A metal framework luminescence based on lone electron-π interaction and its circularly polarized luminescent crystal material

Abstract

The present invention discloses a metal framework luminescence based on lone electron-π interaction and its circularly polarized luminescent crystal material. The metal framework provided by the present invention is prepared by co-assembly with metal ions as shown in Formula I and Formula II or Formula I and Formula III; further, the metal framework and non-chiral molecules or chiral molecules containing lone electrons prepare fluorescent and circularly polarized luminescent materials through host-guest interaction. The present invention first achieves effective fluorescence emission by encapsulating non-chiral guest molecules through the metal framework; and achieves circularly polarized luminescence by encapsulating chiral guest molecules rich in lone electrons. The present invention not only proves that lone electron-π interaction can effectively achieve metal framework fluorescence emission and chirality induction, but also provides a universal method for the development of optical and chiral optical crystal materials.

Description

Technical Field

[0001] The invention relates to a metal frame luminescence based on lone electron-π interaction and a circularly polarized luminescent crystal material thereof, belonging to the field of luminescent materials. Background Art

[0002] Non-covalent interactions play a crucial role in the formation of complex structures in biological systems and the precise control of materials. Among various non-covalent interactions, π-systems involving π-π, XH-π, cation-π, anion-π and lone pair (Lp)-π interactions have attracted increasing attention due to their role in stabilizing high-order structures and developing new functional materials. Compared with other interactions involving π, the significance of Lp-π interactions has only recently been demonstrated and recognized. Lp-π interactions not only affect the stability and reactivity of molecules, but also play a key role in catalysis, molecular recognition, adsorption and the design of new materials. However, their weak interaction force and difficulty in promoting intermolecular charge transfer have limited their application in the field of luminescent materials. The development of luminescent materials based on Lp-π interactions remains a huge challenge.

[0003] Metal-organic frameworks (MOFs) have been extensively studied due to their ordered, confined pores and flexible, tunable structures. They serve as effective platforms for studying weak interactions and chirality. In recent years, circularly polarized luminescence (CPL), an emerging chiral optical phenomenon, has attracted increasing attention due to its promising applications in three-dimensional displays, information security, and asymmetric synthesis. Recently, MOF materials exhibiting CPL have garnered significant attention due to their fabrication flexibility and the wide range of guest molecules they can host. Generally, to construct chiral MOF luminescent materials, chiral elements or scaffolds with point or axial chirality are introduced into the MOF framework. However, the cumbersome synthesis and expensive chiral ligands have limited the development of chiral MOFs. Therefore, it is necessary to explore new mechanisms of action to expand the range of chirally active MOF luminescent materials. Summary of the Invention

[0004] The purpose of the present invention is to provide a metal framework luminescence based on lone electron-π interaction and its circularly polarized luminescent crystal material, which is a metal framework crystal material that emits fluorescence and circularly polarized light by the interaction between a metal organic framework host containing a π system and a guest molecule containing a lone electron.

[0005] The present invention first provides a metal framework crystal material, which is obtained by co-assembling a ligand metal ion and the compound described in 1) or 2) below in an organic solvent by heating, and is a main material with a confined cavity;

[0006] 1) Compounds represented by formula I and compounds represented by formula II;

[0007] 2) Compounds represented by Formula I and compounds represented by Formula III;

[0008]

[0009] Among them, the compound shown in Formula I is a functional molecule of N, N'-di(4-pyridyl)-1,4,5,8-naphthalene diimide (NDIPy) with a π motif. As a basic unit of the metal organic framework, it has an electron-deficient core and serves as an excellent electrophilic group.

[0010] The compound shown in Formula II is 1,4-dicarboxylic acid (BDC), which, as an organic linker of the metal-organic framework, can effectively construct the confined cavity of the metal-organic framework.

[0011] The compound represented by formula III is 4,4'-biphenyldicarboxylic acid (BPDC), which, as an organic linker of the metal-organic framework, can effectively adjust the cavity size of the metal-organic framework.

[0012] Wherein, the molar ratio of the compound represented by formula I to the compound represented by formula II is 1:0.5-2;

[0013] The molar ratio of the compound represented by formula I to the compound represented by formula III is 1:1-3;

[0014] The molar ratio of the compound represented by formula I to the ligand metal ion is 1:0.5-2;

[0015] In the heating co-assembly system, the molar concentration of the compound represented by formula I is 0.25-0.5 mM.

[0016] Preferably, the ligand metal ion is selected from Li + 、Na + , K + , Rb + 、Cs + Mg 2+ , Ca 2+ 、Sr 2+ 、Ba 2+ 、Fe 2+ 、Co 2 + 、Ni 2+ 、Cu 2+ 、Zn 2+ 、Ru 2+ , Rh 2+ 、Cd 2+ , Pb 2+ 、Al 3+ 、Fe 3+ 、Ti 4+ 、Zr 4+ 、Ag + 、Pd2+ , Pt 2+ 、Au 3+ and at least one of Ln-based metal cations.

[0017] Preferably, the organic solvent is N,N-dimethylformamide, N,N-dimethylacetamide or dimethyl sulfoxide;

[0018] The temperature of the heating co-assembly is 70-130° C., and the time is 24-72 hours.

[0019] On the substrate of the metal frame crystal material, the present invention also provides a metal frame fluorescent emitting crystal material, which is constructed by removing the solvent molecules retained in the cavity of the metal frame crystal material and immersing it in achiral solvent guest molecules rich in lone electrons.

[0020] Preferably, the achiral solvent guest molecule is any one of isopropanol, acetone, methyl acetate, n-butyl acetate, isopropyl acetate and tert-butyl acetate, and the structural formula is as follows:

[0021]

[0022] On the substrate of the metal frame crystal material, the present invention further provides a metal frame emitting circularly polarized light crystal material, which is constructed by removing solvent molecules retained in the cavity of the metal frame crystal material and immersing it in a chiral solvent guest molecule rich in lone electrons;

[0023] The present invention encapsulates chiral guest molecules by metal framework, achieves chirality induction of the metal framework, and constructs a metal framework crystal material that emits circularly polarized light;

[0024] Preferably, the chiral solvent guest molecule is any one of tartaric acid-R / S-diethyl ester, tartaric acid-R / S-diisopropyl ester, and dimethyl 2,3-O-isopropyl-R / S-tartrate, and the structural formula is as follows:

[0025]

[0026] In the process of constructing the above materials, the steps to remove the solvent molecules trapped in the cavity are as follows:

[0027] 1) soaking the metal frame crystal material in dichloromethane, and then evaporating the solvent in vacuo;

[0028] 2) The metal framework crystal material is placed in n-hexane for guest exchange, and the solvent is evaporated again in vacuo.

[0029] Preferably, steps 1) and 2) are repeated 3-5 times.

[0030] The present invention constructs an interlocked metal framework crystal material by co-assembling N, N'-di(4-pyridyl)-1,4,5,8-naphthalene diimide (NDIPy) and 1,4-dicarboxylic acid (BDC) or 4,4'-biphenyl dicarboxylic acid (BPDC) ligands with metal ions. Through host-guest interactions, achiral or chiral molecules containing lone electrons are encapsulated in the metal framework cavity to construct efficient fluorescence emission and circularly polarized luminescent crystal materials. This method cleverly utilizes the lone electron-π interaction, not only effectively regulating the luminescence properties, but also providing a new approach for the design of chiral optical crystal materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of preparing luminescent material by encapsulating guest molecules in a metal frame in Example 1 of the present invention.

[0032] Figure 2 This is a fluorescence image of the metal framework A-MOF encapsulating the guest molecule in Example 2 of the present invention.

[0033] Figure 3 This is the fluorescence spectrum of the guest molecule encapsulated in the metal framework A-MOF in Example 2 of the present invention.

[0034] Figure 4 This is a fluorescence image of the guest molecule encapsulated in the metal framework B-MOF in Example 3 of the present invention.

[0035] Figure 5 This is the fluorescence spectrum of the guest molecule encapsulated in the metal framework B-MOF in Example 3 of the present invention.

[0036] Figure 6 Circular dichroism spectrum and circularly polarized luminescence spectrum of R / S-diethyl tartarate encapsulated in the metal frame A-MOF in Example 4 of the present invention.

[0037] Figure 7 Circular dichroism spectrum and circularly polarized luminescence spectrum of R / S-diisopropyl tartarate encapsulated in the metal frame B-MOF in Example 5 of the present invention.

[0038] Figure 8 Circular dichroism spectrum and circularly polarized luminescence spectrum of 2,3-O-isopropylidene-R / S-dimethyl tartrate encapsulated in the metal frame B-MOF in Example 5 of the present invention. DETAILED DESCRIPTION

[0039] The present invention will be further described below with reference to specific examples, but the present invention is not limited to the following examples.

[0040] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0041] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0042] Example 1: Preparation of metal framework A-MOF (Formula I and Formula II) and metal framework B-MOF (Formula I and Formula III), and preparation of metal framework crystal materials that emit fluorescence and circularly polarized light.

[0043] 1) Synthesis of A-MOF: N,N'-di(4-pyridyl)-1,4,5,8-naphthalene diimide (0.21 g, 0.5 mmol), 1,4-dicarboxybenzoic acid (0.083 g, 0.5 mmol), and zinc nitrate hexahydrate (0.149 g, 0.5 mmol) were dispersed in N,N'-methylformamide (50 mL) in a reaction vessel. After ultrasonic mixing, the mixture was heated to 95°C. After being kept at this temperature for 48 hours, the mixture was cooled to room temperature to obtain A-MOF crystals.

[0044] 2) Synthesis of B-MOF: N,N'-di(4-pyridyl)-1,4,5,8-naphthalene diimide (0.105 g, 0.25 mmol), 4,4'-biphenyldicarboxylic acid (0.121 g, 0.5 mmol), and zinc nitrate hexahydrate (0.149 g, 0.5 mmol) were dispersed in N,N'-methylformamide (50 mL) in a reaction vessel. After ultrasonic mixing, the mixture was heated to 80°C. After being kept at this temperature for 48 hours, the mixture was cooled to room temperature to obtain B-MOF crystals.

[0045] 3) Solvent molecules were removed from the original sample from steps 1) and 2) above, retaining the confined cavities. Dichloromethane was added to the original MOF solution and allowed to soak for 60 minutes. The solvent was then evaporated under vacuum, and this step was repeated three times. Subsequently, guest exchange was performed with n-hexane, and the solvent was evaporated again. This process was repeated three times to obtain a solvent-free A-MOF or B-MOF.

[0046] 4) The crystal material obtained in 3) above is directly immersed in a solvent containing the corresponding guest molecule. During this process, the guest molecule is replaced with a new solvent several times to obtain a metal frame crystal material that emits fluorescence or circularly polarized light, such as Figure 1 shown.

[0047] Example 2: Preparation of Luminescent Metal Framework A-MOF Crystal Material

[0048] After pretreatment of the A-MOF crystal material according to step 3) of Example 1, 10 mg of the corresponding crystal material was placed in a 4 ml glass sample vial and filled with 1 ml each of the corresponding solvents, such as isopropyl alcohol (i-PA), acetone (AC), methyl acetate (MA), n-butyl acetate (BA), isopropyl acetate (i-PC), and tert-butyl acetate (t-BA). The sample was immersed in the glass sample vial for 72 hours, with the corresponding solvent replaced every 24 hours. Subsequently, the sample was placed in a 1 mm quartz cuvette for testing and fluorescence imaging.

[0049] like Figure 2 As shown in the figure, under 365 nm UV light irradiation, there was no obvious fluorescence emission in A-MOF@DMF (original solvent), A-MOF@i-PA and A-MOF@t-BA, while blue fluorescence emission was observed in A-MOF@AC, A-MOF@MA, A-MOF@BA and A-MOF@i-PC.

[0050] The A-MOF luminescent metal framework crystal material obtained in step 1) was tested for relevant fluorescence spectra, such as Figure 3 shown.

[0051] Figure 3 The fluorescence spectrum results show that A-MOF is a metal framework crystal material without guest molecules, showing the weakest fluorescence. As the guest molecules rich in lone electrons are encapsulated, the fluorescence gradually increases. In the fluorescence spectrum on the left, A@AC shows a relatively strong blue fluorescence emission at 436nm. This is because the carbonyl lone electron on acetone has better electron donating ability than the encapsulated DMF and i-PA guest molecules. Further, a series of ester guest molecules with strong electron donating ability are encapsulated. Figure 3 The fluorescence spectrum on the right shows that the blue fluorescence intensity at 436 nm gradually decreases, which is consistent with the Figure 1 The phenomenon observed in the fluorescence images is consistent, which is due to the gradual increase in the side chains of the encapsulated ester guest molecules, which hinders the contact between the guest molecules and the A-MOF metal framework cavity sites due to the steric hindrance effect.

[0052] Example 3: Preparation of Luminescent Metal Framework B-MOF Crystal Material

[0053] The luminescent metal framework B-MOF crystal material was prepared according to the method in Example 2.

[0054] like Figure 4As shown in the figure, under 365 nm UV light, B-MOF@DMF (original solvent) and B-MOF@i-PA exhibit light yellow fluorescence. B-MOF@AC, B-MOF@MA, B-MOF@BA, B-MOF@i-PC, and B-MOF@t-BA exhibit bright yellow fluorescence emission.

[0055] The B-MOF luminescent metal framework crystal material obtained in step 1) was tested for related fluorescence spectra, such as Figure 5 shown.

[0056] Figure 5 The fluorescence spectrum results show that B-MOF is a metal framework crystal material without guest molecules, showing the weakest fluorescence. When encapsulating guest molecules rich in lone electrons, as the electron-donating ability of the carbonyl group of the guest molecule gradually increases, fluorescence enhancement is shown at 548nm. Figure 3 Different from the results shown, B-MOF@t-BA also exhibits strong yellow fluorescence emission. This is because the B-MOF building block linker 4,4'-biphenyldicarboxylic acid is longer than the 1,4-dicarboxybenzoic acid molecule of A-MOF, constructing a larger three-dimensional metal framework confined cavity that can accommodate relatively larger and more guest molecules.

[0057] Example 4: Preparation of a Metal-Frame A-MOF Crystal Material Emitting Circularly Polarized Light

[0058] 1) First, a metal framework A-MOF crystal material was prepared by removing the solvent guest molecules according to the method in Example 1. Then, 10 mg of the sample was placed in a 4 ml glass sample vial. 1 ml of R / S-diethyl tartarate chiral guest solvent was added to the sample vial and the sample was immersed for 72 hours, with the corresponding solvent being replaced every 24 hours. Appropriate heating or light grinding can be used to shorten the immersion time. Thus, a metal framework crystal material with chiral properties was obtained.

[0059] 2) Encapsulate the A-MOF in step 1) with tartaric acid-R-diethyl ester ( R Et) or S-diethyl tartarate ( S The crystal materials containing chiral guest molecules (Et) were tested by circular dichroism (CD) and circular polarization (CPL) spectroscopy.

[0060] like Figure 6 As shown in the CD spectrum, A@ R Et shows an upward CD signal, A@ S Et shows a mirror-symmetrical downward CD signal. It can be clearly seen from the CPL spectrum that A@ R Et and A@ SEt showed good CPL signal, g lum The value is 1.0×10 -3 The above experimental results show that the A-MOF crystal material achieves chirality induction when encapsulating chiral guest molecules, and exhibits significant circularly polarized luminescence performance.

[0061] Example 5: Preparation of a Metal-Frame B-MOF Crystal Material Emitting Circularly Polarized Light

[0062] 1) First, the metal framework B-MOF crystal material with the solvent guest molecule removed was prepared according to the method in Example 1, and then 10 mg of sample was taken and placed in a 4 ml glass sample bottle, and 1 ml of tartaric acid-R / S-diisopropyl ester ( R iPr / S iPr) and 1 ml dimethyl 2,3-O-isopropyl-R / S-tartrate ( R isoT / S The chiral guest solvent (isoT) was immersed for 72 hours, with the solvent replaced every 24 hours. The immersion time can be shortened by heating or light grinding. Thus, a metal framework crystal material with chiral properties was obtained.

[0063] 2) Encapsulate R-diisopropyl tartarate ( R iPr) or S-diisopropyl tartarate ( S iPr) and dimethyl 2,3-O-isopropyl-R-tartrate ( R soT) or dimethyl 2,3-O-isopropyl-S-tartrate ( S The circular dichroism (CD) and circular polarization (CPL) spectroscopy of the crystal materials containing isoT) chiral guest molecules were tested respectively.

[0064] like Figure 7 As shown in the CD spectrum, B@ R iPr shows a downward CD signal, B@ S iPr shows an upward CD signal. It can be clearly seen from the CPL spectrum that B@ R iPr and B@ S iPr shows downward and upward CPL signals, g lum The value is 2.8×10 -3 .

[0065] like Figure 8 As shown in the CD spectrum, B@ R soT shows an upward CD signal, B@ S isoT shows a downward CD signal. It can be clearly seen from the CPL spectrum that B@ R soT and B@S isoT represents the downward and upward CPL signals, g lum The value is 3.6×10 -3 .

[0066] The above experimental results show that the B-MOF crystal material achieves chirality induction when encapsulating chiral guest molecules, exhibiting significant circularly polarized luminescence properties.

Claims

1. A metal frame fluorescent crystalline material, which is constructed by removing solvent molecules trapped in the cavity of the metal frame crystalline material and then immersing it in an achiral solvent guest molecule rich in lone electrons; The metal framework crystal material is obtained by co-assembling the ligand metal ion and the compound in 1) or 2) below in an organic solvent by heating: 1) Compounds represented by formula I and compounds represented by formula II; 2) Compounds represented by Formula I and compounds represented by Formula III; 2. The metal frame emitting fluorescent crystal material according to claim 1, characterized in that: The molar ratio of the compound represented by formula I to the compound represented by formula II is 1:0.5-2; The molar ratio of the compound represented by formula I to the compound represented by formula III is 1:1-3; The molar ratio of the compound represented by formula I to the ligand metal ion is 1:0.5-2; In the heating co-assembly system, the molar concentration of the compound represented by formula I is 0.25-0.5 mM.

3. The metal frame emitting fluorescent crystal material according to claim 1 or 2, characterized in that: The ligand metal ion is selected from Li + 、Na + , K + , Rb + 、Cs + Mg 2+ , Ca 2+ 、Sr 2+ 、Ba 2+ 、Fe 2+ 、Co 2+ 、Ni 2+ 、Cu 2+ 、Zn 2+ 、Ru 2+ , Rh 2+ 、Cd 2+ , Pb 2+ 、Al 3+ 、Fe 3+ 、Ti 4+ 、Zr 4+ 、Ag + 、Pd 2+ , Pt 2+ 、Au 3+ and at least one of Ln-based metal cations.

4. The metal frame emitting fluorescent crystal material according to claim 1 or 2, characterized in that: The organic solvent is N,N-dimethylformamide, N,N-dimethylacetamide or dimethyl sulfoxide; The temperature of the heating co-assembly is 70-130° C., and the time is 24-72 hours.

5. The metal frame emitting fluorescent crystal material according to claim 1 or 2, characterized in that: The achiral solvent guest molecule is any one of isopropyl alcohol, acetone, methyl acetate, n-butyl acetate, isopropyl acetate and tert-butyl acetate.

6. The metal frame emitting fluorescent crystal material according to claim 1 or 2, characterized in that: The steps to remove the solvent molecules trapped in the cavity are as follows: 1) soaking the metal frame crystal material in dichloromethane, and then evaporating the solvent in vacuo; 2) The metal framework crystal material is placed in n-hexane for guest exchange, and the solvent is evaporated again in vacuo.

7. The metal frame emitting fluorescent crystal material according to claim 6, characterized in that: Repeat steps 1) and 2) 3-5 times.

8. A metal frame crystalline material that emits circularly polarized light, constructed by removing solvent molecules trapped in the cavity of the metal frame crystalline material and then immersing it in a chiral solvent rich in lone electrons and guest molecules; The metal framework crystal material is obtained by co-assembling the ligand metal ion and the compound in 1) or 2) below in an organic solvent by heating: 1) Compounds represented by formula I and compounds represented by formula II; 2) Compounds represented by Formula I and compounds represented by Formula III; 9. The metal frame emitting circularly polarized light crystal material according to claim 8, characterized in that: The molar ratio of the compound represented by formula I to the compound represented by formula II is 1:0.5-2; The molar ratio of the compound represented by formula I to the compound represented by formula III is 1:1-3; The molar ratio of the compound represented by formula I to the ligand metal ion is 1:0.5-2; In the heating co-assembly system, the molar concentration of the compound represented by formula I is 0.25-0.5 mM.

10. The metal frame emitting circularly polarized light crystal material according to claim 8 or 9, characterized in that: The ligand metal ion is selected from Li + 、Na + , K + , Rb + 、Cs + Mg 2+ , Ca 2+ 、Sr 2+ 、Ba 2+ 、Fe 2+ 、Co 2+ 、Ni 2+ 、Cu 2+ 、Zn 2+ 、Ru 2+ , Rh 2+ 、Cd 2+ , Pb 2+ 、Al 3+ 、Fe 3+ 、Ti 4+ 、Zr 4+ 、Ag + 、Pd 2+ , Pt 2+ 、Au 3+ and at least one of Ln-based metal cations.

11. The metal frame emitting circularly polarized light crystal material according to claim 8 or 9, characterized in that: The organic solvent is N,N-dimethylformamide, N,N-dimethylacetamide or dimethyl sulfoxide; The temperature of the heating co-assembly is 70-130° C., and the time is 24-72 hours.

12. The metal frame emitting circularly polarized light crystal material according to claim 8 or 9, characterized in that: The chiral solvent guest molecule is any one of tartaric acid-R / S-diethyl ester, tartaric acid-R / S-diisopropyl ester, and dimethyl 2,3-O-isopropyl-R / S-tartrate.

13. The metal frame emitting circularly polarized light crystal material according to claim 8 or 9, characterized in that: The steps to remove the solvent molecules trapped in the cavity are as follows: 1) soaking the metal frame crystal material in dichloromethane, and then evaporating the solvent in vacuo; 2) The metal framework crystal material is placed in n-hexane for guest exchange, and the solvent is evaporated again in vacuo.

14. The metal frame emitting circularly polarized light crystal material according to claim 13, characterized in that: Repeat steps 1) and 2) 3-5 times.

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