Design method, material and application of ultrafast broadband optical amplitude limiting material of double-branched chain type molecule based on torsion regulation and control

Abstract

The invention discloses a torsion regulation-based ultrafast broadband optical limiting material design method, a material and application, and relates to the field of optical limiting materials.The torsion regulation-based ultrafast broadband optical limiting material design method comprises the steps that structure optimization is conducted on double-branched-chain polycyclic aromatic hydrocarbon molecules through a computer based on the density functional theory, then the vibration frequency of each molecule is calculated, and the vibration frequency of each molecule is calculated; ensuring that the molecular configuration of the double-branched-chain type polycyclic aromatic hydrocarbon molecule after structure optimization is at the lowest point of a potential energy surface, and obtaining the double-branched-chain type molecule with a polycyclic conjugated structure, wherein the dihedral angle between a core group and a side chain group is 90 degrees; and adjusting a pi bridge between the core group with the polycyclic conjugated structure and the side chain group, so that a dihedral angle between the core group and the side chain group is gradually changed from 90 degrees to 0 degree, thereby obtaining the ultrafast broadband optical limiting material. The research of the invention clearly clarifies the anti-saturated absorption enhancement mechanism of the two-branch anthracene derivatives, and lays a foundation for the development of novel organic optical limiting materials.

Description

Technical Field

[0001] The present invention belongs to the field of optical limiting materials, and in particular relates to a design method, material and application of an ultrafast broadband optical limiting material based on torsion-regulated double-branched molecules. Background Art

[0002] When a strong laser interacts with a medium, a phenomenon called reverse saturation absorption occurs, characterized by a decrease in the transmittance of the medium as the incident light intensity increases. Therefore, reverse saturation absorption is often used in laser protection, which is often referred to as optical limiting applications. With the rapid development of laser technology, the biggest challenge facing laser protection is the diversification of output wavelengths and pulse widths. Traditional optical limiting materials can no longer meet the needs of laser protection. By improving the reverse saturation absorption properties of polycyclic aromatic hydrocarbons, such as two-photon absorption and excited-state absorption, it is expected to solve the problem of diversification of output wavelengths and pulse widths in laser protection. Two-photon absorption is an ideal and effective mechanism for achieving ultrafast broadband optical limiting effects. On this basis, by introducing excited-state absorption to establish the photophysical mechanism of two-photon-induced excited-state absorption, the long pulse response of the material can be further improved. However, the structural-property-based regulation mechanism of reverse saturation absorption of polycyclic aromatic hydrocarbons is still unclear, which hinders its development and application. Summary of the Invention

[0003] The purpose of the present invention is to provide a design method, material and application of ultrafast broadband optical limiting materials based on torsion-regulated double-branched molecules, laying a foundation for the design of new organic optical limiting materials.

[0004] The present invention provides a method for designing an ultrafast broadband optical limiting material based on a torsion-regulated double-branched molecule, wherein the method is carried out according to the following steps:

[0005] Step 1: Structural optimization of the dibranched polycyclic aromatic hydrocarbon molecule is performed by computer based on density functional theory, and then the vibration frequency of each molecule is calculated to ensure that the molecular configuration of the dibranched polycyclic aromatic hydrocarbon molecule after structural optimization is at the lowest point on the potential energy surface, thereby obtaining a dibranched molecule having a polycyclic conjugated structure with a dihedral angle of 90° between the core group and the side chain group;

[0006] Step 2: adjusting the π bridge between the core group and the side chain group having a polycyclic conjugated structure so that the dihedral angle between the core group and the side chain group gradually changes from 90° to 0°, thereby obtaining the ultrafast broadband optical limiting material.

[0007] Furthermore, the vibration frequency of each molecule is calculated as described in step 1, so that the vibration frequency of each molecule is a real frequency, and the molecular configuration of the dibranched polycyclic aromatic hydrocarbon molecule after structural optimization is ensured to be at the lowest point on the potential energy surface.

[0008] Furthermore, in step 1, the molecular configuration of the double-branched polycyclic aromatic hydrocarbon molecule is ensured to be at the lowest point on the potential energy surface after structural optimization, a group having a polycyclic conjugated structure is selected as the core group, the connecting π bridge between the core group and the side chain group is selected as a C-C bond, and the side chain group is a six-membered ring structure, thereby forming a molecular configuration having a double-branched conjugated structure.

[0009] Furthermore, the core group is naphthalene, anthracene or pyrene, and the six-membered ring structure is pyridine or benzene ring.

[0010] Furthermore, the core group is an anthracene derivative having a polycyclic conjugated structure, the side chain group is pyridine, and the dihedral angle between the anthracene core and the side chain group is 90°.

[0011] Furthermore, the anthracene derivative with a dihedral angle of 90° between the anthracene core and the side chain group is a dibranched anthracene derivative ZN1, whose chemical name is 4,4-(9,10-anthracenediyl)bis[pyridine] and whose chemical structure is:

[0012] .

[0013] Furthermore, in step 2, the adjustment of the π bridge between the anthracene nucleus and the side chain group is to select a π bridge connecting bond position C=C bond or C≡C bond, so that the dihedral angle between the anthracene nucleus and the side chain group changes from 90° to 53° or 0°.

[0014] The optical limiting material obtained by the design method of an ultrafast broadband optical limiting material based on a torsion-controlled double-branched molecule of the present invention is a di-branched anthracene derivative ZN2-3, and the chemical structure of the di-branched anthracene derivative ZN2-3 is:

[0015] , where R is C=C or C≡C.

[0016] The optical limiting material of the present invention, the di-branched anthracene derivative ZN2-3 is ZN2, the chemical name is 9,10-di-β-(4-pyridyl)vinylanthracene, and the chemical structure is:

[0017]

[0018] Or ZN3, chemical name 9,10-bis(pyridin-4-ylethynyl)anthracene, chemical structure formula is:

[0019] .

[0020] The application of the optical limiting material of the present invention, the di-branched anthracene derivatives ZN2 and ZN3 are used for laser protection.

[0021] The present invention has the following beneficial effects:

[0022] This paper designs and prepares bibranched polycyclic aromatic hydrocarbon molecules based on quantum chemical calculations, and provides three bibranched anthracene derivatives: ZN1 (4,4-(9,10-anthracenediyl)bis[pyridine]), ZN2 (9,10-di-β-(4-pyridyl)vinylanthracene), and ZN3 (9,10-bis(pyridin-4-ylethynyl)anthracene), verifying their reverse saturation absorption properties. The structural composition of these anthracene derivatives consists of three parts: an anthracene core, pyridine groups located on two side chains, and a π-conjugated bridge, see Figure 1 (a). Geometry optimization (see Figure 1 (b)) shows that by introducing different π bridges (single bond, double bond and triple bond), the dihedral angle between the anthracene core and the peripheral group of the side chain is adjusted from 90° to 0°, resulting in completely different electronic transition characteristics. Hole electron analysis was used to characterize the different electronic transition characteristics: intramolecular charge transfer and localized excitation. Femtosecond z-scan experiments showed that in these di-branched anthracene derivatives, the present invention successfully established the photophysical mechanism of two-photon induced excited state absorption, and significantly improved its broadband anti-saturation absorption performance through the regulation and control of molecular structure. In addition, femtosecond optical limiting experiments showed that anthracene derivatives ZN2 and ZN3 exhibited excellent ultrafast broadband optical limiting performance in the range of 515-650 nm, and the optical limiting threshold of compound ZN3 at 515 nm was as low as 9.11 mJ / cm 2 The research of the present invention clearly illustrates the reverse saturation absorption enhancement mechanism of these di-branched anthracene derivatives, laying a foundation for the development of new organic light-limiting materials.

[0023] Taking di-branched anthracene derivatives as an example, the present invention illustrates the reverse saturation absorption mechanism of di-branched polycyclic aromatic hydrocarbon molecules through torsional regulation to enhance two-photon-induced excited-state absorption, reveals the optimization approach for their femtosecond broadband optical limiting performance, and lays the foundation for the design of new organic optical limiting materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The molecular structures and optimized structures of anthracene derivatives ZN1, ZN2 and ZN3 are shown;

[0025] Figure 2 Frontier molecular orbitals (a) and hole-electron distribution (b) diagrams of anthracene derivatives ZN1, ZN2, and ZN3;

[0026] Figure 3 Femtosecond Z-scan experimental images of anthracene derivatives ZN1, ZN2, and ZN3 at 515 nm (a), 600 nm (b), and 650 nm (c);

[0027] Figure 4These are the experimental images of femtosecond optical limiting of anthracene derivatives ZN2 and ZN3 at 515 nm and 650 nm. DETAILED DESCRIPTION

[0028] In order to make the objectives, technical solutions and advantages of the embodiments of the present invention more clearly understood, the spirit of the contents disclosed in the present invention will be described in detail below. After understanding the embodiments of the contents of the present invention, any technician in the relevant technical field can change and modify the contents of the present invention based on the techniques taught by the contents of the present invention without departing from the spirit and scope of the contents of the present invention.

[0029] The exemplary embodiments of the present invention and the description thereof are used to explain the present invention but are not intended to limit the present invention.

[0030] Example 1

[0031] Through molecular engineering of π-conjugated bridges, this example systematically modulated the dihedral angle (θ) between the anthracene core and the peripheral substituents in these dibranched anthracene derivatives from orthogonal (θ = 90°) to coplanar (θ < 1°). Using time-dependent density functional theory (TDDFT / B3LYP / 6-311g(d,p)), the present invention calculated the first 50 excited states and used sum-of-states theory to calculate the static second-order hyperpolarizability of the molecules, γ(0;0,0,0). The static second-order hyperpolarizabilities of ZN1, ZN2, and ZN3 are γ(0;0,0,0), ... 、 and , achieving a 56.6-fold enhancement.

[0032] Among frontier molecular orbitals, the HOMO orbital represents the highest energy, electron-occupied molecular orbital, while the LUMO orbital represents the lowest energy, unoccupied molecular orbital. Therefore, the narrowest band gap between the HOMO and LUMO orbitals exhibits the highest propensity for electronic transitions due to their minimal energy separation. Calculations show that the HOMO-LUMO band gap decreases monotonically (ZN1: 3.48 eV; ZN2: 2.97 eV; ZN3: 2.64 eV), and this continuous narrowing is directly correlated with the enhanced electronic transition probability. Notably, the 26.7% decrease in the band gap from ZN1 to ZN3 (ΔE = 0.84 eV) indicates a significant reduction in the transition energy barrier and a significant enhancement in the electronic transition probability.

[0033] The orthogonal orientation (90°) of the anthracene core and side chains in ZN1 induces complete localization of the HOMO and LUMO orbitals on the anthracene core, leading to characteristic localized excitation behavior during HOMO-LUMO transitions. The reduced dihedral angle in ZN2 leads to partial delocalization of electron density, with the HOMO remaining primarily localized on the anthracene core, while also appearing on the side chains. Notably, the LUMO distribution encompasses both the anthracene core and the side chains, indicating hybrid excitation behavior in the HOMO-LUMO transition, characterized by concurrent localized excitation and intramolecular charge transfer. The introduction of an acetylene π bridge in ZN3 induces complete planarization of the molecule (dihedral angle < 1°), resulting in complete delocalization of the π orbitals along the conjugated backbone. This structural optimization results in complete delocalization of the HOMO and LUMO orbitals along the conjugated backbone, and the HOMO-LUMO transition exhibits significantly enhanced localized excitation characteristics compared to ZN1.

[0034] Strategic enhancement of two-photon absorption through molecular engineering is key to achieving femtosecond optical limiting. In the centrosymmetric structures ZN1-ZN3, the TPA transition occurs from the ground state S0 (1Ag) to the final excited state S2 (2Ag). The effective overlap of the molecular π orbitals, resulting in an extended conjugated system, leads to a delocalized hole-electron system in the excited state S2, significantly enhancing the two-photon absorption response. A systematic analysis of the hole-electron distribution using transition density matrix calculations reveals the influence of variations in the π-bridge structure on the reverse saturation absorption performance. In the hole-electron distribution, green isosurfaces indicate regions of increased electron density, while blue isosurfaces indicate regions of decreased electron density. The orthogonal (90°) arrangement of the anthracene core and its peripheral side chains in ZN1 confines the hole and electron density to the planar aromatic system, resulting in pronounced localized excitation behavior. The reduced dihedral angle between the anthracene core and the peripheral side chains in ZN2 facilitates electron transfer from the conjugated core to the side chains. The molecular planarization of ZN3 induces a dual electronic effect: (i) a significant enhancement of LE; and (ii) a significant hole-electron delocalization on the conjugated framework. Hole-electron analysis shows that the electron density is redistributed from the anthracene system to the side chain π system.

[0035] Example 2

[0036] Based on the design of Example 1, three di-branched anthracene derivatives ZN1, ZN2 and ZN3 were prepared. The specific synthesis method is as follows:

[0037] Synthesis of ZN1 (4,4-(9,10-anthracenediyl)bis[pyridine]):

[0038] 9,10-Dibromoanthracene (2.0 g, 5.95 mmol), pyridine-4-boronic acid (2.4 g, 17.8 mmol), potassium carbonate ( , 11.6 g, 35.5 mmol), tetrakis(triphenylphosphine)palladium[ , 0.68 g, 0.59 mmol] and a toluene / dimethylformamide mixed solvent (DMF, 6:1 v / v, 300 mL). ) Under atmosphere protection, the reaction mixture was heated to 130 ° C in the dark and stirred at this temperature for 48 hours. After the reaction solution was cooled to room temperature, it was filtered through a diatomaceous earth pad to remove the catalyst. The filtrate was concentrated under reduced pressure to remove the solvent to obtain a crude solid product. The crude solid was dissolved in dichloromethane, washed with distilled water, dried over anhydrous magnesium sulfate, and then concentrated under reduced pressure. An appropriate amount of hydrochloric acid (HCl) aqueous solution was added to the concentrated residue to adjust the pH to 2-3, at which time a solid precipitated. The solid was collected by filtration and redissolved in water. The pH of the aqueous solution was adjusted to 8-9 with a sodium hydroxide (NaOH, 10 M) aqueous solution, and the solid precipitated again. Filter, collect the resulting light yellow solid, and wash with distilled water to finally obtain 1.4 g of the product with a yield of 70%.

[0039] ZN1 is 4,4-(9,10-anthracenediyl)bis[pyridine], chemical structure:

[0040] .

[0041] Synthesis of ZN2 (9,10-di-β-(4-pyridyl)vinylanthracene):

[0042] In nitrogen ( ), 9,10-bis(diethoxyphosphoramidite)anthracene (AEDP, 0.500 g, 1.04 mmol) and potassium tert-butoxide (t-BuOK, 0.468 g, 4.17 mmol) were dissolved in tetrahydrofuran (THF, 70 mL) and stirred. Pyridine-2-carboxaldehyde (0.24 mL, 2.53 mmol) was dissolved in another portion of THF (70 mL). Under ice-cooling, this pyridine-2-carboxaldehyde THF solution was slowly added dropwise to the above-mentioned mixture of AEDP and t-BuOK. After the addition was complete, the ice bath was removed, and the reaction mixture was stirred at room temperature for 12 hours. After the reaction was completed, the precipitate was collected by filtration. The precipitate was washed with methanol (MeOH) and dried to obtain a yellow powder product with a yield of 50%.

[0043] ZN2 is 9,10-di-β-(4-pyridyl)vinyl anthracene, chemical structure:

[0044] .

[0045] Synthesis of ZN3 (9,10-bis(pyridin-4-ylethynyl)anthracene):

[0046] 9,10-Diiodoanthracene (0.86 g, 2.0 mmol), 4-ethynylpyridine (0.50 g, 4.85 mmol), dichlorobis(triphenylphosphine)palladium[ , 70 mg, 5 mol%] and diethylamine (33 mL). The resulting mixture was stirred at room temperature for 10 minutes, and then cuprous iodide (CuI, 19 mg, 5 mol%) was added. The reaction system was then heated to reflux and stirred under these conditions for 8 hours. After the reaction was completed, the mixture was concentrated under reduced pressure using a rotary evaporator. The crude product was purified by neutral alumina column chromatography using ether / methanol (97.5:2.5, v / v) as the eluent. The eluate containing the target product was collected and concentrated under reduced pressure. The residue was dissolved in toluene and recrystallized to obtain 220 mg of the target product with a yield of 29%.

[0047] ZN3 is 9,10-bis(pyridin-4-ylethynyl)anthracene, chemical structure:

[0048] .

[0049] Step 4: The anti-saturation absorption response and optical limiting performance of the experimentally synthesized target compound ZN1-3 in the femtosecond time domain of 515-650 nm were measured, verifying a method for enhancing ultrafast broadband optical limiting performance based on torsional changes.

[0050] Based on the above molecular design, ZN1, ZN2 and ZN3 were synthesized, and the anti-saturation absorption and optical limiting responses of these three molecules were verified by femtosecond Z-scan experiments and femtosecond optical limiting experiments. In the experiment, the excitation light source was a femtosecond laser pulse (1030 nm, HWFM: 190 fs), and an optical parametric amplification system was used to achieve a wavelength output of 350-1500 nm. In the femtosecond Z-scan experiment, the excitation wavelengths were selected as 515 nm, 600 nm and 650 nm. The samples ZN1, ZN2 and ZN3 were dissolved in trichloromethane (TCM) solvent at a concentration of 1.5 mol / L and placed in a quartz cuvette with an optical path of 2 mm. The experimental curves are shown in Figure 2. Figure 3 shown.

[0051] A typical characteristic of reverse saturation absorption is a sharp decrease in sample transmittance at the lens focal point, characterized by a deep valley at the 0 mm position (the focal point of the convex lens). In femtosecond Z-scan experiments, molecule ZN1 exhibited no reverse saturation absorption, while that of molecule ZN2 was initially enhanced. The reverse saturation absorption response of molecule ZN3 was significantly enhanced. Specifically, adjusting the dihedral angle (θ) between the anthracene core and the peripheral substituents from orthogonal (θ = 90°) to coplanar (θ = 0°) significantly enhanced the broadband reverse saturation absorption response. Because the excitation wavelengths of 515 nm, 600 nm, and 650 nm are far from the resonant absorption bands of these three molecules, the linear transmittances of all three molecules in the experiments were greater than 99%, confirming that two-photon absorption is the dominant mechanism of reverse saturation absorption.

[0052] In the femtosecond optical limiting experiment, 515 nm and 650 nm were selected as the excitation wavelengths. Samples ZN1, ZN2, and ZN3 were dissolved in chloroform (TCM) and placed in a quartz cuvette with a pathlength of 10 mm. The experimental curves are shown in Figure 2. Figure 4 As shown. In the experiment, the sample was placed at the focal position of the convex lens, and the input light intensity varied continuously from small to large, while the sample transmittance varied continuously from high to low. The input light intensity corresponding to the sample transmittance being reduced to half of the linear transmittance is defined as the optical limiting threshold. The optical limiting threshold is an important parameter reflecting the optical limiting performance of the sample. The smaller the optical limiting threshold, the stronger the optical limiting performance. Molecule ZN1 does not have optical limiting performance, while molecule ZN2 exhibits initially enhanced ultrafast broadband optical limiting performance, and molecule ZN3 exhibits significantly enhanced ultrafast broadband optical limiting performance. That is, when the dihedral angle (θ) between the anthracene core and the peripheral substituents is adjusted from orthogonal (θ = 90°) to coplanar (θ = 0°), the ultrafast broadband optical limiting response of the molecule is significantly enhanced.

[0053] In dibranched anthracene derivatives, by introducing single, double, and triple π bridges, the dihedral angle between the anthracene core and the side chain is tuned from orthogonal (θ = 90°) to planar (θ < 1°). This results in a significant shift in the characteristics of excited-state electronic transitions: from localized electron excitation confined to the anthracene core to significant intramolecular charge transfer to enhanced localized electron excitation based on the extended π conjugated system. Studies have shown that the effective overlap of π orbitals in dibranched molecules, forming an extended conjugated system, leads to enhanced electron-hole delocalization in the final two-photon transition state, significantly enhancing the molecules' broadband two-photon absorption properties and optimizing their ultrafast, broadband optical limiting response.

Claims

1. A method for designing ultrafast broadband optical limiting materials based on torsion-regulated double-branched molecules, characterized in that: The method is carried out according to the following steps: Step 1: Structural optimization of the dibranched polycyclic aromatic hydrocarbon molecule is performed by computer based on density functional theory, and then the vibration frequency of each molecule is calculated to ensure that the molecular configuration of the dibranched polycyclic aromatic hydrocarbon molecule after structural optimization is at the lowest point on the potential energy surface, thereby obtaining a dibranched molecule having a polycyclic conjugated structure with a dihedral angle of 90° between the core group and the side chain group; Step 2: adjusting the π bridge between the core group and the side chain group having a polycyclic conjugated structure so that the dihedral angle between the core group and the side chain group gradually changes from 90° to 0°, thereby obtaining the ultrafast broadband optical limiting material.

2. The method for designing ultrafast broadband optical limiting materials based on torsion-regulated double-branched molecules according to claim 1, characterized in that: The vibration frequency of each molecule is calculated as described in step 1, so that the vibration frequency of each molecule is a real frequency, and the molecular configuration of the dibranched polycyclic aromatic hydrocarbon molecule after structural optimization is ensured to be at the lowest point on the potential energy surface.

3. The method for designing ultrafast broadband optical limiting materials based on torsion-regulated double-branched molecules according to claim 1, characterized in that: As described in step 1, after ensuring that the molecular configuration of the double-branched polycyclic aromatic hydrocarbon molecule is at the lowest point on the potential energy surface after structural optimization, a group with a polycyclic conjugated structure is selected as the core group, the connecting π bridge between the core group and the side chain group is selected as a C-C bond, and the side chain group is a six-membered ring structure, forming a molecular configuration with a double-branched conjugated structure.

4. The method for designing ultrafast broadband optical limiting materials based on torsion-regulated double-branched molecules according to claim 3, characterized in that: The core group is naphthalene, anthracene or pyrene, and the six-membered ring structure is pyridine or benzene ring.

5. The method for designing ultrafast broadband optical limiting materials based on torsion-regulated double-branched molecules according to claim 3, characterized in that: The core group is an anthracene derivative with a polycyclic conjugated structure, the side chain group is pyridine, and the dihedral angle between the anthracene core and the side chain group is 90°.

6. The method for designing ultrafast broadband optical limiting materials based on torsion-regulated double-branched molecules according to claim 1 or 3, characterized in that: The anthracene derivative with a dihedral angle of 90° between the anthracene nucleus and the side chain group is a dibranched anthracene derivative ZN1, whose chemical name is 4,4-(9,10-anthracenediyl)bis[pyridine] and whose chemical structure is: 。 7. The method for designing ultrafast broadband optical limiting materials based on torsion-regulated double-branched molecules according to claim 1, characterized in that: The adjustment of the π bridge between the anthracene nucleus and the side chain group in step 2 is to select a π bridge connecting a C=C bond or a C≡C bond so that the dihedral angle between the anthracene nucleus and the side chain group changes from 90° to 53° or 0°.

8. An optical limiting material obtained by the method for designing an ultrafast broadband optical limiting material based on a torsion-regulated double-branched molecule according to claim 1, characterized in that: The ultrafast broadband optical limiting material is a di-branched anthracene derivative ZN2-3, and the di-branched anthracene derivative ZN2-3 has the chemical structure: , where R is C=C or C≡C.

9. The optical limiting material according to claim 8, wherein: The di-branched anthracene derivative ZN2-3 is ZN2, chemical name 9,10-di-β-(4-pyridyl)vinylanthracene, and chemical structure is: Or ZN3, chemical name 9,10-bis(pyridin-4-ylethynyl)anthracene, chemical structure formula is: 。 10. Use of the optical limiting material according to claim 9, characterized in that: The di-branched anthracene derivatives ZN2 and ZN3 are used for laser protection.

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