MOF-on-MOF: Oriented Growth of Multiple Layered Thin Films of Metal–Organic Frameworks

The precise alignment of multiple layers of metal–organic framework (MOF) thin films, or MOF-on-MOF films, over macroscopic length scales is presented. The MOF-on-MOF films are fabricated by epitaxially matching the interface. The first MOF layer (Cu₂(BPDC)₂, BPDC=biphenyl-4,4′-dicarboxylate) is grown on an oriented Cu(OH)₂ film by a “one-pot” approach. Aligned second (Cu₂(BDC)₂, BDC=benzene 1,4-dicarboxylate, or Cu₂(BPYDC)₂, BPYDC=2,2′-bipyridine-5,5′-dicarboxylate) MOF layers can be deposited using liquid-phase epitaxy. The co-orientation of the MOF films is confirmed by X-ray diffraction. Importantly, our strategy allows for the synthesis of aligned MOF films, for example, Cu₂(BPYDC)₂, that cannot be grown on a Cu(OH)₂ surface. We show that aligned MOF films furnished with Ag nanoparticles show a unique anisotropic plasmon resonance. Our MOF-on-MOF approach expands the chemistry of heteroepitaxially oriented MOF films and provides a new toolbox for multifunctional porous coatings.