有机及金属有机氢键体系的混合价电子转移

The current research state of the studies on the hydrogen bond-mediated mixed-valent electron transfer is far from statisfactory. This research proposal is devoted to the synthesis and electron transfer studies of redox-acetive multi-center systems with a hydrogen bond, or a functional group that can form a hydrogen bond, as the bridging ligand.The electron transfer processes will be examined in solution, supramolecular systems, and self-assembled monolayers. Materials with high degree of charge delocalization, such as triarylamine, cyclometalated ruthenium, and ferrocene will be used as the redox centers. This is helpful for reducing the near-infrared absorption interference and improving the intensity and resolution of the intervalence charge transfer transitions. Materials that are able to form a hydrogen bond with a large binding constant, such as ureido-pyrimidinone derivatives, will be used as the bridging ligand for the construction of stable mixed-valence systems with distinct intervalence charge transfer transitions. The electron transfer mechanism of these systems will be investigated as well. In addition, urea will be used as the bridging ligand to mediate the electronic coupling between two redox termini, and the degree of electronic coupling is expected to be modulated by forming a side-chain hydrogen bond with certain anions and nitrobenzene derivatives. The aim of this proposal is to systematically examine the electronic coupling of mixed-valence hydrogen-bond systems by using a combination of various experimental and theoretical techniques such as electrochemistry, near-infrared absorptions, DFT and TDDFT calculations, and substituent effect. These studies are pertinent to the development of hydrogen-bond molecular wires and the understanding of the mechanism in the electron transfer processes occurring in nature.

氢键参与的混合价电子转移研究现状还远未能实现它真正的研究意义。本项目拟以含有氢键单元的基团为桥基，设计合成具有两个或多个氧化还原中心的氢键体系，并研究材料在溶液状态、超分子体系、以及自组装单层膜三个层次的电子转移过程。使用三芳胺、环金属钌、二茂铁等电子离域程度大的化合物为氧化还原活性中心，减少近红外区域吸收干扰，提高混合价电荷转移吸收的强度和分辨率。以具有较大结合常数的氢键构筑基元如脲基嘧啶酮等为桥联基团，发展稳定的、具有明显混合价电荷转移吸收的氢键桥联多中心体系，并探索氢键诱导的混合价电子转移机理。以脲基为桥联基团，通过外加互补氢键基团，调控两端氧化还原中心之间的电子耦合程度。考虑不同端基配体和取代基效应，并结合电化学、近红外光谱方法以及理论计算，系统研究氢键混合价体系的价间电子偶合，发展新型氢键分子导线，并为进一步理解自然界中广泛存在的电子转移过程提供理论基础。

氢键诱导的电子转移过程在自然界中广泛存在。开展人工合成氢键超分子体系的电子转移研究对理解自然界的电子转移和发展新型超分子光电材料有重要意义。本项目合成了一系列含有氢键单元的氧化还原活性化合物，研究了氢键诱导或调控的电子转移过程。制备了含有不同锚定基团(吡啶、巯基、苯胺)、不同长短的四重氢键超分子导线。纳米金电极断裂结和石墨烯纳米电极对测试表明，四重氢键超分子体系具有较好的单分子导电性能,表明了它们在超分子电子学中的潜在应用。合成了脲基桥联三芳胺和环金属钌化合物，通过脲基-阴离子氢键相互作用，调控脲基诱导的电子相互作用的强弱。通过氢键辅助或配位组装，制备金属钌配合物的单层及多层膜，利用高效的界面电子转移过程，实现可见光和近红外电致变色。合成了含酸性质子氢(咪唑或酰胺)的金属钌、铂配合物，研究了其pH值或阴离子响应的电化学及发光性质。合成了含有不同桥联基团的三芳胺和环金属钌化合物，对相应的混合价电子转移过程开展系统性研究，表明桥基和取代基对配合物电子性质有重要影响。本项目研究成果在Nat. Commun., J. Am. Chem. Soc., Angew. Chem.等期刊上发表论文25篇, 应邀在Coord. Chem. Rev.和Dalton Trans.撰写综述。培养博士研究生6名。