Use of heteroatom-containing non-conjugated small molecules in fluorescence

Abstract

The application discloses application of a kind of non-conjugated small molecule containing heteroatom in fluorescence field.The non-conjugated small molecule containing heteroatom has any one of the following formula (I)-(IV) structure: compared with most non-conjugated polymers (such as polyacrylonitrile) containing a large number of heteroatoms, the application makes full use of four heteroatoms in small molecules to form intramolecular stable space interaction between lone pair electrons, thereby realizing more efficient luminescent performance, realizing efficient use of lone pair electrons brought by heteroatom.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of fluorescent materials, in particular to the application of non-conjugated small molecules containing heteroatoms in the field of fluorescence. BACKGROUND

[0002] Weakly interacting light emission often occurs in molecules, solids or nanostructures, whose electronic structure and energy level distribution are different from traditional valence bond conjugated materials. Therefore, the luminescence of non-conjugated materials often exhibits different luminescence characteristics and kinetic behavior from traditional valence bond conjugated materials.

[0003] Currently, it is challenging to synthesize long-wavelength non-conjugated light-emitting materials, especially for non-conjugated small molecule materials. In non-conjugated polymers, a class of cluster light-emitting polymer materials containing a large number of heteroatoms has been widely studied (such as polyacrylonitrile and polypeptides). Although this type of material does not contain aromatic structures, it can utilize the polymerization effect to bring a large number of heteroatoms on the polymer chain close to each other to form stable spatial interactions, thereby inducing long-wavelength cluster light emission.

[0004] However, the introduction of a large number of heteroatoms to produce cluster light emission may be accompanied by some drawbacks.

[0005] First, complexity increases: the introduction of a large number of heteroatoms may lead to the complexity of the structure and composition of the material. This may increase the complexity of synthesis, preparation and analysis of the photophysical properties of these materials, making the research and application of cluster light-emitting materials more difficult.

[0006] Second, impurity effect: relatively active heteroatoms may introduce additional impurity levels in trace amounts, which may interfere with the cluster light emission process, leading to unpredictable photophysical phenomena.

[0007] Third, increased spectral width: the introduction of a large number of heteroatoms may lead to an increase in the width of the spectrum, as the distance between the interactions of heteroatoms in the polymer is varied and uncontrollable, which may result in a wide peak emission of cluster light emission and reduce the efficiency of cluster light emission.

[0008] Fourth, material instability: certain heteroatoms may make the material unstable, leading to material decomposition during preparation, storage or use, which may limit the application of cluster light-emitting materials.

[0009] Fifth, resource waste: the synthesis and preparation of cluster light-emitting materials with a large number of heteroatoms may require more heteroatom-containing raw materials, but in fact, a large number of heteroatoms in these polymers are not truly utilized in the photophysical process of cluster light emission, i.e. the utilization efficiency of heteroatoms is low.

[0010] Some partially reported cluster light-emitting materials containing heteroatoms are listed below, most of which are still in the blue light-emitting region and have low quantum efficiency.

[0011]

[0012] In summary, non-conjugated polymer materials can produce non-traditional cluster light-emission by introducing a large number of heteroatoms, but the precise regulation of the interaction between heteroatoms has not been achieved, which can be achieved by introducing heteroatoms into small molecules.

[0013] It is well known that non-conjugated small molecules are excellent research models for studying non-conjugated photophysical processes due to their clear molecular structure, but it is difficult to obtain the heteroatom accumulation effect like polymers due to the small skeleton.

[0014] Therefore, it is a scientific problem worth thinking and exploring to introduce limited heteroatoms at appropriate sites of small molecule skeletons and to introduce which heteroatoms to induce efficient light emission. SUMMARY

[0015] The application provides application of non-conjugated small molecules containing heteroatoms in the field of fluorescence, and the non-conjugated small molecules containing heteroatoms have any one of structures shown in the following formula (I) to (IV):

[0016] which can be recorded as compound o-2Bmz;

[0017] which can be recorded as compound o-1Bmz-1Btz;

[0018] which can be recorded as compound o-2Btz;

[0019] which can be recorded as compound o-2Bxz.

[0020] The four non-conjugated small molecules containing heteroatoms described above can be prepared by the prior art.

[0021] The non-conjugated small molecules containing heteroatoms have an absorption wavelength of 200-500 nm.

[0022] The non-conjugated small molecules containing heteroatoms with the structure shown in formula (III) have a maximum emission wavelength of 470-490 nm.

[0023] The non-conjugated small molecules containing heteroatoms with the structure shown in formula (III) have a fluorescence intensity that is enhanced with decreasing temperature.

[0024] The non-conjugated small molecules containing heteroatoms with the structure shown in formula (IV) have a maximum emission wavelength of 550-600 nm.

[0025] For non-conjugated small molecules containing heteroatoms with the structure shown in formula (IV), the excitation wavelength gradually increases from 340 nm to 440 nm, and the corresponding emission peaks can gradually change from double peaks to single peaks. The maximum emission wavelengths corresponding to the double peaks can be 460–480 nm and 560–680 nm, and the maximum emission wavelengths corresponding to the single peaks can be 520–560 nm.

[0026] The present invention also provides a fluorescent material comprising a solvent and a non-conjugated small molecule containing heteroatoms having a structure as shown in any of formulas (I) to (IV).

[0027] The solvent may include at least one of ethanol, ethyl acetate, n-hexane, dichloromethane, sulfonium chloride, N,N-dimethylformamide, tetrahydrofuran, and water.

[0028] The present invention also provides a fluorescence modulation method for non-conjugated small molecules containing heteroatoms, which increases the concentration of the non-conjugated small molecules containing heteroatoms in the solution, and / or, by adding a poor solvent, causes the non-conjugated small molecules containing heteroatoms to aggregate in the solution, resulting in a red shift of the emission wavelength, the appearance of a new long-wave emission peak, and an enhancement of fluorescence intensity;

[0029] The non-conjugated small molecule containing heteroatoms has a structure as shown in any of formulas (I) to (IV).

[0030] This invention employs a strategy of achieving efficient luminescence in non-conjugated small molecules using heteroatoms. By utilizing a small number of heteroatoms, stable spatial interactions between lone pairs of electrons can be formed within the non-conjugated luminescent small molecules, thereby achieving efficient luminescence at long wavelengths (e.g., above 470 nm). This strategy solves the problem of a large number of heteroatoms in non-conjugated polymers not being utilized for luminescence, achieving efficient heteroatom utilization within small molecules and thus enabling efficient luminescence in non-conjugated small molecules.

[0031] For example, compared to polymer cluster luminescent materials containing a large number of heteroatoms, the compound o-2Bxz of the present invention can form strong intramolecular lone pair electron interactions by introducing only 2 oxygen heteroatoms and 2 N heteroatoms into a relatively rigid diaryl skeleton, thereby inducing efficient luminescence (the quantum efficiency of the crystalline state can reach 24%).

[0032] This invention can also control the emission wavelength of light by regulating the ability of heteroatoms to provide lone pair electrons, wherein the maximum emission peak of the crystal of compound o-2Bxz reaches 560 nm.

[0033] Furthermore, this invention discovers that if the lone pair electrons of a heteroatom participate in hydrogen bonding, it will inhibit the formation of strong spatial interactions between lone pairs electrons with adjacent heteroatoms, thus failing to induce efficient luminescence.

[0034] Compared with the prior art, the beneficial effects of this invention are as follows:

[0035] Compared to most non-conjugated polymers containing a large number of heteroatoms (such as polyacrylonitrile), this invention makes full use of the four heteroatoms within a small molecule to form stable spatial interactions between lone pairs of electrons within the molecule, thereby achieving more efficient luminescence performance and realizing the efficient utilization of lone pairs of electrons carried by heteroatoms. Attached Figure Description

[0036] Figure 1 o-dibenzimidazole methane 1 H NMR spectrum;

[0037] Figure 2 o-dibenzimidazole methane 13 C10 NMR spectrum;

[0038] Figure 3 This is the high-resolution mass spectrum of o-dibenzimidazole methane;

[0039] Figure 4 It is o-benzimidazole-benzothiazolium methane 1 H NMR spectrum;

[0040] Figure 5 It is o-benzimidazole-benzothiazolium methane 13 C10 NMR spectrum;

[0041] Figure 6 This is the high-resolution mass spectrum of o-benzimidazole-benzothiazolium methane;

[0042] Figure 7 o-dibenzothiazolylmethane 1 H NMR spectrum;

[0043] Figure 8 o-dibenzothiazolylmethane 13 C10 NMR spectrum;

[0044] Figure 9 This is the high-resolution mass spectrum of o-dibenzothiazolium methane;

[0045] Figure 10 o-dibenzoxazolemethane 1 H NMR spectrum;

[0046] Figure 11 o-dibenzoxazolemethane 13 C10 NMR spectrum;

[0047] Figure 12 This is the high-resolution mass spectrum of o-dibenzoxazolemethane;

[0048] Figure 13 The UV absorption spectra of acetonitrile solutions containing non-conjugated small molecules from Examples 1-4 are shown.

[0049] Figure 14 The steady-state fluorescence spectra of the non-conjugated small molecule crystals in Examples 1-4 under different excitations (performed on an Edinburgh Instruments FLS1000 fluorescence spectrophotometer equipped with a xenon arc lamp);

[0050] Figure 15 The fluorescence lifetime diagrams are for the non-conjugated small molecules in Examples 1-4;

[0051] Figure 16 The results of the aggregation-induced concentration variation experiment (acetonitrile solution) of non-conjugated small molecules in Examples 1-4 are shown in the figure.

[0052] Figure 17 The figures show the results of solid-state temperature-varying experiments on non-conjugated small molecules in Examples 1-4. Detailed Implementation

[0053] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0054] To address the research challenge of achieving efficient long-wavelength luminescence in small molecules using a small number of heteroatoms, this invention provides a strategy that induces efficient luminescence by introducing four heteroatoms into a small molecule system. Compared to most non-conjugated polymers containing a large number of heteroatoms (such as polyacrylonitrile), this strategy fully utilizes the four heteroatoms within the small molecule to form stable spatial interactions between lone pairs of electrons, thereby achieving more efficient luminescence performance and realizing the efficient utilization of the lone pairs of electrons carried by the heteroatoms.

[0055] Normally, non-conjugated small molecules do not emit long-wavelength light. This is because the emitted light wavelength is related to the molecule's electronic structure and energy levels, as well as its vibrational rotation mode. Non-conjugated small molecules typically have smaller conjugated structures and simpler electronic structures, therefore their light emission is usually in the shorter wavelength range. Therefore, another objective of this invention is to provide a novel and easily prepared small-molecule non-conjugated long-wavelength emitting material through precise molecular design, with emission up to yellow fluorescence, which can be used as a potential organic functional material.

[0056] The formation of intramolecular hydrogen bonds alters the electron distribution within the molecule, leading to a redistribution of electrons and a rearrangement of the electron cloud, thus affecting the molecule's electronic structure and consequently its luminescence properties. Furthermore, this invention delves into the intrinsic relationship between heteroatom-induced intramolecular hydrogen bonds and luminescence performance; that is, once a heteroatom chooses to participate in hydrogen bonding, it will compete with the spatial interactions between heteroatoms, thereby significantly suppressing the luminescence of non-conjugated materials.

[0057] Example 1

[0058] 1,2-Phenylenediamine (2.16 g, 20 mmol) and malonic acid (1.04 g, 10 mmol) were dissolved in 40 mL of 4M hydrochloric acid. The mixture was heated for 48 hours and then slowly cooled to room temperature to form a protonated chloride salt (light green lamellar crystals). Neutralization with concentrated ammonia produced a large amount of white precipitate. The precipitate was filtered and washed with distilled water. The white precipitate was dissolved in 10 mL of CH3CN and 8 mL of CH3OH and stored at -20°C overnight. Finally, the precipitated solid was filtered and dried under vacuum to give o-2Bmz dibenzimidazole methane (o-2Bmz) in 78% yield.

[0059] The reaction formula for 1,2-phenylenediamine and malonic acid is:

[0060]

[0061] Figure 1 o-dibenzimidazole methane 1 H NMR spectrum. Figure 2 o-dibenzimidazole methane 13 C10 NMR spectrum. Figure 3 This is a high-resolution mass spectrometry image of o-dibenzimidazole methane.

[0062] The NMR spectral data of o-benzimidazole methane are as follows: 1 H NMR (400MHz, DMSO-d6) δ12.41 (s, 2H), 7.50 (d, J = 18.5Hz, 4H), 7.19–7.12 (m, 4H), 4.48 (s, 2H). 13 C NMR (100MHz, DMSO) δ150.8,143.7,135.0,122.3,121.6,118.8,111.6,30.0.

[0063] Example 2

[0064] Using a carboxylic acid derivative (3.86 g, 20 mmol) as a substrate, 1,2-phenylenediamine (2.16 g, 20 mmol) was mixed in polyphosphoric acid at 180 °C and heated with stirring for 12–14 hours. After cooling to room temperature, 200 mL of ice water was added. The reaction mixture was mixed with 5 M NaOH solution to a slightly alkaline pH (~9), and allowed to stand for 8 hours to obtain a precipitate. The precipitate was filtered off and washed with cold water. After purification by recrystallization from ethanol, the crystals were filtered and dried under vacuum to give o-benzimidazole-benzothiazolium methane (o-1Bmz-1Btz) in 80% yield.

[0065] The reaction formula for carboxylic acid derivatives and 1,2-phenylenediamine is as follows:

[0066]

[0067] Figure 4 It is o-benzimidazole-benzothiazolium methane 1 H NMR spectrum. Figure 5 It is o-benzimidazole-benzothiazolium methane 13 C10 NMR spectrum. Figure 6 High-resolution mass spectra of o-benzimidazole-benzothiazolium methane.

[0068] The NMR spectral data of o-benzimidazole-benzothiazolium methane are as follows: 1 H NMR (400MHz, DMSO-d6) δ12.56(s,1H),8.06(d,J=7.9Hz,1H),7.97(d,J=8.1Hz,1H),7.46(dt,J=32.1,7.3Hz,4H),7.21–7.14(m,2H),4.77(s,2H). 13 C NMR (100MHz, DMSO) δ167.4,153.0,150.6,135.7,126.6,125.6,122.9,122.6,121.8,119.0,111.7,34.3.

[0069] Example 3

[0070] o-Aminothiophenol (2.50 g, 20 mmol) was mixed with malonic acid (1.04 g, 10 mmol), and the mixture was poured into 50 mL of polyphosphoric acid. The mixture was stirred and heated at 175 °C for 4 hours. The reaction mixture was then poured into ice water and allowed to stand for 12 hours. The precipitate was removed by filtration, washed several times with diluted sodium bicarbonate solution, and finally washed with water. The reaction product was then air-dried and weighed to give o-dibenzothiazolyl methane (o-2Btz) in 71% yield.

[0071] The reaction formula for o-aminothiophenol (2.50 g, 20 mmol) with malonic acid is as follows:

[0072]

[0073] Figure 7 o-dibenzothiazolylmethane 1 H NMR spectrum. Figure 8 o-dibenzothiazolylmethane 13 C10 NMR spectrum. Figure 9 This is a high-resolution mass spectrometry of o-dibenzothiazolium methane.

[0074] The NMR spectrum data of o-dibenzothiazolium methane are as follows: 1 H NMR (500MHz, Chloroform-d) δ8.07(d,J=8.1Hz,2H),7.87(d,J=7.9Hz,2H),7.51(t,J=7.6Hz,2H),7.40(t,J=7.5Hz,2H),4.97(s,2H). 13 C NMR (125MHz, CDCl3) δ165.6,153.1,135.8,126.2,125.3,123.2,121.6,38.9.

[0075] Example 4

[0076] o-Aminophenol (5.6 g, 50.0 mmol) and its hydrochloride (4.62 g, 20 mmol) were dissolved in dichloromethane (DCM) (50 mL). The reaction mixture was heated to 40 °C and reacted for 10 hours. The resulting solution was stored at -30 °C. After standing for 8 hours, the resulting crystals were filtered off and washed with saturated NaHCO3 aqueous solution (2 × 50 mL). The solution was extracted with CH2Cl2 (3 × 20 mL), and the organic phase was dried over anhydrous Na2SO4. After concentration under reduced pressure and drying under vacuum, o-dibenzoxazolemethane (o-2Bxz) was given in 74% yield.

[0077] The reaction formula for o-aminophenol and its hydrochloride is:

[0078]

[0079] Figure 10 o-dibenzoxazolemethane 1 H NMR spectrum. Figure 11 o-dibenzoxazolemethane 13 C10 NMR spectrum. Figure 12 This is a high-resolution mass spectrometry image of o-dibenzoxazolemethane.

[0080] The NMR spectrum data of o-dibenzoxazolemethane are as follows:1 H NMR (400MHz, Chloroform-d) δ7.68–7.62(m,2H),7.53–7.37(m,2H),7.30–7.23(m,4H),4.58(s,2H). 13 C NMR (101MHz, CDCl3) δ159.8,151.2,141.2,125.4,124.6,120.3,110.8,29.4.

[0081] Figure 13 The images show the UV absorption spectra of the non-conjugated small molecules in Examples 1-4 at different concentrations (mol / L) in acetonitrile, demonstrating that the non-conjugated small molecules in Examples 1-4 all exhibit UV absorption characteristics.

[0082] Figure 14 The images show the steady-state fluorescence spectra of the non-conjugated small molecule crystals in Examples 1-4 under different excitations (performed on an Edinburgh Instruments FLS1000 fluorescence spectrophotometer equipped with a xenon arc lamp). It can be seen that the stronger the lone pair electrons of the heteroatom, the more redshifted and stronger its non-conjugated emission. The inset shows the solid-state fluorescence images of the corresponding molecules and their solid-state quantum efficiency under optimal excitation.

[0083] Figure 15 The fluorescence lifetime diagrams of the non-conjugated small molecules in Examples 1-4 demonstrate that the luminescence of the non-conjugated small molecules in Examples 1-4 is short-lifetime fluorescence induced by heteroatoms of the non-conjugated small molecules.

[0084] Figure 16 The figures show the results of the aggregation-induced concentration variation experiment (acetonitrile solution) of non-conjugated small molecules in Examples 1-4, demonstrating that intramolecular spatial interactions are enhanced with aggregation, thereby inducing luminescence.

[0085] Figure 17 The figures show the solid-state temperature-varying experimental results of non-conjugated small molecules in Examples 1-4, demonstrating that if strong steric interactions exist within the molecule, the molecular spectrum does not change significantly with temperature.

[0086] Furthermore, it should be understood that after reading the above description of the present invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A method for fluorescence modulation of non-conjugated small molecules containing heteroatoms, characterized in that, Increasing the concentration of the heteroatom-containing non-conjugated small molecules in the solution, and / or, by adding a poor solvent, causing the heteroatom-containing non-conjugated small molecules to aggregate in the solution, results in a red shift of the emission wavelength, the appearance of a new long-wavelength emission peak, and an enhanced fluorescence intensity; The non-conjugated small molecule containing heteroatoms has the structure shown in formula (III) or (IV) below:

Images