D-A type molecule with phthalimide as acceptor, preparation method, evaluation method and use of excited state dynamics

Abstract

The present invention discloses a D-A type molecule with phthalimide as the acceptor, a preparation method, an evaluation method for excited state dynamics and uses thereof. The D-A type molecule with phthalimide as the acceptor is based on phthalimide as the acceptor and carbazole and its derivatives as donors to prepare three compact D-A binary groups. Through structural characterization and related performance analysis and testing of the D-A type molecule with phthalimide as the acceptor, the photoexcited state dynamics of dense electron donor-acceptor compounds is deeply understood, which is of great significance for designing highly efficient heavy-atom-free triplet photosensitizers and developing high-performance organic sensors, dye-sensitized solar cells and other materials. A D-A type molecule with phthalimide as the acceptor, a preparation method and an evaluation method for excited state dynamics disclosed by the present invention provide several D-A type molecules with phthalimide as the acceptor, and study the influence of the electron-donating ability and solvent polarity on the excited state dynamics of the D-A type molecules.

Description

Technical Field

[0001] The present invention relates to the technical field of organic light-emitting materials, and particularly to D-A type molecules with phthalimide as the acceptor, a preparation method, an evaluation method for excited state dynamics, and uses thereof. Background Art

[0002] Donor-acceptor (D-A) type molecules have attracted much attention from researchers due to their photophysical properties of intramolecular charge transfer (ICT). By adjusting the ICT properties by changing the electron-donating / electron-withdrawing ability or connecting a conjugated linker between the donor and acceptor, excellent photophysical properties such as fluorescence quantum yield, fluorescence lifetime, intersystem crossing efficiency, etc. can be obtained, which have important application values in many fields such as organic light-emitting materials, mechanochromic fluorescence materials, probe molecules, photodynamic therapy, etc. The photophysical properties of compounds are always affected by solvents. For example, solvent polarity, viscosity, etc. Solvent effects are divided into two types: general solvent effects and specific solvent effects. General solvent effects are due to the interaction between the dipole of the fluorescent group and its environment, and solvent polarity is the main factor of general solvent effects. Solvent polarity has a significant impact on the excited state dynamics of compounds. A large number of theoretical calculations have studied the excited state dynamics of fluorophores under different conditions. Therefore, chemical structure and the surrounding environment may be the key factors affecting the photophysical properties of compounds.

[0003] Carbazole (Cz) and its derivatives are a relatively common donor of D-A type molecules. The N atom on Cz can undergo ISC of S1(n–π*)→T n (π-π*). Due to advantages such as strong stability, planar configuration, and easy chemical modification, Cz is widely used in D-A molecules and thus has broad development prospects in many fields.

[0004] Phthalimide has advantages such as strong electron-withdrawing ability, easy chemical structure modification, and simple synthesis, and is often used to design twisted D-A type molecules. D-A type compounds obtained by substituting the 3,4-positions of phthalimide with donor units exhibit excellent TADF performance and are widely used in organic light-emitting diodes, time-resolved fluorescence imaging, etc. However, the research on its basic properties lags far behind the application research, which directly limits the possibility of material development. Therefore, it is necessary to conduct a more in-depth study on the excited state evolution channels and their dynamics of these D-A molecules.

[0005] Ultrafast laser spectroscopy is to restore the excited-state process of a sample by measuring the transient changes in the characteristic spectrum of the sample, and it has wide applications in the photophysics research of new materials. Time-resolved spectroscopy refers to the process of exciting a sample with an ultrashort pulsed light whose duration is much shorter than the decay lifetime of the sample to be measured. After a certain time delay, a relatively continuous probe light is used to monitor in real time the change of the instantaneous state of the sample after being photoexcited over time. Various processes occur in a certain time scale after an organic molecule is photoexcited. For example, the fluorescence lifetime of a fluorophore is generally on the order of nanoseconds; the radiative transition of an exciton usually occurs in the time range of picoseconds to nanoseconds; charge transfer, energy transfer, and proton transfer usually occur in the time range of femtoseconds to nanoseconds. These processes occur very fast, and multiple processes may occur on some time scales. Facing such complex and fast competing processes, ordinary detection instruments can hardly measure them, and we need to use time-resolved spectroscopy technology for testing and further analysis. In recent years, the duration, frequency tunability, and stability of ultrashort light pulses have been rapidly developed, and the ultrafast laser technology has reached a very high technical maturity, which can monitor in real time the kinetic processes of transient species on different time scales after a sample is photoexcited. Summary of the Invention

[0006] At present, the factors and mechanisms affecting the photophysical properties of ICT materials are not yet clear, and the research on the influence of different electron-donating and electron-withdrawing abilities within the molecule on compounds is not deep enough, etc. These problems have hindered the development of high-performance fluorescent materials. The present invention provides several D-A type molecules with phthalimide as the acceptor, and studies the influence of the electron-donating ability and solvent polarity on the excited-state dynamics of D-A type molecules.

[0007] To achieve the above first object, the present invention provides the following technical solution: A D-A type molecule with phthalimide as the acceptor, having a structure with the following general formula:

[0008]

[0009] In the formula, R′ is selected from

[0010] R is selected from

[0011] Furthermore, it has a structure of general formula I or II:

[0012]

[0013] In formula I, R is selected from

[0014] In formula II, R is selected from

[0015] To achieve the above object, the present invention provides the following technical solution: a method for preparing a DA-type molecule using phthalimide as an acceptor, wherein a compound having a structure of Formula I is prepared according to the following method, comprising the following steps:

[0016] S1: Dissolve 4-bromophthalic anhydride and 4-(2-aminoethyl)-morpholine in 20-50 parts by weight of ethanol, react at 70°C for 3 hours, cool to room temperature after the reaction, and then mix the reaction solution with water, filter, wash, and dry to obtain a compound of formula S-1;

[0017]

[0018] S2: Add compound S-1 prepared in step S1, compound R, palladium acetate, tri-tert-butylphosphine and sodium tert-butoxide to 100 parts by weight of anhydrous toluene, and reflux at 120°C for 24 hours under inert gas protection. Monitor by TLC. After the reaction is completed, cool to room temperature. The reaction solution is extracted with water and dichloromethane, dried over anhydrous sodium sulfate, and rotary evaporated to remove the solvent. The crude product is purified by column chromatography using petroleum ether and ethyl acetate (v / v = 3:1) as eluent to obtain a compound having the structure of formula I.

[0019] Furthermore, a compound having the structure of Formula II is prepared according to the following method, comprising the following steps:

[0020] S1: 4-bromophthalic anhydride, n-butylamine, and glacial acetic acid were mixed evenly, and refluxed at 140°C for 6 hours. After the reaction was completed, the reaction solution was cooled to room temperature, and then mixed with ice water, filtered, washed, and dried to obtain compound S-2;

[0021]

[0022] S2: Add compound S-2, 3,6-di-tert-butylcarbazole, palladium acetate, tri-tert-butylphosphine and sodium tert-butoxide prepared in step S1 to anhydrous toluene, and reflux at 120° C. for 24 hours under inert gas protection. Monitor by TLC. After the reaction is completed, cool to room temperature. The reaction solution is extracted with water and dichloromethane, dried over anhydrous sodium sulfate, and rotary evaporated to remove the solvent. The crude product is purified by column chromatography using petroleum ether and ethyl acetate (v / v=3:1) as eluent to obtain a compound having the structure of Formula II.

[0023] Further, in step S1, the molar ratio of 4-bromophthalic anhydride to 4-(2-aminoethyl)-morpholine is (10-20):(10-20), and further, the molar ratio of 4-bromophthalic anhydride to 4-(2-aminoethyl)-morpholine is 15:20;

[0024] In step S2, the molar ratio of compound S-1, compound R, palladium acetate, tri-tert-butylphosphine and sodium tert-butoxide is (15-20): (15-20): (0.5-0.9): (1.0-1.5): (15-20), and further, the molar ratio of compound S-1, compound R, palladium acetate, tri-tert-butylphosphine and sodium tert-butoxide is 16:20:0.6:1.2:18.

[0025] Further, in step S1, the molar ratio of 4-bromophthalic anhydride to n-butylamine is (10-20):(10-20); further, the molar ratio of 4-bromophthalic anhydride to n-butylamine is 15:20;

[0026] In step S2, the molar ratio of compound S-1, compound R, palladium acetate, tri-tert-butylphosphine and sodium tert-butoxide is (15-20): (15-20): (0.5-0.9): (1.0-1.5): (15-20);

[0027] Furthermore, the molar ratio of compound S-1, compound R, palladium acetate, tri-tert-butylphosphine and sodium tert-butoxide is 16:20:0.6:1.2:18.

[0028] To achieve the above-mentioned object, the present invention provides the following technical solutions: a method for evaluating the excited-state dynamics of DA-type molecules with phthalimide as an acceptor: (1) structurally characterizing the DA-type molecules with phthalimide as an acceptor to obtain nuclear magnetic resonance hydrogen spectrum, carbon spectrum and high-resolution mass spectrum of the DA-type molecules; (2) then using visible light to excite the DA-type molecules with phthalimide as an acceptor, and judging the excited-state dynamics of the DA-type molecules by measuring the steady-state spectrum, electrochemical properties, fluorescence lifetime, femtosecond transient absorption and nanosecond transient absorption performance of the excited DA-type molecules.

[0029] Furthermore, visible light was used to excite the DA-type molecules with phthalimide as the receptor;

[0030] The UV-visible absorption spectrum was measured using a UV-visible spectrophotometer to analyze the electron-donating ability of the excited state of the molecule. If the absorption peak of the charge transfer state in the spectrum is more red-shifted and the peak shape becomes broader, it proves that the tert-butyl carbazole group has a stronger electron-donating ability.

[0031] Fluorescence spectra are obtained using a fluorescence spectrometer to analyze the charge transfer ability of the excited state of the molecule. If there is solvation in the fluorescence spectrum, it proves that the molecule has charge transfer properties.

[0032] The cyclic voltammogram is obtained using an electrochemical workstation to analyze the change in Gibbs free energy during the molecular electron transfer process. On the one hand, the magnitude of the oxidation potential obtained can further prove the magnitude of the electron-donating ability. On the other hand, if the change in Gibbs free energy (ΔG CS ) calculated from the oxidation-reduction potential is less than 0, it proves that the charge separation of the molecule belongs to a thermodynamically allowed process. If the change in Gibbs free energy (ΔG CS ) is greater than or equal to 0, it proves that the charge separation process of the molecule cannot occur;

[0033] The time-correlated single-photon counting technique is used to analyze the fluorescence lifetime of the molecule. If the fluorescence lifetime obtained in a high-polarity solvent is significantly shorter than that in a low-polarity solvent, it proves that the molecule has charge transfer properties;

[0034] The femtosecond pump-probe technique is used to obtain the femtosecond transient absorption spectrum to analyze the process of excited-state charge separation and recombination of the molecule. If the generation process of cation and anion radicals on the femtosecond or picosecond time scale and the decay process on the nanosecond time scale are detected after the molecule is photoexcited, it proves that this type of molecule can undergo a charge transfer process; After charge transfer, solventization and structural relaxation processes may occur, and the influence of the electron-donating ability and solvent polarity on the charge transfer state can be further verified by the duration of these processes;

[0035] The signals of femtosecond transient absorption often overlap with each other, and the kinetic process is also relatively complex. The femtosecond transient absorption data needs to be processed by zero-point correction and global fitting;

[0036] The nanosecond transient absorption spectrum is obtained using a nanosecond flash photolysis instrument to analyze the triplet lifetime after the molecule is excited. If the molecule has a triplet signal after being photoexcited, it indicates that this type of molecule can undergo intersystem crossing to reach the triplet state after charge transfer, and the specific triplet lifetime can be further measured.

[0037] Furthermore, in the above characterization method, the visible light excitation light source is an excitation light of 355 nm, and the laser energy is about 5 mJ.

[0038] To achieve the above object, the present invention provides the following technical solution: the use of a D-A type molecule with phthalimide as the acceptor, and the use is in photoluminescence, organic sensors, dye-sensitized solar cells, and can also be used as a triplet photosensitizer.

[0039] In summary, the present invention has the following beneficial effects:

[0040] Based on phthalimide as the acceptor and carbazole and its derivatives as the donors, three compact D-A type dyads were prepared in this invention, which have strong charge transfer state properties. Through steady-state spectral tests, it was found that molecules with strong electron-donating ability have stronger electron coupling effects, and their fluorescence spectra are more sensitive to changes in solvent polarity. Electrochemical studies showed that charge separation is thermodynamically allowed. When positive / negative potentials are applied, the absorption bands of the AI radical anion (AI -· ) and the radical cations of CZ and its derivatives (CZ + · / tBuCZ + ·) can be clearly seen. Using femtosecond transient absorption spectroscopy, the processes of charge separation and charge recombination of the compounds were studied. The results showed that, on the one hand, with the increase in solvent polarity, the processes of charge separation, solvation, and structural relaxation are all faster. On the other hand, the processes of charge separation, solvation, and structural relaxation of molecules with weak electron-donating ability are slower. The possible reason is that the electron-donating ability of CZ is weak, the ICT property is weak, and the time to enter the CS state is slower. Nanosecond transient absorption spectroscopy showed that the AI-tBuCZ and L-AI-tBuCZ molecules have long-lived triplets (τ = 1.6 / 1.4 μs) in low-polarity solvents. The formation of triplets depends on the electron-donating ability and solvent polarity, which is the characteristic of SOCT-ISC. These results contribute to a deeper understanding of the photoexcited state dynamics of dense electron donor-acceptor compounds and are of great significance for designing efficient heavy-atom-free triplet photosensitizers and developing high-performance materials such as organic sensors and dye-sensitized solar cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0042] Figure 1 1H NMR spectrum of the D-A type molecule L-AI-CZ with phthalimide as the acceptor, which is disclosed in Example 1 of the present invention;

[0043] Figure 2 13C NMR spectrum of the D-A type molecule L-AI-CZ with phthalimide as the acceptor, which is disclosed in Example 1 of the present invention;

[0044] Figure 3 High-resolution mass spectrum of the D-A type molecule L-AI-CZ with phthalimide as the acceptor, which is disclosed in Example 1 of the present invention;

[0045] Figure 41H NMR spectrum of the D-A type molecule L-AI-tBuCZ with phthalimide as the acceptor, disclosed in Example 2 of the present invention;

[0046] Figure 5 13C NMR spectrum of the D-A type molecule L-AI-tBuCZ with phthalimide as the acceptor, disclosed in Example 2 of the present invention;

[0047] Figure 6 High-resolution mass spectrum of the D-A type molecule L-AI-tBuCZ with phthalimide as the acceptor, disclosed in Example 2 of the present invention;

[0048] Figure 7 1H NMR spectrum of the D-A type molecule AI-tBuCZ with phthalimide as the acceptor, disclosed in Example 3 of the present invention;

[0049] Figure 8 13C NMR spectrum of the D-A type molecule AI-tBuCZ with phthalimide as the acceptor, disclosed in Example 3 of the present invention;

[0050] Figure 9 Absorption spectrum of the D-A type molecule with phthalimide as the acceptor, disclosed in the present invention;

[0051] Figure 10 Normalized fluorescence spectrum of the D-A type molecule with phthalimide as the acceptor, disclosed in the present invention;

[0052] Figure 11 Cyclic voltammogram of the D-A type molecule with phthalimide as the acceptor, disclosed in the present invention;

[0053] Figure 12 Fluorescence lifetime graph of the D-A type molecule with phthalimide as the acceptor, disclosed in the present invention;

[0054] Figure 13 Femtosecond transient absorption spectra of the D-A type molecule with phthalimide as the acceptor in n-hexane, dichloromethane and N,N-dimethylformamide, disclosed in the present invention;

[0055] Figure 14 Evolution-related difference spectra of the femtosecond transient absorption spectra of the D-A type molecule L-AI-tBuCZ with phthalimide as the acceptor in n-hexane, dichloromethane and N,N-dimethylformamide, disclosed in the present invention;

[0056] Figure 15 Evolution-related difference spectra of the femtosecond transient absorption spectra of the D-A type molecule AI-tBuCZ with phthalimide as the acceptor in n-hexane, dichloromethane and N,N-dimethylformamide, disclosed in the present invention;

[0057] Figure 16 The present invention discloses the differential spectra related to the evolution of the femtosecond transient absorption spectra of the D-A type molecule L-AI-CZ with phthalimide as the acceptor in n-hexane, dichloromethane, and N,N-dimethylformamide.

[0058] Figure 17 The present invention discloses the triplet state lifetime diagrams of the D-A type molecules L-AI-tBuCZ and AI-tBuCZ with phthalimide as the acceptor in n-hexane. Specific Embodiments

[0059] The following further describes the present invention in detail in conjunction with the attached Figures 1 - 17 drawings and Examples 1-3.

[0060] In the present invention, the preparation methods are all conventional methods unless otherwise specified. The raw materials used can all be obtained from public commercial channels unless otherwise specified, and the percentages are all mass percentages unless otherwise specified. The reaction conditions involved in the present invention are all carried out under well-known suitable conditions.

[0061] The nuclear magnetic resonance test method involved in this application is as follows: Take about 3 mg of the sample and dissolve it in 0.5 mL of deuterated chloroform in a nuclear magnetic resonance tube, and place the nuclear magnetic resonance tube in a nuclear magnetic resonance spectrometer Bruker Avance II 400 for testing.

[0062] The mass spectrometry test method involved in this application is as follows: Take a small amount of the sample solid powder and dissolve it in deuterated chloroform to measure the high-resolution mass spectrometry.

[0063] Examples

[0064] Example 1

[0065] Preparation method of the D-A type molecule L-AI-CZ with phthalimide as the acceptor

[0066] The preparation method of the D-A type molecule of formula (1a), and the reaction route is as follows:

[0067]

[0068] The specific steps include:

[0069] S1: Add 2.7112 g (12 mmol) of 4-bromophthalic anhydride and 1.72 mL (13.2 mmol) of 4-(2-aminoethyl)-morpholine to 30 mL of ethanol, heat and react at 70 °C for 3 h. After the reaction is completed, cool to room temperature, pour the cooled reactant into 150 ml of water, filter by suction and wash with water to obtain the crude product; dry the crude product in a vacuum oven to obtain a beige solid compound I.

[0070] S2: Add the beige solid compound I (4 mmol, 1.3521 g) obtained in step S1, carbazole (6 mmol, 1.0032 g), palladium acetate (0.15 mmol, 0.0674 g), tri-tert-butylphosphine (0.3 mmol, 0.1214 g) and sodium tert-butoxide (4.5 mmol, 0.8649 g) into anhydrous toluene (30 mL) and mix well. The mixture is refluxed at 120°C under nitrogen atmosphere for 24 h. The reaction was monitored by TLC during the reaction. After the reaction was completed, the reaction solution was cooled to room temperature and extracted with H2O (3×60 mL) to remove the catalyst. The reaction solution was then extracted with dichloromethane. The organic layer was dried over anhydrous sodium sulfate and the solvent was removed by rotary evaporation. The crude product was purified by column chromatography using petroleum ether and ethyl acetate (v / v=3:1) as eluents (followed by further purification at 7:1) to obtain the target compound L-AI-CZ of formula (1a) as a yellow powder in a yield of 36%.

[0071] The H NMR spectrum of the product of formula (1a) is: 1 H NMR (400MHz, Chloroform-d): δ8.15(dt,J=7.7,1.0Hz,2H),8.12–8.05(m,2H),7.96(dd,J=7.9,1.9Hz,1H),7.51– 7.41(m,4H),7.35(ddd,J=8.0,6.7,1.5Hz,2H),3.90(t,J=6.2Hz,2H),3.70(s,4H),2.72(s,2H),2.58(s,4H).(Refer to Figure 1 );

[0072] The carbon NMR spectrum of the product of formula (1a) is: 13 C NMR (100 MHz, CDCl3): δ = 29.71, 35.22, 53.54, 56.19, 66.99, 76.71, 77.03, 77.34, 109.56, 120.64, 121.15, 121.17, 124.12, 124.98, 126.48, 129.86, 131.50, 134.38, 139.99, 143.51, 167.54, 167.59. (Refer to Figure 2 );

[0073] The mass spectrum of the product of formula (1a) is: MALDI-TOF-HRMS: Calcd C 26 H 23 N3O3[M+H] + ,m / z=426.1773; found,m / z=426.1811.(Ref. Figure 3 ).

[0074] Example 2

[0075] The only difference from Example 1 is that in step S2, the beige solid compound I (4 mmol, 1.3521 g) obtained in step S1, 3,6-di-tert-butylcarbazole (6 mmol, 1.6766 g), palladium acetate (0.15 mmol, 0.0674 g), tri-tert-butylphosphine (0.3 mmol, 0.1214 g) and sodium tert-butoxide (4.5 mmol, 0.8649 g) were added to anhydrous toluene (30 mL) and mixed evenly to obtain the target compound L-AI-tBuCZ of formula (2a) as a yellow powder with a yield of 29%.

[0076] The preparation method of the DA type molecule of formula (2a) is as follows:

[0077]

[0078] The H NMR spectrum of the product of formula (2a) is: 1 H NMR (400MHz, Chloroform-d): δ8.14(d,J=1.9Hz,2H),8.09(d,J=1.8Hz,1H),8.04(d,J=7.9Hz,1H),7.93(dd,J=8.0,1.8Hz,1H),7.49(dd,J =8.7,1.9Hz,2H),7.43(d,J=8.7Hz,2H),3.88(t,J=6.4Hz,2H),3.68(t,J=4.5Hz,4H),2.69(t,J=6.4Hz,2H),2.56(s,4H),1.47(s,18H). (Refer to Figure 4 )

[0079] The carbon-NMR spectrum of the product of formula (2a) is: 13 C NMR (100 MHz, CDCl3): δ = 31.94, 34.82, 35.19, 53.56, 56.22, 67.01, 76.71, 77.03, 77.35, 109.11, 116.60, 120.53, 124.12, 124.21, 124.90, 129.21, 130.80, 134.34, 138.29, 144.04, 144.31, 167.66, 167.70. (Refer to Figure 5 )

[0080] The mass spectrum of the product of formula (2a) is: MALDI-TOF-HRMS: Calcd C 34 H 39 N3O3[M+H] +,m / z=538.3025; found,m / z=538.3062.(Ref. Figure 6 )

[0081] Example 3

[0082] Preparation method of DA type molecule AI-tBuCZ using phthalimide as receptor

[0083] The preparation method of the DA type molecule of formula (3a) is as follows:

[0084]

[0085] The specific steps include:

[0086] S1: 4.067 g (18 mmol) of 4-bromophthalic anhydride and 2.4 mL (23 mmol) of n-butylamine were added to 40 mL of glacial acetic acid, mixed, and refluxed for 6 h. After the reaction was completed, the mixture was cooled to room temperature, poured into ice water, filtered, and washed with water to obtain a crude product; the crude product was dried in a vacuum oven to obtain Compound II as a white solid;

[0087] S2: Add the beige solid compound II (4 mmol, 1.1240 g) obtained in step S2, 3,6-di-tert-butylcarbazole (6 mmol, 1.6766 g), palladium acetate (0.15 mmol, 0.0674 g), tri-tert-butylphosphine (0.3 mmol, 0.1214 g) and sodium tert-butoxide (4.5 mmol, 0.8649 g) into anhydrous toluene (30 mL) and mix well. The mixture was refluxed at 120 ° C under nitrogen atmosphere. The reaction was continued for 24 h. TLC was used to monitor the reaction. After the reaction was completed, the reaction solution was cooled to room temperature and extracted with H2O (360 mL) to remove the catalyst. The reaction solution was then extracted with dichloromethane. The organic layer was dried over anhydrous sodium sulfate and the solvent was removed by rotary evaporation. The crude product was purified by column chromatography using petroleum ether and ethyl acetate (v / v = 3:1) as eluents (followed by further purification at 7:1) to obtain the target compound AI-tBuCZ of formula (3a) as a yellow powder in a yield of 32%.

[0088] The H NMR spectrum of the product of formula (3a) is: 11H NMR (400 MHz, Chloroform-d): δ 8.17 (d, J = 1.9 Hz, 2H), 8.11 (d, J = 1.8 Hz, 1H), 8.07 (d, J = 7.9 Hz, 1H), 7.95 (dd, J = 7.9, 1.8 Hz, 1H), 7.52 (dd, J = 8.7, 1.9 Hz, 2H), 7.45 (d, J = 8.7 Hz, 2H), 3.77 (t, J = 7.2 Hz, 2H), 1.73 (q, J = 7.3 Hz, 2H), 1.50 (s, 19H), 1.01 (t, J = 7.3 Hz, 3H). (Refer to Figure 7 )

[0089] The 13C NMR spectrum of the product of formula (3a) is as follows: 13 13C NMR (100 MHz, CDCl3): δ = 13.67, 20.14, 30.70, 31.94, 34.81, 38.08, 76.71, 77.03, 77.35, 109.11, 116.58, 120.52, 124.11, 124.19, 124.82, 129.26, 130.77, 134.37, 138.31, 143.97, 144.27, 167.77, 167.82. (Refer to Figure 8 )

[0090] Test Example

[0091] The following performance tests were carried out on the D-A type molecules prepared in Examples 1-3:

[0092] 1. Photophysical properties

[0093] Weigh a certain mass of the sample with a one-ten-thousandth balance and transfer it to a 1 mL volumetric flask. Add dichloromethane solvent to make up the volume to prepare a stock solution of 5×10 -3 mol / L. Use a UV-visible spectrophotometer to measure the absorption spectrum. The solvent is n-hexane and the concentration is 50 μM. The test results are shown in Figure 9 .

[0094] Use a fluorescence spectrophotometer to measure the fluorescence emission spectrum. The emission mode is adopted, the slit width is 10 nm, the concentration is 50 μM, and the solvents are n-hexane, toluene, tetrahydrofuran (THF), dichloromethane (DCM), N,N-dimethylformamide (DMF), and acetonitrile (ACN) in turn, and the polarity of the solvents increases in turn. The sample is measured in a quartz cuvette with an optical path of 1 cm. The test results are shown in Figure 10 .

[0095] From Figure 9From the ultraviolet-visible absorption spectrum, it can be seen that the strong absorption peak near 285 nm belongs to the π–π* transition of the aromatic rings including the donor and acceptor; the weak absorption peak at 320 - 340 nm can be attributed to the n–π* transition of Cz or its derivatives; the weak, broad and unstructured absorption peak at 360 - 370 nm is attributed to the absorption of the CT state, which is the result of the electronic coupling between the donor and acceptor parts. Compared with L-AI-CZ prepared in Example 1, the CT state absorption peak of L-AI-tBuCZ prepared by the method of Example 2 is more significantly red-shifted and the peak shape becomes broader. This is because the carbazole group containing tert-butyl has a stronger electron-donating ability, resulting in a stronger electronic coupling effect in the compound.

[0096] From Figure 10 From the fluorescence emission spectrum, it can be seen that when excited at 370 nm, the fluorescence spectrum of the molecule becomes broader and unstructured, the emission intensity decreases, and the emission band is red-shifted in high-polarity solvents. This is a typical characteristic of the solvation of the intramolecular charge transfer state. Compared with L-AI-CZ prepared in Example 1, the emission of L-AI-tBuCZ prepared by the method of Example 2 is more sensitive to the solvent polarity, which is consistent with the result that tert-butyl carbazole has a stronger electron-donor ability.

[0097] 2. Electrochemical properties

[0098] The test method is as follows: Using a CHI610D electrochemical workstation (CHI instruments, Inc., Shanghai, China), the electrochemical properties of D-A type molecules are studied by cyclic voltammetry. The electrochemical curves of the compounds in DCM containing 0.1 M tetrabutylammonium hexafluorophosphate (Bu4NPF6) electrolyte are measured. Ferrocene (Fc) is used as an internal standard (0 V), the counter electrode is a Pt electrode, the working electrode is a glassy carbon electrode, and the reference electrode is an Ag / AgNO3 electrode. It needs to be calibrated with a saturated calomel electrode before use, and nitrogen is bubbled into the solvent for about 15 min before the test. The Gibbs free energy during the electron transfer process is calculated by the Rehm-Weller formula to judge the possibility of electron transfer.

[0099] Figure 11 is the cyclic voltammogram of the D-A type molecule with phthalimide as the acceptor. From Figure 11It can be seen that for the L-AI-CZ compound prepared in Example 1 and the L-AI-tBuCZ compound prepared in Example 2, reversible oxidation peaks were observed at +1.02 V and +0.97 V respectively. By comparison, these two peaks can be attributed to the oxidation signals of the carbazole and tert-butylcarbazole groups, while the reversible reduction peak observed at -1.67 V is the reduction signal of the AI group. It can be seen that under the action of the tert-butyl substituent, the oxidation potential of the carbazole group in L-AI-tBuCZ is 0.05 V lower than that in L-AI-CZ, indicating that the electron-donating group in L-AI-tBuCZ has a stronger electron-donating ability than that in L-AI-CZ. The change in Gibbs free energy ΔG was calculated by the formula CS < 0, indicating that charge separation is thermodynamically allowed.

[0100] 3. Fluorescence lifetime analysis

[0101] Test method: The fluorescence lifetime of the sample was measured by the time-correlated single photon counting method. The instrument response function was about 50 ps, and the sample was excited with a 370 nm laser. The fluorescence peak positions in different solvents were detected, and the experimental data were fitted by the deconvolution method using FluoFit software. Test concentration: 50 μM. The test results are shown in Figure 12 .

[0102] From Figure 12 It can be seen that the charge transfer state of the molecule was directly excited using a 370 nm excitation wavelength, and the fluorescence lifetimes in n-Hexane, DCM, and DMF were measured. Taking L-AI-CZ prepared in Example 1 as an example, the fluorescence lifetime showed obvious biexponential decay characteristics. The short-lived component (0.1 ns) was attributed to the luminescence lifetime of the LE state, and the long-lived component (4.3 ns) was attributed to the luminescence lifetime of the CT state. The luminescence lifetime of the LE state was less affected by the solvent polarity, while the fluorescence lifetime of the CT state was significantly shortened in polar solvents such as DMF. This is consistent with the result that the emission intensity of the compound decreases in polar solvents.

[0103] 4. Femtosecond transient absorption analysis

[0104] Test method: (1) A regeneratively amplified titanium sapphire laser was used, and a mode-locked titanium sapphire femtosecond laser amplifier system (output wavelength: 800 nm, pulse width: 35 fs, frequency: 1000 Hz) was used as the laser light source. The output fundamental light was split into two parts by a beam splitter. Among them, 90% of the light entered an optical parametric amplifier (TOPAS, LightConversion) to generate tunable laser pulses with a wavelength range of 250 nm to 2.5 μm as the pump light. 10% of the light was attenuated by a filter and focused into a 2-mm-thick sapphire window to generate a continuous white light source (White Light Continue, WLC) with a wavelength range of 420 nm to 800 nm for the probe light. During the test, it was necessary to ensure that the pump light and the probe light were completely spatially and temporally coincident on the sample. The sample was tested at room temperature. The sample solution was placed in a 1-mm-thick quartz cuvette. To prevent the sample from being photochemically decomposed, the sample solution was continuously shaken during the test. The meaning of the transient absorption signal is the difference between excited-state absorption and ground-state absorption. In the transient absorption spectrum, a positive signal is excited-state absorption (ESA), and a negative signal is ground-state bleaching (GSB) or stimulated emission (SE), see Figure 13 。

[0105] (2) The transient absorption data of the compounds prepared in Examples 1-3 in different polar solvents were globally fitted to obtain the evolution-associated difference spectrum (EADS) and the time-dependent concentrations of the transient components, see Figures 14 - 16 。

[0106] It can be seen from Figure 13 that when the excitation wavelength is 310 nm, only the AI part is in the excited state. As time prolongs, the transient spectrum changes significantly. Taking L-AI-tBuCZ prepared in Example 1 as an example, there are two strong peaks around 350 nm and 550 nm. The band at 350 nm belongs to the absorption of the radical anion of the AI unit, and the band at 550 nm belongs to the absorption of the radical cation of the tBuCZ unit. Therefore, the appearance of these two ESA peaks proves that charge transfer from the donor to the acceptor has occurred in the molecule.

[0107] Figure 14 It is the evolution-associated difference spectrum of the femtosecond transient absorption spectrum of the D-A type molecule L-AI-tBuCZ with phthalimide as the acceptor in n-hexane, dichloromethane, and N,N-dimethylformamide.

[0108] Figure 15 It is the evolution-associated difference spectrum of the femtosecond transient absorption spectrum of the D-A type molecule AI-tBuCZ with phthalimide as the acceptor in n-hexane, dichloromethane, and N,N-dimethylformamide.

[0109] Figure 16 Differential spectra related to the evolution of the femtosecond transient absorption spectra of the D-A type molecule L-AI-CZ with phthalimide as the acceptor in n-hexane, dichloromethane, and N,N-dimethylformamide.

[0110] From Figure 14 It can be seen that taking the transient absorption of L-AI-tBuCZ prepared in Example 1 in the non-polar solvent n-hexane as an example, the first EADS is attributed to 1 AI * the local excited singlet state with a lifetime of 0.31 ps, indicating that the time of CS is 0.31 ps. As time extends, the transient spectrum changes significantly, and there is absorption of cationic and anionic radicals. Therefore, the second EADS is attributed to the CS state. Within 77.3 ps, the absorption peak is slightly blue-shifted, indicating the structural relaxation of the charge-separated state. The time constant of the third EADS is 1.5 ns, that is, the CR time is 1.5 ns, which is similar to the fluorescence lifetime (1.6 ns) obtained by TCSPC measurement.

[0111] In the medium-polarity solvent DCM and the high-polarity solvent DMF, there is a CT′ (solvation) state in the charge transfer state. Through global fitting with the continuous model, in DCM, the times of charge separation, solvation, structural relaxation, and charge recombination are 185.4 fs, 4.5 ps, 18.9 ps, and 1.2 ns respectively. In DMF, the times of charge separation, solvation, structural relaxation, and charge recombination are 172.6 fs, 2.8 ps, 8.8 ps, and 0.5 ns respectively. The results show that as the solvent polarity increases, the processes of charge transfer, solvation, and structural relaxation all accelerate.

[0112] Combined with Figure 14 , Figure 15 and Figure 16 It can be seen that compared with L-AI-CZ, the times of charge separation, solvation, and structural relaxation of L-AI-tBuCZ and AI-tBuCZ in polar solvents are slower. The possible reason is that the electron-donating ability of CZ is weak, the ICT property is weak, and the time to enter the CS state is slow.

[0113] 5. Nanosecond transient absorption analysis

[0114] Test method: The nanosecond transient absorption spectrum was studied using an LP920 laser flash photolysis spectrometer (Edinburgh Instruments, UK). The sample was purged with N2 for 30 minutes before measurement and excited with a nanosecond pulse laser (Opolette 355II + UV nanosecond pulse laser, OPOTEK) at an excitation wavelength of 355 nm. Test concentration: 30 μM. The wavelength is adjustable in the range of 200–2200 nm. The signal was digitized using a Tektronix TDS3012B oscilloscope, and the data was analyzed using L900 software. The analysis results are shown in Figure 17 .

[0115] It can be seen from Figure 17 that after AI-tBuCZ was excited by a 355 nm laser in deoxygenated n-hexane, the first thing observed was a very strong ground state bleach peak at 386 nm, which was consistent with the position of the UV absorption peak, and the triplet lifetime at 386 nm reached 1.6 μs. L-AI-tBuCZ had similar nanosecond transient absorption spectral characteristics. However, no triplet signal was observed for L-AI-CZ in deoxygenated n-hexane, probably because the electron-donating ability of carbazole was lower than that of 3,6-di-tert-butylcarbazole, resulting in too low CT state energy levels to undergo intersystem crossing.

[0116] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A D-A type molecule with phthalimide as the acceptor, characterized in that, It has the following general structure: wherein, R' is selected from R is selected from 2. The D-A type molecule with phthalimide as the acceptor according to claim 1, characterized in that, Having the structure of general formula I or II: In formula I, R is selected from In Formula II, R is selected from 3. The preparation method of the D-A type molecule with phthalimide as the acceptor according to claim 2, characterized in that, The compound having the structure of formula I is prepared according to the following method, comprising the following steps: S1: Dissolve 4-bromophthalic anhydride and 4-(2-aminoethyl)morpholine in ethanol and react at 70 °C for 3 h to obtain a compound of formula S-1. In the compound of formula S-1, the substituent R is Br - ; S2: Add compound S-1 prepared in step S1, compound R, palladium acetate, tri-tert-butylphosphine and sodium tert-butoxide to anhydrous toluene, and reflux at 120° C. for 24 hours under inert gas protection to obtain a compound having the structure of formula I; compound R is carbazole or 3,6-di-tert-butylcarbazole.

4. The preparation method of the D-A type molecule using phthalimide as the acceptor according to claim 2, characterized in that, The compound having the structure of Formula II is prepared according to the following method, comprising the following steps: S1: Mix 4-bromophthalic anhydride, n-butylamine and glacial acetic acid evenly, and reflux and react at 140 °C for 6 h to obtain compound S-2. In compound S-2, the substituent R is Br - ; S2: Add the compound S-2 prepared in step S1, 3,6-di-tert-butylcarbazole, palladium acetate, tri-tert-butylphosphine and sodium tert-butoxide to anhydrous toluene, and reflux at 120° C. for 24 hours under the protection of an inert gas to obtain a compound having the structure of formula II wherein R is selected from butyl.

5. The preparation method of the D-A type molecule using phthalimide as the acceptor according to claim 3, characterized in that, In step S1, the molar ratio of 4-bromophthalic anhydride to 4-(2-aminoethyl)-morpholine is (10-20):(10-20); In step S2, the molar ratio of compound S-1, compound R, palladium acetate, tri-tert-butylphosphine and sodium tert-butoxide is (15-20): (15-20): (0.5-0.9): (1.0-1.5): (15-20).

6. The preparation method of the D-A type molecule using phthalimide as the acceptor according to claim 4, characterized in that, In step S1, the molar ratio of 4-bromophthalic anhydride to n-butylamine is (10-20): (10-20); In step S2, the molar ratio of compound S-1, compound R, palladium acetate, tri-tert-butylphosphine and sodium tert-butoxide is (15-20): (15-20): (0.5-0.9): (1.0-1.5): (15-20).

7. The method for evaluating excited state dynamics of DA-type molecules using phthalimide as an acceptor according to any one of claims 1 to 3, characterized in that: (1) Structural characterization of DA-type molecules with phthalimide as the receptor was performed, and nuclear magnetic resonance (HNMR) spectra, CNMR spectra, and high-resolution mass spectra of DA-type molecules were obtained; (2) Visible light is then used to excite the DA-type molecule with phthalimide as the receptor, and the excited-state dynamics of the DA-type molecule is determined by measuring the steady-state spectrum, electrochemical properties, fluorescence lifetime, femtosecond transient absorption, and nanosecond transient absorption performance of the excited DA-type molecule.

8. The method for evaluating excited state dynamics of DA-type molecules using phthalimide as an acceptor according to claim 7, characterized in that: The UV-visible absorption spectrum was measured by UV-visible spectrophotometer, the fluorescence spectrum was obtained by fluorescence spectrometer, and the steady-state spectrum test of the molecule was performed; Cyclic voltammetry spectra were obtained using an electrochemical workstation to analyze the change in Gibbs free energy during molecular electron transfer and determine its charge separation performance. Use a time-correlated single photon counter to analyze the molecular fluorescence lifetime and determine its fluorescence lifetime performance; Femtosecond pump-probe technology is used to obtain femtosecond transient absorption spectra, analyze the process of molecular excited state charge separation and recombination, and determine the speed of the excited state process; The nanosecond transient absorption spectrum is obtained by using a nanosecond flash photolysis instrument to analyze the triplet state lifetime after molecular excitation and judge the change in the lifetime of its triplet species.

9. Use of the D-A type molecule with phthalimide as the acceptor according to any one of claims 1-3, characterized in that, The said use is for use in organic light-emitting diodes, organic sensors, and dye-sensitized solar cells.

10. Use of the D-A type molecule with phthalimide as the acceptor according to claim 9, characterized in that, The said use is as a triplet photosensitizer.

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