Study On Organic Room-temperature Phosphorescence Based On Carbazole Benzophenone Derivates

In recent years,pure organic organoluminescent materials have attached attention of researchers due to their unique photoelectric properties,especially thermally-activated delayed fluorescence and room-temperature phosphorescent materials,which have shown great application prospect in many fields such as photoelectric conduction,data encryption,biological imaging and solid-state lighting.It has a huge application prospect.For pure organic compounds,triplet excitons are very sensitive to external conditions such as temperature,oxygen and water in the air,and are prone to vibration or collision and then inactivate by non-radiation transition.In addition,due to the forbidden transition the intersystem crossing rate of singlet excitons is slow and it is difficult to reach the triplet state.Therefore,the number of triplet excitons formed is small,resulting in lower quantum efficiency.To solve these problems,researchers have developed a variety of strategies to enhance the phosphorescence effect in recent years,which can be attributed to two aspects from the perspective of the mechanism: to increase the rate of intersystem crossing,promote the generation of triplet excitons,and promote the generation of triplet excitons.Therefore,how to increase the intersystem crossing rate and restrain the non-radiative transition rate is the key to prepare pure organic room temperature phosphorescent molecules with high-quantum efficiency and long life.This dissertation conduct research from two aspects: the design,preparation and characterization of pure organic materials with optical properties such as thermally activated delayed fluorescence and room temperature phosphorescence;Research on the properties of meterials in terms of photophysics and thermodynamics and discuss the structure-activity relationship between properties and molecular structure.In this thesis,three carbazole derivatives such as benzocarbazole,dibenzocarbazole and 3,3'-bicarbazole are used as electron donors,and benzoyl chloride and its halogensubstituted compounds are used as electron acceptors.The nucleophilic substitution reactions and esterification reaction synthesized a series of donor-acceptor type small molecules,and successfully prepared pure organic molecules with thermally activated delayed fluorescence and room-temperature phosphorescence properties.Through comprehensive analysis of the optical properties of the target product,it can be known that these molecules have obvious properties of intramolecular electron transfer.The products of benzocarbazole and dibenzocarbazole have obvious properties of delayed fluorescence and room temperature phosphorescent double emission,while the products of the bicarbazole system have two properties of phosphorescent double emission with different life.Analyzing and summarizing the experimental data,it is found that the product molecules substituted by chlorine and bromine have stronger phosphorescence performance,including higher quantum efficiency and longer phosphorescence lifetime.It is very likely that the introduction of heavy atoms enhances the spin-orbit coupling effect and then promotes the probability of excitons crossing from the singlet state to the triplet system,thereby enhancing phosphorescence.