Porous materials, most notably metal–organic frameworks (MOFs), covalent organic frameworks (COFs), hydrogen-bonded frameworks (HOFs), and related materials have gained increasing attention for their unique properties and characteristics, which was crowned with the 2025 Nobel Prize in Chemistry (in recognition of the discovery of MOFs). The high internal surface areas, porosity, pore variety, chemical tunability, and high crystallinity have made these next-generation porous solids the subject of intense interest for ∼25 years. The propensity of these solids to form as crystalline materials (which has been highly prized by researchers in the field) provides great benefits with respect to definitive structural characterization and rational design of these compounds. However, crystallinity comes with a cost, which is a lack of processability and malleability. Like most crystalline, microcrystalline, or powdered solids, these next-generation porous solids have a limited ability to be formed into films, fibers, coatings, monoliths, or flexible materials because of their crystalline structure. As these materials become increasingly deployed into potential technological applications, their limited processability will similarly limit their utility and ability to integrate into fully functioning technologies. As such, efforts to integrate MOFs (and related materials) with flexible polymers has become of substantial interest. This Account highlights the research journey of the author to combine MOFs with polymers in various constructs that seek to retain the unique physicochemical properties of MOFs (e.g., crystallinity, functional tunability, porosity), while exhibiting macroscopic processability more like that of organic polymers. Simple mixing of MOFs and polymers to generate mixed-matrix membranes (MMMs) provides a relatively straightforward solution to this challenge. However, selection of appropriate polymers for forming MMMs is required to avoid pore filling and loss of MOF porosity. Thinner membranes and films can be achieved by polymer grafting onto MOF particles to generate self-assembled MOF monolayers (SAMMs). SAMMs achieve ultrathin form factors but are mechanically fragile relative to MMMs. Finally, a true integration of MOFs and polymers is achieved with polyMOFs, where 1-dimensional, organic, noncrystalline polymers are used as the organic building component of the MOF. In polyMOFs, the two components of the composite─the MOF and the polymer─become truly integrated and indistinguishable, whereby the MOF is the polymer and the polymer is the MOF. That stated, the utility and materials characteristics of polyMOFs are presently rather underwhelming compared to MMMs or SAMMs. Taken together, this Account seeks to describe a range of approaches to integrating MOFs and polymers, highlight success, illuminate future challenges, and inspire more creative efforts in the field.
Conspectus The rapidly growing energy cost of artificial intelligence presents an urgent challenge to conventional computing architectures based on separate processing and memory units. Neuromorphic devices, which integrate memory and logic into a single unit and operate in an event-driven manner, offer a promising alternative. A potential avenue to realize neuromorphic architectures is based on materials that can switch between distinct resistance states reversibly, at low voltage, and at room temperature. Transition metal oxides with oxygen-vacancy driven metal–insulator transitions (MITs) are compelling candidates, but the microscopic mechanisms governing these transitions have remained poorly understood, limiting the ability to design and optimize materials for device applications. In this Account, we describe the authors’ effort at developing, and validating experimentally, a quantitative, first-principles understanding of ion migration and oxygen vacancy engineering in cobaltite perovskites, using La1–xSrxCoO3-δ (LSCO) as the primary model system. We started by asking a basic mechanistic question: what drives the MIT in LSCO? Using density functional theory calculations, we found that the MIT is not simply determined by local bonding changes at oxygen-deficient cobalt sites, but rather by cooperative, global structural distortions. Building on this mechanistic foundation, we developed a model to predict the electrical bias required to trigger the MIT electrochemically. The model expresses the threshold voltage in terms of the oxygen vacancy formation free energy, the high-frequency dielectric constant, and the permanent polarization. The identification of these key quantities enables the prediction of concrete design guidelines for minimizing the operating voltage. We also conducted experimental work to map the topotactic phase landscape of LSCO thin films, where we observed the emergence of the Ruddlesden–Popper phase under the most reducing conditions, extending well beyond the well-known perovskite–brownmillerite transition. This result was also confirmed thermodynamically by first-principles calculations. To further refine experimental work on oxygen-deficient phases, we developed a combined experimental and theoretical protocol for quantifying oxygen stoichiometry in thin films through the analysis of X-ray absorption spectra, providing a practical diagnostic tool. Our investigations were further extended in three directions. First, we discovered that direct hydrogenation using H2 gas provides a low-temperature route to phase control, with hydroxyl bond formation catalyzing oxygen vacancy creation at neighboring lattice sites. Second, we predicted that a metallic interface could emerge between two coexisting insulating phases of LSCO as a result of orbital reconstruction driven by charge transfer and symmetry mismatch. This metallic state, which can be switched on or off by strain or gate voltage, opens a new route to low-energy resistive switching. Third, we showed that the cooperative distortion framework established for LSCO generalizes beyond cobaltites: Grenier-phase iron perovskites R1/3A2/3FeO2.67 exhibit tunable ferroelectricity by the same mechanism of concerted octahedral and tetrahedral unit distortions. Further, combining theory and operando synchrotron X-ray diffraction, we identified “hidden” Grenier phases that form transiently during the perovskite-to-brownmillerite transition in LSCO; their metallic or insulating character depends nonmonotonically on Sr doping concentration, a trend that explains the nonmonotonic dependence of the threshold voltage on Sr content observed experimentally.
Conductive metal–organic frameworks (c-MOFs) represent a distinct class of porous conductive materials. Compared with conventional MOFs, c-MOFs integrate intrinsically high electrical conductivity with a high surface area and an ordered porous structure, enabling efficient electron and ion transport. Engineering c-MOFs into continuous and flexible films offers a promising strategy for translating their properties into practical devices. Key strategies for film engineering include solution processing, interfacial growth, and chemical vapor deposition, which allow precise control over the film morphology, thickness, and alignment of conductive channels. Thin-film fabrication preserves structural integrity and pore connectivity, enhances interfacial contact, and facilitates device integration, thereby promoting coupled ionic and electronic transport. These properties render c-MOF films suitable for multimodal energy transformation. In energy storage, their mechanical compliance, flexibility, and high porosity enable conformal integration with deformable and wearable devices while maintaining rapid charge transport and long-term cycling stability. In energy harvesting and conversion, their ordered porous networks, tunable electronic structures, and freestanding mechanically flexible architectures enable efficient adaptation to diverse energy inputs, facilitating energy conversion involving electrical, mechanical, chemical, thermal, and optical processes while maintaining the structural integrity under dynamic deformation. This versatility supports the development of integrated systems capable of simultaneously storing, harvesting, and converting multiple energy modalities for wearable and portable devices. This Account highlights our recent studies on the nanoengineering of c-MOFs on the surface of cellulose nanofibers (CNFs) through interfacial synthesis, enabling the fabrication of freestanding, flexible, and mechanically robust CNF@c-MOF nanopapers, as well as their applications in energy harvesting, conversion, and storage. We discuss the fundamental principles governing the interfacial growth of c-MOF nanostructures on flexible nanofibrous substrates, including the regulation of metal–ligand coordination and interfacial chemical interactions that govern hierarchical assembly toward functional flexible architectures. This Account also summarizes recent advances in the fabrication of flexible c-MOF films, covering representative preparation strategies, structural design approaches, and their unique roles in emerging energy technologies. Future progress in metal center selection, ligand electronic modulation, pore architecture optimization, interface engineering, and composite integration will further improve electron–ion transport, mechanical durability, and device-level compatibility. By combining flexible substrates with multiscale hierarchical structures, flexible c-MOF films can establish interconnected transport networks and adaptive functional interfaces, enabling high-performance, lightweight, and multifunctional energy devices. These advances highlight flexible c-MOF films as a promising platform for next-generation energy technologies that simultaneously demand mechanical flexibility, structural stability, and efficient synergistic electron–ion transport.
