Theoretical Insight Into The Two-photon Absorption Properties Of Transition Metal Complexes Photosensitizers

Two-photon photodynamic(TP-PDT)has crucial roles in curing tumors,and it has drawn much attention in recent years due to its ability to penetrate deeper into tissues and minimize the damage to normal cells.However,the two-photon photosensitizers suffer from several limitations such as poorly penetrate into the biological tissue,poor water solubility,and high cost,which severely limits the practical applications and further development of TD-PDT in the biomedical field.Therefore,it is important to explore new two-photon photosensitizers and explain the mechanism of two-photon photosensitizers.The study of transition metal photosensitizers for TP-PDT is needed to be completed,and it is the area with a great development potential and wide application foreground.In this paper,the properties of a serious of transition metal complexes as photosensitizers were studied by quantum chemistry,including geometrical structures,one-photon and two-photon absorption properties,spin-orbit coupling constants,triplet excited lifetimes.The aim of this study is to explore the relationship between the molecular structure of transition metal complexes and the properties of one and two-photon.It is expected that our study can provide some ideas and guidance for exploring novel photosensitizer with large two-photon absorption cross section,low price and good performance.The main research contents are as follows:1.The OPA and TPA properties of Ru(?)and two Zn(?)polypyridyl complexes were studied by Density Functional Theory(DFT)and Time-Dependent Density Functional Theory(TD-DFT).Result shows that different solvents have little effect on the one-photon absorption(OPA)spectrum.As for two Zn(?)-centric complexes,their absorption wavelengths are blue-shifted in comparison with Ru(?)-centric complex.The central metal ion has a significant effect on the electron absorption spectrum and orbital transition.Furthermore,increasing the ?-conjugate greatly increases the value of TPA cross-section.2.The geometrical structures,electronic structures.OPA and TPA spectrums,TPA cross-sections,triplet excited lifetimes and spin-orbit coupling constants of complexes[Ir(N^C)2(N^N)]-and[Rh(N^C)2(N^N)]+ were studied in detail.The study shows that the TPA peaks of the two complexes are at 749.0 nm and 649.2 nm,respectively.Moreover,the designed Rh(?)complexes have a larger two-photon absorption cross section and longer triplet excied lifetime(549 ?s)than Ir(?)complex.3.To explore the photophysical properties of Ru(?)-centric and two Zn(II)-centric photosensitizers.Through the analysis of hole-electron distribution,orbital characteristic,and fragment charge transfer,it is found that Ru(?)-centric complex exhibits MLCT,MC,and LC characteristics,while two Zn(?)-centric complexes LC character.At the same time,increasing the aromaticity of ligands can efficiently increase the TPA cross-section,which is crucial for the application of potential photosensitizer in photodynamic therapy.4.A series of photophysical properties of three complexes for Ru(?)-centric and Zn(?)-centric were explored in this work.Research shows that the designed Zn(?)-centric complexes process higher T1 energy than Ru(?)-centric complex,which is conducive to the generation of singlet oxygen toxicity.In addition,three complexes can produce not only 1O2 via Type-? mechanism,but also O2·(-)via Type-? mechanism to kill cancer cells in TP-PDT to produce.It indicates that Zn(II)-centirc complexes have the potential to be an excellent photosensitizer for two-photon photodynamic therapy.