown, all chiral ligand-modified quantum dots exhibited a distinct circular dichroism signal, indicating that the prepared chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligands possess significant universality, capable of transmitting the fluorescence and chiral signals of the ligand itself to the quantum dots.

Claims

1. A chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand with the structure shown in formula (I): Formula (I), in, R1 and R2 are selected from hydrogen and , , Any combination of structures, where the carbon marked with * is an R-configuration or S-configuration chiral carbon.

2. The chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand according to claim 1, characterized in that, It has a structure as shown in formula (II) or formula (III) or formula (IV) or formula (V) or formula (VI) or formula (VII): ， The carbon marked with * is an R-configuration or S-configuration chiral carbon.

3. A method for preparing the chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand as described in claim 1, characterized in that, The steps are as follows: 8-hydroxyquinoline compound is reacted with a chiral amine in an organic solvent under the catalysis of an acidic catalyst. After the reaction, the precipitate is collected, centrifuged, washed, and dried to obtain a chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand. The 8-hydroxyquinoline compound is selected from either 8-hydroxyquinoline-2-carboxaldehyde or 8-hydroxyquinoline-5-carboxaldehyde, and the chiral amine is selected from R-α-methylbenzylamine, S-α-methylbenzylamine, (R)-1-(1-naphthyl)ethylamine, (S)-1-(1-naphthyl)ethylamine, (R)-1-(4-nitro-phenyl)ethylamine, and (S)-1-(4-nitro-phenyl)ethylamine.

4. The preparation method according to claim 3, characterized in that, The organic solvent is selected from one or more of methanol, ethanol, propanol, tetrahydrofuran, dioxane, N,N-dimethylformamide, and diethyl ether.

5. The preparation method according to claim 3, characterized in that, The acidic catalyst is selected from any one of acetic acid, dilute hydrochloric acid, dilute sulfuric acid, hydrobromic acid, hydroiodic acid, and phosphoric acid.

6. The preparation method according to claim 3, characterized in that, The molar ratio of the acidic catalyst to the 8-hydroxyquinoline compound is 0.01-1:

1.

7. The preparation method according to claim 3, characterized in that, The molar ratio of the 8-hydroxyquinoline compound to the chiral amine is 1:1-2.

8. The preparation method according to claim 3, characterized in that, The reaction temperature is 50-90℃ and the reaction time is 6-12 h.

9. The preparation method according to claim 3, characterized in that, The reaction is followed by precipitation and washing with water.

10. The use of the chiral 8-hydroxyquinoline skeleton nitrogen-oxygen ligand as described in any one of claims 1-2 in the surface functionalization of quantum dots.

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