Optimization Of Electronic Memory Device Performance Via Tailoring The Structure Of Nitrogen-containing Conjugated Organic Small Molecules

The Twenty-first century we are experiencing now is a new information age which is accompanied by the explosive development of information in a geometrical progression. Although current technologies allow people to store dozens or even hundreds of gigabytes of data on fingernail-sized storage medium, when we face with the age of big data when the storage of large masses of data is critical, our existing information-storage techniques has hit its bottleneck. High information density has attracted increasing interest. In 2010, our research group firstly reported the small organic molecule-based ternary memory device, providing a possible solution for the realization of high-density data storage(HDDS) in the future. Based on this, thirteen conjugated small molecules were rationally designed and successfully synthesized. The relationship between the molecular structure and electrical memory device performance was investigated. The main research works are described as following:(1) Investigation of the influence of cyclic alkyl groups and their spatial distortion on molecular planarity and device performance. Three conjugated small molecules with different planarity which were tailored by the alkyl chain were designed and synthesized. The memory performances based on three molecules were investgated. While the alkyl chain changes from cyclic to methyl, the planarity of the molecules was significantly improved, and the intermolecular π-π stacking become stronger which would facilitate the charge transport through the neighboring molecules and reduce the charge barrier between the film and the electrode, leading to the lower threshold voltages and higher ON/OFF current ratios. We hope these results can provide a reference to the future design of low power consumption storage materials.(2) Investigation of the influence of different molecular aggregation mode in th film state on electrical memory device performance. Two geometrical isomers(p-BQBTZ and m-BQBTZ) which were distinguished by the position of thiazole group were synthesized. The reasults revealed that p-BQBTZ prefers H-aggregation in the film state, whereas m-BQBTZ prefer J-aggregation. It was observed that the switch threshold voltages of p-BQBTZ based device was lower than that of m-BQBTZ due to its stronger π-overlapping which will certainly benefits the chargecarrier mobility in the film state. This work demonstrates that minor adjustments of the molecules structure can significantly influence the molecular aggregation mode in the film state and effectively optimize the performance of memory device, especially the threshold voltages. We also belive that these results can offer useful reference to the future design of low power consumption storage devices.(3) Investigation of the influence of conjugation extent of the terminal electron donating moieties within molecules on electrical memory device performance: Three small organic molecules of the same electron acceptor but different electron donors were synthesized. The results reveal that the fabricated devices from the three molecules exhibited nonvolatile ternary WORM character whilst the switch threshold voltages decreased from TPA to CZ and AN. This is due to the spatial distortion of TPA group leading to the lower quality of film morphology and the weaker conjugation extent between electron donor and acceptor. Further theoretical calculations revealed that AN-PTZO-CN has the smallest dihedral angle between the donor group and its neighboring benzene ring, resulting in the lowest value. These results revealed that tailoring the conjugation degree of the terminal electron donor in the D–A molecules could effectively optimize the device performance, in particular the switch-threshold voltage, which could be instructive for the design of low-energy-consumption memory materials.(4) Investigation of the effect of the number of electron-withdrawing groups in molecular backbone on electrical memory device performance. Three small organic molecules which contain one, two and three electron-withdrawing groups were synthesized and the effect of the number of electron-withdrawing groups in molecular backbone on electrical memory device performance was also investgated. The results confirm that improving the storage hexadecimal by increasing the number of electron-withdrawing groups in molecular backbone is a feasible strategy and provide a solid evidence for our proposed “charge trap” mechanism. Also, through introduction of three electron-acceptors in molecules quanternary memory storage was achieved which provide a possibility for the future realization of HDDS.(5) Synthesis of organic molecules containing three electron-acceptors and the investigation of their quanternary memory characteristics: Two phenothiazine-derived organic small molecules which contain three electron-acceptors were designed and synthesized. The memory characteristics of the two molecules based memory devices were investgated. The results revealed that the memory devices based on the two molecules exhibited a certain quanternary WORM memory characteristics.