A Class of Organic Near-Infrared Luminescent Dye Compounds, Their Crystals, and Applications

Abstract

This invention relates to the field of organic optoelectronic functional materials technology, providing a class of organic near-infrared luminescent dye compounds, their crystals, and applications. The materials of this invention include a series of compounds composed of a 4-(dimethylamino)phenyl and cyanoacrylate conjugate backbone, as well as maronitrile derivatives. They possess simple structures and small molecular weights, and can be efficiently synthesized via a one-step Knoevenagel condensation reaction. This process is simple, low-cost, and easily industrialized. The emission wavelength and performance can be adjusted by changing the end-group substitution or acceptor type. The materials exhibit good self-assembly ability and high crystallinity in the solid state, enabling the formation of stable laser gain media. They achieve stable laser output with narrow spectrum, high brightness, and low threshold in the near-infrared band, with a photoluminescence quantum yield of 24% and excellent stimulated emission performance. The materials possess good chemical stability and device compatibility, showing broad application prospects in near-infrared solid-state dye lasers, optical communications, fiber optic amplifiers, and other fields.

Description

Technical Field

[0001] This invention belongs to the field of organic optoelectronic functional materials technology, specifically relating to a class of organic near-infrared luminescent dye compounds, their crystals, and applications. Background Technology

[0002] With the widespread application of laser technology in short-wave infrared (SWIR) communication, night vision imaging, biological diagnostics, and spectral analysis, the market has created an urgent demand for high-performance, processable, and wavelength-tunable near-infrared organic laser materials. Especially in the context of miniaturized and integrated devices, the structural design and optical properties of these materials must achieve a new balance. Compared to traditional inorganic laser media, organic light-emitting materials possess unique advantages such as strong structural designability, mild processing, low cost, and solution-processability, making them a research hotspot in recent years.

[0003] Currently, common organic near-infrared laser dye material systems mainly include the following categories:

[0004] Polycyclic conjugated dye molecules (such as cyanine, silicocyanine, thiophene derivatives, etc.): These materials generally contain two or more aromatic rings or heterocycles, achieving long-wavelength emission by constructing ultra-long conjugated chains. Molecular lengths can reach 2–5 nm, with high π-electron delocalization. Common structural units include pyridine rings, thiophene, and indole, connecting electron donors and acceptors through conjugated bridges to achieve long-wavelength redshift. Their luminescence depends on excited-state π-π* transitions, with relatively low excitation energies and emission wavelengths covering 700–900 nm. However, they have small band gaps, easily inducing non-radiative processes (such as internal conversion and vibrational relaxation). In practical applications, these materials often exist in solution and must be doped into polymer matrices (such as PMMA and PVA) for use, typically at concentrations <1 wt% to avoid concentration quenching.

[0005] Conjugated polymer materials (such as MEH-PPV, PFO, and PBTTT) have molecular chains composed of repeating conjugated units, resulting in highly regular structures that can form self-assembled microcrystals or amorphous aggregates in the solid state. After excitation, excitons can be transferred along the polymer chain, and the emission wavelength is modulated by the main chain structure. Some materials achieve near-infrared emission by introducing heavy atoms or conjugated bridges, but these materials suffer from problems such as large molecular weight, poor batch consistency, good solution processability but limited emission efficiency, and high laser threshold.

[0006] Emerging trends in organic laser material development include: functional coating (coating traditional dyes with high refractive index and high thermal conductivity media (such as SiO2 shells) to improve thermal stability and quantum efficiency); single-crystal devices (crystallizing small molecule dyes into sheet-like, needle-like, or columnar crystals for use as laser cavities or waveguides; utilizing self-assembly to control molecular stacking direction; reducing non-radiative losses caused by π-π stacking); and enhanced structural design (constructing push-pull molecular structures, such as the donor-π-acceptor (D-π-A) architecture, where D is the electron donor, A is the electron acceptor, and π is the conjugate bridge, enhancing near-infrared absorption and emission efficiency through intramolecular charge transfer (ICT)).

[0007] In summary, existing organic near-infrared laser dye materials mainly suffer from the following technical defects and limitations in practical applications:

[0008] Complex molecular structures and cumbersome synthetic routes: Most current mainstream near-infrared organic dyes rely on polycyclic or long conjugated chain structures (such as anthocyanins, thiophenes, and nitrogen-containing polycyclic systems). Their large molecular weight and numerous synthetic steps lead to difficult purification and low yield, making it difficult to meet the needs of low-cost, large-scale preparation.

[0009] Low luminous efficiency and high laser threshold: Constrained by the "bandgap rule," as the emission wavelength extends into the near-infrared region, the nonradiative relaxation channels of the excited state of organic dyes are significantly enhanced, leading to a sharp decrease in fluorescence quantum yield (PLQY). At the same time, the π-π stacking effect in the solid state or at high concentrations further weakens its luminous efficiency, resulting in a persistently high laser emission threshold.

[0010] Unstable solid-state performance and poor device compatibility: Most dyes rely on solution to work and are difficult to maintain high-efficiency light-emitting performance in solid or thin films. They have poor crystallinity and uncontrollable morphology, making them difficult to be compatible with optical communication or integrated photonic devices, which limits the expansion of practical application scenarios.

[0011] Limited controllability and lack of structure-performance synergistic design: Existing dye materials have low freedom in molecular engineering control, and it is often difficult to simultaneously optimize key parameters such as emission wavelength, quantum efficiency, and crystallinity, resulting in limited performance improvement.

[0012] Therefore, this invention proposes a class of organic near-infrared luminescent dye compounds with simple structure, high synthesis efficiency, tunable wavelength and amplified spontaneous emission (ASE) capability, as well as their crystals and applications. Summary of the Invention

[0013] The purpose of this invention is to provide a class of organic near-infrared luminescent dye compounds, their crystals, and applications, in order to solve the problems mentioned in the background art.

[0014] The objective of this invention is achieved through the following technical solution:

[0015] A class of organic near-infrared luminescent dye compounds, including pentadienoate compounds with ester groups having a D–π–A structure and maleic nitrile derivative compounds;

[0016] The ester-containing pentadienoate compounds include (2Z,4E)-2-cyano-5-(4-(dimethylamino)phenyl)pent-2,4-dienoate, (2Z,4E)-2-cyano-5-(4-(diethylamino)phenyl)pent-2,4-dienoate, and (2Z,4E)-2-cyano-5-(4-(methoxy)phenyl)pent-2,4-dienoate; wherein the substituent R at the ester end is selected from methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, or tert-butyl.

[0017] The maronitrile derivatives include (E)-2-(3-(4-(dimethylamino)phenyl)propenyl)malonitrile, (E)-2-(3-(4-(diethylamino)phenyl)propenyl)malonitrile, and (E)-2-(3-(4-methoxyphenyl)propenyl)malonitrile.

[0018] A method for preparing the organic near-infrared luminescent dye compound as described above:

[0019] For ester-containing pentadienoate compounds, the Knoevenagel condensation reaction is used, with 4-substituted cinnamaldehyde and cyanoacetic acid R ester as raw materials, where R corresponds to the substituent at the ester end, and the reaction is carried out in a solvent under the catalysis of an organic base; the organic base is piperidine or piperazine.

[0020] For malononitrile derivatives, the Knoevenagel condensation reaction is used, with 4-substituted cinnamaldehyde and malononitrile as raw materials, and the reaction is carried out in a solvent under the catalysis of an organic base; the organic base is piperidine, piperazine or triethylamine.

[0021] Furthermore, the solvent is anhydrous ethanol or anhydrous methanol; the reaction temperature is 20~40℃; and the reaction time is 2~4 hours.

[0022] An organic near-infrared luminescent crystal is grown from the aforementioned organic near-infrared luminescent dye compound via solution evaporation-induced method or liquid phase diffusion method. The crystal morphology is blocky, needle-like, or plate-like, and it exhibits near-infrared luminescence and ASE characteristics.

[0023] Furthermore, the photoluminescence quantum yield of the organic near-infrared luminescent crystal is 10-24%, and the amplified spontaneous emission threshold is below 100 kW / cm². 2 The emission wavelength is between 730 and 790 nm.

[0024] An organic optical gain device includes the aforementioned organic near-infrared emitting crystal as an optical gain medium.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] This invention provides organic near-infrared luminescent crystal materials based on single-benzene-ring push-pull molecules, including a series of compounds composed of a conjugated backbone of 4-(dimethylamino)phenyl (donor) and cyanoacrylate (acceptor), as well as malononitrile derivatives. These materials are characterized by simple molecular structures (containing only a single benzene ring) and small molecular weights. They can be efficiently synthesized through a one-step Knoevenagel condensation reaction, which is simple, low-cost, and conducive to industrial production. They are also easy to purify and structurally controllable. The emission wavelength and performance can be controlled by changing the ester-terminal R group or the acceptor type, forming a highly tunable molecular engineering platform. The materials exhibit good self-assembly ability and high crystallinity in the solid state, enabling them to form stable laser gain media and are compatible with existing laser device fabrication processes. It achieves stable laser output in the near-infrared band (730–790 nm) with narrow spectral density (approximately 10 nm half-width), high brightness, and low ASE threshold (below 100 kW / cm², reaching as low as 33.6 kW / cm²), with a photoluminescence quantum yield (PLQY) of 24% and excellent stimulated emission performance. Furthermore, the material exhibits good chemical stability and device compatibility, showing broad application prospects in near-infrared solid-state dye lasers, optical communications, and fiber amplifiers. Attached Figure Description

[0027] Figure 1 The molecular formulas of the target compounds DMAPC (a), DEAPC (b), MAPC (c), and maronitrile derivatives (d) are given.

[0028] Figure 2 The diagram shows single-crystal growth of this series of compounds by slow evaporation and liquid-liquid diffusion methods, as well as the obtained crystals. In the diagram, a is a single-crystal growth of this series of compounds by slow evaporation and the obtained crystals (the left image is a sunlight photograph, and the right image is a fluorescence photograph), and b is a single-crystal growth of this series of compounds by liquid-liquid diffusion methods, as well as the obtained crystals (the left image is a sunlight photograph, and the right image is a fluorescence photograph).

[0029] Figure 3 The analysis includes the leading-edge orbit analysis of the DMAPC-M4 molecule, solar fluorescence images of the crystal, corresponding steady-state absorption / emission spectra, and vertical excitation energy calculations. Among them, a represents the leading-edge orbit analysis results; b represents the solar fluorescence images of the crystal and corresponding steady-state absorption / emission spectra; and c represents the vertical excitation energy calculation results.

[0030] Figure 4 Comparison of crystal structures and molecular packing modes of DMAPC-M2 and DMAPC-M4; where a is the front view and top view of the crystal structure of DMAPC-M2; b is the front view and top view of the crystal structure of DMAPC-M4; c is the molecular packing mode of the DMAPC-M2 crystal along the c-axis; d is the molecular packing mode of the DMAPC-M4 crystal along the c-axis.

[0031] Figure 5 The images show the solar fluorescence of DMAPC-M4 in different polar solvents, along with the corresponding solution absorption and emission spectra. Specifically, a is the solar fluorescence of DMAPC-M4 in different polar solvents; b is the corresponding solution absorption spectrum; and c is the corresponding solution emission spectrum.

[0032] Figure 6 The UV-Vis absorption spectrum and fluorescence emission spectrum of the DMAPC-M2 crystal are shown.

[0033] Figure 7 The ASE behavior of DMAPC-M4 crystal under different laser power excitations includes emission spectra obtained under different laser powers (355 nm pulse excitation) and 636 KW / cm² excitation. -2 Fluorescence images under laser excitation show typical ASE behavior.

[0034] Figure 8 The normalized fluorescence spectra of DMAPC-M4 crystals under laser excitation at different powers are shown.

[0035] Figure 9 The normalized spectrum of ASE emission intensity as a function of time for a DMAPC-M4 crystal under repeated laser pumping (72,000 times, for 2 hours).

[0036] Figure 10 For DMAPC-M2 1 H NMR spectrum (CDCl3, 400 MHz).

[0037] Figure 11 For DMAPC-M3 1 H NMR spectrum (CDCl3, 400 MHz).

[0038] Figure 12 For DMAPC-M4 1 H NMR spectrum (CDCl3, 400 MHz).

[0039] Figure 13 For DMAPC-M8 1 H NMR spectrum (CDCl3, 400 MHz).

[0040] Figure 14 For DMAPC-M9 1 H NMR spectrum (CDCl3, 400 MHz).

[0041] Figure 15 For DMAPC-DCN 1 H NMR spectrum (CDCl3, 400 MHz).

[0042] Figure 16 For DMAPC-M4 13 C10 NMR spectrum (CDCl3, 101 MHz).

[0043] Figure 17 Photographs of DMAPC-M1 to M4, DMAPC-M8, DMAPC-M9 and DMAPC-DCN crystals under sunlight (left) and fluorescence (right).

[0044] Figure 18 The UV-Vis absorption and fluorescence emission spectra of crystals for DMAPC-M1 to M4, DMAPC-M9 and DMAPC-DCN are shown.

[0045] Figure 19 The photoluminescence quantum yield of crystals of DMAPC-M1, DMAPC-M2 and DMAPC-M3.

[0046] Figure 20 Photoluminescence quantum yields of crystals for DMAPC-M4, DMAPC-M9, and DMAPC-DCN.

[0047] Figure 21 The ASE characteristic spectra of crystals from DMAPC-M1 to M4 are shown.

[0048] Figure 22 The direction-selective ASE behavior of different crystal morphologies is shown. Among them, a represents the obvious ASE anisotropy of single crystal samples with different morphologies under 640nm pulsed laser excitation. From top to bottom, the crystals are plate-like, needle-like, and block-like. The green dashed arrows indicate the excitation direction. Depending on whether the excitation direction is along the crystal growth axis, different crystals exhibit differences in whether they have ASE emission (ASE√) (for example, needle-like crystals show strong ASE when excited along the long axis, but no ASE emission when excited in the vertical direction (ASE×)). b represents the ASE emission spectra of the corresponding crystals under different excitation directions.

[0049] Figure 23Schematic diagrams of DMAPC-M4 bulk crystals excited by lasers parallel and perpendicular to the growth direction, and corresponding normalized fluorescence spectra at different pump laser energies, along with the corresponding nonlinear gain relationship curves between the full width at half maximum (FWHM), luminescence intensity, and pump laser energy. Specifically, a is a schematic diagram of DMAPC-M4 bulk crystals excited by lasers parallel to the growth direction; b is a schematic diagram of DMAPC-M4 bulk crystals excited by lasers perpendicular to the growth direction; c is the normalized fluorescence spectrum of diagram a at different pump laser energies; d is the normalized fluorescence spectrum of diagram b at different pump laser energies; e is the nonlinear gain relationship curve between the FWHM, luminescence intensity, and pump laser energy in diagram a; and f is the nonlinear gain relationship curve between the FWHM, luminescence intensity, and pump laser energy in diagram b.

[0050] Figure 24 Image ASE waveguides of DMAPC-M4 needle-shaped and bulk crystals, the acquired emission spectra, and the fitted optical loss coefficients are shown below; where a is the ASE waveguide image of the DMAPC-M4 needle-shaped crystal; b is the ASE waveguide image of the DMAPC-M4 bulk crystal; c is the emission spectrum of the DMAPC-M4 needle-shaped crystal; d is the emission spectrum of the DMAPC-M4 bulk crystal; e is the fitted optical loss coefficient of the DMAPC-M4 needle-shaped crystal; and f is the fitted optical loss coefficient of the DMAPC-M4 bulk crystal. Detailed Implementation

[0051] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0052] This invention aims to prepare a class of organic near-infrared luminescent dye compounds. The following details the preparation of materials, crystal growth and structural characteristics, material characterization and optical performance testing, and the construction and performance evaluation of dye laser devices.

[0053] I. Material Preparation;

[0054] This invention relates to two classes of dye compounds with near-infrared luminescence properties, specifically as follows:

[0055] 1. Pentaenoic acid esters containing ester groups;

[0056] This class of compounds includes (2Z,4E)-2-cyano-5-(4-(dimethylamino)phenyl)pentane-2,4-dienoate (DMAPC for short). Figure 1 (a) (2Z,4E)-2-cyano-5-(4-(diethylamino)phenyl)pentane-2,4-dienoic acid ester (abbreviated as DEAPC) Figure 1(b) (2Z,4E)-2-cyano-5-(4-(methoxy)phenyl)pentane-2,4-dienoic acid ester (MAPC for short) Figure 1 (c) The substituent R at the ester end is classified into nine types, corresponding to the following numbers: M1: R=methyl, M2: R=ethyl, M3: R=n-propyl, M4: R=n-butyl, M5: R=n-pentyl, M6: R=n-hexyl, M7: R=n-heptyl, M8: R=n-octyl, M9: R=tert-butyl. These compounds form a stable π-conjugated push-pull structure by introducing a conjugated diene bridge (pent-2,4-diene) and an ester group between the 4-substituted benzene ring and the terminal cyano group. The cyano group and the ester group together constitute the electron acceptor, while the para-substituents on the benzene ring (such as –N(CH3)2, –N(C2H5)2, –OCH3) provide electron donor functionality, enhancing near-infrared luminescence through intramolecular charge transfer (ICT) effects.

[0057] The synthesis route is as follows:

[0058] ;

[0059] Synthesis method: This type of ester-containing pentadienoate compound is prepared by Knoevenagel condensation reaction, as detailed below (taking DMAPC as an example):

[0060] (1) Aldehyde components: 4-(dimethylamino)cinnamaldehyde, 4-(diethylamino)cinnamaldehyde, 4-(methoxy)cinnamaldehyde, etc.; active methylene components: cyanoacetate (such as methyl cyanoacetate, ethyl cyanoacetate, propyl cyanoacetate, tert-butyl cyanoacetate, etc.).

[0061] (2) Reaction conditions: The solvent is anhydrous ethanol or anhydrous methanol (25~100 mL, adjusted according to the reaction scale); the catalyst is an organic base, such as piperidine, piperazine, etc. (0.05~0.1 eq); the temperature is 20~40℃; the time is 2~4 hours, and the reaction progress is monitored by TLC.

[0062] Synthesis steps: 4-(dimethylamino)cinnamaldehyde (1.0 eq) and R cyanoacetate (1.1~1.2 eq) were added to 25~100 mL of anhydrous ethanol or anhydrous methanol; 5~15 drops of piperidine were added dropwise; the reaction was stirred at 20~40℃ for 2~4 hours, and the reaction was monitored by TLC until the raw materials were basically consumed; if a solid precipitated in the system, it could be directly filtered and washed with cold ethanol or petroleum ether; if no obvious solid precipitated, an appropriate amount of deionized water was added to terminate the reaction, and the product was extracted with dichloromethane; after washing and drying, the organic phase was removed by rotary evaporation to obtain the crude product; finally, the product was purified by column chromatography (eluents could be petroleum ether / ethyl acetate, n-hexane / dichloromethane, etc.) or sublimation to obtain the high-purity target product.

[0063] This method utilizes the properties of Knoevenagel condensation to prepare α,β-unsaturated compounds through the dehydration condensation of an active methylene compound (such as R cyanoacetate) with an aldehyde group under alkaline conditions. It offers advantages such as mild conditions, readily available raw materials, high reaction efficiency, simple operation, and the elimination of the need for high temperature, high pressure, and multi-step reactions.

[0064] 2. Marlonitrile derivatives;

[0065] This class of compounds includes (E)-2-(3-(4-(dimethylamino)phenyl)propenyl)malonitrile (DMAPC-DCN), (E)-2-(3-(4-(diethylamino)phenyl)propenyl)malonitrile (DEAPC-DCN), and (E)-2-(3-(4-methoxyphenyl)propenyl)malonitrile (MAPC-DCN). Figure 1 (d). These compounds use malononitrile (malononitrile) as the terminal strong acceptor to construct a typical D–π–A type conjugated system. The conjugated bridge is usually a single-bonded propylene group (–CH=CH–CH=), which has a relatively short conjugated path, but still achieves excellent optical properties through a strong electronic pull-push effect. It has a high dipole moment, high luminescence quantum yield and low stimulated emission threshold, making it suitable as a gain medium for short-wave infrared organic lasers.

[0066] Synthetic method: Similar to esters, these malononitrile derivatives are also synthesized via Knoevenagel condensation, as detailed below (using DMAPC-DCN as an example):

[0067] (1) Reactants: The aldehyde component is 4-(dimethylamino)cinnamaldehyde (or other 4-substituted cinnamaldehyde); the active methylene component is malononitrile (malononitrile).

[0068] (2) Reaction conditions: The solvent is 25-100 mL of anhydrous ethanol or anhydrous methanol (adjusted according to the reaction scale); the catalyst is an organic base, such as piperidine, piperazine or triethylamine (TEA) (0.05-0.1 eq); the temperature is 20-40℃; the time is 2-3 hours (the reaction progress is monitored by TLC).

[0069] (3) Synthesis steps: Add 4-(dimethylamino)cinnamaldehyde and malononitrile to 25-100 mL of anhydrous ethanol or anhydrous methanol at a molar ratio of 1.0:1.1; add 5-15 drops of piperidine; stir the reaction at 20-40℃ for 2-4 hours, and monitor the reaction by TLC until the raw materials are basically consumed; if solid precipitates in the system, it can be directly filtered and washed with cold ethanol or petroleum ether; if no obvious solid precipitates, add an appropriate amount of deionized water to terminate the reaction and extract with dichloromethane; after washing and drying the organic phase, remove the solvent by rotary evaporation to obtain the crude product; finally, purify by column chromatography (eluent can be petroleum ether / ethyl acetate, n-hexane / dichloromethane, etc.) or sublimation to obtain the pure malononitrile derivative.

[0070] The Knoevenagel condensation reaction is a classic route for preparing α,β-unsaturated cyano esters. It has advantages such as mild reaction conditions, readily available raw materials, simple operation, and high yield, making it suitable for the expansion and industrial scale-up of a series of compounds.

[0071] II. Crystal growth and structural characteristics;

[0072] To achieve high-performance organic laser output, the dye molecules of this invention need to form high-quality single crystals to meet the device's requirements for order, optical anisotropy, and stability, as detailed below:

[0073] 1. Crystal growth methods;

[0074] A series of push-pull dye molecules can be grown into high-quality single crystals under normal pressure and temperature conditions by solution evaporation induction method or liquid phase diffusion method, which has the advantages of simple method, good controllability and stable crystal form.

[0075] A typical crystal growth process is as follows:

[0076] (1) Solvent selection: Based on the polarity and solubility of the compound, organic solvent systems with moderate polarity (such as acetonitrile / methanol, ethyl acetate / n-hexane, dichloromethane / ethanol, etc.) are preferred as solvent / non-solvent pairs;

[0077] (2) Solution preparation: Dissolve the pure target dye in an appropriate amount of good solvent (such as dichloromethane or tetrahydrofuran) to prepare a saturated or near-saturated solution;

[0078] (3) Growth pattern:

[0079] Solution evaporation-induced method: The dye solution is placed in a sealed container, and the solvent is slowly evaporated at room temperature. Granular or flaky crystals precipitate within 1-3 days. Figure 2 (a)

[0080] Liquid-phase diffusion method: A poor solvent (such as methanol, ethanol, or petroleum ether) is slowly added dropwise to the surface of the solution to form a stable interface with the dye solution. Slow diffusion between the solvents promotes crystal formation, and a large number of banded or blocky crystals precipitate in the solution after 7-14 hours. Figure 2 (b)

[0081] (4) Crystal collection and processing: After crystals are formed, the upper solvent is removed with filter paper, the crystals are quickly transferred and gently washed with anhydrous solvent, air-dried or dried in a vacuum dryer for later use.

[0082] This method is applicable to most push-pull molecules, including ester-containing pentadienoate compounds and marlonitrile derivatives. The resulting crystals are generally in the form of blocks, plates, needles, sheets or prisms, with good optical transparency and mechanical stability, meeting the requirements for laser performance testing.

[0083] 2. Analysis of molecular structure and crystal properties;

[0084] The superior optical and laser properties of dye molecules stem from their highly designed molecular structure and suitable crystal stacking method, as detailed below:

[0085] (1) D–π–A push-pull conjugated system: All molecules are constructed based on the D–π–A architecture, with strong electron donors such as dimethylamino (–N(CH3)2), diethylamino (–N(C2H5)2), and methoxy (–OCH3); the π-bridge is a double bond conjugated bridge (electron transport path); the acceptor is a strong electron acceptor composed of a cyano group and an ester group or a dicyano group. This structure endows the molecule with a large intrinsic dipole moment and good charge delocalization. Taking (2Z,4E)-2-cyano-5-(4-(dimethylamino)phenyl)pentane-2,4-dienoic acid butyl ester (DMAPC-M4) as an example, its molecular frontier orbital exhibits a strong intramolecular charge transfer (ICT) effect. Figure 3 (a) A relatively broad absorption band and a redshifted emission peak, along with a large Stokes shift, effectively avoids self-absorption. Figure 3 (b); the enhanced excited-state oscillator strength (1.4527) is beneficial for stimulated emission and laser amplification. Figure 3 (c)

[0086] (2) Compact structure of a single benzene ring: Compared with common polycyclic aromatic hydrocarbon dyes, the molecules of this invention use a single benzene ring as the core skeleton, which has the advantages of small structure and moderate rigidity. Taking DMAPC-M2 and DMAPC-M4 as examples, the molecules are basically coplanar, with twist angles of 6.90° and 7.36°, respectively. The molecules are linearly distributed, which is conducive to π orbital overlap. Figure 4 (a and b) can effectively suppress intramolecular torsion and nonradiative energy consumption, and the smaller volume is conducive to regular arrangement and reduces the probability of exciton annihilation between molecules.

[0087] (3) Aggregation-state optimization and crystal orderliness: Aggregation-induced enhanced emission (AIE) helps maintain high luminescence efficiency in the solid state; the ordered arrangement in the crystal can significantly reduce the non-radiative loss of the excited state and improve laser gain performance. Specifically, the ordered molecular arrangement within the crystal can effectively suppress the non-radiative decay of the excited state and enhance laser gain capability. For example... Figure 4 As shown in c and d, both DMAPC-M2 and DMAPC-M4 exhibit J-aggregation characteristics in the crystal, which is characterized by orderly sliding and stacking of molecules along the a-axis, which is beneficial for exciton coupling and redshift of the emission peak.

[0088] In summary, the push-pull dye molecule of the present invention not only possesses an excellent molecular design basis, but also has good crystal growth capability and controllable aggregated state structure, which helps to achieve high-performance near-infrared laser output, and is particularly suitable as a core material for gain medium in organic laser devices.

[0089] III. Structural characterization and optical property testing of materials;

[0090] To systematically study the photophysical properties of a series of push-pull dye molecules, various methods were used to characterize their structure, spectral behavior, quantum yield, and laser gain behavior, clarifying the differences in luminescence characteristics between solution and crystalline states, and highlighting the advantages of crystalline state laser performance.

[0091] 1. Molecular structure characterization;

[0092] The synthesized target compound is obtained by 1 H / 13 C10 NMR spectroscopy confirmed its molecular structure and purity; the three-dimensional spatial configuration and molecular stacking mode of the grown crystal were obtained by single-crystal X-ray diffraction (SCXRD), with particular attention paid to intermolecular π–π stacking, J-aggregation characteristics and molecular polarization direction, which helps to understand the mechanism of enhanced crystalline luminescence.

[0093] 2. Absorption and emission spectroscopy testing;

[0094] The UV-Vis absorption and fluorescence emission spectra of molecules in dilute solution and crystalline states were measured separately to compare the light absorption and emission behavior of molecules in different states:

[0095] (1) Solution-state spectral testing;

[0096] Absorption spectroscopy: The absorption characteristics of dye molecules in different dilute solutions were measured using a UV-Vis spectrophotometer. Figure 5 (a) The solution concentration is generally controlled at 10. -5 ~10 -6 mol·L -1The solvents used include toluene (Tol), dichloromethane (DCM), chloroform (CHCl3), ethyl acetate (EA), tetrahydrofuran (THF), acetone (Ace), acetonitrile (Acn), dimethylformamide (DMF), and dimethyl sulfoxide (DMSO). The maximum absorption wavelength (λabs) of molecules in each solvent was recorded; the absorption bands typically fall within the 400–600 nm range. For example, DMAPC-M4 exhibits a maximum absorption wavelength of 450 nm in toluene and 481 nm in DMSO, demonstrating significant intramolecular charge transfer (ICT) characteristics. Figure 5 (b)

[0097] Emission Spectroscopy: The emission spectra of dye molecules in different solvents were recorded using a fluorescence spectrophotometer under excitation at a wavelength of 480 nm. The emission band is typically located in the 500–700 nm range. Taking DMAPC-M4 as an example, its emission peak in toluene is located at 528 nm, and in DMSO at 588 nm, showing a significant Stokes shift (approximately 78–107 nm), which helps reduce self-absorption and improve laser emission efficiency and optical purity. Figure 5 (c)

[0098] (2) Crystalline spectral testing;

[0099] Absorption spectroscopy: The diffuse reflectance absorption spectrum of a crystal is measured by pressing a single crystal or crystal powder into a pellet and then using a steady-state fluorescence spectrometer with an integrating sphere.

[0100] Emission spectroscopy: The fluorescence emission spectrum of the crystalline sample was directly measured using a fluorescence spectrophotometer; taking DMAPC-M2 as an example, compared with the solution state, the emission of the crystalline state showed a red shift or narrowing of the spectral band, and the energy transitions were more concentrated, which was beneficial for laser output. Figure 6 ).

[0101] 3. Measurement of photoluminescent quantum yield (PLQY) (crystal state);

[0102] To accurately reflect the luminescence efficiency of materials in practical applications, the integrating sphere method (using a commercial quantum efficiency meter (such as Hamamatsu Quantaurus-QY or Edinburgh FS5)) was employed to measure the PLQY of crystalline samples. Samples were in the form of powder pellets or large-size single crystals, and the excitation wavelength was selected based on the absorption peak (e.g., 450–530 nm). Typical PLQY values ​​reached 10–25%, higher than most π-π stacked quenching dyes, reflecting enhanced luminescence after optimized intermolecular arrangement.

[0103] 4. Preliminary assessment of ASE properties (crystalline state);

[0104] To verify the laser gain potential of dye molecules in the crystalline state, preliminary tests were conducted on the amplified spontaneous emission characteristics of single-crystal samples:

[0105] Sample preparation: Select large single crystals with regular morphology (generally 1~3 mm in size) obtained under natural growth or optimized conditions, or press crystal powder into tablets as test samples;

[0106] Excitation source: A pulsed Nd:YAG laser (such as 355 nm or 532 nm) is used as the pump source, with a pulse width of about 5 ns and a repetition frequency of 10 Hz;

[0107] Experimental setup: Pump light is focused onto the surface of a crystal sample through a lens, and its emission signal is collected by a spectrometer. The change of the emission spectrum with pump energy density is recorded.

[0108] ASE characteristic observation: Taking DMAPC-M4 crystal as a representative sample, it exhibits typical ASE behavior under 355nm pulsed laser excitation. Figure 7 At low pump energy densities (<100 KW / cm²), -2 The crystal exhibits only weak fluorescence emission with a wide bandwidth; as the pump intensity increases, the emission intensity increases nonlinearly, and the spectrum gradually narrows; when the energy density exceeds a certain threshold (>400 KW / cm²), the emission intensity decreases. -2 The emission peak sharpening, bandwidth compression (significant reduction in FWHM), and sharp increase in intensity clearly indicate the occurrence of the ASE process, verifying that DMAPC-M4 has the potential to be used as a laser gain medium in the crystalline state.

[0109] The test preliminarily confirmed that the dye of the present invention has an effective stimulated emission path and low threshold gain characteristics in the crystalline state, laying the foundation for the construction of solid-state organic laser devices.

[0110] IV. Construction and performance evaluation of dye laser devices;

[0111] Based on the aforementioned verification of the properties of crystalline ASE, in order to comprehensively evaluate the laser performance of dye molecules in practical applications, a crystalline organic laser device with a large-size single crystal as the gain medium was constructed, and the output performance of the system was tested. Details are as follows:

[0112] 1. Laser device fabrication and pump configuration;

[0113] Crystal selection: Select dye single crystal samples with regular growth morphology and size greater than 2 mm to ensure a straight laser gain path and avoid scattering loss;

[0114] Excitation source: The pump light is the third harmonic (λ = 355 nm) of a Nd:YAG nanosecond pulsed laser (i.e., a neodymium-doped yttrium aluminum garnet laser), with a pulse width of 5 ns and a repetition frequency of 10 Hz.

[0115] Optical path arrangement: A lens system is used to focus the laser onto the end face or cross-section of the crystal (depending on the crystal geometry), and the detection direction is perpendicular to the pump direction to collect the output signal;

[0116] Laser emission monitoring: Laser output is acquired in real time using a fiber-coupled spectrometer, and the output intensity is recorded using a power meter.

[0117] 2. Excitation Threshold and Gain Criterion: Using a DMAPC-M4 crystal as a representative test sample, the effect of pump energy density on emission intensity and spectral line changes was systematically recorded. When the pump power density gradually increased to ~40.6 kW / cm², the emission intensity exhibited a nonlinear jump, and the spectral lines were significantly compressed. Figure 8 This indicates that an ASE channel has been established within the crystal. Under high-power pumping conditions (~40.6–136 kW / cm²), the emission spectrum FWHM of the DMAPC-M4 crystal can gradually decrease to around 10 nm, exhibiting near-single-mode emission behavior. Figure 8 After the pump power was further increased to >148 kW / cm², the output intensity gradually plateaued and entered the gain suppression stage, indicating that the crystal material had reached the upper limit of saturation pumping.

[0118] 3. Photostability and Photobleaching Resistance Tests: DMAPC-M4 crystal samples were subjected to long-term continuous excitation tests under repetitive pump irradiation. The photobleaching rate and laser lifetime of the material were evaluated by the output intensity decay rate. Experimental results showed that the crystal maintained stable output for over 2 hours (72,000 excitation cycles) under 10 Hz pulse excitation, with an intensity decay of approximately 20%. Figure 9 It has good laser stability; photobleaching mainly originates from surface decomposition or photo-oxidation, and further encapsulation or crystal passivation can extend the device life.

[0119] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0120] Example 1: Near-infrared emission properties of dye molecules with different ester group and strong acceptor substitution;

[0121] (1) Composition and preparation;

[0122] To verify the effectiveness of the strategy of "regulating luminescence properties by adjusting the substituents at both ends" in this invention, a series of conjugated dye molecules with different ester groups (methyl, ethyl, propyl, butyl, and tert-butyl) and strong electron acceptor malononitrile substitutions were designed and synthesized. Their general formula is D–π–A, where donor D is an N,N-dimethylaminophenyl structural unit with strong electron-donating ability; the π-bridge is a styrene conjugated unit, serving as a charge transport pathway to maintain good conjugation and molecular skeleton planarity; and the acceptor A portion is introduced with a polarity-tunable cyanoacetic acid ester group (including methyl, ethyl, propyl, butyl, and tert-butyl) or a strong electron acceptor malononitrile group. The synthesis process of representative molecules is as follows:

[0123] ;

[0124] They are named using the numbers DMAPC-M1 to M4, DMAPC-M8, DMAPC-M9, and DMAPC-DCN.

[0125] Taking DMAPC-M4 as an example: 4-(dimethylamino)cinnamaldehyde (10 mmol, 1.75 g) and butyl cyanoacetate (11 mmol, 1.55 g) were used as starting materials, dissolved in 25 mL of anhydrous ethanol, and piperidine (0.2 mL) was added as a catalyst. The mixture was refluxed at 25 °C for 2 hours. After the reaction, the mixture was placed in ice water for 5 minutes, precipitating a dark red solid. After filtration and drying, the solid was purified by column chromatography using dichloromethane:petroleum ether at a volume ratio of 2:1 to obtain 2.74 g of the target compound, with a yield of approximately 91%. Other substituted molecules were simply replaced with the corresponding cyanoacetate reagent or malononitrile. The synthetic route was consistent, the purification process was similar, and the yields were all between 86% and 93%. The 1H and 1C NMR spectra of some compounds are shown below. Figures 10-16 As shown.

[0126] The purified product was recrystallized. Taking DMAPC-M4 as an example, 1 g of solid was dissolved in 20 mL of dichloromethane, and 2 mL of the solution was placed in 10 test tubes. Then, 4 mL of ethanol was slowly added dropwise along the tube wall. The tubes were sealed with sealing film and left at room temperature for 7 days. After filtration, the solution was naturally dried to obtain a large number of near-infrared emitting crystals. Other dye molecules were grown using the same crystal growth method, and dark red / black needle-like, plate-like, or blocky crystals were obtained. Figure 17 ).

[0127] (2) Effects;

[0128] Absorption / emission spectroscopy display ( Figure 18The series of compounds exhibit broad absorption bands in the 300–800 nm crystal range, with emission peaks all exceeding 700 nm, extending into the near-infrared region and displaying significant Stokes shifts (>100 nm). The minimal overlap between absorption and emission reduces the impact of self-absorption. In contrast, introducing strong acceptor groups such as malononitrile further enhances the ICT effect, extending the emission wavelength above 800 nm. These results demonstrate that the emission performance can be effectively controlled by adjusting the type of substituents, achieving near-infrared excitation-emission output. Furthermore, compared to the solution state, the solid powder or crystalline state exhibits stronger emission, indicating superior excited-state stability in the condensed state.

[0129] PLQY test results show ( Figure 19 and 20 The emission efficiency was 16% for DMAPC-M1, 16% for DMAPC-M2, 24% for DMAPC-M3, and 24% for DMAPC-M4. This shows that as the ester chain length increases, the non-radiative pathways within the molecule are gradually suppressed by steric hindrance, resulting in a significant increase in emission efficiency. This indicates that long-chain ester groups contribute to improving the photoluminescence quantum efficiency. In conclusion, fine-tuning the ester group structure not only affects the emission wavelength and intensity but also significantly modulates the photoluminescence quantum yield. DMAPC-M3 and DMAPC-M4 are the most promising dye candidates for application.

[0130] ASE test results show ( Figure 21 Under strong light excitation, DMAPC-M1 to M4 molecules exhibit excellent stimulated emission (ASE) properties. During the test, a high-intensity third-harmonic Nd:YAG pulsed laser (wavelength 355 nm, pulse width 5 ns, repetition frequency 10 Hz) was used to excite the crystal samples of the above molecules. All samples showed obvious ASE characteristics, with emission wavelengths between 731 and 770 nm and minimum half-widths (FWHM) between 14 and 22 nm.

[0131] Example 2: The excellent laser performance of DMAPC-M4;

[0132] (1) Composition and preparation;

[0133] This embodiment, based on Example 1, selects the representative butyl ester-substituted dye molecule DMAPC-M4 as the laser performance testing object. This molecule possesses strong intramolecular charge transfer (ICT) capability, high photoluminescence quantum yield (PLQY = 24%), and excellent intermolecular stacking behavior. Recrystallization with dichloromethane / ethanol (v / v = 1:1) and tetrahydrofuran / ethanol (v / v = 1:1) yielded well-formed, optically homogeneous blocky, plate-like, and needle-like red crystals, which can be directly used for solid-state spectroscopy and laser behavior testing. Preliminary tests revealed anisotropic characteristics (…). Figure 22 (a) ASE emission was observed in both plate-like and bulk crystals under excitation from multiple directions, indicating a multi-directional gain path. In contrast, needle-like crystals only exhibited ASE emission when excited along their long axis (growth direction), with no amplified emission signal produced during vertical excitation, demonstrating significant anisotropy in their gain channels. The spectra showed enhancement of the ASE peak in the near-infrared region, and crystals of different morphologies exhibited narrower full width at half maximum (FWHM) and higher emission intensity in specific directions, further confirming their anisotropic amplification mechanism. Figure 22 (b)

[0134] (2) Effects;

[0135] A bulk DMAPC-M4 crystal was fixed on a silicon substrate surface, and a pulsed laser beam with a wavelength of 355 nm, a repetition frequency of 10 Hz, and a pulse duration of 5 ns was used to irradiate the central region of the crystal along the growth direction and perpendicular to the growth direction, respectively. Figure 23 (a and b). Under conditions of gradually increasing pump energy, obvious near-infrared luminescence appears inside the crystal and propagates along the crystal axis, forming ASE signals at both ends. Figure 23 As shown in Figures c and d, with increasing excitation power density, the emission intensity increases rapidly, and the spectral lines narrow sharply, indicating that the crystal has entered a stimulated emission-dominated state; its corresponding ASE characteristics are further shown in... Figure 23 The FWHM versus intensity variation curves for e and f are validated. Specifically: when excited along the crystal growth direction, the main emission peak of ASE is located at 750 nm, the threshold is 33.6 kWcm⁻², and the minimum half-width (FWHM) is 10.5 nm; when excited perpendicular to the growth direction, the main emission peak redshifts to 738 nm, the threshold increases to 79.8 kWcm⁻², and the minimum FWHM is 15.1 nm. This difference indicates that the DMAPC-M4 crystal possesses anisotropic laser amplification capabilities in different directions, with superior amplification efficiency and a lower excitation threshold along the growth direction, providing an important foundation for constructing directionally controllable, high-efficiency near-infrared organic lasers.

[0136] The laser waveguide capability of the crystal was tested under the same experimental conditions. A 355nm pulsed laser was focused at different positions on the crystal, and its output signal was collected at the other end (fixed end). Figure 24 (a and b). As the excitation point gradually moves away from the fixed end, the output signal strength attenuates significantly, exhibiting typical waveguide propagation behavior. Figure 24(c and d). The spectrum shows a gradual decrease in output intensity with increasing position, but the spectral shape remains stable, indicating that the crystal possesses good optical signal guiding capabilities. Further calculations using exponential decay fitting show that the optical loss coefficient (OLC) of the needle-like crystal is 0.09 dB·mm. -1 The bulk crystal has a density of 0.10 dB·mm. -1 ( Figure 24 Both the needle-shaped and f-shaped crystals exhibit excellent low-loss waveguide performance. Furthermore, the full width at half maximum (FWHM) of the output spectra of both types of crystals remains within a narrow range, with the needle-shaped crystal exhibiting a range of 13.6–15.7 nm. Figure 24 (e); bulk crystals are narrower, remaining between 9.0 and 10.0 nm. Figure 24 The value of f indicates that its output signal has high spectral purity and quasi-single-mode characteristics, and has the potential to achieve high-quality optical transmission in the near-infrared band.

[0137] In summary, DMAPC-M4 butyl ester substituted dye crystals exhibit excellent near-infrared laser performance due to their unique molecular design (D–π–A conjugated system, compact monobenzene ring structure, and tunable substituents) and optimized aggregation state characteristics (ordered crystal stacking and J-aggregate formation): the crystals emit wavelengths of 750 nm along the growth direction and 738 nm perpendicularly, both within the 730–790 nm near-infrared range; the ASE threshold is as low as 33.6 kW / cm². 2 (Growth direction) and 79.8 kW / cm 2 (Vertical direction), all below 100 kW / cm 2 When the pump energy exceeds the threshold, the emission spectrum narrows significantly, and the minimum half width at half maximum (FWHM) can reach 10.5 nm (growth direction), which shows the characteristics of narrow-spectrum (~10 nm) high-intensity laser emission.

[0138] These materials not only possess low threshold, high strength, and well-directed stimulated emission properties, but also exhibit excellent waveguide effects (optical loss coefficient as low as 0.09~0.10 dB·mm). -1 This material can be used as a high-quality organic laser waveguide material in on-chip lasers, tunable light sources, and integrated optical chips. Compared with existing polycyclic dyes, it effectively solves the problems of low solid-state luminescence efficiency and high laser threshold through the synergistic regulation of molecular structure and aggregation state, showing great potential for practical application.

[0139] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent.

Claims

1. A class of organic near-infrared luminescent dye compounds, characterized in that, This includes pentadienoate compounds and maleic nitrile derivatives with ester groups having a D–π–A structure; The ester-containing pentadienoate compounds include (2Z,4E)-2-cyano-5-(4-(dimethylamino)phenyl)pent-2,4-dienoate, (2Z,4E)-2-cyano-5-(4-(diethylamino)phenyl)pent-2,4-dienoate, and (2Z,4E)-2-cyano-5-(4-(methoxy)phenyl)pent-2,4-dienoate; wherein the substituent R at the ester end is selected from methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, or tert-butyl. The maronitrile derivatives include (E)-2-(3-(4-(dimethylamino)phenyl)propenyl)malonitrile, (E)-2-(3-(4-(diethylamino)phenyl)propenyl)malonitrile, and (E)-2-(3-(4-methoxyphenyl)propenyl)malonitrile.

2. A method for preparing the organic near-infrared luminescent dye compound according to claim 1, characterized in that: For ester-containing pentadienoate compounds, the Knoevenagel condensation reaction is used, with 4-substituted cinnamaldehyde and cyanoacetic acid R ester as raw materials, where R corresponds to the substituent at the ester end, and the reaction is carried out in a solvent under the catalysis of an organic base; the organic base is piperidine or piperazine. For malononitrile derivatives, the Knoevenagel condensation reaction is used, with 4-substituted cinnamaldehyde and malononitrile as raw materials, and the reaction is carried out in a solvent under the catalysis of an organic base; the organic base is piperidine, piperazine or triethylamine.

3. The preparation method according to claim 2, characterized in that, The solvent is anhydrous ethanol or anhydrous methanol; the reaction temperature is 20~40℃; and the reaction time is 2~4 hours.

4. An organic near-infrared luminescent crystal, characterized in that, The organic near-infrared luminescent dye compound of claim 1 is grown by solution evaporation induction or liquid phase diffusion. The crystal morphology is blocky, needle-like or plate-like, and it has near-infrared luminescence and amplified spontaneous emission characteristics.

5. The organic near-infrared luminescent crystal according to claim 4, characterized in that, The photoluminescence quantum yield of the organic near-infrared luminescent crystal is 10-24%, and the amplified spontaneous emission threshold is less than 100 kW / cm². 2 The emission wavelength is between 730 and 790 nm.

6. An organic optical gain device, characterized in that, The organic near-infrared luminescent crystal described in claim 4 or 5 is used as an optical gain medium.

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