skip to main content


Title: 2D molecular crystal lattices: advances in their synthesis, characterization, and application
This review identifies how recent advances in controlling the structure and properties of MOF and COF thin films can be used to establish 2D molecular crystals as a new material platform with key applications in catalysis, sensing, separations, and electronics. In addition to summarizing research efforts surrounding the synthesis, characterization and utilization of 2D and thin film MOFs and COFs, this review identifies exigent challenges in their development, and motivates the search for new synthetic methods, advanced analytical techniques, and creative applications. Ultimately, 2D molecular lattices, be they 2D MOFs or COFs, are a compelling platform through which to discover new and emergent properties and to expand the library of 2D materials.  more » « less
Award ID(s):
1848046
NSF-PAR ID:
10132679
Author(s) / Creator(s):
; ;
Date Published:
Journal Name:
Journal of Materials Chemistry A
Volume:
7
Issue:
41
ISSN:
2050-7488
Page Range / eLocation ID:
23537 to 23562
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Materials with dynamically controlled electronic structures (i.e., upon external stimuli) are at the forefront of the renewable energy sector with applications as memory devices, smart supercapacitors, programmable solar cells, and field‐effect transistors. Moreover, their continued development as device components is critical for the field of optoelectronics since their performance is comparable, or could even surpass, the current benchmarks. Adaptive electronic properties are the main focus of this review that discusses recent developments in the modulation of electronic behavior that can be tuned using external stimuli in metal–organic frameworks (MOFs), covalent–organic frameworks (COFs), primarily inorganic hybrids, polymers, and graphitic‐type materials. Triggers to achieve “dynamic” behavior discussed within this manuscript are primarily light‐based switches that include different classes of photochromic molecules such as naphthalene diimide, viologen, diarylethene, azobenzene, and spiropyran. The effect of material dimensionality and photoswitch connectivity achieved through integration of photochromic moieties inside 0D, 1D, 2D, and 3D hybrid matrices is discussed. This review showcases the prospects of advancing the material and energy landscapes through employment of structural motifs with adaptive electronic structures occurring as a function of their dimensionality and connectivity.

     
    more » « less
  2. Confining proteins in synthetic nanoscale spatial compartments has offered a cell-free avenue to understand enzyme structure–function relationships and complex cellular processes near the physiological conditions, an important branch of fundamental protein biophysics studies. Enzyme confinement has also provided advancement in biocatalysis by offering enhanced enzyme reusability, cost-efficiency, and substrate selectivity in certain cases for research and industrial applications. However, the primary research efforts in this area have been focused on the development of novel confinement materials and investigating protein adsorption/interaction with various surfaces, leaving a fundamental knowledge gap, namely, the lack of understanding of the confined enzymes (note that enzyme adsorption to or interactions with surfaces differs from enzyme confinement as the latter offers an enhanced extent of restriction to enzyme movement and/or conformational flexibility). In particular, there is limited understanding of enzymes' structure, dynamics, translocation (into biological pores), folding, and aggregation in extreme cases upon confinement, and how confinement properties such as the size, shape, and rigidity affect these details. The first barrier to bridge this gap is the difficulty in “penetrating” the “shielding” of the confinement walls experimentally; confinement could also lead to high heterogeneity and dynamics in the entrapped enzymes, challenging most protein-probing experimental techniques. The complexity is raised by the variety in the possible confinement environments that enzymes may encounter in nature or on lab benches, which can be categorized to rigid confinement with regular shapes, rigid restriction without regular shapes, and flexible/dynamic confinement which also introduces crowding effects. Thus, to bridge such a knowledge gap, it is critical to combine advanced materials and cutting-edge techniques to re-create the various confinement conditions and understand enzymes therein. We have spearheaded in this challenging area by creating various confinement conditions to restrict enzymes while exploring experimental techniques to understand enzyme behaviors upon confinement at the molecular/residue level. This review is to summarize our key findings on the molecular level details of enzymes confined in (i) rigid compartments with regular shapes based on pre-formed, mesoporous nanoparticles and Metal–Organic Frameworks/Covalent-Organic Frameworks (MOFs/COFs), (ii) rigid confinement with irregular crystal defects with shapes close to the outline of the confined enzymes via co-crystallization of enzymes with certain metal ions and ligands in the aqueous phase (biomineralization), and (iii) flexible, dynamic confinement created by protein-friendly polymeric materials and assemblies. Under each case, we will focus our discussion on (a) the way to load enzymes into the confined spaces, (b) the structural basis of the function and behavior of enzymes within each compartment environments, and (c) technical advances of our methodology to probe the needed structural information. The purposes are to depict the chemical physics details of enzymes at the challenging interface of natural molecules and synthetic compartment materials, guide the selection of enzyme confinement platforms for various applications, and generate excitement in the community on combining cutting-edge technologies and synthetic materials to better understand enzyme performance in biophysics, biocatalysis, and biomedical applications.

     
    more » « less
  3. Abstract

    2D covalent organic frameworks (2D COFs) are a unique materials platform that combines covalent connectivity, structural regularity, and molecularly precise porosity. However, 2D COFs typically form insoluble aggregates, thus limiting their processing via additive manufacturing techniques. In this work, colloidal suspensions of boronate‐ester‐linked 2D COFs are used as a spray‐coating ink to produce large‐area 2D COF thin films. This method is synthetically general, with five different 2D COFs prepared as colloidal inks and subsequently spray‐coated onto a diverse range of substrates. Moreover, this approach enables the deposition of multiple 2D COF materials simultaneously, which is not possible by polymerizing COFs on substrates directly. When combined with stencil masks, spray‐coated 2D COFs are rapidly deposited as thin films larger than 200 cm2with line resolutions below 50 µm. To demonstrate that this deposition scheme preserves the desirable attributes of 2D COFs, spray‐coated 2D COF thin films are incorporated as the active material in acoustic sensors. These 2D‐COF‐based sensors have a 10 ppb limit‐of‐quantification for trimethylamine, which places them among the most sensitive sensors for meat and seafood spoilage. Overall, this work establishes a scalable additive manufacturing technique that enables the integration of 2D COFs into thin‐film device architectures.

     
    more » « less
  4. null (Ed.)
    Understanding the underlying physical mechanisms that govern charge transport in two-dimensional (2D) covalent organic frameworks (COFs) will facilitate the development of novel COF-based devices for optoelectronic and thermoelectric applications. In this context, the low-energy mid-infrared absorption contains valuable information about the structure–property relationships and the extent of intra- and inter-framework “hole” polaron delocalization in doped and undoped polymeric materials. In this study, we provide a quantitative characterization of the intricate interplay between electronic defects, domain sizes, pore volumes, chemical dopants, and three dimensional anisotropic charge migration in 2D COFs. We compare our simulations with recent experiments on doped COF films and establish the correlations between polaron coherence, conductivity, and transport signatures. By obtaining the first quantitative agreement with the measured absorption spectra of iodine doped (aza)triangulene-based COF, we highlight the fundamental differences between the underlying microstructure, spectral signatures, and transport physics of polymers and COFs. Our findings provide conclusive evidence of why iodine doped COFs exhibit lower conductivity compared to doped polythiophenes. Finally, we propose new research directions to address existing limitations and improve charge transport in COFs for applications in functional molecular electronic devices. 
    more » « less
  5. Abstract

    Covalent organic frameworks (COFs) are an emerging class of functional nanostructures with intriguing properties, due to their unprecedented combination of high crystallinity, tunable pore size, large surface area, and unique molecular architecture. The range of properties characterized in COFs has rapidly expanded to include those of interest for numerous applications ranging from energy to environment. Here, a background overview is provided, consisting of a brief introduction of porous materials and the design feature of COFs. Then, recent advancements of COFs as a designer platform for a plethora of applications are emphasized together with discussions about the strategies and principles involved. Finally, challenges remaining for this type material for real applications are outlined.

     
    more » « less