Novel Triplet Photosensitizers Containing Perylenebisimide:Synthesis And Study Of Photophysical Properties

There are many methods for designing of triplet photosensitizer.How to design heavy-atom-free triplet photosensitizers is crucial.Charge recombination(CR)induced intersystem crossing(ISC),which termed SOCT-ISC,has became a promising design strategy of heavy-atom-free triplet photosensitizers,because of the simple molecular structure with no heavy atom and the formation of intra-molecular charge separated state,which can be controlled by the external condition(such as temperature and solvent polarity).However,the systematic research on this ISC is not sufficient so far,such as the effect of molecular conformation on the ISC effiency and etc.Rationally designed photosensitizers for application by using this mechanism also has not been studied.Therefore,in order to address the above problems,perylenebisimide(PBI)was selected as the chromophore and electron acceptor for desiging molucules in this thesis.Steady state/transient spectroscopy,electron magnetic resonance spectroscopy,electrochemical analysis and theoretical calculation were used to fully investigate photophysical properties of the molecules and the impact factors of SOCT-ISC process.First,three perylenebisimide-phenothiazine(PTZ)dyads were synthesized with the electron donor PTZ substituted at the 6-position of PBI.The C-N/C-C linkage was used to change the steric hindrance of the torsion between PBI and PTZ.The UV-VIS absorption/fluorescence emission spectra of the compounds confirmed that this method can effectively control the geometry of the molecule,thereby changing the intramolecular electronic coupling strength.Femtosecond transient absorption spectroscopy demonstrates the charge separation(0.3-0.6 ps)and charge recombination(130-240 ps)processes of the molecule.The study of nanosecond transient absorption spectroscopy found that PBI-1 with orthogonal configuration had weak ISC ability and generated triplet state in low yield.Whereas,for PBI-3 with more coplanar configuration,the triplet state was formed with the lifetime of 13.7 ?s.Therefore,the orthogonal configuration is not the sufficient prerequisite for the SOCT-ISC,and energy level matching of the charge transfer(CT)states and the triplet states may also be an important factor for SOCT-ISC.Second,to change the substitution position of the electron donor,three perylenemonoimide(PMI)-phenothiazine dyads were synthesized by using the similar steric hindrance method.Singlet oxygen sensitization experiments and nanosecond transient absorption spectroscopy confirmed the molecular orthogonal geometry,relative orientation of the dipole moment of the electron donor and acceptor,electronic coupling as well as solvent polarity affect the SOCT-ISC.The singlet oxygen quantum yield of PMI-N-PTZ is 57% and the triplet state lifetime is up to 200 ?s.Thus,PMI-N-PTZ was used as photosensitizer to induce the delayed fluorescence of some triplet acceptors such as 9,10-biphenylethynyl anthracene and perylene,etc.The fluorescence lifetime was extended to a maximum of 44 ?s.Moreover,PMI-N-PTZ can undergo the intermolecular electron transfer reaction with the sacrificial electron donor triethylamine upon photoirradiation and reversibly produces the radical anion of the PMI moiety.