Study Of Novel Bodipy-Derived Heavy Atom Free Triplet Photosensitizers

Triplet photosensitizers(PSs)are widely used in numerous applications.The intersystem crossing(ISC)of traditional PSs rely on heavy atom effect(HAE)of transition metal atoms or bromine and iodine atoms,which introduce some applied limitation.Heavy atom-free triplet PSs have attached much attention due to its less toxicity,cost efficiency economy and longlived triplet state.Some challenges still exist,for instance,the relationship between molecular structure and photophysical properities is still unclear,the lack of variety of chromophore and indistinct insight on drving force of ISC.Therefore,this thesis focuses on the design and application of Bodipy-derived heavy atom-free triplet PSs based on spin-orbit charge transfer intersystem crossing(SOCT-ISC)and twisted structure enhanced ISC.The research is helpful for design of novel heavy atom-free triplet PSs.SOCT-ISC mechanism was employed to design the electron donor and acceptor(D-A)molecules to study the relationship between molecular structure,mutual orientation and SOCTISC efficiency.A heavy atom-free triplet PS BDP-PXZ-1 was obtained with strong absorption(?=7.4 × 104 M-1 cm-1 at 504 nm),high ISC efficiency(?T=54%)and long triplet state lifetime(?T=539 ?s).BDP-PXZ-1 was applied in triplet-triplet annihilation(TTA)upconversion to realize quantum yield of 12.3%.The relationship between SOCT-ISC and ability of electron donor was studied by Bodipy-thienyl electron D-A dyads.PhenoxazinestyrylBodipy electron D-A dyads with strong red light absorption was accessed with SOCTISC mechanism.A long-lived triplet state(?T=333 ?s)was observed for the new dyad,which is prolonged by a factor of 180 compared to the triplet state of the same styrylBodipy chromophore but accessed by HAE(?T=1.8 ?s).A Bodipy derivative with twisted ?-conjugation(torsion angles 17°)is demonstrated showing efficient ISC(?T=56%)and high triplet state energy(ca.1.5 eV).Without the detrimental effect of the heavy atom,long-lived triplet state was obtained in solution(?T=197.5?s)and in polymer film matrix(?T=4.5 ms),respectively.It is prolonged by a factor of 6 and 2500 compared to diiodoBodipy and diiodostyrylBodipy,respectively.The drving force of ISC was the increase of spin-orbit coupling matrix elements together with the matched energy of S1 and T2/T3 states.Time resolved electron paramagnetic resonance results demonstrate the electron spin selectivity of the twisted Bodipy is different from normal spin orbital coupling ISC.High light toxicity(EC50=1.0?M)and low dark toxicity(EC50=78.5 ?M)was observed for the twisted Bodipy as a novel heavy atom-free photodynamic therapy(PDT)reagent.