Luminescent material based on two-component light-induced single electron transfer stable light-emitting free radicals, method and application

Abstract

The invention discloses a luminescent material based on two-component light-induced single electron transfer stable luminescent free radicals, a method and application. The invention provides a novel strategy for preparing light-emitting free radicals based on a bi-component synergistic stabilization mechanism, benzophenone (BP) with an electron-withdrawing property and triphenylphosphine (TPP) with an electron-donating property are doped, and the triphenylphosphine free radicals are stabilized by virtue of benzophenone; and the light-emitting wavelength and intensity of the bi-component free radicals can be adjusted by changing substituent groups of BP and TPP. According to the invention, the combination of a bi-component stable mechanism and an optical excitation single electron transfer donor-acceptor method is realized, and the problems of complex synthesis steps, high degree of luminophor and matrix structures and the like in the existing stable free radical luminescence method can be effectively solved; the method is expected to provide a novel visual and rapid way for preparation of luminescent materials with the stimulation response function, drug impurity inspection and the like, and has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of luminescent free radical technology, specifically to a luminescent material, method, and application based on a two-component photoinduced single-electron transfer stabilized luminescent free radical. Background Technology

[0002] Free radicals, also known as ionized free radicals, are defined as atoms, molecules, or ions with unpaired electrons. The unique characteristic of free radicals is the presence of unpaired electrons within their molecules, exhibiting an open-shell electronic state. Photoinduced luminescence (PRL) free radicals are a class of free radicals that generate under light irradiation and exhibit unique luminescent properties. Stable organic luminescent free radicals are a class of multifunctional molecular systems possessing optical, electrical, and magnetic properties. These materials exhibit a unique luminescence mechanism due to their open-shell electronic structure, and in terms of applications, organic luminescent free radicals show broad prospects in multiple fields. In the field of optoelectronic devices, they can serve as novel luminescent materials for organic light-emitting diodes (OLEDs). In the intersection of magnetism and optics, they can contribute to the development of magnetoluminescent materials, enabling precise control of photomagnetic coupling effects, and can also be applied to bioimaging and photodynamic therapy. In the biomedical field, due to their excellent photophysical properties, they also demonstrate significant application value in fluorescent imaging probes and photodynamic therapeutic agents.

[0003] However, due to the high reactivity of free radicals due to their unpaired electrons, they are usually difficult to exist stably alone, which is detrimental to the development and application of organic light-emitting radicals. Therefore, improving the stability of light-emitting radicals is particularly important. Currently existing methods for stabilizing light-emitting radicals mainly include multi-dimensional strategies such as chemical modification, crystal stacking, and supramolecular assembly. Chemical modification involves introducing specific functional groups into the radical molecule, such as sterically hindered groups, conjugated groups, and groups with electron-withdrawing or electron-donating properties, to adjust the electronic structure and steric hindrance of the radical. Crystal stacking involves forming molecular chains or specific stacking patterns through ordered geometric arrangement, creating conditions for intermolecular electron transfer. Simultaneously, the rigid environment of the crystal restricts molecular vibration and conformational changes, reducing the probability of nonradiative transitions. Supramolecular assembly utilizes intermolecular non-covalent interactions to embed the light-emitting radical as a side chain into the polymer backbone, assembling it into a specific supramolecular structure.

[0004] However, existing methods for stabilizing radical luminescence face bottlenecks in terms of synthetic efficiency, environmental adaptability, and mechanistic innovation. Strategies based on donor-acceptor structural modification, molecular crystallization, and host-guest interactions generally rely on complex synthetic steps, resulting in high synthesis costs and low yields. Most methods are highly dependent on the matrix; when removed from specific crystal forms or polymer environments, the stability and luminescence performance of the radicals significantly decrease. Furthermore, current mainstream neutral luminescent radicals largely depend on the donor-acceptor chemical structures, limiting structural design. Therefore, developing a simple and efficient new method for radical stabilization is urgently needed.

[0005] Triphenylphosphine (TPP) has a trigonal pyramidal structure formed by a central phosphorus atom and three phenyl groups linked by PC bonds, with the phosphorus atom possessing a lone pair of electrons. In recent years, triphenylphosphine compounds have shown great application potential as precursors to photoinduced luminescent organic radicals. However, current luminescence phenomena based on triphenylphosphine radicals are mainly limited to the crystalline state. Therefore, introducing another compound to form a two-component luminescent radical might solve the crystal-dependent problem. Benzophenone (BP) has a conjugated planar structure formed by two benzene rings bridged by ketone groups. Under ultraviolet light excitation, the ketone group of benzophenone can be reduced to a radical intermediate. Benzophenone possesses a unique conjugated structure and excellent photosensitivity, making it a promising key component for constructing novel luminescent radical materials and providing an effective solution to the crystal-dependent problem of triphenylphosphine radical luminescence. Summary of the Invention

[0006] Given the complexity of existing stable luminescent radical synthesis methods and their strong dependence on the matrix, one objective of this invention is to provide a luminescent material based on a two-component photoinduced single-electron transfer stable luminescent radical. This luminescent material comprises a benzophenone derivative and a triphenylphosphine derivative, wherein the benzophenone derivative and the triphenylphosphine derivative are uniformly mixed via a melt-doping mode. The structural formula of the benzophenone derivative is shown in formula (I); the structural formula of the triphenylphosphine derivative is shown in formula (II).

[0007]

[0008] In this study, the R substituents are independently selected from, but are not limited to, any one of H, F, Cl, CH3, and OCH3. The carbonyl group (C=O) in BP and the P atom in TPP play important roles in the photoinduced radical luminescence phenomenon of the two-component system. By using a melt doping method, benzophenone, which has electron-withdrawing properties, and triphenylphosphine, which has electron-donating properties, are mixed in an appropriate ratio, and BP is used to stabilize the potentially luminescent TPP radical.

[0009] Preferably, R is H.

[0010] Preferably, R is an electron-donating substituent. When both are electron-donating groups, the luminescence response time and intensity of the binary radical are enhanced to some extent.

[0011] Preferably, the electron-donating substituent is methyl (-CH3) or methoxy (-OCH3).

[0012] Preferably, the mass ratio of the benzophenone derivative to the triphenylphosphine derivative is 500:1 to 1:100.

[0013] Preferably, the mass ratio of the benzophenone derivative to the triphenylphosphine derivative is 1:1. The photoinduced fluorescence intensity reaches its maximum when the doping mass ratio is 1:1.

[0014] The second objective of this invention is to provide the application of the above-mentioned luminescent material in the generation of stable luminescent free radicals.

[0015] Furthermore, the stable luminescent free radical is a triphenylphosphine derivative cationic free radical stabilized by a benzophenone derivative anionic free radical. The triphenylphosphine cationic free radical stabilized by the benzophenone anionic free radical is a pink fluorescent substance.

[0016] Furthermore, the luminescent material generates stable luminescent free radicals through photoinduced single-electron transfer, wherein the single-electron transfer is from a triphenylphosphine derivative to a benzophenone derivative, thereby obtaining anionic free radicals of the benzophenone derivative and cationic free radicals of the triphenylphosphine derivative. Photoinduction can be achieved through ultraviolet light irradiation.

[0017] The third objective of this invention is to provide a stable luminescent free radical based on a two-component photoinduced single-electron transfer, wherein the stable luminescent free radical is a triphenylphosphine derivative cationic free radical stabilized by an anionic free radical of benzophenone derivative, and the stable luminescent free radical is obtained by photoinduction of the above-mentioned luminescent material.

[0018] The fourth objective of this invention is to provide a method for stabilizing luminescent free radicals based on two-component photoinduced single-electron transfer, comprising the following steps: melt-doping a benzophenone derivative and a triphenylphosphine derivative, and then photo-inducing the obtained doped product.

[0019] Preferably, the mass ratio of the benzophenone derivative to the triphenylphosphine derivative is from 500:1 to 1:100.

[0020] Preferably, the mass ratio of the benzophenone derivative to the triphenylphosphine derivative is 1:1.

[0021] This invention provides a luminescent material, method, and application based on a two-component photoinduced single-electron transfer stabilized luminescent radical. The carbonyl group (C=O) in BP and the P atom in TPP play crucial roles in the two-component photoinduced radical luminescence phenomenon. By melt-doping BP and TPP, electron-withdrawing BP and electron-donating TPP are photoinduced to obtain a benzophenone derivative anionic radical stabilized by a triphenylphosphine derivative cationic radical. Furthermore, the emission wavelength and intensity of the two-component radical can be adjusted by changing the substituents in BP and TPP. This invention combines a two-component stabilization mechanism with a donor-acceptor method, enabling two-component luminescence under illumination. It overcomes the complex processes and matrix dependence of traditional methods, achieving the goal of efficient and convenient preparation of stable luminescent radicals. This is expected to provide a visualized and rapid new approach for the preparation of stimulus-responsive luminescent materials and drug impurity detection, and has broad application prospects. Attached Figure Description

[0022] Figure 1 The normalized fluorescence spectra of individual compounds of this invention before and after ultraviolet light irradiation are shown (where (a) BP; (b) TPP; the inset shows the corresponding fluorescence photographs after light irradiation, λ). ex =365nm);

[0023] Figure 2 The photophysical properties of BP / TPP before and after ultraviolet irradiation of the present invention are shown (wherein, (a) the normalized photoluminescence spectra of BP / TPP solid powder after ultraviolet irradiation for 0 seconds, 5 seconds and 10 seconds, λ). ex =365nm; (b) Normalized UV absorption spectra of BP / TPP before and after UV irradiation; Insets in (a) and (b) show fluorescence and solid surface color changes before and after irradiation; (c) Emission lifetime of BP / TPP before and after UV irradiation under 380nm excitation; λ before irradiation em =450nm, λ after illumination em =610nm; (d) EPR spectrum of BP / TPP powder before and after UV irradiation at room temperature;

[0024] Figure 3 The EPR spectra at different temperatures and the 1H NMR spectra before and after irradiation are shown in the present invention (wherein, (a) EPR spectra of BP / TPP powder under continuous irradiation at low temperature 200K and room temperature; (b) 1H NMR spectra of solid BP / TPP dissolved in deuterated chloroform before and after irradiation).

[0025] Figure 4 The effect of light irradiation on the molecular structure of the compound in this invention (wherein, (a) infrared spectra of BP / TPP, (b) BP, (c) TPP before and after light irradiation; (d) Raman spectra of BP / TPP, (e) BP, (f) TPP before and after light irradiation);

[0026] Figure 5 For the reproducibility test of the two-component light-emitting system of the present invention (wherein, (a) BP / TPP is repeatedly irradiated after being placed at room temperature for 12 hours after irradiation; (b) BP / TPP photoluminescence phenomenon after repeated melting).

[0027] Figure 6 A comparison of the spectra of intermolecular electron transfer (BP / TPP) and charge transfer (BP / TMPB, Cl-BP / TMPB) phenomena under different UV irradiation times in this invention (wherein, (a) the phenomenon of doping with a mass ratio of 1:1, and (b) the fluorescence spectrum).

[0028] Figure 7 The doped fluorescence spectra of different structural analogs of the present invention are shown (where (a), (b), and (c) are the normalized photoluminescence spectra of biphenyl, diphenylmethane, and diphenylmethanol with triphenylphosphine, respectively; (d), (e), and (f) are the normalized photoluminescence spectra of benzophenone with triphenylmethane, triphenylamine, and triphenylphosphine oxide, respectively; the inset shows the fluorescence emission phenomenon after irradiation and the structure of the corresponding compound).

[0029] Figure 8 The photoluminescence phenomenon of the two-component analogues of the present invention, in which electron-withdrawing substituents and electron-donating substituents are cross-doped in a 1:1 mass ratio;

[0030] Figure 9 EPR spectroscopic characterization of BP and TPP separately for this invention (wherein, (a) EPR spectra of BP under no UV light and under UV light irradiation; (b) EPR spectra of TPP under no UV light and under UV light irradiation).

[0031] Figure 10 This is an LC-MS diagram of the BP and DMPO coupling structure of the present invention;

[0032] Figure 11 The photocurrent diagram of the light-illuminated switch of the present invention is shown (where (a) BP / TPP; (b) BP; (c) TPP).

[0033] Figure 12 The diagram shows the quenching of the pink fluorescence of the present invention under different gas environments. From left to right, the environments are oxygen, air, and argon (wherein, (a) the sample is exposed to different gas environments after ultraviolet light irradiation; (b) the sample is placed in different gas environments before ultraviolet light irradiation).

[0034] Figure 13Characterization of the transformation product of the free radical luminescent triphenylphosphine cationic free radical intermediate of the present invention (wherein, (a) the NMR phosphorus spectrum of BP / TPP after repeated light irradiation; (b) the NMR hydrogen spectrum of TPO extracted by column chromatography after UV irradiation of a large number of BP / TPP samples).

[0035] Figure 14 LC-MS images of TPO were extracted for this invention;

[0036] Figure 15 The present invention provides a dynamic luminescent anti-counterfeiting pattern for BP / TPP (wherein, (a) BP / TPP solid powder is used for font encryption; and (b) BP / TPP liquid is used to arbitrarily draw patterns for encryption after melting).

[0037] Figure 16 This invention relates to a method for preparing a luminescent material containing a two-component photoinduced single-electron transfer stable luminescent free radical and its luminescent principle. Detailed Implementation

[0038] The present invention will be described in detail below with reference to embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of application of the present invention. The present invention is not limited to the following embodiments or examples. Any modifications and variations made without departing from the spirit of the present invention should be included within the scope of the present invention. Unless otherwise specified, the experimental materials and reagents used in the following embodiments are all commercially available conventional products.

[0039] The two-component doped material of this invention can produce fluorescence under photoinduced conditions when the doping mass ratio of benzophenone derivative and triphenylphosphine derivative ranges from 500:1 to 1:100. However, the photoinduced fluorescence intensity is strongest when the doping mass ratio is 1:1. Therefore, unless otherwise specified, the doping mass ratio of the two-component system involved in the following examples is 1:1.

[0040] Example 1: Preparation of BP / TPP dual-component doped materials

[0041] Taking the preparation of a BP / TPP two-component doped material with a mass ratio of 1:1 as an example, the specific operation is as follows: Weigh 50 mg of benzophenone (BP) and 50 mg of triphenylphosphine (TPP) together and place them in a glass vial. Heat the mixture in the vial with a hot air gun to melt and mix it evenly, then let it cool and solidify naturally until the mixture is completely cooled to room temperature. This yields a two-component material doped with BP and TPP in a 1:1 ratio. When the prepared BP / TPP doped material is irradiated with a handheld 365 nm UV lamp, it quickly produces a bright pink glow. Of course, for convenient subsequent detection, operation, or use, the prepared BP / TPP doped material can be pulverized into powder before processing. For doped materials containing different substituents, the preparation method of the BP / TPP two-component doped material is the same.

[0042] Example 2: Single-component photophysical characterization

[0043] Observe the photoresponse behavior of BP and TPP under continuous ultraviolet light irradiation. Figure 1 As shown, neither BP nor TPP alone showed a significant change in fluorescence color after illumination, and both remained in their original blue fluorescence state.

[0044] Example 3: Basic photophysical characterization of dual-component luminescence phenomenon

[0045] Under the optimal 1:1 ratio condition, the effect of UV irradiation time on luminescence intensity was further investigated. Experimental results showed that the BP / TPP sample produced pink fluorescence within only 2 seconds under UV irradiation, and the fluorescence intensity reached its maximum when the irradiation time was extended to 10 seconds. Figure 2 a). Next, the changes in the absorbance spectrum of the sample before and after illumination were analyzed. The normalized spectrum showed a slight change in the visible light region (400-450 nm), which is consistent with the slight yellowing phenomenon that appeared on the solid surface after illumination. Figure 2 b). Next, the lifetimes of the blue and pink fluorescence before and after photoinduction were measured. The lifetime of the blue fluorescence before illumination was 2.59 ns, and the lifetime of the pink fluorescence after illumination was 3.67 ns, both consistent with fluorescence characteristics. Figure 2 c). Simultaneously, to investigate whether this novel luminescence phenomenon is related to the generation of free radicals in BP / TPP after illumination, the electron paramagnetic resonance (EPR) spectrum of the illuminated BP / TPP was measured. The experiment revealed that the illuminated BP / TPP solid exhibited a strong free radical signal with a g-value of 2.002, while the original BP / TPP solid did not show an EPR signal. Figure 2 d). EPR spectroscopy suggests that photogenerated free radicals may be involved in the photoluminescence process.

[0046] Example 4: Characterization of EPR signal of BP / TPP under low temperature conditions

[0047] Next, the EPR signal of BP / TPP was tested at a low temperature (200K). It was found that the EPR signal gradually increased with increasing illumination time. Compared to the EPR signal at room temperature, although the g value remained constant, the EPR signal was much stronger at low temperature. This may be because free radicals are more stable at low temperatures, resulting in a stronger EPR signal. Figure 3 a).

[0048] Example 5: Molecular structure characterization before and after light irradiation

[0049] Since molecular structures are frequently damaged by ultraviolet light irradiation, studying molecular structural information before and after irradiation is crucial. BP / TPP powder was dissolved in deuterated chloroform before and after irradiation, and the proton nuclear magnetic resonance (NMR) spectra were measured. Figure 3 b) No new proton peaks were observed. This indicates that the chemical structure of the compound remained unchanged under light irradiation, and the change in fluorescence may be due to its resistance to light. 1 Free radicals were detected by H-NMR. To further investigate the effect of ultraviolet light irradiation on intermolecular interactions, Fourier transform infrared spectroscopy (FTIR) was used to detect the mixed powder samples before and after irradiation. Figure 4 a). By comparing the peak positions at different wavenumbers, no new bond sites were found to be formed, ruling out the possibility of photoinduced morphological changes. Subsequently, the infrared spectra of BP and TPP after melting and before and after UV irradiation were measured. Comparison showed that, apart from the characteristic C=O and PC bonds, no new chemical bonds were formed. Figure 4 bc). Furthermore, Raman spectroscopy was employed with a 633 nm excitation source to measure the different compounds before and after illumination. The results showed that, for both individual compounds and mixtures, the position of the scattered light wavelength corresponding to each Raman peak remained unchanged before and after illumination. Figure 4 This finding further confirms that light has a limited effect on the molecular structure of compounds, and the main changes are likely concentrated at the microscopic level, which is difficult to detect using conventional spectroscopic methods.

[0050] Example 6: Investigation of the luminescence properties of free radicals

[0051] The investigation of free radical luminescence properties included the reproducibility of the two-component luminescence system and the investigation of the differences in characteristics between two-component free radical luminescence and intermolecular charge-transfer fluorescence. Specifically:

[0052] Two methods were used to examine the reproducibility of the two-component luminescent system: the reproducibility was verified by thoroughly investigating the luminescence characteristics of free radicals. For example... Figure 5As shown, after 24 hours of exposure to light, the pink fluorescence of BP / TPP automatically disappears under ambient conditions, and this fluorescence phenomenon can be reactivated by ultraviolet light irradiation. Figure 5 a). Furthermore, another method was explored, namely, achieving a reversible conversion of fluorescence between blue and pink through remelting and photoactivation steps. BP / TPP consistently exhibited good luminescence performance throughout the four cycles tested. Figure 5 b). This reversibility is consistent with the emission characteristics of free radicals.

[0053] Investigation of the characteristic differences between two-component radical luminescence and intermolecular charge transfer fluorescence: such as Figure 6 As shown, to more intuitively compare the differences in characteristics between two-component radical luminescence and intermolecular charge-transfer fluorescence, benzophenone and 4,4-dichlorobenzophenone (Cl-BP) were selected as acceptors for charge transfer, while N,N,N,N-tetra(p-tolyl)benzidine (TMPB) was selected as a donor for charge transfer. They were melt-doped at a 1:1 mass ratio, and a redshift in the fluorescence wavelength was observed after doping. However, unlike the fluorescence emission of BP / TPP, the fluorescence color of the BP / TMPB and Cl-BP / TMPB systems did not change after continuous illumination, and their fluorescence intensity did not show significant decay after 12 hours. Fluorescence spectra of the radical luminescence combination and the charge-transfer combination were measured. These experimental results indicate that the photoinduced luminescence characteristics of BP / TPP are significantly different from the charge-transfer fluorescence characteristics of BP / TMPB and Cl-BP / TMPB. This further confirms that the BP / TPP system belongs to two-component photoinduced radical luminescence.

[0054] Example 7: Analysis of luminescence phenomena of altered functional groups in a two-component compound

[0055] To further analyze the unique interaction between BP and TPP, a series of structural analogs were selected for doping studies. First, benzophenone was replaced with its carbonyl-free analogs biphenyl, diphenylmethane, and diphenylethanol, which were then melt-interacted with TPP at a 1:1 mass ratio. Experimental results showed that after 10 seconds of UV irradiation, these mixtures did not exhibit pink fluorescence. Figure 7 The presence of ac indicates that the carbonyl group of benzophenone plays a role in the two-component luminescent system. Following this, the study shifted to structural changes in TPP, replacing triphenylphosphine with triphenylmethane, triphenylamine, and triphenylphosphine oxide, thus altering the P atom portion of the original molecule. This was then similarly melt-doped with BP. It was found that neither observing experimental phenomena nor analyzing the normalized changes in fluorescence spectra before and after illumination revealed photoinduced luminescence. Figure 7Through this series of functional group substitution experiments, it can be concluded that the carbonyl group (C=O) in BP and the P atom in TPP play a crucial role in realizing photoinduced radical luminescence in the binary system. This discovery provides clues for further exploration of the interaction mechanism between BP and TPP.

[0056] Example 8: Effects of electron-withdrawing and electron-donating substituents on bicomponent luminescence

[0057] The effects of different types of substituents—electron-withdrawing substituents (-F, -Cl) and electron-donating substituents (-CH3, -OCH3)—on the binary luminescent system were further investigated. BP and TPP with different substituents were melt-interacted at an optimal mass ratio of 1:1, and the fluorescence phenomenon after 10 seconds of illumination was recorded. Figure 8 By comparing the fluorescence spectra of different substituent combinations, it was found that when both BP and TPP substituents were electron-donating groups, the luminescence response time and intensity of the bicomponent radicals were enhanced to some extent. Conversely, when electron-withdrawing substituents were introduced, no significant change in fluorescence properties was observed in most cases. It is speculated that electron-donating substituents may enhance the stability of the generated radicals by increasing the degree of conjugation of the entire system. This increased stability is beneficial to the photoinduced radical luminescence process, thus making the bicomponent system exhibit a stronger fluorescence effect under illumination.

[0058] Example 9: Study on the mechanism of bicomponent luminescence phenomenon

[0059] The study of the mechanism of bicomponent luminescence includes EPR spectral characterization of individual BP and TPP, monitoring and capture of benzophenone-generated free radicals in the bicomponent system, and verification of free radical generation by improving material conductivity. Details are as follows:

[0060] EPR spectral characterization of BP and TPP individually: Since the structures of BP and TPP play irreplaceable roles in photoinduced luminescence, it was hypothesized that radical luminescence occurs due to photoinduced single-electron transfer in both compounds under ultraviolet light, generating free radicals and resulting in pink fluorescence. To verify this hypothesis, EPR spectral characterization of BP and TPP individually was first performed. It was found that no EPR signal was observed without ultraviolet light, but both compounds produced significant free radical signals under ultraviolet light irradiation. Figure 9 This discovery indicates that they possess the ability to generate free radicals under ultraviolet light conditions.

[0061] Monitoring and capture of benzophenone-generated free radicals in a two-component system: Liquid chromatography-mass spectrometry (LC-MS) was used to monitor the free radicals generated by benzophenone in the two-component system, and 5,5-dimethyl-1-pyrrolino-N-oxide (DMPO) was used to capture the free radicals. In the LC-MS spectral analysis, a specific molecular weight (Mr) was observed to form after BP binds to DMPO. Figure 10 This result confirms that benzophenone forms free radicals in the doped compound. In summary, EPR not only supports the hypothesis that BP and TPP can generate free radicals under ultraviolet light, but also directly proves the existence of free radicals through LC-MS analysis, thus deepening our understanding of the photoinduced free radical luminescence mechanism.

[0062] The generation of free radicals was verified by improving the conductivity of the material: the generation of free radicals can also improve the conductivity of the material. In the experiment, sodium sulfite was used as the electrolyte, and BP / TPP powder was uniformly coated on the electrode surface. Its photoconductivity was measured using a xenon lamp electrochemical testing system. The results showed that under ultraviolet light irradiation, the BP / TPP composite exhibited clear photoconductivity behavior. Figure 11 a) Specifically, this manifests as a rapid on / off response of the photocurrent, closely synchronized with the ultraviolet irradiation state. Notably, after completing the photocycle, the fluorescence color of the BP / TPP solid changed from blue to red, indicating a close correlation between the color change and free radical generation. Furthermore, we conducted photoconductivity tests on BP and TPP separately. The test results show that both components also exhibit regular photocurrent changes under ultraviolet irradiation (a) Figure 11 (bc). The above results further demonstrate that the individual components can generate free radicals under ultraviolet light, which is a prerequisite for photoinduced single-electron transfer in the two-component system.

[0063] Example 10: Investigation into the source of luminescence of two-component free radicals

[0064] The investigation into the luminescence source of the two-component free radical included the investigation of the auto-oxidation of the triphenylphosphine radical cation and the confirmation of the relationship between the disappearance of pink fluorescence and the formation of triphenylphosphine oxide. Details are as follows:

[0065] An Investigation into the Auto-oxidation of Triphenylphosphine Radical Cations: To gain a deeper understanding of the luminescence origin of binary radicals, the auto-oxidation process of triphenylphosphine radical cations was specifically investigated, which generates triphenylphosphine oxide (TPO). By controlling the gaseous environment of the pink fluorescent compound after illumination, the actual radicals involved in luminescence were investigated based on the fluorescence intensity decay rate. The experiment was conducted in two groups, each using the same mass of BP / TPP samples placed in glass vials containing different gases, such as... Figure 12As shown. (1) In the light-then-air experiment, the sample was first irradiated with ultraviolet light in the air environment for 10 seconds, causing it to exhibit pink fluorescence. Subsequently, oxygen, air, and argon were introduced into the glass bottle respectively, and the bottle was sealed. After 6 hours, the pink fluorescence in the glass bottle with oxygen almost completely disappeared, while the fluorescence intensity of the samples in the air and argon gas was reduced to similar degrees. Figure 12 a). Analysis suggests that during the process of the sample turning red under light in an air environment, a small amount of oxygen may have bound to the surface of the sample molecules, resulting in similar rates of fluorescence disappearance in air and argon environments. (2) In the experiment of first purging and then irradiating, oxygen, air, and argon were pre-purged into the glass bottles containing the samples, so that the samples were in different gas environments. Then, the samples were irradiated with ultraviolet light for 10 seconds to make them exhibit pink fluorescence. Initially, the fluorescence intensity in the three glass bottles was the same. After 3 hours, the fluorescence intensity in the glass bottle with oxygen purging decreased the most significantly. After 6 hours, the comparison showed that the intensity of pink fluorescence in the glass bottles with oxygen purging, air, and argon purging increased sequentially ( Figure 12 (b) This result indicates that oxygen plays a crucial role in the fluorescence quenching process, providing important experimental evidence for further elucidating the luminescence mechanism of the two-component free radicals. Based on the experimental phenomena, it is inferred that the photoinduced luminescence process of the two-component system involves a photoinduced single-electron transfer between BP (containing an electron-withdrawing carbonyl group) and TPP (containing an electron-donating phosphorus atom) under ultraviolet light. During this process, the BP molecule gains an electron and transforms into an anionic free radical, while the TPP loses an electron to produce a cationic free radical. The substance that produces pink fluorescence is the triphenylphosphine cationic free radical. When the pink fluorescence gradually disappears in the air, the process involves some of the triphenylphosphine cations interacting with a small amount of oxygen in the air, consuming the cations to produce triphenylphosphine oxide. The triphenylphosphine cationic free radicals are consumed, leading to a decrease in the concentration of luminescent species in the system. This also explains why the pink fluorescence intensity cannot be restored to the initial intensity level when the BP / TPP system is repeatedly irradiated. This is because after each irradiation, some of the triphenylphosphine cationic free radicals react with oxygen and are consumed, resulting in a reduction in the number of luminescent free radicals, thus preventing the fluorescence intensity from fully recovering.

[0066] Confirmation of the relationship between the disappearance of pink fluorescence and the formation of triphenyloxyphosphine: To determine whether the disappearance of pink fluorescence after illumination is related to the formation of triphenyloxyphosphine, firstly, using... 31 P-NMR technology determined the peak positions of the phosphorus NMR spectra of the reference materials triphenylphosphine and triphenylphosphine oxide, providing a benchmark for subsequent experimental analysis. Subsequently, BP / TPP (mass ratio 1:1) were measured at different illumination times. 31 P-NMR ( Figure 13a) The results showed that no TPO peak was observed in BP / TPP without light exposure; BP / TPP that maintained pink fluorescence after light exposure produced a small amount of TPO at +29 ppm; the experimental group that underwent repeated light exposure after the pink fluorescence disappeared showed an increase in the amount of TPO generated, and after repeated fluorescence illumination-disappearance experiments, the amount of TPO generated was even greater. Therefore, it was concluded that the amount of TPO generated increased with the number of light exposures. Furthermore, experiments revealed that after UV light exposure, solid BP / TPP would produce new spots on a thin-layer chromatography plate. A small amount of the newly generated compound was extracted by thin-layer chromatography and its concentration was measured. 1 1H-NMR spectrum. Comparison with standard TPO 1H spectrum. Figure 13 (b) It was found that the small amount of new compound produced after ultraviolet light irradiation was TPO. To further determine the quality of the compound, the molecular weight of the new product was measured using LC-MS. Figure 14 The measurement results showed that the molecular weight of the compound was consistent with that of TPO, thus further confirming the previous inference.

[0067] Example 11: BP / TPP Application Case

[0068] Using BP / TPP for font encryption, such as Figure 15 As shown, after the solid powder is used for font encryption and melting, BP / TPP liquid is used for font encryption. Under ultraviolet light irradiation, the blue color starts to turn pink after 2 seconds, and it returns to blue after 12 hours of stopping the irradiation. The process is reversible.

[0069] In summary, this invention proposes a novel strategy for luminescent radicals based on a two-component synergistic stabilization mechanism. By melt-doping electron-withdrawing BP and electron-donating TPP in a specific ratio, the generation and stabilization of triphenylphosphine radicals are achieved by leveraging the properties of benzophenone. The principle and method are summarized as follows: Figure 16 As shown, without the need for a complex stabilizing structure, under ultraviolet light triggering, single-electron transfer occurs between molecules, generating luminescent free radical ion pairs. Simultaneously, the emission of the solid material rapidly changes from blue to pink fluorescence, and this pink fluorescence can be stably maintained for several hours. This invention successfully integrates a two-component stabilization mechanism with a donor-acceptor design method, developing a simple and efficient new method for constructing stable luminescent free radicals. It also provides important theoretical support for extending this method to fields such as the preparation of stimulus-responsive luminescent materials and drug impurity detection.

[0070] The conventional techniques and solutions not described in detail in the above embodiments are all well known in the art, and therefore will not be elaborated upon here. The above embodiments and / or experimental examples describe the preferred embodiments of the present invention in detail. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. A luminescent material based on a two-component photoinduced single-electron transfer stabilized luminescent radical, characterized in that, The mixture includes benzophenone derivatives and triphenylphosphine derivatives, wherein the benzophenone derivatives and the triphenylphosphine derivatives are uniformly mixed in a melt-doping mode; the structural formula of the benzophenone derivative is shown in formula (I); the structural formula of the triphenylphosphine derivative is shown in formula (II).

2. The luminescent material as described in claim 1, characterized in that, R is H.

3. The luminescent material as described in claim 1, characterized in that, R is an electron-donating substituent.

4. The luminescent material as described in claim 1, characterized in that, The mass ratio of the benzophenone derivative to the triphenylphosphine derivative is 500:1 to 1:

100.

5. The luminescent material as described in claim 4, characterized in that, The mass ratio of the benzophenone derivative to the triphenylphosphine derivative is 1:

1.

6. The use of the luminescent material according to any one of claims 1-5 in generating stable luminescent free radicals.

7. The application as described in claim 7, characterized in that, The stable luminescent free radical is a benzophenone derivative anionic free radical stabilized by a triphenylphosphine derivative cationic free radical.

8. The application as described in claim 8, characterized in that, The luminescent material generates stable luminescent free radicals through photoinduced single-electron transfer, wherein the single-electron transfer is from a triphenylphosphine derivative to a benzophenone derivative, thereby obtaining the benzophenone derivative anionic free radical and the triphenylphosphine derivative cationic free radical.

9. A stable luminescent free radical based on two-component photoinduced single-electron transfer, characterized in that, The stable luminescent free radical is a benzophenone derivative anionic free radical stabilized by a triphenylphosphine derivative cationic free radical, and the stable luminescent free radical is obtained by photoinduction from any of the luminescent materials described in claims 1-5.

10. A method for stabilizing luminescent free radicals based on two-component photoinduced single-electron transfer, characterized in that, Includes the following steps: Benzophenone derivatives and triphenylphosphine derivatives were melt-doped, and then the resulting doped products were photoinduced.

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