用于光子应用的高荧光金属-有机骨架纳米复合材料,Nano Letters

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用于光子应用的高荧光金属-有机骨架纳米复合材料
Nano Letters ( IF 9.6 ) Pub Date : 2017-12-15 00:00:00 , DOI: 10.1021/acs.nanolett.7b04536
A. Monguzzi ₁ , M. Ballabio ₁ , N. Yanai _{2,

3} , N. Kimizuka ₂ , D. Fazzi ₄ , M. Campione ₅ , F. Meinardi ₁

Affiliation

金属有机骨架（MOF）是多孔杂化材料，由有机配体通过自组装策略配位至金属离子或簇而构建。根据特定的合成途径，这些材料的独特性是可以同时控制组成和配体排列以控制其光学和能量传输性质的可能性。因此，优化的MOF纳米晶体（nano-MOF）可以潜在地代表具有与其无机前身相似的特征的下一代发光材料，即胶体半导体量子点。荧光纳米MOF的发光是通过配体分子激子的辐射复合而产生的。这些纳米晶体的独特性是可以将配体生色团堆积得足够近，以允许快速的激子扩散，但彼此之间相距足够远，从而防止了有机晶体的聚集诱导效应。特别地，避免了强偶联的二聚体或准分子的形成，从而保留了分离的分子的光学特征。但是，纳米MOF的荧光量子产率（QY）非常小。为了克服此限制并实现高发射系统，我们分析了蓝色发射纳米MOF中的荧光过程，并对光生单重态激子的扩散和猝灭机理进行了建模。我们的结果表明，纳米MOF中的激子猝灭主要归因于表面定位的非辐射复合中心的存在。与它们的无机对应物类似，我们发现纳米MOF表面的钝化是提高发射效率的直接方法。通过将纳米晶体嵌入惰性聚合物主体中，我们观察到了荧光QY的+ 200％增量，从而恢复了溶液中分离的配体的发射特性。

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Highly Fluorescent Metal–Organic-Framework Nanocomposites for Photonic Applications

Metal–organic frameworks (MOFs) are porous hybrid materials built up from organic ligands coordinated to metal ions or clusters by means of self-assembly strategies. The peculiarity of these materials is the possibility, according to specific synthetic routes, to manipulate both the composition and ligands arrangement in order to control their optical and energy-transport properties. Therefore, optimized MOFs nanocrystals (nano-MOFs) can potentially represent the next generation of luminescent materials with features similar to those of their inorganic predecessors, that is, the colloidal semiconductor quantum dots. The luminescence of fluorescent nano-MOFs is generated through the radiative recombination of ligand molecular excitons. The uniqueness of these nanocrystals is the possibility to pack the ligand chromophores close enough to allow a fast exciton diffusion but sufficiently far from each other preventing the aggregation-induced effects of the organic crystals. In particular, the formation of strongly coupled dimers or excimers is avoided, thus preserving the optical features of the isolated molecule. However, nano-MOFs have a very small fluorescence quantum yield (QY). In order to overcome this limitation and achieve highly emitting systems, we analyzed the fluorescence process in blue emitting nano-MOFs and modeled the diffusion and quenching mechanism of photogenerated singlet excitons. Our results demonstrate that the excitons quenching in nano-MOFs is mainly due to the presence of surface-located, nonradiative recombination centers. In analogy with their inorganic counterparts, we found that the passivation of the nano-MOF surfaces is a straightforward method to enhance the emission efficiency. By embedding the nanocrystals in an inert polymeric host, we observed a +200% increment of the fluorescence QY, thus recovering the emission properties of the isolated ligand in solution.

更新日期：2017-12-15

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