Porous Organic Molecules Research Articles

Cooperative Multiscale‐Assembly for Directional and Hierarchical Growth of Highly Oriented Porous Organic Cage Single‐Crystal Microtubes and Arrays

The directional assembly of porous organic molecules into long‐range ordered architectures, featuring controlled hierarchical porosity and oriented pore channels with defined spatial arrangements, is a fundamental challenge in chemistry and materials science. Herein, using porous organic cages as starting units, we present a cooperative multiscale‐assembly strategy enabling the simultaneous alignment of pore channels and directional hierarchical growth in a single step. At the microscopic level, we employed double solvents to manipulate the intermolecular packing of microporous tetrahedral [4+6] imine cages (CC1 and CC3), resulting in pore channel orientation. Concurrently, at the mesoscopic level, convective flow in the double‐solvent system directed the spatial distribution of nuclei species, followed by diffusion limited growth, leading to the directional formation of single‐crystal microtubes. By precisely controlling the direction of convective flow, the nanocages were successfully organized into 2D and 3D single‐crystal microtube arrays while maintaining oriented micropores. This hierarchical porous architecture enhanced mass transfer, as confirmed by adsorption measurements. Interestingly, such 3D hierarchical microtube arrays can be utilized to immobilize Pd clusters and enzymes (lipase or Glucose oxidase) within the micro‐ and macropores, respectively, showing a 3.8‐ to 4‐fold enhancement in one‐pot tandem reaction activity compared to physical mixtures of individual analogues.

Materials Precursor Score: Modeling Chemists' Intuition for the Synthetic Accessibility of Porous Organic Cage Precursors.

Computation is increasingly being used to try to accelerate the discovery of new materials. One specific example of this is porous molecular materials, specifically porous organic cages, where the porosity of the materials predominantly comes from the internal cavities of the molecules themselves. The computational discovery of novel structures with useful properties is currently hindered by the difficulty in transitioning from a computational prediction to synthetic realization. Attempts at experimental validation are often time-consuming, expensive, and frequently, the key bottleneck of material discovery. In this work, we developed a computational screening workflow for porous molecules that includes consideration of the synthetic difficulty of material precursors, aimed at easing the transition between computational prediction and experimental realization. We trained a machine learning model by first collecting data on 12,553 molecules categorized either as “easy-to-synthesize” or “difficult-to-synthesize” by expert chemists with years of experience in organic synthesis. We used an approach to address the class imbalance present in our data set, producing a binary classifier able to categorize easy-to-synthesize molecules with few false positives. We then used our model during computational screening for porous organic molecules to bias toward precursors whose easier synthesis requirements would make them promising candidates for experimental realization and material development. We found that even by limiting precursors to those that are easier-to-synthesize, we are still able to identify cages with favorable, and even some rare, properties.

Cyclotetrabenzoin Acetate: A Macrocyclic Porous Molecular Crystal for CO2 Separations by Pressure Swing Adsorption**

AbstractA porous molecular crystal (PMC) assembled by macrocyclic cyclotetrabenzoin acetate is an efficient adsorbent for CO2 separations. The 7.1×7.1 Å square pore of PMC and its ester C=O groups play important roles in improving its affinity for CO2 molecules. The benzene walls of macrocycle engage in an apparent [π⋅⋅⋅π] interaction with the molecule of CO2 at low pressure. In addition, the polar carbonyl groups pointing inward the square channels reduce the size of aperture to a 5.0×5.0 Å square, which offers kinetic selectivity for CO2 capture. The PMC features water tolerance and high structural stability under vacuum and various gas adsorption conditions, which are rare among intrinsically porous organic molecules. Most importantly, the moderate adsorbate‐adsorbent interaction allows the PMC to be readily regenerated, and therefore applied to pressure swing adsorption processes. The eluted N2 and CH4 are obtained with over 99.9 % and 99.8 % purity, respectively, and the separation performance is stable for 30 cycles. Coupled with its easy synthesis, cyclotetrabenzoin acetate is a promising adsorbent for CO2 separations from flue and natural gases.

Cyclotetrabenzoin Acetate: A Macrocyclic Porous Molecular Crystal for CO2 Separations by Pressure Swing Adsorption*.

A porous molecular crystal (PMC) assembled by macrocyclic cyclotetrabenzoin acetate is an efficient adsorbent for CO2 separations. The 7.1×7.1 Å square pore of PMC and its ester C=O groups play important roles in improving its affinity for CO2 molecules. The benzene walls of macrocycle engage in an apparent [π⋅⋅⋅π] interaction with the molecule of CO2 at low pressure. In addition, the polar carbonyl groups pointing inward the square channels reduce the size of aperture to a 5.0×5.0 Å square, which offers kinetic selectivity for CO2 capture. The PMC features water tolerance and high structural stability under vacuum and various gas adsorption conditions, which are rare among intrinsically porous organic molecules. Most importantly, the moderate adsorbate-adsorbent interaction allows the PMC to be readily regenerated, and therefore applied to pressure swing adsorption processes. The eluted N2 and CH4 are obtained with over 99.9 % and 99.8 % purity, respectively, and the separation performance is stable for 30 cycles. Coupled with its easy synthesis, cyclotetrabenzoin acetate is a promising adsorbent for CO2 separations from flue and natural gases.

Rational design of porous organic molecules (POMs) based on B-heterocyclic carbenes

We have theoretically obtained 36 porous organic molecules (POMs), three novel 2D covalent organic frameworks (COFs) and one metal–organic framework (MOF) based on the B-heterocyclic carbene (BHC) building blocks and –C≡C– and Ag–C≡C–Ag linkers.

Constructing an ultra-adsorbent based on the porous organic molecules of noria for the highly efficient adsorption of cationic dyes.

A novel Noria-POP-1 material has been successfully synthesized by the simple polymerization of the porous organic molecules of noria and aryl diamines. Noria-POP-1 displayed excellent adsorption capacity for cationic dyes from water with selective removal ability. The adsorption experiments show that Noria-POP-1 displays a remarkable capability to selectively adsorb and separate methylene blue with an adsorption capacity of 2434 mg g−1, which is the highest value obtained so far for porous organic polymers.

Predicting solvent effects on the structure of porous organic molecules.

A computational approach for the prediction of the open, metastable, conformations of porous organic molecules in the presence of solvent is developed.

Towards computer-guided tuning of the crystal packing of porous organic cages

Among microporous materials, there has been an increasing recent interest in porous organic cage (POC) crystals, which can display permanent intrinsic (molecular) and extrinsic (crystal network) porosity. These materials can be used as molecular sieves for gas separation and potential applications as enzyme mimics have been suggested since they exhibit structural response toward guest molecules[1]. Small structural modifications of the initial building blocks of the porous organic molecules can lead to quite different molecular assembly[1]. Moreover, the crystal packing of POCs is based on weak molecular interactions and is less predictable that other porous materials such as MOFs or zeolites.[2] In this contribution, we show that computational techniques -molecular conformational searches and crystal structure prediction- can be successfully used to understand POC crystal packing preferences. Computational results will be presented for a series of closely related tetrahedral imine- and amine-linked porous molecules, formed by [4+6] condensation of aromatic aldehydes and cyclohexyl linked diamines. While the basic cage is known to have one strongly preferred crystal structure, the presence of small alkyl groups on the POC modifies its crystal packing preferences, leading to extensive polymorphism. Calculations were able to successfully identify these trends as well as to predict the structures obtained experimentally, demonstrating the potential for computational pre-screening in the design of POCs within targeted crystal structures. Moreover, the need of accurate molecular (ab initio calculations) and crystal (based on atom-atom potential lattice energy minimization) modelling for computer-guided crystal engineering will be discussed.

Porous organic molecules

Most synthetic materials that show molecular-scale porosity consist of one-, two- or three-dimensional networks. Porous metal-organic frameworks in particular have attracted a lot of recent attention. By contrast, discrete molecules tend to pack efficiently in the solid state, leaving as little empty space as possible, which leads to non-porous materials. This Perspective discusses recent developments with discrete organic molecules that are porous in the solid state. Such molecules, which may be either crystalline or amorphous, can be categorized as either intrinsically porous (containing permanent covalent cavities) or extrinsically porous (inefficiently packed). We focus on the possible advantages of organic molecules over inorganic or hybrid systems in terms of molecular solubility, choice of components and functionalities, and structural mobility and responsiveness in non-covalent extended solids. We also highlight the potential for 'undiscovered' porous systems among the large number of cage-like organic molecules that are already known.