Improving The Performance Of The Memory Device Based On Nitrogen-containing Conjugated Molecules By Tuning The Alkyl Chain And Planarity Of The Functional Group

With the development of the information, the amount of the information faced bypeople is increasing fast, so we need to store message by using better devices such asultra-high storage density and faster storage rate. In recent years, we designed a series ofpolymers and small molecules to achieve multilevel data storage, and realize the datastorage changing from2n to3n, but the research of the materials is still in its infancy. Inthis paper, we design a series of small molecules and polymers based on tuning the alkylchain and planarity of the functional group to improve the performance and stability of thememory device, mainly studied by followed aspects:1. The study of changing the alkyl chain effect on the performance of the memorydevice: three organic small molecules with different length alkyl chains based onazobenzene scaffold were designed and synthesized in order to investigate the change ofthe switch voltage by extending the alkyl chain. The switch threshold voltage of memorydevices significantly decreased as the end-capping alkyl chain extending, which are totallyconsistent with the AFM and X-ray diffraction results that the thin films showed smoothermorphologies and closer intermolecular packing with the molecular alkyl-chain lengthprolonging. These results demonstrated that variation of the alkyl-chain length in the endof the conjugated molecules is a powerful strategy of tuning film microstructure andintermolecular packing to enable high performance of the fabricated sandwiched devices.2. Investigation of changing the planarity of the donor moiety effect on theperformance and stability of the memory device: Two conjugated small molecules weresynthesized by Heck coupling reaction, wherein1,8-naphthalimide acted as an electronacceptor, while either carbazole or triphenylamine, acted as electron donors, in order toinvestigate the change of reproducibility of switching phenomenon by enhancing theplanarity of the donor moiety. The results indicated that the reproducibility of the switchingphenomenon for the memory device based on the carbazole containing naphthalimide derivative was much better due to the rigid carbazole moiety which improved the surfacemorphology as revealed by atomic force microscopy measurement. Therefore, thesignificance of the coplanarity of the donor moiety on improving reproducibility ofswitching phenomenon for memory device applications was revealed.3. Investigation of changing the planarity of the donor moiety effect on theperformance of the ternary memory device: On the base of system2, we add a nitro to theend of molecule to form two A-D-A molecules in order to investigate the change ofmemory performance by enhancing the planarity of the donor moiety and effect of thestorage mechanism by the nitro group. The results showed the performance of memorydevice based on the carbazole derivative was better due to the planar carbazole beneficialfor the surface morphology as revealed by atomic force microscopy measurement and thedevice based on the both materials showed ternary memory characteristics.4. Investigation of changing the bridge length in the liquid crystal polymers effect onthe performance of memory device: two polymers were synthesized with the sameazobenzene skeleton in the centre and different bridge length. Both polymers showedliquid crystal behavior. Results showed that the device based on the both materials showedternary memory characteristics when they were in the liquid crystal state, mainly due to themore orderly molecular packing in the liquid crystal state.