Excited State Properties Of Pt(Ⅱ)/Ir(Ⅲ) Complexes With Long-Lived Triplet State

In the past few years,transition metal complexes showing strong visible light harvesting ability and long-lived triplet state have attracted much attention.The stronger light harvesting the higher concentration of excited state molecules can be obtained under same excitation conditions.Moreover,long-lived triple state is favorable for driving electron transfer or energy transfer.A series of this kind of new transition metal complexes have been prepared.However,there is still very few lacking in molecular designing rationales,application and excited state regulation of such molecules.Because there are few studies on excited state photophysical processes of these novel complexes,such as intramolecular single/triplet energy transfer,Sm→Tn intersystem crossing(ISC),pathways of triplet excited states generation and its influencing factors and so on.Therefore,this thesis mainly studies on excited state properties of Pt(Ⅱ)/Ir(Ⅲ)complexes showing long-lived triplet state(usually rrl>5μs,τTn>1 ps).Steady-state and transient absorption spectroscopy were used to study ultrafast ISC dynamics of two perylenebisimide(PBI)containing Ir(Ⅲ)complexes.The Sm→Tn ISC dynamics of these complexes is ultrafast,similar to the conventional Ir(Ⅲ)complexes bearing a 1MLCT→3MLCT transition.Much longer triplet decay lifetimes were observed(Ir-PBI,τT=11 μs;Ir-NPBI,τT = 7.4 μs).T1 in these Ir-PBI complexes is 3IL(intraligand)character,which has weak heavy atom effect.This result can be rationalized by theoretical computations.Spin-orbit coupling matrix elements(SOCMEs)of SmμTn in PBI containing complexes can reach to 66 cm-1,and SOCMEs of Ti-So is only 3 cm-1.In the presence of a sacrificial electron donor,coordinated PBI ligands were transformed into their radical form under an inert atmosphere,either with or without photoexcitation.The doublet excited state has a lifetime in the range of 4-7 ps.And triplet-state quenched of a certain extent with formation of radical.To study Sm→T,ISC process,a series of anthracene containing Pt(Ⅱ)complexes were prepared,due to ISC process in anthracene ligand is S1→T2.Excited state properties of these complexes were studied mainly by femtosecond transient absorption spectroscopy,long-lived upper triplet excited state(T2,τ=3-8 ns)was directly observed.By changing excitation wavelength,the generation pathway of Ti state can be changed(with or without passing long-lived upper triplet excited state),photophysical process and rate can be greatly influence.Broadband light sorce cannot be effectively utilized.Strong broadband visible(503 nm)/near-IR(731 nm)absorbing Pt(Ⅱ)complex Pt-1 was prepared with different Bodipy derivatives as ligands.Molecular structure of Pt-1 was confirmed by single crystal X-ray diffraction.Photophysical properties were well studied with steady-state/transient absorption spectroscopies,electrochemical characterization and theoretical calculations.Dual fluorescence(518 and 754 nm)was observed for Pt-1.Singlet energy transfer(TBET)rate constant in Pt-1 was determined as 2.2 × 1010 s-1,whcich from Bodipy moiety to styryl Bodipy moiety.Intramolecular triplet-triplet energy transfer(TTET)in Pt-1 was proved.And follow this process established an intermolecular TTET model,the EnT rate and energy transfer efficiency were determined as 2.5 × 104 s-1 and 94.7%,respectively.In singlet oxygen(1O2)photosensitizing experiment,Pt-1 showed the advantage of having broadband absorption ability.The above research on photophysical properties of excited state in complexes can further promote molecule design,application and property regulation.