Patent Application
20250155373
Applicant informs that the subject matter of this patent application was disclosed by the inventor or joint inventor or by another who obtained the subject matter disclosed directly or indirectly from the inventor or joint inventor one year or less than before the effective filing date of a claimed invention which do not qualify as prior art under 35 U.S.C. 102(b)(1) for the following non-patent literature.
The present invention relates to a highly fluorescent conjugated silole polymer and an explosive vapor sensor using the same, and more particularly, to the highly fluorescent conjugated silole polymer having benzene subunits containing sterically hindered functional groups (X) at the 2,5 positions of the silole backbone, which promote explosive vapor permeability through the cavity structure of the silole polymer in the solid state, and in particular, is capable of detection of nitroaromatic explosive vapors, and exhibits a fluorescence-quenching process upon exposure to explosive vapors and a photoluminescence (PL) recovery process upon removal of explosive vapors, which are repeated in real time, and an explosive vapor sensor using the same.
The detection of ultratrace nitroaromatic explosives (NAEs) such as 2,4,6-trinitrotoluene (TNT) and picric acid (PA) has become increasingly critical due to rising concerns over international terrorism and environmental impact. To enhance detection sensitivity, new materials and transduction methods are required.
Conjugated polymers have emerged as candidate materials for NAE detection, offering the potential for signal amplification and well-defined morphology structures. The electron transport properties of conjugated polymers are particularly relevant for fluorescence-based sensors, as they can enhance sensitivity signals through electron-transfer fluorescence.
As representative conjugated polymers, siloles have garnered attention as promising π-electronic materials, which may find applications in photovoltaic cells, light-emitting diodes (LEDs), flexible memory storage, and chemical sensors, owing to their exceptional photoluminescence and electroluminescence properties.
Siloles, characterized by their five-membered rings with σ*-π* conjugation between the silicon atom and butadiene moiety, possess increased electron affinities and lowered LUMO energy levels due to conjugation. This unique electronic structure enables siloles to exhibit AIE in aggregate states by restricting intramolecular rotations of the phenyl moiety.
Since the aggregation-induced emission enhancement (AIEE) properties of siloles were reported in Non-Patent Document 1, interest in conjugated polymers with AIE properties has increased significantly, and extensive research has focused on developing new AIE chromophores that exhibit significantly higher emission in aggregated states compared to dilute solutions.
Patent Document 1 relates to an organic optical semiconductor chemical sensor for heavy metal detection containing nanoaggregates or nanoparticles of polymetallole, a silole-germole copolymer or a metallole-silane copolymer. According to Patent Document 1, it is possible to detect chromium (VI) and arsenic (V), which are ultra-trace amounts of carcinogenic heavy metals present in drinking water, immediately on site by measuring the degree of quenching of the photoluminescence of the nanoaggregates or nanoparticles whose photoluminescence has been amplified compared to that of the molecular states of polymers, and easy-to-operate and expensive materials are used.
Patent Document 2 utilizes the optical properties of distributed Bragg reflection-type porous silicon whose reflection peak in a desired wavelength range has been adjusted by chemically etching the surface of porous silicon (PSi), wherein polysilole, a photoluminescent polymer solution, is applied to the lower surface of the porous silicon film.
The siloles used in Patent Document 1 or 2 are 1,1-polysilols or a polysilole solution. While the 1,1-polysiloles exhibit aggregation-induced emission enhancement (AIEE) in a water environment, they possess a helical structure as confirmed in a space-filling model of 1,1-polysilole polymers shown in
Accordingly, the inventors of the present invention have made efforts to solve the above-described problems occurring in the related art, and as a result, have designed a novel conjugated silole polymer having benzene subunits containing sterically hindered functional groups (X) at the 2,5 positions of the silole backbone, and have found that a rigid 2,5-polysilole-based conjugated polymer having cavities in the solid-state silole polymer structure have high fluorescence properties not only in the solution state but also in the solid state, and in particular, facilitates the penetration of the analyte explosive vapor in the solid state compared to the solution state, and exhibits excellent sensing performance upon removal of the silole polymer to explosive vapors, and fast fluorescence recovery upon removal of explosive vapors, thereby completing the present invention.
An object of the present invention is to provide a novel highly fluorescent conjugated silole polymer.
Another object of the present invention is to provide a nitroaromatic explosive vapor sensor using the highly fluorescent conjugated silole polymer.
To achieve the above objects, the present invention provides a highly fluorescent conjugated silole polymer based on a rigid 2,5-polysilole having a cavity structure in the silole polymer backbone.
Preferably, the present invention provides a highly fluorescent conjugated silole polymer represented by Formula 1 below, which has benzene subunits containing sterically hindered functional groups (X) at the 2,5 positions of the silole backbone.
wherein X is a C2-C12 alkyl group or a C2-C12 alkoxy group, m is 2 to 20, and n is 1 to 5.
In an embodiment of the present invention, the benzene subunits containing sterically hindered functional groups (X) are octyloxybenzene subunits.
The highly fluorescent conjugated silole polymer is a 2,5-polysilole polymer having a semicrystalline structure, which has a cavity structure in the solid state and thermal stability.
The present invention also provides an explosive vapor sensor using the highly fluorescent conjugated silole polymer.
It provides an explosive vapor detection sensor in which the fluorescence quenching process upon exposure to explosive vapors and the photoluminescence (PL) recovery process upon removal of explosive vapors are repeated in real-time, and it is particularly useful for detecting nitroaromatic explosives (NAEs).
As the present invention provides a rigid 2,5-polysilole-based conjugated polymer having benzene subunits containing sterically hindered functional groups (X) at the 2,5 positions of the silole backbone, compared to 1,1-polysilole known as an explosive sensor, the penetration of the analyte explosive vapor is facilitated by cavities formed in the solid-state silole polymer structure, and in particular, the polysilole-based conjugated polymer is useful for detecting vapors of nitroaromatic explosives (NAEs).
The rigid 2,5-polysilole-based conjugated polymer of the present invention has a cavity structure in the solid-state silole polymer and binding strength with explosive vapors. Therefore, it can provide an explosive vapor detection sensor capable of real-time detection, where fluorescence quenching upon exposure to explosive vapors and rapid photoluminescence (PL) recovery processes upon removal of explosives are reproduced.
Hereinafter, the present invention will be described in detail.
The present invention provides a highly fluorescent conjugated silole polymer based on a rigid 2,5-polysilole having a cavity structure in the silole polymer backbone.
More specifically, the present invention provides a highly fluorescent conjugated silole polymer represented by Formula 1 below, which has benzene subunits containing sterically hindered functional groups (X) at the 2,5 positions of the silole backbone:
wherein X is a C2-C12 alkyl group or a C2-C12 alkoxy group, m is 2 to 20, and n is 1 to 5.
In a preferred example of the present invention, 2,5-polysilole P1 (X=C8 alkoxy, n=2, and m=10) and 2,5-polysilole P2 (X=C8 alkoxy, n=3, and m=10), in which X has an octyloxy group, were synthesized, and the fluorescence characteristics and AIEE and ICT properties thereof were investigated.
In addition, the 2,5-polysilol polymer of the present invention exhibits high solubility in organic solvents such as tetrahydrofuran (THF), toluene, CH2Cl2, and CHCl3, owing to the presence of a large number of free spaces within the polymer repeat units along with the octyloxy chains.
Spectroscopic results of the UV-VIS absorption and fluorescence properties of the 2,5-polysilole P1 or P2 polymers and 1,1-polysilole of the embodiment in various states such as solution, film, and aggregates [Table 1] show the differences in optical properties and emission behavior between polymers in different states. The 2,5-polysilole P1 or P2 polymers have consistent maximum absorption wavelengths (λab) due to the same polymer backbone structure, but the maximum emission wavelength (λem) of the fluorescence spectrum shows a red-shift behavior according to the solution-film-aggregate state. In particular, the emission peak of the P1 polymer showed a red-shift of 93 nm in the solid state compared to the THF solution and exhibited a high absolute quantum yield (QY) value of 44% in the solid state, surpassing the result of 1,1-polysilole (31.9%).
This aggregation process leads to the formation of larger structures or assemblies of polymer molecules, enhancing the absorption intensity. This phenomenon is consistent with the concept of AIEE, where the fluorescence properties of specific molecules are enhanced upon aggregation.
The water-induced aggregation of P1 and P2 at high water fractions is due to the hydrophobic interactions between polymer chains and the exclusion of water molecules in the hydrophobic regions, promoting the formation of larger aggregate structures by the polymer chains and increasing the absorption intensity.
The results in
According to the DLS result, the average diameters of the particles were about 113 nm for P1 aggregates in fw=99% and 194 nm for P2 aggregates in fw=80%, respectively, indicating that, as the water fraction increased, the particle size of polymer aggregates decreased. In addition, SEM images of (c) P1 and (d) P2 aggregates in THF/H2O mixtures confirm the formation of well-dispersed spherical nanoparticles in aqueous solution for both polymers.
In addition, fluorescence images of the 2,5-polysilole P2 polymer of the present invention under 365 nm UV and sunlight in various solvent conditions provide a visual representation of its emission behavior in different solvent environments [not shown].
Thus, the 2,5-polysilole polymers of the present invention can withstand high temperatures and may be suitable for use in various luminescent devices, and the thermal behavior of the polymers is important for ensuring the stability and longevity of devices including the polymers.
Furthermore, the present invention provides an explosive vapor sensor using the highly fluorescent conjugated silole polymer.
Upon contact with explosive vapors, sensing of the explosive vapors in the solid state can be confirmed by fluorescence quenching of the highly fluorescent conjugated silole polymer.
In general, when the binding forces between the polymer and analyte are strong, they prevent the escape of the analyte molecules from the polymer matrix, and thus can lead to irreversible quenching or very slow fluorescence recovery.
While 1,1-polysilole show minimal decreases in fluorescence intensity and require a considerably longer period to recover, the P1 polymer film of the present invention has a very weak binding affinity for TNT vapors and exhibits a semi-reversible response to TNT vapors or a very fast self-recovery process.
Thus, in the case of the 2,5-polysilols polymer of the present invention and explosive (TNT) vapor, the porous space due to the pore structure of the polymer and the TNT vapor interact with relatively weak binding forces, indicating that the 2,5-polysilole polymer can successfully detect TNT vapors on the film and can exhibit efficient fluorescence quenching and rapid recovery of PL intensity upon TNT removal.
From the above-described results, the highly fluorescent conjugated silole polymer of the present invention exhibits a fluorescence quenching process upon exposure to explosive (TNT) vapors and a fast photoluminescence (PL) recovery process upon removal of explosive (TNT) vapors, suggesting that it can be applied as an explosive vapor sensor capable of real-time detection.
In addition, the quenching behavior of the polymer was investigated for picric acid (PA) and TNT in both THF solution and aggregated states to investigate sensing performance for explosive vapors.
In the embodiment of the present invention, nitroaromatic explosives (NAE), including 2,4,6-trinitrotoluene (TNT) and picric acid (PA), are described as examples of explosives, but the present invention is not limited thereto.
Specifically, in addition to examples of the nitroaromatic explosives of the present invention, DNT (dinitrotoluene), TATB (triaminotrinitrobenzene or 2,4,6-triamino-1,3,5-trinitrobenzene), HNS (hexanitrostilbene), and tetryl may be included. In addition to the above-mentioned group of nitroaromatic explosives, at least one selected from the group consisting of cyclic nitramine-based compounds, non-cyclic nitramine-based compounds, and aromatic nitrogen heterocyclic compounds may be included.
Hereinafter, the present invention will be described in more detail by way of examples.
These examples are intended to explain the present invention in more detail, and the scope of the present invention is not limited to these examples.
This Example was carried out according to Reaction Scheme 1 below. A solution of compound 3 (dibutyl bis(phenylethynyl)silane, 5 g, 14.51 mmol) in 50 ml THF was added dropwise to a LiNaph solution over 10 minutes at room temperature. The mixture was stirred for an additional 40 minutes and then cooled to 0° C. ZnCl2 (7.9 g, 58 mmol) was added to the mixture, followed by dilution with 30 mL THF, thus obtaining intermediate Compound 5 as a black suspension. The mixture was stirred for 40 minutes at room temperature, and Compound 4 (1,4-diiodo-2,5-bis(octyloxy)benzene, 8.5 g, 14.51 mmol) and Pd(PPh3)2Cl2 (102 mg, 1 mol %) were added successively to the mixture, thus synthesizing Compound 6 as the reaction mixture. Compound 7 was synthesized through a one-pot reaction between Compound 6 and excess ZnCl2, and then the synthesized Compound 7 and Compound 6 were coupled to produce a 2,5-polysilole P1 polymer [1H NMR spectroscopy (300 MHz, CDCl3): δ 7.56-6.23 (multiplet, 14H, aromatic protons), 4.0-3.42 (multiplet, 8H, methylene groups) and 1.80-0.86 (multiplet, 78H, alkyl and silane groups). Weight-average molecular weight (Mw)=9,862, number-average molecular weight (Mn)=6,237, and polydispersity index (PDI)=1.581.
According to Reaction Scheme 1 below, intermediate Compound 5 obtained from Compound 3 was reacted with compound 4 (1,4-diiodo-2,5-bis(octyloxy)benzene) to synthesize Compound 6. Compound 7 was synthesized through a one-pot reaction between Compound 6 and excess ZnCl2, and then the synthesized Compound 7 and Compound 4 were coupled to produce a 2,5-polysilol P2 polymer [1H NMR spectroscopy (300 MHz, CDCl3): δ 7.56-6.23 (multiplet, 16H, aromatic protons), 4.0-3.42 (multiplet, 12H, methylene groups), and 1.80-0.86 (multiplet, 108H, alkyl and silane groups). Weight-average molecular weight (Mw)=4,970, number-average molecular weight (Mn)=3,764, and polydispersity index (PDI)=1.32].
A 1,1-polysilole polymer was produced according to Reaction Scheme 2 below.
To evaluate the spectroscopic properties of the 2,5-polysilol P1 and P2 polymers produced in Examples 1 and 2 and the 1,1-polysilol compound of Comparative Example 1, UV-VIS absorption spectra and fluorescence properties were evaluated in various states, including solution, film, and aggregate.
Referring to the results in Table 1 above, the 2,5-polysilole P1 polymer of Example 1 exhibited blue emission at 410 nm in the THF solution, while P2 emitted at 405 nm. The maximum absorption wavelength (λab) of the P1 and P2 polymers remained consistent in the THF solution due to the same conformation of the polymer backbones, and the maximum emission wavelength (λem) of the P1 and P2 polymers shifted to a longer wavelength (red-shift) depending on the state of solution→film→aggregate. However, the slight blue shift observed for P2 was attributed to the presence of an additional phenyl linker, which resulted in a slightly twisted structure in the excited state, reducing the long conjugation interaction in the polymer backbone.
On the other hand, the 1,1-polysilole of Comparative Example 1 has a maximum absorption wavelength of 368 nm in solution, and maintains the same emission wavelength of 513 nm in the solution, film and aggregate states.
In particular, the emission peak of P1 polymer showed a red shift of 93 nm in the solid state compared to the THF solution and exhibited a higher absolute quantum yield (QY) value of 44% in the solid state, surpassing that of 1,1-polysilole (31.9%).
From the results in
The emission spectra of the 2,5-polysilole P1 and P2 polymers of the present invention were measured in THF and THF/H2O mixtures to investigate the AIEE and ICT properties thereof.
As a result, it was confirmed that, in THF solution (fw—0 vol %), P1 emitted at 410 nm and P2 emitted at 405 nm. As the water fraction (fw) increased, the polymers underwent aggregation, resulting in changes in their emission behavior.
Furthermore, as the water fraction (fw) increases, the solvent polarity increases, and the ICT effect becomes more prominent in P1. This result is clearly observed in the solvatochromism, where the emission color of the polymer changes upon addition of water to the solution. Specifically, the increase in fw decreases the emission intensity of P1 up to fw—50 vol %, and at fw≥50 vol %, P1 aggregates, blocking the ICT channel and inducing the AIEE effect.
Consequently, the emission intensity of P1 increased, and the polymer mainly exhibited AIEE behavior. Notably, the PL intensity of the P1 aggregates at fw—99% was 7 times higher than that of the P1 aggregates at fw—60%. These results show that P1 exhibits dual active properties of AIEE and ICT depending on the solvent polarity and aggregation state, and both phenomena contribute to the emission behavior of the polymer.
Similarly, PL spectra of the P2 polymer according to the mole fraction showed quenching behavior due to aggregation (aggregation-caused quenching, ACQ) up to fw—60 vol % due to strong π-π interactions. However, at fw—80 vol % or higher, P2 exhibits AIEE behavior due to the presence of (octyloxy)benzene groups, which prevent π-π stacking interactions in the aggregated state. The restriction of intramolecular rotation (RIR) in the aggregated state blocks non-radiative decay and enhances emission intensity [not shown].
Both the 2,5-polysiole P1 and P2 polymers show ICT behavior due to the presence of electron-donating and electron-accepting units in their molecular structures.
In pure THF solution (fw—0 vol %), the absolute quantum yield (ΦF) values of P1 and P2 are 35.1% and 33.9%, respectively. In contrast, at fw—60 vol %, the ΦF value of P1 decreases to 16%, and in the case of P2, it decreases by 14.7%. However, as the water fraction (fw) gradually increases, the ΦF values of both polymers gradually increase, reaching maximum values of 39.5% for P1 and 19.4% for P2.
P1 shows a remarkable AIE effect with a ΦF value 2.4 times higher than that at fw—60 vol %, while P2 shows a 1.3 times higher ΦF value when it reaches fw—80 vol %.
To demonstrate the aggregation formation and the morphology of the 2,5-polysilole polymers of Examples 1 and 2 in THF/H2O mixtures, the dynamic light scattering (DLS) measurements and scanning electron microscope (SEM) morphologies were investigated.
According to the DLS results, the average diameters of the particles were about 113 nm for P1 in THF/H2O (fw—99 vol %) (
In addition, SEM images of P1 (
The 2,5-polysilole P1 and P2 polymers of Examples 1 and 2 were evaluated for their solvatochromism behaviors, as well as their emission spectra and absolute fluorescence quantum yields (QYs) in different solvents with varying polarities.
The PL spectra in different solvents indicate that, in hexane, P1 emits at 400 nm and P2 emits at 398 nm. As the solvent polarity increases to moderately polar solvents such as dichloromethane (DCM), the emission peaks red shift to 425 nm for P1 and 413 nm for P2.
Furthermore, when the solvent polarity becomes even higher such as N,N-dimethylformamide (DMF), the emission peaks of P1 and P2 continue to shift to longer wavelengths, reaching 424 and 418 nm, respectively. This solvatochromic shift in emission wavelength is a characteristic of fluorophores with D-A moieties, where the polarity of the solvent affects the stability of the excited state. That is, in highly polar solvents, the excited state of ICT-based polymers is more stable, resulting in a bathochromic shift (red shift) in the emission wavelength. This shift is accompanied by a decrease in quantum efficiency and emission intensity,
For the 2,5-polysilole P1 and P2 polymer powders of Examples 1 and 2, powder X-ray diffraction (PXRD) spectra were measured.
Specifically, the regular repeating units in the polymer structures contribute to the formation of these crystalline regions. Additionally, broad peaks suggest the presence of an amorphous component, and the broadness of the peaks indicates the presence of regions with disordered or less-defined molecular arrangement within the polymers.
The thermal properties of the 2,5-polysiole P1 and P2 polymers of Examples 1 and 2 were investigated using thermogravimetric analysis (TGA).
For the 2,5-polysilol P1 polymer of Example 1, it was evaluated whether TNT vapors could be detected by fluorescence quenching in the solid state.
TNT powder (1 g) was placed in a glass chamber and allowed to saturate for 1 hour at room temperature. The sensor device, containing polymer P1, was then positioned in front of the chamber with the gate open for 10 seconds to allow exposure to TNT vapors, during which the fluorescence intensity was recorded. Subsequently, the sensor device was removed from the chamber for 20 seconds to observe the recovery process as described above.
After removing the TNT analyte, about 85% of the photoluminescence (PL) intensity was recovered within 10 seconds. These results support that the P1 polymer film can detect TNT vapor through fluorescence quenching, as evidenced by the significant decrease in fluorescence intensity when exposed to TNT. At the same time, the P1 polymer film showed fast self-recovery performance within a very short time after removing the analyte.
The explosive sensing performance of the 2,5-polysilol P1 and P2 polymers of the Examples was evaluated by investigating the quenching behavior of the polymers for picric acid (PA) and TNT in both THF solution and aggregate states.
In the presence of the explosives (TNT or PA), the polymers showed fluorescence quenching characteristics in all states. The quenching data were analyzed using the Stern-Volmer equation, which relates the fluorescence intensities in the absence (I0) and presence (I) of the analyte [A] through the Stern-Volmer constant (Ksv), and the results are shown in Table 2 below. At this time, for the nanoaggregates, THF/H2O (fw—99 vol %) was used for P1 and THF/H2O (fw—80 vol %) was used for P2.
The Stern-Volmer plots showed a linear relationship under all conditions of solution and nanoaggregate states of P1 and P2. As confirmed in Table 2 above, the Stern-Volmer constants (Ksv) of P1 and P2 nanoaggregates for PA and TNT were observed to be significantly higher than those of the solution state.
In addition, the Stern-Volmer constants of P1 nanoaggregates for PA and TNT were determined to be 2,344 and 800 M−1, respectively. The Stern-Volmer constant of P2 nanoaggregates was similar to that of P1 for TNT, while it was twice as high as P1 for PA.
On the other hand, the Stern-Volmer constants (Ksv) of the 1,1-polysilole of Comparative Example 1 in the presence of the TNT analyte in the solution and nanoaggregate states showed larger Ksv values compared to the P1 and P2 nanoaggregates.
These results suggest that the 1,1-polysilole molecule has a flexible molecular structure that can easily interact with explosives, resulting in higher PL quenching. On the other hand, the lower Ksv values of P1 and P2 can be explained by the reduced intercalation of explosive analytes in both solution and nanoaggregate states.
Therefore, the 2,5-polysilole P1 and P2 polymers with smaller Stern-Volmer constants than 1,1-polysilole can be explained by their relatively non-flexible structure, and the significantly weak binding affinity between polysiloles and explosives (TNT or PA) supports the reversible results of quenching or very fast recovery.
To evaluate the fluorescence lifetime of the 2,5-polysilol P1 polymer of the Example, the fluorescence decay of P1 in the solution state and nanoaggregate state was observed for various concentrations of picric acid (PA).
Although the present invention has been described in detail only with respect to the described embodiments, it is apparent to those skilled in the art that various changes and modifications are possible without departing from the technical idea of the present invention. It is to be understood that these changes and modifications fall within the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2023-0156790 | Nov 2023 | KR | national |
