Design And Synthesis Of Thermally Activated Delayed Fluorescence Polymers And Their Application In Electroluminescence Devices And Bioimaging

Pure organic thermally activated delayed fluorescence（TADF）materials can utilize the process of reverse intersystem crossing（RISC）to harvest efficiently the triplet excitons,which possess 100%internal quantum efficiency compared to phosphorescent materials and low cost.TADF materials,as the third generation of organic luminescent materials after the fluorescent and phosphorescent materials,is blowing the development of organic light-emitting diodes（OLED）.In addition,TADF materials with long lifetime delayed fluorescence feature also are suitable for time-resolved luminescence imaging（TRLI）,which can efficiently avoid short-lived fluorescence signals from spontaneous fluorescence in organisms and scattered lights.It is beneficial to improve greatly the signal-to-noise ratio in bioimaging and achieve more real signals and clear images.Herein,several TADF polymers based on through-space charge transfer（TSCT）and fluorescence resonance energy transfer（FRET）were designed,synthesized and investigated systematically their photophysical properties.They were then successfully applied in OLED and TRLI.The research contents of this paper are summarized as follows:In chapter 1,the luminescence mechanism of organic luminescent materials was firstly introduced.Then the properties of three generations of OLED materials,fluorescence,phosphorescence and TADF were introduced,respectively.The design strategies of TADF small molecules and polymers and the research progress of TADF materials were briefly introduced.Finally,the design ideas and research contents in this thesis were described.In chapter 2,two series of“face-to-face”TSCT-based polymers P（N-co-B）and P（N-co-T）with polyethylene backbone were synthesized,where benzo[5,6][1,4]oxazino[2,3,4-kl]phenoxazine（NO）was used as the electron donor,5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracene（BO）and 2,4,6-triphenyl-1,3,5-triazine（TRZ）were used as electron acceptors,respectively.Both polymers showed distinct TADF properties,good solubility and high thermal stability.The device based on P（N8-co-T2）realized the best device efficiency of 15.2%among them,which is achieved high level in TSCT-based TADF polymers.In chapter 3,a series of the alternating polymers P（D-alt-TR_n）were constructed via the alternating sequence poly（maleimide-alt-styrene）as backbone,acridine as electron donors and triazine derivatives as electron acceptors in the side chains of the non-conjugated polymers.By adjusting the TSCT intensity between the donor and the acceptor through regulating the electron-acceptor ability of the acceptors,the alternating polymers realized multi-color emission from blue to yellow,which exhibited distinct TADF and aggregation-induced emission（AIE）properties.The device based on P（D-alt-TR₃）achieved maximum external quantum efficiency(EQE_max)of 20.9%,which is one of the best device efficiency in TSCT-based TADF polymers.In chapter 4,a series of amphiphilic TADF polymers PEO-b-P（D-co-TR_n）with TSCT effect were prepared by living radical polymerization where acridine as electron donors,triazine derivatives as electron acceptors and trithiocarbonate derivatives as reversible addition-fragmentation chain transfer（RAFT）reagent.PEO-b-P（D-co-TR₃）devices achieved EQE_max of 7.7%.Meanwhile,the polymers were formed the stable and hypotoxic nanoparticles via self-assembly method,the TSCT luminescence could be effectively protected within the nanoparticles and inhibited quenching by the oxygen in the environment,which were successfully applied in high signal-to-noise ratio confocal and TRLI.In chapter 5,the green-emitting TADF molecule 4-（9-（4-（（4-（10H-phenoxazol-10-yl）phenyl）sulfonyl）phenyl）-9H-carbazol-3-yl）phenyl acrylate（PDC-DA）was used as the energy transfer donor and the energy-matched photoswitchable compound 2-（3’,3’-dimethyl-6-nitrospiro[chromene-2,2’-indolin]-1’-yl）ethyl methacrylate（SPMA）as the energy transfer acceptor.A class of photoswitchable TADF polymeric nanoparticles（PDFPNs）based on FRET mechanism was prepared by one-pot miniemulsion polymerization,which were achieved high-contrast dual-color fluorescence and tunable fluorescence lifetime upon visible light and UV light irradiation.The luminescence from the T₁ state of TADF molecules could not quenched by oxygen in the environment due to the well protection of PDFPNs.The nanoparticles possessed good water dispersion and photostability,fast photoresponsiveness and stable reversibility,good long-term stability and low biotoxicity.The PDFPNs were successfully applied in bioimaging and achieved reversible dual-color confocal fluorescence imaging and TRLI with high signal-to-noise ratio.