Study On Cocrystal And Luminescence Properties Of Fluorene And Its Analogues

Mechanical optical functional materials are widely used in the fields of lightemitting diodes,thin film transistors,solar cells,laser materials,photorefractive devices and sensors.However,these materials have many defects that will limit their own development.For example,these materials have poor photothermal stability and short luminescent life.At the same time,the traditional organic light-off functional materials rely heavily on the synthesis of large planar and complex molecular structures,and there are practical problems in the actual production and application process,such as purification difficulties,product quality and production capacity are difficult to guarantee.These problems have to some extent prevented the development and application of organic optical functional materials in various fields,so it is necessary to design and create new energy-saving and environment-friendly organic optical functional materials.The organic eutectic was constructed by charge transfer,?-?interaction,hydrogen bond,halogen bond and van der Waals force.In contrast,these materials do not need those complex synthesis processes in the preparation process,but this simple production process can also obtain eutectic materials with high yield and good stability.In the early stage of the synthesis of eutectic materials,different acceptors can be selected to selectively regulate the photophysical properties of eutectic materials according to the crystal engineering theory.In recent years,the method of manufacturing new organic optical functional materials by eutectic has become a research hotspot.In the second chapter of this thesis,fluorene(FR),dibenzofuran(DBF)and dibenzothiophene(DBT)were used as electron donors,all of which have simple five membered ring bridged biphenyl structures.With the acceptor molecule 7,7,8,8-tetracyano-p-benzoquinone dimethane(TCNQ)common in charge transfer eutectic as electron acceptor,FR-TCNQ,DBF-TCNQ and DBT-TCNQ were successfully prepared by ball milling and suspension methods,and their single crystal structures were analyzed,Hirshfeld surface analysis and density functional theory calculation were carried out.The solid-state characterization and photophysical properties of the system were studied by powder X-ray diffraction analysis,thermal analysis,infrared spectroscopy,UV visible absorption spectroscopy and fluorescence spectroscopy,and preliminary electrochemical analysis was carried out.The results show that the binding ratio of donor to acceptor in the three eutectic is 1:1,and all of them form the classical "dadada" mixed stacking mode through ?-? interaction.The main interactions among the molecules include C-H ···· n,?-? stacking and van der Waals interaction;Homo of eutectic is provided by donor molecules and LUMO is provided by acceptor molecules,and its HOMO-LUMO energy gap is significantly reduced compared with donor molecules,indicating that the formation of charge transfer state between donor and acceptor may lead to red shift of absorption and emission spectra;The crystal phase of eutectic powder sample is consistent with that of single crystal.The endothermic peaks of thermal decomposition of FR-TCNQ,DBF-TCNQ and DBT-TCNQ appear at 251.2225.4 ? and 251.2 ? respectively;After the formation of eutectic,the characteristic peaks of C-H and c=c in the infrared spectrum of TCNQ are blue shifted,while the characteristic peaks of C ? n are red shifted,indicating that the electron cloud density of the benzene ring conjugated structure increases.This is because after TCNQ is combined with the donor compound,electrons are transferred from the donor to TCNQ,which also proves that there is a charge transfer state in the eutectic;The absorption peak of the eutectic absorption spectrum and the emission peak of the fluorescence spectrum appear at 200-650 nm and 550-800 nm respectively,which are significantly red shifted compared with the donor,which is consistent with the DFT calculation results,confirming the formation of the charge transfer state between the donor and the acceptor;In addition,compared with the donor,the fluorescence lifetime of eutectic increases and the quantum yield decreases;SEM photos show that eutectic can be uniformly coated on the surface of ITO glass;Electrochemical tests show that the eutectic has a certain resistance value and is an n-type semiconductor structure;The transient photocurrent curves show that the eutectic has good photocurrent response performance and has certain application potential in the semiconductor field.In the third chapter of this thesis,fluorene and a series of halogenated benzene ring compounds were prepared by ball milling and suspension methods,including octafluoronaphthalene,1,4-diiodotetrafluorobenzene and 1,3,5-triiodotrifluorobenzene.Co-crystallization,single-crystal structure and Hirshfeld surface analysis show that FROFN co-crystallization is mainly based on intermolecular ?···? stacking;FR-DITF and FR-TITF co-crystals are mainly based on halogen bonds;powder X-ray diffraction patterns,thermal analysis data And Fourier infrared spectroscopy performed solid-state characterization of the three co-crystals;the absorption peak and emission spectrum of the solid ultraviolet-visible absorption spectrum of the co-crystal have changed with the change of the stacking mode in the co-crystal,and the absorption and emission spectra have a little Moving,and the performance of the emission spectrum has also changed to different degrees.The temperature-variable emission spectrum shows that the emission peak intensity of the co-crystal increases significantly with the decrease of temperature.The research work in this thesis shows that charge transfer co-crystallization is an effective means to adjust the absorption spectrum and emission spectrum peak of organic molecules.It can also play a certain role in regulating the quantum yield and luminescence lifetime of the emission spectrum.It is for new optical functional materials.The development has good potential.