Organic radicals can potentially play important roles in functional materials owing to an unpaired electron, but they are usually highly reactive and difficult to use. Therefore, stabilization of ...organic radicals is important. Among organic radicals, carbon‐centered radicals are promising because of their trivalent nature, which enables structural diversity and elaborate designs, but they are also less stable because of the reactivities towards carbon–carbon bond formation and atmospheric oxygen. Recently, stable carbon‐centered radicals across diverse molecular platforms have been increasingly explored. This Minireview highlights these newly explored, stable carbon‐centered radicals, with a focus on porphyrinoid‐stabilized radicals because of their remarkable spin delocalization abilities.
Spin control: Stable carbon‐centered radicals have been extensively developed as attractive building blocks for molecule‐based materials because of their structural diversity and tunable spin characteristics. This Minireview describes the electronic structures and stabilities of these radicals, with a focus on the developments within the last decade.
Installation of various substituents is a reliable and versatile way to alter the properties of macrocyclic molecules, but high-yield and controlled methods are not always available especially for ...multifold reactions. Herein, we report 10- and 12-fold introduction of aryl substituents onto both rims of cylinder-shaped pillarnarenes, which usually have alkoxy substituents slanting to the cylinder axes. Although alkoxy pillar5arenes exist as D 5-symmetric enantiomeric pairs, arylated pillar5arenes provide crushed single-crystal structures and stereoisomerism including C 2-symmetric conformations depending on the aryl groups. Pillarnarenes with 2-benzofuranyl groups display bright fluorescence with quantum yields of 88–90% and no host–guest complexation with electron-deficient molecules in solution due to large deviation from alkoxy compounds. A benzofuran-appended pillar6arene instead captures small gaseous molecules in the solid state, probably owing to outside spaces surrounded by aromatic rings.
Chirality transfer is widely observed in life processes, and many artificial chiral transfer systems have been developed. In these systems, chiral information is transferred from chiral inducers to ...chiral acceptors by a direct chiral induction process and a direct chiral memorization process. We have developed ternary nondirect chiral transfer systems based on pillar5arenes, in which a third factor was introduced as a regulator. The planar chirality of an acceptor was induced and memorized by a chiral inducer with precise control by a regulator. In the chiral induction period, the feed sequence of the chiral inducer and regulator affected the chiral induction behavior of the chiral acceptor. The chiral memory ability of the acceptor was substantially improved by the combined action of the chiral inducer and regulator.
Ternary nondirect chiral transfer systems based on pillar5arenes are reported in which a third factor was introduced as a regulator. The planar chirality of an acceptor was induced and memorized by a chiral inducer with precise control by a regulator. The chiral memory ability of the acceptor was substantially improved by the combined action of the chiral inducer and regulator.
A statistical approach, which was previously developed to correct scattering data for X‐ray response non‐uniformity (XRNU) in microstrip detectors, has been improved to significantly reduce the ...correcting time. The improved algorithm has succeeded in increasing the utilization rate of data acquired for reference intensity to 98%. As a result, the correcting time was reduced from half a day to half an hour, which was shorter than the typical measuring time of a sample. Moreover, the present approach was found to yield better correction results than the previous one. The data‐driven approach enabled the on‐demand correction for XRNU according to the detector and experimental settings. The present study will encourage the correction of scattering data for XRNU in area detectors.
A data‐driven approach has been developed to correct scattering data for X‐ray response non‐uniformity in microstrip detectors on demand. The present study will facilitate the correction in all types of X‐ray detectors.
Porphyrin‐Based Air‐Stable Helical Radicals Kato, Kenichi; Furukawa, Ko; Mori, Tadashi ...
Chemistry : a European journal,
January 12, 2018, Volume:
24, Issue:
3
Journal Article
Peer reviewed
Stable helical radicals are promising multi‐functional molecules in light of intriguing magnetic and chiroptical properties. Attempts were made to extend diphenylmethyl‐fused NiII porphyrin radical ...to helical system as the first air‐stable organic neutral helical radicals. Intramolecular Pd‐catalyzed twofold C−H arylation of methyl‐ or methoxy‐introduced meso‐diphenylmethyl NiII porphyrins gave a mixture of the target and rearranged radicals. Oxidative fusion reaction of meso‐(bis(1‐naphthyl)methyl) NiII porphyrins provided doubly fused NiII porphyrin radicals. One of the helical radicals was separated into enantiomers that showed mirror‐image circular dichroism (CD) spectra up to 1300 nm. The helical dinaphthylmethyl‐fused NiII porphyrin radical displayed solid‐state magnetic property mostly arising from monomeric radicals, different from the parent diphenylmethyl‐fused NiII porphyrin radical that showed antiferromagnetic coupling due to π‐stacked pairing.
Radical behavior: Diarylmethyl‐fused NiII porphyrin radicals have been extended to a helical system as the first air‐stable organic neutral helical radicals. Di(1‐naphthyl)methyl‐fused NiII porphyrin radicals thus synthesized were separated into enantiomers that showed mirror‐image CD spectra up to 1300 nm, indicating the effective desymmetrization of the frontier molecular orbitals.
Triple helicene‐like semi‐fused trimeric NiII porphyrins were constructed by alkyne trimerization of an ethynyl‐substituted porphyrin and subsequent three‐fold Grignard addition to the formyl groups ...and acid‐catalyzed intramolecular cyclization. The presence of stereogenic sp3 carbons in the central bridge leads to small inter‐porphyrin conjugative interactions as was revealed by electrochemical and optical properties. Two diastereomers with stable chiral conformations were optically resolved, and the separated enantiomers displayed considerably intense circular dichroism. Importantly, the chiroptical response of C3‐symmetric helical isomer (|Δϵ|=830 m−1 cm−1) is 1.8 times amplified from that of C1‐symmetric one (|Δϵ|=470 m−1 cm−1). The observed amplification has been interpreted in terms of different spatial arrangements of the three porphyrins.
Tribenzylbenzene‐fused porphyrin trimers were synthesized as two diastereomeric pairs of enantiomers owing to three stereogenic sp3 carbons. These trimers showed highly twisted triple helicene‐like structures and optically resolved through a chiral column. The observed CD signals were intense (up to |Δϵ|=830 m−1 cm−1) and 1.8 times amplified in the C3‐symmetric isomer, indicating the importance of spatial arrangement of three porphyrin chromophores.
We demonstrate a metal–organic framework (MOF) design for the inclusion of hydroxide ions. Salt inclusion method was applied to an alkaline-stable ZIF-8 (ZIF = zeolitic imidazolate framework) to ...introduce alkylammonium hydroxides as ionic carriers. We found that tetrabutylammonium salts are immobilized inside the pores by a hydrophobic interaction between the alkyl groups of the salt and the framework, which significantly increases the hydrophilicity of ZIF-8. Furthermore, ZIF-8 including the salt exhibited a capacity for OH– ion exchange, implying that freely exchangeable OH– ions are present in the MOF. ZIF-8 containing OH– ions showed an ionic conductivity of 2.3 × 10–8 S cm–1 at 25 °C, which is 4 orders of magnitude higher than that of the blank ZIF-8. This is the first example of an MOF-based hydroxide ion conductor.
This is a first report on a novel approach for a significant enhancement in the ionic conductivity of Mg ions in solid, induced by organic vapor. The Mg ions located inside the pores of a ...metal–organic framework (MOF) exhibited a drastic change in mobility in the presence of anhydrous organic vapors of various guest molecules such as MeOH and MeCN. A systematic study on the ionic conductivity of the model compound, Mg-MOF-74 ⊃ {Mg(TFSI)2} x (x ≤ 0.15), incorporating only the Mg salts inside the pores, under various organic vapors, showed that the MOF adsorbed the guest molecules to form highly mobile ionic carriers and provide an excellent ion-conducting pathways for high ionic conductivity at ambient temperature. Mg-MOF-74 ⊃ {Mg(TFSI)2}0.15 showed a superionic conductivity of 2.6 × 10–4 S cm–1 at 25 °C under MeOH vapor. In addition, this is the first case of the “Mg ion”-conductive MOF with direct evidence of Mg2+ transport (t Mg2+ = 0.47, for Mg-MOF-74 ⊃ {Mg(TFSI)2}0.15 under MeCN vapor).
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