A C₃-symmetric macrocycle-based, hydrogen-bonded, multiporous hexagonal network as a motif of porous molecular crystals

A C₃-symmetric π-conjugated macrocycle combined with an appropriate hydrogen bonding module (phenylene triangle) allowed the construction of crystalline supramolecular frameworks with a cavity volume of up to 58 %. The frameworks were obtained through non-interpenetrated stacking of a hexagonal sheet possessing three kinds of pores with different sizes and shapes. The activated porous material absorbed CO₂ up to 96 cm³ g-¹ at 195 K under 1 atm.This is the accepted version of the following article: Hisaki I., Nakagawa S., Tohnai N., et al. A C₃-symmetric macrocycle-based, hydrogen-bonded, multiporous hexagonal network as a motif of porous molecular crystals. Angewandte Chemie - International Edition 54, 3008 (2015), which has been published in final form at https://doi.org/10.1002/anie.201411438.[Link to final article]. This article may be used for non-commercialpurposes in accordance with the Wiley Self-ArchivingPolicy [https://authorservices.wiley.com/author-resources/Journal-Authors/licensing/self-archiving.html

Designing Hydrogen-Bonded Organic Frameworks (HOFs) with Permanent Porosity

Designing organic components that can be used to construct porous materials enables the preparation of tailored functionalized materials. Research into porous materials has seen a resurgence in the past decade as a result of finding of self-standing porous molecular crystals (PMCs). Particularly, a number of crystalline systems with permanent porosity that are formed by self-assembly through hydrogen bonding (H-bonding) have been developed. Such systems are called hydrogen-bonded organic frameworks (HOFs). Herein we systematically describe H-bonding patterns (supramolecular synthons) and molecular structures (tectons) that have been used to achieve thermal and chemical durability, a large surface area, and functions, such as selective gas sorption and separation, which can provide design principles for constructing HOFs with permanent porosity.This is the accepted version of the following article: Hisaki I., Xin C.,Takahashi K., et al. Designing Hydrogen-Bonded Organic Frameworks (HOFs) with Permanent Porosity. Angewandte Chemie - International Edition 58, 11160 (2019), which has been published in final form at https://doi.org/10.1002/anie.201902147. This article may be used for non-commercialpurposes in accordance with the Wiley Self-ArchivingPolicy [https://authorservices.wiley.com/author-resources/Journal-Authors/licensing/self-archiving.html

A Proton Conductive Porous Framework of an 18-Crown-6-Ether Derivative Networked by Rigid Hydrogen Bonding Modules

A rigid hydrogen-bonded organic framework (HOF) was constructed from a C3-symmetric hexatopic carboxylic acid with a hydrophilic 18-crown-6-ether (18C6) component. Despite the flexible macrocyclic structure with many conformations, the derivative with three 4,4’-dicarboxy-o-terphenyl moieties in the periphery yielded a rigid layered porous framework through directional intermolecular hydrogen bonding. Interestingly, the HOF possesses 1D channels with bottleneck composed of 18C6 rings. The HOF shows proton conductivity (1.12×10−7 S cm−1) through Grotthuss mechanism (Ea=0.27 eV) under 98 %RH. The present unique water channel structure provides an inspiration to create molecular porous materials.This is the accepted version of the following article:Chen X., Huang R.K., Takahashi K., et al. A Proton Conductive Porous Framework of an 18-Crown-6-Ether Derivative Networked by Rigid Hydrogen Bonding Modules. Angewandte Chemie - International Edition 61, e202211686 (2022), which has been published in final form at https://doi.org/10.1002/anie.202211686. This article may be used for non-commercialpurposes in accordance with the Wiley Self-ArchivingPolicy [https://authorservices.wiley.com/author-resources/Journal-Authors/licensing/self-archiving.html

Transition Behaviors of Isostructural Hydrogen-Bonded Frameworks Composed of Naphthalene, Quinoxaline, and Pyrazinopyrazine Derivatives

Kubo H., Konishi S., Oketani R., et al. Transition Behaviors of Isostructural Hydrogen-Bonded Frameworks Composed of Naphthalene, Quinoxaline, and Pyrazinopyrazine Derivatives. Chemistry - A European Journal 30, e202401645 (2024); https://doi.org/10.1002/chem.202401645.A series of isostructural reticular frameworks with systematic differences on chemical structures allows us to disclose correlations between specific structural factors and properties, providing insights for designing novel porous materials. However, even slight differences in the molecular structure often lead to non-isostructural polymorphic frameworks particularly in the case of hydrogen-bonded organic frameworks (HOFs) because the structures of HOFs are based on a subtle balance of reversible interactions. In this study, we found that three simple analogues of tetracarboxylic acids with naphthalene, quinoxaline, and pyrazinopyrazine cores (NT, QX, and PP, respectively) yielded isostructural solvated HOFs (NT-1, QX-1, and PP-1, respectively), where hydrogen-bonded sql-networked sheets were slip-stacked with closely similar manners. More importantly, these isostructural HOFs underwent structural transformations in different manners upon removal of the guest solvents. Comparison of the crystal structures of the HOFs before and after the transformation revealed that intermolecular interactions of the core significantly affected on rearrangements of hydrogen bonds in the transformation. The results suggest the potential to control the properties and functions of isostructural HOFs by elements in the core

Docking Strategy To Construct Thermostable, Single-Crystalline, Hydrogen-Bonded Organic Framework with High Surface Area

Enhancing thermal and chemical durability and increasing surface area are two main directions for the construction and improvement of the performance of porous hydrogen-bonded organic frameworks (HOFs). Herein, a hexaazatriphenylene (HAT) derivative that possesses six carboxyaryl groups serves as a suitable building block for the systematic construction of thermally and chemically durable HOFs with high surface area through shape-fitted docking between the HAT cores and interpenetrated three-dimensional network. A HAT derivative with carboxybiphenyl groups forms a stable single-crystalline porous HOF that displays protic solvent durability, even in concentrated HCl, heat resistance up to 305 °C, and a high Brunauer–Emmett–Teller surface area [SA(BET)] of 1288 m2 g−1. A single crystal of this HOF displays anisotropic fluorescence, which suggests that it would be applicable to polarized emitters based on robust functional porous materials.This is the accepted version of the following article: Hisaki I., Suzuki Y., Gomez E., et al. Docking Strategy To Construct Thermostable, Single-Crystalline, Hydrogen-Bonded Organic Framework with High Surface Area. Angewandte Chemie - International Edition 57, 12650 (2018), which has been published in final form at https://doi.org/10.1002/anie.201805472. This article may be used for non-commercialpurposes in accordance with the Wiley Self-ArchivingPolicy [https://authorservices.wiley.com/author-resources/Journal-Authors/licensing/self-archiving.html

Hexaazatriphenylene-Based Hydrogen-Bonded Organic Framework with Permanent Porosity and Single-Crystallinity

Hydrogen-bonded organic frameworks (HOFs) have drawn unprecedented interest because of their high crystallinity as well as facile process for construction, deconstruction, and reassembly arising from reversible bond formation-dissociation. However, structural fragility and low stability frequently prevent formation of robust HOFs with permanent porosity. Here, we report that hexakis(4-carboxyphenyl)-hexaazatriphenylene (CPHAT) forms three dimensionally networked H-bonded framework CPHAT-1. Interestingly, the activated framework CPHAT-1 a retains not only permanent porosity but single-crystallinity, enabling precise structural characterization and property evaluation on a single crystal. Moreover, CPHAT-1 a retains its framework up to 339 °C or in hot water and in acidic aqueous solution. These results clearly show that even a simple H-bonding motif can be applied for the construction of robust HOFs, which creates a pathway to establish a new class of porous organic frameworks. We also characterize its uptake of gases and I2, in addition to a detailed photophysical study (spectroscopy and dynamics of proton and charge transfers) of its unit in solution, and of its single crystal under fluorescence microscopy, in which we observed a marked strong anistropy and narrow distribution. The results bring new findings to the area of HOFs and their possible applications in science and technology.This is the accepted version of the following article: Hisaki I., Ikenaka N., Gomez E., et al. Hexaazatriphenylene-Based Hydrogen-Bonded Organic Framework with Permanent Porosity and Single-Crystallinity. Chemistry - A European Journal 23, 11611 (2017), which has been published in final form at https://doi.org/10.1002/chem.201701893. This article may be used for non-commercialpurposes in accordance with the Wiley Self-ArchivingPolicy [https://authorservices.wiley.com/author-resources/Journal-Authors/licensing/self-archiving.html

Photo-Responsive Hydrogen-Bonded Molecular Networks Capable of Retaining Crystalline Periodicity after Isomerization

Kasuya K., Oketani R., Matsuda S., et al. Photo-Responsive Hydrogen-Bonded Molecular Networks Capable of Retaining Crystalline Periodicity after Isomerization. Angewandte Chemie - International Edition 63, e202404700 (2024); https://doi.org/10.1002/anie.202404700.The molecular conformation, crystalline morphology, and properties of photochromic organic crystals can be controlled through photoirradiation, making them promising candidates for functional organic materials. However, photochromic porous molecular crystals with a networked framework structure are rare due to the difficulty in maintaining space that allows for photo-induced molecular motion in the crystalline state. This study describes a photo-responsive single crystal based on hydrogen-bonded (H-bonded) network of dihydrodimethylbenzo[e]pyrene derivative 4BDHP. A crystal composed of H-bonded undulate layers, 4BDHP-2, underwent photo-isomerization in the crystalline state due to loose stacking of the layers. Particularly, enantio-pure crystal (S,S)-4BDHP-2 allowed to reveal the structure of the photoisomerized crystal, in which the closed form (4BDHP) and open form (4CPD) were arranged alternately with keeping crystalline periodicity, although side reactions were also implied. The present proof-of-concept system of a photochromic framework that retains crystalline periodicity after photo-isomerization may provide new light-driven porous functional materials

Acid Responsive Hydrogen-Bonded Organic Frameworks

A porous hydrogen-bonded organic framework (HOF) responsive to acid was constructed from a hexaazatrinaphthylene derivative with carboxyphenyl groups (CPHATN). Precise structures of both 1,2,4-trichlorobenzene solvate [CPHATN-1(TCB)] and activated HOF with permanent porosity (CPHATN-1a) were successfully determined by single-crystalline X-ray diffraction analysis. Permanent porosity of CPHATN-1a was evaluated by gas sorption experiments at low temperature. CPHATN-1a also shows significant thermal stability up to 633 K. Its crystals exhibit a rich photochemistry thanks to intramolecular charge-transfer and interunit proton-transfer reactions. Femtosecond (fs) experiments on crystals demonstrate that these events occur in ≤200 fs and 1.2 ps, respectively. Moreover, single-crystal fluorescence microscopy reveals a shift of the emission spectra most probably as a result of defects and a high anisotropic behavior, reflecting an ordered crystalline structure with a preferential orientation of the molecular dipole moments. Remarkably, CPHATN-1a, as a result of the protonation of pyradyl nitrogen atoms embedded in its π-conjugated core, shows reversible vapor acid-induced color changes from yellow to reddish-brown, which can be also followed by an ON/OFF of its emission. To the best of our knowledge, this is the first HOF that exhibits acid-responsive color changes. The present work provides new findings for developing stimuli responsive HOFs.Hisaki I., Suzuki Y., Gomez E., et al. Acid Responsive Hydrogen-Bonded Organic Frameworks. Journal of the American Chemical Society. 141(5), 2111-2121, (2019), 6 February 2019; © 2019 American Chemical Society. https://doi.org/10.1021/jacs.8b12124

Stacked Antiaromatic Porphyrins

Aromaticity is a key concept in organic chemistry. Even though this concept has already been theoretically extrapolated to three dimensions, it usually still remains restricted to planar molecules in organic chemistry textbooks. Stacking of antiaromatic π-systems has been proposed to induce three-dimensional aromaticity as a result of strong frontier orbital interactions. However, experimental evidence to support this prediction still remains elusive so far. Here we report that close stacking of antiaromatic porphyrins diminishes their inherent antiaromaticity in the solid state as well as in solution. The antiaromatic stacking furthermore allows a delocalization of the π-electrons, which enhances the two-photon absorption cross-section values of the antiaromatic porphyrins. This feature enables the dynamic switching of the non-linear optical properties by controlling the arrangement of antiaromatic π-systems on the basis of intermolecular orbital interactions

Three-dimensional aromaticity in an antiaromatic cyclophane

Understanding of interactions among molecules is essential to elucidate the binding of pharmaceuticals on receptors, the mechanism of protein folding and self-assembling of organic molecules. While interactions between two aromatic molecules have been examined extensively, little is known about the interactions between two antiaromatic molecules. Theoretical investigations have predicted that antiaromatic molecules should be stabilized when they stack with each other by attractive intermolecular interactions. Here, we report the synthesis of a cyclophane, in which two antiaromatic porphyrin moieties adopt a stacked face-to-face geometry with a distance shorter than the sum of the van der Waals radii of the atoms involved. The aromaticity in this cyclophane has been examined experimentally and theoretically. This cyclophane exhibits three-dimensional spatial current channels between the two subunits, which corroborates the existence of attractive interactions between two antiaromatic π-systems