Thermally Activated Delayed Fluorescence Emitters With Longer Emission Wavelength: Design,Synthesis And Biological Applications

Fluorescence imaging and sensing have become indispensable technologies for studying biological systems because they provide dynamic information about the location and quantity of target molecules.Since traditional fluorescence imaging and sensing are based on the absolute intensity of a single emission,they will be interfered by penetration depth,probe distribution,autofluorescence interference,and signal fluctuations caused by instrument parameters,and thus cannot accurately quantify analyte concentration information.With the introduction of self-calibrated reference signals,proportional fluorescence imaging can provide more accurate and reliable quantitative information.Therefore,this technology has been widely used to visualize the temporal and spatial distribution of metal ions,p H,biological enzymes,and signal biomolecules in vitro.Due to the interference of light scattering and tissue autofluorescence,when people perform in vivo biological imaging and sensing,the current ratio fluorescence imaging probe in visible range still has the problem of extremely low resolution,especially when the false ratio signal comes from those of the scatter and autofluorescence background.Recently,with the development of organic electronics,numerous organic semiconductors with unique emissive properties have been invented.By the combination of electron-donating and electron-deficient moieties in the conjugated sketelon,emitters with near-infrared（NIR）emissive wavelength and high photoluminescent quantum yields（PLQY）can be designed and synthesis.These conjugated emitters were further converted into water-dispensible nanoparticals through nano-self-assembly methodology,and the so-prepared organic semiconductor NPs were consequently used in vivo for sensing,imaging or anti-cancer/bacterials reagents.Thermally activated delayed fluorescence（TADF）emitters are the hotest species for organic light-emitting diodes.The small energy difference(（35）E_ST)between their excited singet state（S₁）and their excited triplet state（T₁）enable the TADF emitters hold many unique properties,such as long decay lifetime,high PLQY and long lived T₁states.Therefore,TADF emitters were found applications in time-resolved fluorescence imaging and as photosensitizers for photodynamic therapy.However,most of the TADF emitters reported were designed under the guideline of OLEDs applications,there is rarely invented by focusing biological aims.So,it is very necessary to be expoited in this field.With all these considerations in mind,this thesis is focusing on developing NIR emissive TADF emitters to prepare the nanotherostic reagents for anti-cancer and anti-bacterials applications.e Principlly,electron-deficient units of 2,1,3-benzothiadiazole and acenaphtho[1,2-b]pyrazine were both chosen as the acceptor and the strong electron-donating triphenylamine building block were chosent as the electron donor.Two series of small molecules were synthesis through the well-known Suzuki-Miyaura reaction or other ring-fusion steps in high yields.The key intermediates and the targeted molecules were fully characterized by using many modern instruments,such as TGA,DSC,SEM and laser confocal microscopy.The main content of the thesis includes the following two sections:1.Synthesis,properties research and biological application of quaternary ammonium salt compounds based on TPA-thiono-styrene-BT core.Two photosensitizers of M1 and M2 with good water solubility were synthesized by tuning the chemical structures with thiophene-bridge unit.Since M1 and M2 have a rigid planar structure at one end and a hydrophilic ionic structure at the other end,they can be well dispersed in water and therefore have good biocompatibility.Meanwhile,their extended conjugated length enabled them with longer emissive peak maxium.They all have the characteristics of low dark toxicity and obvious phototoxicity.Both M1 and M2 can be used as probes for cellular fluorescence imaging and show potentials as PSs in photodynamic therapy.2.Design and synthesis of NIR emissive TADF molecules.In this chapter,four TADF molecules,M3,M4,M5,and M6 with J-aggregating properties were synthesized.Their intrinsic TTA effect limited their fluorescence emission in solid states,which also impart deterimentals for bioimaging and photodynamic therapy.We adopted the method of host-guest doping to address this issue.A series of nanoparticles were prepared by using the target molecule as the guest,CBP as the host,and DSPE-PEG2000 as the coating agent.After testing,it is found that the prepared nanoparticles have good luminous efficiency and photodynamic therapy ability.