Method for preparing near-infrared region ii fluorescent small molecule

A method for preparing a near-infrared region II fluorescent small molecule, wherein a near-infrared region H fluorescent small molecule with a D-π-A system structure is constructed by using a naphthalimide salt as a strong electron acceptor, dioxythiophene as a π bridge and an N, N-dimethylstyrene structure as an electron donor, and the structure of the naphthalimide salt F1 is as follows:

• the structure of the dioxythiophene F2 is as follows:
• the structure of the N, N-dimethylstyrene F3 is as follows:
• the structure of the near-infrared region IT fluorescent small molecule F4 is as follows:
• the method for preparing the near-infrared region II fluorescent small molecule comprises the following steps:
• A, Synthesis of intermediate I M1
• N,N-dimethylformamide, 1,8-naphthaleneimide and anhydrous lithium hydroxide are successively added into a reactor with a stirrer and then heated to 125-150° C. under the condition of stirring, air in the reaction system is replaced with nitrogen, 1,4-dibromobutane is dropwise added under the protection of nitrogen, the reaction is preserved for 30-100 min, subsequently, a stabilizer is added, the above materials are stirred for 15-60 min and then subjected to reduced rectification, ethanol is added in a bottom liquid, and finally the intermediate I M1 is obtained by crystallizing, filtering and drying is obtained by crystallizing, filtering and drying;
• B, synthesis of naphthalimide salt F1
• the intermediate I M1 is added into tetrahydrofuran and heated to 52-58° C. under the conditions of stirring and nitrogen protection, a methyl magnesium chloride solution is dropwise added, the above reaction is heated to 62-66° C. after dropwise addition is completed and then the reaction is preserved for 0.5-2.5 h, a solvent is recovered by distillation, a proper amount of water is added into the bottom liquid, a 20 wt % of fluoroboric acid solution is slowly dropwise added at room temperature, a reaction speed is controlled, stirring is maintained for 0.5-1 h after dropwise addition is completed, and the naphthalimide salt F1 is obtained by suction filtration;
• C, synthesis of dioxythiophene F2
• 5-bromo-2-(3,4-vinyldioxythiophene) formaldehyde and (formylmethylene) triphenylphosphine are mixed in a solution of toluene and heated to reflux, the reaction is maintained for 12-18 h, a solvent is evaporated at reduced pressure to obtain a crude product and the crude product is purified on a silica gel column, and white powdered dioxythiophene F2 is obtained by using a petroleum ether/dichloromethane mixture as an eluting agent;
• D, synthesis of intermediate II M2
• a metered catalyst 1 is added into N,N-dimethylformamide, 4-vinyl-N,N-dimethylaniline F3 and dioxythiophene F2 are successively added under the condition of stirring, then the mixed solution is heated to 125-150° C. and stirred to react for 12-20 h under the protection of nitrogen, the reaction solution is extracted with water and dichloromethane after the reaction is ended, each phase is separated, a combined organic phase is dried with Na2SO4, the solvent is evaporated at reduced pressure, and the left residue is purified by column chromatography to obtain the intermediate II M2;
• and
• E, synthesis of near-infrared region II small molecule F4
• the intermediate II M2 and the naphthalimide salt F1 are mixed in ethanol, a proper amount of catalyst 2 is added, the above materials are stirred for 4-12 h under the protection of nitrogen, a solvent is evaporated at reduced pressure after the reaction is ended, the left residue is purified by column chromatography to obtain the final product near-infrared region II small molecule F4.