Conjugated Microporous Polymers Cooper, Andrew I.
Advanced materials (Weinheim),
March 26, 2009, Volume:
21, Issue:
12
Journal Article
Peer reviewed
Conjugated microporous polymers are of great interest because they have potential to combine high surface areas in the dry state with physical properties relevant to organic electronics. A series of ...recent reports has shown that materials such as poly(aryleneethynylene)s (PAEs), poly(phenyl‐ene butadiynylene)s, poly(phenylene vinylene), poly(p‐phenylene)s, polysilanes, polyanilines, and polytriazines can be produced as microporous networks with apparent Brunauer–Emmett–Teller surface areas of more than 1000 m2 g−1 in some cases. Micropore size and surface area can be synthetically fine tuned in amorphous PAE polymers and copolymers, something which was previously thought to be the preserve of ordered crystalline materials such as metal organic frameworks. We review in this Research News article recent progress made by our group and others with particular emphasis on the possible future applications of these materials.
Conjugated microporous polymers combine extended conjugation with small pore sizes (d < 2 nm) and surface areas in excess of 1000 m2 g−1 in some cases. This new class of materials is discussed with particular emphasis on potential future applications which might exploit these large interfacial areas.
Porous organic molecular materials are a subclass of porous solids that are defined by their modular, molecular structures, and the absence of extended covalent or coordination bonding in the ...solid‐state. As a result, porous molecular materials are soluble and they can be processed into different forms, such as mixed matrix membranes. The structure of the porous modules can be fine‐tuned for specific applications, such as gas isotope separations, and in some cases the solid‐state properties of these materials can be defined by the structure of the porous molecule as viewed in isolation. In this review, the authors focus on the design of porous organic molecular materials and how their properties can be tuned for specific applications by using crystal engineering techniques. The authors distinguish between strategies where porosity is defined largely by the molecule itself, for example, in porous organic cages, and cases where porosity is generated by the solid‐state crystalline assembly. They emphasize the importance of computational techniques in the de novo design of functional, porous organic molecular materials, and how molecular modeling is applied to understand the properties of these materials.
Porous organic molecular materials are a subclass of porous solids that are defined by their modular molecular structures and the absence of extended covalent or coordination bonding. Their solid‐state structures can be tuned for specific applications by using crystal engineering and processing techniques, often using computation as a design guide.
Function-led design of new porous materials Slater, Anna G.; Cooper, Andrew I.
Science (American Association for the Advancement of Science),
05/2015, Volume:
348, Issue:
6238
Journal Article
Peer reviewed
It's all about the holes
From kitchen sieves and strainers to coffee filters, porous materials have a wide range of uses. On an industrial scale, they are used as sorbents, filters, membranes, and ...catalysts. Slater and Cooper review how each application will limit the materials that can be used, and also the size and connectivity of the pores required. They go on to compare and contrast a growing range of porous materials that are finding increasing use in academic and industrial applications.
Science
, this issue
10.1126/science.aaa8075
BACKGROUND
Porous materials are important in established processes such as catalysis and molecular separations and in emerging technologies for energy and health. Porous zeolites have made the largest contribution to society so far, and that field is still developing rapidly. Other porous solids have also entered the scene in the past two decades, such as metal-organic frameworks (MOFs), covalent organic frameworks (COFs), and porous organic polymers. No single class of porous material is ideal for all purposes. For example, crystallinity and long-range order might enhance selectivity for a molecular separation while also reducing mechanical stability or processability with respect to less ordered structures. To have an impact on real applications, porous materials must be scalable and must satisfy multiple functional criteria such as long-term stability, selectivity, adsorption kinetics, and processability, all within a viable cost envelope. This presents a broad design challenge, and it requires us to be able to control structure and to understand multiple structure-property relationships at a detailed level.
ADVANCES
In addition to MOFs, COFs, and porous polymer networks, other classes of molecular porous solids have emerged in the past 10 years, such as polymers of intrinsic microporosity and porous organic cages. The range of possible functions for porous solids is thus much broader than before. For example, conjugated microporous polymers and some COFs have extended, conjugated structures that are not present in zeolites or MOFs and have led to porous organic photocatalysts and electronic materials. The crystal engineering approaches developed for zeolites, MOFs, and COFs cannot be applied directly to amorphous solids such as porous polymers, but analogous modular strategies have allowed functions such as porosity and electronic band gap to be controlled by choosing the appropriate molecular building blocks. Rapid advances in the computational prediction of structure and function offer a strategy for identifying the best porous materials for specific applications, for example, via large-scale screening of gas adsorption in hypothetical MOFs.
OUTLOOK
Advances in synthesis have produced new classes of functional porous solids as well as fundamental breakthroughs in areas such as selective carbon dioxide capture, molecular separations, and catalysis. As yet, these rapid developments in basic understanding are unmatched by large-scale commercial implementation, but enhanced functions (such as enzyme-like CO
2
selectivity) and new processing options (such as soluble porous solids) present exciting opportunities. A general challenge will be to reengineer porous materials where scale-up is prohibited by cost, retaining the advanced function but using cheaper and more sustainable building blocks. It is therefore important to develop structure-property relationships to understand how promising materials work. Not all future opportunities for porous solids involve improving on existing materials or the development of more scalable preparation routes. For example, porous photocatalysts that can perform direct solar water splitting might provide a completely new platform for energy production. As we seek increasingly complex functions for porous materials, the use of in silico computational design to guide experiment will become more important.
Porous materials can be defined by type or by function, but it is function that will determine the scope for practical applications.
Our ability to design functions in porous solids has advanced markedly in the past two decades as a result of developments in modular synthesis, materials characterization, and (more recently) computational structure-property predictions. This figure is based on the pore channels, shown in yellow, for an organic cage molecule, a new type of solution-processable porous solid developed over the past 6 years.
Porous solids are important as membranes, adsorbents, catalysts, and in other chemical applications. But for these materials to find greater use at an industrial scale, it is necessary to optimize multiple functions in addition to pore structure and surface area, such as stability, sorption kinetics, processability, mechanical properties, and thermal properties. Several different classes of porous solids exist, and there is no one-size-fits-all solution; it can therefore be challenging to choose the right type of porous material for a given job. Computational prediction of structure and properties has growing potential to complement experiment to identify the best porous materials for specific applications.
Conjugated microporous polymers (CMPs) are a unique class of materials that combine extended π-conjugation with a permanently microporous skeleton. Since their discovery in 2007, CMPs have become ...established as an important subclass of porous materials. A wide range of synthetic building blocks and network-forming reactions offers an enormous variety of CMPs with different properties and structures. This has allowed CMPs to be developed for gas adsorption and separations, chemical adsorption and encapsulation, heterogeneous catalysis, photoredox catalysis, light emittance, sensing, energy storage, biological applications, and solar fuels production. Here we review the progress of CMP research since its beginnings and offer an outlook for where these materials might be headed in the future. We also compare the prospect for CMPs against the growing range of conjugated crystalline covalent organic frameworks (COFs).
Until recently, porous molecular solids were isolated curiosities with properties that were eclipsed by porous frameworks, such as metal–organic frameworks. Now molecules have emerged as a functional ...materials platform that can have high levels of porosity, good chemical stability, and, uniquely, solution processability. The lack of intermolecular bonding in these materials has also led to new, counterintuitive states of matter, such as porous liquids. Our ability to design these materials has improved significantly due to advances in computational prediction methods.
Conjugated polymers are an emerging class of photocatalysts for hydrogen production where the large breadth of potential synthetic diversity presents both an opportunity and a challenge. Here, we ...integrate robotic experimentation with high-throughput computation to navigate the available structure–property space. A total of 6354 co-polymers was considered computationally, followed by the synthesis and photocatalytic characterization of a sub-library of more than 170 co-polymers. This led to the discovery of new polymers with sacrificial hydrogen evolution rates (HERs) of more than 6 mmol g–1 h–1. The variation in HER across the library does not correlate strongly with any single physical property, but a machine-learning model involving four separate properties can successfully describe up to 68% of the variation in the HER data between the different polymers. The four variables used in the model were the predicted electron affinity, the predicted ionization potential, the optical gap, and the dispersibility of the polymer particles in solution, as measured by optical transmittance.
An alternative explanation: The new microporous organic polymer framework PAF‐1 displays exceptional physicochemical stability along with an extremely high surface area (BET surface area 5640 m2 ...g−1). The question arises whether this material displays the high degree of crystalline order presumed necessary for this high surface area.
Three-dimensional (3D) covalent organic frameworks (COFs) are rare because there is a limited choice of organic building blocks that offer multiple reactive sites in a polyhedral geometry. Here, we ...synthesized an organic cage molecule (Cage-6-NH 2 ) that was used as a triangular prism node to yield the first cage-based 3D COF, 3D-CageCOF-1. This COF adopts an unreported 2-fold interpenetrated acs topology and exhibits reversible dynamic behavior, switching between a small-pore (sp) structure and a large-pore (lp) structure. It also shows high CO2 uptake and captures water at low humidity (<40%). This demonstrates the potential for expanding the structural complexity of 3D COFs by using organic cages as the building units.
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