Validating Eaton's Hypothesis: Cubane as a Benzene Bioisostere

Pharmaceutical and agrochemical discovery programs are under considerable pressure to meet increasing global demand and thus require constant innovation. Classical hydrocarbon scaffolds have long assisted in bringing new molecules to the market place, but an obvious omission is that of the Platonic solid cubane. Eaton, however, suggested that this molecule has the potential to act as a benzene bioisostere. Herein, we report the validation of Eaton's hypothesis with cubane derivatives of five molecules that are used clinically or as agrochemicals. Two cubane analogues showed increased bioactivity compared to their benzene counterparts whereas two further analogues displayed equal bioactivity, and the fifth one demonstrated only partial efficacy. Ramifications from this study are best realized by reflecting on the number of bioactive molecules that contain a benzene ring. Substitution with the cubane scaffold where possible could revitalize these systems, and thus expedite much needed lead candidate identification.     

All‐Inorganic Perovskite CsSnBr3 as a Thermally Stable,Free‐Carrier Semiconductor

Hybrid organic‐inorganic perovskites, especially methylammonium lead triiodide (MAPbI₃), are intensely studied for their optoelectronic properties. The organic MA⁺ cation is held responsible for the superior performance of MAPbI₃ but also its instability toward moisture and heat. To explore compositions beyond MAPbI₃, we performed experiments and calculations on two isomorphous perovskites CsSnBr₃ and MASnBr₃. CsSnBr₃ is slightly smaller than MASnBr₃ in cell dimension, but outperforms MASnBr₃ in band gap energy, charge‐carrier reduced effective mass, and optical dielectric constant all by ≈19 %. These merits accumulate to drastically cut the exciton binding energy from 33 meV for MASnBr₃ to 19.6 meV for CsSnBr₃, making CsSnBr₃ a black, free‐carrier semiconductor. CsSnBr₃ also exhibits distinctly higher stability toward moisture and heat than its organic counterparts. These advantages suggest ecofriendly applications for CsSnBr₃, such as tandem solar cells and direct X‐ray detectors.     

Diazirines as Potential Molecular Imaging Tags: Probing the Requirements for Efficient and Long‐Lived SABRE‐Induced Hyperpolarization

Diazirines are an attractive class of potential molecular tags for magnetic resonance imaging owing to their biocompatibility and ease of incorporation into a large variety of molecules. As recently reported, ¹⁵N₂‐diazirine can be hyperpolarized by the SABRE‐SHEATH method, sustaining both singlet and magnetization states, thus offering a path to long‐lived polarization storage. Herein, we show the generality of this approach by illustrating that the diazirine tag alone is sufficient for achieving excellent signal enhancements with long‐lasting polarization. Our investigations reveal the critical role of Lewis basic additives, including water, on achieving SABRE‐promoted hyperpolarization. The application of this strategy to a ¹⁵N₂‐diazirine‐containing choline derivative demonstrates the potential of ¹⁵N₂‐diazirines as molecular imaging tags for biomedical applications.     

Ladder‐type Heteroarenes: Up to 15 Rings with Five Imide Groups

A series of novel imide‐functionalized ladder‐type heteroarenes with well‐defined structure and controllable conjugation lengths were synthesized and characterized. The synthetic route shows remarkable efficacy for constructing the electron‐deficient ladder backbones. π‐Conjugation extension leads to narrowed band gaps with enhanced electron affinities. The ladder arenes are incorporated into organic thin‐film transistors, and show encouraging electron mobilities of 0.013–0.045 cm² V⁻¹ s⁻¹. The heteroarenes reported here provide a remarkable platform for fundamental physicochemical studies and materials innovation in organic electronics.     

A Selection Rule for Hydrofluoroether Electrolyte Cosolvent: Establishing a Linear Free‐Energy Relationship in Lithium–Sulfur Batteries

Hydrofluoroethers (HFEs) have been adopted widely as electrolyte cosolvents for battery systems because of their unique low solvating behavior. The electrolyte is currently utilized in lithium‐ion, lithium–sulfur, lithium–air, and sodium‐ion batteries. By evaluating the relative solvating power of different HFEs with distinct structural features, and considering the shuttle factor displayed by electrolytes that employ HFE cosolvents, we have established the quantitative structure–activity relationship between the organic structure and the electrochemical performance of the HFEs. Moreover, we have established the linear free‐energy relationship between the structural properties of the electrolyte cosolvents and the polysulfide shuttle effect in lithium–sulfur batteries. These findings provide valuable mechanistic insight into the polysulfide shuttle effect in lithium–sulfur batteries, and are instructive when it comes to selecting the most suitable HFE electrolyte cosolvent for different battery systems.     

Isomerism in Titanium‐Oxo Clusters: Molecular Anatase Model with Atomic Structure and Improved Photocatalytic Activity

Phase isomerism is a common and important phenomenon in inorganic materials, but the molecular isomerism of their nanocluster models is still rare. In this work, we report the first pair of isomeric titanium‐oxo clusters. Through combining pentagonal {Ti(Ti₅)} building units in corner‐sharing or edge‐sharing forms, the two obtained Ti₂₀‐oxo clusters take vertical and horizontal core configurations, respectively, which are both functionalized by the same organic ligands. More interestingly, the vertical type Ti₂₀‐oxo core contains an identical {Ti₈O₁₄} moiety as anatase, making it the first molecular model of anatase TiO₂. As a result, the vertical type cluster exhibits better photocatalytic H₂ evolution activity, higher photocurrent response and faster charge transfer to external acceptors than its horizontal isomer. Thus, this work provides a cluster isomer method to understand the structure–property relationship of import titanium oxide materials.     

Development of a Universal Fluorescent Probe for Gram‐Positive Bacteria

The rapid and sensitive classification of bacteria is the first step of bacterial community research and the treatment of infection. Herein, a fluorescent probe BacGO is presented, which shows the best universal selectivity for Gram‐positive bacteria among known probes with a minimum staining procedure for sample detection and enrichment of the live bacteria. BacGO could also be used to assess of the Gram status in the bacterial community from wastewater sludge. Furthermore, BacGO could sensitively and selectively detect a Gram‐positive bacterial infection, not only in vitro but also using an in vivo keratitis mouse model. BacGO provides an unprecedented research tool for the study of dynamic bacterial communities and for clinical application.     

ABi2(IO3)2F5 (A=K,Rb, and Cs): A Combination of Halide and Oxide Anionic Units To Create a Large Second‐Harmonic Generation Response with a Wide Bandgap

A family of nonlinear optical materials that contain the halide, oxide, and oxyhalide polar units simultaneously in a single structure, namely ABi₂(IO₃)₂F₅ (A=K ( 1 ), Rb ( 2 ), and Cs ( 3 )), have been designed and synthesized. They crystallize in the same polar space group (P 2₁) with a two‐dimensional double‐layered framework constructed by [BiF₅]²⁻ and [BiO₂F₄]⁵⁻ units connected to each other by four F atoms, in which two [IO₃]⁻ groups are linked to [BiO₂F₄]⁵⁻ unit on the same side. A hanging Bi−F bond of [BiF₅]²⁻ unit is located on the other side via ionic interaction with the layer‐inserted alkali metal ions to form three‐dimensional structure. The well‐ordered alignments of these polar units lead to a very strong second‐harmonic generation response of 12 ( 1 ), 9.5 ( 2 ), and 7.5 ( 3 ) times larger than that of potassium dihydrogen phosphate under 1064 nm laser radiation. All of them exhibited a wide energy bandgap over 3.75 eV, suggesting that they will have a high laser damage threshold.