Mixed-Valence BN-Doped Corannulene Trimer Radical Cations

Mixed-valence (MV) dimers have been extensively investigated, however, the structure and properties of purely organic MV trimers based on open-shell polycyclic aromatic hydrocarbons remain elusive. Herein, unprecedented MV BN-doped corannulene radical cations [ BN-Cor1 ]₃⋅⋅²⁺ ⋅ 2[BAryl^F₄]⁻ and [ BN-Cor2 ]₃⋅⋅²⁺ ⋅ 2[BAryl^F₄]⁻ were synthesized via chemical oxidation, and their structures were unambiguously confirmed by single-crystal X-ray diffraction. These uncommon radical cations consist of three corannulene cores and two [BAryl^F₄]⁻ anions, and three corannulene motifs [ BN-Cor1 ]₃⋅⋅²⁺ and [ BN-Cor2 ]₃⋅⋅²⁺ in the unit cell exhibit a trimer structure with a slipped π-stacking configuration. Detailed structural analyses further revealed that the corannulene cores exhibit an infinite layered self-assembly configuration, allowing their potential applications as building blocks for molecular conductors. The detection of a forbidden transition (Δm_s=±2) by electron paramagnetic resonance (EPR) spectroscopy further confirmed the existence of two unpaired electrons in the π-trimers and the MV characteristic of these two species. Variable-temperature EPR and conductivity measurements suggested that the BN-doped π-trimers exhibited antiferromagnetic coupling and conductivity properties.     

Inhibiting Ion Migration Through Chemical Polymerization and Chemical Chelation Toward Stable Perovskite Solar Cells

The migration of ions is known to be associated with various detrimental phenomena, including current density-voltage hysteresis, phase segregation, etc., which significantly limit the stability and performance of perovskite solar cells, impeding their progress toward commercial applications. To address these challenges, we propose incorporating a polymerizable organic small molecule monomer, N-carbamoyl-2-propan-2-ylpent-4-enamide (Apronal), into the perovskite film to form a crosslinked polymer (P-Apronal) through thermal crosslinking. The carbonyl and amino groups in Apronal effectively interact with shallow defects, such as uncoordinated Pb²⁺ and iodide vacancies, leading to the formation of high-quality films with enhanced crystallinity and reduced lattice strain. Furthermore, the introduction of P-Apronal improves energy level alignment, and facilitates charge carrier extraction and transport, resulting in a champion efficiency of 25.09 %. Importantly, P-Apronal can effectively suppress the migration of I⁻ ions and improve the long-term stability of the devices. The present strategy sets forth a path to attain long-term stability and enhanced efficiency in perovskite solar cells.     

Charge-Transfer and Spin-Flip States: Thriving as Complements

Transition metal complexes with photoactive charge-transfer excited states are pervasive throughout the literature. In particular, [Ru(bpy)₃]²⁺ (bpy=2,2′-bipyridine), with its metal-to-ligand charge-transfer emission, has been established as a key complex. Meanwhile, interest in so-called spin-flip metal-centered states has risen dramatically after the molecular ruby [Cr(ddpd)₂]³⁺ (ddpd=N,N′-dimethyl-N,N′-dipyridin-2-yl-pyridine-2,6-diamine) led to design principles to access strong, long-lived emission from photostable chromium(III) complexes. This Review contrasts the properties of emissive charge-transfer and spin-flip states by using [Ru(bpy)₃]²⁺ and [Cr(ddpd)₂]³⁺ as prototypical examples. We discuss the relevant excited states, the tunability of their energy and lifetimes, and their response to external stimuli. Finally, we identify strengths and weaknesses of charge-transfer and spin-flip states in applications such as photocatalysis and circularly polarized luminescence.     

Two-Dimensional Supramolecular Polymerization of a Bis-Urea Macrocycle into a Brick-Like Hydrogen-Bonded Network

We report on a dendronized bis-urea macrocycle 1 self-assembling via a cooperative mechanism into two-dimensional (2D) nanosheets formed solely by alternated urea-urea hydrogen bonding interactions. The pure macrocycle self-assembles in bulk into one-dimensional liquid-crystalline columnar phases. In contrast, its self-assembly mode drastically changes in CHCl₃ or tetrachloroethane, leading to 2D hydrogen-bonded networks. Theoretical calculations, complemented by previously reported crystalline structures, indicate that the 2D assembly is formed by a brick-like hydrogen bonding pattern between bis-urea macrocycles. This assembly is promoted by the swelling of the trisdodecyloxyphenyl groups upon solvation, which frustrates, due to steric effects, the formation of the thermodynamically more stable columnar macrocycle stacks. This work proposes a new design strategy to access 2D supramolecular polymers by means of a single non-covalent interaction motif, which is of great interest for materials development.     

1,3-Sulfinate Migration Triggered by α-Imino Carbene and Divergent Zwitterion Cyclization: Synthesis of Cyclopropane,Dihydropyrrole, and Azepane Ring Systems

Cyclopropane, dihydropyrrole, and azepane ring systems were synthesized conveniently from sulfinate-tethered triazoles. The divergent synthetic strategy started with the unique 1,3-sulfinate migration of an α-imino carbene. The efficient reaction allowed control of the zwitterion bearing multiple reactive sites depending on the increased stability of the resulting carbocation and anion. The sulfinate was converted to a sulfone after the group migration, and a stable anion bearing two electron-withdrawing groups was thus formed. Catalytic amounts of iodide acted as a switch for the synthesis of cyclopropanes and dihydropyrroles. The reaction merits including readily available substrates, mild reaction conditions, and excellent functional group compatibility qualified this protocol a possible synthetic tool for cyclic compounds, especially for N-heterocycles.     

Pd(II)/Lewis Acid Catalyzed Intramolecular Oxidative C−H Amination to Construct Carbazoles with Dioxygen

Transition-metal-catalyzed oxidative C−H amination reactions are among the most attractive topics in organic synthesis to construct nitrogen-containing motifs. The challenge is that most of these reactions employed stoichiometric oxidants to achieve satisfied catalytic efficiencies. Herein, we report a Pd(II)/LA-catalyzed (LA: Lewis acid) oxidative C−H amination reaction of 2-acetaminobiphenyls to construct carbazoles by using dioxygen balloon as the sole oxidant source, and the presence of LA sharply improved the catalytic efficiency of Pd(OAc)₂. Remarkably, in certain cases, the deacetylation of the annulation product happened under standard conditions to afford free carbazoles as the final product. The H/D exchange studies confirmed the reversibility of C−H activation and also disclosed multiple C−H activation sites by using −NAc and −NTs as the directing groups. In addition, the palladacycle compound was identified through ¹H NMR characterizations and proved to be the intermediate prior to the carbazole formation.     

Synthetic K+ Channels Constructed by Rebuilding the Core Modules of Natural K+ Channels in an Artificial System

Different types of natural K⁺ channels share similar core modules and cation permeability characteristics. In this study, we have developed novel artificial K⁺ channels by rebuilding the core modules of natural K⁺ channels in artificial systems. All the channels displayed high selectivity for K⁺ over Na⁺ and exhibited a selectivity sequence of K⁺≈Rb⁺ during the transport process, which is highly consistent with the cation permeability characteristics of natural K⁺ channels. More importantly, these artificial channels could be efficiently inserted into cell membranes and mediate the transmembrane transport of K⁺, disrupting the cellular K⁺ homeostasis and eventually triggering the apoptosis of cells. These findings demonstrate that, by rebuilding the core modules of natural K⁺ channels in artificial systems, the structures, transport behaviors, and physiological functions of natural K⁺ channels can be mimicked in synthetic channels.     

Photoredox-Enabled Self-(3+2) Cyclization of Vinyldiazo Reagents: Synthesis of Cyclopentenyl α-Diazo Compounds

A photocatalytic self-(3+2) cycloaddition of vinyldiazo compounds is described, which provides cyclopentene derivatives with conservation of one diazo functional group. Experimental insights and density functional theory indicate that the reaction is triggered by an unusual single electron oxidation of vinyldiazo compounds, while the photolysis for the generation of free carbene species is not involved. The synthetic applications of the resulting cyclopentenyl α-diazo compounds were demonstrated based on the rich chemistry of the diazo functional group.     

Heteroleptic Square Planar Cobalt(I/II) Complexes

Reduction of the cobalt(II) chloride complex, Ph₂B(^tBuIm)₂Co(THF)Cl ( 1 ) in the presence of ^tBuN≡C affords the diamagnetic, square planar cobalt(I) complex Ph₂B(^tBuIm)₂Co(C≡N^tBu)₂ ( 2 ). This is a rare example of a 16-electron cobalt(I) complex that is structurally related to square planar noble metal complexes. Accordingly, the electronic structure of 2 , as calculated by DFT, reveals that the HOMO is largely d_z² in character. Complex 2 is readily oxidized to its cobalt(II) congener [Ph₂B(^tBuIm)₂Co(C=N^tBu)₂]BPh₄ ( 3 -BPh₄), whose EPR spectral parameters are characteristic of low-spin d⁷ with an unpaired electron in an orbital of d_z² parentage. This is also consistent with the results of DFT calculations. Despite its 16-electron configuration and the d_z² parentage of the HOMO, the only tractable reactions of 2 involve one electron oxidation to afford 3 .     

Azulene-Indole Fused Polycyclic Heteroaromatics

Linear polycyclic systems are promising candidates in the area of organic electronics. Herein, we present the syntheses of three azulene-indole (AzIn) fused polycyclic heteroaromatics (PHAs), AzIn - 1 , AzIn - 2 and DGAzIn , which have nitrogens and nonhexagonal rings simultaneously. The chemical structures, optical and electrochemical properties of three AzIn-based PHAs have been investigated, as well as their protonation behaviors with trifluoroacetic acid (TFA). All three AzIn-based PHAs exhibit narrow optical band gaps with moderate to good air stability, anti-Kasha emission and reversible stimuli-responsiveness. Furthermore, these straightforward and simple synthetic routes would provide a new entry for constructing novel azulene-embedded π-conjugates, especially for the seven-membered ring of azulene unit, wherein the regioselective transformation is not well developed.