High-Spin Diradical Dication of Chiral π-Conjugated Double Helical Molecule
| Autor: | Suchada Rajca, Andrzej Rajca, Chan Shu, Arnon Olankitwanit, Hui Zhang |
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| Rok vydání: | 2019 |
| Předmět: |
Models
Molecular 010402 general chemistry Heterocyclic Compounds 4 or More Rings 01 natural sciences Biochemistry Article Catalysis chemistry.chemical_compound Colloid and Surface Chemistry Cations Electrochemistry Molecule Singlet state Density Functional Theory Aza Compounds Molecular Structure Chemistry Diradical Electron Spin Resonance Spectroscopy Temperature General Chemistry Oxidants Resonance (chemistry) Dibutyl Phthalate 0104 chemical sciences Dication Crystallography Models Chemical Radical ion Helicene Bignoniaceae Anisotropy Spin Labels Ground state Oxidation-Reduction Half-Life |
| Zdroj: | J Am Chem Soc |
| ISSN: | 1520-5126 0002-7863 |
| Popis: | We report an air-stable diradical dication of chiral D(2)-symmetric conjoined bis[5]diazahelicene with unprecedented high spin (triplet) ground state, singlet triplet energy gap, ΔE(ST) = 0.3 kcal mol(−1). The diradical dication possesses closed-shell (Kekulé) resonance forms with 16 π-electron perimeters. The diradical dication is monomeric in dibutylphthalate (DBP) matrix at low temperatures, and it has a half-life of more than two weeks at ambient conditions in the presence of excess oxidant. A barrier of ~35 kcal mol(−1) has been experimentally determined for inversion of configuration in the neutral conjoined bis[5]diazahelicene, while the inversion barriers in its radical cation and diradical dication were predicted by the DFT computations to be within a few kcal mol(−1) of that in the neutral species. Chiral HPLC resolution provides the chiral D(2)-symmetric conjoined bis[5]diazahelicene, enriched in (P,P)- or (M,M)-enantiomers. The enantiomerically enriched triplet diradical dication is configurationally stable for 48 h at room temperature, thus providing the lower limit for inversion barrier of configuration of 27 kcal mol(−1). The enantiomers of conjoined bis[5]diazahelicene and its diradical dication show strong chirooptical properties that are comparable to [6]helicene or carbon-sulfur [7]helicene, as determined by the anisotropy factors, |g| = |Δε|/ε = 0.007 at 348 nm (neutral) and |g| = 0.005 at 385 nm (diradical dication). DFT computations of the radical cation suggest that SOMO and HOMO energy levels are near-degenerate. |
| Databáze: | OpenAIRE |
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