Pyridyl-enolato Spiroborates And [2.2]paracyclophanyl BF₂ Complexes: Synthesis And Photophysical Properties

In recent years,because of the excellent photophysical properties of borofluorodipyrrole?BODIPY?,such as high fluorescence quantum yield,high molar extinction coefficient,adjustable absorption and emission wavelength,easy modification and good light stability,it have been widely recognized and applied in the fields of biology,chemistry,materials and medicine.However,the classical BODIPY molecules also have shortcomings.Firstly,due to the high symmetry of the BODIPY molecule,the difference in energy level between the ground state and the excited state is small,resulting in a small Stokes shift?7-15 nm?.As a result,its molecular self-absorption is more serious.Then,most of the classical BODIPY molecules are planar structures,which make the?-?stacking in the aggregate state severely,leads to the quenching of the molecules in the aggregated state.These shortcomings have plagued researchers for many years,and have also limited the application of classical BODIPY molecules in many aspects,such as in the solid-state luminescent materials.The AIE strategy has been successfully applied to the development of solid-state emissive boron complexes.A variety of AIE based boron complexes with large Stokes shifts have been reported.However,there are few examples of AIE-active boron complexes have been reported and the photophysical properties in the solid state need to be further clarified.Besides,the light-source usually emit isotropic natural light,which has poor efficiency in the light conversion.Such as in Color Liquid Crystal Display,the utilization rate of light source is less than 30%,Using CPL?circularly polarized luminescence?materials as the emitting layer of emitting devices,the light utilization rate can reach almost 100%.Therefore,the small organic molecules with strong emission,switchability and CPL property have attracted much attention and research.The interest in developing CPL-active organic molecules?CPL-SOMs?is growing due to its ease of derivatization,excellent processability,high quantum yield and wavelength-adjustable advantages,and application prospects in optical devices and sensors.Therefore,the synthesis of fluorescent small molecules with large Stokes shifts and high-efficiency solid-state luminescence and strong circularly polarized luminescence has been the goal of researchers.In order to achieve this goal,we designed and synthesized a series of novel chiral fluorofluoride molecules with large Stokes shift,high solid state luminescence and high circularly polarized luminescence?CPL?.The properties and tests of the obtained molecules are mainly carried out in several parts:1.Firstly,some N?O asymmetric bidentate ligands were combined with AIE strategy,and some pyridine-enols N with propeller structures were synthesized by conjugated2-benzylpyridine with ethyl 4-benzoate and its derivatives N?O asymmetric complex.And through the reaction of the ligand with catechol and salicylic acid,a series of novel propeller-type structure of spiroborate Sborepy 1-6 were synthesized.Sborepy 3-6conforms to the characteristics of typical AIE molecules,has a lower quantum yield in solution?1%-16%?,and exhibits a high fluorescence quantum yield?25%-32%?in the solid state.The absorption and emission wavelengths can be regulated by modification of different functional groups,and the range of movement of the wavelength can be predicted by theoretical calculations.The results showed that the boronic acid ester synthesized by N?O asymmetric bidentate ligand combined with AIE strategy can effectively improve the properties of the classical BODIPY molecular aggregation state quenching,but the quantum yield required for the application to solid state luminescent materials is still lacking.So it is necessary to further increase the fluorescence quantum yield for the compound.In addition,Sborepy 6 exhibits a reversible acid gas discoloration behavior.For the characters of tunable structure,easily synthesized,low cost,good thermostability and excellent in photophysical properties under solution and solid state conditions,Sborepy 6 have has the extensive application prospect in solid-state fluorescent sensors of acidic vapor.2.In order to obtain a novel chiral fluorescent molecules with high-solid quantum yield and high circular-polarized luminescence?CPL?,the third chapter is based on the N?O asymmetric bidentate ligand combined with AIE strategy,and introduced C₂symmetric 1,1'-binaphthol?BINOL?into the molecule.Four novel C₂-spiral spiro borate?R?-/?S?-2a-2d with different chiral C₂ symmetry were successfully designed and synthesized.The series of compounds exhibit high circularly polarized luminescence?CPL?and high solid state fluorescence quantum yields.In addition,?R?-/?S?-2c exhibits good force-induced discoloration behavior,and?R?-/?S?-2d exhibits good acid-base gas sensing properties.Such compounds with high solid state quantum yield,high circularly polarized luminescence?CPL?,forcechromic,and acid gas sensing have developmental potential for applications in 3D displays,pressure sensitive materials,and sensors.3.In order to make the chirality play a greater role in the fluorescent molecule,and obtain a molecule with better asymmetry,absorption and emission with larger asymmetry factors,in this chapter we will use the chiral[2,2]Paracyclophane skeleton as a building block.Two types of fluorescent molecules were designed and synthesized by two different construction strategies.In the first class,we used a fluorophore-linked chiral source strategy to design a series of novel BODIPY chiral fluorescent molecules of BP-1-BP-4with a chirality by introducing a chiral[2,2]Paracyclophane skeleton into the Meso position of the classical BODIPY molecule.The introduction of the[2,2]Paracyclophane skeleton,the planar structure of the BODIPY molecule was effectively improved,and the?-?stacking was suppressed,so that exhibited efficient solid-state luminescence.At the same time,the maximum emission wavelengths of BP-3 and BP-4 in the solid state reached the near-infrared region,882 and 996 nm,respectively,.In the second class,we directly modified the chiral[2,2]Paracyclophane skeleton,and linked to the[2,2]Paracyclophane through BF₂.These two different design ideas will provide effective theoretical support for the design and synthesis of novel chiral BODIPY fluorescent molecules and promote the development of BODIPY chemistry.