Regulation Of Excited State Of Organic Triplet State Photosensitizers Based On BODIPY And Its Application

Triplet photosensitizers have been widely used in photon upconversion,photodynamic therapy,photocatalytic chemical reactions,and photolysis of water to produce hydrogen.The traditional photosensitizers are mainly transition metal complexes such as ruthenium,platinum,rhodium,iridium,starvation and osmium.The complexes generally have shortcomings such as short absorption wavelength,low molar extinction coefficient and high price,which greatly limit their application.Recently,a series of organic triplet photosensitizers have gradually emerged,such as of perylene,antheracene and benzophenone.However,such compounds also have the disadvantages of low molar extinction coefficient and short absorption wavelength.The fluoroboron dipyrrole(BODIPY)molecule has the advantages of easy synthesis and modification,high molar extinction coefficient,and adjustable absorption wavelength.By introducing heavy elements such as iodine and bromine,it has high inter-system efficiency and can be used as a kind of triplet state photosensitizers with excellent performance.It has been widely used in photon upconversion and photodynamic therapy in recent years.For the BODIPY triplet photosensitizers,the following problems mainly exist in the current research.First: how the number of heavy elements introduction affects the triplet performance,the research is still not clear enough;second: the absorption band is mostly concentrated in the visible region,and the triplet state photosensitizer is strongly absorbed by near-infrared;third: through the heavy element promotion system The method of squatting is relatively simple,and there are limitations in the application of heavy element photosensitizers,such as dark toxicity in biological applications and easy dehalogenation under illumination.Aiming at the above problems,this paper uses the BODIPY molecule as the parent unit to control the excited state of the molecule by introducing heavy element iodine and increasing the conjugated structure,and studies the effect of heavy elements on the transition between BODIPY molecules.A series triplet photosensitizers containing no heavy elements were synthesized based on the spin orbit charge transfer intersystem crossing(SOCT-ISC)mechanism.In this paper,several photophysical properties of their excited states are studied in detail by steady state and transient absorption/emission spectroscopy combined with density functional theory(DFT)calculations,and their basic applications in upconversion and sensitized singlet oxygen are studied.Research.details as follows:First,we used BODIPY as the parent unit and introduced different numbers of heavy element iodine at its central position to synthesize single-point,double-iodide,tetraiodide BODIPY molecules(MIBDP,DIBDP,TIBDP).The photophysical properties were studied in detail.Studies have shown that the iodo BODIPY molecule can effectively obtain the triplet state under the driving of light.However,as the number of iodine increases,the efficiency of their intersystems decreases,and the quantum yield of sensitized singlet oxygen also decreases.In addition,the MIBDP and DIBDP molecules can realize the upconversion of green light to blue light under 532 nm excitation,among them,MIBDP upconversion quantum yield can reach 9.15%.and the TIBDP molecular solution can realize the upconversion emission of orange light to green light under the excitation of 589 nm light.However,the photosensitizer in the above work still has the shortcoming of short absorption wavelength.Therefore,we introduce thiophene vinyl groups at the 3,5 positions of the BODIPY molecule to increase the conjugation of the molecule,and promote the intersystem enthalpy by heavy element iodine substitution.The more efficient the strategy,the synthesis of a class of BODIPY molecules with adjustable absorption wavelengths,as well as their photophysical properties were studied in detail.The introduction of thiophene at the 3,5 position of the molecule can significantly shift the absorption red,and the absorption wavelength is regulated from 501 nm to 650 nm.However,the study found that while the redshift is absorbed,the triplet lifetime is shorter,and their triplet lifetime is only 2.4 ?s and 1.3 ?s.When BDP-2I-1S,BDP-2I-2S molecules were used to sensitize singlet oxygen,their singlet oxygen quantum yields were 98% and 35%,respectively.Finally,in order to explore a new method to improve the efficiency of intersystem crossing,we synthesized a class of triplet photosensitizers BODIPY based on SOCT-ISC by introducing a series of different electron donor groups at the 8 position of BODIPY molecules.BDP-O,BDP-2-MN,BDP-2-EN.Studies on their photophysical properties revealed that there is a significant electronic coupling(2.11 D,2.49D)between the ground state and charge transfer state of BDP-2-MN and BDP-2-EN,which can generate charge separation.Femtosecond transient absorption tests were used to confirm that they generate charge separation and charge rearrangement under excitation of light,which further induces intersystem crossing.The nanosecond transient absorption test yielded triplet lifetimes of BDP-2-MN and BDP-2-EN molecules of 37 ?s and 42 ?s,respectively.The synthesized pure organic triplet photosensitizer is applied to the triplet-triplet state quenching upconversion,and the upconversion quantum yield can reach 4.88%.