The Friedel-crafts Steric Hindrance,Ladder-like Grid And Singlet Fission Of Diketopyrrolopyrrole

Diketopyrrolopyrrole(DPP),a common molecular building block with a strong?-?conjugated structure,and its planar frame structure is easy to form hydrogen bonds,which can promote the superposition of?-?electron clouds,and the high electron mobility has been achieved;the amide structure makes it have a strong electron withdrawing ability.For its high planarization and high mobility,it is widely used in the field of organic optoelectronics.Such as,it is often used in organic photovoltaic(OPV),organic light-emitting diodes(OLED),organic field effect transistors(OFET),biological/chemical sensors(Sensor),two-photon absorpion(TPA)material and a singlet fission(SF)material,etc.In the field of organic solar cell applications,Singlet Fission is a very promising strategy to improve photovoltaic efficiency,currently,but it is not suitable for solar cells due to the difficulty of energy level matching between the material layers.In order to achieve the singlet fission to be widely used in solar cells and play an important role,it is urgent to design and develop new singlet fission optoelectronic materials.The singlet fission material should contain good stability(in the air),strong light absorption,excellent solution processability and low price.The chromophore,diketopyrrolopyrrole(DPP),fits these criteria very well,and is an ideal skeleton unit for the design of singlet fission photoelectric materials.We have carried out systematic research on DPP materials,and our work is mainly carried out from the following three aspects:First,based on our previous work,the molecular structure was modified by introducing DPP fragments into the fluorene-based framework to explore whether DPP and fluorene tertiary alcohol can undergo Friedel-Crafts reaction.From the perspective of molecular design,D-A fragments were introduced,that is,fluorene tertiary alcohol as an electron-donating fragment and DPP as an electron-withdrawing fragment.Based on the relatively mature Friedel-Crafts reaction in the group,it's confirmed that DPP and fluorene tertiary alcohol can undergo Friedel-Crafts reaction by continuous optimization of the reaction conditions,different reaction substrates were expanded,comparisons were made,the series laws of Friedel-Crafts reaction were obtained,and four materials(DPFC8DPP,PFC8DPP,TBr PFC8DPP and DBr PFC8DPP)based on the DPP-I-shaped bromine-containing mono-substituted and double-substituted sterically hindered framework were prepared.For the design and synthesis of subsequent materials,a series of optical and electrical tests were performed.The test shows that compared with the mono-substituted molecules(PFC8DPP and DBr PFC8DPP),the absorption and emission spectra of di-substituted molecules(DPFC8DPP and TBr PFC8DPP)have no new characteristic peaks,and the absorption and emission spectra of the solution state show partial red shifts,which may be caused by the introduction of the disubstituted fluorenyl skeleton;compared with DPFC8DPP and PFC8DPP,the absorption and emission spectra of bromine substituted molecules(TBr PFC8DPP and DBr PFC8DPP)have no new characteristic peaks,and the emission spectra of the solution state show a partial red shifts.The reason may be the introduction of halogen atoms;the electrochemical stability of double substituted molecules(DPFC8DPP and TBr PFC8DPP)has been improved to a certain extent.This work provides a basis for the subsequent design and development of new DPP singlet fission materials,and broadens the research scope of DPP materials.Second,on the basis of the work in the first part,the molecular structure is further modified,To study whether the gridization strategy can be used to react between DPP and difluorenol to obtain a grid,that is,to explore whether DPP and difluorenol can undergo Friedel-Crafts reaction.Based on the Friedel-Crafts reaction,three different close-loop methods for preparing the ladder-shaped grid have been explored:L-shaped close-loop,U-shaped close-loop and one-step close-loop with four-bond or six-bond.Through continuous optimization of the reaction conditions,the production of the ladder-shaped grid prepared by one-step close-loop with four-bond or six-bond is more suitable,with fewer synthesis steps,and four target synthons and grids can be obtained in one step.This part of the work provides a path reference for the design of DPP materials with richer synthetic structures,and also provides a basis for further research on the relationship between structure and performance.Third,based on the work of the second part,the singlet fission properties of the two grids that have been successfully prepared in the second part are studied.We found that DPP dimer 2grid has singlet fission,and DPP trimer 3grid doesn't have singlet fission.Steady-state absorption and fluorescence spectroscopy tests show that the polarity of the solvent plays the most important role in the CT state or SBCS state.The CT state mediates i-SF,and non-polar solvents such as toluene are harmful to any triplet excited state,only polar solvents such as benzonitrile can form triplet excited state pairs ¹(T₁T₁),and there is a singlet fission process;For 2grid,femtosecond and nanosecond transient absorption spectroscopy tests show that the absorption signal of the intermediate state(S₁S₀)_CT and the triplet excited state pairs ¹(T₁T₁)can be observed in the polar solvent benzonitrile,(S₁S₀)_CT as the intermediate state can effectively promote the singlet fission process,for 3grid,the absorption signal of the intermediate state SBCS can be observed in the polar solvent benzonitrile,and the absorption signal of the possible triplet excited state T₁ is not observed.The SBCS with only obvious CT characteristics is not conducive to the singlet fission process.This work is an important development of DPP"ladder-shaped grid"sterically hindered framework materials in the study of intramolecular singlet fission(i-SF)of DPP dimers.It provides a very feasible solution for the design of subsequent DPP dimers,trimers and even multi-polymer singlet fission materials.There are obvious differences in the singlet fission properties before and after gridization,that is,gridization is conducive to the singlet fission process,and the gridization method provide a new way for the preparation and the properties of singlet fission materials.