Performance And Applications Of Small-Molecule-Doped Organic Crystals With Long-Persistent Luminescence

At present,great progress has been made in the research of inorganic longpersistent luminescence(LPL)materials.Researchers have developed a large number of inorganic LPL materials.Compared with inorganic LPL materials,organic LPL materials have become the research focus due to their advantages of low price,simple synthesis,good biocompatibility,flexibility and group tunability.The organic crystalline LPL materials are important in molecular design and mechanism research,because the organic crystalline LPL materials have many advantages that the amorphous LPL materials do not have.In this paper,the controllable preparation,photophysical properties and the mechanism of the LPL crystal materials of D-A system are studied.1.We used two cheap and easily available organic small molecules to produce LPL crystal materials of D-A system,which have visible LPL performance with a duration of more than 6 s upon low-energy photoexcitation by simple ultrasound at room temperature.The LPL duration is more than 6 s.The thermal stability,electrochemical properties and photophysical properties of the doped crystals were studied,and the LPL emission mechanism was analyzed.The donor molecule 2,7-di-(N,N-diphenylamino)-9,9-dimethyl-9H-fluorene(DDF)and acceptor molecule 2,8-bis(diphenylphosphoryl)dibenzo[b,d] thiophene(PPT)selected in the experiment have good thermal stability.The doped crystals have high single crystal quality.Through a series of photophysical analysis,we can see that the formation of LPL emission has been explained as a synergistic effect of delayed fluorescence from the charge-separated states and persistent room temperature phosphorescence from the DDF triplet state.2.We regulate the LPL duration of the doped crystal by changing the amount of donor molecule or the type of donor molecule.Through a series of experiments and photophysical analysis,it can be known that when the D-A system is prepared by ultrasonic crystallization at room temperature,the energy levels of donor and acceptor molecules should match each other to form the D-A system.The structure of the donor molecule must be smaller than the maximum gap in the crystal structure of the host molecule.Since the photophysical properties of the donor molecules can affect the photophysical properties of the prepared doped crystals,the LPL duration can be regulated by the selection of the donor molecules.The LPL duration also depends strongly on the doping concentration of donor.By doping the dye molecules whose energy levels and molecular structure can match the doped crystals into the doped crystals,it is expected to realize the regulation of the LPL duration and color.These provide some new ideas for us to design D-A system with LPL property.3.On the basis of previous work,we further explore the application value of the small-molecule-doped organic crystals with controllable LPL duration.We apply them to anti-counterfeiting and biological imaging.Because the anti-counterfeiting material not only needs to achieve the purpose of anti-counterfeiting,but also can not cause information leakage,so we choose the doping crystal with the LPL duration of 6 s as the anti-counterfeiting material in the experiment.The results show that its anti-counterfeiting effect is excellent.We apply the doped crystal with the LPL duration of25 min to biological imaging,and the results prove its good potential application.