氧化还原控制层状夹心金属碳硼烷作为非线性光学多态开关的DFT研究

Nonlinear optical (NLO) molecular switches have significant applications in data storage, optical signal processing and sensing. The multi-state NLO molecular switches become the necessary requirement in the NLO molecular switches field because they can significantly improve the function and efficiency of the molecular devices. However, there are some questions in most research systems, such as poor physical performance, slow response, or unremarkable switching. Our previous theoretical studies have shown that the peanut-shaped sandwich metallacarboranes possess significant second-order NLO switching effect induced by redox, but they are limited to be applied in multi-state NLO molecular switches because of their simplex structures and electrochemical properties. Considering the structures diversity, tailoring ability, rich electrochemical properties, and high thermal stability, the layered sandwich metallacarboranes are used to study the multi-state switchable NLO properties by density functional theory (DFT) methods in this project. We plan to analyze the relationships of second-order NLO properties of the target systems with their configurations, bonding, and metal-metal communication to reveal the microscopic nature of second-order NLO responses; summarize the calculation methods for the electronic structures and properties of target systems; design the significant multi-state switchable NLO systems through controlling the metal-metal communications based on the multi-step redox behavior of the target systems. This project will provide reliable theoretical basis to obtain a novel multi-state switchable NLO material in the experiment.

非线性光学(NLO)分子开关在数据存储、光信号处理和传感等方面的分子器件中有重要应用，而多态的NLO分子开关由于可以实现分子器件的多功能性和高效性成为该领域发展的必然要求。但目前多数研究体系存在物理性能差、响应速度慢、或开关效应不显著等问题。我们前期通过理论计算发现金属碳硼烷中花生型化合物在氧化还原过程中具有显著的二阶NLO开关效应，但结构和电化学性质的单一性使其在多态NLO分子开关的研究中受到限制。本项目拟采用密度泛函理论(DFT)方法研究结构多样、剪裁能力强、电化学性质丰富、热稳定性高的层状夹心金属碳硼烷的多态NLO分子开关效应：分析目标体系的二阶NLO性质与构型、成键方式、金属-金属相互作用的关系，揭示二阶NLO响应的微观本质；归纳计算电子结构和性质的合理方法；以多步氧化还原为参考，调节金属-金属相互作用以得到显著的多态NLO开关效应。为实验获得这类新的NLO开关材料提供理论依据。

多态的非线性光学(NLO)分子开关由于可以实现分子器件的多功能性和高效性成为该领域发展的必然要求。然而，多数研究体系存在物理性能差、响应速度慢、以及开关效应不显著等问题。理论计算研究发现，花生型金属碳硼烷化合物在氧化还原过程中具有显著的二阶NLO开关效应，但花生型金属碳硼烷的结构和电化学性质的单一性使其在多态NLO分子开关的研究中受到限制。因此，我们采用密度泛函理论(DFT)方法研究了结构多样、剪裁能力强、电化学性质丰富、热稳定性高的层状夹心金属碳硼烷的多态NLO分子开关效应。项目中利用DFT方法研究了电化学行为诱导的层状夹心Co碳硼烷及其不同连接方式构筑的化合物的二阶、三阶NLO性质和多态开关效应。计算表明NLO响应随着层数的增加而增强。TDDFT结果表明这类化合物的NLO响应主要是由C2B3配体内C到B的电荷转移和金属中心d→d跃迁引起的。并且经过两个连续的单电子氧化还原过程，β值有明显变化。而不同的连接方式构筑导致了不同的电荷转移类型和方向。

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