Design,Synthesis,Properties And Application Of Pure Organic Room Temperature Phosphorescence Compounds Containing Carbonyl Group

Room temperature phosphorescence(RTP)compounds,which have attracted much attention due to their longer lifetime compared to their fluorescent counterparts,can be applied in many fields such as electronic devices,biomedicine,anti-counterfeiting,encryption.Traditional RTP compounds are usually inorganic materials or organometallic complexes containing heavy metal atoms,which suffer from high production cost,difficult processing,high toxicity and limited application.Over the years,broad interests and prospective applications have emerged in the development of pure organic RTP systems.However,RTP is hard to achieve in pure organic compounds.Also,the structure-property relationship and photophysical process also need further clarification.To address these issues,in this dissertation,a series of pure organic RTP compounds were designed and synthesized by introduction of carbonyl group to promote spin-orbit coupling and intersystem-crossing,as well as formation of strong intermolecular interactions.Photophysical properties,phosphorescence mechanism and potential applications of these compounds in anticounterfeiting and biological imaging were also studied.The major contents are summarized as follows:1.In this research,we found that 2-MBACZ has RTP lifetime up to865.2 ms in its crystalline state,and it could emit persistent RTP in amorphous state.Carbazole is known as a common donor for its high triplet energy level,which can enhance intersystem crossing.On the other hand,methyl benzoate is commonly used as an acceptor for its aromatic carbonyls and benzene ring,which can contribute to spin-orbit coupling and persistent RTP.To obtain persistent RTP compounds,methyl 2-(9Hcarbazol-9-yl)benzoate(2-MBACZ),methyl 3-(9H-carbazol-9-yl)benzoate(3-MBACZ),and methyl 4-(9H-carbazol-9-yl)benzoate(4-MBACZ)were synthesized through reactions of carbazole with methyl 2-bromobenzoate,methyl 3-bromobenzoate and methyl 4-bromobenzoate.Crystals of 4-MBACZ,3-MBACZ and 2-MBACZ are found to emit prompt fluorescence,delayed fluorescence and persistent RTP.Among them,2-MBACZ has the longest RTP lifetime,which exceeds those of general RTP compounds(?700 ms)reported so far.The RTP lifetimes of4-MBACZ and 3-MBACZ are 222.1 and 513.9 ms,respectively.The difference between RTP lifetimes is ascribed to intermolecular interactions,molecular packing,and torsion angles between carbazole and benzene ring.On the other hand,the amorphous powders of the above-mentioned compounds could still emit RTP.Powders of 3-MBACZ,2-MBACZ could even emit persistent RTP,which can be ascribed to the conformation restriction on molecular motion,thus reducing non-radiative energy dissipation and insulation from quenchers.Such single-component materials with persistent RTP emissions at both crystalline and amorphous states could lay a strong foundation for broadening the future application of RTP materials.2.In this research,we found that RTP lifetime of 4-BACZ is longer than 550 ms,and phosphorescence efficiency of it is up to 6.9%,which exceeds that of general pure organic persistent RTP compounds.Enhancement of intermolecular interactions is helpful to nonradiative transition reduction,thus contributing to RTP.In order to enhance phosphorescence efficiency,two carbazole aromatic acids 4-(9Hcarbazol-9-yl)benzoic acid(4-BACZ)and 2-(9H-carbazol-9-yl)benzoic acid(2-BACZ),were synthesized via hydrolyzation of the target esters in the previous chapter.The crystals of 4-BACZ and 2-BACZ could emit persistent RTP with lifetimes longer than 550 ms.When compared with the corresponding esters,the acids show improved phosphorescence quantum efficiencies up to 25 times.That's because that the presence of carboxyl groups enables the formation of hydrogen bonds between molecules,which enhances intermolecular interactions.We found that nanoparticles of 4-BACZ and 2-BACZ behaved clear afterglow images in living animals,and the signal-to-background ratio(SBR)of the afterglow images of 4-BACZ nanoparticles reaches 62.Nanoparticles of 4-BACZ and 2-BACZ were injected subcutaneously into a mouse.They exhibit a clear afterglow image in mice,which is less affected by the self-illumination of the organism,and is unmatched by fluorescent probe materials,suggests that these carbazole-containing aryl acids can be potentially applied in afterglow imaging field.3.In this research,we found that two crystals of carbazole diester compound could emit persistent RTP with lifetimes as 772.8 and 896.9 ms,respectively.Carbonyl group can promote spin orbital coupling and intersystem crossing of electrons,thus facilitating compound in RTP emission and obtaining high SBR afterglow imaging material.In order to obtain such material,carbazole diester compound,dimethyl 5-(3,6-dibromo-9H-carbazol-9-yl)isophthalate(3,5-DMBACZ),was synthesized based on 3-MBACZ.Both crystals of this compound could emit prompt fluorescence,delayed fluorescence and persistent RTP.Besides,both of them still emit persistent RTP in amorphous state,which could be explained by the conformatioin restriction on molecular motions and insulation from quenchersWe observed that nanoparticles made from one crystal of this compound could show a clear afterglow image in a living animal.With an ultrahigh SBR up to 1040,this material is considered to be the best when compared with the other afterglow image organic compounds reported so far.Also,clear RTP signal could still be detected after 1-hour body circulation after NPs were injected into its front paws of a mice.Such material,which does not require external real-time stimulation,is of great significance in lymph node mapping.4.In this research,we found that's pace-conjugated compound in which carbonyl group participates in intramolecular through-space conjugation could emit persistent RTP with lifetime as long as 1584.3 ms,which is a record for space-conjugated compounds.This compound's polymorphism enables it possible to adjust phosphorescence.To investigate the influence of space-conjugation and crystal structure on photophysical properties,9,10-dihydro-9,10-[3,4]furanoanthracene-12,14-dione(AN-MA)was synthesized.It is observed that this compound exhibits aggregation-enhanced luminescence,crystal-induced RTP,polymorphism(crystal A and B),through-space conjugation and fluorescence-RTP dual emission.Upon irradiation with 260 nm UV light,both crystal A and B show major emission peaks around 292 nm resembling that of benzene,indicating the existence of relatively isolated benzene rings in their structures.RTP lifetime for crystal A and B are 915.3ms and 1584.3 ms,respectively.Crystal B has a longer RTP,which is ascribed to its much shorter through-space-conjugation interactions in its crystalline structure.This also means through-space-conjugation interactions play an important role in the RTP of AN-MA.This work provides a foundation for further designing and studying space-conjugated RTP compounds.