A tetraphenylethylene spiropolymer and its asymmetric synthesis method

Abstract

The present invention relates to a tetraphenylethylene helix and its asymmetric synthesis method, belonging to the fields of chemistry and materials. By using an optically active chiral p-phenylenediamine derivative to carry out an intramolecular nucleophilic substitution reaction with TPE dicyclic tetrachloromethylene, two enantiomers of the left helix (M) and the right helix (P) of the TPE tetracyclic tetraamine helix are obtained, avoiding the time-consuming and costly chiral separation by high-performance liquid chromatography. The M-TPE helix and the P-TPE helix obtained in the present invention can display circular dichroism (CD) and circularly polarized light (CPL) signals with very good mirror symmetry. After the M-TPE and P-TPE helices are respectively doped into the liquid crystal molecule 5CB, the CPL signal can be greatly amplified, and the CPL signal can be transmitted to achiral Nile red. The absolute CPL asymmetry factor can reach 0.43, and the fluorescence quantum yield reaches 71%, showing the potential for use as a display material.

Description

Technical Field

[0001] The present invention belongs to the fields of chemistry and materials. More specifically, it relates to a tetraphenylethylene helix and an asymmetric synthesis method thereof, and particularly to the asymmetric synthesis of tetraphenylethylene helix enantiomers and the chiral optical properties of helical enantiomers. Background Art

[0002] Circularly-polarized luminescence (CPL) has great application potential in 3D display, information processing and storage, molecular switches, biological probes and identification, chiral sensors, asymmetric photoreactions, etc. In recent years, it has attracted extensive attention and research and has become a research frontier in the fields of chemistry and materials (Sci. China Chem. 2021, 64, 2060–2104). The two most basic indicators for measuring the performance of CPL active materials are the dissymmetry factor and the fluorescence quantum yield. However, the two main indicators of the currently reported CPL materials are generally relatively low, which limits their applications. Aggregation-Induced Emission (AIE) organic compounds have great application value in optoelectronic materials, chemical and biological sensors, etc. Their chiral AIE molecules also have great advantages in constructing CPL active materials because they have strong fluorescence in the solid state (Chem. Rev. 2015, 115, 11718–11940), which has attracted more and more research interest. We previously used the most typical AIE molecule TPE, connected it into four rings within the molecule, or connected methyl groups at the ortho positions of the four benzene rings of TPE to increase steric hindrance to fix the propeller conformation of TPE, and obtained the racemate of TPE helix. Then, chiral separation was carried out using a high-performance liquid chromatography (HPLC) chiral column to obtain M- and P-type enantiomers, which can not only exhibit strong CPL activity but also have a nearly quantitative fluorescence quantum yield (Mater. Horiz. 2020, 7, 3209-3216; Chinese invention patents, patent numbers: 201610688164.7 and 202110849970.9), and have the potential for use in screen displays. However, splitting these TPE helices into two pure enantiomers of M- and P-types requires expensive HPLC instruments and chiral columns for separation, which is very time-consuming and laborious. For some enantiomers with very low polarity, multi-stage tandem separation is also required, and only a few milligrams of samples can be separated, which is not convenient for large-scale preparation. Summary of the Invention

[0003] The purpose of the present invention is to provide two enantiomers of TPE helix, without the need for chiral separation. The obtained enantiomers have strong CD signals and CPL signals, thereby solving the technical problem of complex steps in the separation of TPE helix in the prior art.

[0004] According to the first aspect of the present invention, there is provided a compound having the structure shown in Formula I below:

[0005]

[0006] Wherein: R = cyclohexyl, phenyl or n-hexyl.

[0007] According to another aspect of the present invention, there is provided a method for preparing the compound, characterized in that a compound of Formula II, a compound of Formula III, anhydrous cesium carbonate and tetrahydrofuran are mixed evenly, heated under reflux, the solvent is distilled off under reduced pressure, and then column purification is carried out to obtain the compound shown in Formula I. The reaction formula is as follows:

[0008]

[0009] When the configuration of the compound of Formula III is (R,R), the compound of Formula I obtained is the right helix; when the configuration of the compound of Formula III is (S,S), the compound of Formula I obtained is the left helix.

[0010] Preferably, the feeding ratio of the compound of Formula II, the compound of Formula III, anhydrous cesium carbonate and tetrahydrofuran is in turn: (1 - 3) g : (0.5 - 2) g : (0.3 - 1) g : (100 - 1000) mL.

[0011] Preferably, the time for heating under reflux is 4 - 30 hours.

[0012] Generally speaking, compared with the prior art through the above technical solutions conceived by the present invention, the following technical advantages are mainly possessed:

[0013] (1) By using an optically active chiral p-phenylenediamine derivative in the present invention, an intramolecular nucleophilic substitution reaction is carried out with TPE dicyclotetrachloromethylene to obtain two enantiomers of the left helix (M) and the right helix (P) of the TPE tetracyclic tetraamine helix, avoiding the time-consuming and costly chiral separation by high-performance liquid chromatography. The obtained M-TPE helix and P-TPE helix enantiomers can display circular dichroism (CD) spectra and CPL spectra with good mirror symmetry and strong signals. After being doped into the liquid crystal molecule 5CB, the CPL signal can be greatly amplified, and the CPL signal can be transmitted to achiral Nile red. The absolute CPL asymmetry factor can reach 0.43, and the fluorescence quantum yield can reach 71%, having the potential to be used as a screen display material.

[0014] (2) In the present invention, the tetraphenylethylene helix compound can obtain a single left helix (M) and a single right helix (P) respectively through a one-step reaction, and has the performance of emitting circularly polarized fluorescence (CPL).

[0015] (3) The structure of the present invention is determined by means of tests such as NMR, HRMS, single crystal X-ray diffraction, IR, Mp, UV-Vis, optical rotation, fluorescence spectrum, etc., and the yield reaches 40%-90%. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 1H-NMR spectrum of the TPE helical molecule I (R = phenyl) in CDCl 3 3 1 .

[0017] Figure 2 13C-NMR spectrum of the TPE helical molecule I (R = phenyl) in CDCl 3 3 13 .

[0018] Figure 3 High resolution mass spectrum (HRMS spectrum) of the TPE helical molecule I (R = phenyl).

[0019] Figure 4 Crystal structures of the left-handed helix M-I and right-handed helix P-I of the TPE helical molecule I (R = phenyl).

[0020] Figure 5 CD spectra and absorption spectra of the enantiomers of the TPE helical molecules M-I and P-I (R = phenyl); solvent THF, concentration 1.0×10 -3 -5M.

[0021] Figure 6 -3 CPL spectra and absorption spectra of the enantiomers of the TPE helical molecules M-I and P-I (R = phenyl); solvent THF, concentration 1.0×10

[0022] Figure 7 CPL spectra of the enantiomers of the TPE helical molecules M-I and P-I (R = n-hexyl) respectively doped in the liquid crystal 5CB; the doping amount is in weight percentage.

[0023] Figure 8 CPL spectra of the enantiomers of the TPE helical molecules M-I and P-I (R = n-hexyl) respectively doped with Nile red (N) in the liquid crystal 5CB; the doping amount is 0.5% by weight for both. DETAILED DESCRIPTION OF THE INVENTION

[0024] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0025] The compound of the structure shown in formula I of the present invention:

[0026]

[0027] Wherein: R = cyclohexyl, phenyl or n-hexyl.

[0028] Figure 1 TPE helical molecule I (R = phenyl) in CDCl 3 In 1 H-NMR spectrum.

[0029] Figure 2 TPE helical molecule I (R = phenyl) in CDCl 3 In 13 C-NMR spectrum.

[0030] Figure 3 This is the high-resolution mass spectrum (HRMS spectrum) of TPE helical molecule I (R = phenyl).

[0031] Figure 4 This is the crystal structure of TPE helical molecule I (R = phenyl) left-handed helical MI and right-handed helical PI.

[0032] The following are specific embodiments

[0033] Example 1

[0034]

[0035] Cs 2 CO 3 / THF / reflux.

[0036] The compound of formula II (1-3 g), the compound of formula (R,R)-III (R = phenyl) (0.5-2 g), anhydrous cesium carbonate (0.3-1 g) and tetrahydrofuran (100-1000 mL) are added to a round-bottom flask. After the reaction mixture is heated to reflux for 4-30 hours, the solvent is evaporated under reduced pressure and the residue is purified by silica gel chromatography to obtain a white P-type enantiomer with a yield of 80-90%.

[0037] Example 2

[0038]

[0039] Cs 2 CO 3 / THF / reflux.

[0040] The compound of formula II (1 - 3 g), the compound of formula (S,S)-III (R = phenyl) (0.5 - 2 g), cesium carbonate anhydrous (0.3 - 1 g) and tetrahydrofuran (100 - 1000 mL) were added to a round-bottom flask. After the reaction mixture was heated under reflux for 4 - 30 hours, the solvent was evaporated under reduced pressure. The residue was purified by silica gel column chromatography to obtain the white M-form enantiomer with a yield of 80 - 90%.

[0041] Example 3

[0042] In tetrahydrofuran with a concentration of 5 mg / mL, the specific rotation [α] of M-I (R = phenyl) 20 D = +700°. In tetrahydrofuran with a concentration of 4 mg / mL, the specific rotation [α] of P-I (R = phenyl) 20 D = -700°.

[0043] Example 4

[0044] The two helical enantiomers of formula I (R = phenyl) were separately dissolved in a THF solution to prepare a solution with a concentration of 1.0×10 -3 M. The CD spectrum was measured. The maximum CD signal intensity of M-I in the long-wavelength direction was +230 mdeg, and that of P-I was -230 mdeg. And there was a double-signal band at 230 nm - 450 nm, indicating the TPE helical structure. Moreover, the CD spectra of M-I and P-I were mirror images of each other, indicating that one was a left-handed helix and the other was a right-handed helix.

[0045] Its CD spectrum is shown in Figure 5 .

[0046] Example 5

[0047] The two helical enantiomers of formula I (R = phenyl) were separately dissolved in a THF solution to prepare a solution with a concentration of 1.0×10 -3 M. The CPL spectrum was measured. At about 500 nm, M-I showed a positive CPL signal with an asymmetry factor of +2.0×10 -3 , and P-I showed a negative CPL signal with an asymmetry factor of -2.0×10 -3 , which were mirror images of each other.

[0048] Its CPL spectrum is shown in Figure 6 .

[0049] Example 6

[0050] The TPE helical molecule I (R = n-hexyl) was doped in the liquid crystal 5CB, and the doping weight percentage varied from 0.2%, 0.3%, 0.5% to 1%. In the M-I-5CB mixture, the CPL signal of M-I around 520 nm enhanced in the negative direction with the increase of the doping amount; while in the P-I-5CB mixture, the CPL signal around 520 nm enhanced in the positive direction with the increase of the doping amount, showing a mirror image relationship. When the CPL signal was the strongest, the CPL asymmetry factors at around 520 nm were +0.08 and -0.08 respectively, which was 30 times higher compared with that in the THF solution.

[0051] Its CPL spectrum is shown in Figure 7 .

[0052] Example 7

[0053] The TPE helical molecule I (R = n-hexyl) and the achiral fluorescent molecule Nile Red were co-doped in the liquid crystal 5CB, and the doping weight percentage of both was 0.5%. In the CPL spectrum of the M-I-Nile Red-5CB mixture, a strong CPL signal of Nile Red appeared at around 600 nm, indicating that the chirality of the helical molecule I was transferred to the achiral Nile Red molecule, and M-I induced a positive CPL signal while P-I induced a negative CPL signal, and the direction of the Nile Red CPL signal was controlled by the helical direction of the helical molecule I. The CPL asymmetry factors were +0.43 and -0.43 respectively. At this time, the fluorescence quantum yields of both the M-I-Nile Red-5CB mixture and the P-I-Nile Red-5CB mixture were 71%.

[0054] Its CPL spectrum is shown in Figure 8 .

[0055] Those skilled in the art can easily understand that the above description is only the preferred embodiments of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A compound having the structure shown in Formula I: Wherein: R = phenyl or n - hexyl.

2. The preparation method of the compound according to claim 1, Characterized in that Mix the compound of Formula II, the compound of Formula III, cesium carbonate anhydrous and tetrahydrofuran, heat under reflux, then distill off the solvent under reduced pressure, and then carry out column chromatography purification to obtain the compound of Formula I. The reaction formula is as follows: When the configuration of the compound of Formula III is (R,R) type, the obtained compound of Formula I is a right - handed helix; when the configuration of the compound of Formula III is (S,S) type, the obtained compound of Formula I is a left - handed helix.

3. The preparation method according to claim 2, Characterized in that The feeding ratio of the compound of Formula II, the compound of Formula III, cesium carbonate anhydrous and tetrahydrofuran is (1 - 3) g:(0.5 - 2) g:(0.3 - 1) g:(100 - 1000) mL in sequence.

4. The preparation method according to claim 2 or 3, Characterized in that The time of heating under reflux is 4 - 30 hours.

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