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1. Enhancing the Acceptor Character of Conjugated Organoborane Macrocycles: A Highly Electron‐Deficient Hexaboracyclophane

   https://doi.org/10.1002/ange.202001904  

   Baser‐Kirazli, Nurcan ; Lalancette, Roger A. ; Jäkle, Frieder ( March 2020 , Angewandte Chemie)

   We introduce a new boron‐doped cyclophane, the hexabora[1₆]cyclophaneB6‐^FMes, in which six tricoordinate borane moieties alternate with short conjugatedp‐phenylene linkers. Exocyclic 2,4,6‐tris(trifluoromethyl)phenyl (^FMes) groups serve not only to further withdraw electron density but at the same time sterically shield the boron atoms, resulting in a macrocycle that is both highly electron‐deficient and stable. The optical and electronic properties are compared with those of related linear oligomers and the electronic structure is further evaluated by computational methods. The studies uncover unique properties ofB6‐^FMes, including a low‐lying and extensively delocalized LUMO and a wide HOMO–LUMO gap, which arise from the combination of a cyclic π‐system, strong electronic communication between the closely spaced borons, and the attachment of electron‐deficient pendent groups. The binding of small anions to the electron‐deficient macrocycle and molecular model compounds is investigated and emissive exciplexes are detected in aromatic solvents.

    

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2. A New Platform of B/N‐Doped Cyclophanes: Access to a π‐Conjugated Block‐Type B 3 N 3 Macrocycle with Strong Dipole Moment and Unique Optoelectronic Properties

   https://doi.org/10.1002/anie.202200612  

   Li, Pengfei ; Shimoyama, Daisuke ; Zhang, Niu ; Jia, Yawei ; Hu, Guofei ; Li, Chenglong ; Yin, Xiaodong ; Wang, Nan ; Jäkle, Frieder ; Chen, Pangkuan ( March 2022 , Angewandte Chemie International Edition)

   We herein describe a new design principle to achieve B/N‐doped cyclophane where an electron‐donor block of three triarylamines (Ar₃N) and an acceptor block of three triarylboranes (Ar₃B) are spatially separated on opposite sides of the π‐extended ring system. DFT computations revealed the distinct electronic structure of theblock‐type macrocycleMC‐b‐B3N3with a greatly enhanced dipole moment and reduced HOMO–LUMO energy gap in comparison to its analogue with alternating B and N sites,MC‐alt‐B3N3. The unique arrangement of borane acceptor Ar₃B and amine donor Ar₃N components inMC‐b‐B3N3induces exceptionally strong intramolecular charge transfer in the excited state, which is reflected in a largely red‐shifted luminescence at 612 nm in solution. The respective linear open‐chain oligomerL‐b‐B3N3was also synthesized for comparison. Our new approach to donor–acceptor macrocycles offers important fundamental insights and opens up a new avenue to unique optoelectronic materials.

    

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3. A New Platform of B/N‐Doped Cyclophanes: Access to a π‐Conjugated Block‐Type B 3 N 3 Macrocycle with Strong Dipole Moment and Unique Optoelectronic Properties

   https://doi.org/10.1002/ange.202200612  

   Li, Pengfei ; Shimoyama, Daisuke ; Zhang, Niu ; Jia, Yawei ; Hu, Guofei ; Li, Chenglong ; Yin, Xiaodong ; Wang, Nan ; Jäkle, Frieder ; Chen, Pangkuan ( March 2022 , Angewandte Chemie)

   We herein describe a new design principle to achieve B/N‐doped cyclophane where an electron‐donor block of three triarylamines (Ar₃N) and an acceptor block of three triarylboranes (Ar₃B) are spatially separated on opposite sides of the π‐extended ring system. DFT computations revealed the distinct electronic structure of theblock‐type macrocycleMC‐b‐B3N3with a greatly enhanced dipole moment and reduced HOMO–LUMO energy gap in comparison to its analogue with alternating B and N sites,MC‐alt‐B3N3. The unique arrangement of borane acceptor Ar₃B and amine donor Ar₃N components inMC‐b‐B3N3induces exceptionally strong intramolecular charge transfer in the excited state, which is reflected in a largely red‐shifted luminescence at 612 nm in solution. The respective linear open‐chain oligomerL‐b‐B3N3was also synthesized for comparison. Our new approach to donor–acceptor macrocycles offers important fundamental insights and opens up a new avenue to unique optoelectronic materials.

    

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4. Meso ‐Carbon Atom Nucleophilic Attack Susceptibility in the Sterically Strained Antiaromatic Bis‐BODIPY Macrocycle and Extended Electron‐Deficient BODIPY Precursor**

   https://doi.org/10.1002/chem.202201261  

   Zatsikha, Yuriy V. ; Schrage, Briana R. ; Blesener, Tanner S. ; Harrison, Laurel A. ; Ziegler, Christopher J. ; Nemykin, Victor N. ( August 2022 , Chemistry – A European Journal)

   A sterically strained 32π‐electron antiaromatic bis‐BODIPY macrocycle in which two BODIPY fragments are linked byp‐divinylbenzene groups was prepared and characterized. Unlike regular BODIPYs, the fluorescence in this macrocycle is quenched. The broad signals in the NMR spectra of the macrocycle were explained by the vibronic freedom of thep‐divinylbenzene fragments. The possible diradicaloid nature of the macrocycle was excluded on the basis of variable‐temperature EPR spectra in solution and in solid state, which is indicative of its closed‐shell quinoidal structure. Themeso‐C−H bond in the macrocycle and its precursor BODIPY dialdehyde3forms a weak hydrogen bond with THF and is susceptible for the nucleophilic attack by organic amines and cyanide anion. The reaction products of such a nucleophilic attack havemeso‐sp³carbon atoms and were characterized by NMR, mass spectrometry and, in one case, X‐ray crystallography. Unlike the initial bis‐BODIPY macrocycle, the adducts have strong fluorescence in the 400 nm region. The electronic structure and spectroscopic properties of new chromophores were probed by density functional theory (DFT) and time‐dependent DFT (TDDFT) calculations and correlate well with the experimental data.

    

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5. Density Functional Theory and ab Initio Computational Evidence for Nitrosamine Photoperoxides: Hammett Substituent Effects in the Photogeneration of the Nitrooxide Intermediate

   https://doi.org/10.1111/php.12941  

   Greer, Edyta M. ; Kwon, Kitae ( July 2018 , Photochemistry and Photobiology)

   Little attention has been focused on diradical and zwitterionic photoperoxides formed from nitrosamine compounds. Here, an attempt is made to probe the electronic character of the nitrooxide intermediate formed in photochemical reactions with triplet oxygen (³O₂). Theoretical studies have been conducted to screenpara‐substituted phenyl nitrosamines. In particular, we find that electron‐withdrawing substituents produce low‐lying triplet nitrooxide diradicals. A clear electronic dependence in theS₀–T₁andS₀–S₁energy gaps of nitrooxides was found using Hammett plots. Computed geometries show a twisted diradical triplet nitrooxide moiety, which contrasts to the nearly flat singlet zwitterionic ground state nitrooxide moiety; analyses of charges (natural bond order), molecular orbitals (HOMO/LUMO) and spin densities enable these assignments. Calculations predict the former triplet species is photogenerated initially from nitrosamine with O₂. The conversion of the triplet nitrooxide diradical to the singlet ground state is an example where longer‐lived zwitterionic nitrooxide structures become possible. The reaction mechanism is consistent with a zwitterionic ground state nitrooxide playing an important role in the bimolecular oxygen‐transfer reaction with phosphine and phosphite trapping agents as has been observed experimentally.

    

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