Metal–organic frameworks (MOFs), with their crystalline nanoporous three-dimensional structures, have emerged as unique multifunctional materials that combine high porosity with catalytic, photophysical, or other properties to reveal new fundamental science and applications. Because MOFs are composed of organic molecules linking metal centers in ways that are not usually conducive to the formation of free-charge carriers or low-energy charge-transport pathways, they are typically insulators. Accordingly, applications so far have harnessed the unique structural properties and porosity of MOFs, which depend only to a small extent on the ability to manipulate their electronic structure. An exciting new area has emerged due to the recent demonstration of MOFs with controlled electronic and optical properties, which is enabling new fundamental science and opens up the possibility of applications in electronics and photonics. This article presents an overview of the fundamental science issues related to controlling electronic and optical properties of MOFs, and how research groups worldwide have been exploring such properties for electronics, thermoelectrics, photophysics, and charge storage.

The development of metal–organic frameworks (MOFs) as microporous electronic conductors is an exciting research frontier that has the potential to revolutionize a wide range of technologically and industrially relevant fields, from catalysis to solid-state sensing and energy-storage devices, among others. After nearly two decades of intense research on MOFs, examples of intrinsically conducting MOFs remain relatively scarce; however, enormous strides have recently been made. This article briefly reviews the current status of the field, with a focus on experimental milestones that have shed light on crucial structure–property relationships that underpin future progress. Central to our discussion are a series of design considerations, including redox-matching, donor–acceptor interactions, mixed valency, and π-interactions. Transformational opportunities exist at both fundamental and applied levels, from improved measurement techniques and theoretical understanding of conduction mechanisms to device engineering. Taken together, these developments will herald a new era in advanced functional materials.

The well-known synthetic versatility of metal–organic frameworks (MOFs) is rooted in the ability to predict the metal-ion coordination geometry and the vast possibilities to use organic chemistry to modify the linker groups. However, the use of molecules occupying the pores as a component of framework design has been largely ignored. Recent reports show that the presence of these so-called “guests” can have dramatic effects, even when they are a seemingly innocuous species such as water or polar solvents. We term these guests “non-innocent” when their presence alters the MOF in such a way as to create a new material with properties different from the MOF without the guests. Advantages of using guest molecules to impart new properties to MOFs include the relative ease of introducing new functionalities, the ability to modify the material properties at will by removing the guest or inserting different ones, and avoidance of the difficulties associated with synthesizing new frameworks, which can be challenging even when the basic topology remains constant. In this article, we describe the “Guest@MOF” concept and provide examples illustrating its potential as a new MOF design element.

Metal–organic frameworks (MOFs) are porous ordered arrays of inorganic clusters connected by organic linkers. The compositional diversity of the metal and ligand, combined with varied connectivity, has yielded more than 20,000 unique structures. Electronic structure theory can provide deep insights into the fundamental chemistry and physics of these hybrid compounds and identify avenues for the design of new multifunctional materials. In this article, a number of recent advances in materials modeling of MOFs are reviewed. We present the methodology for predicting the absolute band energies (ionization potentials) of porous solids as compared to those of standard semiconductors and electrical contacts. We discuss means of controlling the optical bandgaps by chemical modification of the organic and inorganic building blocks. Finally, we outline the principles for achieving electroactive MOFs and the key challenges to be addressed.

Motivated by low cost, low toxicity, mechanical flexibility, and conformability over complex shapes, organic semiconductors are currently being actively investigated as thermoelectric (TE) materials to replace the costly, brittle, and non-eco-friendly inorganic TEs for near-ambient-temperature applications. Metal–organic frameworks (MOFs) share many of the attractive features of organic polymers, including solution processability and low thermal conductivity. A potential advantage of MOFs and MOFs with guest molecules (Guest@MOFs) is their synthetic and structural versatility, which allows both the electronic and geometric structure to be tuned through the choice of metal, ligand, and guest molecules. This could solve the long-standing challenge of finding stable, high-TE-performance n-type organic semiconductors, as well as promote high charge mobility via the long-range crystalline order inherent in these materials. In this article, we review recent advances in the synthesis of MOF and Guest@MOF TEs and discuss how the Seebeck coefficient, electrical conductivity, and thermal conductivity could be tuned to further optimize TE performance.

Metal–organic framework (MOF) materials are well known as elegant gaseous energy-storage materials, but their potential for electrical energy storage has only recently been explored. Although numerous studies have focused on MOF-derived porous carbon or nanoscale metal oxide materials, less attention has been paid to the intrinsic properties achievable through the molecular design of MOFs. Indeed, the porous nature of MOF architectures is highly suitable for accommodating electrolyte ions in electrochemical processes, suggesting their potential as high-performance active materials for batteries. In this article, we consider recent examples employing MOF materials as battery electrode materials. Redox-active sites were incorporated on metal junctions, ligands, or both, in the MOF structures. In addition, we introduce novel electrochemical mechanisms observed in the electrochemical process of MOF electrode materials.

The development of new hierarchical materials capable of efficient energy transfer along a predesigned pathway will boost various applications, ranging from organic photovoltaics to catalytic systems. Due to their exceptional tunability and structural diversity, metal–organic frameworks (MOFs) offer a unique platform to study and model directional energy-transfer processes and, thereby, an efficient path for energy utilization. This article summarizes the latest advances in MOF applications in the fields of optoelectronics, photoswitching, sensing, and photocatalysis, for which development is highly dependent on fundamental studies of MOF photophysics.

Future electronics will be conformal, bendable, and wearable. Taking inspiration from the characteristics of human skin, we are developing a new generation of electronic materials to enable devices that are flexible, stretchable, biodegradable, and self-healable. We have developed various sensors and circuits, all of which are based on organic materials, polymers, and carbon nanomaterials. These materials will provide us with a long-term path toward adding various skin-inspired functions.