| Organic materials are receiving increasing attentions due to their near-infinite structure and abundant functions.Investigations of the organic optoelectronic materials with good flexibility and rich functions become a popular research topic.Especially in the field of organic light-emitting diodes(OLED),the efficiencies are now comparable to the commercial inorganic light-emitting diodes(LEDs).Remarkably,organic solid state lighting and flat panel display have been commercialized preliminarily.For organic materials,their optoelectronic properties are mostly derived from?-conjugated systems.Introducing heteroatoms instead of hydrocarbons into the?-system is one effective approach to modulate the?-electrons.Numerous experimental results have proved that heteroatom modification can not only tune the optical and electrical properties,but also modify excited state properties of materials to achieve high performance and multifunctionalization of organic optoelectronic materials.However,systematic investigation of tuning the properties of materials synergistically by utilizing multiple heteroatoms is still rare,especially in the emerging fields of thermal activated delayed fluorescence(TADF)and organic afterglow,in which structure–activity relationships and synergistic effects between heteroatoms remain unknown.To address the issues mentioned above,the present work concentrates on synthesizing a series of heteroatom-containing materials which act as hosts of phosphorescent OLED,emitters of TADF devices and organic afterglow materials,and investigating their structure–activity relationships:(1)Phenazasiline unit containing both N and Si atoms was constructed.Thermal properties of these two all-aryl phenazasiline molecules were significantly improved via strengthening intramolecular weak interactions,thus the device efficiencies were increased.Moreover,owing to the failure of Rh-catalysted approach in synthesizing all-aryl phenazasilines,a newly metal-free radical-catalysted method was developed.With the new molecules acting as host materials of phosphorescent OLED devices,external quantum efficiency up to 21%and efficiency roll-off low to 1.4%at 1000 cd·m-2 were achieved.(2)To further improve the optoelectronic properties of phenazasiline,ladder-type and bridge-linked all-aryl phenazasiline molecules containing multiple N and Si atoms were constructed.On the basis of preserving optical properties,electrical properties were selectively enhanced with charge carrier mobilities up to the order of 10-5 cm2·V-1·s-1,further increasing the external quantum efficiency to 27.6%for phosphorescent OLED devices.Moreover,introduction of multi-resonance effect endows the bridge-linked molecule with bipolar property,which possesses hole and electron mobilities both more than 10-5 cm2·V-1·s-1.(3)A new type of multi-resonance TADF unit containing both B and N atoms was constructed.It has extending conjugation area to increase the electron delocalization area,thus achieves reduced ?EST and increased quantum efficiency simultaneously.An external quantum efficiency of 16.3% for greenish-blue emission was obtained accordingly when applied to the solution-processed type TADF-OLED device.Changing amount of transferred charge can tune the emission color,which lay a foundation for realizing full-color emissions of multi-resonance TADF.(4)Organic afterglow molecules containing both N and helogen atoms were constructed.Afterglow emission was achieved by using nitrogen-containing carbazole groups,while Lifetime and efficiency were further tuned by introducing different numbers and types of halogen atoms. Among six synthesized molecules,a quantum efficiency of approximately 30%and lifetime of 0.9 s were achieved.It was revealed that the introduction of halogens is capable of establishing various types of intramolecular and intermolecular interactions,which inhibits the vibration and non-radiative transition of molecules,and thus extends the lifetime of organic afterglow. |
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