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1. Spin‐Crossover Properties of an Iron(II) Coordination Nanohoop

   https://doi.org/10.1002/anie.202013374  

   Heras Ojea, María José; Van Raden, Jeff M.; Louie, Shayan; Collins, Richard; Pividori, Daniel; Cirera, Jordi; Meyer, Karsten; Jasti, Ramesh; Layfield, Richard A. (December 2020, Angewandte Chemie International Edition)

   Abstract Addition of the bipyridyl‐embedded cycloparaphenylene nanohoop bipy[9]CPP to [Fe{H₂B(pyz)₂}] (pyz=pyrazolyl) produces the distorted octahedral complex [Fe(bipy[9]CPP){H₂B(pyz)₂}₂] (1). The molecular structure of1shows that the nanohoop ligand contains a non‐planar bipy unit. Magnetic susceptibility measurements indicate spin‐crossover (SCO) behaviour with aT_1/2of 130 K, lower than that of 160 K observed with the related compound [Fe(bipy){H₂B(pyz)₂}₂] (2), which contains a conventional bipy ligand. A computational study of1and2reveals that the curvature of the nanohoop leads to the different SCO properties, suggesting that the SCO behaviour of iron(II) can be tuned by varying the size and diameter of the nanohoop. 

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2. A High‐Yielding Active Template Click Reaction (AT−CuAAC) for the Synthesis of Mechanically Interlocked Nanohoops

   https://doi.org/10.1002/anie.202401823  

   May, James H.; Fehr, Julia M.; Lorenz, Jacob C.; Zakharov, Lev N.; Jasti, Ramesh (April 2024, Angewandte Chemie International Edition)

   Abstract Mechanically interlocked molecules (MIMs) represent an exciting yet underexplored area of research in the context of carbon nanoscience. Recently, work from our group and others has shown that small carbon nanotube fragments—[n]cycloparaphenylenes ([n]CPPs) and related nanohoop macrocycles—may be integrated into mechanically interlocked architectures by leveraging supramolecular interactions, covalent tethers, or metal‐ion templates. Still, available synthetic methods are typically difficult and low yielding, and general methods that allow for the creation of a wide variety of these structures are limited. Here we report an efficient route to interlocked nanohoop structures via the active template Cu‐catalyzed azide‐alkyne cycloaddition (AT−CuAAC) reaction. With the appropriate choice of substituents, a macrocyclic precursor to 2,2′‐bipyridyl embedded [9]CPP (bipy[9]CPP) participates in the AT−CuAAC reaction to provide [2]rotaxanes in near‐quantitative yield, which can then be converted into the fully π‐conjugated catenane structures. Through this approach, two nanohoop[2]catenanes are synthesized which consist of a bipy[9]CPP catenated with either Tz[10]CPP or Tz[12]CPP (whereTzdenotes a 1,2,3‐triazole moiety replacing one phenylene ring in the [n]CPP backbone). 

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3. Highly strained [6]cycloparaphenylene: crystallization of an unsolvated polymorph and the first mono- and dianions

   https://doi.org/10.1039/C8CC03693D  

   Spisak, Sarah N.; Wei, Zheng; Darzi, Evan; Jasti, Ramesh; Petrukhina, Marina A. (January 2018, Chemical Communications)

   An X-ray diffraction study of [6]cycloparaphenylene ( 1 ), crystallized under solvent-free conditions, revealed a unique solid state structure with tight packing of individual molecules that minimizes empty internal space. The controlled chemical reduction of this highly strained nanohoop with Group 1 metals resulted in the first isolation and structural characterization of its mono- and dianions, allowing for the evaluation of core transformations for the series ranging from 1 0 to 1 1− and 1 2− . 

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4. Scalable synthesis of [8]cycloparaphenyleneacetylene carbon nanohoop using alkyne metathesis

   https://doi.org/10.1039/D1CC04776K  

   Zhou, Xin; Kwon, Hyejin; Thompson, Richard R.; Herman, Robert J.; Fronczek, Frank R.; Bruns, Carson J.; Lee, Semin (October 2021, Chemical Communications)

   Large scale synthesis of cycloparaphenyleneacetylenes has been challenging due to low macrocyclization yields and harsh aromatization methods that often decompose strained alkynes. Herein, a cis -stilbene-based building block is subjected to alkyne metathesis macrocylization. The following sequence of alkene-selective bromination and dehydrobromination afforded a [8]cycloparaphenyleneacetylene derivative in high yield with good scalability. X-Ray crystal structure and computational analysis revealed a unique same-rim conformation for the eight methyl groups on the nanohoop. 

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5. Bethe–Salpeter equation spectra for very large systems

   https://doi.org/10.1063/5.0100213  

   Bradbury, Nadine C.; Nguyen, Minh; Caram, Justin R.; Neuhauser, Daniel (July 2022, The Journal of Chemical Physics)

   We present a highly efficient method for the extraction of optical properties of very large molecules via the Bethe–Salpeter equation. The crutch of this approach is the calculation of the action of the effective Coulombic interaction, W, through a stochastic time-dependent Hartree propagation, which uses only ten stochastic orbitals rather than propagating the full sea of occupied states. This leads to a scaling that is at most cubic in system size with trivial parallelization of the calculation. We apply this new method to calculate the spectra and electronic density of the dominant excitons of a carbon-nanohoop bound fullerene system with 520 electrons using less than 4000 core hours. 

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