MOFs have attracted great attention in a field of gas sorption and separation, heterogeneous catalysis, sensor technology and optical/electrical devices. For several applications of MOFs, a thin film is required for sophisticated devices. Multiple-layered MOF (MOF-on-MOF) system allows for introduction of multi-functionality into the MOF film through rational choice of organic linkers and/or guest molecules in each layer. Such multifunctionalities can be strongly enhanced by pore alignments through crystallographic orientations in MOF-on-MOF thin films^[1]. However, MOF-on-MOF films reported so far exhibited only out-of-plane orientation, order along the axis perpendicular to the interfaces, because the in-plane orientation of the initial MOF layer was hardly controllable. Recently, a significant advance was achieved for oriented MOF thin films: we reported the alignment of MOF crystals in the film for all three crystallographic directions (both in-plane and out-of-plane alignments) via epitaxial growth on oriented Cu(OH)₂ nanobelts as scaffolds^[2-4]. This motivates us to fabricate fully oriented MOF-on-MOF thin films over industrial scales (>cm). In the present work, fully oriented Cu2(L1)2-on-Cu2(L2)2 thin films (L1, L2: dicarboxylate linker) were successfully fabricated by using the fully oriented MOF film as an initial layer. The crystallographic orientation of the epitaxial MOF-on-MOF (e-MoM) thin films was confirmed by X-ray diffraction analyses.

 A salient aspect of our e-MoM strategy is that it facilitates the synthesis of oriented MOFs from other metal sources and organic linkers that are not applied to one-pot synthesis. For example, Cu2(BPYDC)2 (BPYDC = 2,2’-bipyridine-5,5’-dicarboxylate) were unable to grow on Cu(OH)2 nanobelts due to the metal-binding properties of the bipyridine. Zn2(BDC)2 (BDC = benzene 1,4-dicarboxylate) was also not capable of the epitaxially growth on Cu(OH)2 because Cu(OH)2 preferentially react with organic linkers to form Cu-based MOFs. The e-MoM strategy can afford the fabrication of oriented Zn2(BDC)2 and Cu2(BPYDC)2 as an upper MOF layer on the Cu-based MOF thin films, because the underlying initial MOF layer prevents the reaction of linkers with Cu(OH)2^[5]. The Cu2(BPYDC)2 layer allows for introducing silver nanoparticles (Ag NPs) into the e-MoM thin film by employing metal-binding properties of BPYDC part. In our ePoster presentation, details of optical properties of Cu2(BPYDC)2-on-Cu2(BPDC)2 (BPDC = biphenyl-4,4’-dicarboxylate) with Ag NPs will be shown.