Investigation Of The Photoredox Reaction Mechanism Of 1,4-naphthoquinone Derivatives Using Time-resolved Spectroscopy And DFT Calculations

Naphthoquinone and its derivatives have been widely used in drug synthesis.The aromatic carbonyl group in the chemical structure of naphthoquinone is a good chemical reaction site,which can take place in many photochemical reactions such as Norrish reaction,photocyclization reaction,and photorearrangement reaction.Therefore,naphthoquinone compound is a model molecule for studying the hydrogen and electron transfer processes.Recently,a new class of intramolecular photoredox reaction of naphthoquinone has been reported.Under the irradiation,naphthoquinone derivatives generated photocyclization products,where the carbonyl group was reduced into alcohol,and the alkyl in the side chain was oxidized by losing a hydrogen atom.The intramolecular photoredox reaction attracts wide attentions of researchers due to the high efficiency of the reaction and environmental friendliness.Therefore,it has important application prospects in the new photochemical synthesis methods of naphthoquinone derivatives.The mechanism study of the photoredox reaction for naphthoquinone compounds could guide the development and application of naphthoquinone drugs.In this thesis,comprehensive time-resolved spectroscopies,including femtosecond time-resolved transient absorption spectroscopy,nanosecond time-resolved transient absorption spectroscopy,and time-resolved resonance Raman spectroscopy,combined with density functional theory(DFT)calculations,were utilized to study the photoredox reaction mechanism of naphthoquinone compounds of NQ and MNQ with different substituents.It is unraveled that upon irradiation,the excited triplet state of NQ was produced via an efficient intersystem crossing process due to the existence of the methoxyl group.Then,the biradical intermediate was produced by an intramolecular hydrogen atom transfer reaction,which took place during the intramolecular electron transfer to produce a zwitterion specie.Finally,the intramolecular photoredox product was formed by a cyclization reaction.Irradiation of MNQ containing an isoamyl olefin side chain,generated the ionic intermediate 1,3-QM by proton transfer in the excited singlet state,then the conjugated alkene formula 1,2-QM was obtained by the configuration alternation.Finally,the cyclization product was obtained through the electron cyclization process.This thesis consists of four chapters.The first chapter is the introduction part,which summarizes the photoredox reaction background and the research progress of naphthoquinone compounds,and introducing the time-resolved spectroscopy and density functional theory.In chapter 2,based on the results of time-resolved spectroscopy and density functional theory,the photoredox reaction mechanism of NQ is clarified in details.The third chapter studies the photoredox reaction mechanism of the MNQ through time-resolved spectroscopy and density functional theory calculation results.In chapter 4,the effects of substituents and solvents for the photoredox reaction pathways of 1,4-naphthoquinone compounds are summarized and discussed,and the future directions in this research area are proposed.