Helical Bilayer Nonbenzenoid Nanographene Bearing a [10]Helicene with Two Embedded Heptagons

The precision synthesis of helical bilayer nanographenes (NGs) with new topology is of substantial interest because of their exotic physicochemical properties. However, helical bilayer NGs bearing non-hexagonal rings remain synthetically challenging. Here we present the efficient synthesis of the first helical bilayer nonbenzenoid nanographene ( HBNG1 ) from a tailor-made azulene-embedded precursor, which contains a novel [10]helicene backbone with two embedded heptagons. Single-crystal X-ray analysis reveals its highly twisted bilayer geometry with a record small interlayer distance of 3.2 Å among the reported helical bilayer NGs. Notably, the close interlayer distance between the two layers offers intramolecular through-space conjugation as revealed by in situ spectroelectrochemistry studies together with DFT simulations. Furthermore, the chiroptical properties of the P/M enantiomers of HBNG1 are also evaluated by circular dichroism and circularly polarized luminescence.     

Electron Spin Catalysis with Graphene Belts

Here, we report kinetic studies using electron spin resonance spectroscopy on spin catalysis reactions caused by using graphene belts which were synthesized by a radical coupling method. The results show that σ-type free radical species provide the dominant sites for catalytic activity through the spin-spin interaction, although there are some other influencing factors. The spin catalysis mechanism can be applied both in the oxygen reduction reaction (ORR) and in organic synthesis. The graphene belt spin catalyst shows excellent performance with a high ORR half-wave potential of 0.81 V and long-term stability with almost no loss of activity after 50 000 cycles in alkaline media. It also shows excellent performance in a benzylamine coupling with molecular oxygen to generate the corresponding imine at an average conversion of ≈97.7 % and an average yield of ≈97.9 %. This work opens up a new research direction for understanding aerobic processes in the field of spin catalysis.     

Photo-Response with Radical Afterglow by Regulation of Spin Populations and Hole-Electron Distributions

No matter photoinduced organic radicals have been reported frequently, they are usually non-luminescent at ambient conditions. The internal mechanism on stability and electronic transitions of photoinduced radicals, is thus crucial for the development of relevant materials. Herein, a series of photoinduced radical emission systems were developed conveniently through doping benzoic acids into the hydrogen donor polyvinyl alcohol (PVA) matrix. Visual photoinduced radical emission and photochromism could be observed on Ph-3COOH @PVA film with the formation of cyclohexadienyl-type structure. For the first time, radical afterglow appeared with energy transfer from triplet state. The appropriate introduction of carboxylic groups to three nonadjacent carbon atoms on the benzene ring was the best for decreasing spin population and promoting electronic transitions of the radical. This study largely expands the radical emission property from both internal mechanism and practical application.     

Binding of a Ruthenium Complex to a Thioether Ligand Embedded in a Negatively Charged Lipid Bilayer: A Two‐Step Mechanism

The interaction between the ruthenium polypyridyl complex [Ru(terpy)(dcbpy)(H₂O)]²⁺ (terpy=2,2′;6′,2“‐terpyridine, dcbpy=6,6′‐dichloro‐2,2′‐bipyridine) and phospholipid membranes containing either thioether ligands or cholesterol were investigated using UV–visible spectroscopy, Langmuir–Blodgett monolayer surface pressure measurements, and isothermal titration calorimety (ITC). When embedded in a membrane, the thioether ligand coordinated to the dicationic metal complex only when the phospholipids of the membrane were negatively charged, that is, in the presence of attractive electrostatic interaction. In such a case coordination is much faster than in homogeneous conditions. A two‐step model for the coordination of the metal complex to the membrane‐embedded sulfur ligand is proposed, in which adsorption of the complex to the negative surface of the monolayers or bilayers occurs within minutes, whereas formation of the coordination bond between the surface‐bound metal complex and ligand takes hours. Finally, adsorption of the aqua complex to the membrane is driven by entropy. It does not involve insertion of the metal complex into the hydrophobic lipid layer, but rather simple electrostatic adsorption at the water–bilayer interface.     

Spin State in (Porphinato)iron(III) Complex. A Spin‐Crossover Complex with Two Magnetically Distinct Sites

The results of low temperature X‐ray determination, Mössbauer and magnetic measurement of spin‐crossover (isothiocyanato)(porphinato)iron(III) hemipyridine are reported. The features in 77 K Mössbauer spectrum include two doublets, one with a quadrupole splitting (ΔE_Q) of 1.961 mm s^?1 (low‐spin site) and the other with ΔE_Q = 0.792 mm s^?1 (high‐spin site). As the temperature of the sample is increased to 300 K, the signal intensity of the high‐spin site grows to 92% at the expense of the low‐spin signal. The variable‐temperature magnetic susceptibility data also support that the tetraphenyl complex is a spin‐crossover complex.     

A Model for Characterization of Successive Hydrogen Bonding Interactions with Electrochemically Generated Charged Species. The Quinone Electroreduction in the Presence of Donor Protons

In this work, it is considered that charged molecules, such as the semiquinone (Q^.?) and the benzoquinone dianion (Q^2?), interact with weak donor protons (DH) via hydrogen bonding through consecutive association steps which depend on the concentration of DH. On the basis of a reversible voltammetric behavior, a model is presented for determining integer numbers of associated molecules of DH and the thermodynamic constants (β_i) related with each association equilibrium. The electrochemical reduction of 1,4‐benzoquinone (Q) in the presence of different aliphatic alcohols and diols, in dimethylsulfoxide (DMSO), illustrates the utility of the model. Based on analysis of half‐wave potential variation according to the DH concentration, the association constants were determined for the Q^.? and Q^2? complexes with the different alcohols studied and mole‐fraction distribution diagrams were constructed. These diagrams explain the fractional values, produced using the typical model, widely reported in the literature, for study the hydrogen bonding between the electrochemically generated charged species with donor protons.