§Department of Chemistry and Department of Applied Physical Sciences, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States.
∥IBS Center for Soft and Living Matter and the Department of Chemistry, Ulsan National Institute of Science and Technology (UNIST), Ulsan, South Korea.
J Am Chem Soc. 2015 Jul 1;137(25):8169-75. doi: 10.1021/jacs.5b03263. Epub 2015 Jun 19.
Metal-organic frameworks (MOFs) are typically poor electrical conductors, which limits their uses in sensors, fuel cells, batteries, and other applications that require electrically conductive, high surface area materials. Although metal nanoclusters (NCs) are often added to MOFs, the electrical properties of these hybrid materials have not yet been explored. Here, we show that adding NCs to a MOF not only imparts moderate electrical conductivity to an otherwise insulating material but also renders it photoconductive, with conductivity increasing by up to 4 orders of magnitude upon light irradiation. Because charge transport occurs via tunneling between spatially separated NCs that occupy a small percent of the MOF's volume, the pores remain largely open and accessible. While these phenomena are more pronounced in single-MOF crystals (here, Rb-CD-MOFs), they are also observed in films of smaller MOF crystallites (MIL-53). Additionally, we show that in the photoconductive MOFs, the effective diffusion coefficients of electrons can match the typical values of small molecules diffusing through MOFs; this property can open new vistas for the development of MOF electrodes and, in a wider context, of electroactive and light-harvesting MOFs.
金属-有机骨架（MOFs）通常是电的不良导体，这限制了它们在传感器、燃料电池、电池和其他需要导电、高表面积材料的应用中的使用。尽管金属纳米团簇（NCs）通常被添加到 MOF 中，但这些混合材料的电学性质尚未得到探索。在这里，我们表明，将 NC 添加到 MOF 中不仅赋予了原本不导电的材料适度的导电性，而且还使其具有光电导性，在光照射下，导电性增加了多达 4 个数量级。由于电荷通过占据 MOF 体积一小部分的空间分离的 NC 之间的隧道传输，因此孔仍然保持很大的开放性和可及性。虽然这些现象在单晶 MOF 晶体（这里是 Rb-CD-MOF）中更为明显，但在较小 MOF 微晶的薄膜中也观察到了这些现象（MIL-53）。此外，我们表明，在光电导 MOF 中，电子的有效扩散系数可以与小分子通过 MOF 扩散的典型值相匹配；这一特性为 MOF 电极的发展开辟了新的前景，从更广泛的角度来看，为电活性和光收集 MOF 开辟了新的前景。
