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

• Published in: Chemistry : a European journal 2022-09, Vol.28 (54), p.e202201261-n/a
• Main Authors: Zatsikha, Yuriy V., Schrage, Briana R., Blesener, Tanner S., Harrison, Laurel A., Ziegler, Christopher J., Nemykin, Victor N.
• Format: Article
• Language: English
• Subjects: Adducts; Amines; antiaromaticity; Atomic properties; BODIPY; Carbon; Chemistry; Chromophores; Crystallography; Cyanides; Density functional theory; Divinylbenzene; Electronic structure; expanded porphyrin; Fluorescence; Fragments; hydrogen bond; Hydrogen bonds; macrocycle; Mass spectrometry; Mass spectroscopy; NMR; Nuclear magnetic resonance; nucleophilic addition; Precursors; Reaction products; Spectra
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202201261

A sterically strained 32π‐electron antiaromatic bis‐BODIPY macrocycle in which two BODIPY fragments are linked by p‐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 the p‐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. The meso‐C−H bond in the macrocycle and its precursor BODIPY dialdehyde 3 forms 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 have meso‐sp3 carbon 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. A sterically strained and non‐fluorescent antiaromatic macrocycle which has two BODIPY subunits linked by p‐divinylphenyl bridges has been prepared and characterized by a variety of spectroscopic and theoretical methods. It has an unusual susceptibility to the nucleophilic attack at the meso‐carbon atom.