| Luminescent ?-conjugated organic materials have been widely used in the applications of optoelectronics,including organic light-emitting diodes(OLEDs),organic solid-state lasers(OSLs),chemsensing,bioimaging and etc.The ring-fused structures of organic compounds are easily modified and can effectively circumvent the disorder of the molecules,thereby making the luminescent properties more unique.The doping of a main-group elements with unique properties in the ring is a developed trend in the design of organic conjugated molecules.The organoboron compounds which contain boron element have been proved to be a family of high-efficiency luminescent materials.Organoborane reagents have high reactivity towards bidentate organic ligands due to the vacant p-orbital of the boron atom,which can not only allows the formation of a rigid four-coordinate boron-bridged ring but also causes intramolecular electron delocalization of the ?-system.The produced ring-fused structures can effectively constrain the molecular rotations and hence may intensify the emission.In addition,the rigidified ?-system may decrease the lowest unoccupied molecular orbital(LUMO)level,which in turn endows the formed boron-containing materials with high electron affinity.By changing the substituents on the ligands,the organoboron compounds can obtain the desired properties more easily.Through the efforts of scientific researchers,many organic tetra-coordinate boron compounds emitting from dark blue to near-infrared luminescence have been recently constructed,and some of them have strong fluorescence emission in the solid state.The structure of a material determines the properties and a deep understanding of the relationship between structure and properties is the prerequisite for the development of high-performance materials.Organic crystals have a well-defined single-molecule and intramolecular aggregation structure and are ideal systems for studying the relationship between structure and properties.In this research,we synthesized a series of boron diaryl-?-diketonate compounds with conjugated structures through simple and effective routes,and carefully studied their crystal structure and photophysical properties.1.In Chapter II,we synthesized ligands 1–4 with high yields by a simple Claisen condensation reaction.The phenyl boron reagents such as triphenylborane and fluorobis(pentafluorophenyl)borane reacted with the ligands,and the compounds 1–8 were obtained after purification by recrystallization.The structure of the compounds was confirmed by characterization methods such as NMR spectra,mass spectra,and elemental analysis.2.In Chapter III,we studied the luminescent properties of Compound 3.Compound 3 produced two polymorphs,orange-emissive 3OC and red-emissive 3RC.The difference in the arrangement of the two crystal phases led to the difference in their luminescence.Molecules in crystal 3OC form dimers and the dimers are arranged in a special network structure,which is less stable than other arrangements.Through the stimulation of external forces,the crystal arrangement tends to change,The crystal is fragmented into small pieces when it is smashed,and under the action of the tensile force,the crystal is broken,and the generated fracture surface emits significantly blue shift fluorescence with increased emission intensity.This is because the relatively weak supramolecular interaction between dimers is destroyed,and the distance between dimers becomes larger,which is equivalent to the process of disaggregation,and the fluorescence is blue shifted and the efficiency becomes higher.Under the effect of grinding pressure,the crystals become amorphous powder,and the light emission is red-shifted and darkened.This is due to the fact that under the action of anisotropic shear forces,the arrangement of molecules changes and the distance between dimers decreases,forming a strong ? interaction between dimers,which is equivalent to the aggregation process.As a result,the fluorescence red shift and the efficiency become lower.We also apply isotropic hydrostatic pressure to the crystals.Under the action of ultra-high pressure,the molecules are arranged more closely and the distance between molecules is reduced.In turn,the intramolecular supermolecular effect is enhanced,and the molecules further aggregate tightly.Based on such a model,we not only revealed the influence of the distance between supramolecular molecules on the luminescent properties,but also obtained the response characteristics of three different pressures on the luminescent properties of the material for first time.3.In chapter IV,we studied the photophysical properties of compound 4.By crystal growth,compound 4 produces orange crystals 4OC and red crystals 4RC.First,after a simple mechanical grinding,the orange crystals turned to a solid powder,and the emission peak changed from 580 nm to 610 nm.The material was further subjected to a high pressure test and the emission redshifted to 655 nm under isotropic high pressure.Second,heating the orange crystal 4OC,its fluorescence emission will also change,when it is heated to 235°C,the fluorescence blue shift and display a green light emission(520 nm).The third,the dimethylamine group on the compound is prone to protonation and changes the luminescent properties by affecting the electronic properties of the molecule.Compound 4 was placed in a strong volatile acid atmosphere and the emission peak of the compound shifted to 450 nm.The above three process are reversible.Based on the above studies,we achieved red,green,and blue primary colors by stimulating a single compound.4.In Chapter V,we studied symmetrically substituted boron diaryl-?-diketonates complexes 5–8 and carefully studied their photophysical properties and explored their applications.The solids of these four compounds were all red emissive,and the efficiencies of compounds 5 and 6 reached 0.32 and 0.48,respectively.This efficiency is quite prominent in red luminescent materials.Considering that the fluorescence efficiency of compounds 7 and 8 much lower than that of 5 and 6,we focused on comparative studies of compounds 5 and 6.Through crystal growth,Compounds 5–8 all produce crystals suited for X-ray single crystal diffraction.Compound 5 produced two polymorphs,red colored form 5a with flake-like morphology and orange-red colored form 5b with a block shape.Compound 6 also produced two polymorphs,red block crystal 6a and red needle crystal 6b.Both compounds showed bright green and greenish-blue fluorescence in dichloromethane solution,respectively.At the same time,we have found that crystal 5a and crystal 6b show amplified spontaneous emission(ASE)phenomena,thus demonstrating the potential application of four-coordinate organoboron materials in the field of organic lasers.In summary,we designed and synthesized eight organoboron compounds based on diaryl-?-diketonates,and carefully studied their photophysical properties as well as crystal structure.What is interesting is that some of these compounds produce fluorescent changes to external stimuli.Based on the research of such compounds,it is of great significance to reveal the relationship between structure and properties,a major scientific issue in the field of materials science.At the same time,it provides reference for the follow-up study of tetra-coordinate organoboron compounds. |
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