A Three-Dimensional Porous Organic Semiconductor Based on Fully sp2 -Hybridized Graphitic Polymer

Tuning (Photo)Electronic Properties of an Electron Deficient Porous Polymer via n-Doping with Tetrathiafulvalene

Charge-transfer complex formation within the pores of porous polymers is an efficient way to tune their electronical properties. Introduction of electron accepting guests to the electron donating hosts to conduct their p-doping is intensively studied in this context. However, the vice versa scenario, n-doping by treating the electron deficient (i.e., n-type) porous polymers with electron donating dopants, is rare. In this work, synthesis of an n-type phenazine based conjugated microporous polymer and its exposure to strong electron donating tetrathiafulvalene (TTF) dopants are presented. The fundamental physical characterizations (e.g., elemental analysis, gas sorption) showed that the vacuum impregnation technique is a good approach to load the guest molecules inside the pores. Moreover, the formation of charge-transfer complexes between the phenazine building blocks of the polymeric network and TTF dopants are confirmed via spectral techniques such Fourier transform infra-red, UV-vis, steady-state/time-resolved photoluminescence, and transient absorbance spectroscopies. Effect of the doping to the electronical properties is monitored by employing photoelectrochemical measurements, which showed lower charge-transfer resistivity and nearly doubled photocurrents after the doping. The study is, therefore, an important advancement for the applicability of (n-type) porous polymeric materials in the field of photo(electro)catalysis and organic electronics.

Nanofibrous Porous Organic Polymers and Their Derivatives: From Synthesis to Applications

Engineering porous organic polymers (POPs) into 1D morphology holds significant promise for diverse applications due to their exceptional processability and increased surface contact for enhanced interactions with guest molecules. This article reviews the latest developments in nanofibrous POPs and their derivatives, encompassing porous organic polymer nanofibers, their composites, and POPs-derived carbon nanofibers. The review delves into the design and fabrication strategies, elucidates the formation mechanisms, explores their functional attributes, and highlights promising applications. The first section systematically outlines two primary fabrication approaches of nanofibrous POPs, i.e., direct bulk synthesis and electrospinning technology. Both routes are discussed and compared in terms of template utilization and post-treatments. Next, performance of nanofibrous POPs and their derivatives are reviewed for applications including water treatment, water/oil separation, gas adsorption, energy storage, heterogeneous catalysis, microwave absorption, and biomedical systems. Finally, highlighting existent challenges and offering future prospects of nanofibrous POPs and their derivatives are concluded.

Mixed-Valence CuI /CuIII Metal-Organic Frameworks with Non-innocent Ligand for Multielectron Transfer

We report two novel three-dimensional copper-benzoquinoid metal-organic frameworks (MOFs), [Cu4 L3 ]n and [Cu4 L3  ⋅ Cu(iq)3 ]n (LH4 =1,4-dicyano-2,3,5,6-tetrahydroxybenzene, iq=isoquinoline). Spectroscopic techniques and computational studies reveal the unprecedented mixed valency in MOFs, formal Cu(I)/Cu(III). This is the first time that formally Cu(III) species are witnessed in metal-organic extended solids. The coordination between the mixed-valence metal and redox-non-innocent ligand L, which promotes through-bond charge transfer between Cu metal sites, allows better metal-ligand orbital overlap of the d-π conjugation, leading to strong long-range delocalization and semiconducting behavior. Our findings highlight the significance of the unique mixed valency between formal Cu(I) and highly-covalent Cu(III), non-innocent ligand, and pore environments of these bench stable Cu(III)-containing frameworks on multielectron transfer and electrochemical properties.

Fully Conjugated Benzyne‐Derived Three‐Dimensional Porous Organic Polymers

Porous organic polymers (POPs) have gained tremendous attention owing to their chemical tunability, stability and high surface areas. Whereas there are several examples of fully conjugated two‐dimensional (2D) POPs, three‐dimensional (3D) ones are rather challenging to realize in the absence of structural templates. Herein, we report the base‐catalyzed direct synthesis of a fully conjugated 3D POPs, named benzyne‐derived polymers (BDPs), containing biphenylene and tetraphenylene moieties starting from a simple bisbenzyne precursor, which undergoes [2+2] and [2+2+2+2] cycloaddition reactions to form BDPs primarily composed of biphenylene and tetraphenylene moieties. The resulting polymers exhibited ultramicroporous structures with surface areas up to 544 m2 g−1 and very high CO2/N2 selectivities.

Using molecular straps to engineer conjugated porous polymer growth, chemical doping, and conductivity

Controlling network growth and architecture of 3D-conjugated porous polymers (CPPs) is challenging and therefore has limited the ability to systematically tune the network architecture and study its impact on doping efficiency and conductivity. We have proposed that π-face masking straps mask the π-face of the polymer backbone and therefore help to control π-π interchain interactions in higher dimensional π-conjugated materials unlike the conventional linear alkyl pendant solubilizing chains that are incapable of masking the π-face. Herein, we used cycloaraliphane-based π-face masking strapped monomers and show that the strapped repeat units, unlike the conventional monomers, help to overcome the strong interchain π-π interactions, extend network residence time, tune network growth, and increase chemical doping and conductivity in 3D-conjugated porous polymers. The straps doubled the network crosslinking density, which resulted in 18 times higher chemical doping efficiency compared to the control non-strapped-CPP. The straps also provided synthetic tunability and generated CPPs of varying network size, crosslinking density, dispersibility limit, and chemical doping efficiency by changing the knot to strut ratio. For the first time, we have shown that the processability issue of CPPs can be overcome by blending them with insulating commodity polymers. The blending of CPPs with poly(methylmethacrylate) (PMMA) has enabled them to be processed into thin films for conductivity measurements. The conductivity of strapped-CPPs is three orders of magnitude higher than that of the poly(phenyleneethynylene) porous network.

Topologically Porous Heterostructures for Photo/Photothermal Catalysis of Clean Energy Conversion

As a straightforward way to fix solar energy, photo/photothermal catalysis with semiconductor provides a promising way to settle the energy shortage and environmental crisis in many fields, especially in clean energy conversion. Topologically porous heterostructures (TPHs), featured with well-defined pores and mainly composed by the derivatives of some precursors with specific morphology, are a major part of hierarchical materials in photo/photothermal catalysis and provide a versatile platform to construct efficient photocatalysts for their enhanced light absorption, accelerated charges transfer, improved stability, and promoted mass transportation. Therefore, a comprehensive and timely review on the advantages and recent applications of the TPHs is of great importance to forecast the potential applications and research trend in the future. This review initially demonstrates the advantages of TPHs in photo/photothermal catalysis. Then the universal classifications and design strategies of TPHs are emphasized. Besides, the applications and mechanisms of photo/photothermal catalysis in hydrogen evolution from water splitting and CO_x hydrogenation over TPHs are carefully reviewed and highlighted. Finally, the challenges and perspectives of TPHs in photo/photothermal catalysis are also critically discussed.

Porous and Water Stable 2D Hybrid Metal Halide with Broad Light Emission and Selective H2 O Vapor Sorption

In this work we report a strategy for generating porosity in hybrid metal halide materials using molecular cages that serve as both structure-directing agents and counter-cations. Reaction of the [2.2.2] cryptand (DHS) linker with Pb^II in acidic media gave rise to the first porous and water-stable 2D metal halide semiconductor (DHS)₂ Pb₅ Br₁₄ . The corresponding material is stable in water for a year, while gas and vapor-sorption studies revealed that it can selectively and reversibly adsorb H₂ O and D₂ O at room temperature (RT). Solid-state NMR measurements and DFT calculations verified the incorporation of H₂ O and D₂ O in the organic linker cavities and shed light on their molecular configuration. In addition to porosity, the material exhibits broad light emission centered at 617 nm with a full width at half-maximum (FWHM) of 284 nm (0.96 eV). The recorded water stability is unparalleled for hybrid metal halide and perovskite materials, while the generation of porosity opens new pathways towards unexplored applications (e.g. solid-state batteries) for this class of hybrid semiconductors.

Antiaromatic Covalent Organic Frameworks Based on Dibenzopentalenes

Despite their inherent instability, 4n π systems have recently received significant attention due to their unique optical and electronic properties. In dibenzopentalene (DBP), benzanellation stabilizes the highly antiaromatic pentalene core, without compromising its amphoteric redox behavior or small HOMO-LUMO energy gap. However, incorporating such molecules in organic devices as discrete small molecules or amorphous polymers can limit the performance (e.g., due to solubility in the battery electrolyte solution or low internal surface area). Covalent organic frameworks (COFs), on the contrary, are highly ordered, porous, and crystalline materials that can provide a platform to align molecules with specific properties in a well-defined, ordered environment. We synthesized the first antiaromatic framework materials and obtained a series of three highly crystalline and porous COFs based on DBP. Potential applications of such antiaromatic bulk materials were explored: COF films show a conductivity of 4 × 10^-8 S cm^-1 upon doping and exhibit photoconductivity upon irradiation with visible light. Application as positive electrode materials in Li-organic batteries demonstrates a significant enhancement of performance when the antiaromaticity of the DBP unit in the COF is exploited in its redox activity with a discharge capacity of 26 mA h g^-1 at a potential of 3.9 V vs. Li/Li⁺. This work showcases antiaromaticity as a new design principle for functional framework materials.

Nanocellulose Paper Semiconductor with a 3D Network Structure and Its Nano-Micro-Macro Trans-Scale Design

Semiconducting nanomaterials with 3D network structures exhibit various fascinating properties such as electrical conduction, high permeability, and large surface areas, which are beneficial for adsorption, separation, and sensing applications. However, research on these materials is substantially restricted by the limited trans-scalability of their structural design and tunability of electrical conductivity. To overcome this challenge, a pyrolyzed cellulose nanofiber paper (CNP) semiconductor with a 3D network structure is proposed. Its nano-micro-macro trans-scale structural design is achieved by a combination of iodine-mediated morphology-retaining pyrolysis with spatially controlled drying of a cellulose nanofiber dispersion and paper-crafting techniques, such as microembossing, origami, and kirigami. The electrical conduction of this semiconductor is widely and systematically tuned, via the temperature-controlled progressive pyrolysis of CNP, from insulating (1012 Ω cm) to quasimetallic (10-2 Ω cm), which considerably exceeds that attained in other previously reported nanomaterials with 3D networks. The pyrolyzed CNP semiconductor provides not only the tailorable functionality for applications ranging from water-vapor-selective sensors to enzymatic biofuel cell electrodes but also the designability of macroscopic device configurations for stretchable and wearable applications. This study provides a pathway to realize structurally and functionally designable semiconducting nanomaterials and all-nanocellulose semiconducting technology for diverse electronics.

Porous organic polymers in solar cells

Owing to their unique porosity and large surface area, porous organic polymers (POPs) have shown their presence in numerous novel applications. The tunability and functionality of both the pores and backbone of the material enable its suitability in photovoltaic devices. The porosity induced host-guest configurations as well as periodic donor-acceptor structures benefit the charge separation and charge transfer in photophysical processes. The role of POPS in other critical device components, such as hole transporting layers and electrodes, has also been demonstrated. Herein, this review will primarily focus on the recent progress made in applying POPs for solar cell device performance enhancement, covering organic solar cells, perovskite solar cells, and dye-sensitized solar cells. Based on the efforts in recent years in unraveling POP's photophysical process and its relevance with device performances, an in-depth analysis will be provided to address the gradual shift of attention from an entirely POP-based active layer to other device functional components. Combining the insights from device physics, material synthesis, and microfabrication, we aim to unfold the fundamental limitations and challenges of POPs and shed light on future research directions.

Fully Conjugated Tetraoxa[8]circulene-Based Porous Semiconducting Polymers

Tetraoxa[8]circulenes (TOCs) are a class of hetero[8]circulenes featuring a planar cyclooctatetraene core with a mixed aromatic/antiaromatic motif that governs their electronic properties. Polymeric TOCs (pTOCs) have been the subject of several computational simulations because they are predicted to be low-band-gap semiconductors, but they have not been available synthetically yet. Here, we report the first example of pTOCs, a new family of porous semiconductors, synthesized under ionothermal conditions through the intermolecular cyclization of 1,4,5,8-anthracene tetrone. pTOCs are porous, with surface areas up to 1656 m2  g-1 , and exhibit light-switchable and tunable semiconducting properties.

Fully Conjugated Tetraoxa[8]circulene‐Based Porous Semiconducting Polymers

Tetraoxa[8]circulenes (TOCs) are a class of hetero[8]circulenes featuring a planar cyclooctatetraene core with a mixed aromatic/antiaromatic motif that governs their electronic properties. Polymeric TOCs (pTOCs) have been the subject of several computational simulations because they are predicted to be low‐band‐gap semiconductors, but they have not been available synthetically yet. Here, we report the first example of pTOCs, a new family of porous semiconductors, synthesized under ionothermal conditions through the intermolecular cyclization of 1,4,5,8‐anthracene tetrone. pTOCs are porous, with surface areas up to 1656 m2 g−1, and exhibit light‐switchable and tunable semiconducting properties.

Porous nanographene formation on γ-alumina nanoparticles via transition-metal-free methane activation

γ-Al₂O₃ nanoparticles promote pyrolytic carbon deposition of CH₄ at temperatures higher than 800 °C to give single-walled nanoporous graphene (NPG) materials without the need for transition metals as reaction centers. To accelerate the development of efficient reactions for NPG synthesis, we have investigated early-stage CH₄ activation for NPG formation on γ-Al₂O₃ nanoparticles via reaction kinetics and surface analysis. The formation of NPG was promoted at oxygen vacancies on (100) surfaces of γ-Al₂O₃ nanoparticles following surface activation by CH₄. The kinetic analysis was well corroborated by a computational study using density functional theory. Surface defects generated as a result of surface activation by CH₄ make it kinetically feasible to obtain single-layered NPG, demonstrating the importance of precise control of oxygen vacancies for carbon growth.

Oxygen vacancies on the (100) surface of γ-Al₂O₃ nanoparticles catalyse CH₄-CVD for single-layered nanoporous graphenes with no transition metal reaction centre. The rate-limiting step is the proton transfer (PT) in the activation of CH₄ on them.

A Three-Dimensional sp2 Carbon-Conjugated Covalent Organic Framework

A first example of an sp² carbon-conjugated three-dimensional (3D) covalent organic framework (COF) (BUCT-COF-4) is synthesized via the Knoevenagel condensation of the saddle-shaped aldehyde-substituted cyclooctatetrathiophene and 1,4-phenylenediacetonitrile. Ascribed to the extended π-conjugation and long-range ordered structures, BUCT-COF-4 displays high Hall electron mobility of 1.97 cm² V^-1 s^-1 at room temperature. After it is doped with iodine, the material not only exhibits an enhanced electron mobility up to 2.62 cm² V^-1 s^-1 in ambient air but also presents an unexpected metal-free ferromagnetic phase transition arising from the formation of aligned spins unidirectional across the whole sp² carbon-conjugated 3D framework. This is the first report of a ferromagnetic phenomenon in 3D COF materials, which would broaden promising applications and open a new frontier in COF materials.

Catalyst- and Solvent-Free Synthesis of a Chemically Stable Aza-Bridged Bis(phenanthroline) Macrocycle-Linked Covalent Organic Framework

Developing new linkage-based covalent organic frameworks (COFs) is one of the major topics in reticular chemistry. Electrically conductive COFs have enabled applications in energy storage and electrochemical catalysis, which are not feasible using insulating COFs. Despite significant advances, the construction of chemically stable conductive COFs by the formation of new linkages remains relatively unexplored and challenging. Here we report the solvent- and catalyst-free synthesis of a two-dimensional aza-bridged bis(phenanthroline) macrocycle-linked COF (ABBPM-COF) from the thermally induced poly-condensation of a tri-topic monomer and ammonia gas. The ABBPM-COF structure was elucidated using multiple techniques, including X-ray diffraction analysis combined with structural simulation, revealing its crystalline nature with an ABC stacking mode. Further experiments demonstrated its excellent chemical stability in acid/base solutions. Electrical-conductivity measurements showed that the insulating ABBPM-COF becomes a semiconducting material after exposure to iodine vapor.

Saddle-Shaped Building Blocks: A New Concept for Designing Fully Conjugated 3D Organic Semiconducting Materials

Currently, most organic semiconducting materials (OSMs) are π-conjugated structures in one or two dimension (2D), where the lack of layer-layer π-conjugation connection greatly blocks their electron delocalization and transport. The 3D fully conjugated materials could solve this issue because they can provide efficient charge-transport pathways throughout the whole 3D skeleton, in which the suitable 3D building block is the key to the development of fully conjugated 3D OSMs. Cyclooctatetraene (COT) and its derivatives are good candidates due to their π-conjugation with 3D saddle-shaped architecture. In this Concept, we discuss the key features of saddle-shaped COT-based derivatives and their synthetic strategy, then we present the current development of using the COT derivatives as building blocks to construct the 3D fully conjugated organic small compound- and polymer-based OSMs. The properties and perspectives of these OSMs in photovoltaics, electro-catalysis and electrical conductivities are also discussed. These recent advances in the developing 3D fully conjugated materials could potentially open up a new frontier in the design of OSMs.

Beyond structural motifs: the frontier of actinide-containing metal-organic frameworks

In this perspective, we feature recent advances in the field of actinide-containing metal-organic frameworks (An-MOFs) with a main focus on their electronic, catalytic, photophysical, and sorption properties. This discussion deviates from a strictly crystallographic analysis of An-MOFs, reported in several reviews, or synthesis of novel structural motifs, and instead delves into the remarkable potential of An-MOFs for evolving the nuclear waste administration sector. Currently, the An-MOF field is dominated by thorium- and uranium-containing structures, with only a few reports on transuranic frameworks. However, some of the reported properties in the field of An-MOFs foreshadow potential implementation of these materials and are the main focus of this report. Thus, this perspective intends to provide a glimpse into the challenges, triumphs, and future directions of An-MOFs in sectors ranging from the traditional realm of gas sorption and separation to recently emerging areas such as electronics and photophysics.

The Prospect of Dimensionality in Porous Semiconductors

With the advent of silicon-based semiconductors, a plethora of previously unknown technologies became possible. The development of lightweight low-dimensional organic semiconductors followed soon after. However, the efficient charge/electron transfers enabled by the non-porous 3D structure of silicon is rather challenging to be realized by their (metal-)organic counterparts. Nevertheless, the demand for lighter, more efficient semiconductors is steadily increasing resulting in a growing interest in (metal-)organic semiconductors. These novel materials are faced with a variety of challenges originating from their chemical design, their packing and crystallinity. Although the effect of molecular design is quite well understood, the influence of dimensionality and the associated change in properties (porosity, packing, conjugation) is still an uncharted area in (metal-)organic semiconductors, yet highly important for their practical utilization. In this Minireview, an overview on the design and synthesis of porous semiconductors, with a particular emphasis on organic semiconductors, is presented and the influence of dimensionality is discussed.