Open‐Shell π‐Conjugated Hydrocarbons

Kubo, Takashi

doi:10.1002/9781118858981.ch9

Cited by 4 publications

(6 citation statements)

References 109 publications

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“…The decrease (ease) of potentials for 1 and 2 from DCM to DMSO is about 0.5 V and for 3 is about 0.4 V from DCM to DMF and were attributed to the biradical character of the compounds. This class of compounds with a p -quinodimethane backbone are known to have a singlet biradical nature. , Our CASSCF(6,6)/6-31G(d) calculations provide a moderate biradical character (10.3%, 7.90%, and 13.4% for 1 , 2 , and 3 , respectively, based on natural orbital occupancy). Their HOMO–LUMO gaps (Figure S11 and Table S4) determined from the CV onset potentials are noticeably small and decrease further with increasing solvent polarity from DCM to DMSO, suggesting a more open-shell behavior in high polar media .…”

Section: Resultsmentioning

confidence: 81%

“…Their HOMO−LUMO gaps (Figure S11 and Table S4) determined from the CV onset potentials are noticeably small and decrease further with increasing solvent polarity from DCM to DMSO, suggesting a more open-shell behavior in high polar media. 42 The small HOMO−LUMO gaps signify orbital mixing, which is considered as a measure of the biradical character 40 and acts as a contributory factor to the open-shell nature. Measured EPR signals (Figure S12) of the compounds in the solid state also clearly point out their openshell character.…”

Section: Absorption and Emissionmentioning

confidence: 99%

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Solvent Effect on the Photoinduced Intramolecular Charge–Transfer and Redox Potentials of Three Difuranones

et al. 2023

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We report solvent-dependent excited state properties of three difuranone derivatives with a quinoidal backbone by steady-state and lifetime fluorescence measurements and theoretical calculations. Remarkable bathochromic shifts in fluorescence with diminished intensity indicate the occurrence of strong intramolecular charge-transfer transitions in high polar solvents. Cyclic voltammetric redox potentials reveal an interesting variation of biradical characters of the compounds with increasing solvent polarity. Solvent polarity also significantly modulates the energy levels of the charge-transfer (CT) states, as observed from the combined analyses of redox potentials and photophysical data via the Rehm–Weller equation. When high polar solvents favor forward CT by a more exoergic driving force and stabilize the charge-separated states, the reverse CT process diminishes. Estimated free energies of activation for CT suggest that high polar solvents lessen the activation barrier. Calculated excited state energies of the compounds at the CAM-B3LYP/6-31+G* level fulfill the primary conditions required for singlet fission, a process that can substantially increase the efficiency of solar cells, and the crystal packing for compound 1 also reveals a favorable geometry for singlet fission.

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Section: Resultsmentioning

confidence: 81%

Section: Absorption and Emissionmentioning

confidence: 99%

Solvent Effect on the Photoinduced Intramolecular Charge–Transfer and Redox Potentials of Three Difuranones

et al. 2023

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“…b). Unlike the indenofluorene and bisphenalenyl scaffolds mentioned above, teranthene is an alternant π‐conjugated hydrocarbon that only consists of six‐membered rings and allows the “α sites” and “β sites” to be perfectly separated in an alternative manner (not possible with a five‐membered ring), which might contribute to the larger SNO eigenvalue (or “degree of unpairing”) (Fig. ).…”

Section: Resultsmentioning

confidence: 99%

Revitalizing Spin Natural Orbital Analysis: Electronic Structures of Mixed‐Valence Compounds, Singlet Biradicals, and Antiferromagnetically Coupled Systems

2019

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Chemical systems with open-shell electronic structure have been gaining attention these days. Their potential applications in firstrow transition metal catalysis, molecular wires, photovoltaics and other potential applications have urged the adoption of a simple analysis tool to better understand their open-shell electronic structures, especially the role played by the unpaired electrons. Despite its lack of popularity, spin natural orbital (SNO) analysis is a tool we found to well-suit this purpose. We have therefore re-examined how the SNO could help us analyze some interesting open-shell systems, including mixed-valence compounds, singlet biradicals, and antiferromagnetically coupled systems. We found that some interesting patterns emerge from SNO analysis, especially those associated with exchange interaction.The SNO analysis, the main method we wish to discuss in this article, approaches the "correspondence" problem from a different angle. Although at the first glance the definition does not suggest a correspondence relationship, we will present its intimate connection with the COT and why it will always give such correspondence in a single-determinant calculation.

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“…46 On reduction by a single electron they can generate the corresponding open-shell phenalenyl radical, which can then act as reductant, transferring the electron from its singly occupied molecular orbital (SOMO) via SET processes ( Figure 11). [46][47] In 2017 Mandal and co-workers found that an open-shell phenalenyl-based radical is able to promote the Gomberg-Bachmann reaction of heteroarenes with aryl radicals generated by reduction of arenediazonium salts. 48 The optimized reaction conditions, found through a preliminary screening carried out with thiazole and 4chlorobenzenediazonium tetrafluoroborate as the model coupling partners, involved the use of a catalytic amounts of 9-(methylamino)-1H-phenalen-1-one (PLY-1) ( Figure 12) and t-BuOK in DMSO as the solvent at room temperature for 24h.…”

Section: Phenalenyl-based Radicals As Reductantsmentioning

confidence: 99%

“…46 On reduction by a single electron they can generate the corresponding open-shell phenalenyl radical, which can then act as a reductant, transferring the electron from its singly occupied molecular orbital (SOMO) via SET processes (Figure 11). 46,47 Figure 11 The closed-shell and open-shell electronic states of phenalenyl…”

Section: Review Synthesismentioning

confidence: 99%

Real Metal-Free C–H Arylation of (Hetero)arenes: The Radical Way

Bellina¹

2021

Synthesis

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Synthetic methodologies involving the formation of carbon-carbon bonds from carbon-hydrogen bonds are of significant synthetic interest, both for efficiency in terms of atom economy and for their undeniable usefulness in late-stage functionalization approaches. Combining these aspects with being metal-free, the radical C-H intermolecular arylation procedures covered by this review represent a powerful green means for the synthesis of (hetero)biaryl systems. 1. Introduction 2. Arylation with arenediazonium salts and related derivatives 2.1. Ascorbic acid as reductant 2.2. Hydrazines as reductants 2.3. Gallic acid as reductant 2.4. Polyanilines as reductants 2.5. Chlorpromazine hydrochloride as reductant 2.6 Phenalenyl-based radicals as reductants 2.7 Electrolytic reduction of diazonium salts 2.8 Visible-light mediated arylation 3. Arylation with arylhydrazines: generation of aryl radicals using an oxidant 4. Arylation with diaryliodonium salts 5. Arylation with aryl halides 6. Conclusions

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Open‐Shell π‐Conjugated Hydrocarbons

Cited by 4 publications

References 109 publications

Solvent Effect on the Photoinduced Intramolecular Charge–Transfer and Redox Potentials of Three Difuranones

Solvent Effect on the Photoinduced Intramolecular Charge–Transfer and Redox Potentials of Three Difuranones

Revitalizing Spin Natural Orbital Analysis: Electronic Structures of Mixed‐Valence Compounds, Singlet Biradicals, and Antiferromagnetically Coupled Systems

Real Metal-Free C–H Arylation of (Hetero)arenes: The Radical Way

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