Studies On Photophysical And Photochemical Properties Of BODIPY Compounds Based On PET/PCT Mechanism

In recent years,BODIPY has been used as a new photosensitizer in photodynamic therapy（PDT）of tumors.In the presence of light and oxygen,the modified BODIPY compound can effectively produce singlet oxygen,which plays a major role in the irreversible cell damage and cell death of normal tissues and malignant tumors.Therefore,how to effectively increase the singlet oxygen production of BODIPY compound rate has become a hot research topic.In this thesis,the core of BODIPY was modified,and different groups were introduced at the meso position.Three different series of BODIPY compounds were synthesized.For the first series of BODIPYs,meso-phenyl and meso-naphthyl substituted BODIPY derivatives were synthesized as singlet oxygen photosensitizers.Studies have found that the introduction of-OCH₃or-OH groups on phenyl and naphthyl can enhance the electron donating ability of phenyl or naphthyl.The increase in the ability to donate electrons leads to an increase in the ability to generate singlet oxygen.For the second series of BODIPYs,seven compounds of BODIPY-electron acceptor（A）type were synthesized,in which an x-nitro-phenyl（x=ortho,meta,and para）or a pyridyl subunit on the BODIPY meso-position acts as the acceptor.The excited triplet state and singlet oxygen formation efficiency decreased with the increase in the electron withdrawing ability of the phenyl moiety.Attaching the electron acceptors to BODIPY cannot mediate excited triplet state formation via CS-CR mechanism,which is in sharp contrast to the case of BODIPY-electron donor type conjugates.For the third series of BODIPYs,different dialkyl-modified amino groups were introduced at the meso position.It was found that the dialkylamino,a small non-aryl electron donor,could generate singlet oxygen and excited triplet state selectively and very efficiently in nonpolar media.It was found that these BODIPY compounds could effectively produce singlet oxygen and the formation of excited triplet state was related to the CSS/CTS state,which is different from previous BODIPY photosensitizers.It was also found that with the increase of the electron-donating ability of the aryl group,the PET/PCT efficiency increased significantly,which led to an increase in the yields of singlet oxygen;when the solvent polarity increases,the fluorescence quantum yields decreased;the introduction of the steric hindrance could hinder the rotation of the aromatic ring,which resulted in significantly higher quantum yields for singlet oxygen formation.The results above can be explained by the involvement of photoinduced electron or charge transfer process in the lowest lying excited singlet state.It is believed that the PET or PCT based donor-BODIPY type photosensitizers have good potential for application in PDT and theranostics.