Design And Synthesis Of A-d-a Small Molecule Materials Based On Porphyrin

The research on non-fullerene acceptor materials in the field of organic solar cells is international hotspot.Thanks to the development of A-D-A(acceptor-donor-acceptor)small molecule acceptor materials,the current energy conversion efficiency of batteries is constantly being refreshed,which further encourages people to carry out more in-depth research on such small molecule acceptors about their molecular design and the relationship between molecular structure and performance.Porphyrin has an electron-rich planar rigid conjugated large ?-ring structure,unique photoelectric properties,and plays an important role in the energy conversion process in nature.Small molecular acceptor materials based on porphyrin also exhibit encouraging performance.This paper mainly focuses on the research of porphyrin-based A-D-A small molecule compounds.With the aim of improving the synthesis yield of porphyrin monomers,clarifying the regulation laws of the absorption spectrum of A-D-A porphyrin small molecule photovoltaic materials,three A-D-A porphyrin small molecule materials with electron-rich porphyrin derivative as the core D unit and pyrrolopyrrole dione(DPP),or isoindigo(Iso)or 1,1-dicyanomethylene-3-Indanone(DCI),which possess different electron withdrawing ability,as A unit,were designed and synthesized.The synthesis law of porphyrin monomer and the relationship between molecular structure and its absorption spectrum and energy level structure were deeply studied.First,we designed and synthesized a porphyrin derivative core unit—5,15-bis-(4-isooctyloxy-benzene)porphyrin,and studied the effect of synthetic route and conditions on the yield of porphyrin derivative monomers.The yield were successfully increased to 48%.Subsequently,the alkyne bridge was introduced into the meso position of porphyrin,and two types of A-D-A porphyrin small molecule photovoltaic materials DPP-P(Zn)-DPP and Iso-P(Zn)-Iso were constructed through the Sonogashira coupling reaction.It was found that these two small molecules have excellent thermal stability and good optical absorption characteristics.Their thermal decomposition temperatures are 330?and 380?,and their optical band gaps are 1.34 eV and 1.36 eV,which are typical narrow band Gap compounds.Due to the strong electron-withdrawing ability of the DPP unit,the absorption of the material in the near infrared region is more sufficient.Compared with Iso-P(Zn)-Iso,the absorption spectrum of DPP-P(Zn)-DPP is significantly red-shifted by about 20 nm.LUMO energy level is also lower.From the DFT simulation calculations,it can be seen that the strong charge absorption will pull the electron cloud more towards the end group position,which is conducive to enhancing the ICT effect and reducing the energy level of the material.The design and selection of end group units can effectively adjust the molecular arrangement and photoelectric properties of the material.We combined 1,1-dicyanomethylene-3-indanone and its fluoro derivatives with porphyrin core units to synthesize small molecule ICT-P-ICT and star compounds Por-TIC and Por-TICF.Their geometric structure and molecular orbital electron cloud distribution were studied by density functional theory calculation(DFT).The results showed that ICT-P-ICT has lower energy levels and stronger intermolecular forces,which is more conducive to improve the absorption in the near infrared region.For star compounds,due to the planarization effect of the four acetylene bridges,the dihedral angle formed by the end group unit and the porphyrin core is only 19°,which is smaller than the dihedral angle of other small molecule acceptors containing porphyrin units reported previously.It is conducive to enhancing ?-? stacking between molecules and improving the carrier's transmission capacity.In addition,compared with Por-TIC,the LUMO energy level of Por-TICF is significantly lower,which is attributed to the strong electron-withdrawing ability of fluorine atoms,this fluorination end group can reduce the energy level of the material.