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1. Cyclotetrabenzil-Based Porous Organic Polymers with High Carbon Dioxide Affinity

   https://doi.org/10.1055/a-1512-5753  

   Ashirov, Timur; Alrayyani, Maymounah; Song, Kyung-Seob; Miljanić, Ognjen Š.; Coskun, Ali (April 2021, Organic Materials)

   null (Ed.)

   Porous organic polymers (POPs) incorporating macrocyclic units have been investigated in recent years in an effort to transfer macrocycles' intrinsic host–guest properties onto the porous networks to achieve complex separations. In this regard, highly interesting building blocks are presented by the family of cyclotetrabenzoin macrocycles with rigid, well-defined, electron-deficient cavities. This macrocycle shows high affinity towards linear guest molecules such as carbon dioxide, thus offering an ideal building block for the synthesis of CO2-philic POPs. Herein, we report the synthesis of a POP through the condensation reaction between cyclotetrabenzil and 1,2,4,5-tetraaminobenzene under ionothermal conditions using the eutectic zinc chloride/sodium chloride/potassium chloride salt mixture at 250 °C. Notably, following the condensation reaction, the macrocycle favors three-dimensional (3D) growth rather than a two-dimensional one while retaining the cavity. The resulting polymer, named 3D-mPOP, showed a highly microporous structure with a BET surface area of 1142 m2 g−1 and a high carbon dioxide affinity with a binding enthalpy of 39 kJ mol−1. Moreover, 3D-mPOP showed very high selectivity for carbon dioxide in carbon dioxide/methane and carbon dioxide/nitrogen mixtures. 

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2. Self-assembled Janus base nanotubes: chemistry and applications

   https://doi.org/10.3389/fchem.2023.1346014  

   Zhang, Wuxia; Chen, Yupeng (January 2024, Frontiers in Chemistry)

   Janus base nanotubes are novel, self-assembled nanomaterials. Their original designs were inspired by DNA base pairs, and today a variety of chemistries has developed, distinguishing them as a new family of materials separate from DNA origami, carbon nanotubes, polymers, and lipids. This review article covers the principal examples of self-assembled Janus base nanotubes, which are driven by hydrogen-bond and π-π stacking interactions in aqueous environments. Specifically, self-complementary hydrogen bonds organize molecules into ordered arrays, forming macrocycles, while π-π interactions stack these structures to create tubular forms. This review elucidates the molecular interactions that govern the assembly of nanotubes and advances our understanding of nanoscale self-assembly in water. 

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3. Polystyrene and poly(methyl methacrylate) interfaces reinforced with diblock carbon nanotubes

   https://doi.org/10.1002/pen.25665  

   Seyni, Fatoumata_Ide; Barrett, Lawrence; Crossley, Steven; Grady, Brian_P (February 2021, Polymer Engineering & Science)

   Abstract An asymmetric double cantilever beam test was used to determine the ability of carbon nanotubes with varying chemistry along their lengths, that is, diblock nanotubes, to compatibilize the polystyrene/poly(methyl methacrylate) (PS/PMMA) interface. PS molecules were grafted primarily to one of the blocks to cause that block to migrate to the PS phase since otherwise both blocks would prefer to reside in PMMA. Fracture toughnesses increased monotonically with increasing diblock carbon nanotube concentration and maximum values were like those for block copolymer‐reinforced interfaces while single‐chemistry nanotubes showed no reinforcing effect. However, the abrupt increase in fracture toughness with added compatibilizer indicative of a transition to crazing was not found consistent with nanotubes suppressing crazing in homopolymers. Scanning electron microscopy images of the fractured surfaces show agglomerates of carbon nanotubes present which are likely limiting the efficacy of carbon nanotubes at toughening the interface. 

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4. Symmetry breaking and the turn-on fluorescence of small, highly strained carbon nanohoops

   https://doi.org/10.1039/C9SC00169G  

   Lovell, Terri C.; Colwell, Curtis E.; Zakharov, Lev N.; Jasti, Ramesh (March 2019, Chemical Science)

   [ n ]Cycloparaphenylenes, or “carbon nanohoops,” are unique conjugated macrocycles with radially oriented π-systems similar to those in carbon nanotubes. The centrosymmetric nature and conformational rigidity of these molecules lead to unusual size-dependent photophysical characteristics. To investigate these effects further and expand the family of possible structures, a new class of related carbon nanohoops with broken symmetry is disclosed. In these structures, referred to as meta [ n ]cycloparaphenylenes, a single carbon–carbon bond is shifted by one position in order to break the centrosymmetric nature of the parent [ n ]cycloparaphenylenes. Advantageously, the symmetry breaking leads to bright emission in the smaller nanohoops, which are typically non-fluorescent due to optical selection rules. Moreover, this simple structural manipulation retains one of the most unique features of the nanohoop structures—size dependent emissive properties with relatively large extinction coefficients and quantum yields. Inspired by earlier theoretical work by Tretiak and co-workers, this joint synthetic, photophysical, and theoretical study provides further design principles to manipulate the optical properties of this growing class of molecules with radially oriented π-systems. 

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5. Synthesis and Properties of Fluorenone‐Containing Cycloparaphenylenes and Their Late‐Stage Transformation

   https://doi.org/10.1002/chem.202303490  

   Bliksted_Roug_Pedersen, Viktor; Price, Tavis_W; Kofod, Nicolaj; Zakharov, Lev_N; Laursen, Bo_W; Jasti, Ramesh; Brøndsted_Nielsen, Mogens (December 2023, Chemistry – A European Journal)

   Abstract Cycloparaphenylenes (CPPs) are the smallest possible armchair carbon nanotubes, the properties of which strongly depend on their ring size. They can be further tuned by either peripheral functionalization or by replacing phenylene rings for other aromatic units. Here we show how four novel donor–acceptor chromophores were obtained by incorporating fluorenone or 2‐(9H‐fluoren‐9‐ylidene)malononitrile into the loops of two differently sized CPPs. Synthetically, we managed to perform late‐stage functionalization of the fluorenone‐based rings by high‐yielding Knoevenagel condensations. The structures were confirmed by X‐ray crystallographic analyses, which revealed that replacing a phenylene for a fused‐ring‐system acceptor introduces additional strain. The donor–acceptor characters of the CPPs were supported by absorption and fluorescence spectroscopic studies, electrochemical studies (displaying the CPPs as multi‐redox systems undergoing reversible or quasi‐reversible redox events), as well as by computations. The oligophenylene parts were found to comprise the electron donor units of the macrocycles and the fluorenone parts the acceptor units. 

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