"Photochemical Surgery" of 1D Metal-Organic Frameworks with a Site-Selective Solubilization/Crystallization Strategy

One-dimensional (1D) hybrid MOFs are attractive if they consist of different MOF blocks with interconnected channels. However, the precision synthesis of such 1D multiblock MOFs with the desired block lengths and sequences remains a formidable challenge. Herein we propose the "photochemical surgery" method, which combines top-down and bottom-up approaches to enable the site-selective solubilization (removal)/crystallization (reconstruction) of 1D MOFs. We employed photoreactive MOFs, which were prepared by complexing either Cd²⁺ or Zn²⁺ with a mixture containing a photochromic bispyridyl ligand (^PyDTE_open or ^PyDTZE_open) and an isophthalate (5-nitroisophthalate (nip^2-) or 5-bromoisophthalate (bip^2-)). These MOFs were obtained as high-aspect-ratio, needlelike, colorless crystals that bore 1D channels oriented parallel to the long needle axis. When photoreactive ^DTECdMOF_NO ([Cd(nip)(^PyDTE_open)(H₂O)]), for example, was immobilized at both ends with a metal alloy on a glass substrate and exposed to UV light through a photomask for 60 min in N,N-dimethylformamide/methanol (DMF/MeOH), the unmasked part was removed via solubilization to produce a 50 μm gap. The resulting specimen was immersed for 24 h at 25 °C in DMF/MeOH containing the necessary components for the construction of ^DTZECdMOF_NO ([Cd(nip)(^PyDTZE_open)(H₂O)]). Eventually, the gap was filled with ^DTZECdMOF_NO to produce a triblock hybrid MOF (^DTECdMOF_NO-^DTZECdMOF_NO-^DTECdMOF_NO). The result of a guest diffusion experiment confirmed that the newly formed ^DTZECdMOF_NO block shared its 1D channels with the host ^DTECdMOF_NO blocks. "Photochemical surgery" can be applied to synthesize 1D hybrid MOFs bearing unconventional sequences and morphologies, e.g., honeycomb- and inverted-honeycomb-patterned hybrids.