| Dihydrophenazine,phenothiazine,and phenoxazine,as classic dibenzoazepine six-membered ring compounds,have excellent physical and chemical properties,such as redox activity,optical activity and pharmaceutical activity.Therefore,they are widely used in many aspects such as batteries,catalysis,dyes,light-emitting devices and drug development,which have attracted great attention from chemists,physicists,materials scientists,and biologists.In particular,dihydrophenazine,phenothiazine,and phenoxazine generate stable radical cations under conditions such as chemical oxidation,electrochemical oxidation,or light,and their excellent(photo)redox activity endows these compounds with unique photocatalytic activity.Therefore,as a class of photocatalysts,they have been successfully used in catalytic conversion reactions such as atom transfer radical polymerization(ATRP)and reversible addition-fragmentation chain transfer polymerization(RAFT)driven by visible light.However,there are still many scientific problems to be solved in the research on dihydrophenazine,phenothiazine,and phenoxazine,mainly including the single means of regulating the radical characteristics,the lack of in-depth research on molecular structure-redox property relationship,and limited types of functionalization,etc.In response to the above problems,this thesis intends to conduct research from the following three aspects:1)design and synthesize a novel phenoxazine derivative diradical system,understand its free radical characteristics at the molecular level and realize effective regulation of its free radical characteristics;2)systematically study the redox properties of dihydrophenazine derivatives,and clarify the intrinsic relationship between structure and performance;3)construct a series of redox active supramolecular coordination cages based on dihydrophenazine,phenothiazine and phenoxazine,and explore the application of coordination cages in supramolecular anion binding photocatalysis and modulation of active metal complex properties.The main research content of the thesis includes the following parts:Chapter 1 In this chapter,firstly,the structure and properties of dihydrophenazine,phenothiazine,and phenoxazine derivatives were introduced,all above three types of compounds were electron-rich structures and contain multiple modifiable active sites.Subsequently,the main methods for the modification of these three types of compounds are described in detail,including N-aryl functionalization,core substitution,expansion of the core π system,oxidation of thioether,and applications in different aspects,including batteries,drugs,luminescent materials,single-molecule magnets,photocatalysis,etc.Then,the construction of dihydrophenazine,phenothiazine,and phenoxazine supramolecular coordination cage systems and their related applications are summarized,mainly referring to the construction of M2L4-type and M4L6-type metal coordination cages and their redox properties,host-guest chemistry,self-classification,photocatalysis,etc.Finally,according to the results of the literature survey above,the current problems and challenges in this field were proposed,mainly including the single means of regulating the radical characteristics of dihydrophenazine,phenothiazine,and phenoxazine derivatives,lack of in-depth research on the relationship between molecular structure and redox properties,and limited types of functionalization,etc.In view of this,the thesis gave the corresponding research plan,including designing and synthesizing a new double radical system and realizing the effective regulation of its free radical characteristics;systematically study the redox properties of dihydrophenazine,phenothiazine and phenoxazine derivatives and summarize their intrinsic structure-activity relationship;construct a series of redox-active supramolecular coordination cages based on dihydrophenazine,phenothiazine,and phenoxazine,and explore the application of coordination cages in anion binding,photocatalysis,and active species stabilization.Chapter 2 In this chapter,a novel phenoxazine derivative diradical system was successfully synthesized through novel and convenient molecular design,and multiple regulation of its open-shell diradical properties was realized.Firstly,a phenoxazinebased open-shell nitrogen-centered diradical was efficiently and conveniently synthesized by a two-step synthesis method,and the obtained radical product was highly stable and could be purified only by simple recrystallization.Subsequently,the basic electronic structure characteristics such as the ground state and the eigenvalues of the open-shell diradical,and the energy gap between the singlet and triplet states were analyzed through single crystal X-ray diffraction,temperature-variable NMR,electron paramagnetic resonance spectroscopy(EPR),UV-vis absorption spectrum,superconducting quantum interference device(SQUID)and confirmed by density functional theory calculations(DFT).Finally,the acid-base reaction of Bronsted or Lewis acids with open-shell diradical was found to be effective in enhancing their radical characteristics.Specifically,after the formation of acid-base adducts,new absorption bands appear in the near-infrared region of the ultraviolet absorption spectrum,the EPR signal,and the magnetic susceptibility measured by SQUID increased,etc.In particular,photocontrolled modulation of radical characteristics could be achieved when photoacids were used as proton sources.Therefore,the work in this chapter developed a new class of open-shell diradical with adjustable radical characteristics based on phenoxazines,which provided a new way for the development of stimuli-responsive open-shell diradical from two aspects: molecular design and radical property characteristics.Chapter 3 In this chapter,the redox properties of N,N’-diphenyldihydrophenazine and N,N’-diphenyldihydrodibenzo-[a,c]phenazine were systematically studied.Firstly,N,N’-diphenyldihydrodibenzo-[a,c]phenazine and a series of dihydrophenazine derivatives with different substituents were synthesized according to the method reported in the literatures.Cyclic voltammetry(CV)results showed that the above two dihydrophenazine derivatives could undergo two one-electron oxidation processes,and can stabilize divalent cation species through the expansion of the dihydrophenazine core π system or the effect of substituents.Subsequent oxidation titration experiments based on ultraviolet-visible-near-infrared(UV-vis-NIR)absorption spectroscopy showed that chemical oxidation could be used to achieve two oxidation processes,in which N,N’-diphenyldihydrophenazine required an excess of oxidant to achieve twostep oxidation,consisted with high oxidation potential as demonstrated by cyclic voltammetry.Finally,this work successfully obtained the single crystal structures of all oxidation states of N,N’-diphenyldihydrophenazine and N,N’-diphenyldihydrodibenzo-[a,c]phenazine for the first time,including radical cations as well as dications.The single crystal structures showed that both two species had a skeleton planarization phenomenon during the oxidation process.Therefore,this chapter systematically studied the redox properties of dihydrophenazine derivatives,clarified the internal relationship between their structures and properties,and built a good foundation for the subsequent research on the construction and properties of supramolecular coordination cages based on dihydrophenazine.Chapter 4 In this chapter,a Pd2L4-type coordination cage based on a conformation-adaptive dihydrophenazine ligand was successfully constructed through a coordination assembly strategy,and the carbon-halogen bond cleavage was acieved by utilizing the unique halide ion binding properties of the coordination cage.Firstly,N-aryl-substituted 3,7-dipyridine-phenothiazine derivatives were synthesized by Buchwald-Hartwig coupling,and then the phenothiazine derivatives were combined with [Pd(CH3CN)4(BF4)2] in 2 :1 molar ratio to build a Pd2L4-type coordination cage through a coordination-bond-directed self-assembly strategy.Subsequently,host-guest chemistry studies for the coordination cage and anions showed that the coordination cage has a strong binding ability with halogen ions such as chlorine,bromine,and iodine,as well as tetrafluoroborate ions,nitrate ions,etc.,and the binding constant with chloride ions was greater than 1014 M-1.Subsequently,this work obtained the single crystals of all host-guest complexes.The single crystal results clarified the super strong binding ability between the coordination cage and the halogen ion from the molecular level,that is,there were multiple interactions between the coordination cage and the halogen ions,such as electrostatic interaction,coordination interaction and hydrogen bond interaction.Finally,the activation and cleavage of the sp3 carbon-halogen bond was successfully achieved through the SN1 mechanism by utilizing the super-strong binding effect between the coordination cage and the halide ions.In addition,the introduction of a radical mechanism using the synergistic effect of the photoredox activity of the coordination cage could further enhance the effect of carbon-halogen bond activated cleavage.Therefore,the work in this chapter has successfully constructed a Pd2L4-type dihydrophenazine coordination cage with a super-strong binding ability to halide ions.The coordination cage has excellent carbon-halogen bond activation ability,which laid a good foundation for the subsequent development of anion-binding photocatalytic systems based on supramolecular coordination cages.Chapter 5 In this chapter,based on the research basis of the previous chapter,Using the photoredox activity of the Pd2L4-type phenothiazine coordination cage developed by the research group and its specific binding ability to chloride ions,the extremely challenging photocatalytic selective dehalogenation of organic chlorides has been successfully realized.Firstly,the Pd2L4-type phenothiazine coordination cage developed by our group was successfully constructed through the coordination selfassembly strategy.Subsequently,it was found that the phenothiazine coordination cage had a strong specific binding ability for chloride ion,its binding constant reached the order of 109,but was much smaller than the binding constant between chloride ion and dihydrophenazine coordination cage in the work in the previous chapter.Benefiting from its excellent photoredox activity and strong binding capacity for chloride ions,the phenothiazine-based coordination cage achieved good catalytic effect in photocatalytic dehalogenation reduction reactions firstly.Then,in the dehalogenation reaction of polyhalogenated aromatic hydrocarbons,the selective dechlorination reduction was further realized based on the specific recognition of chloride ions by the phenothiazine coordination cage photocatalytic system.The above ability was successfully extended to selective dehalogenation functionalization,which changed the activation sequence of carbon-halogen bonds in some classic organic synthesis reactions,so that the cage was applied in photocatalytic dehalogenation,borylation,C-N coupling and reductive coupling reactions of polyhalogenated hydrocarbons with good yield and selectivity.Therefore,the work in this chapter successfully established a supramolecular anionbonded photocatalytic system based on Pd2L4-type phenothiazine coordination cages,and realized selective dehalogenation functionalization,providing a new model and scheme for the research in the field of supramolecular photocatalysis.Chapter 6 In this chapter,stable two-coordinated Pd Cl2 species obtained for the first time through host-guest interactions between Pd2L4-type phenothiazine coordination cages and Pd Cl2,and the regulation of the spin state of divalent palladium was also realized.First,the Pd2L4-type phenothiazine coordination cage and the Pd2L4-type phenoxazine coordination cage developed by our group were successfully constructed through the coordination self-assembly strategy.Subsequently,NMR and single crystal structures showed that there were host-guest interactions between the two coordination cages and Pd Cl2.In particular,the single crystal structure showed that Pd Cl2 formed a stable linear two-coordinate compound in the cavity of the phenothiazine coordination cage,but combined two acetonitrile molecules in the cavity of the phenoxazine coordination cage to form a conventional four-coordinate palladium complexes.Subsequently,competitive experiments revealed that the high stability of the dicoordinated PdCl2 complex was primarily attributed to the effective exclusion of external ligands by the restricted space of the phenothiazine coordination cage,so that common ligands of palladium ions such as acetonitrile,triphenylphosphine and norbornadiene could not coordinate with it,but phenoxazine coordination cage could not achieve it,indicating that the cavity structure of the coordination cage had a great influence on the regulation coordination mode and stability of Pd Cl2.More importantly,the results of NMR,EPR,and SQUID experiments all revealed that the divalent palladium in the phenothiazine coordination cage was in high spin state,indicating that the phenothiazine coordination cage significantly reduced energy gap between low spin state and high spin state of divalent palladium.Therefore,the work in this chapter obtained a stable dicoordinated divalent palladium species through a supramolecular strategy for the first time,and realized the regulation of its spin state,which opened up a new path for the research of highly active metal complexes.In conclusion,in this thesis,a series of redox-active systems were designed and synthesized based on dihydrophenazine,phenothiazine and phenoxazine,including small molecule radical derivatives system and supramolecular coordination cage system,and their structures,properties and applications were carried out in-depth research.In the small molecule radical derivatives system,the redox process of classic dihydrophenazine derivatives and novel phenoxazine-based open-shell diradical has been systematically studied.In particular,the precise regulation of open-shell diradical characteristics has been successfully achieved by using multiple external stimuli.In the supramolecular coordination cage system,benefited from its photoredox activity and host-guest chemistry between cage and halide ions,the polarized cleavage and the dehalogenation functionalization of the carbon-halogen bond had been successfully realized,and finally,the adjustment of the coordination mode and stability of the highly active two-coordinated Pd Cl2 was also realized by coordination cage.Therefore,the thesis systematically studied dihydrophenazine,phenothiazine,and phenoxazine derivatives from the molecular design,property exploration,and function expansion,which provided more possibilities for the development of this field. |
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