Construction And Application Of Long-Lived Heavy Atom-Free Triplet Photosensitizers

Heavy atom-free triplet photosensitizers(PSs)have attracted much attention due to its low cost,less toxicity and the long-lived triplet lifetime.However,as heavy atom-free PSs are still in its infancy,most of the PSs have to rely on heavy atoms.It is still challenging to design heavy atom-free triplet PSs.This thesis focuses on the design of heavy atom-free triplet PSs,the exploration of its molecular structure-intersystem crossing(ISC)relationship,and its application in photodynamic therapy(PDT)and triplet-triplet annihilation(TTA)upconversion.Radical enhanced intersystem crossing(EISC)mechanism was employed to enhance the ISC of Bodipy(BDP-TEMPO-2).For the first time,both highly efficient ISC(?T=80%)and long-lived triplet state(?T=62 ?s)were achieved through a flexible linker with appropriate length.Due to the flexible linker,two kinds of conformation are present in one molecule:the extended conformation(r=13 A,electron spin-spin exchange integral JTR=170 MHz)weakens the electron exchange interation and prolongs the triplet state lifetime,and the folded conformation(r=8 A,JTR=1.2×104 MHz)remains strong electron exchange interation and high triplet quantum yield.BDP-TEMPO-2 was applied in TTA upconversion with an upconversion quantum yield of 6.7%.With similar flexible linker,Pery-TEMPO was designed.Compared with radical labeled perylene dyads reported in literature(?T=0.1?s),Pery-TEMPO has a significantly longer triplet lifetime(?T=90.2 ?s).With a red-light absorption chromophore naphthalenediimide,NDI-TEMPO was designed for biological application and it exhibits excellent PDT effect(light toxicity EC50=3.22 ?M)due to its high triplet quantum yield(?T=74%)and long triplet lifetime(?T=8.7 ?s).Spin-orbit charge transfer(SOCT)was employed to enhance the ISC of Bodipy(BDP-AN and BDP-Pery compounds).With various molecular structures and orientations,the structure-SOCT-ISC relationship was investigated in the view of molecular geometry,spin density and polarity of solvent.BDP-AN-1 was applied in TTA upconversion and high upconversion quantum yield was achieved(?UC=15.8%).BDP-Pery-2 was applied in PDT in vitro and potent PDT effect(high light toxicity EC50=76 nM and low dark toxicity EC50=85.1 ?M)were presented.These new-type heavy atom-free triplet PSs increased the diversity of the photosensitizers for TTA upconversion and PDT regents.Direct excitation of the charge transfer absorption band(So?1CT)minimized the energy loss of ISC,being a novel method to increase anti-Stokes shift in TTA upconversion.