基于卟啉化聚酰亚胺的电双稳信息存储材料的制备及其机理研究

A series of porphyrinated polyimides, including porphyrin polyimides, mono-metal porphyrin polyimides, mono-metal porphyrin copolyimides, and bi-metal porphyrin copolyimides, are planned to be synthesized in this work through the condensation polymerization of the diamino compounds of tetraphenylporphyrin as well as their metal (13 kinds) complexes, which function as the electron-donating species, with selected dianhydrides possessing different electron-withdrawing ability. The electrical bistable memory behaviors of the synthesized porphyrinated polyimides will be evaluated. Various factors influencing the electrical bistable characteristics, such as the chemical structure (including the metal speciation, the metal content, the different bi-metal combination and bi-metal ratio, and the dianhydride structure) and the spatial structure of the porphyrinated polyimides, will be investigated to establish the structure and property relationship. Simultaneously, we will elucidate the prerequisite structural characteristics of the porphyrinated polyimides which exhibit superior electrical bistable memory performances, and subsequently realize the preparation of porphyrinated-polyimide-based electrical bistable memory materials with the optimum properties. Furthermore, the electrical bistable properties of the porphyrinated polyimides under light irradiation will be examined with the expectation to prepare electrical bistable memory materials with light-induced or light-controlled characteristic, since porphyrin unit has been reported to have excellent photo-induced charge transfer effect. Finally, based on molecular simulation, the electronic structure of the porphyrinated polyimides will be calculated and systematically compared. The influence of the electronic structure variation of the metal element on the electrical property of the porphyrinated polyimide will be elaborately investigated to clarify the relationship between the electronic structure and material property. Based on the above results, we will try to setup reasonable physical model to disclose the charge transfer process in the material and explain the operation mechanism of the electrical bistable or light-controlled electrical bistable memory effects observed in the current work.

本课题拟以二氨基四苯基卟啉及其金属（13种）化合物作为电子给体，通过与具有不同电子受体能力的二酐缩聚，来合成一系列不同结构的卟啉化聚酰亚胺，包括卟啉聚酰亚胺、单金属卟啉聚酰亚胺以及单金属和双金属卟啉共聚酰亚胺；研究其电双稳存储行为，考察分子化学结构（金属元素种类、含量、不同双金属组合及比例、二酐结构）和分子空间构型对电双稳性能的影响，建立它们之间的关系，理清具有优异电双稳性能的卟啉化聚酰亚胺的结构特征，制备出性能优异的电双稳信息存储材料。进而，考察卟啉化聚酰亚胺在光激发下的电双稳性能，基于卟啉优异的光诱导电荷转移特性，以期制备具有光控行为的电双稳信息存储材料，弄清其关键影响因素。最后，通过分子模拟对卟啉化聚酰亚胺的电子结构进行系统研究，重点考察卟啉中心金属元素电子结构的变化对材料性能的影响，弄清材料的电子结构与性能关系；构建合理模型，揭示材料内部的电荷传输过程和其电双稳及光控电双稳机理。

对于聚酰亚胺存储材料，建立准确的化学结构和存储性能之间的关系是这一领域的核心挑战，在本项目中从三个角度解决这一问题。首先基于电子结构灵活可调的卟啉类化合物，通过调节卟啉中心金属离子的种类来调节聚酰亚胺的存储性能，建立金属离子电子结构与材料性能之间的关系，研究发现Zn2+和Co2+的引入有效促进杂化局域-电荷转移激发态的形成，起到金属“桥梁”的作用，促使电子在给体和受体之间激发的过程，有利于电荷转移络合物的形成和解离，分别赋予聚酰亚胺易失型SRAM和DRAM存储行为，而Cu2+和Ni2+则没有这一作用。Mn2+则可以起到金属“陷阱”的作用，吸引周围卟啉环上的电子，减弱卟啉电子给体的能力，致使聚酰亚胺无法形成电荷转移络合物，器件不具有存储行为。当调节Zn2+在聚酰亚胺中的含量时，可以有效调节“锌桥”效应，精准调控聚酰亚胺的保留特性，使得其保留时间在10秒到7分钟之间进行调节。而将“锌桥”效应引入卟啉侧基时则会额外促使电子给体内电荷转移过程的发生，使得聚酰亚胺的存储模式由二阶提升到三阶，极大的提升了其存储容量，为设计具有三阶存储功能的聚酰亚胺提供了新的策略然后调节电子给体-受体的相对含量研究电子给受体比例对聚酰亚胺的存储性能的影响，当增加聚酰亚胺中电子给体的比例时，有利于电荷转移络合物的形成和稳定，聚酰亚胺存储行为由易失型向非易失型转变。对于酰亚胺小分子，增加电子受体的数量和空间位置的分离则有利于激发态下电荷转移络合物的稳定，其存储行为由易失型向非易失型转变，证明了这一策略的有效性。最后研究了决定聚酰亚胺存储行为的另一个重要的因素—空间效应。电子给体和受体之间的空间位置决定了聚酰亚胺电荷转移过程的难易程度。当增大电子给体和受体之间的二面角或在电子给体和受体之间引入饱和脂肪链，均会破坏二者之间的共轭路径，为电荷转移络合物的解离提供一较大的能垒，使得聚酰亚胺的存储行为展现出非易失性的特征。