新型半导体“量子点”材料：金属硫族超四面体簇的离散化和表面功能化

Metal chalcogenide quantum dots have attracted increasing attention because of their diverse technological applications on some important research fields such as nanomaterials, biosensor and biomedical image etc. Metal chalcogenide supertetrahedral clusters, being structurally precise fragments of the well-known cubic zinc sulfide type semiconductors, can be regarded as the smallest semiconductor "quantum dots" and bridge the size gap between colloidal quantum dot structures and molecular species in solution. Compared with traditional colloidal quantum dots, these metal-chalcogenide-supertetrahedral-cluster-based "quantum dots" possess small size (1-3nm) and high uniformity, which have also been found to exhibit size-dependent optical properties. Early studies on construction of metal chalcogenide supertetrahedal clusters suggested they prefer self-assemblying or co-assemblying with organic linkers to form three-dimensional covalent superlattices. It is really hard to obtain discrete (also called isolated) supertetrahedral clusters which stay in crystal lattice and also show good solubility in solution. Up to now, there has always been a strong interest in discrete molecular supertetrahedral clusters, because they are directly related to both nanosized and nanoporous materials. In the area of open-framework metal chalcogenide materials, supertetrahedral clusters can serve as pseudo-tetrahedral building blocks (artificial atoms with tunable "radii") to allow a rational construction of multi-dimensional inorganic frameworks or hybrid organic-inorganic frameworks through modular assembly processes. Discrete clusters are also directly comparable to semiconductor nanoparticles in terms of properties such as quantum confinement effects. Furthermore, discrete soluble clusters are amenable for solution processing into various forms such as thin films, or incorporated into functionalized semiconducting mesoporous structures or porous gels and aerogels, for potential applications in nanotechnology. This proposed project is to aim at creating series of discrete pure inorganic or organic-inorganic hybrid metal chalcogenide supertetrahedral clusters with variable size and composition as well as good solubility in organic solvents through superbase-involved solvothermal or ionotherml reactions. Further studies will center on functionalizing these discrete clusters with active organic functional groups, which can be further modified by other carbon-based materials (such as fulleren, carbon nanotube and graphene) and serve as new type of composite materials in the construction of semiconductor film and solar cell divices. By virtue of combination of crystalline solid materials chemistry with other relevant disciplines such as nanostructure chemistry and organic chemistry, this project will hold great promise for the development of this new type of semiconductor "quantum dots" materials.

金属硫族化合物量子点是当前纳米材料学、分析化学、生物化学等多个重要学科领域的研究热点。具有立方相硫化锌晶格点阵片段的金属硫族超四面体簇，目前被视作具有精确结构的最小尺度的四面体"量子点"，起到连接小分子簇合物和胶体半导体纳米粒子的桥梁作用。相对于传统胶体半导体量子点，该新型四面体"量子点"尺寸更小，且具有高度的均一性。早期研究表明，该类簇通常以自聚合或共价聚合的方式形成三维共价超晶格网络，很难实现单个簇在晶相中的离散性和在液相中的良好溶解性能。本项目的研究目标就在于通过采用超强碱参与的水热、溶剂热或离子热反应，探索合成系列组份可调、尺寸可变的且可离散溶解的纯无机或无机有杂化超四面体簇，并通过其表面有机官能化研究，实现它们在半导体薄膜材料和太阳能电池方面的应用。该项目通过晶态固体材料化学与结构化学、有机化学、半导体材料学等多个相关领域的交叉，为新型功能半导体"量子点"的开发应用提供新的思路。

具有立方相硫化锌晶格碎片结构的金属硫族超四面体纳米团簇被视作具有精确结构的超小"量子点"，起到连接小分子簇合物和胶体半导体纳米粒子的桥梁作用。相对于传统胶体半导体量子点，该类新型四面体"量子点"尺寸更小，且具有高度的尺寸均一性。然而，该类团簇通常以自聚合或共价聚合的方式形成三维共价超晶格网络，很难实现单个簇在晶相中的离散性和在液相中的良好溶解性能，这严重制约了其作为溶液相组份的后修饰及功能化研究。本项目的研究目标和研究内容就在于：（1）构筑晶格中可离散的金属硫族超四面体纳米团簇；（2）提高簇的溶解性能和功能化其表面；（3）探究簇与碳基共价复合材料的光电性能。目前，我们合成了一例尺寸最大的、表面无有机配体保护的、且在晶格中离散的金属硫族超四面体纳米团簇。该超四面体纳米团簇的核中心具有一个固有缺陷位，基于该团簇的固相材料在特定溶剂中亦表现出一定的溶解性能。我们针对此纳米团簇特有的缺陷位，利用双步合成策略，成功地实现了过渡金属离子在缺陷位点的定向精确掺杂，深入探究了铜和锰掺杂团簇的光电响应性、光致发光性和电化学发光性能，建立了掺杂剂种类、掺杂位点以及固有缺陷位于上述性能之间的内在联系。此外，我们在现有的基于团簇的多孔类分子筛材料内部植入有机染料分子，成功实现了无机半导体主体框架参与的能量转移过程。最后，我们构建了基于超四面体纳米团簇的、且具有端基缺陷位的类分子筛开放骨架，并成功确立纳米团簇端基的缺陷位为该材料电催化氧还原的活性位点。该项目研究结果在一定程度上确立了超四面体纳米团簇在溶液中具有一定溶解性能，团簇内不同位点的金属原子和非金属元素对于团簇的功能调控具有不同的作用。本研究通过晶态固体材料化学与结构化学、有机化学、半导体材料学等多个相关领域的交叉，为新型功能半导体"量子点"的开发应用提供新的思路。