The Propertyd Study Of Thermally Activated Delayed Fluorescent And Room-Temperature Phosphorescent Materials Based On Carbazole And Aromatic Ketone Derivatives

Recently,purely organic luminescent materials,especially thermally activated delayed fluorescent?TADF?and room-temperature phosphorescent?RTP?materials,have captured worldwide researchers' attention due to their enormously potential applications in sensors,optoelectronic devices,bioimaging,and data encryption and so on.For now,the key method for designing TADF and RTP materials is to enhance the efficiency of reverse intersystem crossing?RISC?and intersystem crossing?ISC?.Here are two common methods:?1?utilizing intra-/intermolecular charge-transfer?CT?states as a mediate bridge to promote communication between singlet and triplet excitons;?2?rationally designing molecular structure with spatially separated highest occupied molecular orbitals?HOMOs?and lowest unoccupied molecular orbitals?LUMOs?to realize small energy gap between singlet and triplet states??EST?.Generally,luminogens are made into crystals or dispersed in polymer matrices to circumvent aggregation-caused quenching?ACQ?effect.In this thesis,the research works are mainly divided into two parts;?1?the design and development of AIE-based TADF and RTP materials;?2?the design and development of RTP materials utilizing polymers as dispersed matrices.The detailed contents are summarized as follows:1.Based on the donor,carbazole,and acceptor,cyanobenzene,a series of TADF-based donor-acceptor dyads with AIE were synthesized.In good solvents,cyanobenzene is able to quench carbazole excitons via photo-induced electron transfer?PET?effect.However,in the aggregated state,CT states formed by carbazole and cyanobenzene can serve as a bridge between singlet and triplet states,resulting in TADF generation.It is noteworthy that these dyads can self-assemble into centimeter-long macroscopic wires in THF/water mixtures,of which absolute quantum yield is up to 39%.Finally,to determine electroluminescence properties,these dyads were fabricated into organic light-emitting diode as the emitting layer.2.Based on biscarbazole,benzophenone and diphenyl sulfone derivatives,four chemically conjugated donor-acceptor dyads with distinct aggregation-induced RTP were developed.In solution,these dyads are almost non-emissive in that intramolecular motion and twisted intramolecular CT?TICT?can quench excitons while in the aggregated state,intramolecular motion and TICT are extremely restricted,leading to exciton transition to the ground state in the radiative transition mode.It is noteworthy that biscarbazole-benzophenone dyads exhibit conspicuous dual-phosphorescence with the absolute quantum yield of up to 64%.Theoretical calculations in consistency with experimental results further demonstrate these AIE dyads have high-efficiency dual-phosphorescence properties.To show a vast application foreground,these AIE molecules were fabricated into non-doped OLED as the emitting layer.As experimental results show,the maximal external quantum efficiency?EQE?of as-fabricated OLED is up to 5.8%,which surpasses that of conventional fluorescence-based OLED.3.Three types of donor-acceptor molecules were synthesized via tuning acceptor species.Besides,to avoid ACQ effect,these small molecules were used as initiators to initiate ring-opening polymerization of D,L-lactide to form RTP polylactides?PLAs?.Due to the rigid matrix effect of PLA,molecular motion and intramolecular collisions of luminogens are suppressed,which results in maximal quantum yield of 39.4%.Besides,CZBP-PLA and CZAQ-PLA have been endowed with dual-phosphorescence emission.Finally,these PLAs were prepared into nanoparticles as bioimaging agents.According to cell imaging results,the signal-to-noise ratio for phosphorescent CZAQ-PLA nanoparticle is higher than that of fluorescent CZNI-PLA nanoparticles.4.Several single-component dual-emissive waterborne polyurethanes?WPUs?with fluorescence and RTP were developed based on naphthalimide diols.By incorporating luminogens covalently into polymeric main chains,thermal vibrational relaxation can be restrained,which generally cause the quenching o excitons.Besides,given that heavy atoms can promote spin-orbit coupling,the bromine atom was introduced into naphthalimide to enhance the ISC process to produce high-efficiency RTP.By analyzing experimental results,bromine-substituted naphthalimide-based WPUs show obvious dual-emissive property with fluorescence and RTP while non-substituted naphthalimide-based WPUs only exhibit conventional fluorescence emission.With the increase in dye's ratio in WPUs,excimers are formed,contributing to decreasing ?E_ST,which is likely to promote ISC efficiency between singlet and triplet states.Therefore,tuning?E_ST via controlling the excimer ratio is a promising method to design RTP materials.