Extremely Stable Perylene Bisimide-Bridged Regioisomeric Diradicals and Their Redox Properties.

Excellent stability is an essential premise for organic diradicals to be used in organic electronic and spintronic devices. We have attached two tris(2,4,6-trichlorophenyl)methyl (TTM) radical building blocks to the two sides of perylene bisimide (PBI) bridges and obtained two regioisomeric diradicals (1,6-TTM-PBI and 1,7-TTM-PBI). Both of the isomers show super stability rather than the monomeric TTM under ambient conditions, due to the increased conjugation and the electron-withdrawing effects of the PBI bridges. The diradicals show distinct and reversible multistep redox processes, and a spectro-electrochemistry investigation revealed the generation of organic mixed-valence (MV) species during reduction processes. The two diradicals have singlet ground states, very small singlet-triplet energy gaps (ΔES-T ) and a pure open-shell character (with diradical character y0 =0.966 for 1,6-TTM-PBI and 0.967 for 1,7-TTM-PBI). This work opens a window to developing very stable diradicals and offers the opportunity of their further application in optical, electronic and magnetic devices.

Illustrating the Fate of Methyl Radical in Photocatalytic Methane Oxidation over Ag-ZnO by in situ Synchrotron Radiation Photoionization Mass Spectrometry.

Photocatalysis has emerged as an ideal method for the direct activation and conversion of methane under mild conditions. In this reaction, methyl radical (⋅CH3 ) was deemed a key intermediate that affected the yields and selectivity of the products. However, direct observation of ⋅CH3 and other intermediates is still challenging. Here, a rectangular photocatalytic reactor coupled with in situ synchrotron radiation photoionization mass spectrometry (SR-PIMS) was developed to detect reactive intermediates within several hundred microseconds during photocatalytic methane oxidation over Ag-ZnO. Gas phase ⋅CH3 generated by photogenerated holes (O- ) was directly observed, and its formation was demonstrated to be significantly enhanced by coadsorbed oxygen molecules. Methoxy radical (CH3 O⋅) and formaldehyde (HCHO) were confirmed to be key C1 intermediates in photocatalytic methane overoxidation to CO2 . The gas-phase self-coupling reaction of ⋅CH3 contributes to the formation of ethane, which indicates the key role of ⋅CH3 desorption in the highly selective synthesis of ethane. Based on the observed intermediates, the reaction network initiated from ⋅CH3 of photocatalytic methane oxidation could be clearly illustrated, which is helpful for studying the photocatalytic methane conversion processes.

Crystal structure of (Z)-2,3-di-chloro-1,4-bis-(4-meth-oxy-phen-yl)but-2-ene-1,4-dione.

The title compound, C18H14Cl2O4, adopts a Z conformation around the cental C=C bond. The two aromatic rings of the mol-ecule are nearly perpendicular to each other, with a dihedral angle between of 86.22 (14)°. The meth-oxy substituents lie close to the plane of the attached benzene rings. The C(ar)-C(ar)-O-C(Me) torsion angles are -2.4 (7) and 7.5 (6)°. Weak C-H⋯O inter-actions link the mol-ecules forming a three-dimensional network. The crystal packing also displays short [3.160 (3) Å] Cl⋯O halogen-bonding contacts between mol-ecules related by the screw axis. The structure exhibits disorder of one carbonyl O atom with a refined occupancy ratio of 0.21 (6):0.79 (6).

Investigating radical pair reaction dynamics of B12 coenzymes 2: Time-resolved electron paramagnetic resonance spectroscopy.

The chemistry of B12 coenzymes is highly sensitive to the nature of their upper axial ligand and can be further tuned by their environment. Methylcobalamin, for example, generates RPs photochemically but undergoes non-radical biochemistry when bound to its dependent enzymes. Owing to the transient nature of the reaction intermediates, it remains a challenge to investigate how their environment controls reactivity. Here, we describe how to use time-resolved electron paramagnetic spectroscopy to directly monitor the generation and evolution of transient radicals that result from the photolysis of a B12 coenzyme. This method produces evolving, spin-polarized spectra that are rich in mechanistic detail.