Synthesis And Properties Of D-A Luminescent Materials Containing Oxygen,sulfur-bridged Triarylboron Electron Acceptor Unit

The development and utilization of boron containingπ-conjugated organic units have been a research hotspot in the field of organic optoelectronic functional materials for a long time.Currently,most of the boron-containingπ-conjugated units used in various luminescent materials are non-bridged triarylboron,while relatively few reports on heteroatomic bridged triarylboronπ-conjugated units.Compared with traditional non-bridged triarylboron units,heteroatom-bridged triarylboron units have better planarity,rigidity,and stability,which can enhance luminescence efficiency and reduce luminescence full width at half peak（FWHM）,thereby improving color purity.Based on this,in this thesis,we selected oxygen-bridged and sulfur-bridged triarylboronπ-conjugated units as electron acceptor units to design and synthesize a series of D-A type light-emitting materials,and conducted detailed characterization and research on the structure,excited state properties and photophysical properties of these compounds.This study broadens the selection range of boron containing electron acceptor in D-A type organic light-emitting materials,and provides a new research idea for constructing high-performance boron containing D-A type organic light-emitting materials.The research content of this thesis mainly includes the following three parts:1.Synthesis and properties of D-A type luminescent materials containing oxygen-bridged triarylboron electron acceptor unitThree novel D-A luminescent compounds（BO-CZ,BO-N and BO-NO）were designed and synthesized by Suzuki-Miyaura C-C coupling reaction using the oxygen-bridged triarylboron as the electron acceptor unit,and the phenylcarbazole,triphenylamine and oxygen-bridged triphenylamine as different electron donor units.The structures of the compounds were characterized and confirmed by NMR spectra,high-resolution mass spectra and X-ray single crystal diffraction analysis methods,and the photophysical and electrochemical properties of these compounds were investigated by ultraviolet spectrograph,fluorescence spectrograph and electrochemical workstation.The results show that the luminescent molecules have strongπ-πinteractions in the crystalline state due to the good planarity of the oxygen-bridged triarylboronπ-conjugated unit.More importantly,by changing different electron donor units,the luminescence color of these compounds can be tuned from deep blue to yellow,and the photoluminescent quantum yield（PLQY）can be up to nearly 100%.Notably,the compound BO-CZ exhibits deep blue light with high color purity in PS film with narrow FWHM of 36 nm and CIE coordinates of（0.164,0.019）.Finally,these boron-containing D-A type luminescent materials were used as Lewis acids,and their interactions with Lewis bases such as pyridine and pyridine derivatives（DMAP）were studied by absorption/fluorescence spectroscopy,and the experimental phenomena were analyzed and explained by DFT theoretical calculations.2.Synthesis and properties of D-A thermally activated delayed fluorescent materials containing oxygen-bridged triarylboron electron acceptor unitThree boron-containing D-A type light-emitting molecules（BO-PST,BO-DMC and BO-POT）were synthesized by Buchwald Hartwig C-N coupling reaction using oxygen-bridged triarylboron as electron acceptor unit and 9,9-dimethylacridine（DMC）,phenoxazine（POT）and phenothiazine（PST）as electron donor units.The structure of these compounds was characterized and confirmed by analytical methods such as NMR spectra,high-resolution mass spectra,and X-ray single crystal diffraction.The photophysical and electrochemical properties of these compounds were studied by instruments such as ultraviolet spectrograph,fluorescence spectrograph,and electrochemical workstations.The research indicated that the compound BO-PST based on the flexible donor unit phenothiazine（PST）has two conformations:quasi-equatorial and quasi-axial,while the other two compounds（BO-DMC and BO-POT）both have quasi equatorial conformations.Under the quasi-equatorial conformation,with the continuous enhancement of electron donating ability of DMC,POT,and PST groups,the PL spectra of these compounds showed a gradual red-shift,and the corresponding luminescence color gradually changes from green to orange yellow.Interestingly,due to the presence of another quasi-axial conformation of BO-PST,its PL spectra exhibited dual emission peaks,at 602 nm and 410 nm,respectively.In addition,all three compounds exhibited significant thermal activation delayed fluorescence（TADF）characteristics,two lifetimes corresponding to fluorescence emission and delayed fluorescence emission were displayed in the lifetime decay diagram,respectively.Finally,the excited state properties of these compounds were studied by DFT theoretical calculation,especially for the two conformations of compound BO-PST showing different photophysical properties.3.Synthesis and properties of D-A type luminescent materials containing sulfur-bridged triarylboron electron acceptor unitTwo novel sulfur-containing D-A light-emitting molecules（BS-CZ and BS-N）were designed and synthesized by Suzuki Miyaura C-C coupling reaction using sulfur-bridged triarylboron as the electron acceptor unit and carbazole and triphenylamine as the electron donor units.The structure of these compounds was characterized and confirmed by analytical methods such as NMR spectra,high-resolution mass spectra and X-ray single crystal diffraction.The photophysical and electrochemical properties of these compounds were studied by instruments such as ultraviolet spectrograph,fluorescence spectrograph,and electrochemical workstations.The results show that compared to the blue PL of compound BS-CZ,compound BS-N exhibits a more red-shift orange PL,which is due to the stronger electron donating ability of the triphenylamine unit compared to the carbazole unit.Notably,BS-CZ exhibited TADF properties with a smallΔE_STof 0.16 e V and narrow band blue emission（FWHM=35 nm and 33 nm）in both solution and doped film.Quantitative calculations show that compound BS-CZ exhibits multiple resonance thermal activation delayed fluorescence（MR-TADF）characteristics,while compound BS-N exhibits traditional fluorescence（FL）characteristics.Due to the good blue luminescence of BS-CZ,we ultimately chose it as the guest material in luminescent layer of the OLED device to obtain saturated blue electroluminescence.The BS-CZ device shows blue EL at 456 nm with small FWHM of about 39 nm and CIE coordinates of（0.12,0.21）,respectively.