Synthesis And Electrical Bistable Memory Performance Of Metalloporphyrin Polyimides

Organic memory materials have become one of the alternative materials for new generation memory devices because of their ability to make molecular-sized devices.Compared with the conventional materials,organic memory device has the advantages of rich structural flexibility,high expandability,low cost,three-dimensional stacking capability,high memory density and ease of processing.Polyimide has excellent thermal properties,high mechanical strength and rich structural diversity making it one of the best choices for organic memory materials.In recent years,porphyrin polyimides have become a research hotspot in the fields of photoconductive materials,thin film chemical sensors,and electric bistable memory materials because of their good photoelectric properties.Porphyrin are easy to chemically modify,and can form stable complexes with a variety of metals,resulting in unique structures and properties.Porphyrin polyimide and three kinds of metalloporphyrin polyimides were synthesized to investigate the influence of different metal ions complexed in the middle of porphyrin ring on the memory properties.We design porphyrin polyimide and three kinds of metalloporphyrin polyimides(Por-cis-DATPP-6FDA,ZnPor-cis-DATPP-6FDA,CuPor-cis-DATPP-6FDA and NiPor-cis-DATPP-6FDA)with porphyrin groups as electron donors and hexafluoro dianhydride(6FDA)as electron acceptors.Their photophysical properties and electrochemical performance show that the energy gap become bigger and the charge transfer of metalloporphyrin polyimide becomes more difficult.At the same time,the charge transfer complex formed within the molecule is more stable.A sandwich structure device with porphyrin polyimides as the working layer,ITO as the bottom electrode and Al as the top electrode was prepared,and its memory performance were tested:Por-cis-DATPP-6FDA is non-volatile WORM storage characteristics,while the other three metalloporphyrin polyimides ZnPor-cis-DATPP-6FDA,CuPor-cis-DATPP-6FDA and NiPor-cis-DATPP-6FDA all exhibit volatile SRAM memory characteristics.The electronic structure and geometric conformation of porphyrin polyimides were calculated by molecular simulation.It was found that the metalloporphyrin polyimides have slightly larger energy gap and dipole moments than the porphyrin polyimides.The charge transfer process becomes difficult and the charge transfer complex formed is more stable.In addition,as the work function of the complexed metal increases,the dihedral angle between the donor groups and the acceptor groups of the metalloporphyrin polyimide increases,which also makes the charge transfer more difficult and the charge transfer complexes become more stable.Combining the memory properties of porphyrin polyimide and metalloporphyrin polyimides,it is considered that metal ions act as internal bridges making charge transfer between the donor groups and the acceptor groups easier.After the external electric field was removed,the charge transfer complex decomposed and device recovers from ON state to OFF state,the metalloporphyrin polyimide memory device exhibits a volatile property.The effect of complexing different metals on the memory properties of porphyrin polyimides and their mechanism were investigated,provides new research ideas for designing polymer-based information storage materials with different memory behaviors,and at the same time provides research foundation for realizing polyimide memory materials with light control behavior.