Role of Solvent in the Oriented Growth of Conductive Ni-CAT-1 Metal-Organic Framework at Solid-Liquid Interfaces

A controlled growth of two-dimensional (2D) pi-conjugated metal-organic frameworks (MOFs) on solid substrates can open exciting opportunities for the application of 2D MOFs as optoelectronic devices. Some factors like solvent composition and type of substrates are known to influence the properties of solution-processed 2D MOF crystals; however, a mechanistic understanding of how interactions between solvent, substrate, and precursors affect heterogeneous nucleation has been limited. Here, it is reported that the structure of Ni-catecholate (Ni-CAT-1) MOFs at a solid-liquid interface is controlled by solvent-substrate and solvent-MOF precursor interactions. Specifically, the structure of the MOF film can be controlled by varying the affinity of the solvent to the substrate. As a fraction of N,N-dimethylformamide (DMF) in a binary solvent mixture of water and DMF increases, the arrangement of Ni-CAT-1 crystals varies from vertically aligned nanorods to the graphite substrate to less ordered nanorods with the lower initial nucleation number density of Ni-CAT-1 crystals on the surface. The arrangement of two-dimensional metal-organic frameworks varies from well-aligned nanorods orthogonal to substrate to less ordered nanorods by modulating solvent composition which affects interactions of solvent-substrate and solvent-precursor molecule. The results provide insights into the role of solvents in directing heterogeneous nucleation of crystals on substrates, which is essential for solution-processed crystal growth for optoelectronic application. image