The Photophysical Properties And Dna Interaction Of 5,10,15-tris(4-pyridyl)corrole Complexes

Corrole is a porphyrinoid tetrapyrrolic macrocycle.Due to its superior photophysical and photochemical properties,corrole has versatile applications in photodynamic therapy(PDT),photodynamic inhibition(PDI),organic solar cell and photocatalysis.Although a number of metallocorroles have been proved as promising PDT photosensitizers,reports on their excited-state dynamics are rare.An insight into the ultrafast photophysical processes is crucial to manipulating corroles as efficient photosensitizers.In this work,the photophysical properties,DNA binding and singlet oxygen generation of a series of pyridyl corroles have been reported.Firstly,the 5,10,15-tris(4-pyridyl)corrole(1)and its phosphorus(1-P),gallium(1-Ga)and tin(1-Sn)complexes were synthesized and well characterized by UV-vis,NMR,HR-MS,and IR.Secondly,DFT calculations were performed in order to obtain their optimized geometries and frontier molecular orbitals(MOs).Both the phosphorus and gallium complexes adopted a more planar structure while the tin derivative exhibited a “domed” structure.The HOMO-LUMO gaps in the three complexes were slightly larger than that in the free-base corrole.Thirdly,their photophysical properties were investigated using femtosecond transient absorption along with steady-state and time-resolved fluorescence spectroscopy.Both 1-P and 1-Ga were highly fluorescent attributed to an acceleration in their radiative transition rate.The heavier tin atom contributed significantly to an ultrafast intersystem crossing in 1-Sn,which led to the quenching fluorescence with a lifetime as short as 233 ps.Fourthly,the DNA binding affinity of these corroles were studied by means of spectroscopic titration,circular dichroism and viscosity tests,which pointed to a more likely outside binding mode between the pyridyl corroles and DNA with an order of 1-Sn>1-Ga>1>1-P.Fifthly,their photostability and photo-induced singlet oxygen generation were evaluated to explore the potential application of these corroles as PDT photosensitizers.The three complexes showed a better photostability than the free-base corrole.All of the four pyridyl corroles were proved to be good singlet oxygen generators,of which,1-Sn showed a best yield as high as 0.71.Finally,the photo-generated reactive oxygen species in 1-Sn were detected by EPR and thus confirmed the formation of both singlet oxygen and superoxide anion.