One-dimensional pyrene-based organic framework nonlinear optical material and preparation and application thereof

Abstract

This invention relates to one-dimensional pyrene-based organic framework nonlinear optical materials, their preparation, and applications. These materials are prepared by direct Schiff base condensation reactions of pyrene-based amino monomers (Py) with different dialdehyde monomers (PTDE, PTBE, PDA) under solvothermal conditions, constructing a series of one-dimensional linear organic framework (COF) segments, which are then further fabricated into thin film materials. The resulting materials exhibit highly ordered crystallinity, an extended π-conjugated framework, and distinct donor-acceptor (D-A) charge transfer channels. This invention is the first to achieve a significant reverse saturation absorption (RSA) effect in one-dimensional pyrene-based D-A COFs (Py-PTDE, Py-PTBE, Py-PDA) under femtosecond laser excitation (800 nm, 1550 nm). In particular, the Py-PTDE material exhibits a significantly higher effective nonlinear absorption coefficient (β). eff It reaches 116.89 cm·GW at 800 nm and 1550 nm, respectively. ‑1 With 337.03 cm·GW ‑1 This invention not only significantly outperforms the precursor material and two other COF materials, but also exhibits a lower optical limiting threshold in the near-infrared band. This superior performance is primarily attributed to its more efficient D–A interactions, narrower optical bandgap, and more efficient intramolecular charge transfer channels. The material preparation method of this invention is simple and highly reproducible, and the resulting COF thin film possesses excellent thermal and optical stability, making it directly applicable to the fabrication of optical limiting devices, ultrafast optical response devices, and other third-order nonlinear optical applications.

Description

Technical Field

[0001] This invention belongs to the field of nonlinear optics technology, and relates to one-dimensional pyrene-based organic framework nonlinear optical materials and their preparation and application. Background Technology

[0002] Covalent organic frameworks (COFs) are a class of crystalline porous materials formed by organic building blocks linked by reversible covalent bonds. Due to their lightweight, highly designable structure, large specific surface area, and excellent chemical and thermal stability, they have attracted widespread attention in recent years in the fields of photocatalysis, gas adsorption, energy storage, and photonics. Particularly in optical applications, the π-conjugated structure of COFs enables effective light absorption and electron delocalization, making them an important candidate system for developing next-generation nonlinear optical materials.

[0003] However, current research on nonlinear optics of COFs mainly focuses on two-dimensional and three-dimensional structures. Two-dimensional COFs generally rely on interlayer π-π stacking to construct electronic coupling pathways, but strong interlayer interactions easily lead to decreased dispersion, and random interlayer slip causes discontinuous charge channels, thus limiting the third-order nonlinear response. In addition, the synthesis of two-dimensional COFs often requires strict solvent systems and reaction conditions, making structural control quite difficult.

[0004] Three-dimensional COFs are usually formed by connecting polyhedral units in space. Their three-dimensional conjugated paths often make it difficult to achieve effective three-dimensional conjugated electron delocalization, resulting in limited optical bandgap control capabilities. Consequently, their performance in antisaturation absorption and laser limiting is generally weaker than that of two-dimensional conjugated systems. In contrast, one-dimensional COFs, as a novel topological structure that has emerged in recent years, have unique structural advantages: (1) One-dimensional chain segments extend regularly along a certain direction, forming highly oriented linear channels for functional groups, which is beneficial for electron coupling and exciton migration; (2) The linear structure avoids the problem of strong interlayer π-π stacking in two-dimensional COFs, resulting in materials with better dispersibility and processability; (3) The donor-acceptor (D-A) structure can be arranged along the chain direction, maximizing the intramolecular charge transfer (ICT) effect, thereby reducing the bandgap, enhancing light absorption, and improving the third-order polarizability. On the other hand, constructing a D-A conjugated network with strong ICT characteristics is an effective strategy to improve the third-order nonlinear response. Among them, pyrene molecules, as highly conjugated planar aromatic rings, possess excellent electron-donating ability, a rigid framework, and stable excited-state properties, and are widely used in fluorescent and optical functional materials. Existing research has mainly focused on the application of pyrene molecules in two-dimensional COF or small molecule systems, and the construction of regularly arranged one-dimensional pyrene D–A COF structures has not yet been applied to the field of nonlinear optics.

[0005] In recent years, researchers have mostly focused on preparing COF thin films to improve their nonlinear optical properties. Doping COF with organic polymers is a promising strategy, which requires the COF material to have good dispersibility in solvents. One-dimensional COFs exhibit weaker interlayer interactions, which is a significant advantage over two-dimensional / three-dimensional COFs. This invention is proposed based on this background. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies by providing one-dimensional pyrene-based organic framework nonlinear optical materials, their preparation, and applications. It aims to solve problems such as poor dispersion, limited bandgap tunability, and difficulty in post-processing into thin films in existing COF applications. This material, when further fabricated into thin-film devices, exhibits excellent nonlinear optical anti-saturation absorption response under ultrafast laser excitation, and can be further used in fields such as optical integration.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] One of the technical solutions of the present invention provides a method for preparing a one-dimensional pyrene-based organic framework nonlinear optical material, comprising the following steps:

[0009] (1) Weigh the monomers 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetraphenylamine (Py) and dialdehyde monomers (PDA, PTDE, PTBE), mix them, disperse and dissolve them in an organic solvent, sonicate for 10 minutes, and then add an aqueous solution of acetic acid.

[0010] (2) Transfer the reaction solution from step (1) into a glass tube, seal it, place it in an oven, heat it to react, wash it, and dry it to obtain the target product;

[0011] (3) Disperse the product of step (2) in an organic solvent, add polymethyl methacrylate (PMMA), heat and stir to obtain a uniform dispersion, spin coat the obtained dispersion onto the substrate, put it in a vacuum drying oven, heat and dry to obtain a thin film material for nonlinear optical testing.

[0012] Furthermore, in step (1), the molar ratio of dialdehyde monomer to pyrene monomer is 1:2 to 4.

[0013] Furthermore, in step (1), the solvents for dissolving the pyrene monomer and the dialdehyde monomer are o-dichlorobenzene and n-butanol, and the volume ratio of o-dichlorobenzene to n-butanol is 1:2 to 4.

[0014] Furthermore, in step (1), the concentration of the acetic acid aqueous solution is 6–12 mol. L -1 The volume ratio of the aqueous acetic acid solution to the total solvent of the dispersed monomer is 1:5 to 10.

[0015] Furthermore, in step (2), the reaction glass tube is degassed by three consecutive freezing, vacuuming, and thawing cycles in a liquid nitrogen bath, and then sealed with a flame. The reaction temperature is 100-130 °C and the reaction time is 72-120 h.

[0016] Furthermore, in step (2), the washing process is as follows: the washing solution is repeatedly washed with tetrahydrofuran, methanol, ethanol and deionized water in sequence until the washing solution is clear and colorless. The drying temperature is 60-80 ℃.

[0017] Furthermore, in step (3), the dispersing solvent is N,N-dimethylformamide, the dispersion method is ultrasonic dispersion, and the concentration of COF in the dispersion is 1–2 mg. mL -1 The concentration of PMMA is 2–2.5 g. mL -1 The reaction temperature is 60–80 °C, and the reaction time is 6–12 h.

[0018] Furthermore, in step (3), the spin coating speed is 100 rpm, the heating and drying temperature is 60-80 ℃, and the time is 12-24 h.

[0019] The second technical solution of the present invention is the application of one-dimensional pyrene-based organic framework materials in the fabrication of nonlinear optical devices.

[0020] The one-dimensional pyrene-based organic framework nonlinear optical materials prepared in this invention were validated by Z-scan results, which showed excellent RSA responses of the three one-dimensional COF materials under femtosecond (fs) pulses at 800 and 1550 nm. Notably, Py-PTDE exhibited a significantly higher effective nonlinear absorption coefficient (β0.05) than Py-PDA and Py-PTBE. eff This verifies that its more pronounced D-A structure and enhanced ICT are key factors in constructing high-performance nonlinear optics. Meanwhile, optical confinement performance tests of Py-PTDE show that its OL thresholds under femtosecond pulses at excitation wavelengths of 800 and 1550 nm are 2.39 and 0.38 mJ, respectively. cm -2 This finding, which outperforms most recently reported two-dimensional organic / inorganic nonlinear optical materials, underscores the importance of developing one-dimensional COF systems based on pyrene electron donors.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] 1. The one-dimensional pyrene-based organic framework nonlinear optical material prepared by the present invention reduces interlayer π-π stacking, and overcomes the problems of poor dispersibility of traditional two-dimensional COFs and limited conjugation paths of three-dimensional COFs. The material of the present invention can maintain a stable and uniform dispersion state in polymer matrices such as PMMA without obvious agglomeration, which ensures the transparency and uniformity of the optical film. Meanwhile, the formed solid film can stably withstand femtosecond laser irradiation at a high repetition frequency, exhibiting good optical and mechanical stability.

[0023] 2. The present invention regulates the D-A interaction strength by utilizing the order of strength of acceptor units (PDA<PTBE<PTDE), realizing precise adjustment of the band gaps of three one-dimensional COFs within the range of 2.10–2.32 eV. At the same time, the strong electron-withdrawing ability of PTDE greatly enhances the chainwise ICT, forming a stable narrow-bandgap structure, thereby significantly improving the nonlinear optical absorption performance at near-infrared 800 nm and 1550 nm.

[0024] 3. The one-dimensional pyrene-based organic framework nonlinear optical material prepared in the present invention can be used in photoresponsive devices, exhibits reverse saturable absorption under the excitation of ultrafast laser pulses, and the optical limiting thresholds at 800 nm and 1550 nm reach 2.39 mJ cm -2 and 0.38 mJ cm -2 , which are lower than the thresholds of reported traditional optical limiting materials. The present invention provides a simple preparation method for the one-dimensional pyrene-based organic framework nonlinear optical material, which is of great significance for the application of one-dimensional framework film materials in ultrafast photonic devices. Brief Description of the Drawings

[0025] Figure 1 is a schematic diagram of the synthesis of the one-dimensional pyrene-based organic framework material prepared by the present invention.

[0026] Figure 2 is the infrared spectra of the one-dimensional pyrene-based organic framework material prepared by the present invention and the raw materials.

[0027] Figure 3 are the X-ray diffraction pattern, simulated stacking model structure and X-ray diffraction refinement data graph of the one-dimensional pyrene-based organic framework material prepared by the present invention.

[0028] Figure 4 is the scanning electron microscope image of the one-dimensional pyrene-based organic framework material prepared by the present invention.

[0029] Figure 5 is the transmission electron microscope image of the one-dimensional pyrene-based organic framework material prepared by the present invention.

[0030] Figure 6These are the UV-Vis diffuse reflectance absorption spectra and Tauc dot plots of the one-dimensional pyrene-based organic framework material and raw materials prepared in this invention.

[0031] Figure 7 This is a nonlinear Z-scan spectrum of the one-dimensional pyrene-based organic framework material prepared in this invention at 800 nm and 1550 nm under femtosecond laser light, and a graph showing the variation of normalized transmittance with input laser intensity. Detailed Implementation

[0032] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0033] In the following examples, unless otherwise specified, the raw materials or processing techniques are conventional commercially available raw materials or conventional processing techniques in the field.

[0034] Example 1:

[0035] The preparation of one-dimensional organic framework materials specifically includes the following steps:

[0036] (1) Weigh the same amount of pyrene monomer Py (0.015 mmol, 8.5 mg) into each of three glass tubes, and add diformaldehyde monomers PTDE (0.03 mmol, 7.1 mg), PTBE (0.03 mmol, 11.6 mg), and PDA (0.03 mmol, 4.1 mg), respectively. Disperse the three glass tube samples in a mixed solvent of 0.8 mL n-butanol and 0.2 mL o-dichlorobenzene, sonicate for 10 minutes, and then add 0.1 mL 6 mol of [a specific solvent] to each sample. mL -1 An aqueous solution of acetic acid.

[0037] (2) The three glass tubes were subjected to solvent degassing treatment by three consecutive freezing-evacuation-thawing cycles in liquid nitrogen. After the treatment was completed, the tubes were sealed with a flame. Then the reaction mixture was heated at 120°C for a long time for 72 hours.

[0038] (3) After the reaction is complete, a yellow precipitate is formed at the bottom of the glass tube. The precipitate is filtered and washed repeatedly with tetrahydrofuran, methanol, ethanol and deionized water until the washing liquid is clear and colorless. The target products are obtained by vacuum drying and are named Py-PTDE, Py-PTBE and Py-PDA, respectively.

[0039] Example 2:

[0040] The one-dimensional Py-PTDE, Py-PTBE, and Py-PDA synthesized in Example 1 were used to dope PMMA, resulting in Py-PTDE / PMMA, Py-PTBE / PMMA, and Py-PDA / PMMA films, respectively, which were then used for nonlinear Z-scan testing. The specific steps are as follows:

[0041] (1) Weigh out one-dimensional organic framework material (5 mg) and disperse it in 5 mL of N,N-dimethylformamide. Sonicate for 30 minutes to make it uniformly dispersed. Then add PMMA (2 g) and stir at 80°C for 12 h to form a uniform mixture.

[0042] (2) The mixed dispersion from step (1) in Example 2 was spin-coated onto a glass substrate at 100 rpm for 10 s. Then it was dried in a vacuum drying oven at 60 ℃ for 24 h to obtain PMMA films doped with Py-PTDE, Py-PTBE and Py-PDA, respectively.

[0043] The thin film material prepared above was used for ultrafast laser optical testing. Under pulsed laser excitation at 35 fs, with wavelengths in the 800–1600 nm band, nonlinear optical performance was tested using Z-scan technology.

[0044] Figure 1 This is a schematic diagram illustrating the synthesis of the one-dimensional pyrene-based organic framework material prepared in Example 1 of this invention. The Py-PDA, Py-PTDE, and Py-PTBE prepared in this invention were obtained by a Schiff base reaction of Py with PDA, PTDE, and PTBE at 120 °C under acetic acid solution catalysis for 72 h. According to the design principle, Py-PDA is formed by Py and PDA bonded at 120°, while Py-PTDE and Py-PTBE are constructed by Py bonded to PTDE and PTBE at 60°, respectively.

[0045] Figure 2 Infrared spectra of the one-dimensional pyrene-based organic framework material and raw materials prepared in Example 1 of this invention. Figure 2 It can be seen that for these three one-dimensional COFs, the range is 3200-3340 cm. -1 The characteristic peak is attributed to the stretching vibration of the N−H bonds in Py, located at 1700 cm⁻¹. -1 1691 cm -1 and 1712 cm -1 The peaks can be attributed to the stretching vibrations of the C=O bonds in PTDE, PTBE, and PDA, respectively, and their intensity is significantly weaker compared to the raw materials. In Py-PTDE, Py-PTBE, and Py-PDA, the peak at 1618 cm⁻¹ is particularly strong. -1 1612 cm -1 and 1625 cm -1The appearance of the C=N bond stretching vibration peak indicates that the amine monomer and the aldehyde monomer have successfully condensed to form a new COF bridging group: an imine bond.

[0046] Figure 3 X-ray diffraction pattern, simulated stacking model structure, and refined X-ray diffraction data of the one-dimensional pyrene-based organic framework material prepared in Example 1 of this invention. Figure 3 It can be seen that all three one-dimensional COFs exhibit good crystallinity, and the refined data all show low residual values, indicating that the experimental data results match the simulated one-dimensional AA packing model.

[0047] Figure 4 Scanning electron microscope (SEM) images of the one-dimensional pyrene-based organic framework materials prepared in Example 1 of this invention. The SEM images show that these three one-dimensional COFs have different nanorod morphologies. Py-PTDE exhibits a relatively smooth surface (…). Figure 4 a), while Py-PTBE ( Figure 4 b) and Py-PDA ( Figure 4 c) The surface of the nanorods has a nanoflower-like pattern.

[0048] Figure 5 Transmission electron microscopy (TEM) image of the one-dimensional pyrene-based organic framework material prepared in Example 1 of this invention. From... Figure 5 As can be seen, all three one-dimensional COFs exhibit a nanorod-like nanosheet morphology. The clear lattice fringes indicate that the one-dimensional COFs possess high crystallinity. The measured lattice spacings are: 1.65 nm for Py-PTDE, 2.03 nm for Py-PTBE, and 1.55 nm for Py-PDA. These values, along with X-ray diffraction (…),… Figure 3 The observed height of the (110) crystal plane corresponds to this.

[0049] Figure 6 The UV-Vis diffuse reflectance absorption spectrum and Tauc diagram of the one-dimensional pyrene-based organic framework material prepared in Example 1 of this invention are shown. Figure 6 As can be seen, the absorption peaks of Py-PTDE, Py-PTBE, and Py-PDA are approximately 625, 575, and 555 nm, respectively, indicating that they possess strong visible light absorption capabilities and a broad spectral coverage. Analysis of the Tauc plots of the absorption spectra... Figure 6 (b) The optical band gaps were found to be 2.10 eV for Py-PTDE, 2.26 eV for Py-PTBE, and 2.32 eV for Py-PDA. These results indicate that the introduction of 1,10-phenanthroline leads to a more significant band gap narrowing effect compared to pyridine, which is attributed to its stronger electron-withdrawing properties and electron delocalization.

[0050] Figure 7The nonlinear Z-scan spectrum and normalized transmittance as a function of input laser intensity for the one-dimensional pyrene-based organic framework thin film material prepared in Example 2 of this invention under femtosecond laser excitation are shown. At wavelengths of 800 nm and 1550 nm, with a pulse width of 35 fs, the one-dimensional pyrene-based organic framework thin film material exhibits an anti-saturable absorption response, and the Py-PTDE optical limiting threshold reaches 2.39 mJ. cm -2 and 0.38 mJ cm -2 At the focal point, their normalized transmittance is as low as 0.43 and 0.27, respectively, and the optical limiting thresholds of Py-PTBE and Py-PDA at 1550 nm wavelength reach 1.06 mJ, respectively. cm -2 and 1.43 mJ cm -2 The superior nonlinear optical performance of Py-PTDE compared to Py-PDA stems from its extended intramolecular π-conjugation and enhanced donor-acceptor interactions, which facilitate more efficient ICT transitions and lead to a narrower optical bandgap. However, in Py-PTBE, the introduction of an additional benzene ring may partially offset this effect by altering the electronic structure and increasing the spatial separation of the conjugated segments, ultimately resulting in a wider bandgap and relatively weaker nonlinear optical performance compared to Py-PTDE.

[0051] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing one-dimensional pyrene-based organic framework nonlinear optical materials, characterized in that, Includes the following steps: (1) Weigh out the pyrene monomer 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetraphenylamine and the dialdehyde monomers 1,10-phenanthroline-2,9-dicarboxaldehyde, 2,9-bis[P-(formyl)phenyl]-1,10-phenanthroline and 2,6-pyridinedicarboxaldehyde respectively. Mix the pyrene monomer and the three dialdehyde monomers separately and disperse them in an organic solvent. After sonication for 10 minutes, add an aqueous acetic acid solution. The molar ratio of the pyrene monomer and the three dialdehyde monomers is 1:2 to 4. (2) Transfer the reaction solution from step (1) into a glass tube, seal it, place it in an oven, heat it to react, wash it, and dry it to obtain the target product; (3) The product from step (2) was dispersed in N,N-dimethylformamide organic solvent, polymethyl methacrylate was added, and the mixture was heated, stirred, and ultrasonically dispersed to obtain a uniform dispersion. The resulting dispersion was spin-coated onto a glass substrate and placed in a vacuum drying oven for drying to obtain a homogeneous thin film material for nonlinear optical testing. The dispersion used in the preparation of the uniform dispersion was N,N-dimethylformamide, and the dispersion method involved was ultrasonic dispersion. The concentration of the one-dimensional pyrene-based organic framework material in the dispersion in the organic solvent was 1–2 mg. mL -1 The concentration of polymethyl methacrylate in the dispersion in the organic solvent was 0.4 g. mL -1 The dispersion was heated and stirred at a temperature of 60–80 °C for 6–12 h.

2. The method for preparing the one-dimensional pyrene-based organic framework nonlinear optical material according to claim 1, characterized in that, In step (1), the solvent for dissolving the pyrene monomer and the dialdehyde monomer is composed of o-dichlorobenzene and n-butanol, and the volume ratio of o-dichlorobenzene to n-butanol is 1:2 to 4.

3. The method for preparing the one-dimensional pyrene-based organic framework nonlinear optical material according to claim 1, characterized in that, In step (1), the concentration of the acetic acid aqueous solution is 6–12 mol. L -1 The volume ratio of the aqueous acetic acid solution to the total solvent of the dispersed monomer is 1:5 to 10.

4. The method for preparing the one-dimensional pyrene-based organic framework nonlinear optical material according to claim 1, characterized in that, In step (2), the reaction glass tube is degassed in a liquid nitrogen bath through three consecutive freezing-vacuuming-thawing cycles, and then sealed with a flame. The reaction temperature is 100-130 °C and the reaction time is 72-120 h.

5. The method for preparing a one-dimensional pyrene-based organic framework nonlinear optical material according to claim 1, characterized in that, In step (2), the washing process is as follows: the washing is repeated with tetrahydrofuran, methanol, ethanol and deionized water in sequence until the washing liquid is clear and colorless, and the drying temperature is 60-80 ℃.

6. The method for preparing a one-dimensional pyrene-based organic framework nonlinear optical material according to claim 1, characterized in that, In step (3), the rotation speed is 100 rpm, the heating and drying temperature is 60-80 ℃, and the time is 12-24 h.

7. The one-dimensional pyrene-based organic framework nonlinear optical material as described in claim 1, characterized in that, Used for the construction of ultrafast laser-responsive thin-film devices.

8. The one-dimensional pyrene-based organic framework nonlinear optical material as described in claim 7, characterized in that, The ultrafast laser-response thin-film device is applicable to ultrafast broadband laser wavelengths of 800–1600 nm.

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