WO2022253343A1 - Single molecular mass conjugated fluorene-azobenzene oligomer having accurate sequence, synthesis method therefor and application thereof - Google Patents

Abstract

Disclosed in the present invention are a single molecular mass conjugated fluorene-azobenzene oligomer having an accurate sequence, a synthesis method therefor and an application thereof, for use in enriching and expanding the use in the research of a main chain containing fluorene and azobenzene. Specifically, a polymer of the present invention is prepared by the following steps: 1) obtaining azobenzene and fluorene donors; 2) obtaining different algebraic fluorenes; and 3) obtaining the conjugated monodisperse polymer of which the main chain contains azobenzene and fluorene in different sequences. The monodisperse conjugated polymer of the present invention has better product processing performance and physical performance; at the same time, according to the present invention, an iterative step-growth policy is combined with a click reaction, and the position of azobenzene is accurately controlled to precisely synthesize a polymer having an accurate structure and different sequences. The experimental operation is simple and easy to implement, and the theoretical basis is provided for accurately researching the relation between the structure and the performance. In addition, the chemical reagents used in the method of the present invention are stable in air; the method is simple and convenient to operate, high in efficiency, and convenient for industrial production.

Description

A single molecular weight conjugated fluorene-azobenzene precise sequence oligomer and its synthesis method and application technical field

The invention belongs to the field of monodisperse conjugated polymers, and relates to a preparation method and application of a conjugated monodisperse polymer whose main chain contains precise sequences of fluorene and azobenzene.

Background technique

As a common class of organic materials, conjugated polymers are widely used in fields such as organic light-emitting diodes, solar cells, field-effect transistors, and photoelectric detection due to their rigid conjugated structures, excellent thermal and chemical stability, and unique optoelectronic properties. (Schelkle, KM; Bender, M.; Jeltsch, K.; Buckup, T.; Mullen, K.; Hamburger, M.; Bunz, UH, Angew Chem Int Ed Engl 2015, 54 (48), 14545-8. Segura, JL; Martín, N.; Guldi, DM, Chem. Soc. Rev. 2005, 34 (1), 31-47.). Inspired by their unique properties and broad application prospects, single-molecular-weight conjugated polymers with precise structures have attracted extensive attention in the field of chemistry. Through the precise design and study of conjugated polymers, a deeper understanding of the relationship between properties and structures can be gained. Small differences in polymer sequence structure (chain length, dispersion, monomer order) will have significant differences in its photoelectric properties, crystallinity, etc., such as the dependence of the molecular weight of a single molecular weight conjugated oligomer on its optical and thermal properties (Zhang, X.; Qu, Y.; Bu, L.; Tian, H.; Zhang, J.; Wang, L.; Geng, Y.; Wang, F., Chem-Eur. J. 2007, 13 (21), 6238-6248. Liu, Q.; Liu, W.; Yao, B.; Tian, H.; Xie, Z.; Geng, Y.; Wang, F., Macromolecules 2007, 40 (6) , 1851-1857.) Dependence of polymer monomer order and optical properties (Okano, K.; Tsutsumi, O.; Shishido, A.; Ikeda, T., Journal of the American Chemical Society 2006, 128 (48 ), 15368-15369.Yu, Z.; Hecht, S., Angew.Chem. 2013, 52 (51), 13740-13744.) However, how to prepare artificial polymers with precise structure, composition and monomer sequence becomes another big challenge.

technical problem

In view of the above situation, the object of the present invention is to provide a preparation method and application of a conjugated monodisperse polymer containing fluorene and azobenzene in the main chain. Among the products of the present invention, polyfluorene, as a class of conjugated polymers, has the advantages of rigid structure, excellent thermal and chemical stability, easy modification of side chains, and high fluorescence quantum efficiency. It is the most promising high-efficiency blue Chromatic light-emitting materials; azobenzene, as a common stimuli-responsive group in response to light, heat and reduction, can undergo reversible cis-trans isomerization under light irradiation or heating. When it is introduced into the main chain of the polymer, the photoinduced cis-trans isomerization will significantly affect the molecular configuration of the oligomer/polymer, forming a reversible curl/uncurl process. Furthermore, azobenzene-containing conjugated polymers possess rapid photoisomerization capabilities and efficiencies, and are generally regarded as one of the most promising optoelectronic materials. The invention introduces the stimulus-responsive azobenzene into the polyfluorene conjugated polymer, and prepares the monodisperse fluorene-azobenzene polymer to obtain a photoelectric material with better performance.

Specifically, the present invention firstly uses a series of chemical reactions such as Sonogashira coupling, diazo coupling, nucleophilic substitution, esterification, nitration, and reduction to synthesize fluorene and azobenzene monomers in multiple steps. Nitrate the C7 position on the fluorene ring first, and introduce an octyl group at the C9 position, then use the Sonogashira coupling reaction to change the Br at the C2 position into a TBS-protected alkynyl group, and reduce the nitro group at the C7 position to an amino group with iron powder A fluorene monomer with an alkynyl group protected by TBS at one end and an amino group at the other end is obtained. First oxidize the amino group on the azobenzene benzene ring to a nitroso group, then synthesize azobenzene through the Mills reaction, then hydrolyze acetanilide into an amino group to obtain a TBS-protected alkynyl group, an azobenzene monomer with an amino group at one end . Then carry out TBS deprotection or amino azidation reaction, and then use the iterative stepwise growth strategy and "CuAAC" click reaction to prepare a single molecular weight conjugated fluorene-azobenzene oligomer with a precise sequence of azobenzene at different positions in the main chain , respectively named 4F-Azo, 2F-Azo-2F and F-Azo-3F. Relevant tests have proved that conjugated monodisperse polymers containing fluorene and azobenzene in the main chain can be effectively synthesized by this method, and the physical properties of oligomers, such as hydrodynamic volume, thermal properties, optical properties and photoisomerization Behavior etc. are sequence dependent.

technical solution

In order to achieve the above object, the present invention adopts the following technical scheme: a single molecular weight conjugated fluorene-azobenzene precise sequence oligomer, whose structure is one of the following structural formulas:

.

Among them, the azobenzenes of 4F-Azo, 2F-Azo-2F and F-Azo-3F are located at the chain end, core (symmetric position) and middle (asymmetric position), respectively.

A fluorene monomer having the following chemical structural formula:

.

Among them, n is 0~3, when n is 0, it is the first generation fluorene (TBS-F-NH ₂ ), when n is 1, it is the second generation fluorene (TBS-2F-NH ₂ ), when n is 2, it is the third generation Fluorene (TBS-3F-NH ₂ ), when n is 3, it is a quaternary fluorene (TBS-4F-NH ₂ ).

An azobenzene monomer (TBS-Azo-NH ₂ ) with the following chemical structure:

.

In the present invention, TBS is t-butyldimethylsilane.

The invention discloses the application of the above fluorene monomer and azobenzene monomer in the preparation of the single molecular weight conjugated fluorene-azobenzene precise sequence oligomer.

The invention discloses a preparation method of the above-mentioned single molecular weight conjugated fluorene-azobenzene precise sequence oligomer. The azobenzene monomer is diazotized and then azide-reacted to obtain TBS-Azo-N ₃ ; the fluorene monomer After deprotection, click chemical reaction with TBS-Azo-N ₃ to obtain a single molecular weight conjugated fluorene-azobenzene oligomer with precise sequence.

Specifically, when the single-molecular-weight conjugated fluorene-azobenzene oligomer with precise sequence is 4F-Azo, deprotect the four-generation fluorene (TBS-4F-NH ₂ ) and perform a click chemical reaction with TBS-Azo-N ₃ , to obtain 4F-Azo; when the single molecular weight conjugated fluorene-azobenzene oligomer with precise sequence is 2F-Azo-2F, deprotect the second generation fluorene (TBS-2F-NH ₂ ) and TBS-Azo-N ₃ Carry out a click chemical reaction to obtain TBS-Azo-2F-NH ₂ and then deprotect it with TBS, and react with TBS-2F-N ₃ to obtain 2F-Azo-2F; when the precise sequence of single molecular weight conjugated fluorene-azobenzene When the oligomer is F-Azo-3F, deprotect the first-generation fluorene (TBS-F-NH ₂ ) and perform a click chemical reaction with TBS-Azo-N ₃ to obtain TBS-Azo-F-NH ₂ TBS is deprotected and reacted with TBS-3F-N ₃ to obtain F-Azo-3F.

The diazotization reaction of the fluorene monomer is followed by an azidation reaction to obtain TBS-FN ₃ , TBS-2F-N ₃ , TBS-4F-N ₃ or TBS-3F-N ₃ .

In the present invention, the click chemical reaction is "CuAAC" click reaction, using PMDETA as a ligand and CuBr as a catalyst. The inherent properties of the conjugated monodisperse polymer containing fluorene and azobenzene in the main chain prepared by the invention are closely related to the predetermined structure, especially the thermal and optical properties of the polymer are found to be sequence-dependent.

The invention discloses the application of the above single molecular weight conjugated fluorene-azobenzene precise sequence oligomer as a photoisomerization material.

Beneficial effect

Due to the application of the above-mentioned technical scheme, the present invention has the following advantages compared with the prior art: 1. The present invention successfully introduces azobenzene stimulus-responsive groups into the main chain of conjugated polymers to construct new-type azobenzene-containing functional groups. Conjugated polymers enrich and expand the research on fluorene and azobenzene in the main chain, and promote the development of the field of azobenzene materials.

2. The present invention combines the iterative step-by-step growth strategy with the CuAAC "click reaction, and precisely controls the position of azobenzene to precisely synthesize polymers of different sequences, providing a method for efficient modular synthesis of a single molecular weight and broadening the application of this method scope.

3. The present invention provides a theoretical basis for studying the influence of sequence on the physical properties of conjugated polymers, and for the study of the precise relationship between structure and performance.

4. The chemical reagents used in the method of the present invention are stable in the air, and the reaction in the method is easy to operate and efficient, and has important application prospects.

Description of drawings

Figure 1 is the H NMR spectrum (DMSO -d ₆ ) of fluorene monomer, azobenzene monomer, and TBS-Azo-N ₃ .

Figure 2 is the H NMR spectrum, SEC elution curve and MALDI-TOF MS diagram of conjugated monodisperse polymers containing fluorene and azobenzene in the main chain of different sequences, using THF as the mobile phase.

Figure 3 is the TGA and DSC curves of conjugated monodisperse polymers containing fluorene and azobenzene in the main chain of different sequences.

Figure 4 is the change of SEC elution curves of conjugated monodisperse polymers containing fluorene and azobenzene in the main chain of different sequences before and after irradiation, with THF as the mobile phase, before 365 nm light irradiation (black), and after 365 nm light irradiation (red) , after irradiation with 435 nm light (blue), the light intensity is 0.5 mW/cm ² .

Figure 5 is the UV/Vis absorption spectrum and fluorescence emission spectrum of conjugated monodisperse polymers containing fluorene and azobenzene in the main chain of different sequences in chloroform solution (a/c) and film (b/d), e It is the enlargement of c; the concentration is 2.0×10 ^-2 mg/mL.

Figure 6 is a histogram of fluorescence quantum yields of oligomers with different sequences (4F-Azo, F-Azo-3F and 2F-Azo-2F) before and after 365 nm UV irradiation in chloroform. The excitation wavelength is 320 nm.

Figure 7 shows different sequences of oligomers 4F-Azo (a, b), F-Azo-3F (c, d) and 2F-Azo-2F (e, f) in chloroform at different times under light conditions UV-Vis absorption spectrum. (a, c, e) 365 nm ultraviolet light irradiation, (b, d, f) 435 nm visible light irradiation, the concentration of all solutions is 2.0×10 ^-2 mg/mL.

Figure 8 is the UV-Vis absorption spectra of 4F in chloroform under (a) 365 nm UV light or (b) 435 nm visible light irradiation for different times, and the concentration of all solutions is 2.0×10 ^-2 mg/ mL.

Figure 9 shows the different sequence oligomers (a) 4F-Azo, (b) F-Azo-3F, (c) 2F-Azo-2F and (d) 4F before and after 365 nm UV irradiation in the thin film state UV-Vis absorption spectra.

Fig. 10 is a graph showing the first-order kinetics of photoisomerization of oligomers of different sequences (4F-Azo, F-Azo-3F and 2F-Azo-2F) in chloroform.

Figure 11 shows oligomers of different sequences 4F-Azo (a, b), F-Azo-3F (c, d), 2F-Azo-2F (e, f) and 4F (g, h) in chloroform ) Fluorescence emission spectra at different times under 365 nm ultraviolet light irradiation. (a, c, e, g) normalized by the absorbance intensity at 470 nm, (b, d, f, h) normalized by the absorbance intensity at 370 nm. The concentration of all solutions was 2.0×10 ^-2 mg/mL, and the excitation wavelength was 320 nm.

Figure 12 is the fluorescence emission spectra of different sequence oligomers (4F-Azo, F-Azo-3F and 2F-Azo-2F) in chloroform before (a) irradiation and (b) after irradiation with 365 nm ultraviolet light Comparison chart. The excitation wavelength is 320 nm.

Embodiments of the present invention

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

Proton nuclear magnetic resonance spectrum ( ¹ H NMR) was measured by Bruker 300 MHz nuclear magnetic resonance instrument at room temperature, with tetramethylsilane (TMS) as internal standard and DMSO- d ₆ as solvent.

The number average molecular weight ( M _n ) and molecular weight distribution index ( Đ = M _w / M _n ) of the polymer were measured by a TOSOH HLC-8320 size exclusion chromatography (SEC) using a differential refraction detector and a UV detector. The range of molecular weight measured by the instrument is 500～2×10 ⁵ g/mol. Tetrahydrofuran was used as the mobile phase at a temperature of 40 ^o C, and the flow rate was 0.35 mL/min for testing. Data acquisition was performed using EcoSEC software, and the number-average molecular weight of the polymer was calibrated using narrow molecular weight distribution polystyrene (PS) as a standard.

Trans-2-[3- (4-tert-butylphenyl-2-methyl-2-propenylidene] malononitrile (DCTB, Aldrich, > 98 %) as matrix at a concentration of 20 mg/mL (CHCl ₃ ). The sample concentration was 10 mg/mL. PMMA with a molecular weight of 2,000 and 4,000 Da was used as the standard sample for calibration before testing.

Fourier transform infrared (FT-IR) spectra were measured using KBr pellets at room temperature on a Bruker TENSOR-27 FT-IR spectrometer (Saarbrücken, Germany).

Example 1: Synthesis of azobenzene donor.

1. Synthesis of azobenzene intermediate (1): Dissolve potassium monopersulfate compound salt (983.60 mg, 1.60 mmol) in water and add K ₂ CO3 (331.20 mg, 2.40 mmol); then add 4-aminoacetyl Aniline (120.10 mg, 0.80 mmol), gray-green foam and precipitate appeared, when the foam completely turned into precipitate, continue to stir for 10 min, filter the reaction solution and collect the precipitate, then dissolve the precipitate in hot ethanol, and then filter with suction Impurities were removed, the filtrate was rotary evaporated, and vacuum-dried at 35 ^o C to obtain 990.00 mg of the target product; the reaction scheme was as follows:

.

2. Synthesis of azobenzene intermediate (2), i.e. azobenzene with iodine at one end and acetamido at the other end: Mix and dissolve intermediate (1) (200.00 mg, 1.22 mmol) and glacial acetic acid (10 mL) uniformly , add 4-iodoaniline (133.50 mg, 0.61 mmol) and stir regularly. After the completion of the reaction monitored by TLC, the reaction solution is suction-filtered to obtain a cake-like solid, which is extracted in dichloromethane, dried, concentrated by rotary evaporation, and column chromatography (methanol :dichloromethane=1:200) to purify and spin dry to obtain 180.10 mg of the target product; the reaction schematic is as follows:

.

3. Synthesis of azobenzene intermediate (3), namely azobenzene with an alkynyl group protected by TBS at one end and acetamido at the other end: under argon atmosphere, intermediate (2) (110.00 mg, 0.27 mmol) Dissolve in 9 mL of a mixed solvent of tetrahydrofuran and diisopropylamine (5:4). Then PdCl ₂ (pph ₃ ) ₂ (12.29 mg, 0.011 mmol), CuI (4.04 mg, 0.021 mmol), TBS-protected alkynyl (89.00 mg, 0.64 mmol) were added sequentially, and stirred at 40 ^o C for 12 h. After the completion of the reaction monitored by TLC, extraction was carried out in dichloromethane, dried, concentrated by rotary evaporation, purified by column chromatography (petroleum ether: ethyl acetate = 1:1), and 104.57 mg of the target product was obtained after spin-drying; the reaction scheme is as follows:

.

4. Synthesis of azobenzene donor, that is, azobenzene with TBS-protected alkynyl at one end and amino group at the other end: Dissolve intermediate (3) (140.00 mg, 0.37 mmol) in 6 mL of methanol and THF (1: 1) into the mixed solvent, then add 1.33 mL HCl (3N), stir at 80 ^o C for 9 h, add NaOH (3N), saturated NaHCO ₃ aqueous solution to adjust the pH to neutral, a yellow precipitate appears, collect by suction filtration, column layer Purified by analysis (dichloromethane), spin-dried to obtain 103.25 mg of the target product TBS-Azo-NH ₂ (compound 4); the reaction scheme is as follows:

.

The obtained azobenzene monomer was characterized by hydrogen nuclear magnetic resonance spectrum, and its spectrum is shown in Figure 1a, indicating that the purity of the monomer is relatively high.

Example 2: Synthesis of fluorene donor: 1. Synthesis of fluorene intermediate (1), fluorene with bromine at one end and nitro at the other end: nitric acid (10 mL) and 1,2-dichloroethane (80 mL) was mixed and stirred for 10 min, then 2-bromofluorene (10.00 g, 41.15 mmol) was added and stirred for 1 h. After the reaction was monitored by TLC, ice methanol settled, and the precipitate was collected by suction filtration and dried to obtain 10.61 g of the target product; the reaction schematic as follows:

.

2. Synthesis of fluorene intermediate (2), namely 9,9-dioctylfluorene with bromine at one end and nitro at the other end: Mix KOH (10.00 g, 178.50 mmol) and DMSO (50 mL) uniformly for 10 min. Then intermediate (1) (5.00 g, 17.30 mmol) was added and stirring was continued for 20 min. Then 1-bromooctane (6.64 mL, 37.80 mmol) was added and stirred for 12 h. After the completion of the reaction monitored by TLC, extraction was performed in dichloromethane, dried, concentrated by rotary evaporation, purified by column chromatography (petroleum ether: ethyl acetate = 64:1), and 8.16 g of the target product was obtained after spin-drying; the reaction diagram is as follows:

.

3. Synthesis of fluorene intermediate (3), namely 9,9-dioctylfluorene with TBS-protected alkynyl at one end and nitro at the other end: Intermediate (2) (256.50 mg, 0.50 mmol) was dissolved in 10 mL of a mixed solvent of triethylamine and anhydrous toluene (1:1). Then PdCl ₂ (pph ₃ ) ₂ (14.10 mg, 0.02 mmol), CuI (7.60 mg, 0.04 mmol), TBS-protected alkynyl (168.00 mg, 1.20 mmol) were added sequentially, and stirred at 80 ^o C for 12 h. After the completion of the reaction monitored by TLC, it was extracted in dichloromethane, dried, concentrated by rotary evaporation, purified by column chromatography (petroleum ether: ethyl acetate = 32:1), and 202.00 mg of the target product was obtained after spin-drying. ; The reaction is as follows:

.

4. Synthesis of fluorene donor, which is an alkynyl group protected by TBS at one end and 9,9-dioctylfluorene at the other end: Dissolve ammonium chloride (280.08 mg, 5.24 mmol) in water, add iron powder (68.41 mg, 1.22 mmol) was activated at 105 ^o C for 1 h, and then cooled to 75 ^o C. Then intermediate (3) (200.00 mg, 0.35 mmol) dissolved in absolute ethanol was added to react for 12 h. After the completion of the reaction monitored by TLC, a layer of diatomaceous earth was spread for suction filtration, and the filtrate was extracted with dichloromethane, dried, concentrated by rotary evaporation, and purified by column chromatography (petroleum ether: ethyl acetate = 32:1) , and spin-dried to obtain 80.00 mg of the target product TBS-F-NH ₂ ; the reaction scheme is as follows:

.

The obtained fluorene monomer was characterized by hydrogen nuclear magnetic resonance spectrum, and its spectrum is shown in Figure 1b, indicating that the purity of the monomer is high.

Example 3: Synthesis of fluorene with different algebras: 1. Synthesis of 9,9-dioctylfluorene with TBS-protected alkynyl at one end and azide at the other end of fluorene intermediate (5): diazonium reaction: fluorene The donor TBS-F-NH ₂ (216.00 mg, 0.40 mmol) was dissolved in 5 mL of ethyl acetate, then added dropwise to aqueous hydrochloric acid (0.15 mL, 1.51 mmol), aqueous NaNO ₂ (32.94 mg, 0.48 mmol), and placed in an ice-water bath After conventional stirring for 1 h, urea was added to react with excess NaNO ₂ to obtain a diazo solution; azide reaction: NaN ₃ (51.74 mg, 0.80 mmol) aqueous solution was added dropwise to the above diazo solution; conventional stirring was performed under an ice-water bath 1 h, after the reaction was completed, the reaction solution was poured into water, extracted with ethyl acetate, dried, concentrated by rotary evaporation, purified by column chromatography (petroleum ether:dichloromethane=8:1), and 199.18 mg of the target product was obtained after spin-dried ; The reaction is as follows:

.

2. Synthesis of fluorene intermediate (6), 9,9-dioctylfluorene with an alkynyl group at one end and an amino group at the other end: Dissolve the fluorene donor (1.00 g, 1.84 mmol) in 30 mL tetrahydrofuran, add tetrahydrofuran A solution of butylammonium fluoride in tetrahydrofuran (1.08 mL, 3.68 mmol) was stirred at room temperature for 0.5 h. After the reaction was monitored by TLC, tetrahydrofuran was removed by rotary evaporation, extracted with ethyl acetate, dried, and concentrated by rotary evaporation to obtain 726.21 mg of the target product alkyne-F-NH ₂ . The reaction scheme is as follows:

.

3. Synthesis of second-generation fluorene: add fluorene intermediate (5) (329.00 mg, 0.58 mmol) and fluorene intermediate (6) (340.00 mg, 0.97 mmol), then add PMDET (137.25 mg, 0.79 mmol) and CuBr (82.91 mg, 0.58 mmol) respectively, pump three times to deoxygenate and seal the tube, react at room temperature for 48 h, remove THF by rotary evaporation, and extract with ethyl acetate , dried, concentrated by rotary evaporation, purified by column chromatography (petroleum ether: ethyl acetate = 4:1), and spin-dried to obtain 518.20 mg of the target product TBS-2F-NH ₂ (2F). The reaction is as follows:

.

According to the method in step 1, TBS-2F-N ₃ can be obtained. According to the method in step 2, alkyne-2F-NH ₂ can be obtained.

4. Synthesis of third-generation and fourth-generation fluorene: the synthesis steps of third-generation and fourth-generation fluorene are the same as those of second-generation fluorene, and TBS-2F-N ₃ and alkyne-F-NH ₂ are clicked to synthesize TBS-3F-NH ₂ (3F) , TBS-2F-N ₃ and alkyne-2F-NH ₂ were subjected to a click reaction to synthesize TBS-4F-NH ₂ (4F).

.

.

According to the method in step 1, TBS-3F-N ₃ can be obtained.

Example 4: Synthesis of conjugated monodisperse polymers containing fluorene and azobenzene in main chains of different sequences: 1. Synthesis of 4F-Azo with azobenzene at the end group:

.

First, use sodium azide to carry out azidation of the azobenzene donor, replace the TBS-F-NH ₂ in Step 1 of Example 3 with TBS-Azo-NH ₂ , and change the rest to heavy Nitrogen salt, followed by an azide reaction using sodium azide, post-treatment to obtain a dark yellow solid with a yield of 91.0%, which is TBS-Azo-N ₃ , and the amino group is converted to an azide group; see Figure 1. According to the method of step 2 of Example 3, the tetrabutylammonium fluoride tetrahydrofuran solution was used to remove the tetra-generation fluorene by TBS to obtain a dark brown solid alkyne-4F-NH ₂ with a yield of 94.0%; then the azide The product TBS-Azo-N ₃ (60.00 mg, 0.16 mmol) and the product alkyne-4F-NH ₂ (447.58 mg, 0.25 mmol) after removal of TBS were dissolved in anhydrous and oxygen-free THF and added to a 50 mL Schlenk tube, Then PMDETA (pentamethyldiethylenetriamine, 43.32 mg, 0.25 mmol) and CuBr (23.80 mg, 0.16 mmol) were added, pumped three times to deoxygenate and seal the tube, reacted at room temperature for 48 h, and rotated to remove tetrahydrofuran and acetic acid Ethyl was extracted, dried, concentrated by rotary evaporation, purified by column chromatography (petroleum ether: ethyl acetate = 3:1), and spin-dried to obtain 306.58 mg of the target product with a yield of 85.3%. ¹ H NMR (300 MHz, CDCl ₃ ) δ 8.10 (dd, J = 29.1, 10.1 Hz, 4H), 7.92 (d, J = 8.8 Hz, 2H), 7.85-7.52 (m, 24H), 7.39 (dt, J = 21.0, 7.8 Hz, 4H), 6.78-6.54 (m, 2H), 2.05-1.67 (m, 19H), 1.18-0.71 (m, 105H), 0.70-0.32 (m, 48H), -0.00 (s , 6H).

2. Synthesis of F-Azo-3F and 2F-Azo-2F with azobenzene in the middle and core position:

.

The synthesis method of F-Azo-3F is the same as that of 4F-Azo. First synthesize TBS-Azo-F-NH ₂ and then deprotect it with TBS, react with TBS-3F-N ₃ to obtain F-Azo-3F. TBS-Azo-F-NH ₂ was synthesized using TBS-Azo-N ₃ and alkyne-F-NH ₂ . To a 25 mL Schlenk tube, first add TBS-Azo-N ₃ (108.00 mg, 0.30 mmol) and alkyne-F-NH ₂ (152.70 mg, 0.36 mmol) dissolved in 10 mL of anhydrous and oxygen-free THF, then Add PMDETA (77.81 mg, 0.45 mmol) and CuBr (42.89 mg, 0.30 mmol), pump argon three times to remove oxygen and seal the tube, react at room temperature for 48 h, column chromatography (silica gel, eluent: V _PE / V _EA = 8/1), concentrated and dried by rotary evaporation to obtain the product TBS-Azo-F-NH ₂ . Next, the TBS-Azo-F-NH ₂ (270.00 mg, 0.34 mmol) product was dissolved in 30 mL of tetrahydrofuran, and TBAF (0.89 mL, 3.42 mmol) was added thereto, and stirred at room temperature for 0.5 h. After the reaction was completed, the post-treatment was dried to obtain alkyne-Azo-F-NH ₂ . Next, add TBS-3F-N ₃ (250.00 mg, 0.17 mmol) and alkyne-Azo-F-NH ₂ (170.00 mg, 0.25 mmol) dissolved in 30 mL of anhydrous anaerobic THF to a 50 mL Schlenk tube. ), then add PMDETA (43.84 mg, 0.25 mmol) and CuBr (24.24 mg, 0.17 mmol), pump argon three times to remove oxygen and seal the tube, react at room temperature for 48 h, remove THF by rotary evaporation, use ethyl acetate The ester was extracted, washed three times with saturated brine, the organic phase was collected and dried, and purified by column chromatography (silica gel, eluent: V _PE / V _EA = 4/1). The product was concentrated by rotary evaporation and dried in vacuo to obtain an orange-red solid (281.90 mg) with a yield of 77.4%. ¹ H NMR (300 MHz, CDCl ₃ ) δ 8.36 (dd, J = 14.1, 7.9 Hz, 4H), 8.21-7.72 (m, 24H), 7.71-7.40 (m, 5H), 7.03-6.72 (m, 3H ), 2.32-1.89 (m, 17H), 1.38-0.92 (m, 88H), 0.94-0.46 (m, 37H), 0.24 (d, J = 3.2 Hz, 5H).

The synthesis method of 2F-Azo-2F is the same as that of F-Azo-3F. First synthesize TBS-Azo-2F-NH ₂ and then deprotect it with TBS, react with TBS-2F-N ₃ to obtain 2F-Azo-2F. TBS-Azo-2F-NH ₂ was synthesized using TBS-Azo-N ₃ and alkyne-2F-NH ₂ . To a 25 mL Schlenk tube, first add TBS-Azo-N ₃ (100.00 mg, 0.28 mmol) and alkyne-2F-NH ₂ (306.09 mg, 0.35 mmol) dissolved in 10 mL of anhydrous and oxygen-free THF, then Add PMDETA (59.96 mg, 0.35 mmol) and CuBr (39.74 mg, 0.28 mmol), pump argon three times to remove oxygen and seal the tube, react at room temperature for 48 h, and perform column chromatography (silica gel, eluent: V _PE / V _EA = 8/1), concentrated and dried by rotary evaporation to obtain the product TBS-Azo-2F-NH ₂ ; then the product TBS-Azo-2F-NH ₂ (155.00 mg, 0.12 mmol) was dissolved in 30 mL tetrahydrofuran, and TBAF (0.16 mL, 0.62 mmol) was added thereto, and stirred at room temperature for 0.5 h. After the reaction was monitored by TLC, the reaction was dried to obtain alkyne-Azo-2F-NH ₂ . Next, add TBS-2F-N ₃ (90.55 mg, 0.09 mmol)) and alkyne-Azo-2F-NH ₂ (150.00 mg, 0.13 mmol), add PMDETA (23.05 mg, 0.13 mmol) and CuBr (12.77 mg, 0.09 mmol), pump three times with argon to seal the tube for deoxygenation, react at room temperature for 48 h, remove THF by rotary evaporation, use acetic acid ethyl ester, washed three times with saturated brine, collected organic phase and dried, and purified by column chromatography (silica gel, eluent: V _PE / V _EA = 4/1). The product was concentrated by rotary evaporation and dried in vacuo to obtain an orange-red solid (190.5 mg) with a yield of 78.3%. ¹ H NMR (300 MHz, CDCl ₃ ) δ 8.47-8.24 (m, 4H), 8.22-7.99 (m, 9H), 8.23-7.98 (m, 9H), 7.99-7.74 (m, 14H), 7.99-7.74 (m, 13H), 7.73-7.44 (m, 5H), 7.03-6.69 (m, 2H), 2.14 (t, J = 34.6 Hz, 16H), 1.40-0.94 (m, 87H), 0.93-0.54 (m , 41H), 0.27 (d, J = 20.1 Hz, 6H).

The resulting conjugated monodisperse polymers containing fluorene and azobenzene in the main chain of different sequences were characterized by H NMR spectroscopy, SEC elution curve and MALDI-TOF MS diagram, as shown in Figure 2.

As mentioned above, there are few reports on polymers containing both azobenzene and fluorene in the main chain and their properties. However, these reports did not pay attention to the effect of sequence on polymers. The synthesis and research of the conjugated monodisperse polymers containing fluorene and azobenzene in the main chain of different sequences in the present invention enrich and expand the research on the main chain containing fluorene and azobenzene, and promote the development of the field of azobenzene materials. At the same time, the precise sequence structure provides an opportunity for the study of the precise relationship between structure and performance.

Example 5: The ultraviolet-visible (UV-vis) absorption spectrum was measured at room temperature using a Shimadzu UV-2600 spectrophotometer. The oligomer was dissolved in chloroform (CHCl ₃ ) to form a solution with a concentration of 0.02 mg/mL or a solution with a concentration of 1 mg/mL, and was spin-coated on a quartz plate to form a film. The light source for the photoresponse test is a diode-pumped solid-state laser (DPSSL), the model is LSR532NL-500, the wavelengths are 365 nm and 435 nm, and the intensity is 0.5 mW/cm ² .

Fluorescence emission spectra were measured at room temperature with a HITACHI F-4600 fluorescence spectrophotometer. The oligomer was dissolved in chloroform (CHCl ₃ ) to make a sample solution with a concentration of 0.02 mg/mL or a solution of 1 mg/mL to spin-coat on a quartz plate to form a film.

The thermogravimetric analysis was carried out using SDT2960 thermogravimetric analyzer, under continuous nitrogen purging ( ^{100 mL} /min), the thermal degradation temperature ( T _d , mass loss 5 % corresponding to the temperature) test, the mass of the test sample is about 5.00 mg. Using DSC2010 under continuous nitrogen purging (100 mL/min) to test the glass transition temperature ( T _g ) in the range of 20-140 ^o C with a heating/cooling rate of 10 ^o C/min to test the quality of the sample At about 5.00 mg, a second-order transition occurred at the maximum of the endothermic peak of the second heating curve.

Wide-angle X-ray diffraction (WXRD) was performed on a Philips X'Pert-Pro MPD diffractometer. The rays are Cu-K α rays with a wavelength of 0.154 nm. The sample is ground into powder and placed on a standard single crystal silicon carrier, and the measurement angle range is 2θ = ^5o - ^90o .

Theoretical calculations use the GAUSSIAN 2009 software package, and the molecular geometry is optimized using the DFT method of B3LYP and 6-31+G(d,p). The half-peak width of the calculated ultraviolet absorption spectrum is 0.333 eV. Study on the ultraviolet fluorescence properties of different sequences of fluorene-azobenzene oligomers: the different sequences of fluorene-azobenzene oligomers were prepared into chloroform solution with a concentration of 2.0×10 ^-2 mg/mL or a concentration of 1.0 mg/mL mL of chloroform solution was dropped on a quartz plate and spin-coated to form a film (rotational speed: 1000 r/min; acceleration: 100 m/s ² ) and dried at room temperature for UV-Vis absorption and fluorescence emission spectroscopy tests.

Measurement of fluorescence quantum yields of different sequences of fluorene-azobenzene oligomers: Accurately prepare different sequences of fluorene-azobenzene oligomers into chloroform solutions with a concentration of 2.0×10 ^-2 mg/mL, diphenyl Anthracene was used as the standard substance, and the UV absorption value and the integrated value of the fluorescent emission peak area of the oligomer and the standard substance were measured at an excitation wavelength of 320 nm. According to the calculation formula of quantum yield: Φ/Φ _s =FA _s /F _s A to calculate the fluorescence quantum yield of different sequences of fluorene-azobenzene oligomers.

Study on photoisomerization properties of different sequences of fluorene-azobenzene oligomers: accurate preparation of different sequences of fluorene-azobenzene oligomers into chloroform solutions with a concentration of 2.0×10 ^-2 mg/mL or Chloroform solution with a concentration of 1.0 mg/mL was dropped on a quartz plate and spin-coated to form a film, and different sequences of oligomers were irradiated with ultraviolet light with a wavelength of 365 nm and visible light with a wavelength of 435 nm, and their UV- Visible absorption spectrum and fluorescence emission spectrum, until the spectrum does not change, that is, the isomerization of azobenzene reaches an equilibrium state.

As shown in Figure 3, TGA and DSC were used to test the thermal decomposition temperature ( T _d , the temperature corresponding to 5% mass loss) and the glass transition temperature ( T _g ) of the obtained polymers with different sequences. The introduction of azophenyl groups into the main chain of the conjugated polymer decreased T _d and increased T _g . Compared with the other two polymers, 4F-Azo with azobenzene at the end of the chain has a lower T _d and a higher T _g because of the azobenzene at the end group. This fully shows that the sequence of polymer chains has a significant impact on the thermal properties of polymers.

As shown in Figure 4, for the obtained polymers of different sequences, the changes of the SEC elution curves before and after ultraviolet/visible light were tested, and THF was used as the mobile phase. Before 365 nm light irradiation (black), after 365 nm light irradiation (red), after 435 nm light irradiation (blue), the light intensity is 0.5 mW/cm ² becomes smaller, and the outflow time becomes longer. On the contrary, under visible light, the efflux time becomes shorter, and the change of SEC efflux time of 4F-Azo before and after light is the smallest. The results show that different positions of azobenzene in the main chain have different effects on the size change before and after photoisomerization.

As shown in Figure 5, for the obtained polymers with different sequences, the UV-visible absorption spectrum and fluorescence emission spectrum were tested. It can be found that in solution or film, compared with fluorenyl polymers, the maximum absorption wavelength of 4F-Azo occurs Red-shifted, while the maximum absorption wavelengths of F-Azo-3F and 2F-Azo-2F were blue-shifted, indicating that different positions of azobenzene in the main chain have an impact on the conjugation of the polymer chain. And due to the quenching effect of the azobenzene group, different sequences of fluorene-azobenzene oligomers showed different degrees of weak fluorescence emission in solution, and 4F-Azo showed slightly stronger fluorescence emission than the other two oligomers. Fluorescent emission, no fluorescence was observed in the film.

In order to further quantitatively study the differences in the fluorescence properties of three different sequences (azobenzene in different positions) conjugated fluorene-azobenzene oligomers, the three oligomers were accurately prepared into a concentration of 2.0×10 ^-2 mg/mL Chloroform solution, using diphenylanthracene as a standard sample to calculate the fluorescence quantum yield. Calculate the quantum yield (Φ) according to the following formula: Φ/Φ _s =FA _s /F _s A, where Φ is the fluorescence quantum efficiency, F is the integral value of the fluorescence emission peak area, and A is the corresponding ultraviolet light at the excitation wavelength The absorbance value, the subscript s represents the standard solution. The specific calculation results are shown in Figure 6 (the fluorescence quantum yield histogram before and after 365 nm UV irradiation. The excitation wavelength is 320 nm). Before and after UV irradiation, the fluorescence quantum yield (Φ) of 4F-Azo is higher than that of F-Azo -3F and 2F-Azo-2F are larger, indicating that compared with azobenzene located in the middle of the main chain, the fluorescence quenching effect of the alignment polymer is smaller when it is located at the end.

Table 1 Summary of thermal and optical data of different sequences of conjugated fluorene-azobenzene oligomers.

.

^a adopts the glass transition temperature measured by DSC; ^b adopts the thermal decomposition temperature measured by TGA (the corresponding temperature when the mass loss is 5%) ^; Absorption wavelength; ^d k _e : photoisomerization rate constant of azobenzene trans configuration to cis configuration under 365 nm light (light intensity 0.5 mW cm ^-2 ); ^e k _H : 435 nm light (Light intensity 0.5 mW cm ^-2 ) Photoisomerization rate constants of azobenzene cis configuration to trans configuration under irradiation.

In order to investigate the dependence of the sequence on the photoisomerization properties of fluorene-azobenzene oligomers, the chloroform solutions and films of different sequences (different positions of azobenzene) conjugated fluorene-azobenzene oligomers in chloroform were studied. Photoisomerization behavior under 365 nm ultraviolet light and 435 nm visible light irradiation. In the solution state, the UV-Vis absorption spectra of three different sequence oligomers during UV/Visible light irradiation, as shown in Figure 7, under the condition of 365 nm UV light irradiation, the configuration of azobenzene From trans to cis, the absorbance value corresponding to the π→π* transition at around 375 nm gradually decreases, while the absorbance value corresponding to the n→π* transition at 475 nm gradually increases, and when reaching the equilibrium state, the absorbance value remains constant. Then, the three oligomer solutions that reached the equilibrium state after UV irradiation were irradiated with 435 nm visible light, and the absorbance values at 375 nm were gradually increased, and the absorbance values at 475 nm were slightly recovered. Prolonged, the absorption intensity no longer changes, indicating that the cis-trans isomerization has reached an equilibrium state, but cannot return to the initial position, because the rigid conjugated skeleton of the fluorene-azobenzene oligomer weakens the photoisomerization efficiency, As a result, the cis-to-trans configuration of azobenzene cannot be completely converted. Careful study found that under the irradiation of 365 nm ultraviolet light, unlike F-Azo-3F and 2F-Azo-2F, 4F-Azo also had a significant decrease near 350 nm and a significant increase at 450 nm. As shown in Figure 8, under the same UV irradiation conditions, the absorbance of 4F also decreased significantly at around 350 nm, and increased significantly at around 450 nm, showing the same trend as 4F-Azo. Prolonged, the absorption spectrum did not recover, it was found that 4F-Azo has more effective energy transfer due to the influence of the azophenyl group at the end, compared with the other two oligomers, under ultraviolet light irradiation It is more likely that the photooxidation behavior of fluorene similar to 4F will occur. Then, the chloroform solution of the three sequence oligomers was dropped on the quartz plate to form a film by spin coating and then dried naturally to study the difference in the photoisomerization behavior of different sequence oligomers in the film state, as shown in Figure 9. Taking 4F as a comparison, when 4F-Azo, F-Azo-3F and 2F-Azo-2F in the thin film state were irradiated with ultraviolet light, the absorption intensities of the three oligomers did not change significantly (Figure 9a, b, c ), however, the absorption intensity of 4F showed obvious decreases and increases around 350 nm and 450 nm (Fig. 9d). The experimental results show that under ultraviolet light, the fluorene-azobenzene oligomer film has better spectral stability than polyfluorene. Based on the absorbance values of UV-Vis absorption spectra at different time intervals at 375 nm and 475 nm corresponding to the photoisomerization of different sequences of fluorene-azobenzene oligomers in Figure 7, according to formulas 2.1 and 2.2, the three The first-order kinetic curves ( k _e , k _H ) of the trans-to-cis configuration and cis-to-trans configuration photoisomerization of different sequences of fluorene-azobenzene oligomers are shown in Figure 10, And the data are summarized in Table 2.

The first-order rate constant k _e for the trans-to-cis configurational isomerization of azobenzene was calculated according to Equation 2.1:

.

where A _∞ , A _t and A ₀ are the π→π* transition characteristic absorption peaks corresponding to trans-azobenzene at 375 Absorbance value at nm. k _e is the rate constant for the trans-to-cis configurational isomerization of azobenzene.

The first-order rate constant k _H for the cis-to-trans configurational isomerization of azobenzene was calculated according to Equation 2.2:

.

where A _∞ , A _t and A ₀ are the n→π* transition characteristic absorption peak corresponding to cis-azobenzene when the system reaches the equilibrium state, different time points t and initial state under the irradiation of visible light at 435 nm at 475 nm absorbance value at . k _H is the rate constant for the cis to trans configurational isomerization of azobenzene.

From Figure 10a, it can be found that the photoisomerization kinetic curve of 4F-Azo deviates from the first-order linear relationship, and the k _{e value} of F-Azo-3F is slightly larger than that of 2F-Azo-2F, indicating that azo in different positions The difference in steric hindrance caused by benzene makes the photoisomerization process of F-Azo-3F faster than that of 2F-Azo-2F. In addition, using the DFT method to analyze the HOMO/LUMO energy level gap difference of three different sequences of conjugated fluorene-azobenzene oligomers, the trans and cis configurations are the most stable corresponding energy and the transition from trans to cis The enthalpy required for the transformation of the formula configuration was theoretically calculated, and the data are summarized in Table 2. Among the three oligomers with different sequences, the enthalpy change required for the isomerization of F-Azo-3F is the smallest (△ H _f = 12.586 Kcal/mol), indicating that the main chain azobenzene changes from trans to cis configuration The least energy required in the process is easier to undergo isomerization configuration transformation than the other two oligomers. Moreover, the configuration corresponding to the lowest trans energy of 2F-Azo-2F is the most stable, and the configuration corresponding to the highest cis energy is the most unstable, which makes its photoisomerization difficult. Theoretical calculations are consistent with the experimental results.

Table 2 Calculation parameters of different sequences of fluorene-azobenzene oligomers.

.

^a △ E ₀ represents the relative energy difference between the oligomer energy and the absolute energy corrected by the 0-point energy; ^b △ H _f represents the enthalpy change from trans to cis configuration, where 1 au= 627.5 Kcal/mol . This theoretical calculation was optimized using the DFT method and calculated using the GAUSSIAN 2009 software package.

In the prior art, there are different explanation mechanisms for the fluorescence enhancement of azobenzene and its derivatives. The present invention compares the chloroform (CHCl ₃ ) solution and film under the irradiation of 365 nm ultraviolet light, the difference in photoluminescence (PL) spectrum, and the fluorescence emission of 4F was also tested under the same conditions for comparison, as shown in Figure 11. From the change diagram of the fluorescence emission spectrum (Fig. 11g, h) of 4F under ultraviolet light irradiation, it can be seen that in chloroform solution, the emission intensity of 4F around 360 nm and 380 nm gradually decreases, and the emission intensity around 500 nm increases slowly The equilibrium saturation state was reached after 120 min of irradiation. 4F-Azo showed a more pronounced change in fluorescence than the other two oligomers. The fluorescence of 4F-Azo around 475 nm was significantly enhanced with the continuous extension of UV light irradiation time (Figure 11b and Figure 12b).

The above results fully show that the sequence of the polymer chain has a significant impact on its properties.

Claims (10)

1. A single molecular weight conjugated fluorene-azobenzene precise sequence oligomer, its structure is one of the following structural formulas:

   

   .
2. A fluorene monomer having the following chemical structural formula:

   

   Wherein, n is 0-3, and TBS is tert-butyldimethylsilane.
3. A kind of azobenzene monomer, has following chemical structure formula:

   

   Wherein, TBS is tert-butyldimethylsilane.
4. The application of the fluorene monomer described in claim 2 and the azobenzene monomer described in claim 3 in the preparation of the single molecular weight conjugated fluorene-azobenzene precise sequence oligomer described in claim 1.
5. The preparation method of the single molecular weight conjugated fluorene-azobenzene precise sequence oligomer described in claim 1 is characterized in that, after the diazotization reaction of the azobenzene monomer, an azide reaction is carried out to obtain TBS-Azo-N ₃ ; After the deprotection of the fluorene monomer, the click chemical reaction with TBS-Azo-N ₃ was performed to obtain a single molecular weight conjugated fluorene-azobenzene oligomer with precise sequence.
6. According to the preparation method of the described single molecular weight conjugated fluorene-azobenzene precise sequence oligomer of claim 5, it is characterized in that, when single molecular weight conjugated fluorene-azobenzene precise sequence oligomer is 4F-Azo, will After the deprotection of the fourth-generation fluorene, click chemical reaction with TBS-Azo-N ₃ to obtain 4F-Azo; After deprotection, perform a click chemical reaction with TBS-Azo-N ₃ to obtain TBS-Azo-2F-NH ₂ and then deprotect it with TBS, and react with TBS-2F-N ₃ to obtain 2F-Azo-2F; when a single molecular weight When the precise sequence oligomer of conjugated fluorene-azobenzene is F-Azo-3F, deprotect the first-generation fluorene and perform click chemical reaction with TBS-Azo-N ₃ to obtain TBS-Azo-F-NH ₂ Carry out TBS deprotection, react with TBS-3F-N ₃ to obtain F-Azo-3F.
7. According to the preparation method of the single molecular weight conjugated fluorene-azobenzene precise sequence oligomer according to claim 6, it is characterized in that the azide reaction is carried out after the fluorene monomer is diazotized to obtain TBS-FN ₃ , TBS-2F -N ₃ , TBS-4F-N ₃ or TBS-3F-N ₃ .
8. According to the preparation method of single molecular weight conjugated fluorene-azobenzene precise sequence oligomer according to claim 5, it is characterized in that the click chemical reaction is "CuAAC" click reaction, using PMDETA as ligand and CuBr as catalyst.
9. The application of the single molecular weight conjugated fluorene-azobenzene precise sequence oligomer as claimed in claim 1 as a photoisomerization material.
10. The application of the fluorene monomer described in claim 2 and the azobenzene monomer described in claim 3 in the preparation of photoisomerization materials.