Coronoids as polycyclic aromatic macrocycles enclosing a cavity have attracted a lot of attention due to their distinctive molecular and electronic structures. They can be also regarded as nanoporous graphene molecules whose electronic properties are critically dependent on the size and topology of their outer and inner peripheries. However, because of their synthetic challenges, the extended hexagonal coronoids with zigzag outer edges have not been reported yet. Here, we report the on-surface synthesis of C144 hexagonal coronoid with outer zigzag edges on a designed precursor undergoing hierarchical Ullmann coupling and cyclodehydrogenation on the Au(111) surface. The molecular structure is unambiguously characterized by bond-resolved noncontact atomic force microscopy imaging. The electronic properties are further investigated by scanning tunneling spectroscopy measurements, in combination with the density functional theory calculations. Moreover, the values of the harmonic oscillator model of aromaticity are derived from calculations that suggest that the molecular structure is ideally represented by Clar's model. Our results provide approaches toward realizing a hexagonal coronoid with zigzag edges, potentially inspiring fabrication of hexagonal zigzag coronoids with multiple radical characters in the future.

Precise control in reaction selectivity is the goal in modern organic synthesis, and it has been widely studied throughout the synthetic community. In comparison, control of divergent reactivity of a given reagent under different reaction conditions is relatively less explored aspect of chemical selectivity. We herein report an unusual reaction between polycyclic aromatic hydrocarbons and periodic acid H5IO6 (1), where the product outcome is dictated by the choice of reaction conditions. That is, reactions under solution-based condition give preferentially C–H iodination products, while reactions under solvent-free mechanochemical condition provide C–H oxidation quinone products. Control experiments further indicated that the iodination product is not a reaction intermediate toward the oxidation product and vice versa. Mechanistic studies unveiled an in situ crystalline-to-crystalline phase change in 2 during ball-milling treatment, where we assigned it as a polymeric hydrogen-bond network of 1. We believe that this polymeric crystalline phase shields the more embedded electrophilic I O group of 1 from C–H iodination and bias a divergent C–H oxidation pathway (with I O ) in the solid state. Collectively, this work demonstrates that mechanochemistry can be employed to completely switch a reaction pathway and unmask hidden reactivity of chemical reagents.

Recently, polymer mechanochemistry has attracted much scientific interest due to its potential to develop degradable polymers. When the two ends of a polymer chain experience a linear pulling stress, molecular strain builds up, at sufficiently strong force, a bond scission of the weakest covalent bond results. In contrast, bond‐breaking events triggered by conformational stress are much less explored. Here, we discovered that a Zn salen complex would undergo conformational switching upon allosteric complexation with alkanediammonium guests. By controlling the guest chain length, the torsional strain experienced by Zn complex can be modulated to induce bond cleavage with chemical stimulus, and reactivity trend is predicted by conformational analysis derived by DFT calculation. Such strain‐release reactivity by a Zn(salen) complex initiated by guest binding is reminiscent of conformation‐induced reactivity of enzymes to enable chemical events that are otherwise inhibited.

Pd‐based molecular square Pd4L4 and triangle Pd3L3 represent the molecular ancestors of metal‐coordination polyhedra that have been an integral part of the field for the last 30 years. Conventional solution‐based reactions between cis‐protected Pd ions and 2,2′‐bipyridine exclusively give Pd4L4 and/or Pd3L3 as the sole products. We herein show that, under solvent‐free mechanochemical conditions, the self‐assembly energy landscape can be thermodynamically manipulated to form an elusive cyclic dimer Pd2L2 for the first time. In the absence of solvent, Pd2L2 is indefinitely stable in the solid‐state, but converts rapidly to its thermodynamic products Pd3L3 and Pd4L4 in solution, confirming Pd2L2 as a short‐lived kinetic species in the solution‐based self‐assembly process. Our results highlight how mechanochemistry grants access to a vastly different chemical space than available under conventional solution conditions. This provides a unique opportunity to isolate elusive species in self‐assembly processes that are too reactive to both “see” and “capture”.

A late-stage macrocycle-to-macrocycle-to-macrocycle strategy to form a wide range of 9,10-disubstituted- pillar[4]naphthalenes from a common calix[4]furan building block, via pillar[4](1,4-epoxynapthalene) intermediates, is developed. Since post-transformation begins with a structurally well-defined macrocycle template, conventional issues in macrocyclization, such as unwanted polymerization, and non-selective macrocycle formation, are thus avoided. Albeit low conversion, this method even leads to the formation of pillar[4]anthracene, which is confirmed by HR-MALDI spectroscopy. Moreover, pillar[4]naphthalene is shown to be highly selective for NH4+ over other alkali metals in gas phase. Theoretical studies revealed that the selective complexation between pillar[4]naphthalene and NH4+ guest is directed solely by favorable multiple N-H interactions. Collectively, since calix[4]furan template is constructed from bio-renewable resources, our work is expected to inspire future efforts to employ biomass waste-derived building blocks to construct unique petroleum-based functional materials inaccessible by conventional methods.