Enantioselective Oxidation of Thioanisole to Metyl Phenyl Sulfoxide by Chiral Compounds Bearing <i>N</i>-Cl Bond

<div><p>GRAPHICAL ABSTRACT</p><p></p></div

Search for a Small Chromophore with Efficient Singlet Fission: Biradicaloid Heterocycles

Of the five small biradicaloid heterocycles whose S₁, S₂, T₁, and T₂ adiabatic excitation energies were examined by the CASPT2/ANO-L-VTZP method, two have been found to meet the state energy criterion for efficient singlet fission and are recommended to the attention of synthetic chemists and photophysicists

The 16 CB₁₁(CH₃)_<i>n</i>(CD₃)_{12–<i>n</i>}^• Radicals with 5‑Fold Substitution Symmetry: Spin Density Distribution in CB₁₁Me₁₂^•

The syntheses of all 16 CB₁₁(CH₃)_<i>n</i>(CD₃)_{12–<i>n</i>}^• radicals with 5-fold substitution symmetry are described. The variation in the width of their broad and featureless electron paramagnetic resonance signals as a function of the deuteriation pattern is used to deduce the relative values of the average hyperfine coupling constants <i>a</i>_H of the hydrogen atoms in the ipso (1), ortho (2–6), meta (7–11), and para (12) methyl groups, <i>a</i>_H(<i>i</i>):<i>a</i>_H(<i>o</i>):<i>a</i>_H(<i>m</i>):<i>a</i>_H(<i>p</i>) = (0.18 ± 0.09):(0.71 ± 0.02):(1.00 ± 0.03):(0.52 ± 0.05), and these can be compared with ratios expected from a B3LYP/EPRII calculation, 0.04:0.55:1:0.51

The 16 CB₁₁(CH₃)_<i>n</i>(CD₃)_{12–<i>n</i>}^• Radicals with 5‑Fold Substitution Symmetry: Spin Density Distribution in CB₁₁Me₁₂^•

The syntheses of all 16 CB₁₁(CH₃)_<i>n</i>(CD₃)_{12–<i>n</i>}^• radicals with 5-fold substitution symmetry are described. The variation in the width of their broad and featureless electron paramagnetic resonance signals as a function of the deuteriation pattern is used to deduce the relative values of the average hyperfine coupling constants <i>a</i>_H of the hydrogen atoms in the ipso (1), ortho (2–6), meta (7–11), and para (12) methyl groups, <i>a</i>_H(<i>i</i>):<i>a</i>_H(<i>o</i>):<i>a</i>_H(<i>m</i>):<i>a</i>_H(<i>p</i>) = (0.18 ± 0.09):(0.71 ± 0.02):(1.00 ± 0.03):(0.52 ± 0.05), and these can be compared with ratios expected from a B3LYP/EPRII calculation, 0.04:0.55:1:0.51

The 16 CB₁₁(CH₃)_<i>n</i>(CD₃)_{12–<i>n</i>}^• Radicals with 5‑Fold Substitution Symmetry: Spin Density Distribution in CB₁₁Me₁₂^•

The syntheses of all 16 CB₁₁(CH₃)_<i>n</i>(CD₃)_{12–<i>n</i>}^• radicals with 5-fold substitution symmetry are described. The variation in the width of their broad and featureless electron paramagnetic resonance signals as a function of the deuteriation pattern is used to deduce the relative values of the average hyperfine coupling constants <i>a</i>_H of the hydrogen atoms in the ipso (1), ortho (2–6), meta (7–11), and para (12) methyl groups, <i>a</i>_H(<i>i</i>):<i>a</i>_H(<i>o</i>):<i>a</i>_H(<i>m</i>):<i>a</i>_H(<i>p</i>) = (0.18 ± 0.09):(0.71 ± 0.02):(1.00 ± 0.03):(0.52 ± 0.05), and these can be compared with ratios expected from a B3LYP/EPRII calculation, 0.04:0.55:1:0.51

Covalent Dimers of 1,3-Diphenylisobenzofuran for Singlet Fission: Synthesis and Electrochemistry

The synthesis of covalent dimers in which two 1,3-diphenylisobenzofuran units are connected through one phenyl substituent on each is reported. In three of the dimers, the subunits are linked directly, and in three others, they are linked via an alkane chain. A seventh new compound in which two 1,3-diphenylisobenzofuran units share a phenyl substituent is also described. These materials are needed for investigations of the singlet fission process, which promises to increase the efficiency of solar cells. The electrochemical oxidation and reduction of the monomer, two previously known dimers, and the seven new compounds have been examined, and reversible redox potentials have been compared with results obtained from density functional theory. Although the overall agreement is satisfactory, some discrepancies are noted and discussed

Covalent Dimers of 1,3-Diphenylisobenzofuran for Singlet Fission: Synthesis and Electrochemistry

The synthesis of covalent dimers in which two 1,3-diphenylisobenzofuran units are connected through one phenyl substituent on each is reported. In three of the dimers, the subunits are linked directly, and in three others, they are linked via an alkane chain. A seventh new compound in which two 1,3-diphenylisobenzofuran units share a phenyl substituent is also described. These materials are needed for investigations of the singlet fission process, which promises to increase the efficiency of solar cells. The electrochemical oxidation and reduction of the monomer, two previously known dimers, and the seven new compounds have been examined, and reversible redox potentials have been compared with results obtained from density functional theory. Although the overall agreement is satisfactory, some discrepancies are noted and discussed

Excitation Localization/Delocalization Isomerism in a Strongly Coupled Covalent Dimer of 1,3-Diphenylisobenzofuran

Two isomers of both the lowest excited singlet (S₁) and triplet (T₁) states of the directly para, para′-connected covalent dimer of the singlet-fission chromophore 1,3-diphenylisobenzofuran have been observed. In one isomer, excitation is delocalized over both halves of the dimer, and in the other, it is localized on one or the other half. For a covalent dimer in solution, such “excitation isomerism” is extremely rare. The vibrationally relaxed isomers do not interconvert, and their photophysical properties, including singlet fission, differ significantly

Toward Designed Singlet Fission: Solution Photophysics of Two Indirectly Coupled Covalent Dimers of 1,3-Diphenylisobenzofuran

In order to identify optimal conditions for singlet fission, we are examining the photophysics of 1,3-diphenylisobenzofuran (<b>1</b>) dimers covalently coupled in various ways. In the two dimers studied presently, the coupling is weak. The subunits are linked via the para position of one of the phenyl substituents, in one case (<b>2</b>) through a CH₂ linker and in the other (<b>3</b>) directly, but with methyl substituents in ortho positions forcing a nearly perpendicular twist between the two joint phenyl rings. The measurements are accompanied with density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. Although in neat solid state, <b>1</b> undergoes singlet fission with a rate constant higher than 10¹¹ s^–1; in nonpolar solutions of <b>2</b> and <b>3</b>, the triplet formation rate constant is less than 10⁶ s^–1 and fluorescence is the only significant event following electronic excitation. In polar solvents, fluorescence is weaker because the initial excited singlet state S₁ equilibrates by sub-nanosecond charge transfer with a nonemissive dipolar species in which a radical cation of <b>1</b> is attached to a radical anion of <b>1</b>. Most of this charge transfer species decays to S₀, and some is converted into triplet T₁ with a rate constant near 10⁸ s^–1. Experimental uncertainties prevent an accurate determination of the number of T₁ excitations that result when a single S₁ excitation changes into triplet excitation. It would be one if the charge-transfer species undergoes ordinary intersystem crossing and two if it undergoes the second step of two-step singlet fission. The triplet yield maximizes below room temperature to a value of roughly 9% for <b>3</b> and 4% for <b>2</b>. Above ∼360 K, some of the S₁ molecules of <b>3</b> are converted into an isomeric charge-transfer species with a shorter lifetime, possibly with a twisted intramolecular charge transfer (TICT) structure. This is not observed in <b>2</b>