Organic near-infrared luminescent dye compound as well as crystal and application thereof

Abstract

The invention relates to the technical field of organic photoelectric functional materials, and provides an organic near-infrared luminescent dye compound as well as a crystal and application thereof. The material disclosed by the invention comprises a series of compounds consisting of 4-(dimethylamino) phenyl and a cyanoacrylate yoke skeleton and malononitrile derivative compounds. The compound is simple in structure and small in molecular weight, is efficiently synthesized through one-step Knoevenagel condensation reaction, is simple in step, is low in cost, is easy for industrial production, and can adjust emission wavelength and performance by changing terminal group substitution or acceptor types. The material has good self-assembly capability and high crystallinity in a solid state, and can form a stable laser gain medium. The narrow-spectrum, high-brightness and low-threshold stable laser output is realized in the near-infrared band, the photoluminescence quantum yield reaches 24%, and the stimulated emission performance is excellent. The material has good chemical stability and device compatibility, and shows wide application prospects in the fields of near-infrared solid dye lasers, optical communication, optical fiber amplifiers and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of organic photoelectric functional materials, and particularly relates to an organic near-infrared luminescent dye compound, a crystal thereof and an application thereof. BACKGROUND

[0002] With the wide application of laser technology in the fields of short-wave infrared (SWIR) communication, night vision imaging, biological diagnosis and spectral analysis, the market has an urgent demand for near-infrared organic laser materials with excellent performance, friendly processing and adjustable wavelength. Especially in the environment of miniaturization and integration, the structural design and optical performance of the materials must achieve a new balance. Compared with traditional inorganic laser media, organic luminescent materials have unique advantages such as strong structural designability, mild processing, low cost and solution processing, and have become a research hotspot in recent years.

[0003] At present, common organic near-infrared laser dye material systems mainly include the following categories: Polycyclic conjugated dye molecules (such as cyanine, silicon cyanine, thiophene derivatives, etc.): These materials generally contain two or more aromatic rings and heterocyclic rings, realize long-wave emission by constructing an ultralong conjugated chain, the molecular length can reach 2-5 nm, and the degree of π electron delocalization is high. Common structural units include pyridine ring, thiophene, indole, etc., which connect the electron donor and acceptor through a conjugated bridge to realize long-wave red shift. Its luminescence depends on the excited state π-π* transition, the excitation energy is low, and the emission wavelength can cover 700-900 nm, but the energy gap is small, which is easy to cause non-radiative processes (such as internal conversion and vibration relaxation). In practical applications, this kind of material is mostly in a solution state and must be doped into a polymer matrix (such as PMMA, PVA) for use, and the general concentration is <1 wt% to avoid concentration quenching.

[0004] Conjugated polymer materials (such as MEH-PPV, PFO, PBTTT): The molecular chain is composed of repeating conjugated units, the structure is highly regular, and the self-assembled microcrystals or amorphous aggregate state can be formed in solid state; the exciton can be transferred on the polymer chain after excitation, and the emission wavelength is regulated by the main chain structure. Some materials realize near-infrared emission by introducing heavy atoms or conjugated bridges, but there are problems such as large molecular weight, poor batch consistency, good solution processing but limited emission efficiency, and high laser threshold.

[0005] Emerging trends in the development of new organic laser materials: functional coating method (encapsulating traditional dyes in high refractive index and high thermal conductivity media such as SiO2 shell to improve thermal stability and quantum efficiency); single crystal device (crystallizing small molecule dyes into sheet, needle, and columnar crystals for use as laser cavities or waveguides. Control the molecular packing direction using self-assembly; reduce non-radiative losses caused by π-π stacking), enhanced structure design (construct push-pull molecular structures such as donor-π-acceptor (D-π-A) architecture, where D is an electron donor, A is an electron acceptor, and π is a conjugated bridge, to enhance near-infrared absorption and emission efficiency through intramolecular charge transfer (ICT)).

[0006] In summary, the existing organic near-infrared laser dye materials have the following technical defects and limitations in practical applications: Complex molecular structure, complicated synthesis route: Current mainstream near-infrared organic dyes rely on polycyclic or long conjugated chain structures (such as cyanine, thiophene, nitrogen heterocyclic system, etc.), which have large molecular weight and many synthesis steps, making purification difficult and low yield, which is difficult to meet the demand of low cost and large-scale production.

[0007] Low emission efficiency, high laser threshold: Limited by the "energy gap law", as the emission wavelength extends to the near-infrared region, the non-radiative relaxation channel of the excited state of organic dyes is significantly enhanced, leading to a sharp decline in fluorescence quantum yield (PLQY). At the same time, the π-π stacking effect in solid state or high concentration state further weakens the emission efficiency, resulting in a high laser emission threshold.

[0008] Unstable solid-state performance, poor device compatibility: Most dyes rely on solution state, and it is difficult to maintain high-efficiency emission performance in solid state or thin film, with poor crystallinity and uncontrolled morphology, which limits the expansion of practical application scenarios.

[0009] Weak controllability, lack of structure-property synergistic design: The existing dye materials have low freedom in molecular engineering control, and it is often difficult to optimize key parameters such as emission wavelength, quantum efficiency, and crystallinity at the same time, which limits the performance improvement.

[0010] Therefore, the present application proposes a class of organic near-infrared luminescent dye compounds with simple structure, efficient synthesis, tunable wavelength, and amplified spontaneous emission (ASE) capability, as well as their crystals and applications. SUMMARY

[0011] The present application aims to provide a class of organic near-infrared luminescent dye compounds and their crystals and applications, which aims to solve the problems raised in the above background art.

[0012] The application is achieved by the following technical solutions. The application relates to a kind of organic near-infrared luminescent dye compounds, including ester group-containing pentadienoate compounds and maleonitrile derivative compounds with D-pi-A structure. The ester group-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 end of the ester group is selected from methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl or t-butyl. The maleonitrile derivative compounds include (E)-2-(3-(4-(dimethylamino) phenyl) prop-2-enylidene) malononitrile, (E)-2-(3-(4-(diethylamino) phenyl) prop-2-enylidene) malononitrile and (E)-2-(3-(4-methoxyphenyl) prop-2-enylidene) malononitrile.

[0013] A preparation method of the organic near-infrared luminescent dye compound is also provided. For the ester group-containing pentadienoate compound, Knoevenagel condensation reaction is adopted, 4-substituted cinnamaldehyde and cyanoacetic acid R ester are used as raw materials, R corresponds to the substituent at the end of the ester group, and the reaction is carried out in a solvent under the catalysis of an organic base; the organic base is piperidine or piperazine. For the maleonitrile derivative compound, Knoevenagel condensation reaction is adopted, 4-substituted cinnamaldehyde and malononitrile are used 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.

[0014] Further, the solvent is anhydrous ethanol or anhydrous methanol; the reaction temperature is 20-40 DEG C; and the reaction time is 2-4 hours.

[0015] An organic near-infrared luminescent crystal is grown from the organic near-infrared luminescent dye compound by solution evaporation induction method or liquid phase diffusion method, and the crystal morphology is blocky, needle-like or flaky, and the crystal has near-infrared luminescent and ASE characteristics.

[0016] Further, the photoluminescence quantum yield of the organic near-infrared luminescent crystal is 10-24%, the amplified spontaneous emission threshold is lower than 100 kW / cm 2 , and the emission wavelength is 730-790 nm.

[0017] An organic optical gain device comprises the organic near-infrared luminescent crystal as an optical gain medium.

[0018] Compared with the prior art, the present application has the beneficial effects that: The present application provides an organic near-infrared luminescent crystalline material based on a single benzene ring push-pull molecule, including a series of compounds with a conjugated skeleton composed of a 4-(dimethylamino) phenyl (donor) and a cyano acrylate (acceptor), and malononitrile derivative compounds. These materials have the characteristics of simple molecular structure (containing only a single benzene ring) and small molecular weight, can be efficiently synthesized through one-step Knoevenagel condensation reaction, have simple steps, low cost and are conducive to industrial production, are easy to purify and structure control, and can realize controllable adjustment of emission wavelength and performance by changing the ester end R group or acceptor type, forming a highly adjustable molecular engineering platform. The material exhibits good self-assembly ability and high crystallinity in a solid state, can form a stable laser gain medium, and is compatible with existing laser device processing technology. It realizes stable laser output with narrow spectrum (half-width of about 10 nm), high brightness and low threshold (ASE threshold is lower than 100 kW / cm2, and the lowest is 33.6 kW / cm2) in the near-infrared waveband (730-790 nm), has a photoluminescence quantum yield (PLQY) of 24%, and has excellent stimulated emission performance. In addition, the material has good chemical stability and device compatibility, and has broad application prospects in the fields of near-infrared solid dye lasers, optical communication, optical fiber amplifiers and the like. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 Molecular formula of target compounds DMAPC (a), DEAPC (b), MAPC (c) and malononitrile derivative compounds (d).

[0020] Figure 2 Schematic diagram of growing single crystals of the series of compounds by slow evaporation method and liquid-liquid diffusion method and the obtained crystals; wherein a is a schematic diagram of growing single crystals of the series of compounds by slow evaporation method and the obtained crystals (the left side is a daylight photo and the right side is a fluorescence photo), b is a schematic diagram of growing single crystals of the series of compounds by liquid-liquid diffusion method and the obtained crystals (the left side is a daylight photo and the right side is a fluorescence photo).

[0021] Figure 3 Frontier orbital analysis of DMAPC-M4 molecule, daylight fluorescence photo and corresponding steady-state absorption / emission spectrum of the crystal, and vertical excitation energy calculation analysis; wherein a is the result of frontier orbital analysis; b is the daylight fluorescence photo and corresponding steady-state absorption / emission spectrum of the crystal; c is the result of vertical excitation energy calculation analysis.

[0022] Figure 4Comparison of crystal structure and molecular packing pattern of DMAPC-M2 and DMAPC-M4; a is the front view and top view of DMAPC-M2 crystal structure; b is the front view and top view of DMAPC-M4 crystal structure; c is the molecular packing pattern of DMAPC-M2 crystal along c axis; d is the molecular packing pattern of DMAPC-M4 crystal along c axis; Figure 5 Daylight fluorescence photographs of DMAPC-M4 in different polar solvents, corresponding solution absorption and emission spectra; a is the daylight fluorescence photographs of DMAPC-M4 in different polar solvents; b is the corresponding solution absorption spectrum; c is the corresponding solution emission spectrum.

[0023] Figure 6 UV-Vis absorption spectrum and fluorescence emission spectrum of DMAPC-M2 crystal.

[0024] Figure 7 ASE behavior of DMAPC-M4 crystal under different laser power excitation, including the emission spectra obtained under different laser power (355 nm pulsed excitation) and the normalized fluorescence spectra of DMAPC-M4 crystal under different laser power excitation. -2 Fluorescence photographs under laser excitation, showing typical ASE behavior.

[0025] Figure 8 Normalized fluorescence spectra of DMAPC-M4 crystal under different power laser excitation.

[0026] Figure 9 Normalized spectra of ASE emission intensity of DMAPC-M4 crystal under the condition of laser repeated pumping (72,000 times, lasting for 2 hours) with time.

[0027] Figure 10 Fluorescence photographs of DMAPC-M2 under different laser power excitation. 1 H NMR spectrum (CDCl3, 400 MHz).

[0028] Figure 11 Fluorescence photographs of DMAPC-M3 under different laser power excitation. 1 H NMR spectrum (CDCl3, 400 MHz).

[0029] Figure 12 Fluorescence photographs of DMAPC-M4 under different laser power excitation. 1 H NMR spectrum (CDCl3, 400 MHz).

[0030] Figure 13 Fluorescence photographs of DMAPC-M8 under different laser power excitation. 1 H NMR spectrum (CDCl3, 400 MHz).

[0031] Figure 14DMAPC-M9 1 H NMR spectra (CDC13, 400 MHz).

[0032] Figure 15 DMAPC-DCN 1 H NMR spectra (CDC13, 400 MHz).

[0033] Figure 16 DMAPC-M4 13 C NMR spectra (CDC13, 101 MHz).

[0034] Figure 17 Photographs of DMAPC-M1 to M4, DMAPC-M8, DMAPC-M9 and DMAPC-DCN crystals under sunlight (left) and fluorescence (right).

[0035] Figure 18 UV-Vis absorption and fluorescence emission spectra of DMAPC-M1 to M4, DMAPC-M9 and DMAPC-DCN crystals.

[0036] Figure 19 Photoluminescence quantum yield of DMAPC-M1, DMAPC-M2 and DMAPC-M3 crystals.

[0037] Figure 20 Photoluminescence quantum yield of DMAPC-M4, DMAPC-M9 and DMAPC-DCN crystals.

[0038] Figure 21 ASE characteristic spectra of DMAPC-M1 to M4 crystals.

[0039] Figure 22 Directional selective ASE behavior of different crystal morphologies; a, different morphology single crystal samples show obvious ASE anisotropy under 640 nm pulsed laser excitation; from top to bottom, the crystals are flaky, needle-like and blocky, the green dashed arrow indicates the excitation direction, according to whether the excitation direction is along the crystal growth axis, different crystals show different characteristics of whether they have ASE emission (ASE √) or not (ASE ×) (for example, needle-like crystals show strong ASE when excited along the long axis, but no ASE emission (ASE ×) when excited vertically); b, the ASE emission spectra of the corresponding crystals under different excitation directions.

[0040] Figure 23Figures a, b, c, d, e and f are schematic diagrams of exciting DMAPC-M4 bulk crystal by laser parallel and perpendicular to the growth direction, and corresponding normalized fluorescence spectra under different pump laser energies, and nonlinear gain relationship curves between half peak width, luminescence intensity and pump laser energy; wherein, a is a schematic diagram of exciting DMAPC-M4 bulk crystal by laser parallel to the growth direction; b is a schematic diagram of exciting DMAPC-M4 bulk crystal by laser perpendicular to the growth direction; c is corresponding normalized fluorescence spectra under different pump laser energies of the a figure; d is corresponding normalized fluorescence spectra under different pump laser energies of the b figure; e is a nonlinear gain relationship curve between half peak width, luminescence intensity and pump laser energy of the a figure; f is a nonlinear gain relationship curve between half peak width, luminescence intensity and pump laser energy of the b figure.

[0041] Figure 24 Figures a, b, c, d, e and f are ASE waveguide photos of DMAPC-M4 needle-like crystal and bulk crystal, corresponding emission spectra collected and fitted optical loss coefficients; wherein, a is an ASE waveguide photo of DMAPC-M4 needle-like crystal; b is an ASE waveguide photo of DMAPC-M4 bulk crystal; c is an emission spectrum of DMAPC-M4 needle-like crystal; d is an emission spectrum of DMAPC-M4 bulk crystal; e is a fitted optical loss coefficient of DMAPC-M4 needle-like crystal; f is a fitted optical loss coefficient of DMAPC-M4 bulk crystal. DETAILED DESCRIPTION

[0042] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present application, the technical solutions of the present application will be described in detail below, but it should not be understood as limiting the scope of the present application.

[0043] The present application aims to prepare a class of organic near-infrared luminescent dye compounds, which will be described in detail from four aspects of material preparation, crystal growth and structural characteristics, material characterization and optical performance test, and construction and performance evaluation of dye laser devices.

[0044] I. Material preparation The present application relates to two types of dye compounds with near-infrared luminescent properties, specifically as follows: 1. Pentadienoate compounds containing ester groups; This class of compounds includes (2Z, 4E)-2-cyano-5-(4-(dimethylamino) phenyl) pent-2, 4-dienoate (abbreviated as DMAPC, Figure 1 (2Z, 4E)-2-cyano-5-(4-(diethylamino) phenyl) pent-2, 4-dienoate (abbreviated as DEAPC, Figure 1(2Z,4E)-2-cyano-5-(4-(methyloxy)phenyl)pent-2,4-dienoate (MAPC, for short), Figure 1 M9: R = tert-butyl. The ester group at the end of the molecule is substituted by 9 different groups, which are numbered as 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. 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, a stable π-conjugated push-pull structure is formed. Among them, the cyano group and the ester group together constitute an electron acceptor, and the para-substituted group of the benzene ring (such as -N(CH3)2, -N(C2H5)2, -OCH3) provides an electron donor function, which enhances the near-infrared light-emitting ability through intramolecular charge transfer (ICT) effect.

[0045] The synthesis route is as follows: ; Synthesis method: This kind of ester-containing pentadienoate compounds is prepared by Knoevenagel condensation reaction, as follows (take DMAPC as an example): (1) Aldehyde component: 4-(dimethylamino)cinnamaldehyde, 4-(diethylamino)cinnamaldehyde, 4-(methoxy)cinnamaldehyde, etc.; active methylene component: cyanoacetate (such as methyl, ethyl, propyl, tert-butyl cyanoacetate, etc.).

[0046] (2) Reaction conditions: solvent is anhydrous ethanol or anhydrous methanol (25~100 mL, adjusted according to the reaction scale); catalyst is an organic base, such as piperidine, piperazine, etc. (0.05~0.1 eq); temperature 20~40℃; time 2~4 hours, TLC monitoring reaction progress.

[0047] Synthesis steps: 4-(dimethylamino)cinnamaldehyde (1.0 eq) and cyanoacetate R ester (1.1~1.2 eq) are added to 25~100 mL of anhydrous ethanol or anhydrous methanol; 5~15 drops of piperidine are added dropwise; stir at 20~40℃ for 2~4 hours, monitor by TLC during the reaction until the raw material is basically consumed; if solid is precipitated from the system, it can be directly filtered and washed with cold ethanol or petroleum ether; if no obvious solid is precipitated, add appropriate amount of deionized water to terminate the reaction, extract with dichloromethane; the organic phase is washed, dried, and then the solvent is removed by rotary evaporation to obtain the crude product; finally, the high-purity target product is obtained by column chromatography (eluent can be selected petroleum ether / ethyl acetate, n-hexane / dichloromethane, etc.) or sublimation method.

[0048] The method is prepared by the dehydration condensation of active methylene compound (such as cyanoacetic acid R ester) and aldehyde group under alkaline conditions through the characteristics of Knoevenagel condensation reaction. It has the advantages of mild conditions, easy to obtain raw materials, high reaction efficiency, simple operation, no need for high temperature and high pressure and multi-step reaction.

[0049] 2. Malononitrile derivative compounds; The compounds include (E)-2-(3-(4-(dimethylamino)phenyl)propenylene) malononitrile (DMAPC-DCN), (E)-2-(3-(4-(diethylamino)phenyl)propenylene) malononitrile (DEAPC-DCN), (E)-2-(3-(4-methoxyphenyl)propenylene) malononitrile (MAPC-DCN) Figure 1 d). The compounds use malononitrile (malononitrile) as the terminal strong acceptor, and construct a typical D-pi-A conjugated system. The conjugated bridge is usually a single bond connected propenylene (-CH=CH-CH=), which has a relatively short conjugation path, but still achieves excellent optical performance through strong electron pull-push effect, has high dipole moment, high luminescent quantum yield and low stimulated emission threshold, and is suitable for use as short-wave infrared organic laser gain medium.

[0050] Synthesis method: similar to the ester structure, the malononitrile derivative compounds are also synthesized by Knoevenagel condensation reaction, as follows (take DMAPC-DCN as an example): (1) Reaction raw materials: the aldehyde component is 4-(dimethylamino)cinnamaldehyde (or other 4-substituted cinnamaldehyde); the active methylene component is malononitrile (malononitrile).

[0051] (2) Reaction conditions: the solvent is anhydrous ethanol or anhydrous methanol 25-100 mL (adjust 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 (TLC monitors the reaction progress).

[0052] (3) Synthesis steps: 4-(dimethylamino)cinnamaldehyde and malononitrile are added to 25-100 mL of anhydrous ethanol or anhydrous methanol according to the molar ratio of 1.0:1.1; 5-15 drops of piperidine are added dropwise; stir at 20-40℃ for 2-4 hours, monitor by TLC during the reaction until the raw materials are basically consumed; if solid is precipitated from the system, it can be directly filtered and washed with cold ethanol or petroleum ether; if no obvious solid is precipitated, add appropriate amount of deionized water to terminate the reaction, extract with dichloromethane; the organic phase is washed, dried, and then the solvent is removed by rotary evaporation to obtain the crude product; finally, the pure malononitrile derivative is obtained by column chromatography (eluent can be selected petroleum ether / ethyl acetate, n-hexane / dichloromethane, etc.) or sublimation method.

[0053] The Knoevenagel condensation reaction is a classic route for preparing α,β-unsaturated cyano ester compounds. It has the advantages of 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.

[0054] 2. Crystal growth and structural characteristics; In order to achieve high-performance organic laser output, the dye molecules of the present invention need to form high-quality single crystals that meet the device requirements for order, optical anisotropy, and stability, as follows: 1. Crystal growth method; A series of push-pull dye molecules can be grown into high-quality single crystals under normal pressure and temperature conditions through solution evaporation induction method or liquid phase diffusion method, which has the advantages of simple method, good controllability and stable crystal form.

[0055] The typical crystal growth process is as follows: (1) Solvent selection: Based on the polarity and solubility of the compound, a medium-polarity organic solvent system (such as acetonitrile / methanol, ethyl acetate / n-hexane, dichloromethane / ethanol, etc.) is preferred as the solvent / non-solvent pair; (2) Solution preparation: dissolve the pure target dye in an appropriate amount of good solvent (such as dichloromethane, tetrahydrofuran) to prepare a saturated or nearly saturated solution; (3) Growth pattern: Solution evaporation induction method: Place the dye solution in a sealed container and slowly evaporate the solvent at room temperature. Granular or flaky crystals will precipitate within 1 to 3 days ( Figure 2 (a) Liquid phase diffusion method: Slowly add a poor solvent (such as methanol, ethanol, petroleum ether) to the surface of the solution to form a stable interface with the dye solution. Slow diffusion between the solvents promotes crystal formation. After 7 to 14 days, a large number of strip-shaped or block-shaped crystals will precipitate in the solution ( Figure 2 (b) (4) Crystal collection and processing: After the crystals are formed, remove the upper layer of solvent with filter paper, quickly transfer the crystals and gently wash them with anhydrous solvent, air dry them or dry them in a vacuum dryer for later use.

[0056] This method is applicable to most push-pull molecules, including ester-containing pentadienoic acid ester compounds and malononitrile derivatives. The resulting crystals are generally block-shaped, plate-shaped, needle-shaped, flake-shaped or prism-shaped, with good optical transparency and mechanical stability, meeting the requirements of laser performance testing.

[0057] 2. Analysis of molecular structure and crystal properties; The excellent optical and laser properties of dye molecules are derived from their highly designed molecular structure and suitable crystal stacking, as follows: (1) D-pi-A push-pull conjugated system: All molecules are constructed based on the D-pi-A architecture, the donors are strong electron donors such as dimethylamino (-N(CH3)2), diethylamino (-N(C2H5)2) and methoxy (-OCH3); the pi-bridge is a double bond conjugated bridge (electron transport path); the acceptor is a strong electron acceptor composed of cyano and ester group or dicyano. This structure gives the molecule a larger intrinsic dipole moment and good charge delocalization. For example, (2Z, 4E)-2-cyano-5-(4-(dimethylamino) phenyl) pent-2, 4-dienyl butyrate (DMAPC-M4), the molecular frontier orbital shows a strong intramolecular charge transfer (ICT) effect (Fig. 1a); a wider absorption band and a red-shifted emission peak, a larger Stokes shift, effectively avoiding self-absorption (Fig. 1b); enhanced excited state vibronic strength (1.4527), which is conducive to stimulated emission and laser amplification (Fig. 1c). Figure 3 Figure 3 Figure 3

[0058] (2) Single benzene ring compact structure: Compared with common polycyclic aromatic hydrocarbon dyes, the molecules of the present application use a single benzene ring as the core skeleton, which has the advantages of small structure and moderate rigidity. For example, DMAPC-M2 and DMAPC-M4, the molecules are basically coplanar, with a twist angle of 6.90° and 7.36°, and the molecules are linearly distributed, which is conducive to the overlap of pi orbitals (Fig. 2a and b), which can effectively inhibit intramolecular twisting and non-radiative energy consumption, and the smaller volume is conducive to regular arrangement and reduces the probability of exciton annihilation between molecules. Figure 4

[0059] (3) Aggregation state optimization and crystal order: The aggregation-induced emission (AIE) effect helps to maintain high luminescent efficiency in the solid state; the ordered arrangement in the crystal can significantly reduce the non-radiative loss of the excited state and improve the laser gain performance. As shown in Fig. 3c and d, DMAPC-M2 and DMAPC-M4 both exhibit J-aggregation characteristics in the crystal, which is manifested as the ordered sliding accumulation of molecules along the a-axis direction, which is conducive to exciton coupling and emission peak red shift. Figure 4

[0060] In summary, the push-pull dye molecules of the present application not only have excellent molecular design basis, but also have good crystal growth ability and controllable aggregation state structure, which is helpful to realize high-performance near-infrared laser output, and is especially suitable for use as core material for gain medium in organic laser devices.

[0061] III. Structure characterization and optical performance test of the material ​​​​​In order to systematically study the photophysical properties of a series of push-pull dye molecules, a variety of methods were used to characterize their structure, spectral behavior, quantum yield and laser gain behavior, clarify the differences in luminescence properties between solution and crystal states, and highlight the advantages of crystal state laser performance.

[0062] 1. Molecular structure characterization; The target compound was synthesized by 1 H / 13 C NMR spectroscopy confirmed its molecular structure and purity; single crystal X-ray diffraction (SCXRD) was used to obtain the three-dimensional spatial configuration and molecular stacking mode of the grown crystals, with particular attention paid to intermolecular π-π stacking, J-aggregation characteristics, and molecular polarization direction, which helps to understand the mechanism of crystalline luminescence enhancement.

[0063] 2. Absorption and emission spectrum test; The UV-visible absorption spectra and fluorescence emission spectra of the dilute solution state and the crystal state were tested respectively to compare the light absorption and emission behaviors of the molecules in different states: (1) Solution spectroscopy test; Absorption spectroscopy: The absorption characteristics of dye molecules in different dilute solutions are measured using an ultraviolet-visible (UV–Vis) spectrophotometer ( Figure 5 In a), the solution concentration is generally controlled at 10 -5 ~10 -6 mol·L -1 . The 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 the molecules in each solvent was recorded, and the absorption band is usually distributed in the range of 400~600 nm. Taking DMAPC-M4 as an example, its maximum absorption wavelength in toluene is 450 nm and in DMSO is 481 nm, showing obvious intramolecular charge transfer (ICT) characteristics ( Figure 5 Middle b).

[0064] Emission spectra: The emission spectra of dye molecules in different solvents were recorded using a fluorescence spectrophotometer under 480 nm excitation. The emission band is usually between 500 and 700 nm. Taking DMAPC-M4 as an example, its emission peak is at 528 nm in toluene and 588 nm in DMSO. The Stokes shift is significant (approximately 78 to 107 nm), which helps to reduce self-absorption and improve laser emission efficiency and light purity. Figure 5 Middle c).

[0065] (2) Crystalline spectrum test; Absorption spectrum: The diffuse reflectance absorption spectrum of the crystal was measured by steady-state fluorescence spectrometer with an integrating sphere by pressing single crystal or crystal powder into a tablet; Emission spectrum: The fluorescence emission spectrum of the crystal sample was directly determined using a fluorescence spectrophotometer; taking DMAPC-M2 as an example, compared with the solution state, the crystal state has red shift or spectral band narrowing, the energy transition is more concentrated, which is beneficial to laser output. Figure 6 ).

[0066] 3. Photoluminescence quantum yield (PLQY) measurement (crystal state); In order to accurately reflect the luminescent efficiency of the material in the actual application state, the PLQY of the crystal sample was determined by the integrating sphere method (using a commercial quantum efficiency measuring instrument such as Hamamatsu Quantaurus-QY or Edinburgh FS5). The sample form is powder tablet or large size single crystal, and the excitation light wavelength is selected according to the absorption peak (such as 450-530 nm); the typical PLQY value can reach 10-25%, which is higher than that of most π-π stacking quenched dyes, and reflects the luminescence enhancement after optimization of the intermolecular arrangement.

[0067] 4. Preliminary evaluation of ASE properties (crystal state); In order to verify the laser gain potential of the dye molecule in the crystal state, the single crystal sample was preliminarily tested for amplified spontaneous emission characteristics: Sample preparation: Regular morphology large size single crystal (size generally 1-3 mm) obtained under natural growth or optimized conditions, or crystal powder tablet was selected as the test sample; Excitation light source: A pulsed Nd:YAG laser (such as 355 nm or 532 nm) was used as the pump source, with a pulse width of about 5 ns and a repetition frequency of 10 Hz; Experimental configuration: The pump light was focused on the surface of the crystal sample through a lens, and the emission signal was collected by a spectrometer to record the change of the emission spectrum with the pump energy density; ASE feature observation: Taking DMAPC-M4 crystal as a representative sample, under the excitation of 355 nm pulsed laser, it showed typical ASE behavior. Figure 7 At low pump energy density (<100 KW / cm -2 ), the crystal only showed weak intensity and wide bandwidth fluorescence emission; with the increase of pump intensity, the emission intensity was nonlinearly enhanced, and the spectrum was gradually narrowed; when the energy density exceeded a certain threshold (>400 KW / cm -2 ), the emission peak was sharpened, the bandwidth was compressed (FWM was significantly reduced), the intensity was sharply increased, which clearly marked the occurrence of ASE process, and verified that DMAPC-M4 had the potential to be used as a laser gain medium in the crystal state.

[0068] The test preliminarily proves that the dye in the crystal state has an effective stimulated radiation path and a low threshold gain characteristic, and lays a foundation for constructing a solid-state organic laser device.

[0069] IV. Construction and performance evaluation of the dye laser device On the basis of the aforementioned verification of the crystal ASE properties, in order to comprehensively evaluate the laser performance of the dye molecules in practical application, a crystal-state organic laser device with a large-size single crystal as a gain medium is constructed, and systematic output performance tests are carried out. Specifically as follows: 1. Construction of the laser device and pump configuration Crystal selection: A dye single crystal sample with a regular growth morphology and a size greater than 2 mm is selected to ensure that the laser gain path is straight and scattering loss is avoided; Excitation light source: A Nd:YAG nanosecond pulse laser (i.e., a neodymium-doped yttrium aluminum garnet laser) third harmonic (λ = 355 nm) is used as the pumping light, with a pulse width of 5 ns and a repetition frequency of 10 Hz; Optical path arrangement: A lens system is used to focus the laser on the end face or cross section of the crystal (depending on the geometric morphology of the crystal), and the detection direction is perpendicular to the pumping direction to collect the output signal; Laser emission monitoring: The laser output is collected in real time by a fiber-coupled spectrometer, and the output intensity is recorded by a power meter.

[0070] 2. Excitation threshold and gain criterion: Taking the DMAPC-M4 crystal as a representative test sample, the system records the influence of the pump energy density on the emission intensity and spectral line variation. When the pump power density gradually increases to ~40.6 kW / cm², the emission intensity shows a non-linear jump, and the spectral line is obviously compressed (λ = 650-680 nm) Figure 8 ), indicating that an ASE channel is established in the crystal. Under high-power pumping conditions (~40.6-136 kW / cm²), the FWHM of the emission spectrum of the DMAPC-M4 crystal can be gradually reduced to about 10 nm, showing an approximate single-mode emission behavior (λ = 650-680 nm) Figure 8 ). When the pump power is further increased to >148 kW / cm², the output intensity gradually tends to be flat, entering the gain suppression stage, indicating that the crystal material has reached the upper limit of saturated pumping.

[0071] 3. Optical stability and light bleaching resistance test: Under repeated pump irradiation, the DMAPC-M4 crystal sample is tested for long-time continuous excitation; the material light bleaching rate and laser lifetime are evaluated by the output intensity decay rate; the experimental results show that the crystal maintains stable output for more than 2 hours under 10 Hz pulse excitation, with a total of 72,000 excitation periods, and the emission intensity decays by about 20% (λ = 650-680 nm) Figure 9 ), showing good laser stability; light bleaching is mainly caused by surface decomposition or photooxidation, and further encapsulation or crystal face passivation can prolong the device lifetime.

[0072] The specific implementation of the present application is described in detail below in combination with specific examples.

[0073] Example 1: Near-infrared emission performance of dye molecules with different ester groups and strong acceptor substitutions; (1) Composition and preparation; To verify the effectiveness of the strategy of "adjusting the two end substituents to regulate the light-emitting performance" in the present application, a series of conjugated dye molecules with different ester groups (methyl ester, ethyl ester, propyl ester, butyl ester, tert-butyl ester) and strong electron acceptor malononitrile substitutions were designed and synthesized. The general structure is D-π-A, where the donor D is a N,N-dimethylamino phenyl structural unit with strong electron donating ability, the π-bridge is a phenylethylene conjugated unit as a charge transport path to maintain good conjugation and planarity of the molecular skeleton, and the acceptor A part introduces a polarity-adjustable cyanoacetate group (including methyl ester, ethyl ester, propyl ester, butyl ester, tert-butyl ester) or a strong electron acceptor malononitrile group. The synthesis process of the representative molecules is as follows: ; DMAPC-M1 to M4, DMAPC-M8, DMAPC-M9 and DMAPC-DCN are numbered.

[0074] Take DMAPC-M4 as an example: take 4-(dimethylamino) cinnamaldehyde (10 mmol, 1.75 g) and butyl cyanoacetate (11 mmol, 1.55 g) as starting materials, dissolve them in 25 mL of anhydrous ethanol, add piperidine (0.2 mL) as a catalyst, and reflux at 25°C for 2 hours. After the reaction is completed, place it in ice water for 5 minutes, and the dark red solid is precipitated. After being filtered and dried, the target compound 2.74 g is obtained after column chromatography purification with dichloromethane: petroleum ether (volume ratio 2:1) as eluent, and the yield is about 91%. The synthesis route of other substituted molecules is consistent, and the purification process is similar, and the yield is between 86% and 93%. The nuclear magnetic resonance hydrogen spectrum and carbon spectrum of part of the compounds are shown in Figures 10-16 .

[0075] The purified product is recrystallized. Take DMAPC-M4 as an example: take 1 g of solid and dissolve it in 20 mL of dichloromethane, take 2 mL of the solution and place it in 10 test tubes, then slowly drop 4 mL of ethanol along the tube wall, seal the tube with a sealing film, and place it at room temperature for 7 days. After being filtered and naturally dried, a large amount of near-infrared emitting crystals is obtained. Other dye molecules are grown by the same crystal growth method, and dark red / black needle-shaped, flaky or block-shaped crystals are obtained Figure 17 ).

[0076] (2) Effects; The absorption / emission spectrum shows thatFigure 18 The crystals of the series of compounds have a wide absorption band at 300-800 nm, and the emission peak position is greater than 700 nm, entering the near-infrared region, and has a large Stokes shift (> 100 nm), and a small absorption-emission overlap reduces the influence of self-absorption. In contrast, the introduction of strong acceptor groups such as malonitrile can further enhance the ICT effect, and the emission wavelength extends to more than 800 nm. The above results show that by adjusting the type of substituent group, the emission performance can be effectively regulated to realize near-infrared excitation-emission output. At the same time, compared with the solution state, the solid powder or crystal state has stronger emission, indicating that it has better excited state stability in the condensed state.

[0077] The PLQY test results show that Figure 19 and 20 ): DMAPC-M1: 16%; DMAPC-M2: 16%; DMAPC-M3: 24%; DMAPC-M4: 24%. As can be seen, with the increase of the length of the ester group, the non-radiative path in the molecule is gradually inhibited by steric hindrance, and the emission efficiency is significantly improved, indicating that the long-chain ester group helps to improve the luminescence quantum efficiency. In summary, the structure of the ester group not only affects the emission wavelength and emission intensity, but also significantly regulates the photoluminescence quantum yield, and DMAPC-M3 and DMAPC-M4 are the most promising dye candidates.

[0078] The ASE test results show that Figure 21 Under strong light excitation conditions, the DMAPC-M1 to M4 molecules exhibit excellent stimulated emission performance. During the test, a high-intensity third-harmonic Nd:YAG pulse laser (wavelength 355 nm, pulse width 5 ns, repetition frequency 10 Hz) was used to excite the crystal samples of the above molecules, and obvious ASE characteristics were observed for all samples, with an emission wavelength of 731-770 nm and a minimum half-peak width of 14-22 nm.

[0079] Example 2: Excellent laser performance of DMAPC-M4; (1) Composition and preparation; On the basis of Example 1, the representative butyl ester substituted dye molecule DMAPC-M4 was selected as the object of laser performance test. The molecule has strong intramolecular charge transfer (ICT) ability, high photoluminescence quantum yield (PLQY = 24%) and excellent intermolecular packing behavior. Dichloromethane / ethanol (v / v = 1:1) and tetrahydrofuran / ethanol (v / v = 1:1) were used for recrystallization, and regular, optically uniform block, flaky and needle-shaped red crystals were obtained, which can be directly used for solid-state spectrum and laser behavior test. Preliminary tests found that it has anisotropic characteristics Figure 22In the middle a), ASE emission can be observed in multiple directions for both flake and block crystals, indicating that their gain paths are more multi-directional, while the needle-like crystal only appears ASE when excited along the long axis (growth direction) of the crystal, and no amplification emission signal is generated when excited vertically, indicating that its gain channel has significant anisotropy. The spectrum shows that the ASE peak is enhanced in the near-infrared region, and different morphology crystals have narrower full width at half maximum (FWHM) and higher emission intensity in a specific direction, further confirming its anisotropic amplification mechanism Figure 22 In the middle b).

[0080] (2) Effect; The block DMAPC-M4 crystal was fixed on the surface of the silicon substrate, and a pulsed laser beam with a wavelength of 355 nm, a repetition frequency of 10 Hz, and a pulse time of 5 ns was used to irradiate the central region of the crystal along the growth direction and perpendicular to the growth direction Figure 23 In the middle a and b). Under the condition of gradually increasing pump energy, obvious near-infrared luminescence appears in the crystal, and propagates along the axial direction of the crystal, forming ASE signals at both ends. As shown in Figure 23 In the middle c and d, as the excitation power density rises, the emission intensity rapidly increases and the spectral line sharply narrows, indicating that the crystal enters the dominant state of stimulated emission; its corresponding ASE characteristics are further verified in Figure 23 In the middle e and f FWHM and intensity change curve. Specifically, when excited along the growth direction of the crystal, the main emission peak of ASE is located at 750 nm, the threshold is 33.6 kWcm⁻², and the minimum FWHM is 10.5 nm; when excited perpendicular to the growth direction, the main emission peak red shifts to 738 nm, the threshold increases to 79.8 kWcm⁻², and the minimum FWHM is 15.1 nm. This difference shows that the DMAPC-M4 crystal has anisotropic laser amplification ability in different directions, among which the growth direction has more excellent optical amplification efficiency and lower excitation threshold, providing an important foundation for constructing direction-controllable and high-efficiency near-infrared organic lasers.

[0081] Under the same experimental conditions, the laser waveguide ability of the crystal was tested. The 355 nm pulsed laser was focused on different positions of the crystal, and the output signal was collected at the other end (fixed end) Figure 24 In the middle a and b). As the excitation point gradually moves away from the fixed end, the output signal intensity significantly decays, showing a typical waveguide propagation behavior Figure 24 In the middle c and d). The spectrum shows that the output intensity gradually decreases with the position away, but the spectral shape remains stable, indicating that the crystal has good light signal guiding ability. Further through exponential decay fitting calculation, the optical loss coefficient (OLC) of the needle-like crystal is 0.09 dB·mm -1, the bulk crystal is 0.10 dB·mm -1 ( Figure 24 , the bulk crystal is 0.10 dB·mm Figure 24 , the bulk crystal is 0.10 dB·mm Figure 24 , the bulk crystal is 0.10 dB·mm

[0082] In summary, the DMAPC-M4 butyl ester substituted dye crystal exhibits excellent near-infrared laser performance due to unique molecular design (D-pi-A conjugated system, single benzene ring compact structure and adjustable substituent) and optimized aggregate characteristics (crystal ordered packing, J-aggregate formation): the crystal emits a wavelength of 750 nm along the growth direction, and 738 nm in the perpendicular direction, both of which are in the near-infrared range of 730-790 nm; the ASE threshold is as low as 33.6 kW / cm 2 (growth direction) and 79.8 kW / cm 2 (perpendicular direction), both of which are lower than 100 kW / cm 2 ; after the pump energy exceeds the threshold, the emission spectrum line is significantly narrowed, with the minimum full width at half maximum (FWHM) of 10.5 nm (growth direction), which exhibits narrow spectrum (~10 nm) high-intensity laser emission characteristics.

[0083] Such materials not only have low threshold, high intensity and good directionality of stimulated emission performance, but also have excellent waveguide effect (optical loss coefficient as low as 0.09-0.10 dB·mm -1 ), which can be used as high-quality organic laser waveguide materials and applied to on-chip lasers, tunable light sources and integrated optical chips. Compared with existing polycyclic dyes, through the synergistic regulation of molecular structure and aggregate state, the problems of low solid-state light efficiency and high laser threshold are effectively solved, which exhibits a very potential practical prospect.

[0084] The above is only the preferred embodiment of the present application, it should be noted that for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which should be considered as the protection scope of the present application, these will not affect the effect and practicality of the present application.

Claims

1. An organic near-infrared luminescent dye compound, characterized in that: Including ester-containing pentadienoic acid ester compounds and maleonitrile derivative compounds with D–π–A structure; The ester-containing pentadienoate compounds include (2Z,4E)-2-cyano-5-(4-(dimethylamino)phenyl)penta-2,4-dienoate, (2Z,4E)-2-cyano-5-(4-(diethylamino)phenyl)penta-2,4-dienoate, and (2Z,4E)-2-cyano-5-(4-(methoxy)phenyl)penta-2,4-dienoate; wherein the substituent R at the end of the ester group is selected from methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, or tert-butyl; The malononitrile derivative compounds include (E)-2-(3-(4-(dimethylamino)phenyl)propenylene)malononitrile, (E)-2-(3-(4-(diethylamino)phenyl)propenylene)malononitrile, and (E)-2-(3-(4-methoxyphenyl)propenylene)malononitrile.

2. A method for preparing the organic near-infrared luminescent dye compound according to claim 1, characterized in that: For ester-containing pentadienoic acid ester compounds, a Knoevenagel condensation reaction is used, using 4-substituted cinnamaldehyde and R cyanoacetate as raw materials, where R corresponds to the substituent at the ester end, to react in a solvent under the catalysis of an organic base; the organic base is piperidine or piperazine; For malononitrile derivatives, a 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° C.; 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 according to claim 1 is grown by a solution evaporation induction method or a liquid phase diffusion method, and has a block-shaped, needle-shaped or flake-shaped crystal morphology and 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 lower than 100 kW / cm 2 , the emission wavelength is between 730~790nm.

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

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